Document ID: EPA-HQ-OAR-2014-0827-0118
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2015-07-13T04:00Z

May 27, 2015

MEMORANDUM

SUBJECT:	Vocational Vehicle Aerodynamic Testing Program

FROM:	Lauren Steele, Environmental Engineer, OTAQ/ASD

TO:	Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles - Phase 2 - Docket EPA-HQ-OAR-2014-0827

Introduction

      This memorandum describes a possible approach that EPA and NHTSA could use to recognize the fuel efficiency and GHG emission improvements from use of aerodynamic devices on vocational vehicles as part of the Phase 2 program.  The data summarized below are from work completed as of March 2015 under an agreement with the California Air Resource Board (ARB) the National Renewable Energy Laboratory (NREL).  NREL performed a series of coastdown tests on heavy-duty vocational vehicles with and without aerodynamic improvement devices to assess their performance. Excerpts of progress reports from which this summary is derived are attached as an appendix to this memorandum. 
      
      The devices tested were not intended to include all aerodynamic devices available for vocational vehicles, rather they are a sampling of the most common types of technologies that are currently commercially available.  Recognition of vocational aerodynamic technology within the Phase 2 GHG program would not need to be based solely on data obtained through this ARB-NREL agreement. Should other data become available, it would be taken into consideration as well.

Background

      The vast majority of aerodynamic improvement technologies that have been evaluated through U.S. EPA's SmartWay program and for compliance with the Phase 1 heavy-duty vehicle greenhouse gas standards have been devices primarily intended for heavy-duty Class 8 tractor-trailers. There is a data gap regarding the potential benefits of aerodynamic improvement technologies for use on heavy-duty vocational vehicles. ARB staff gathered information about aerodynamic controls for this vehicle category though literature reviews and stakeholder discussions prior to initiating the NREL study under ARB Agreement Number 11-600, NREL Contract Number FIA-12-1763. It is the intention of this current NREL study to complement previous work and explore the potential benefits of the most common aerodynamic improvement devices on box trucks using both coastdown and on-road steady-state techniques. The testing utilized two common vocational vehicle designs, a Class 4 and a Class 6 box truck, which often operate at duty cycles with sufficient high-speed operation where aerodynamic devices could provide significant fuel savings.  The overall intent of the NREL work is to estimate the expected benefits of several common types of vocational aerodynamic devices, as accurately as possible given limited test time and budget. 

Summary of NREL Test Program

      Table 1 compares some features of the two heavy-duty vocational vehicles were that were tested and measured by NREL.
      
                          Table 1: Truck Descriptions
Vehicle Descriptor
Class 6 Box Truck
Class 4 Box Truck
Cab Style
Conventional
Low Cab Forward
GVWR
26,000 lbs
14,500 lbs
Nominal Box Length
26 feet
16 feet
Full Vehicle Length
37 feet
23 feet
Full Vehicle Height
12 ft 10 inches
11 feet
Average Width[a]
8 ft 4 inches
8 feet 1 inch
Minimum Ground Clearance
10 inches
5 inches
Note: 
[a] This calculation made by EPA not NREL

      The NREL team evaluated the performance of three aerodynamic devices on the Class 6 truck and one device on the Class 4 truck, as shown in Table 2.  Images of aerodynamic devices tested can be found in the Appendix to this document.

             Table 2: Vocational Aerodynamic Technologies Assessed
VEHICLE
                              BOX CHASSIS SKIRTS
                             FRONT (ROOF) FAIRING
                                 REAR FAIRING
                                 WHEEL COVERS
Class 6 Box Truck
                                       X
                                       X
                                       
                                       X
Class 4 Box Truck
                                       
                                       
                                       X
                                       
Device Weight (lbs)
                                      101
                                      34
                                      109
                                       5

      Coastdown testing was performed following the guidelines from SAE J1263, "Road Load Measurement and Dynamometer Simulation Using Coastdown Techniques" and SAE J2263, "Road Load Measurement Using Onboard Anemometry and Coastdown Techniques" with the additional calculation step of normalizing the results to STP from 40 CFR §1066.310-4. Table 3 presents preliminary coastdown results, which have been corrected for road grade, headwind/tailwind, air temperature, and air pressure. The NREL results are preliminary, whereas planned future work under the ARB agreement includes repeated coastdown tests, steady-state tests, and further analysis of the data and refinement of the processing code.
      
      
                    Table 3: Preliminary Coastdown Results
                                 VEHICLE TYPE
                                 CONFIGURATION
                                  CD*A [m][a]
                               DELTA CD*A [m][b]
Class 6 Box Truck
Reference
Average 5.64
 - 

With Chassis Skirt
4.86
0.82

With Front Fairing
5.24
0.52

With Chassis Skirt & Front Fairing
5.16
0.60

With Wheel Covers
5.34
0.03

With Chassis Skirt, Front Fairing, and Wheel Covers
5.25
0.49[c]
Class 4 Box Truck
Reference
5.28
 - 

With Rear Fairing
5.01
0.27
     Notes:
     [a] Central values are presented for CDA and Delta CDA. See appendix for high/low estimates.
     [b] Changes in CDA (deltas) are determined for each device using separate baseline test runs, not the average of the reference runs shown here. 
     [c] Crosswind conditions on this test date put these results in question.
      
Possible Phase 2 Approach to Vocational Aerodynamics
      
      The agencies are considering adopting provisions in the Phase 2 HD GHG program to enable chassis manufacturers to obtain credit for installation of aerodynamic devices on vocational vehicles. One potential approach is to offer delta CDA values as optional inputs in the GEM simulation tool associated with certain aerodynamic devices. Manufacturers who install (or instruct another entity to install) an eligible device on an eligible vehicle would select the appropriate input and GEM would apply the pre-defined delta CDA to the default CDA that is already programmed in GEM for the applicable vehicle weight class.
      
      For such an approach to be practical, the agencies believe this would require that the certifying manufacturer have knowledge of and some degree of control over the size and shape of the vehicle in its final built form.  To address cases where business relationships or other factors enable chassis manufacturers to do this, the agencies are proposing delegated assembly provisions in the regulations. See 40 CFR 1037.621.  
      
      If the agencies were to adopt this approach based on the preliminary NREL results, it would likely be necessary to restrict eligibility of vocational vehicles that could be certified with an improved CDA in GEM to those meeting the characteristics described in Table 4 below.  If additional data become available to the agencies, quantifying the effect of changes in vehicle frontal area and/or length on delta CDA for specific devices, the vehicle size eligibility could be broadened.  To ensure that vehicles applying for this credit would be most likely to benefit from aerodynamic technology in the real world, the agencies may choose to restrict eligible vehicles to those that meet the segmentation criteria in 40 CFR 1037.510(c) specifying certification using the Regional duty cycle in GEM.  
Table 4: Characteristics of Vehicles Potentially Eligible to Gain GEM Credit for Aerodynamics
                                 VEHICLE TYPE
                                     GVWR
                                CHASSIS LENGTH
                                 FRONTAL AREA
LOW CAB FORWARD Box Truck
                        10,001 to 19,500 lb (Class 3-5)
                                7 M (+- 0.3 m)
                            8.0 m[2] (+- 0.2 m[2])
CONVENTIONAL CAB BOX TRUCK
                      16,001 lb to 33,000 lb (Class 5-7)
                                11 m (+- 0.3 m)
                            9.3 m[2] (+- 0.2 m[2])
      
      The frontal areas in Table 4 are based on calculations using measurements of vehicle dimensions from NREL that are found in the appendix plus other dimensions transmitted to the ARB and EPA during this project.  The formula specified in SAE J1263 (used with light-duty vehicles) where frontal area is estimated by multiplying the total vehicle height and the maximum vehicle width by 80 percent, was not used.  If that protocol had been used, the resulting estimates of frontal area would have been 7.0 m[2] for the low cab forward truck and 8.1 m[2] for the conventional cab truck versus 8.0 m[2] and 9.3 m[2], respectively, from Table 4.

      Based on the preliminary NREL results, the agencies are considering a narrow range of eligible aerodynamic devices:  box chassis skirts and front (roof) fairings for larger trucks; and rear fairings (tails) for smaller trucks.  Depending on additional data that may become available to the agencies during the comment period, quantifying the effect of different devices on delta CDA for specific vehicles, the device eligibility could be broadened.  Table 5 presents some ranges of possible delta CDA values (derived from Table 3), which could be in the range of pre-defined technology improvement values made available in GEM under certain circumstances.
      
 Table 5: Possible Aerodynamic Technology Improvement Values (Delta CDA, m[2])
BOX CHASSIS SKIRTS
                                 FRONT FAIRING
                           FRONT FAIRING AND SKIRTS
                                 REAR FAIRING
Conventional Cab Box Truck (Class 5-7)
                                  0.6 to 0.9
                                  0.4 to 0.6
                                  0.5 to 1.0
                                       -
Low Cab Forward Box Truck (Class 3-5)
                                       -
                                       -
                                       -
                                  0.1 to 0.4
Certification Conditions
               Regional duty cycle, Delegated assembly agreement
      
      To illustrate the effect on vehicle fuel efficiency reflected in GEM of changes in a vocational vehicle's CDA, the agencies have simulated some example effectiveness values for the following combinations of devices and vehicles: a LHD vocational vehicle with only a rear fairing and both a chassis skirt and a front fairing; and a MHD vocational vehicle with only a front fairing and both a chassis skirt and a front fairing. These cases are shown in Table 6.  
      
                    Table 6: Vehicle Cases Simulated in GEM
VEHICLE
                                  TECHNOLOGY
                                 WEIGHT IN LBS
                           EXAMPLE DELTA CDA (m[2])
Light heavy-duty vocational vehicle  (Class 3-5)
                                 Rear Fairing
                                      109
                                      0.2

                      Chassis Skirts & Front Fairing
                                      135
                                      1.0
Medium heavy-duty vocational vehicle (Class 6-7)
                                 Front Fairing
                                      34
                                      0.4

                      Chassis Skirts & Front Fairing
                                      135
                                      1.0
      
      Each of these cases was run in GEM twice: once ignoring the added weight of the device and a second time adding the weight of the device, as reported by NREL.  This is done for illustrative purposes, to show the likely effects of added weight on the simulated vehicles in GEM.  Physics would suggest that added mass may cause the overall effectiveness of an aerodynamic device to be diminished by varying amounts depending on the driving patterns of a vehicle.
      
      The results in Table 7 represent technology effectiveness where the mass of the aerodynamic device has been disregarded.  The results in Table 8 represent technology effectiveness where the mass of the aerodynamic device has been taken into account by allocating half to the static test weight and half to a diminished payload.
      
      In the results presented below, some of the cases involve the same combination of technologies - chassis skirt and front fairing - on both a LHD vehicle and a MHD vehicle. The differences in these results reflect the differences in the vehicle parameters in GEM, including a different engine, transmission, chassis weight and payload.  In comparing these cases, it appears the LHD vehicle benefits more from the aerodynamic technology than the MHD vehicle does, though it also appears to be more sensitive to changes in weight.
                                       
                       Table 7: Example GEM Improvements
Vocational Aerodynamics Effectiveness 
Disregarding Weight Effects
                               MEDIUM HEAVY-DUTY
                               LIGHT HEAVY-DUTY

Baseline
Front Fairing
Chassis Skirt & Front Fairing
Baseline
Rear Fairing
Chassis Skirt & Front Fairing
CDA
                                                                            5.4
                                                                              5
                                                                            4.4
                                                                            5.4
                                                                            5.2
                                                                            4.4
65mph CO2 Emission (g CO2/ton-mi)
                                                                            211
                                                                            201
                                                                            186
                                                                            401
                                                                            391
                                                                            353
55mph CO2 Emission (g CO2/ton-mi)
                                                                            171
                                                                            164
                                                                            153
                                                                            314
                                                                            308
                                                                            280
Transient CO2 Emission (g CO2/ton-mi)
                                                                            244
                                                                            243
                                                                            240
                                                                            367
                                                                            365
                                                                            358
Effectiveness over 65 mph
                                       
                                                                           4.5%
                                                                          11.8%
                                       
                                                                           2.4%
                                                                          12.0%
Effectiveness over 55 mph

                                                                           4.1%
                                                                          10.5%

                                                                           2.2%
                                                                          10.8%
Effectiveness over Transient

                                                                           0.6%
                                                                           1.8%

                                                                           0.5%
                                                                           2.4%
Regional Cycle Effectiveness  
   (50% Transient, 28% 55 mph, 22% 65 mph)

                                                                           2.3%
                                                                           5.8%

                                                                           1.3%
                                                                           6.7%
Multi-Purpose Cycle Effectiveness  
   (82% Transient, 15% 55 mph, 3% 65 mph)

                                                                           1.2%
                                                                           3.0%

                                                                           0.8%
                                                                           3.7%
Urban Cycle Effectiveness  
   (94% Transient, 6% 55 mph)

                                                                           0.8%
                                                                           2.1%

                                                                           0.6%
                                                                           2.7%
                                       

              Table 8: Example GEM Improvements with Added Weight
Vocational Aerodynamics Effectiveness 
With Added Device Weight
                               MEDIUM HEAVY-DUTY
                               LIGHT HEAVY-DUTY

Baseline
Front Fairing
Chassis Skirt & Front Fairing
Baseline
Rear Fairing
Chassis Skirt & Front Fairing
CDA
                                                                            5.4
                                                                              5
                                                                            4.4
                                                                            5.4
                                                                            5.2
                                                                            4.4
Static Test Weight (kg)
                                                                        11,408 
                                                                        11,416 
                                                                        11,439 
                                                                         7,257 
                                                                         7,282 
                                                                         7,288 
Payload (tons)
                                                                           5.60
                                                                           5.59
                                                                           5.57
                                                                           2.85
                                                                           2.82
                                                                           2.82
65mph CO2 Emission (g CO2/ton-mi)
                                                                            211
                                                                            201
                                                                            187
                                                                            401
                                                                            395
                                                                            357
55mph CO2 Emission (g CO2/ton-mi)
                                                                            171
                                                                            164
                                                                            154
                                                                            314
                                                                            311
                                                                            284
Transient CO2 Emission (g CO2/ton-mi)
                                                                            244
                                                                            243
                                                                            242
                                                                            367
                                                                            369
                                                                            363
Effectiveness over 65 mph
                                                                              
                                                                           4.5%
                                                                          11.2%
                                                                              
                                                                           1.4%
                                                                          10.9%
Effectiveness over 55 mph
                                                                               
                                                                           4.1%
                                                                           9.9%
                                                                               
                                                                           1.2%
                                                                           9.7%
Effectiveness over Transient
                                                                               
                                                                           0.6%
                                                                           1.1%
                                                                               
                                                                          -0.6%
                                                                           1.1%
Regional Cycle Effectiveness
   (50% Transient, 28% 55 mph, 22% 65 mph)
                                                                               
                                                                           2.1%
                                                                           5.1%
                                                                               
                                                                           0.3%
                                                                           5.4%
Multi-Purpose Cycle Effectiveness  
   (82% Transient, 15% 55 mph, 3% 65 mph)
                                                                               
                                                                           1.0%
                                                                           2.2%
                                                                               
                                                                          -0.3%
                                                                           2.4%
Urban Cycle Effectiveness  
   (94% Transient, 6% 55 mph)
                                                                               
                                                                           0.7%
                                                                           1.4%
                                                                               
                                                                          -0.6%
                                                                           1.4%
                                       

                                   APPENDIX
                                       
Aerodynamic Drag Reduction Technologies for Heavy-Duty Vocational Vehicles  -  Preliminary Coastdown Results

                                                     January and February, 2015
                                       
Aerodynamic Drag Reduction Technologies for Heavy-Duty Vocational Vehicles  -  Preliminary Coastdown Results

The National Renewable Energy Laboratory (NREL) under ARB Agreement Number 11-600, NREL Contract Number FIA-11-1763 has performed a series of coastdown tests on heavy-duty vocational vehicles with and without aerodynamic improvement devices to assess their performance. These results are preliminary and future work under this agreement will include additional repeats and steady-state tests to help refine these results at a later date.  The procedure used for coastdown testing followed the general guidelines outlined in SAE J1263 and SAE J2263 and uses calculation from CFR 1066.310 where applicable.
Coastdown Track
The current coastdown track is located at the Front Range Airport east of Denver, CO. The east runway, which runs in a north-south direction, has an access road along the east side of it. A portion of that road, as seen by the red line in Figure 1, is used for coastdowns. The track runs in a north-south direction. The southern end of the track has an average grade of 0.4%.

Track Profile
 
                              North end of track
                                Avg. 0.4% grade
Data Processing
Data is collected at 5Hz during the coastdown. An ISAAC data recorder monitors OBD information as well as logging velocity from a Garmin 18x-5Hz which is used in the data post processing. Since the track has a slight grade the north and south profiles differ.
                                     South
                                     North
The following road load equation is used to describe the behavior of the vehicle:
F-mg∆h∆x= μmg+ 12ρACdV2
At each time step interval the total force on the vehicle can be calculated using the following equation:
F=ma
Fi= meVi-Vi-1∆t
The effective mass (me) was calculated for the class 6 box truck by adding 56.7 kg to the measured vehicle mass for each tire making road contact. For the class 4 city van the ratio of rotating mass to measured vehicle mass was kept the same. After correcting for elevation change using the road grade survey each interval point in plotted and a least-squares regression is used to determine the coefficients.

In the polynomial fit the `B' term is fixed at zero and `A' and `C' coefficients are assigned as follows
A= μmg
C=D= 12ρACd
Then `D' term can be corrected for standard conditions as follows
Dadj=DT29398.21P
The Vehicles

The Aerodynamic Devices
                                    Device
                                    Vehicle
                                 Total Weight
                                 Wheel Covers
                                26' Box Truck
                               2.2 kg (4.8 lbs)
                                 Front Fairing
                                26' Box Truck
                              15.5 kg (34.1 lbs)
                                  Side Skirts
                                26' Box Truck
                               45.9 kg (101 lbs)
                                 Rear Fairing
                                16' LCF Truck
                               49.5 kg (109 lbs)

Preliminary Results
All error estimates shown are 95% confidence intervals.

 

                                       
                                       
                   Observed Change Without Wind Correction 
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                     Observed Change With Wind Correction
                                       

Discussion
These results are preliminary and planned future work includes additional repeats and steady-state tests. Also, data analysis efforts and refinement of the processing code are ongoing and may also affect future results. Under the test condition of "All* (see note)" please note that changing wind conditions shown in the weather conditions table for this test, predominately the eastern crosswind which increased dramatically between the baseline (all), and the test condition. This may have significantly affected this data point and the condition will be repeated once weather permits.