Document ID: EPA-HQ-OAR-2010-0162-3627
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-08-29T04:00Z

DATE:		July 28, 2011

TO:  		EPA-HQ-OAR-2010-0162

FROM:  	Cleophas Jackson, Jay Smith, Julian Davis, Chien Sze, Zuimdie Guerra, Prashanth Gururaja, James Sanchez, Peter Smith, Arvon Mitcham, Daniel Cullen
	William Courtois, Carl Ryan, Sam Waltzer, Ryan Szpara, Robert Caldwell, Carl Paulina, Ethan Schauer, Brian Ratkos, Maria Peralta

--------------------------------------------------------------------------------
SUBJECT:	Heavy-Duty Greenhouse Gas and Fuel Consumption Test Program 2 Summary

This memorandum summarizes the results of testing and analysis conducted in support of the Heavy-Duty Greenhouse Gas and Fuel Consumption final rulemaking by the United States Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHTSA).  The test program included the development of test protocols for hybrid engine and vehicle system performance evaluation, modification of test protocols for use with heavy-duty vehicles for assessment of aerodynamic performance, and recommendations for use of existing protocols and software essential to develop the engine and vehicle performance inputs that will be used to characterize Greenhouse Gas and Fuel Consumption performance for medium and heavy-duty vehicles.  This memorandum is intended to complement the testing memorandum docketed prior to the Notice of Proposed Rulemaking (NPRM) - Heavy-Duty Greenhouse Gas and Fuel Consumption Test Program Summary.  This memorandum provides details regarding the test data, generated by the agencies, used to support decisions made by the agencies to revise test protocols and establish additional provisions for hybrid testing and conventional vehicle performance evaluation for GHG and fuel consumption performance.  This memorandum will include the following:

   1. Hybrid Testing and Protocol Development  (James Sanchez, Peter Smith, Cleophas Jackson, Ryan Szpara, Carl Ryan, William Courtois, Robert Caldwell, Carl Paulina, Maria Peralta)
      * Test Program (Summary of Each)
      * Comparison across Methods
      * PTO Testing
   2. Coastdown (Chien Sze, Prashanth Gururaja, Zuimdie Guerra, Cleophas Jackson, Robert Caldwell, Jay Smith, Ethan Schauer, Brian Ratkos, Julian Davis, Maria Peralta) 
      * Summary of Test Program 1 Analysis Method
      * Summary of Test Program 2
      * Summary Tables of Test Program 2 Coastdown Runs at ATDS-Lancaster, CA and APG  -  Wittman, AZ
      * Detailed Test Article Descriptions
      * Wind Analysis
      * Method Comparison
      * Test Data Summary
   3. Wind Tunnel Testing (Arvon Mitcham, Sam Waltzer, Cleophas Jackson)
      * Contractor's Summary Report (NRC)  -  docketed separately 
      * Summary of NRC Method Comparison Reports  -  docketed separately 
      * EPA Summary / Assessment
   4. Scale Wind Tunnel Testing (Arvon Mitcham and Sam Waltzer)
      * Contractor Report Summary
      * EPA Summary
   5. CFD Analysis (Sam Waltzer and Arvon Mitcham)
      * Summary of Results from Navier-Stokes Test Runs
      * Summary of Results from Lattice-Boltzmann Test Runs
      * Recommendations for Analysis Using Each Method
   6. Summary Comparison Across All Aerodynamic Assessment Methods (Arvon Mitcham and Sam Waltzer)
         * Single test article results across methods
         * Correlation factor method for comparison to standard reference method
1.0  Hybrid Testing and Protocol Development

Introduction

As a part of the HD GHG rule the Agency performed a number of test programs at the National Vehicle and Fuels Emission Laboratory (NVFEL) and with other partner agencies to understand the intricacies of testing heavy-duty hybrid vehicles and systems.   The results were used to quantify the benefit of these systems over various duty cycles and to refine and create test procedures for both chassis and powerpack testing.  The testing preformed consisted of powerpack testing at EPA and chassis testing at California Air Resources Board (CARB) and Environment Canada (EC).  Existing light duty chassis test procedures were used as a basis for the new HD hybrid test procedures.   

Powerpack Test Program

The goal of the laboratory powertrain test was to simulate, as closely as possible, the real-world operation of a complete vehicle over a vehicle speed profile.  It is conceptually the same as performing a chassis type vehicle test, except using only a few key components from the vehicle.  

For the testing done at the EPA, the test cell host automation system was used to implement the control software needed to conduct powertrain testing.  This software included a driver model, and a vehicle model.  These models simulate the operation of a vehicle, and determine the road load forces on the drivetrain.  Figure 1.1 is a block diagram of the how the test cell host automation system is integrated with the test cell hardware.

Figure 1.1  Diagram of the Integration between the Hardware, Driver, and Vehicle Model.

Driver Model

The driver model simulates the actions of a human driver and controls the accelerator and brake to follow a vehicle speed profile.  This was implemented in the test cell at EPA by creating multiple states for the driver model depending on what the simulated vehicle was doing in the cycle.  These states were stopped, launch, accelerating/cruising, and braking.  For each of these states the throttle and the dynamometer were controlling either the speed or the torque at the transmission output shaft.

Driver model "stopped" state was configured two different ways, depending on if a hybrid with an automated manual transmission (AMT) or a conventional transmission with a torque convertor was being tested.  For the hybrid powertrain, the dynamometer controlled the torque of the transmission output shaft to zero and when a conventional powertrain was tested, the dynamometer controlled speed of the output shaft to zero.  The need for the different control modes was due to how the transmissions worked when the engine throttle was at zero and the brake was pressed.   For the hybrid system the electric motor was in speed control when the vehicle was stopped.  If the dynamometer was controlling speed, and if there was even a slight difference in the readings of the transmission output shaft speed between the dynamometer and the electric motor, they would be working against each other and cause the hybrid to do unrepresentative work.  For the conventional transmission the speed had to be controlled to zero or the transmission would have spun when the vehicle was supposed to be stopped.    

The "launch" state was created to simulate the static friction of the vehicle.  To do this the dynamometer controlled the speed to zero until the torque measured at the transmission output shaft was greater than the torque calculated by the vehicle model.  Once the torque met the torque calculated by the vehicle model, the driver model changed to the "acceleration/cruising" state.

The "accelerating/cruising" state was controlled two different ways after learning that the initial way we chose to control had unintended consequences when we tried to test an AMT with the hybrid function turned off.  This was due to the fact that during a shift, the engine was not connected to the transmission so small torque offsets caused the transmission to change speeds unrepresentatively, thus causing the transmission to miss shifts.  Figure 1.2 is an illustration of how torque control affected the transmission output shaft speed.  You can see that when the powertrain was tested in torque control the vehicle speed deceleration during shift was greater and the shifts took longer.   This caused the transmission to miss shifts and caused it to fall behind the cycle.  Controlling the output shaft torque worked fine when the conventional transmission was tested because the engine was always connected to the transmission through the torque convertor.  Thus there was always torque on the transmission output shaft.
                                       
                                       
Figure 1.2 Example of How Torque Control Changed Transmission Speed Unrepresentatively
                                       
The first type of control that was implemented was using the dynamometer to control torque at the output shaft while the throttle was used to control the speed of the output shaft.  In the second method that we implemented, both the dynamometer and the throttle were used to control the speed of the output shaft, but with different setpoints.  The setpoint for the dynamometer was determined by the road load equation and the throttle setpoint came from the cycle.  From this state the driver model could either choose to go to the "stopped" state if the future speed of the cycle was zero or to the "braking" state if the vehicle speed was above the cycle speed and the throttle was at the minimum.  

The last state of the driver model is the "braking" state.  For this state the dynamometer controlled the output shaft speed to the cycle when the throttle was set to the minimum and the brake signal was on.  From this state the vehicle could either go to the "accelerating/cruising" state or the "stopped" state.  If the torque measured at the output shaft was less than the force calculated by the vehicle model (more negative) and the future speed of the cycle was greater than zero, the driver model would go back to the "accelerating/cruising" state.  If the future speed was zero the driver model would go to the "stopped" state.  

Vehicle Model
 
The vehicle model determines transmission output shaft speed setpoint from the cycle and either the transmission output speed or torque based on the current road load force.

To calculate a transmission output shaft speed target based on the cycle, the vehicle model uses equation 1.
                                      Eq. 1
For the "accelerating/cruising" state of the driver model where the dynamometer is controlling torque, equations 2 and 3 are used.

                                      Eq. 2
                                      Eq. 3

When the driver model is using the dynamometer to control speed, equations 4 and 5 are used.  Equation 3 is the same as equation 5 except that equation 3 is solving for the instantaneous road load force while equation 5 is solving for instantaneous vehicle speed.  Equation 4 is similar to equation 1 except that the linear speed is not the cycle speed but instead the target vehicle speed based on the road load equation.
                                      Eq. 4
                                      Eq. 5
                                       
Where:
fnrefcycle = the reference angular speed at the transmission output shaft from the cycle.
S = linear speed of the drive cycle. 
kd = the final drive ratio of the simulated vehicle.
r = load tire radius of the simulated vehicle. 
FR = total road-load force to be applied at the surface of the roll.  The total force is the sum of the individual tractive forces applied at each roll surface.
i = a counter to indicate a point in time over the driving schedule.  For a dynamometer operating at 10-Hz intervals over a 600-second driving schedule, the maximum value of i is 6,000.
A = constant value representing the vehicle's frictional load in lbf or Newtons.
 B = coefficient representing load from drag and rolling resistance, which are a function of vehicle speed, in lbf/mph or N∙s/m.
S = linear speed at the roll surfaces as measured by the dynamometer, in mph or m/s.  Let Si-1 = 0.
C = coefficient representing aerodynamic effects, which are a function of vehicle speed squared, in lbf/mph[2] or N∙s[2]/m[2].
M = mass of vehicle in lbm or kg.  Determine the vehicle's mass based on the test weight, taking into account the effect of rotating axles, as specified in §1066.404 and dividing the weight by the acceleration due to gravity as specified in 40 CFR 1065.630, consistent with good engineering judgment.
t = elapsed time in the driving schedule as measured by the dynamometer, in seconds.  Let ti-1 = 0.
Tref = the reference torque at the transmission output shaft for the dynamometer.
fnrefdyno = the reference angular speed at the transmission output shaft for the dynamometer.

Other signals that had to be simulated to run the tests were the ABS brake signal and the wheel speed.  Both of these signals were sent over the CAN network using standard J1939 protocol. 

Criteria for a Valid Test

Validation criteria for the driver model were the same as what is currently required for chassis testing.  The details can be found §1066.430(e), but in summary the driver has to be within +-2 mph of the maximum or minimum speed of the cycle in a 2 second window.  An illustration of this can be seen in Figure 1.3.
                                       
     Figure 1.3 Example of the allowable ranges for the driver's trace.
                                       
The criterion to validate the speed and torque control of the output shaft for the dynamometer is similar to what is required for engine testing.  The specific criterion of both speed and torque control are in Table 1.1.

          Table 1.1 - Statistical criteria for validating duty cycles
                                   Parameter
                                 Speed Control
                                Torque Control
                                  Slope, a1 
                           0.950 < a1 < 1.030
                           0.950 < a1 < 1.030
                       Absolute value of intercept, |a0|
                       < 2.0 % of maximum test speed
                         < 2.0 % of maximum torque
                       Standard error of estimate, SEE 
                        < 5 % of maximum test speed
                          < 10 % of maximum torque
                      Coefficient of determination, r[2] 
                                  > 0.970
                                  > 0.850

Test Cell Setup

The hardware set-up consisted of a stock diesel engine with a hybrid powerpack, which was then coupled to an engine dynamometer.  Table 1.2 is an overview of the test cell controls and equipment.  Figure 1.4 shows the layout of how the powerpack integrates with the dynamometer.  The picture in Figure 1.5 is of the Cummins ISB and Eaton hybrid system in the powertrain test cell.
                                       

           Table 1.2  -  Powertrain test cell equipment and controls
Dynamometer
GE DC, 600 hp, base speed 2000 rpm, maximum absorption 2100 Nm 
Torque Meter
HBM, In-line 
Test Cell Temperature
25 °C
Test Cell Humidity
65%
Fuel Measurement
AVL Micro Motion Fuel System
Emission Measurement
Horiba Full Flow CVS and Dilution Tunnel for Gaseous & Particulate Sampling
Test Cell Automation
A&D i-Test Software

 

           Figure 1.4  -  Diagram of powerpack layout in test cell.

                                       
Figure 1.5  -  Picture of Cummins ISB and Eaton hybrid in powertrain test cell.
                                       

Vehicle Parameters for Simulated Vehicles
For the powerpack testing multiple vehicles were simulated on two different hardware configurations.  The Eaton hybrid was tested with the hybrid active and inactive.  The only difference between the hybrid active and inactive was the mass of the vehicle with the hybrid active was greater than the vehicle with the hybrid inactive.   A conventional transmission was also tested with the Cummins engine and was tested at the lower test weight.  For the hybrid active and hybrid inactive tests the tire radius and final drive ratio was selected to match the class 7 tractor we tested at EC.

      Table 1.3  -  Vehicle parameters used for powerpack testing at EPA
                                       
                             Hybrid Active Vehicle
                            Hybrid Inactive Vehicle
                             Conventional Vehicle
                                    m (kg)
                                     6450
                                     5883
                                     5883
                                     A (N)
                                     506.1
                                     506.1
                                     506.1
                                  B (N/(m/s))
                                     7.345
                                     7.345
                                     7.345
                                C (N/(m/s)[2])
                                     1.960
                                     1.960
                                     1.960
                                  Tire Radius
                                     0.498
                                     0.498
                                     0.381
                                  Final Drive
                                     5.57
                                     5.57
                                      3.7

California Air Resources Board Chassis Testing
Working with CARB, conventional and hybrid class 6 utility trucks were tested over a number of cycles and different test weights.  The class 6 coastdown coefficients were measured for the hybrid vehicle and used for testing both hybrid and conventional vehicles.  The vehicles were also tested as class 4 vehicles in order to compare the results to the powerpack testing performed at EPA.  The specific mass and coefficients that were used can be found in Table 1.4.

       Table 1.4  -  Vehicle parameters used for chassis testing at CARB
                                       
                            Class 6 Hybrid Vehicle
                         Class 6 Conventional Vehicle
                            Class 4 Hybrid Vehicle
                         Class 4 Conventional Vehicle
                                    m (kg)
                                     11886
                                     11886
                                     6450
                                     5883
                                     A (N)
                                     937.7
                                     937.7
                                     506.1
                                     506.1
                                  B (N/(m/s))
                                    -13.32
                                    -13.32
                                     7.345
                                     7.345
                                C (N/(m/s)[2])
                                     2.928
                                     2.928
                                     1.960
                                     1.960

Environment Canada Chassis Testing
Working with EC and Eaton, a Class 7 tractor with a Cummins ISB coupled to an Eaton hybrid transmission was tested.  The main purpose of this testing was to compare the results with the EPA powerpack testing results.   In order to perform this testing, the engine calibration was changed to a 200 hp rating, and hybrid transmission calibration was changed to match the calibration of the transmission used in the powerpack testing.  A picture of the vehicle can be found in Figure 1.6 below along with the corresponding vehicle specifications in Table 1.5.

The vehicle was then tested with the hybrid active and inactive.  The vehicle test weights and coast down coefficients were the same as those used in the powerpack testing in Table 1.3.  Each vehicle configuration was tested over the Transient, 55 mph Cruise, 65 mph Cruise, and CILCC cycles.
                                       
                                       
                  Figure 1.6  -  Picture of Kenworth tractor.
                                       
               Table 1.5  -  Specifications of Kenworth tractor.
Manufacturer
Kenworth
Model
S21-170
Color
Green
Vin
2XKHMAM7A3BM277905
Serial #
K0779381
Build Date
2/3/2010
Engine
PX-6 280 Cummins  #73073877
Transmission
Model EH-8E406A-T
Aftertreatment
Urea-SCR, DOC and DPF
Rear axle
Spicer Serial # U100340280
Miles
20235
# of Axles
One
Rear Axle Ratio
5.57
GVWR
33000
Tires
Front/Rear  11R 22.5
Wheelbase
152"
Width
96"
                                       
Battery Net Energy Change

For all tests, the energy flow in and out of the battery was measured and compared to the fuel energy over the cycle.  The procedures in SAE 2711 were used to determine if the results needed to be corrected for NEC.  

Results and Analysis

The results from the different test programs were summarized to compare CO2, NOx, and fuel economy.  Figures 1.7, 1.8, and 1.9 show the results for systems utilizing the Eaton hybrid that were tested as a class 4 vehicle.  The charts show the mean with the error bars representing one standard deviation.   

Class 4 Hybrid Results
                                       
                                       
Figure 1.7  -  CO2 (g/ton-mile) for the vehicles with an Eaton hybrid tested as a class 4 vehicle.

                                       
Figure 1.8  -  Fuel economy (mpg) for the vehicles with an Eaton hybrid tested as a class 4 vehicle.

                                       
                                       
Figure 1.9  -  NOx (g/ton-mile) for the vehicles with an Eaton hybrid tested as a class 4 vehicle.

It can be seen in Figures 1.7, 1.8, and 1.9 that results at the different labs are different but can be explained.  The powerpack results for CO2 in g/ton-mile are lower than the same system tested at EC except for the 55 mph cruise cycle.  The powerpack CO2 emissions being lower was expected since the powerpack system had lower accessory loads, for example the cooling fan is not on the powerpack system.  The 55 mph cruise cycle didn't follow the trend but since it is a steady state test is it possible that the lower fuel consumption was due to the engine of the vehicle tested at EC had a slightly different BSFC map and had lower fuel consumption at the point in the map were the engine operated during the 55 mph cruise cycle.  Since the engine and transmission calibrations between the vehicles tested at EC and CARB were different, the results were not expected to match.  In fact since the engine for the system at CARB was rated at 280 hp vs. 200 hp for the EC vehicle, it was anticipated that the vehicle tested at CARB would have higher CO2 emissions, which testing showed to be true.  The other difference, with respect to NOx and CO2 emissions, that needs to be factored in regarding the two vehicles was that the vehicle at CARB did not have a urea-SCR emission control system for NOx reduction.  Therefore, even though the EC vehicle was regulated to a lower tailpipe NOx standard, it probably had higher engine out NOx which correlates with the lower fuel consumption (lower CO2 emissions) when compared to the CARB vehicle.  The lack of NOx aftertreatment on the CARB vehicle also explained why the NOx emissions were higher for the vehicle tested at CARB.

CO2 Reduction from Hybrid Transmission

The other notable comparison derived from this data was how the reduction in CO2 emissions, or improvement factor, for the hybrid active over the hybrid inactive or conventional vehicle compared across tests.  Even though the absolute CO2 emissions for the EC vehicle and the powerpack system were different, the reduction in CO2 emissions was almost the same.  This confirms that the test methods were equivalent on an A to B basis.  The other correlation that should be noted in Table 1.6 was that the vehicle tested at CARB at two different weights and coefficient gave similar reductions in CO2 over the transient cycles.  The 55 and 65 MPH cruise cycle tests didn't line up as well but this is probably due to either the engine for the hybrid or conventional vehicle not having a flat brake specific fuel consumption map at the speeds and loads that the engine was operated at over the cruise cycle tests.  Since the cruise cycles are only comparing the fuel consumption at one point on the engine map it is not too surprising that the reduction in CO2 emissions is not the same for the two test weights.   
                                       
Table 1.6  - CO2 emission reduction with the hybrid active to the hybrid inactive or the conventional transmission
                                     Test
                                 EPA Powerpack
                                  EC Chassis
                             CARB Chassis Class 4
                            CARB Chassis Class 6/7
                                  Comparison
                       Hybrid Active to Hybrid Inactive
                       Hybrid Active to Hybrid Inactive
                         Hybrid Active to Conventional
                         Hybrid Active to Conventional
                                    55 mph
                                     1.0%
                                     3.0%
                                     16.1%
                                     8.3%
                                    65 mph
                                     3.0%
                                     1.1%
                                     18.2%
                                     8.9%
                                   Transient
                                     17.3%
                                     15.7%
                                     21.9%
                                     20.0%
                                     CILCC
                                     19.5%
                                       -
                                     22.0%
                                     21.0%

The data from the conventional transmission tested using the powerpack method is not shown in this report because we were not able to fully validate the data.
                                       

      Table 1.7  -  Results from CARB on a 2007 SoCal Edison Hybrid Truck
                                     Cycle
                                     Phase
                                     Run #
                                      THC
                                      CO
                                      NOx
                                      CO2
                                      NO
                                      NO2
                                   Fuel Eco
                                Inertia Weight
                                       
                                       
                                       
                                    (g/mi)
                                    (g/mi)
                                    (g/mi)
                                    (g/mi)
                                    (g/mi)
                                    (g/mi)
                                   (mi/gal)
                                     (lbm)
                                 55 mph Cruise
                                       1
                                       1
                                       -
                                     0.02
                                     1.79
                                     1119
                                     0.74
                                     1.05
                                     8.94
                                     26204
                                       
                                       1
                                       2
                                       -
                                     0.03
                                     1.79
                                     1104
                                     0.74
                                     1.06
                                     9.05
                                     26204
                                       
                                       1
                                       3
                                       -
                                     0.03
                                     1.87
                                     1145
                                     0.80
                                     1.07
                                     8.70
                                     26204
                                       
                                       1
                                       4
                                       -
                                     0.03
                                     1.81
                                     1123
                                     0.76
                                     1.05
                                     8.87
                                     26204
                                 65 mph Cruise
                                       2
                                       1
                                       -
                                       -
                                     2.57
                                     1509
                                     1.24
                                     1.32
                                     6.84
                                     26204
                                       
                                       2
                                       2
                                       -
                                     0.03
                                     2.67
                                     1503
                                     1.33
                                     1.34
                                     6.85
                                     26204
                                       
                                       2
                                       3
                                       -
                                     0.04
                                     2.80
                                     1551
                                     1.47
                                     1.33
                                     6.66
                                     26204
                                       
                                       2
                                       4
                                       -
                                     0.05
                                     2.76
                                     1553
                                     1.48
                                     1.28
                                     6.65
                                     26204
                                 Cummins VFTP
                                       1
                                       1
                                       -
                                       -
                                     3.54
                                      974
                                     0.96
                                     2.58
                                     10.59
                                     26204
                                       
                                       1
                                       3
                                     0.02
                                     0.38
                                     3.53
                                      952
                                     1.14
                                     2.40
                                     10.64
                                     26204
                                       
                                       1
                                       4
                                     0.02
                                     0.37
                                     3.75
                                      985
                                     1.44
                                     2.31
                                     10.39
                                     26204
                                   Transient
                                       1
                                       2
                                     0.02
                                     0.35
                                     3.93
                                     1258
                                     1.27
                                     2.66
                                     8.13
                                     26204
                                       
                                       1
                                       4
                                     0.02
                                     0.23
                                     4.43
                                     1250
                                     1.57
                                     2.87
                                     8.13
                                     26204
                                       
                                       1
                                       5
                                     0.02
                                     0.21
                                     4.23
                                     1229
                                     1.48
                                     2.76
                                     8.29
                                     26204
                              Allison School Bus
                                       1
                                       1
                                       -
                                     0.18
                                     5.72
                                     1730
                                     2.54
                                     3.18
                                     5.97
                                     26204
                                       
                                       1
                                       2
                                       -
                                     0.22
                                     6.04
                                     1769
                                     2.54
                                     3.51
                                     5.71
                                     26204
                                       
                                       1
                                       3
                                       -
                                       -
                                     5.98
                                     1770
                                     2.58
                                     3.41
                                     5.81
                                     26204
                                       
                                       1
                                       4
                                       -
                                     0.20
                                     6.43
                                     1796
                                     2.82
                                     3.61
                                     5.70
                                     26204
                                    FTP4bag
                                       1
                                       2
                                     0.06
                                       -
                                     5.83
                                       -
                                     4.03
                                     1.80
                                       -
                                     26204
                                       
                                       2
                                       2
                                       -
                                     0.14
                                     5.73
                                     1385
                                     2.15
                                     3.58
                                     7.40
                                     26204
                                       
                                       3
                                       2
                                       -
                                     0.13
                                     4.45
                                     1360
                                     2.01
                                     2.44
                                     7.54
                                     26204
                                       
                                       4
                                       2
                                       -
                                     0.14
                                     5.21
                                     1364
                                     1.98
                                     3.23
                                     7.51
                                     26204
                                 Manhattan Bus
                                       1
                                       1
                                       -
                                     0.42
                                     8.52
                                     2156
                                     3.37
                                     5.15
                                     4.74
                                     26204
                                       
                                       1
                                       2
                                       -
                                       -
                                     8.80
                                     2216
                                     3.44
                                     5.36
                                     4.61
                                     26204
                                       
                                       1
                                       3
                                       -
                                     0.58
                                     8.63
                                     2215
                                     3.41
                                     5.22
                                     4.65
                                     26204
                               Allison Food Dist
                                       1
                                       1
                                       -
                                     0.05
                                     2.32
                                     1126
                                     0.89
                                     1.43
                                     9.16
                                     26204
                                     CILCC
                                       1
                                       2
                                       -
                                     0.28
                                     3.98
                                     1102
                                     1.08
                                     2.90
                                     9.29
                                     26204
                                       
                                       1
                                       3
                                       -
                                     0.32
                                     3.46
                                     1066
                                     1.01
                                     2.45
                                     9.61
                                     26204
                                       
                                       1
                                       4
                                       -
                                     0.20
                                     3.74
                                     1085
                                     1.09
                                     2.65
                                     9.42
                                     26204
                                       
                                       2
                                       2
                                       -
                                     0.13
                                     3.79
                                     1292
                                     1.50
                                     2.29
                                     7.93
                                     26204
                                       
                                       2
                                       3
                                       -
                                     0.11
                                     3.87
                                     1288
                                     1.80
                                     2.07
                                     7.90
                                     26204
                                       
                                       2
                                       4
                                       -
                                     0.14
                                     3.75
                                     1249
                                     1.65
                                     2.10
                                     8.21
                                     26204
                                       
                                       3
                                       2
                                     0.04
                                     0.29
                                     4.36
                                     1231
                                     1.61
                                     2.75
                                     8.34
                                     26204
                                       
                                       3
                                       3
                                     0.03
                                     0.36
                                     4.03
                                     1163
                                     1.51
                                     2.52
                                     8.80
                                     26204
                                       
                                       3
                                       4
                                     0.01
                                     0.25
                                     4.21
                                     1204
                                     1.79
                                     2.42
                                     8.49
                                     26204
                                       
                                       4
                                       2
                                     0.02
                                     0.35
                                     4.78
                                     1310
                                     1.88
                                     2.90
                                     7.84
                                     26204
                                       
                                       4
                                       3
                                     0.03
                                     0.27
                                     4.26
                                     1283
                                     1.87
                                     2.39
                                     7.98
                                     26204
                                       
                                       4
                                       4
                                     0.16
                                       -
                                     4.38
                                     1162
                                     1.85
                                     2.53
                                       -
                                     26204
                                   Transient
                                       1
                                       1
                                     0.02
                                       -
                                     3.56
                                      906
                                     1.34
                                     2.22
                                     11.30
                                     14220
                                       
                                       1
                                       2
                                     0.02
                                     0.30
                                     3.57
                                      920
                                     1.27
                                     2.30
                                     11.12
                                     14220
                                       
                                       1
                                       3
                                     0.02
                                     0.31
                                     3.65
                                      923
                                     1.21
                                     2.44
                                     11.10
                                     14220
                                 55 mph Cruise
                                       1
                                       1
                                       -
                                     0.03
                                     1.74
                                      882
                                     0.67
                                     1.07
                                     11.26
                                     14220
                                       
                                       1
                                       2
                                       -
                                     0.05
                                     1.69
                                      865
                                     0.68
                                     1.01
                                     11.56
                                     14220
                                       
                                       1
                                       1
                                       -
                                     0.04
                                     1.79
                                      873
                                     0.68
                                     1.11
                                     11.47
                                     14220
                                 65 mph Cruise
                                       2
                                       1
                                       -
                                     0.04
                                     2.15
                                     1148
                                     0.92
                                     1.23
                                     8.99
                                     14220
                                       
                                       2
                                       2
                                       -
                                     0.05
                                     2.00
                                     1148
                                     0.87
                                     1.14
                                     9.00
                                     14220
                                       
                                       2
                                       1
                                       -
                                     0.04
                                     2.00
                                     1148
                                     0.85
                                     1.15
                                     9.01
                                     14220
                                     CILCC
                                       1
                                       1
                                       -
                                     0.35
                                     2.52
                                      809
                                     0.56
                                     1.97
                                     12.59
                                     14220
                                       
                                       1
                                       2
                                       -
                                     0.55
                                     3.19
                                       -
                                     0.72
                                     2.47
                                       -
                                     14220
                                       
                                       1
                                       3
                                       -
                                     0.46
                                     2.88
                                      833
                                     0.72
                                     2.16
                                     12.40
                                     14220
                                       
                                       2
                                       1
                                       -
                                     0.45
                                     3.04
                                      997
                                     1.14
                                     1.90
                                     10.26
                                     14220
                                       
                                       2
                                       2
                                       -
                                     0.46
                                     2.96
                                      987
                                     1.18
                                     1.78
                                     10.35
                                     14220
                                       
                                       2
                                       3
                                       -
                                     0.38
                                     3.17
                                      969
                                     1.48
                                     1.69
                                     10.58
                                     14220
                                       
                                       3
                                       1
                                       -
                                     0.74
                                     3.49
                                      902
                                     1.37
                                     2.12
                                     11.22
                                     14220
                                       
                                       3
                                       2
                                     0.26
                                     0.65
                                     3.83
                                      944
                                     1.60
                                     2.22
                                     10.76
                                     14220
                                       
                                       3
                                       3
                                     0.05
                                     0.79
                                     3.55
                                     1012
                                     1.67
                                     1.88
                                     10.01
                                     14220
                                       
                                       4
                                       1
                                       -
                                     0.51
                                     3.87
                                      943
                                     2.03
                                     1.84
                                     10.80
                                     14220
                                       
                                       4
                                       2
                                     0.05
                                     0.51
                                     3.91
                                     1083
                                     1.95
                                     1.97
                                     9.41
                                     14220
                                       
                                       4
                                       3
                                     0.06
                                     0.50
                                     3.94
                                      996
                                     2.32
                                     1.62
                                     10.18
                                     14200
                                     UDDS
                                       1
                                       1
                                       -
                                       -
                                       -
                                       -
                                     0.36
                                       -
                                       -
                                     14220
                                       
                                       1
                                       2
                                     0.01
                                     0.05
                                     0.99
                                      217
                                     0.71
                                     0.27
                                     47.44
                                     14220
                                       
                                       1
                                       3
                                       -
                                     0.02
                                     0.89
                                      206
                                     0.52
                                     0.37
                                     50.07
                                     14220
                                       
                                       
    Table 1.8 -  Results from CARB on a 2007 SoCal Edison Non-Hybrid Truck
                                     Cycle
                                     Phase
                                     Run #
                                      THC
                                      CO
                                      NOx
                                      CO2
                                      NO
                                      NO2
                                   Fuel Eco
                                Inertia Weight
                                       
                                       
                                       
                                    (g/mi)
                                    (g/mi)
                                    (g/mi)
                                    (g/mi)
                                    (g/mi)
                                    (g/mi)
                                   (mi/gal)
                                     (lbm)
                                   Transient
                                       1
                                       1
                                     0.02
                                     0.07
                                     2.66
                                     1560
                                     1.05
                                     1.61
                                     6.55
                                     26204
                                       
                                       1
                                       2
                                       -
                                     0.07
                                     2.46
                                     1560
                                     1.20
                                     1.26
                                     6.55
                                     26204
                                       
                                       1
                                       3
                                     0.02
                                       -
                                     2.43
                                     1551
                                     1.21
                                     1.22
                                     6.58
                                     26204
                                 55 mph Cruise
                                       1
                                       1
                                       -
                                     0.05
                                     1.81
                                     1218
                                     0.79
                                     1.02
                                     8.21
                                     26204
                                       
                                       1
                                       2
                                       -
                                     0.06
                                     1.87
                                     1226
                                     0.79
                                     1.09
                                     8.15
                                     26204
                                       
                                       1
                                       3
                                       -
                                     0.04
                                     1.91
                                     1227
                                     0.82
                                     1.10
                                     8.16
                                     26204
                                 65 mph Cruise
                                       2
                                       1
                                       -
                                     0.05
                                     2.88
                                     1662
                                     1.33
                                     1.55
                                     6.21
                                     26204
                                       
                                       2
                                       2
                                       -
                                     0.06
                                     2.91
                                     1677
                                     1.36
                                     1.55
                                     6.15
                                     26204
                                       
                                       2
                                       3
                                       -
                                     0.04
                                     3.04
                                     1696
                                     1.45
                                     1.59
                                     6.08
                                     26204
                                     CILCC
                                       1
                                       1
                                       -
                                     0.13
                                     3.23
                                     1562
                                     1.42
                                     1.82
                                     6.55
                                     26204
                                       
                                       1
                                       2
                                       -
                                     0.10
                                     3.69
                                     1535
                                     1.74
                                     1.95
                                     6.67
                                     26204
                                       
                                       1
                                       3
                                       -
                                     0.16
                                     3.38
                                     1534
                                     1.53
                                     1.85
                                     6.71
                                     26204
                                       
                                       2
                                       1
                                       -
                                     0.10
                                     3.02
                                     1525
                                     1.68
                                     1.34
                                     6.73
                                     26204
                                       
                                       2
                                       2
                                       -
                                     0.14
                                     3.13
                                     1516
                                     1.87
                                     1.27
                                     6.82
                                     26204
                                       
                                       2
                                       3
                                       -
                                     0.10
                                     2.97
                                     1512
                                     1.72
                                     1.24
                                     6.79
                                     26204
                                       
                                       3
                                       1
                                     0.02
                                     0.16
                                     3.32
                                     1581
                                     1.93
                                     1.39
                                     6.46
                                     26204
                                       
                                       3
                                       2
                                       -
                                     0.11
                                     3.69
                                     1555
                                     2.22
                                     1.48
                                     6.59
                                     26204
                                       
                                       3
                                       3
                                       -
                                     0.13
                                     3.61
                                     1564
                                     2.09
                                     1.52
                                     6.52
                                     26204
                                       
                                       4
                                       1
                                     0.01
                                       -
                                     3.42
                                     1578
                                     2.07
                                     1.36
                                     6.46
                                     26204
                                       
                                       4
                                       2
                                       -
                                     0.06
                                     3.73
                                     1485
                                     2.29
                                     1.44
                                     6.87
                                     26204
                                       
                                       4
                                       3
                                       -
                                     0.06
                                     3.62
                                     1557
                                     2.18
                                     1.44
                                     6.54
                                     26204
                                   Transient
                                       1
                                       1
                                       -
                                     0.08
                                     2.53
                                     1191
                                     1.43
                                     1.10
                                     8.56
                                     12970
                                       
                                       1
                                       2
                                     0.04
                                     0.05
                                     2.63
                                     1165
                                     1.61
                                     1.02
                                     8.74
                                     12970
                                       
                                       1
                                       3
                                     0.02
                                     0.09
                                     2.68
                                     1154
                                     1.62
                                     1.06
                                     8.83
                                     12970
                                       
                                       1
                                       4
                                     0.03
                                     0.06
                                     3.30
                                     1184
                                     2.17
                                     1.13
                                     8.59
                                     12970
                                 55 mph Cruise
                                       1
                                       1
                                       -
                                     0.04
                                     2.13
                                     1035
                                     0.96
                                     1.16
                                     9.67
                                     12970
                                       
                                       1
                                       2
                                       -
                                     0.05
                                     2.13
                                     1067
                                     0.97
                                     1.16
                                     9.40
                                     12970
                                       
                                       1
                                       3
                                       -
                                     0.04
                                     2.02
                                     1020
                                     0.98
                                     1.05
                                     9.80
                                     12970
                                 65 mph Cruise
                                       2
                                       1
                                       -
                                     0.05
                                     2.55
                                     1415
                                     1.15
                                     1.40
                                     7.33
                                     12970
                                       
                                       2
                                       2
                                       -
                                     0.05
                                     2.75
                                     1433
                                     1.25
                                     1.49
                                     7.22
                                     12970
                                       
                                       2
                                       3
                                       -
                                     0.05
                                     2.48
                                     1360
                                     1.16
                                     1.32
                                     7.58
                                     12970
                                     CILCC
                                       1
                                       1
                                       -
                                     0.15
                                     3.12
                                     1272
                                     1.65
                                     1.48
                                     8.10
                                     12970
                                       
                                       1
                                       2
                                       -
                                     0.09
                                     3.21
                                     1248
                                     1.71
                                     1.51
                                     8.25
                                     12970
                                       
                                       1
                                       3
                                     0.01
                                     0.09
                                     2.92
                                     1212
                                     1.57
                                     1.35
                                     8.23
                                     12970
                                       
                                       2
                                       1
                                       -
                                     0.10
                                     2.71
                                     1172
                                     1.84
                                     0.87
                                     8.75
                                     12970
                                       
                                       2
                                       2
                                     0.03
                                     0.06
                                     2.77
                                     1200
                                     1.88
                                     0.90
                                     8.56
                                     12970
                                       
                                       2
                                       3
                                     0.05
                                     0.07
                                     2.57
                                     1179
                                     1.75
                                     0.82
                                     8.50
                                     12970
                                       
                                       3
                                       1
                                     0.01
                                     0.10
                                     3.40
                                     1255
                                     2.36
                                     1.05
                                     8.10
                                     12970
                                       
                                       3
                                       2
                                     0.05
                                     0.08
                                     3.33
                                     1229
                                     2.26
                                     1.07
                                     8.34
                                     12970
                                       
                                       3
                                       3
                                       -
                                       -
                                     3.17
                                     1267
                                     2.41
                                     0.76
                                     8.08
                                     12970
                                       
                                       4
                                       1
                                       -
                                     0.08
                                     3.42
                                     1270
                                     2.51
                                     0.91
                                     8.02
                                     12970
                                       
                                       4
                                       2
                                     0.07
                                     0.09
                                     3.34
                                     1263
                                     2.34
                                     1.00
                                     8.06
                                     12970
                                       
                                       4
                                       3
                                     0.10
                                     0.14
                                     3.13
                                     1252
                                     2.22
                                     0.91
                                     8.18
                                     12970
                                       
                                       
                                       
                                       
           Table 1.9  -  EC Chassis Results with Eaton Hybrid Active
                                     Cycle
                                     Run #
                                   Fuel Eco
                                      CO2
                                      CO
                                      HC
                                      NOx
                                      CH4
                                      N2O
                                      PM
                                       
                                       
                                     (mpg)
                                   (g/mile)
                                   (g/mile)
                                   (g/mile)
                                   (g/mile)
                                   (g/mile)
                                   (mg/mile)
                                   (mg/mile)
                                 55 mph Cruise
                                       1
                                     14.4
                                      719
                                       0
                                    0.0000
                                     0.325
                                       -
                                     44.8
                                      6.1
                                       
                                       2
                                     14.3
                                      725
                                       0
                                    0.0000
                                     0.139
                                       -
                                     36.1
                                      7.4
                                       
                                       3
                                     14.1
                                      732
                                       0
                                    0.0000
                                     0.267
                                       -
                                     82.3
                                       -
                                       
                                       4
                                     14.6
                                      708
                                       0
                                    0.0000
                                     0.033
                                     1.729
                                     125.0
                                      2.0
                                       
                                       5
                                     14.5
                                      713
                                       0
                                    0.0000
                                     0.158
                                     0.000
                                     42.2
                                      5.6
                                 65 mph Cruise
                                       1
                                     11.3
                                      911
                                       0
                                    0.0000
                                     0.045
                                       -
                                     153.0
                                      3.1
                                       
                                       2
                                     11.2
                                      923
                                       0
                                    0.0000
                                     0.098
                                       -
                                     103.7
                                     19.0
                                       
                                       3
                                     11.1
                                      931
                                       0
                                    0.0000
                                     0.105
                                       -
                                     122.7
                                       -
                                       
                                       4
                                     11.0
                                      936
                                       0
                                    0.0000
                                     0.071
                                     0.000
                                     201.1
                                      4.3
                                       
                                       5
                                     11.2
                                      923
                                       0
                                    0.0000
                                     0.060
                                     0.000
                                     101.5
                                      2.4
                                   Transient
                                       1
                                     11.2
                                      920
                                       0
                                    0.0230
                                     2.073
                                     8.264
                                       -
                                      8.4
                                       
                                       2
                                     11.4
                                      906
                                       0
                                    0.0065
                                     1.057
                                     3.053
                                       -
                                       -
                                       
                                       3
                                     11.8
                                      879
                                       0
                                    0.0098
                                     1.944
                                     2.493
                                       -
                                     10.5
                                       
                                       4
                                     12.1
                                      857
                                       0
                                    0.0032
                                     1.194
                                     2.072
                                       -
                                       -
                                       
                                       5
                                     11.6
                                      888
                                       0
                                    0.0096
                                     1.963
                                     7.541
                                       -
                                      4.6
                                       
                                       6
                                     12.0
                                      859
                                       0
                                    0.0064
                                     1.105
                                     0.917
                                       -
                                       -
                                     CILCC
                                       1
                                     12.9
                                      799
                                       0
                                    0.0151
                                     1.650
                                       -
                                       -
                                       -
                                       
                                       2
                                     12.5
                                      828
                                       0
                                    0.0047
                                     1.437
                                     4.414
                                     40.9
                                      1.3
                                       
                                       3
                                     12.2
                                      846
                                       0
                                    0.0135
                                     1.633
                                    13.340
                                     54.1
                                      1.0
                                       
                                       4
                                     13.1
                                      787
                                       0
                                    0.0060
                                     0.705
                                     8.513
                                      0.0
                                      3.0
                                     vFTP
                                       1
                                     12.7
                                      811
                                       0
                                    0.0000
                                     0.897
                                     0.175
                                     34.2
                                      3.0
                                       
                                       2
                                     12.4
                                      833
                                       0
                                    0.0000
                                     0.903
                                     6.919
                                     20.5
                                      2.4
                                       
                                       3
                                     12.6
                                      820
                                       0
                                    0.0000
                                     0.889
                                     0.790
                                     16.2
                                      2.9
                                       
         Table 1.10  -  EC Chassis Results with Eaton Hybrid Inactive
                                     Cycle
                                     Run #
                                   Fuel Eco
                                      CO2
                                      CO
                                      HC
                                      NOx
                                      CH4
                                      N2O
                                      PM
                                       
                                       
                                     (mpg)
                                   (g/mile)
                                   (g/mile)
                                   (g/mile)
                                   (g/mile)
                                   (g/mile)
                                   (mg/mile)
                                   (mg/mile)
                                 55 mph Cruise
                                       1
                                     13.6
                                      758
                                     0.009
                                     0.000
                                    11.758
                                       0
                                       -
                                     0.00
                                       
                                       2
                                     13.9
                                      741
                                     0.011
                                     0.000
                                    11.783
                                       -
                                       -
                                     0.00
                                       
                                       3
                                     14.3
                                      725
                                     0.011
                                     0.000
                                     0.000
                                       0
                                       -
                                     0.00
                                 65 mph Cruise
                                       1
                                     10.9
                                      949
                                     0.013
                                     0.000
                                    11.478
                                       0
                                       -
                                     0.00
                                       
                                       2
                                     11.2
                                      921
                                     0.013
                                     0.000
                                    11.276
                                       -
                                       -
                                     0.00
                                       
                                       3
                                     11.1
                                      934
                                     0.009
                                     0.000
                                     0.000
                                       0
                                       -
                                     0.00
                                   Transient
                                       1
                                      9.6
                                     1081
                                     0.666
                                     0.018
                                     1.416
                                     20.28
                                     84.1
                                     7.84
                                       
                                       2
                                      9.6
                                     1072
                                     0.131
                                     0.003
                                     0.713
                                     16.46
                                     83.8
                                       -
                                       
                                       3
                                      9.9
                                     1045
                                     0.816
                                     0.021
                                     1.994
                                     7.67
                                     100.3
                                     5.97
                                       
                                       4
                                     10.2
                                     1009
                                     0.545
                                     0.003
                                     0.784
                                     1.33
                                     75.9
                                       -
                                       
                                       5
                                      9.9
                                     1046
                                     0.874
                                     0.038
                                     2.006
                                     12.96
                                     82.3
                                     2.63
                                       
                                       6
                                      9.9
                                     1044
                                     0.400
                                     0.014
                                     1.026
                                     11.33
                                     70.6
                                       -
                                    HD UDDS
                                       1
                                     11.2
                                      920
                                     0.272
                                     0.000
                                     0.584
                                     8.40
                                     54.6
                                     7.79
                                       
                                       2
                                     11.3
                                      917
                                     0.226
                                     0.000
                                     0.894
                                     2.63
                                     25.0
                                     7.79
                                       
                                       3
                                     11.7
                                      882
                                     0.281
                                     0.000
                                     1.264
                                     3.68
                                     41.4
                                     4.06
                                     WTVC
                                       1
                                     13.5
                                      767
                                     0.040
                                     0.005
                                     0.966
                                     13.38
                                     75.9
                                     0.00
                                       
                                       2
                                     13.4
                                      772
                                     0.065
                                     0.004
                                     0.674
                                     0.00
                                     53.0
                                     1.24
                                       
                                       3
                                     13.7
                                      754
                                     0.036
                                     0.005
                                     0.542
                                     8.80
                                     45.4
                                     1.67
                                       

Comparison of Test Results Across Test Protocol Options
Test data from EPA's protocol development program indicates similar performance improvements for hybrid versus conventional systems when tested as a complete vehicle chassis configuration or post-transmission powerpack configuration.  
            Table 1.10 Hybrid Improvements across Test Methods
                                     Test
                                 EPA Powerpack
                                  EC Chassis
                                  Comparison
                       Hybrid Active to Hybrid Inactive
                       Hybrid Active to Hybrid Inactive
                                    55 mph
                                     1.0%
                                     3.0%
                                    65 mph
                                     3.0%
                                     1.1%
                                   Transient
                                     17.3%
                                     15.7%
                                     CILCC
                                     19.5%
                                       -
				

PTO Testing and Protocol Development

Introduction

The fourth part of testing was split into three different segments.  The first was data collection and analysis to create a composite PTO duty cycle.  This work was performed at Southwest Research Institute (SwRI) in San Antonio, Texas.  Initial work at SwRI was also focused on creating a hydraulic test rig designed to simulate loading on a vehicle's PTO system.  The composite cycle and test equipment was then provided to EPA's NVFEL lab in Ann Arbor, MI where a control system was designed and built for the PTO test rig and initial hydraulic testing was performed to verify proper operation.  Lastly, the test equipment was used in an Agency test program at a California Air Resources Board (CARB) lab in Los Angeles, CA where two Class 6 utility vehicles equipped with hydraulic PTO's were tested.  

Data Collection and Duty Cycle Development

      The initial part of the work at SwRI focused on determining the proper types of vehicles to test and subsequently to construct representative PTO drive cycles.  Work began by performing research on annual sales volumes for PTO-equipped vehicle groups/applications that were either already being hybridized or had the potential to be in the very near future.  Two major applications were picked as being candidates, utility boom trucks (utility) and automated side loader (ASL) refuse trucks.  It is generally accepted that there are approximately 150,000 utility boom trucks in operation in the United States and approximately 100,000 refuse trucks in operation, of which 20,000 are ASL-type refuse trucks.   Based on the understanding that these two classes of vehicles either currently have hybrid PTO operation as an option (utility) or will have the feature available soon (ASL Refuse), these two applications were chosen as a basis for representative PTO drive cycles based on actual operation of these two types of vehicles.  
      
      SwRI obtained one utility boom truck and one refuse truck to instrument for data collection while in-use.  The utility truck, a 2008 Ford F-750, as shown in Figure 1.10, was equipped with a Caterpillar C7 diesel engine, an automatic Allison five-speed transmission, and Eaton PTO and pump.  The specifications of this truck are listed in Table 1.11.  A turbine-style flow meter and a pressure transducer were installed on the outlet side of the hydraulic pump to allow the pump flow and pressure, shown in Figure 1.11.  The truck and engine used the SAE J1939 CAN communication protocol which was used to record vehicle speed, engine speed, engine fuel rate, and engine load.  An example of the data recorded is shown in Figure 1.13.  Together, the data was used to determine the amount of time the PTO was used compared to the amount of time the vehicle was in operation.  The utility truck was operated for a total of four weeks, two weeks each in two different geographic locations, urban and rural, for this project.
      
      
      
      
      
      
      
      
      
                    Table 1.11 Utility Truck Configuration
                                    Vehicle
                                2008 Ford F-750
                             VIN 3FRXF75T99V100971
                                    Engine
                                Caterpillar C7
                               Emission controls
                                   EGR, DPF
                                Rated power, hp
                                      250
                                 Transmission
                          Allison Automatic, 5-speed
                                   GVWR, lb
                                    33,000
                                   PTO Pump
                             Eaton, 14 gpm@700 RPM
      
      
                                          
      
               Figure 1.10 Utility Truck Used For In-Use Data Logging
      
      
                                          
                                          
      Figure 1.11 Flow Meter and Pressure Transducer Installed on Utility Truck 
      
      The second vehicle to be instrumented was an automated side loader (ASL) type refuse truck.  This was done due to their increasing popularity, industry feedback and that this application was a likely candidate for hybridization in the near future.  The truck instrumented for this project was a 2010 Mack equipped with a Mack 10L diesel engine and an Allison automatic 5-speed transmission.  The specifications for this truck are shown in Table 1.12.   As with the utility truck, the ASL truck's J1939 CAN communication was used to record vehicle speed, engine speed, engine fuel rate, and engine load.  Data collected from the instrumented vehicles were formatted as in Figure 1.13.
TABLE 1.12 Refuse Truck Configuration

                                    Vehicle
                                   2010 Mack
                             VIN 1M2AU02C6AM004642
                                    Engine
                                 Mack MP7-405M
                               Emission controls
                                   EGR, DPF
                                Rated power, hp
                                      405
                                 Transmission
                               Allison 4500 RDS
                                   GVWR, lb
                                    56,000
                                   PTO Pump
                          Arm: Parker, 16 gpm@700 RPM
                       Compactor: Parker, 23 gpm@700 RPM
                                          
       Figure1.12  Example of an Automated Side Load Loader (ASL) Refuse Truck
                                          
         Figure 1.13 Example of Loader Data Recorded from ASL Refuse Truck 
                                          
After the data was collected from the two instrumented vehicles, work was done to create a representative drive cycle based on real world vehicle PTO operation.  For the purposes of the cycle development, data were selected only during the component operation when the truck was not moving (i.e., vehicle speed = 0).  In addition, pump flow and pump pressure conditions were also analyzed in order to identify idle and PTO operations.  If a single data recording resulted in the pump pressure >= 200 and the pump flow > 0, then the PTO was considered to be operating (i.e., "on").  Alternatively, the PTO was considered "off' if the pump pressure < 200 and the pump flow = 0.  Data was not included in the duty cycle analyses for the PTO "off" condition.  The utility truck was operated in two different environments, rural and urban.  These two operating environments gave drastically different modes of operation.  For the rural mode, 9.66% of the time was spent in PTO "on" operation while 90.34% of the time was spent in the idle conditions.   For the urban test environment, 49.89% of the time was spent in PTO "on" operation while 50.11% of the time was spent in the idle and PTO `off' conditions.  Statistical analysis of the pressure data resulted in the majority of the data being centered around 2500 psi.  The maximum pump pressure allowed on the vehicle was 3000 psi.  The pressures were normalized resulting in the rural setting operating at 80.45% of the rated maximum pump pressure and the urban setting operating at 83.47% of the rated maximum pump pressure.  
Similar analysis was done for the refuse truck application resulting in 22.01% of the time being spent in the loader only PTO `on' operation, 25.96% of the time being spent in the compactor only PTO `on' operation, and 20.07% of the time being used when both the compactor and the loader were operating in the PTO `on' condition.  Idle conditions comprised 31.96% of the total available time.   Cluster analysis was used to determine appropriate normalized pressures for each ASL circuit.
      
      
      The PTO cycle was then created from all sets of data from the utility and refuse applications.  The duration of the cycle was targeted to be 10 minutes in duration.  Table 1.12, below, shows the time for the periods of the composite cycle.
      
                 TABLE 1.13 Composite 10-minute cycle times by
                            vehicle and application

                                    Vehicle
                            Population Weighting %
                                  Application
                            Application Weighting %
                          Composite Cycle Weighting %
                          Composite Cycle Time (min)
                          Composite Cycle Time (sec)
                                 Utility Truck
                                      60
                                     Rural
                                      20
                                      12
                                      1.2
                                      72
                                       
                                       
                                     Urban
                                      80
                                      48
                                      4.8
                                      288
                                 Refuse Truck
                                      40
                                  Residential
                                      100
                                      40
                                      4.0
                                      240

Table 1.14 on the next page shows the completed composite cycle.  This cycle is designed so that vehicles with only one hydraulic circuit will be tested on the utility truck circuit (Circuit 1) while those vehicles with two hydraulic circuits will be tested on both circuits running concurrently.

             Table 1.14 Final Composite 10-Minute PTO Duty Cycle 
                                       
                                   Time, sec
                           Utility Truck (Circuit 1)
                                       
Refuse Compactor Pump 1
                              Refuse (Circuit 2)
                                    Vehicle
                                  Application
                                     Mode
                                  Time (sec)
                                     0-32
                                       0
                                       0
                                    Utility
                                     Rural
                                   2 (Idle)
                         32  (1/2 of total idle time)
                                     33-39
                                     80.45
                                       0
                                    Utility
                                     Rural
                                       1
                                       7
                                     40-72
                                       0
                                       0
                                    Utility
                                     Rural
                                   2 (Idle)
                         33  (1/2 of total idle time)
                                    73-144
                                       0
                                       0
                                    Utility
                                     Urban
                                   2 (Idle)
                         72  (1/2 of total idle time)
                                    145-288
                                     83.47
                                       0
                                    Utility
                                     Urban
                                       1
                                      144
                                    289-360
                                       0
                                       0
                                    Utility
                                     Urban
                                   2 (Idle)
                         72  (1/2 of total idle time)
                                    361-362
                                       0
                                      13
                                    Refuse
                                    Loader
                                       1
                                       2
                                    363-372
                                       0
                                      38
                                    Refuse
                                    Loader
                                       2
                                      10
                                    373-383
                                       0
                                      53
                                    Refuse
                                    Loader
                                       3
                                      11
                                    384-387
                                       0
                                     72.99
                                    Refuse
                                    Loader
                                       4
                                       4
                                    388-400
                                       0
                                       0
                                    Refuse
                                    Loader
                                   5 (idle)
                                      13
                                    401-402
                                       0
                                      13
                                    Refuse
                                    Loader
                                       1
                                       2
                                    403-412
                                       0
                                      38
                                    Refuse
                                    Loader
                                       2
                                      10
                                    413-423
                                       0
                                      53
                                    Refuse
                                    Loader
                                       3
                                      11
                                    424-427
                                       0
                                     72.99
                                    Refuse
                                    Loader
                                       4
                                       4
                                    428-440
                                       0
                                       0
                                    Refuse
                                    Loader
                                   5 (idle)
                                      13
                                    441-466
                                     11.24
                                       0
                                    Refuse
                                   Compactor
                                       1
                                      26
                                    467-471
                                     29.28
                                       0
                                    Refuse
                                   Compactor
                                       2
                                       5
                                    472-484
                                       0
                                       0
                                    Refuse
                                   Compactor
                                   3 (idle)
                                      13
                                    485-510
                                     11.24
                                       0
                                    Refuse
                                   Compactor
                                       1
                                      26
                                    511-515
                                     29.28
                                       0
                                    Refuse
                                   Compactor
                                       2
                                       5
                                    516-528
                                       0
                                       0
                                    Refuse
                                   Compactor
                                   3 (idle)
                                      13
                                    529-530
                                     12.81
                                     11.08
                                    Refuse
                             Compactor and Loader
                                       1
                                       2
                                    531-539
                                     12.81
                                    38.162
                                    Refuse
                             Compactor and Loader
                                       2
                                       9
                                    540-548
                                     12.81
                                     53.42
                                    Refuse
                             Compactor and Loader
                                       3
                                       9
                                    549-551
                                     12.81
                                     73.53
                                    Refuse
                             Compactor and Loader
                                       4
                                       3
                                    552-564
                                       0
                                       0
                                    Refuse
                             Compactor and Loader
                                   5 (idle)
                                      13
                                    565-566
                                     12.81
                                     11.08
                                    Refuse
                             Compactor and Loader
                                       1
                                       2
                                    567-575
                                     12.81
                                    38.162
                                    Refuse
                             Compactor and Loader
                                       2
                                       9
                                    576-584
                                     12.81
                                     53.42
                                    Refuse
                             Compactor and Loader
                                       3
                                       9
                                    585-587
                                     12.81
                                     73.53
                                    Refuse
                             Compactor and Loader
                                       4
                                       3
                                    588-600
                                       0
                                       0
                                    Refuse
                             Compactor and Loader
                                   5 (idle)
                                      13
      

      A diagram of the test rig hydraulic circuit is shown below.  The theory of operation is to install the test rig into the vehicle's PTO system and use it to simulate load on the hydraulic PTO.  In this manner, each vehicle can be tested the same way and with the same normalized pressure.   The rig operates by flowing the hydraulic fluid from the pump through a dynamically controlled restriction valve (PC1 and 2 on the drawing), which is controlled via software to command the system pressures follow those of the 10 minute PTO duty cycle.  The bypass valve BV1&2 direct the fluid flow to either the return or pressure controlled circuits of the test rig.  Work done by the pump is calculated by measuring the system pressure and fluid flow from the pump.

    Figure 1.14 PTO Test Rig Hydraulic Schematic

Once the mechanical assembly of the test rig was completed at SwRI, it was sent to EPA's NVFEL for software completion, testing and final validation.  While at NVFEL the work done to the rig consisted of adding additional valves to accommodate testing, writing software for control and data acquisition and initial testing and validation of the design.

Figure 1.15  -  Completed PTO Test Rig Minus Software and Data Acquisition

When the test rig arrived at NVFEL it was outfitted with a National Instruments NIDAQ system for control and data logging.  The 10 minute duty cycle was converted to a time trace as shown below for a control input into the software.  The blue trace was the utility circuit (for vehicles with only one PTO pump circuit), while the red trace was the refuse circuit (or used concurrent with the utility circuit) for vehicles with dual PTO pump circuits.

Figure 1.16  -  PTO Duty Cycle

Software was written in Labview to allow control of the hydraulic valves on the main valve body.  A two part pressure control strategy was used.  The software creates a lookup table of pressures to map the system during calibration to the test vehicle and then a PID loop is employed to keep the pressure consistent at each test point during the test.  The system was pressure tested at NVFEL up to 3200 psi, which is at the maximum for most typical hydraulic systems used on these vehicles.  Further tuning on the PID controller was done to ensure the test system's pressure followed that of the commanded cycle as closely as possible.  

A sample data file from the test rig development at NVFEL is shown below.  As can be shown, the system follows the commanded PTO duty cycle quite closely.  An expanded version is also shown to show pressure detail with the system.

Figure 1.17  -  NVFEL PTO Test Rig Development Data

Figure 1.18  -  Close-up of System Response to 1[st] and 2[nd] Utility Cycle Pressure `Hill'

Once the validation work was completed at NVFEL, the test rig was sent to the California Air Resources Board (CARB) as a part of the hybrid chassis test program being conducted.  Two fairly identical Class 6 vehicles were tested over a series of chassis cycles as well as the PTO duty cycle.  The vehicles underwent emissions testing on the chassis dynamometer at the California Air Resources Board's (ARB's) Heavy-Duty Emissions Test Facility located at the Regional Rebuild Center of the Los Angeles Metropolitan Transit Authority (Metro) in Los Angeles, CA.  They were procured from Southern California Edison (SCE) Company.  One was outfitted with a conventional power-train and the other was equipped with an Eaton hybrid system.  The details on the hybrid version are listed below.  The conventional vehicle is similar.

   o 2009 Trucks with GVWR of 30,000 lbs
   o Equipped with International DT466 engines
   o Engine Model Year:		2009	
   o Engine Displacement:		7.6L 	GDT245 (model)    
   o Engine Family:		9NVXH0466.AGA
   o Emissions Controls:		Diesel Particulate Filter, Exhaust Gas Recirculation
   o Transmission: 			Automatic	
   o Power Take-off:		Altec AT37-G Manlift

Figure 1.19 Hybrid Vehicle tested at CARB laboratory

Both vehicles were equipped with International DT466 engines.  The engine data plate for the hybrid version is shown below.

Figure 1.20  -  Engine Data Plate for Eaton AMT Hybrid Equipped Truck

The trucks were tested for GHG and criteria pollutants on several chassis cycles and both vehicles were tested using the PTO test rig.  The test rig was attached to each vehicle in such a manner to remove the Manlift device from the hydraulic PTO system.  The fluid flowed through the test rig and back to the hydraulic cooler and return tank.  During testing, both vehicles' PTO systems were set to the `ON' position for the duration of testing.   All test runs were made with fully warmed up vehicles and PTO systems.  A test vehicle was considered warm after the engine was idled, PTO exercised and both hydraulic fluid, transmission oil and engine coolant reached normal operating levels.

The conventional vehicle's PTO system was run by starting the truck and turning the PTO system on.  When the acquisition equipment was ready, a test was begun by simultaneously beginning emission measurement and the PTO test cycle.  Four (4) cycles of the 10 minute PTO cycle were run continuously with emission measurement collecting data.  After the PTO cycles were complete, the engine was stopped and the test was concluded.   Each test segment was repeated four times.  The average CO2 output calculated in units of gram per ton mile for each test is shown below.

Figure 1.21  -  CO2 Emissions from Conventional PTO Operation

The emissions per PTO cycle varied from a high of 105 to a low of 99 grams per ton mile for a difference of 5.7%.

Figure 1.22 - CO2 Emissions from Hybrid PTO Operation

The hybrid vehicle had its PTO system tested using two different methods.  In both cases the vehicle was preconditioned by operating the PTO system until the engine started.  Once the engine started, PTO operation ceased allowing the engine to charge the battery pack.  Once the engine turned off, it was assumed that the battery was fully charged and ready for testing.  The preconditioning was performed before each PTO test run to achieve the best possible results.

For the first three hybrid PTO runs, four cycles of the PTO duty cycle were run consecutively with emissions sampling throughout.  Engine start stop was not controlled with the exception of at the end of testing if the engine was running (charging the battery) then the emissions sampling would keep running as long as the engine did to capture those emissions emitted in order to return the system to a full state of charge as at the beginning of testing.  This happened during the second test in this manner.  The averaged results per PTO duty cycle are shown above in Figure 1.22 as the first three runs.    Averaging the results gives 70.33 grams of CO2 in grams per ton mile when run in hybrid mode.   Contrast that to conventional operation, using the same test method, of 101 grams per duty cycle for a 30.4% reduction in GHG emissions.

Due to the large variance in test data the next hybrid PTO runs were run as single sets.  System preconditioning consistent with the prior test method was maintained to achieve repeatable results.  A single test was run starting with a full RESS and running the PTO duty cycle.  The cycle or cycles were run until the engine started, at which point the duty cycle was stopped and emission sampling continued until the engine stopped.  The purpose of this test method was to obtain the emissions produced by one charge-discharge cycle on the RESS and to measure the amount of work done by the PTO system over the cycle(s).  On average it took about one PTO duty cycle run to fully discharge the battery and trigger an engine start event.  

When tested in this manner, the results were more consistent run to run as compared to the first test method in which a series of runs were made back to back.  CO2 emissions ranged from a low of 96 to a high of 108 grams per ton mile for an average of 100.6 grams per ton mile.  Compared to the test average from the conventional system of 101 grams per ton mile, this gave a hybrid benefit of 0% or no improvement versus the conventional system when tested in this manner.
After reviewing the results, it was reasoned that the single run way of testing, while consistent, produced inaccurate results for the following reasons.  Firstly, it could be reasoned that this was not representative operation for the PTO system.  If during use, the engine would need to start to charge the RESS, the operator would not stop PTO operation until the RESS was charged again.  The procedure used was to continue to use the PTO system until the needed operation was completed.  Thus it was reasoned that representative PTO operation included periods of RESS recharge with no PTO load demand as well as RESS recharge with PTO load demand.  Secondly, measured PTO base pressure with the PTO test rig installed was greater than that of an unmodified system.  While the base pressure of this vehicle was not measured during the testing, similar systems experienced values in the 25-50 psi range.  With the PTO test rig installed, base pressure was measured at 175 psi in a ready to run state.  This extra pressure resulted in additional work demanded from the PTO system that was not accounted for during the testing, resulting in a detriment to the percent improvement over the conventional system.
  
Based on these findings the Agency has since incorporated into 40 CFR 1037 provisions regarding PTO testing to include a test method that requires the base pressure of the PTO system with a PTO test rig installed to be the same as that of an unmodified system, as well as modifying the single run test method so as not to require PTO load demand to cease when the engine restarts to charge the RESS.

2.0 - Coastdown Testing
Coastdown Program 1 for Heavy-Duty Tractors (SAE J2263-based)
For the heavy-duty aerodynamics research and coastdown feasibility investigation, EPA conducted several coastdown testing programs to evaluate the feasibility of Class 7 and 8 combination tractor coastdown testing based off of SAE J2263, which requires onboard anemometry.  This memorandum details the process which we undertook upon generating or receiving coastdown data files.  We conducted two separate test programs.  
     
     Test Programs
Our initial testing was performed by EPA itself, procuring tractors from nearby locations with help from onsite contractor URS.  The testing was done largely overnight on Michigan State Highway 50 (M-50) between Dundee and Britton.  We chose this location due to its proximity to our home base, NVFEL, smooth road conditions, and low overnight traffic.  Our second major test program was done through contractors URS and Automotive Testing and Development Services (ATDS) in Lancaster, California.  This location was chosen due to its road conditions and the opportunity to close off the road to all other vehicular traffic.  Testing here was performed during daytime hours.

In each program, a boom was fabricated and attached to the tractor such that an anemometer could be placed approximately 2-3 meters in front of the tractor at the approximate midpoint of the tractor's cross section.  A sample setup in the Michigan testing is shown in 2.1.  An ultrasonic anemometer was used in the Michigan testing, whereas a propeller-style anemometer was used in Lancaster.
     
                                       
      Figure 2.1 Photo of Boom and Anemometer Setup for Michigan Testing

First, we determined which runs were valid, based on instrument readings, weather, and other criteria.  We largely based this on data quality and SAE J2263 weather restrictions.  

Using the onboard anemometer required a few corrections to the measured wind speed, which is, naturally, measured relative to the vehicle.  During the coastdown, air will "pile up" near the front of the tractor.  This causes our anemometer wind speed readings to be offset from the actual relative wind speed.  To correct for this, we calculated the ratio between the vehicle speed and measured wind speed at each data point.  For the initial Michigan program, this was calculated on the coastdown data themselves.  For the Lancaster tests, after gaining knowledge from our Michigan program, this was calculated on constant speed runs at 40 mph, 50 mph, and 60 mph, which were performed prior to the coastdowns.  We then averaged this ratio by run direction.  We then averaged each run direction's ratio for each test and applied this ratio back to the measured wind speed to estimate actual wind speed.  This calculation is described by Equation 1.
Equation 1

Vr = Relative wind speed
V = Vehicle speed
i = i[th] data record
n = number of records in each direction
dir = direction (to or from: i.e. north or south, SE or NW, etc.)

We also observed an offset to the anemometer's wind direction measurements.  For the Michigan testing, we corrected this by assuming that at high speeds, wind direction is head-on (zero degrees).  For each date, we averaged the first five seconds (25 measurements for 5-hz data) of wind direction for each run direction.  We then averaged the two directions' average.  We then subtracted the resulting value from all of the measured wind direction values to get our correct wind direction.
Equation 2

In general, the J2263 analysis method and equations were used as a foundation for this analysis:
Equation 3

We used a mixed model (through SAS(R) software) to describe our 5-hz data with the above equation.  A mixed model allows us to accurately predict the mean coefficients for each vehicle, while accounting for the scatter within each run and also the run-to-run variability when determining the standard error of the coefficient estimates.  This takes into account the fact that measurements are not independent within each run, but each run is independent from all other runs.
The equations below represent the versions of Equation 3 we modeled to determine means and significances of each of the variables.  As an initial simplification, a1, a3, and a4 were eliminated in all iterations since we determined that yaw angle did not vary enough during testing to warrant such a complex polynomial characterization.  We also set a0=1 so that the drag coefficient could be characterized by the D term.  Since our elevation change was negligible in the stretch of road on which we conducted coastdowns, the grade term was also eliminated for all runs.  The following mixed models were run:
Equation 4

Equation 5

, rewritten as
, where 
MM1
Equation 6

MM2
Equation 7

MM3
Equation 8

MM4
Equation 9

MM5
Equation 10

MM6
Based on statistical significance of the various effects, one of the mixed models was chosen as the model to appropriately determine the road load coefficients.  For heavy-duty trucks, this was usually MM6.
Michigan results
In each mixed model (MM1-MM6), we found that the Bm, Cm, and E were not consistently significant from zero.  As examples, models MM4 and MM6 are described below.

In MM4, the results consistently show that Bm -  is not significant from zero.  Table 2.1 summarizes these results from the Michigan testing.  The inclusion of Bm often causes the estimates and uncertainties of the other terms to vary.

Table 2.1  -  Mixed Model MM4 Does Not Show a Significant Linear Effect on Road Load.
Date
Truck configuration (tractor_trailer_payload)
Am [lb]
% Std err
Sig from zero?
Bm [lb/mph]
Std err
Sig from zero?
D [lb/mph[2]]
% Std err
Sig from zero?
5-Aug-09
FL60_N/A_full
153.8
7.75%
Yes
0.165
497.00%
No
0.143
9.64%
Yes
6-Aug-09
FL60_N/A_full
137.7
5.24%
Yes
1.105
41.42%
Yes
0.127
5.86%
Yes
1-Sep-09
Int'l_flatbed_full
490.5
10.94%
Yes
-2.070
-177.70%
No
0.233
25.87%
Yes
2-Sep-09
Int'l_flatbed_full
483.3
7.69%
Yes
-2.065
-122.70%
No
0.237
17.99%
Yes
3-Sep-09
Int'l_flatbed_full
551.5
7.76%
Yes
-6.123
-47.40%
No
0.291
16.55%
Yes
18-Sep-09
Int'l_flatbed_half
372.2
9.72%
Yes
-1.979
-127.80%
No
0.244
17.38%
Yes
23-Sep-09
Int'l_flatbed_empty
226.3
9.38%
Yes
1.153
119.90%
No
0.174
12.27%
Yes
24-Sep-09
Int'l_box_full
521.5
6.51%
Yes
-3.480
-63.15%
No
0.248
14.11%
Yes
25-Sep-09
Int'l_box_full
495.7
8.47%
Yes
-1.149
-238.00%
No
0.208
21.04%
Yes

In MM6, the elimination of Bm shows confident and stable estimates of Am and D, with lower relative standard errors.  This indicates that the road load curve is best described by just Am and D.

Table 2.2  -  Mixed Model MM6 Shows the Most Confident Estimates of A and D.
Date
Truck configuration
(tractor_trailer_payload)
Am [N]
Am [lb]
% Std error
D [N/(m/s)[2]]
D [lb/mph[2]]
% Std error
5-Aug-09
FL60_N/A_full
693.9
156.0
3.81%
3.24
0.145
2.05%
6-Aug-09
FL60_N/A_full
676.8
152.2
2.63%
3.23
0.145
1.13%
1-Sep-09
Int'l_flatbed_full
2060.3
463.2
4.85%
4.45
0.200
6.08%
2-Sep-09
Int'l_flatbed_full
2030.6
456.5
3.71%
4.51
0.203
4.59%
3-Sep-09
Int'l_flatbed_full
2093.6
470.7
3.89%
4.25
0.191
5.55%
18-Sep-09
Int'l_flatbed_half
1539.8
346.2
3.92%
4.71
0.212
4.09%
23-Sep-09
Int'l_flatbed_empty
1076.2
242.0
4.53%
4.27
0.192
2.39%
24-Sep-09
Int'l_box_full
2119.1
476.4
3.87%
4.32
0.194
4.06%
25-Sep-09
Int'l_box_full
2136.5
480.3
4.12%
4.23
0.190
4.88%

Compared to the MM4, MM6 produces more confident mean coefficient values.  Also, for the same configurations, the MM6 shows better day-to-day variability, confirming that the coastdown procedure is repeatable from one day to the next.  Often, the MM6 model is used to simplify the road load versus speed curve through rolling resistance and aerodynamic drag coefficients.  The EPA MOVES heavy-duty inventory model and the CRC E-55/59 chassis dynamometer emissions test program are two examples of this.  In general, the equation implemented during a coastdown is:
Equation 11
                                       
Therefore, 
Equation 12
                                     and  
Equation 13
Equation 11 and Equation 12 assume that the rolling resistance coefficient  is wholly contained in the Am coefficient and the drag coefficient cd is wholly contained in the D coefficient.  The equations also imply that any values of Bm and Cm that would be used in the other mixed models are mechanical drag forces, other than rolling resistance, that are dependent on vehicle speed.  To check the reasonability of our results and feasibility of using our coefficients to accurately determine  and Cd, we can compare our results to other measurements of rolling resistance and drag coefficients.  

Rolling Resistance Coefficient
For the International truck, we recorded the tire model and obtained different laboratory results of tire rolling resistance coefficients.  These values were determined through the SAE J1269 standard.  This standard does not contain a provision that lets a laboratory result be corrected against a reference laboratory result.  As a result, each laboratory has its own bias for any given tire.  When we weighed the truck, we recorded the weight measured over each axle: steer, drive, and trailer.  Since we had no more than one tire model on any one axle, we can weight-average the laboratory rolling resistance coefficients to estimate the truck's overall rolling resistance coefficient.
Equation 14

Figure 2.2 below compares our coastdown rolling resistance results with those from three different tire labs.  We are not naming the tire models or the laboratories to protect confidential business information.  The dimensionless rolling resistance coefficient is multiplied by 1000 for convenience (resulting "unit" is often referred to as kg/metric ton).

Figure 2.2 Coastdown-Determined and Independent Lab Rolling Resistance Coefficients Match Reasonably Well.

There are only three different labs, with four unique weightings (flatbed full, flatbed half, flatbed empty, and box full) for each lab.  Lab results were only available for the tires used on the International truck.  Our coastdown results show reliable day-to-day repeatability for the same truck configuration (Sep 1-3, Sep 24-25).  Also, when we reduced the weight on the flatbed trailer, we found that our coastdowns produced a higher theoretical tire rolling resistance.  This is most likely due to the fact that reducing weight from full payload increases the relative weight over the drive axle.  Since the tires on the drive axle have a higher rolling resistance coefficient (inverse relation with grip for a given tire material and surface), the overall rolling resistance coefficient increased.  This is confirmed by the lab tests, which showed higher rolling resistance coefficients for the drive and steer axles tire models.  Our coastdown results do, however, show a larger increase in coefficient due to complete payload removal compared to the lab results.  
While investigation of rolling resistance coefficient from coastdowns was performed for the Michigan testing, coastdown testing will not be used to determine the tire rolling resistance.  The separate tire test procedures are discussed in RIA Section 3.3.  

Drag Coefficient

We estimated frontal area of the International truck to be 99 ft[2] (9.2 m[2]) by measuring the various dimensions of the tractor cab and other equipment such as exterior mirrors and tires.  We used this value as a placeholder estimate for the FL60 vehicle also.  Using these frontal area estimates and Equation 13, Figure 2.3 shows our coastdown-estimated drag coefficients for each date and truck configuration.

Figure 2.3 Drag Coefficient Calculated from D from Mixed Model

Unlike rolling resistance, we do not expect our drag coefficient to change with payload removal because the physical configuration of the tractor-trailer is not significantly altered, which is reflected in Figure 2.3.  Also, while we are using a frontal area of 9.2 m[2] specific to the International tractor, a uniform frontal area, such as an average box trailer frontal area or typical tractor frontal area, may be used for all trucks of a certain class when determining drag coefficient as an input to the compliance model.
Lancaster results
     The Lancaster test program involved more trucks and more truck configurations.  Comparing drag from one vehicle configuration to the next was better done using a term called drag area, or CdA.
     
Equation 15

	Table 2.3 summarizes the results of our Lancaster testing using MM6.  We were able to clearly see coarse differences due to different configurations.  For example, running a box trailer with a low-roof tractor, which creates a bluff body from the top of the tractor roof to the top of the trailer, resulted in a higher drag area than high-roof with box trailer configurations.  Similarly, high-roof tractors tested with flatbed trailers generally had higher drag areas than their low-roof counterparts due to their higher frontal areas.  Standard errors of the drag areas range from 2 to 6 percent.
Table 2.3 Summary of Results from Lancaster Coastdown Testing Using MM6
Truck #
Date
Truck configuration
# of runs
Am [N]
Crr
CdA [m[2]]
HD-01
17-Mar-10
Intl-Prostar_sleeper-highroof-aero_flatbed_68k
18
2666
0.0087
5.26
HD-01
18-Mar-10
Intl-Prostar_sleeper-highroof-aero_box_68k
18
2595
0.0086
5.20
HD-01
19-Mar-10
Intl-Prostar_sleeper-highroof-aero_box_68k
16
2494
0.0082
5.45
HD-01
24-Mar-10
Intl-Prostar_sleeper-highroof-aero_twin_68k
16
2595
0.0084
5.35
HD-02
26-Feb-10
Intl-Prostar_day-lowroof-nonaero_flatbed_68k
18
2666
0.0091
4.64
HD-02
5-Mar-10
Intl-Prostar_day-lowroof-nonaero_box_68k
10
2445
0.0081
8.00
HD-02A
13-Aug-10
Intl-Prostar_day-highroof-aero_box_68k
18
2579
0.0085
5.81
HD-03
1-Mar-10
Intl-Prostar_day-highroof-nonaero_flatbed_68k
10
2460
0.0084
6.60
HD-03
19-Mar-10
Intl-Prostar_day-highroof-nonaero_box_68k
16
2673
0.0088
6.04
HD-06
1-Jul-10
Volvo-D16_sleeper-midroof-aero_emptytanker_33k
18
1099
0.0078
5.16
HD-07
1-Jul-10
Frliner-Century_sleeper-highroof-nonaero_box_68k
16
2991
0.0074
5.72
HD-08
6-Aug-10
Intl-Prostar_day7-lowroof-aero_flatbed_51k
18
1734
0.0063
4.41
HD-08
12-Aug-10
Intl-Prostar_day7-lowroof-aero_flatbed_51k
18
1729
0.0072
5.74
HH-09
6-Aug-10
Peter-389_sleeper-lowroof-nonaero_flatbed_68k
18
2319
0.0057
4.25
HD-10
24-Sep-10
Frliner-Col_sleeper-lowroof-aero_box_68k
18
1923
0.0063
5.58

      Upon further investigation, a general linear model (more commonly thought of as a regression) yields very similar results for the fixed effect (D coefficient) in MM6.  Therefore, given that the general linear model feature is available in nearly every statistical or spreadsheet software, we recommend using that as the model to estimate drag area.  
      
      Also, the agency conducted an additional study of the airflow over the tractor with and without a tractor-mounted boom using CFD.  This study showed that the flow structure is altered by such a setup compared to not having the boom (i.e. normal operation).  We have described this study in RIA Chapter 3.  As a result, based on this and stakeholder feedback, we are recommending finalizing our coastdown procedure based on SAE J1263, which does not require onboard anemometry.

                  Coastdown Program 2 for Heavy-Duty Tractors
                                       
         ATDS- Lancaster Test Site Tractor-Trailer Configuration Table

       ATDS- Arizona Proving Grounds Tractor-Trailer Configuration Table

                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                      Complete Test Article Descriptions
                     ATDS at Arizona Proving Grounds Site
                               Wittmann, Arizona

                                       
                                       

                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                      ATDS at Lancaster, California Site
 
Coastdown Wind Analysis

Introduction

The Agency through a contract with Automotive Testing and Development Services, Inc. (ATDS) conducted extensive coastdown testing of Class 7/8 heavy-duty trucks at Lancaster, California and at the Arizona Proving Grounds (APG) in Wittmann, Arizona during the months of May to July 2011. 

The ambient wind velocity and direction were collected using two anemometers located at track-side or road-side locations. One anemometer was positioned approximately at one-quarter distance from the start of the test track or road and the other anemometer was positioned approximately at three-quarter from the start of the test track or road. Each anemometer was mounted at a height of 81 inches +- 6 inches (about half of the test vehicles maximum height), and positioned > 127.5 inches (or >= 2.5 vehicle widths) away from the test vehicle's centerline while it was running along the test track or road.

Wind data was gathered when the vehicle was running from a maximum speed of 70 mph down to 9 mph. The average wind speed during each coastdown run must be <10 mph, the maximum wind speed must be <12.3 mph, and the average cross wind speed must be <5 mph to comply with the wind speed requirements of SAE J1263.

When the wind speed exceeded the requirements of SAE J1263, the SAE J2263 procedure for data collection and analysis was used. To comply with the wind speed requirements of SAE J2263 the average wind speed during each coastdown run must be <21.7 mph, the maximum wind speed must be <31.3 mph, and the average cross wind speed must be <9.3 mph. If the SAE J2263 procedure was required, an additional anemometer mounted to a boom about mid-point of vehicle and approximately 6.6 feet (2 meters) in front of the vehicle was used to measure the wind speed.

The testing in Lancaster was done in a recently paved public road that had less than 0.25% grade. During testing, the road was closed to traffic going in the same direction of travel as the test vehicle, but traffic on the opposite direction of travel was allowed. 

The testing in APG was done at a straight line test track that had less than 0.02% grade. The test track is not long enough to allow for the vehicle decelerate from 70 mph down to 9 mph. Therefore, split runs were conducted in accordance to the guidelines of SAE J2263. 

Lancaster Wind Speed Analysis

By the time of this report we had gathered data of fifteen tests in twelve days of testing. The average wind speed, maximum wind speed and average crosswind for each test are shown in Table 2.4. The test usually had about 10 paired runs; but when noted, calculations were done with at least a minimum of five paired runs. Tests within SAE J1263 conditions are shown in green. Test that are within the average wind speed requirements of SAE J1263 but failed the maximum wind speed of SAE J1263 are shown in yellow. Tests that fail the conditions on SAE J1263 but were within the conditions of SAE J2263 are shown in red.

Of the fifteen tests, eight tests (53%) were within the wind conditions of SAE J1263, two tests (14%) had the average wind speed and cross wind speed of SAE J1263 but failed the maximum wind speed. Five of the tests (33%) were outside of the SAE J1263 wind conditions but were within the SAE J2263 wind conditions. No test was conducted when the wind conditions exceeded the SAE J2263 requirements.

Table 2.4 Wind Speeds During Testing at Lancaster, California

                               ATDS Wind Speeds
                                 Average Wind
                                 Maximum Wind
                                Avg Cross Wind
                             Lancaster, California
                                     (MPH)
                                     (MPH)
                                     (MPH)
                                  C4XM71CTGTW
                                      2.5
                                     10.5
                                      1.6
                                 C3JM32KTGTW*
                                      2.7
                                     11.3
                                      1.7
                                 C4XM71CTRHR*
                                      2.7
                                     11.4
                                      1.7
                                  C3JM22HTXCR
                                      3.6
                                     10.9
                                      2.4
                                  C3JM22KTGTW
                                      3.6
                                     10.7
                                      2.5
                                 C3JM21FTXCR 
                                      4.3
                                     11.6
                                      2.7
                                 C3JM21BQXCZ*
                                      5.4
                                     11.9
                                      3.4
                                 C3JM32KTRJR*
                                      5.5
                                     11.9
                                      3.4
                                  C3JM22HTXER
                                      7.6
                                     20.2
                                      4.9
                                  C3JM21BTXCR
                                      9.6
                                     26.1
                                      3.2
                                  C4XM71CTRHS
                                     10.2
                                     26.6
                                      6.5
                                  C3XM21AQXCZ
                                     10.9
                                     30.5
                                      3.7
                                  C3XE21DTXCR
                                     12.9
                                     28.2
                                      6.5
                                 C3XM21ATXCR*
                                     14.8
                                     29.1
                                      6.4
                                 C3JM21BTXBR*
                                     15.4
                                     28.9
                                      9.2

* Does not uses all the test's pair runs, but uses at least 5 pair runs.

The range of the average wind speed for tests that complied with SAE J1263 was 2.5 mph to 5.5 mph with an average of 3.8 mph. The range of the maximum wind speed for tests that complied with SAE J1263 was 10.5 mph to 11.9 mph with an average of 11.3 mph. The range of the average crosswind speed for tests that complied with SAE J1263 was 1.6 mph to 4.7 mph with an average of 2.7 mph.

APG Wind Speed Analysis

At APG we have data for sixteen tests in thirteen days of testing. The average wind speed and maximum wind speed for each test are shown in Table 2.5. At the time of this report, we had not received the summary of the crosswind on APG. The test usually had about 10 paired runs; but when noted, calculations were done with at least a minimum of five paired runs. Tests within SAE J1263 conditions are shown in green. Tests that fail the maximum wind speed of SAE J1263 are shown in yellow.

Of the sixteen tests, twelve tests (75%) were within the wind conditions of SAE J1263, four tests (25%) had the average wind speed and cross wind speed of SAE J1263 but fail the maximum wind speed. 

Table 2.5: Wind Speeds during Testing at APG Wittmann, Arizona

                               ATDS Wind Speeds
                                 Average Wind
                                 Maximum Wind
                            APG Wittmann, Arizona 
                                     (MPH)
                                     (MPH)
                                  B3JJ32KTRER
                                      2.9
                                      9.4
                                 B3JM22KTXER*
                                      3.7
                                      9.8
                                 B3JE71DTXBR*
                                      3.8
                                     12.0
                                 B3XM24MTBCR*
                                      3.8
                                     11.5
                                  B3JM32KTGTW
                                      3.9
                                      8.7
                                 B3XM21AQXCZ*
                                      4.0
                                     11.9
                                 B3JV22HTRER*
                                      4.0
                                     11.7
                                 B3JM71DTXBR*
                                      4.3
                                     11.9
                                 B3JM24NTXCR*
                                      4.3
                                     11.7
                                  B3JX32KTRER
                                      4.7
                                     11.1
                                 B3JM32KTRJR*
                                      5.2
                                     10.9
                                 B3JM21DTXBR*
                                      5.3
                                     12.1
                                  B3JM22HTXER
                                      6.0
                                     17.7
                                 B3JM21DTXCR*
                                      8.2
                                     17.4
                                  B3XM21ATXCR
                                      8.8
                                     25.5
                                  B3JM21DQXCZ
                                      9.8
                                     25.0

* Does not uses all the test's pair runs, but uses at least 5 pair runs.
The range of the average wind speed for tests that complied with SAE J1263 was 2.9 mph to 5.3 mph with an average of 4.2 mph. The range of the maximum wind speed for tests that complied with SAE J1263 was 8.7 mph to 12.1 mph with an average of 11.1 mph. 

Observations

Average wind speeds of less than 2 mph during a complete set of testing were not obtained at either test site. But we were able to have average wind speeds of less than 6 mph during the complete set of testing for all the vehicle tests that complied with the wind speed conditions requirements of SAE J1263.

Maximum wind speeds of less than 8 mph during a complete set of testing were not obtained at either test site. No maximum wind speeds less than 10 mph during a complete set of testing were obtained at Lancaster. All the times that the wind speed conditions requirements of SAE J1263 failed it was due to the maximum wind speed being exceeded.

For this report, only information on average crosswind speed was obtained for the Lancaster test site. Average crosswind speeds of less than 2 mph during a complete set of testing were obtained on three out of eight tests (38%) at Lancaster that complied with the wind speed conditions requirements of SAE J1263. But it was only three out of all the fifteen tests (20%) conducted at Lancaster. Average crosswind speeds of less than 4 mph during a complete set of testing were obtained for all the vehicle tests that complied with the wind speed conditions requirements of SAE J1263 at Lancaster. 

Regarding the average crosswind speed at APG, it is almost certain than the average cross wind stayed within the requirements of SAE J1263 of <5 mph because the maximum average wind speed of the tests that complied with the SAE J1263 conditions was 5.3 mph and the average crosswind speed is always less than the average wind speed.

Based on our observations on wind speeds at two test sites, the data does not support the recommendation proposed by the Engine Manufacturers Association of setting the average wind speed and average crosswind speed < 2 mph. Based on the data the Agency does feel confident that wind speed conditions that conform with requirements of SAE J1263 are achievable and are not overly stringent. The data do support recommending doing coastdown testing when the predicted average wind speed is lower than 6 mph because at that condition the maximum wind speed and average crosswind speed stayed within the SAE J1263 requirements.

Comparison of Coastdown Analysis

Introduction

As the agency reviewed use of on-board and stationary, road side anemometry, it became important to compare results from SAE J1263 and SAE J2263 analyses. 

The SAE J2263 program was designed to use wind speed and direction information obtained from a boom mounted anemometer affixed to the front of the vehicle. To use the road side stationary anemometer wind speed and direction information obtained using the SAE J1263 procedure, the true wind speed and direction would have to be converted to the relative wind speed and direction that the anemometer would have recorded if attached to a boom in the front of the vehicle.

To convert from the true wind speed and direction to the relative wind speed and direction we use a simple vector analysis. Figure 2.4 shows a representation of the vector diagram used for this analysis.
W
 V
   R

        180-



Figure 2.4: Vector Diagram

The vehicle speed and direction is considered to be a vector in which the vehicle speed is the vector's magnitude (V), and the direction of travel of the vehicle is the vector's angle (). To simplify the mathematical calculations the vehicle's travel direction is considered to be along the axis so its angle will be zero ( =0).

Similarly, the true wind speed and direction is considered to be a vector in which the wind speed is the vector's magnitude (W), and the direction of travel of the vehicle is the vector's angle (). 
Knowing the magnitude and direction of vehicle and the wind, we can add these two vectors to obtain the resultant vector for relative wind speed (R) and direction (), which corresponds to the wind speed and direction that would have being measured by a boom mounted anemometer to the front of the vehicle.

The equation for the resultant relative wind speed (R) and direction () are:

Cosine Law 	R = (W[2] + V[2] -2VW COS(180-[][][] 

Sine Law	 = SIN[-1]((W/R) SIN(180-) 

The SAE J2263 uses the vehicle speed (V) and the relative wind speed (R) and direction () to determine the A mechanical, B mechanical and C total values. The result is the road load force (F) as a function of vehicle velocity (V):

F = A mechanical + B mechanical V + C total V[2]

Analysis

The testing was conducted with class 7/8 heavy-duty trucks with aerodynamic treatments. Several different combinations were tested. The vehicles included high, mid or low roof trucks. The tractors were run bobtail, with a trailer box 53 feet in length or 28 feet in length, with a tank trailer, and with a flat bed. 

The vehicles in this analysis were tested at Lancaster, California. The testing was conducted by Automotive Testing and Development Services, Inc. (ATDS) during the months of May to July 2011 through a contract awarded by the EPA.

The testing in Lancaster was done in a recently paved public road that had less than 0.25% grade. During testing, the road was closed to traffic going in the same direction of travel as the test vehicle, but traffic on the opposite direction of travel was allowed. 

The ambient wind velocity and direction were collected using two anemometers located at track-side or road-side locations. One anemometer was positioned approximately at one-quarter distance from the start of the test track or road and the other anemometer was positioned approximately at three-quarter from the start of the test track or road. Each anemometer was mounted at a height of 81 +- 6 inches (205.74 +- 15.24cm) or about half of the test vehicles maximum height, and positioned > 127.5 inches (323.85cm) or >= 2.5 vehicle widths away from the test vehicle's centerline while it was running along the test track or road.
Wind data was gathered when the vehicle was running from a maximum speed of 70 mph down to 9 mph. But the analysis of the data was conducted using only data from 70 mph down to 15 mph. Since we were comparing results from tests using equations from SAE J1263 and SAE J2263, the data presented here is from testing that comply with the more stringent wind speed conditions, which are these of SAE J1263. The average wind speed during each coastdown run must be <10 mph, the maximum wind speed must be <12.3 mph, and the average cross wind speed must be <5 mph.

Table 2.6 shows the A mechanical, B mechanical and C total obtained using the equations on SAE J1263 and using the program provided by SAE using the SAE J2263 equations. The test usually had about 10 paired runs, but for some runs the wind conditions were outside the requirements of SAE J1263. When that was the case, the noncompliant run and its paired run were taken out of the analysis. The paired runs used in the calculation are noted in the table. Since testing was conducted using two separate anemometers, the results using the SAE J2263 program are shown for each anemometer. The road load force is a function of speed; for this analysis the force was calculated for a vehicle speed of 55mph. The difference () between the road load force obtained using the SAE J1263 equations and the SAE J2263 program is shown. The average wind speed during testing is also shown as a reference.

                        Table 2.6: Analysis of Results

Figures 2.5 to 2.12 show the road load force as function of speed obtained using the equations on SAE J1263 and the SAE J2263 program for each vehicle. 

                 Figure 2.5 C3JM21FTXCR Force vs. Speed Curve

                 Figure 2.6 C3JM21BQXCZ Force vs. Speed Curve

                 Figure 2.7 C3JM22HTXCR Force vs. Speed Curve

                 Figure 2.8: C3JM22KTGTW Force vs. Speed Curve

                 Figure 2.9: C3JM32KTGTW Force vs. Speed Curve

                 Figure 2.10 C3JM32KTRJR Force vs. Speed Curve

                 Figure 2.11 C4XM71CTGTW Force vs. Speed Curve

                Figure 2.12  C4XM71CTRHR Force vs. Speed Curve

For the purpose of generating the coefficient of drag (Cd) for heavy-duty vehicles, the agencies are using the equations of SAE J1263. There remains some uncertainty regarding Cd values generated by the SAE J2263 program for heavy-duty vehicles and therefore the agencies are not using it at this time. 

Observations

Table 2.6 shows good correlation between the road load force obtained using the SAE J2263 program and the road load force using the SAE1263 equations.

The difference () between the road load force using the SAE J1263 equations and the road load force using the SAE J2263 program for both anemometers varies between 0.2% to 7.9%, with an average difference of 4.6%. This difference is not excessive, and it is within what could be expected given that we are expanding the use of the SAE program beyond its original intent. 

There was no correlation between average wind speed during testing and the difference () between the road load forces obtained using the SAE J2263 program and the SAE J1263 equations. The lower wind speeds tests do not have the lower difference in road load force; it was completely random.

The agencies previous testing was done following the SAE J2263 procedure and requirements and used the provided SAE J2263 program. The agencies were able to get comparable road load force curves using the SAE J2263 program with the calculated resultant relative wind speed and direction, to the road load force curves obtained with the SAE J1263 equations. The fact that we were able to have some correlation between the two different methods increases the agencies confidence that the SAE J1263 is a good method. Since the testing was done using the conditions specified in SAE J1263, the agencies are confident that the analysis of the data using SAE J1263 equations is valid and we recommend using the SAE J1263 approach. 

Test Data Summary

           Table 2.7 Results for Configurations Not Included in RIA
                                       
Cab type
Roof height
Aero type
Trailer
Configuration ID
Weight [lb]
CdA [m2]
Std error
# of valid runs
Sleeper
Mid
Aero
28 ft-box
B-3JX3-2K-TRER
27778
6.79
1.5%
18
Sleeper
High
Aero
28 ft-box
B-3JM2-2K-TXER
27878
5.59
1.6%
18
Sleeper
High
Aero
28-ft box
C-3JM2-2H-TXER
27900
6.33
2.1%
10
Sleeper
Low
Non-Aero
28-ft box
B-3JE7-1D-TXBR
30284
7.40
1.4%
20
Sleeper
Mid
Aero
Tank
B-3JM3-2K-TRJR
33300
6.00
2.3%
14
Sleeper
Mid
Aero
Tank
C-3JM3-2K-TRJR
32220
6.48
1.8%
18
Sleeper
High
Aero
53-ft box
C-3JM2-1B-QXCZ
69820
6.79
3.5%
16
Day 
(Class 7)
Low
Aero
Flatbed
C-4XM7-1C-TRHR
25260
5.18
2.3%
18

3.0 - Full Scale Wind Tunnel Testing

Introduction

For full-scale wind tunnel testing, we used the National Resources Council-Canada (NRC-C) wind-tunnel in Ottawa, Ontario.  The 9 meter x 9 meter Low Speed Wind Tunnel facility is located on the National Research Council (NRC) campus adjacent to the Ottawa International Airport and has been in operation since 1970.  The wind tunnel is a horizontal closed circuit atmospheric facility with a large test section (9.1 m wide x 9.1 m high x 22.9 m long (30 ft x 30 ft x 75 ft)). It is powered by an air-cooled 6.7 MW (9000 hp) DC motor that drives an 8-bladed fan.  Its speed may be varied and set at any value from 0 to 230 rpm and can be maintained within +-0.1 rpm. The maximum wind speed is about 55 m/s (180 ft/s).  The wind tunnel can accommodate a full-size tractor and a trailer of length up to 28 feet (see Figure 3.1 below).  As seen in the figure, the vehicle can be yawed up to positive or negative ten degrees via rotating turntable.  Models in the tunnel are supported directly by extensions to the balance turntable and rectangular air bearings with instrumented pressure taps to isolate and measure the full aerodynamic forces  on the model.  In addition, the floor is static for full size tractor testing but does possess a moving belt system for smaller scale testing (e.g., 1/2 scale models).

Source:  National Research Council-Canada

Figure 3.1 Full-scale, Fixed Floor Test in the NRC 9-meter Wind Tunnel (model tested for this program not shown)

For our test program, we recruited a commercially-available, Class 8, heavy-duty, on-highway, high roof, sleeper cab tractor with full aerodynamics package.  For our test runs, we used a base tractor-trailer gap of 45 inches as specified in this rulemaking.  Baseline testing was performed using the as-received configuration with full aerodynamics package components on the tractor.  The 28' trailer used for this testing was acquired from the tractor OEM and is the same trailer they use for testing in this facility.  Full yaw sweeps from positive to negative 10 degrees were conducted with equal increments of 2.5 degrees in between zero and +/- 10 degrees.  Redundant zeros were conducted before, between the positive-negative transitions, and at the end of the sweep.  

Analysis

NRC provided the corrected results of the full yaw sweeps in the full scale wind tunnel.  We calculated the average of all the zero Cd values and normalized the data by dividing each result by the average to give us an idea of the spread for each individual point.  Figure 3.2 shows the results of the zero yaw Cd results as compared to the average of all of the zero yaw Cd results.  

Figure 3.2 Delta between Individual Zero Yaw Cd Values and the Average of All Zero Yaw Cd Values for Full Scale Wind Tunnel Testing of Class 8, High Roof, Aero Tractor with a 28' Trailer in the NRC Wind Tunnel

Observations

The deltas for each individual result are well below 0.5%, approximately 0.2% of the zero yaw Cd result average with an overall standard deviation of -0.0009 for all zero yaw Cd results showing excellent agreement from test to test.  

Summary/Conclusions

The data confirms that the full-scale wind tunnel test is highly repeatable and, once a manufactured has approval to use a certified facility, there is high confidence in the results from a single test on a tractor model with a 28 foot trailer.  Later, we will compare this data with the other aerodynamic methods.

4.0 - Reduced Scale Wind Tunnel Testing

Introduction

For reduced-scale wind tunnel testing, we used the Automotive Research Center (ARC) in Indianapolis Indiana.  The ARC wind tunnel is a closed single return tunnel with 3/4 open-jet working section and moving ground plane (2.3 m wide x 2.1 m high x 5.5 m long (7.5 ft x 6.8 ft x 18 ft)).  It is powered by an air-cooled 373 kW (274 hp) variable speed DC motor that drives a 9-bladed fan with carbon fiber blades.  Its speed may be varied and set at any value from 0 to 610 rpm. The maximum wind speed is about 50 m/s (164 ft/s). The wind tunnel can accommodate a model up to 50% scale (1/2 scale) for race car applications down to 12.5% scale (1/8th scale) for Class 8 tractor and trailer combinations.  The wind tunnel is equipped with a moving ground plane (i.e., rolling road), four-stage boundary layer suction system, and a top-mounting "Sting" system allowing for yawing of the model.  For model development, ARC has in-house model developers and can create highly detailed scale models using original computer aided design and engineering (CAD/CAE) drawings or using in-house scanning equipment to perform scanning and digitizing to create CAD/CAE drawings (see Figure 4.1 below).
      
                     Table 4.1 Scale Model Testing Summary

Figure 4.1 1/8th Scale Tractor-Trailer Model in ARC Reduced Scale Wind Tunnel

For our test program, we assumed a base tractor-trailer gap of 45 inches as specified in this rulemaking and the full aerodynamics package components that are sold on the full size version of the tractor.  We were fortunate to test 1/8[th] scale models from three out of the four North American manufacturers of Class 8, heavy-duty, on-highway, high roof, aero, sleeper cab tractors.  All test runs were performed with a full yaw sweep from positive to negative 9 degrees in equal increments of 3 degrees in between zero and +/- 9 degrees.  Redundant zeros were conducted before, between the positive-negative transitions, and at the end of the sweep.  

Analysis

ARC provided the results of the full yaw sweeps in the reduced-scale wind tunnel for all three models.  Each truck was assigned a generic moniker:  Truck A, B and C.  We calculated the average of all the zero Cd values and normalized the data by dividing each result by the average to give us the spread for each individual point.  Below are graphs showing the results of the zero yaw Cd results as compared to the average of all of the zero yaw Cd results for Truck A, B and C (see Figures 4.2-4.4).  

Figure 4.2 Delta between Individual Zero Yaw Cd Values and the Average of All Zero Yaw Cd Values for Truck A Reduced-Scale Wind Tunnel Testing

Figure 4.3 Delta between Individual Zero Yaw Cd Values and the Average of All Zero Yaw Cd Values for Truck B Reduced-Scale Wind Tunnel Testing

Figure 4.4 Delta between Individual Zero Yaw Cd Values and the Average of All Zero Yaw Cd Values for Truck C Reduced-Scale Wind Tunnel Testing

Observations

As with full scale wind tunnel testing, the reduced-scale wind tunnel results showed excellent agreement from test to test.  The standard deviations for reduced-scale wind tunnel results were very low from 0.0008 for Truck B up to 0.003 for Truck C, with Truck A in between the other two at 0.002.  In addition, the highest variation for an individual result when look across all of the trucks is 0.00565 for Truck C.

Summary/Conclusions

The data confirms that the full-scale wind tunnel test is highly repeatable and, once a manufactured has approval to use a certified facility, there is high confidence in the results from a single test on a tractor model with a 28 foot trailer.  Later, we will compare this data with the other aerodynamic methods.

5.0 - Computational Fluid Dynamics (CFD) Analysis

Introduction

Computational Fluid Dynamics, or CFD, capitalizes on today's computing power by modeling a full size vehicle and simulating the flows around this model to examine the fluid dynamic properties, in a virtual environment.  CFD tools are used to solve either the Navier-Stokes equations that relate the physical law of conservation of momentum to the flow relationship around a body in motion or a static body with fluid in motion around it, or the Boltzmann equation that examines fluid mechanics and determines the characteristics of discreet, individual particles within a fluid and relates this behavior to the overall dynamics and behavior of the fluid.  Therefore, there are predominantly two types of commercially-available software code either Navier-Stokes or Lattice  - Boltzmann based.  We will discuss the set up and results for each of these separately since their approaches and calculations are different.

                            Table 5.1 CFD Analysis

For this test program, we acquired a full scale, Class 8, high-roof, aero sleeper tractor-trailer and had a third-party, Southwest Research Institute, scan and digitize the tractor and trailer.  The vehicle was elevated and the surface and underbody details, as much as possible, was scanned to create a digital model of the tractor and trailer.  Below are some figures from the scanning and digitizing process (Photos courtesy of Southwest Research Institute).  More details on the scanning and digitizing process can be found in the docket in the report titled "EPA SwRI Truck Digitization Summary.pdf".

                                       

Figure 5.1 Photo of the Class 8, High-roof, Aero Sleeper Tractor Acquired for Scanning and Digitizing Purposes

                                       

Figure 5.2 Class 8, High-roof, Aero Sleeper Tractor Elevated for Scanning and Digitizing Purposes 

 

                                       
                                       
Figure 5.3 Southwest Research Institute (SwRI) Personnel Collecting Reference Grid Points on the Tractor

                                       
                                       
Figure 5.4  Laser Scanning the Surface with the Portable Arm

                                       

Figure 5.5 Spatial Analyzer Screen Capture of Reference Grid Points for the Tractor

                                       
                                       
Figure 5.6 Partial View of Raw Scan Data from the Tractor

                                       
Figure 5.7 Front Perspective View of the Final 3D Model (SolidWorks 2011)

                                       
Figure 5.8 Rear Perspective View of the Final 3D model (SolidWorks 2011)

We supplied the digitized model information to three sources, two using Navier-Stokes and one using Lattice-Boltzmann based CFD software codes.  The results for one of the Navier-Stokes based CFD sources was not available at this time and will be added later to the docket for the rulemaking.  Therefore, we will discuss the analysis conditions and results for the two available sources.

Based on the digitized model provided, the sources were able to prepare the model for CFD analysis by ensuring closed-surfaces, accurate component connections, and representative, component spatial relationships.  Due to simplification, the digitized tractor model fidelity was less than 100% realistic as compared to the actual tractor model.  Therefore, the sources either used the digitized the model as provided, made some assumptions and modifications based on experience, or had enough experience with the OEM that they were able to add OEM-level of detail to the digitized model.  We will discuss the set up process for each software code separately below.

Navier-Stokes Based CFD Software  -  CD Adapco

CD-Adapco has been developing commercial CDF tools since 1987 beginning with their STAR-CD and continuing with the recent generation of their CFD tool, STAR-CCM+.  CD-Adapco used the simplified digitized model we provided to them with minimal changes (see Figure 5.9).  

                                       
                                       
Figure 5.9 Bottom/Front Perspective View of 3D Model Prepared by CD-Adapco
                                       

The analysis process for the digitized model involves three main steps:  meshing, where the model and surrounding environment are divided up into discreet elements to form a grid; solving which involves calculations to solve the Navier-Stokes equations; and post-processing to quality assure/quality check (QA/QC) the run and the data.  If the run passes the QA/QC, the analysis results are output to a Powerpoint presentation for easier viewing (see Figure 5.10 below).

                                       

Figure 5.10 Overview of CFD Analysis Process Used by CD-Adapco

For setting up the mesh, CD-Adapco used the following parameters:

      High Reynolds Region
            :: Target Y+: 30-300
                   -  2 Layers, 4mm Wide
                   -  Near Wall ~ 1mm
            :: Trailer uses 20mm prism layer with 6 Layers to blend outward.
      
      Low Reynolds Region
            :: Target Y+: < 5
                   -  Minimum: 8 Layers
                   -  Near Wall ~0.05mm
            :: Applied to CAB and tires (not treads grooves)

The Y+ value is a calculated value using the equation:  (u* x y) / ν, where u* is the frictional velocity near the wall, y is the distance to the nearest wall, and ν is the fluid kinematic viscosity.  The y+ value determines where to put the first grid line in the mesh by identifying the first point where the frictional stresses acting between the fluid and the wall are significant enough to cause velocity differences in the fluid (i.e., the fluid adheres to the wall and the forces act on the fluid changing its velocity profile).  By lowering this Y+ value, the distance to the wall is shortened where the boundary lines are defined and, consequently, resulting in the mesh grid in Figure 5.11.  The darker areas represent higher cell concentrations in areas where resolution of the flow is critical, such as closer to the surface of the tractor-trailer or other obstructions in the flow.  Conversely, the lighter areas represent lower cell concentrations in areas where flow resolution is not that critical, such as areas further away from the surface of the tractor-trailer.  This helps to give an accurate analysis of the model aerodynamics while minimizing the computing time to resolve the flow relationship between cells.

                                       

Figure 5.11 Overview of Mesh Grid for Tractor-trailer Model Prepared by CD-Adapco

For the test conditions, the analysis assumed an open road with moving ground plan and rotating wheels with the grill open on the tractor.  Vehicle speed was assumed to be 24.585 meters per second (55 miles per hour) with an assumed air density of 1.185 kilograms per cubed meter (kg/m[3]).  Using these environmental conditions, they conducted analysis at a range of yaw angles:  0, +3, +6, +9, -3, -6, and -9.  The Navier-Stokes based CFD code results are discussed in the analysis section below.  More details on the analysis performed by CD-Adapco can be found in the docket under the document titled "CD Adapco Comments on EPA update 7.13.2011.pdf".

Lattice-Boltzmann Based CFD Software  -  Exa Corporation

Exa Corporation develops, markets, and supports simulation software for fluids engineering with a full suite of engineering consulting services. PowerFLOW, their flagship product, is a revolutionary CFD solution for simulating some of the most complex fluid flow problem and utilizes a unique methodology called the Lattice Boltzmann method.  Using existing knowledge and established relationships, Exa was able to prepare and analyze a highly detailed model, as shown in Figure 5.12, of the tractor-trailer including addition of detailed engine bay and suspension components.  Exa estimated that the process to create this model took 3 days for one person or 72 "man" hours.
   

Figure 5.12 Detailed Tractor-trailer Model Prepared by Exa Corporation

The analysis process for the digitized model involves the same three main steps above for Navier-Stokes based code but the meshing process is very different.  Exa uses a mesh grid process that defines regions and assigns a number to each region with varying cell size as shown in Table 5.2.    

Table 5.2 Exa Mesh Grid Definition Using Regions and Cell Size to Define Critical Flow Areas
                                       
The larger-number regions are areas closest to the surface of the tractor trailer and use a smaller cell size and consequently, the cells in this area are more concentrated (i.e., smaller in size and are thus more densely packed or closer together).  As a result, the mesh grid is similar in concept as stated above for the Navier-Stokes based CFD software code.   The darker areas represent higher cell concentrations in where resolution of the flow is critical, such as closer to the surface of the tractor-trailer or other obstructions in the flow.  Conversely, the lighter areas represent lower cell concentrations in areas where flow resolution is not as critical, such as areas further away from the surface of the tractor-trailer (see Figures 5.13 and 5.14 below).

                             VR6: 24 mmVR5: 48 mm
                                       
Figure 5.13 Mesh Grid Preparation Showing Finer Levels of Cell Concentration in Critical Flow Areas/Regions Prepared by Exa Corporation

                              VR7: 12 mmVR8: 6 mm
                                       
Figure 5.14 Mesh Grid Preparation Closer to the Surface of the Tractor-trailer Model Prepared by Exa Corporation

For the test conditions, the analysis assumed an open road with moving ground plan and rotating wheels with the grill open on the tractor.  Vehicle speed was assumed to be 26.82 meters per second (60 miles per hour) with an assumed air density of 1.204 kilograms per cubed meter (kg/m^3).  Using these environmental conditions, they conducted analysis at a range of yaw angles:  0, +1, +3, +6, +9.  For minimum cell size, Exa used their best practices recommendation of 6mm.  They also explored a smaller case of 1.5mm, as close to the suggested 1mm case in our proposed rulemaking, and an interim cell size of 3mm.  In this case, model symmetry was assumed and the negative cases were not conducted to save costs.  The Lattice-Boltzmann based CFD code results are discussed in the analysis section below.  More details on the analysis performed by Exa Corporation can be found in the docket under the documents titled "20110526-Exa-Full-Results-Overview-for-EPA-final.pdf", "Exa-Mtg-with-EPA-070611-final.pdf" and "20110708-Exa-Additional-Results.pdf".

Analysis

For CFD, there is no issue regarding repeatability since the software will repeatedly give the same answer once the conditions are defined.  Therefore, a more useful comparison for the purposes of this memo is a cross-method and cross-source comparison.  The cross-method comparison is useful since manufacturers may uses either of the software codes to perform and submit their Cd values and we would like to know if they give wildly divergent results.  The cross-source comparison is important because different programmers and different conditions can impact the results and this would provide some quantification of that difference.

Accordingly, Table 5.3 shows the difference between the two results.  Since they conducted different yaw angles, we are only presenting data for overlapping yaw angles between the sources.

Table 5.3 Percent Difference for Cd Results from Exa and CD-Adapco CFD Analysis
                                       
                                   Yaw Angle
                   Delta (Exa Results  -  CD-Adapco Results
                    Exa and CD-Adapco Result Difference (%)
                                       0
                                     0.056
                                    11.75%
                                       3
                                     0.057
                                    11.14%
                                       6
                                     0.066
                                    11.33%
                                       9
                                     0.071
                                    10.76%

Observations

Despite the lack of consistent model details, base assumptions and software code differences, the 10.8 to 11.8 percent difference between the source results is in the realm of acceptability.  The data does show a consistent percentage difference indicating a structural bias either due to the assumptions by the modeler or the level of model detail.  Without further study, we are not able to isolate the source of this structural bias but it does highlight an area of concern.  

Summary/Conclusions

To get consistent results from CFD analysis, regardless of the software code used, we took the following steps on CFD analysis.  First, for any CFD analysis the most accurate result will require original CAD/CAE files of the tractor to support the development of a model with sufficient detail and fidelity.  In addition, the environmental conditions from the coastdown test used to develop the aerodynamic correction factor so that the analysis will closely match the real conditions experienced by the vehicle.  Second, to ensure data consistency, a minimum set of characteristics and criteria must be included in this rulemaking for CFD analysis to ensure that the boundary and surface conditions are not too coarse and, thus, not representative of the real truck and environmental conditions.  The latter point also overlaps with the key issue of boundary/surface condition sensitivity and the secondary issue of trade-offs between model fidelity and cost/run-time.  As a result, we looked at cell size, one of the main input conditions, to assess the trade-offs between model fidelity and human resources and computing cost/run-time and tables below provide more information.  

We originally proposed a mesh cell size of 1.0mm everywhere in the mesh.  We were informed that this is extremely rigorous and, instead, the smallest mesh cell size of 1.5 mm was used as a starting point.  We were also informed that this minimum cell size is used at the localized areas/regions where high flow/high pressure regions are typically expected or occur.  Therefore, as shown above, this was used in the VR8 region (shown in Figure 5.14) and the cell sizes increased from that point.

Table 5.4 Zero Yaw Angle Results from the CFD Analysis for Localized Cell Sizes of 1.5, 3.0 and 6.0 mm
                             Finest Cell Size (mm)
                   Cd Delta Change vs. cell size resolution
                                       6
                                      --
                                       3
                                    0.421%
                                      1.5
                                    2.360%

                                       
                                       
                                       
                                       
                                       
                                       
                                       
Table 5.5 Delta and Percent Difference for Cd Values at Positive 0, 1, 3 6, 9 Yaw Angles for the 1.5 mm and 6.0 mm Case
                                   Yaw Angle
                                     Delta
                                 % Difference
                                       0
                                    0.0136
                                     2.77%
                                       1
                                    0.0139
                                     2.80%
                                       3
                                    0.0062
                                     1.21%
                                       6
                                    -0.0065
                                    -1.14%
                                       9
                                    -0.0026
                                    -0.39%

                                       
Table 5.6 Case Size Estimates of Computational Cost and Computer Run-time in CPU Hours
                                       

As the tables show, there is little difference for Cd values between the 1.5, 3.0 and 6.0 mm cell size case.  Further, there is little difference for the Cd values between the 1.5 and 6.0 mm cell size but a very high cost in computing run time and, ultimately, cost.  We also looked at cell size beyond 6.0 mm as shown in Figure 5.15.  Beyond about 9 mm, the mesh becomes too coarse and the values begin to fall out of the acceptable error band.  Based on this, we used the smallest cell size, 6.0 mm, as the smallest allowable cell size for Lattice-Boltzmann based CFD analysis.  For Navier-Stokes based analysis, we established similar criteria using the Y+ value instead of actual cell size.

Figure 5.15 Cd Results for Cross Method Comparison Using Normalized, Nominal Frontal Area of 10.4 Meters Squared

6.0 - Summary Comparison for All Aerodynamic Assessment Methods

Introduction

As shown above, the full scale wind tunnel, reduced-scale wind tunnel, and CFD all have the ability to yield repeatable test results.  The other remaining question was how well do the coefficient of drag (Cd) results compare to each other across the methods on the same tractor model.  To explore this further, we compared the results for each of the methods above and to the coastdown test results.  Specifically, the same tractor-trailer model (i.e., Truck A) that we used for scanning/digitizing and CFD analysis was also coastdown tested and full scale wind tunnel tested.  Although the 1/8[th] scale tractor-trailer model tested in the reduced-scale wind tunnel was not created using our actual tractor-trailer model, the model type and aerodynamic components are identical. Therefore, the results from the reduced-scale wind tunnel are reasonably comparable to the other results.

In addition to Truck A, we also procured a "clone" or second tractor (i.e., Truck B) that matched the specifications of Truck A.  This model was not tested in a wind tunnel nor did receive a CFD analysis, but was coastdown tested.  This was performed to understand the influence that using different tractor models (i.e., truck-to-truck variability) has on Cd estimation.  

In addition, we also coastdown tested Truck B in two different locations to understand the impact that test source on the same vehicles (i.e., source-to-source variability) has on Cd estimation.  Coastdown testing was performed by Automotive Testing & Development Services, Inc. (ATDS) in Ontario, California and at the Arizona Proving Grounds (APG) in Yucca, Arizona.  The three Cd results, one for Truck A at APG and two for Truck B at ATDS and APG, were compared to the wind tunnel and CFD Cd results.

Analysis

Prior to the comparison, we had to normalize the data for frontal areas.  NRC assumed a frontal area of 10.595 square meters (114.04 square feet) for full scale wind tunnel testing, ARC assumed a frontal area of 10.69 square meters (115.07 square feet) for the reduced-scale wind tunnel testing, Exa assumed a frontal area of 10.595 square meters (114.04 square feet) and CD-Adapco assumed a frontal area of 10.595 square meters (114.04 square feet) for CFD analysis.  In the rulemaking, we assume a frontal area of 10.4 square meters (111.94 square feet) in the rulemaking and we are using this as the nominal frontal area for all testing.  Therefore, we took all of the Cd values, multiplied by the assumed frontal areas and divided them by 10.4 square meters to get Cd values corrected for the rulemaking frontal area.  

Finally, to make the comparisons more obvious, we normalized all the data to the Truck A coastdown result by dividing all the other Cd values by the Truck A coastdown Cd after correction for frontal area.  For multiple test results from the same source and test conditions, we took the average of the corrected, normalized Cd values and used this value to simplify the comparison.  Given the repeatability shown above for wind tunnel and CFD, this was not an issue.  Below is a graph showing the Cd results from all the aerodynamic methods considered in the rulemaking (see Figure 6.1).  

Figure 6.1 Cd Results for Cross Method Comparison Using Normalized, Nominal Frontal Area of 10.4 Meters Squared.

Observations

Initially, we hoped that the results from each method would be exact but, once the coastdown test procedure was selected as the reference method, this became less of an issue.  Manufacturers would simply have to correlate their results from the other aerodynamic methods to the coastdown procedures and this would be sufficient, given the repeatability of the other aerodynamic methods.  Therefore, it came more important to understand how equivalent each method is to the coastdown to anticipate the range of necessary correction and overall trends when comparing the methods.

The graph shows some of that cross-methodology equivalence, with a couple of caveats for some of the methods.  First, the full scale wind tunnel's use of a shorter trailer (28 feet for the test vs. 53 feet in the field) and the lack of a moving ground plane create some divergence.  With additional research, it may be possible to improve this estimate by developing a static floor and a trailer correction factor.  For now though, the results are in the range of acceptability when comparing them to the coastdown test.  

Second, for CFD analysis, the lack of matching environmental conditions and consistent model fidelity, in one case, also produced some divergent results.  Addressing these two areas should help reduce some of the divergence between the CFD analysis and coastdown.

Finally, the reduced-scale wind tunnel produced the most comparable results to the coastdown test.  Specifically, the wind-average coefficient of drag (WACd) nearly matches the coastdown results with a 95.5% level of agreement.  Since the WACd takes into account the full yaw sweep, this may indicate that, although the coastdown test is primarily concerned with zero yaw, it may be capturing some of the non-zero yaw wind affects.

Summary/Conclusions

Based on the results, we confirmed that although the results from all the methods were not exact, they were equivalent. Therefore, we believe that any of the aerodynamic methods discussed in this memorandum are acceptable for generating Cd values.  However, since the coastdown test is being used as the reference method, a correlation to the coastdown test is necessary if the other aerodynamic assessment methods, wind tunnels or CFD, is used.

Accordingly, there is a need for an aerodynamic method adjustment factor when aerodynamic methods other than the coastdown reference method are used and we developed the following equation to calculate the adjustment factor:

	Adjustment Factor  =  Cd result (coastdown) / Cd result (wind tunnel or CFD).

Once a manufacturer performs a correlation between the coastdown method and the other aerodynamic method, and receives agency approval for this other aerodynamic method, the manufacturer can use the other aerodynamic method to test all of their models.  Subsequently, the adjustment factor would be applied to all the test results from the other aerodynamic method and a manufacturer would be able to continue using this method for all testing.