United States

Environmental Protection Agency Air and Radiation EPA420-R-02-025
October 2002



# Study of Exhaust **Emissions from Idling Heavy-Duty Diesel**  **Trucks and Commercially Available Idle-Reducing** 
**Devices**

Printed on Recycled Paper

### EPA420-R-02-025

October 2002



# Study of Exhaust Emissions from **Idling Heavy-Duty Diesel Trucks and Commercially Available Idle-Reducing Devices** 

Han Lim

Certification and Compliance Division Office of Transportation and Air Quality U.S. Environmental Protection Agency

NOTICE

This technical report does not necessarily represent final EPA decisions or positions. It is intended to present technical analysis of issues using data that are currently available. The purpose in the release of such reports is to facilitate the exchange of technical information and to inform the public of technical developments which may form the basis for a final EPA decision, position, or regulatory action.Page 1 of 10 **ABSTRACT**

Heavy duty diesel truck id ling contributes significantly to

energy consumption in the Uni t ed States. President
Bush’s May 2001 National Energy Policy tasks the U.S.

Environmental Protection Agency (EPA) and the U.S. Depar tment of Transportation (DOT) to reduce truck idling. Consequently, the EPA initiated a study that

would qu antify long duration idling emissions and fuel consumption rates.

The idling study was conducted over a two year period at
the U.S. Army’s Aberd een Test Center (ATC). A short

intr oductory study with five tests was done in June 2001 and a larger study with 37 tests in May 2002. In the
lar ger study, EPA worked with Oak Ridge National Laboratory (ORNL) and Rowan University with funding
fr o m the New Jersey Department of Transportation (NJDOT).

In total, ATC pe rformed 42 tests on nine class-8 trucks (model years ranging from 1980's to 2001). Two of those

truc ks were equipped with 11 hp diesel auxiliary power
units (APU’s ), and one was equipped with a diesel direct
fired heater (DFH). The APU powers electrical accessories, heating, and air conditioning, w hereas a

DFH heats the cab in lieu of truck idling. All tests were

run in a climate control led chamber, where the trucks
idled at high and low RPMs in the fo llowing

e nvironments: 90 O F with air conditioning on, 0 O F with the
heater on, and 65 O F with no accessories on. ATC test technicians adjusted the air conditioning or heater to
maintai n a target cab temperature of 70 O F. Each idling test was run for approximately three hours.

EP A’s ROVER (Realtime On-road Vehicle Emissions Reporter) and ORNL laboratory em issions instruments were simultaneously used for measuring fuel consumption rates, HC (hydrocarbons), NOx (nitrogen oxides), CO (carbon monoxide), CO 2 (carbon dioxide), O 2 (oxygen), and PM (particulate matter) (ORNL only) during the May 2002 test runs. Only the ROVER was

used du ring June 2001. The test data showed that,
ba s ed on the data obtained from this study: (a) on
average, a typical 1980s-2001 model year idling truck
emits 144 g/hr of NOx and 8224 g/hr CO 2 and consumes about 0.82 gal/hr of diesel f uel; (b) there is good test repeatability when m easuring idling emissions; and (c)

use o f an APU can reduce idling fuel consumption by 50% to 80% and reduce NOx by 89% to 9 4 % whereas

use of a DFH can re duce fuel consumption by 94% to 96% and reduce NOx by 99%.

**INTRODUCTION**

In May 2 001, President Bush issued the N ational Energy Policy directing EPA and DOT to work with the trucking

i ndustry to establish a program to r educe emissions and
fuel consumption from lo ng-haul trucks. Responding to
this directive, EPA initiated a comprehensive program aimed at reducing idling. This includes organizing workshops, issuing grants, implem e nting demonstration projects, and most importantly, closely examining idling fuel consumption and exhaust emissions.

EPA ran a two-phase test program. Phase 1 consisted of a small sample of trucks and one APU, which was completed in June 2001. The results of this phase prompted EPA to develop a more comprehensive test program (Phase 2), completed in May 2002.

Certain stakeholders reviewed and commented on the May 2002 test protocol and actual field tests, including the American Trucking Association (ATA), Rowan University, and the 21 st Century Truck Partnership (a government-industry partnership). The phase 2 test program was funded by the New Jersey Department of Transportation (NJDOT) using the DOT Congestion Mitigation and Air Quality (CMAQ) funds. The final test protocol that was used for the May 2002 testing incorporated comments from the above mentioned organizations, as well as ATC and ORNL.

Long haul truck drivers idle their engines during their rest periods to provide heat or air conditioning for the sleeper compartment, keep the engine warm during cold weather, and to maintain adequate battery voltage while using electrical appliances such as a microwave oven or
television set. Other reasons cit ed by truck drivers for idling include safety (i.e., keeping the windows closed, thereby needing cooling or heating) and habit (i.e., protecting the engine by not turning it off).

The precise number of long-durat ion idling tr ucks is not known. Estimating the potential number of idling trucks requires examining several sources. The U.S. CensusPage 2 of 10 Bureau, Vehicle Inventory and Use Survey (VIUS) (1997), estimates that approximately 500,000 heavy duty trucks (> 26,001 lbs) travel more than 500 miles as their average daily trip length. Driving this distance may require an eight hour rest period, and during this rest period truck drivers may idle their engines.

The uncertainty on idling trucks extends to the hours and number of days over a year spent idling. Some reports indicate 6-8 hours per day over 250-300 days per year. Since DOT mandates a rest period of 8 hours after a maximum of 10 hours of driving, it is possible to conclude idling times of 1,500-2,400 hours per year.

While exact numbers, hours, and days are currently unavailable, the objective of the test program was to better understand the fuel consumption and exhaust

emissions associated with idli ng trucks under different weather and accessory loads.

**METHODOLOGY**

To measure actual emissions from a truck’s tailpipe, EPA
used t he EPA-developed ROVER (Realtime, Onhighway Vehicle Emi s sions Reporter) system. ROVER

allows mass emissions data to be obtained simultaneously with vehicle/engine parameter data from

the truck’s diagnostic port along with vehicle loca tion and speed data using an integrated glob al positioning system (GPS). Other instruments can also be used by communicating through auxiliary analog cha nnels or serial ports.

Initially, ATC was directed to perform a 6 hour idling test to determine the point when the pollutants reach steady state conditions. Initial tests showed steady state emissions at 3 hours. Therefore, every subsequent test was run for 3 hours. Once the data were collected, EPA staff analyzed the data and evaluated the baseline idling

emissions for these nine trucks, two APU’s, and one

DFH.

Truck Selection

Trucks of various ages that represent highway trucks from the 1980's to present day were obtained for testing.

ATC used class-8 trucks that were available at the Aberdeen Test Proving Grounds and commercially

available truck rentals such as Ryder that ranged from

mid-1980's to 2001. Various m odel year trucks were selected including three representing the model years near the pivotal highway diesel engine standards change years 1997 (5.0 g/bhp•hr NOx standard) to 1998 (4.0 g/bhp•hr NOx standard). Table 1 below shows the descriptions of each truck. The grey blo cks in Table 1 represent trucks and APU tested in J une 2001, the white blocks represent trucks, APU, and DFH tested in May

2002. Table 1: Truck and Engine Identification

Truck and Engine Rated HP and engine displacement Additional Truck

Information as available

1985 Volvo White**

1990 Volvo NTC-400 400 @ 2100 rpm 855 CID (14.0 L) Engine # 11611170, date

of mfr. 12/90

1992 Ford* 1992 Caterpillar 3406B 425 @ 2000 rpm 890 CID (14.6 L) Engine Family

NCT0893FPB9

Serial No. 3ZJ23694

1995 International (Navistar) 1995

Detroit Diesel S60 470 @ 2100 rpm 774 CID (12.7 L) Engine Family:

SDD12.EJDARA approx. age: 650,000miles

1997 International (Navistar) 1997 Caterpillar 3406 410 @ 1800 rpm 890 CID (14.6 L) Engine Family:
VCP893EZDARX
Serial No. 6TS09138

1998 Freightliner

1997 Cummins 370/435 @ 1800

rpm Engine Family:

VCE855FJDARA

Serial No. 11861993

1999 Volvo

1999 Detroit Diesel S60 470 @ 2100 rpm 774 CID (12.7 L) Engine Family:

XDDXH12.7EGL

Serial No. 06R0-547668

1999 KenworthT800 1998 Caterpillar 3406 410 @ 1800 rpm 890 CID (14.6 L) Engine Family:

WCPXH0893ERK

2000 Volvo 2000 Detroit

Diesel Series 60 470 @ 2100 rpm 774 CID (12.7 L) Engine Family

YDDXH12.7EGL

4V4NC9RH31N247483

2001 Freightliner

2000 Detroit Diesel

Series 60 500 @ 2100 rpm 774 CID (12.7 L) Engine Family

YDDXH12.7EGL

Serial No. 06R0612467

Idle Reducing Devices:

1995 Pony Pack APU:

Kubota Z200

2000 Pony Pack APU:

Kubota Z482 11 @ 3600 rpm

29.23 CID (0.482 L) Engine Family

YKBXL.719KCB

Serial # YC4323

1990's Espar Diesel

Direct Fired Heater

Model D1LC

NOTES : Grey blocks represent June 2001; elsewhere May 2002 * Only truck without a sleeper cab nor ECM data port ** No ECM (engine control module diagnostic port) available The horsepower ratings are obtained from the engine label (advertised hp)

Each truck was equipped with a sleeper cab (ex cept as noted in Table 1) air conditioning and heating.

Trucks were not subjected to any special maintenance procedures (e.g., oil changes, tune-ups, etc.). All trucks

were tested as received or as rented, including the
standard diesel fuel (standard filli ng station fuel) that all trucks were equipped with.

Test Conditions / Scenarios / Variables

All tests were ru n in a climate controlled chamber, approximately 40 ft x 40 ft x 2 4 ft, where the trucks werePage 3 of 10 idled at high and low RPMs in the following

env ironments: 90 O F with air conditioning operating, 0 O F

with the heater operating, and 65 O F with no accessories operating. Table 2 shows all the test scenarios for phase 1 (June 2001) and phase 2 (May 2002).

Table 2: Test Matrix

JUNE 2001 TEST SCENARIOS

A/C On
Chamber Temp=90 O F Heater On
Chamber Temp=0 O F No Accessory
Chamber Temp=65 O F

1985 Volvo White - 1 test 750 RPM N/A N/A

1995 International - 1 test 600 RPM N/A N/A

1999 Kenworth - 1 test 600 RPM N/A N/A

2000 Volvo - 1 test 1000 RPM N/A N/A

1995 APU - 1 test 3600 RPM N/A N/A

MAY 2002 TEST SCENARIOS

1992 Ford - 6 tests 600 RPM 600 RPM 600 RPM

1200 RPM 1200 RPM 1200 RPM

1997 International

6 tests 700 RPM 700 RPM 700 RPM

1100 RPM 1100 RPM 1100 RPM

1998 Freightliner - 8 tests* 600 RPM 600 RPM 600 RPM

800 RPM* N/A N/A

1000 RPM* N/A N/A

1200 RPM 1200 RPM 1200 RPM

1999 Volvo - 6 tests plus 2 repeats** 600 RPM 600 RPM 600 RPM x3**

1200 RPM 1200 RPM 1200 RPM

2001 Freightliner - 6 tests 600 RPM 600 RPM 600 RPM

1200 RPM 1200 RPM 1200 RPM

2000 APU - 2 tests 3600 RPM 3600 RPM N/A

1997 DFH - 1 test N/A High Heat N/A

NOTES : Total number of tests = 42 A/C = air conditioning; none = no accessories active * Performed additional tests at the intermediate speed to examine emissions/ fuel consumption rates with varying engine RPM. ** Performed two repeat tests at 600 RPM with no accessories active to assure good test to test repeatability

The APU tests were run with the air conditioning operating and heater on in the 90 O F and 0 O F environments, respectively. However, the DFH test was

run only in the 0 O F environment. ATC test technicians adjusted the air conditioning or heater to maintain a target cab temperature of 70 O F. EPA staff developed a

test matrix to examine the following pr imary test variables: engine RPM, truck age, and accessory load.

The engine RPM was usually dialed in vi a electronic
onboard controls in the truck cab, except for the 1985 Volvo White truck which did not have the electronic
control feature. The 1985 Volvo truck was only tested at

one rpm. Most trucks were capable of idling from 600 to 1200 rpm. The RPM was set at one value throughout a
three hour test.

Test Equipment

ATC staff used the EPA-dev eloped ROVER system

whic h is comprised of an IBM PC based data acquisition system running EPA developed software, a S n ap-On TM

gas analyzer, an optional Horiba MEXA-120 zirconia

N Ox sensor, and specially designed exhaust gas
flowmeter modules of various sizes.

ROVER is used to measure fuel consumption rate, HC, CO, CO 2 , and NOx em issions. In the Snap-On MT3505 analyzer, non-dispersive infrared technology is used to

measure HC, CO, and CO 2 , whereas an electrochemical

sensor is used to measure NOx and O 2 . Generally, the

ele ctrochemical and zirconia based NOx measurements

s howed good comparability, however during the second phase of this testing program, there was a zero-drift error in the electrochemical s ensor which could not be readily
rectified. Hence, only the Horiba NOx results are presented. Furthermo re, a zirconia NOx instrument

such as the Hor i ba MEXA-120 was appropriate for the experiments in this study. SAE Paper 2001-01-3619

contains inform ation that shows a zirconia NOx instrument has a 4 to 1500 ppm linear calibration at ± 5%

meas ured point accuracy versus primary standards (Schenk et al, 2001) . The appropriate gas flowmeter
module was attached to the ex haust pipe of the specimen truck.

Since the Pony Pack TM engine was equipped with a smaller diamete r exhaust pipe than the main engine, a
smaller flowmeter was used. The appropriate flowmeter module also provided the gas sample to the gas analyzer
and temperature and pressure measurements needed
for mass determinations. Fuel consumption rate was
determined by carbon balance. Systems checks were performed before and after a set of tes ts by the zero and span gas method using calibration gases. The flowmeter

w as calibrated using a laminar flow element. The
ROVER ins t ruments were placed near the driver’s seat during idling tests (s ee Figure 1). The flowmeter module mounting was different for various exhaust pipe configuratio ns. Figure 2 shows the typical horizontal mounting of the flowmeter, which replaced the normal tailpipe on a class-8 truck. ATC technicians adapted to

various configurations by making support ji gs specific to

an exhaust pipe orientation or e xhaust pipe size (i.e.,

sma ller flowmeter for Pony Pack T M engine). Since this idling study was a joint effort with O RNL, ORNL staff

measured the same pollutant s with a separate sampling
line that was connected to their own instrumentation.Page 4 of 10 Figure 1: ROVER system installed on the passenger seat

Figure 2: Mounting of ROVER flow pipe / sampling lines

Note : Figure is NOT to scale.

Although PM measurements were obtai ned by ORNL staff, only the ROVER test data will be presented, with the focus on fuel consumption rates and NOx and C O 2 emissions. ORNL staff will present their PM results in their own SAE paper. O RNL PM data ar e not presented in this paper.

Test Procedure

For the five t e sts performed during the June 2001 runs,

an initi al 10 to 15 minute ‘warm-up’ drive was performed
before the idling test began. An ATC driver drove the

truck on the highway at a bout 55 miles per hour, then parked the truck in the climate chamber with the ROVER system fully attached. The ROVER data acquisition

program was started once the truck was i n motion. The

test technician noted wh en the idling portion of the test began. The chamber technician ensured that the test cham ber maintained a steady temperature of 90 o F, 0 o F,

or 65 o F, then shut the chamber doors and began the idling test. For safety, the ATC technicians ran flexible

exhaust h o ses from the flowmeters to ports available in
the test c hamber to remove unwanted exhaust gases.
The same procedure was used for the May 2002 tests, except the warm up drive porti on was not done. EPA
staff determined from the June 2001 data that the drive portion did not appear to affect the emissions or fuel consumption data.

During the idling tests, the ATC technicians performed

routine instrumentation chec ks every 30 minutes to

ensure the highest quality data even under the re latively
low exhaust flow rate under idle conditions. This was perfo r med by temporarily applying no-flow conditions to
the flowmeter module transducers while recording their

ou tputs. Each pollutant and the volume flow rate during
these half-hourly checks show u p as zeros or close to
zero in the ROVER data files.

All tests for the f irst phase were performed over a three day period, where two climate controlled chambers were
used to test two tr ucks per day. The order of the tests

was randomized to minimize bias i n the data collection (i.e., a 1990's truck was tested on the same day as a 1980's truck; two 1990's t rucks were not tested the same day). Tests for the second phase were run in a single

climate controlled chamber over a three w e ek period.
Similar to phase 1, the order of tests was randomized to the extent practicable.

Data Post-processing and Analysis

T he ROVER portable emissions measurement syst e m has the capability to create a text file with columns of

data f or time, HC, CO, CO 2 , NOx, engine speed, fuel consumption rate, etc. The data from each test were sampled ever y second (1 Hz). The ROVER data text
files were imported into Microsoft Ex cel T M for data analysis.

**RESULTS AND DISCUSSION**

Idling emissions data were collected for nine class-8 heavy duty diesel trucks, two APU Pony Pack TM engines, and one Espar TM DFH. The first part of this section will discuss sample calculations that show how the emissions and emissions reductions were obtained; the second part will discuss the data analyses of the June 2001 testing; the third part will discuss the data analyses of the May 2002 testing.

Sample Calculations

Determining the masses for the pollutants was important for determining the tons of emissions. The ROVER program was set up to determine mass emissions in real time. The gas concentrations in parts per million (ppm)Page 5 of 10 or percent age (%) for the various pollutants, CO, CO 2 , NOx, and HC, the measured exhaust gas flow rate, and the gas analyzer transport and res ponse time delays are

used. Table 3 shows the densities and other constants used for performing various mass and fuel consumption

rate calculations in real time.

Table 3: Constants used in Emissions Calculations

CO CO 2 HC NOx O 2

Density (g/ft 3 ) 32.97 51.81 16.33 54.16 37.18

Density of diesel fuel = 3212 g/gal;

Weight fraction of C in diesel fuel = 12.011 = [12.011 + (1.80 • 1.008)]

= 0.869 from the relation CH 1.80

Mass of C in 1 gal. of diesel fuel = 3212 g/gal • 0.869 = 2791 g C/gal

An example record from the ROVER data file is shown in

Table 4.

Table 4: Sample excerpt from a ROVER Excel Data File

Delta t (s) 1.001 Lambda 9.450 EngineLoad % 0.000 AnalyCorFac 1.015
FUEL RATE G/H 0.900 GPS_Speed(mph) 0.000
ENGINE RPM 1,199 Accel(mph/s) 0.000
OIL TEMP F 209 Road Grade(%) 0.000 Ann_dP ("H2O)L 3.706 Climb Rate(ft/s) 0.000 Ann_dP ("H2O)H 3.734 Altitude(ft) 0.000 Exh_Temp (F) 223.202 Latitude(deg) 0.000 Amb_P ("Hg) 30.237 Longitude(deg) 0.000 Exh_dP ("Hg) 0.008 #_Satellites 0.000 Chamber_T (F) 62.798 PDOP 0.000 Vmix'(scfm) 259.813 T_Heading(deg) 0.000 Vmix_CF 1.000 GPS_Time

Mode MT GPS_Status Waiting for
GPS Time HC(ppm) 10.000 miles driven 0.000 CO(%) 0.010 HC(mg) 8.373 CO2(%) 1.510 CO(mg) 14.087 O2(%) 18.580 CO2(mg) 3,342.595 NOx(ppm) 239 O2(mg) 29,912

TEMP 82.800 mpg 0.000 Lambda_SO 0.000 mgal 0.332 Lambda(B) 9.320 NOx (mg) 55.306
A/F 136.96 Values in the white blocks are used in the sample calculation.

For illustration purposes, sample calc u lations are provided below:

Mass of CO 2 = [ß • V • C • dt] / F where:

ß = Density of CO 2 = 51.81 g/ft 3

V = Volum e Flow Rate = 259.813 ft 3 /min
C = CO 2 concentration = 1.51%

F = water condensation in the sample line factor = 1.01
dt = delta time = 1 second

Plugging in the values shown above, yields a mass of
CO 2 value equal to 3.342 g = 334 2 mg, as shown in
Table 4.

A lso, using the relation 0.273 grams of C in 1 gram of
CO 2 yields the following:

[3.342 g CO 2 • (0.273 g C/1 g CO 2 )] / [(2791 g C/1 gal)] =

0.332 mgal = instantaneous milligallons in 1 second.

To determin e the gallons per hour fuel consumption rate,

a half hour’s worth of instantaneous milligallon nu m bers (not shown in Table 4) are summed up and calculated to yield 1.25 gal/hr.

Data Analyses of June 2001 Tests

As mentioned earlier, the ATC te chnicians performed
routine instrumentation checks every 30 mi n utes by zeroing the gas analyzer, the MEXA- 120, and by checking the zero of the exhaust flowmeter module

transducers to detect any drifts in the emission measurement system.

The HC and CO data s howed low level emissions that

are typica l of diesel engines. Although HC and CO data

w ere collected, these data were not relevant to this study, and therefore detailed analys es of HC and CO are

not presented in this paper. NOx showed some dynamics during the first few hours of idling, then

rea ched st eady state. Therefore, the NOx data were

used as the criteria for determinin g steady state
conditions.

In the idling tests, NOx emissions typically ex hibited the
behavior se en in Figure 3. After about three hours of idling, the emissions reach a stead y state condition.
When the Kenworth truck w a s tested the first day, ATC
staff ran the test for six hours. It appeared that a three
hour idle test would be adequate for determining the steady state emission rates from an idling truck.

CO 2 remains at a fairly constant steady state condition throughout an idling test. However, some tests involving

no access ory loads and heater loads showed an initial high CO 2 value in the same manner as the NOx curve in Figure 3 and then reached steady state in about 3 hours.
This phenomenon is perhaps due to a ‘co ld enginePage 6 of 10 Figure 3: NOx versus time for 1999 Kenworth Truck

Figure 4: Details/close-up of Figure 3 star ting’ scenario where the increased work initially
needed to pump the cold engine oil would resu l t in a higher initial CO 2 and then a leveling off (stea dy state pattern) over time as the engine warms up.

For i llustration purposes, Figure 4 shows the detailed steady state NOx patterns for the last hour of the idle

test. The emission data (in a verage grams/ hour) for the

five trucks are presented in Table 5. As mentioned before, the averaged values we re calculated over a steady state portion of the idling data file, typically the last hour or half hour of the idling test.

In Phase 1 , the idle speeds were not adjusted for any of

the tests, except for the 2000 Volvo. The 2000 Volvo
truck has a feature that will shut down the engine if the

on-board controls detect that the eng ine is idling at less
than 1 0 00 rpm; therefore, the 2000 Volvo was manually

set to idle at 1000 rpm. The idle speed data were
obtained either automatically via diagnostic tool port or a direct reading of the dashboard tachometer. Table 5: Emission Data Summary for 2001 Test Runs

Idling

RPM NOx g/hr CO 2 g/hr NOx* tons/yr CO 2 * tons/yr gal/

hr

1985 Volvo

White 750 19.80 4830 0.05 12.78 0.49

1999
Kenworth 600 81.40 4650 0.22 12.30 0.46

1995
International 600 84.54 4256 0.22 11.26 0.42

2000 Volvo 1000 112.50 8078 0.30 21.37 0.80

1995 Pony Pack Engine 3600 10.13 2199 0.03 5.82 0.22

* These figures were calculated assuming a truck idles at 2400 hrs/year per truck (using the assumptions described in the Introduction section, 8 hr/day, 300 days/yr)

The engine idle speed had a significant effect on the fuel consumption rate, and con sequently, CO 2 emissions.
The 2000 Volvo truck, which was run at 1 000 rpm, produced nearly twice the CO 2 and nearly double the fuel

con sumption rate compared to a truck run at 600 or 750

rp m. This result is not surprising, considering that if an engine is idling at a faster s peed, fuel will be injected into

the engine many more times per second, which will lead to a higher fuel consumption rate.

The Pony Pack TM engine is a commerciall y available idling reduction technology used in thousands of heavy duty diese l trucks in the United States. The Pony Pack T M

is a 2-cylinder Kubota TM diesel engine, model Z -200 that practically replaces the main engine ’ s functions during idling peri ods. It powers the air conditioning, heating,
and electrical accessories. The emission data in Table 5
show th at there are significant reductions in fuel consumption and emi s sions when compared to the 1995
International Truck with 1995 Detroit Diesel e n gine or the
othe r engines tested for this study. There is about an

88% reduction in NOx and 50% reduction in CO 2 . When
the Pony Pack TM engine emissions ar e compared to
other engines, the reductions can be higher. For

e xample, if a Pony Pack T M is used for idling instead of
the stock 2000 Volvo engine, E PA staff estimates a 73%
reduction in CO 2 and 90% r eduction in NOx could be

achieved.

Data Analyses of May 2002 Tests

The May 2002 tests were run in a similar manner to that
of the June 2001 tests, except more tru cks and idle reducing devi ces were tested with other variables including heating loads, air conditioning loads, and
various R PMs. The following table shows a summary of the test results from the May 2002 tests:Page 7 of 10 Table 6: Test Results from May 2002

1992 Ford Truck with 1992 Caterpillar Engine NCT0893FPB9:

Test # RPM chmbr. temp ( O F) NO

x (g/hr) CO 2 (g/hr) gal/hr

21 600 0 76.64 5965 0.60

22 1200 0 63.99 11404 1.15

9 600 65 69.41 4653 0.46

10 1200 65 55.76 11342 1.13

11 600 90 75.50 6040 0.60

12 1200 90 69.32 14711 1.47

1998 Freightliner Truck with 1997 Cummins Engine VCE855FJDARA:

20 1200 0 328.59 12599 1.26

13 600 65 154.49 5348 0.53

14 800 65 164.29 7335 0.73

15 1000 65 163.13 9452 0.94

16 1200 65 199.05 12433 1.26

17 600 90 174.68 6813 0.68

18 1200 90 251.42 16577 1.65

2001 Freightliner Truck with 2000 Detroit Diesel Engine YDDXH12.7EGL:

Test # RPM chmbr. temp ( O F) NO

x (g/hr) CO 2 (g/hr) gal/hr

30 600 0 136.23 6848 0.69

29 1200 0 193.57 10460 1.07

23 600 65 77.69 4392 0.44

24 1200 65 135.31 9787 0.98

25 600 90 94.36 4787 0.48

26 1200 90 186.95 12090 1.21

1997 International Truck with 1997 Caterpillar Engine VCP893EZDARX:

34 700 0 137.02 7099 0.71

33 1100 0 196.76 10232 1.02

31 700 65 146.01 5596 0.55

32 1100 65 214.62 10043 0.99

36 700 90 174.17 7262 0.72

37 1100 90 267.27 13575 1.34

The test numbers denote the sequence in which the tests

were run. Test instrumentation issues were worked out early in the testing by running triplica te identical tests to

assure good test repeatability as can be seen with test numbers 1, 2, and 4 (see double lined entries in Table 6). Table 6 (continued):

1999 Volvo Truck with 1999 Detroit Diesel Engine XDDXH12.7EGL:

Test # RPM chmbr. temp ( O F) NO

x (g/hr) CO 2 (g/hr) gal/hr

6 600 0 54.83 5878 0.61

7 1200 0 170.28 10877 1.17

1 600 65 80.98 4102 0.41

2 600 65 86.64 3968 0.40

4 600 65 83.24 3915 0.39

3 1200 65 240.98 9251 0.92

5 600 90 104.58 5042 0.50

8 1200 90 288.42 11679 1.16

2000 Pony Pack APU Engine YKBXL.719KCB (for 2001 Freightliner Truck):

28 3600 0 7.27 2053 0.20

27 3600 90 10.01 2353 0.23

Espar Direct Fired Heater Model D1LC (for 1997 International Truck):

38 N/A 30 0.21 402 0.04

NOTES : “Chmbr. temp” = Chamber Temperature “RPM” = Engine idling RPM set during a three hour test
Tests for the 1997 International truck were run at 700 and 1100 RPMs since these were the high and low engine speeds available. Test with 1998 Freightliner at 0 O F was omitted due to instrumentation problems (excessive freezing on the sample line). Tests 1, 2, and 4 are repeat tests intended to demonstr ate repeatability of

test instrumentation (outlined in double lines in this table).

For te sts 1, 2, and 4, the standard deviations for NOx, CO2, a nd fuel consumption were 4.85 g/hr, 96 g/hr, and

0.01 gal/hr, respectively. The coefficients of variation (standard deviation divided by the mean) for NOx, CO2, and fuel consumption were 0.06, 0.02, and 0.025. These
values indicate low variability and good test repeatabilit y

.

Several tests on the 1998 Freightliner truck showed a good linear relationship betwee n fuel consumption rate

and engine rpm. Upon analyzing the data at the various

rpm, EPA staff concluded that running tes ts on a high
and low rpm would be adequate t o predict intermediate
f uel consumption rates at intermediate rpm’s. Figure 5
shows a graphical representation of the 1 998 Freightliner
truck data shown in Table 6 . An R 2 value of 0.99 shows

a strong linear relationship. All tests in Figure 5 were run
without any accessories activ e (at 65 o F). Different

accessories produced different NOx emission patterns during the idling tests. Tests with no accessories active

or heater active showed flat line responses as shown in Figure 6.Page 8 of 10 Figure 5: Linear relation between gal/hr and rpm

Figure 6: Example Plot with No Accessories Active Figure 7: Example Plot of Air Conditioning Test

Figure 8: NOx data sorted by RPM for 2002 Tests

Air conditioning tests, however, showed cyclical pat t erns, which is caused by the engine fan and the air conditioner
electro magnetic clutch engaging during the tests (see Figure 7). Furthermore, Figure 7 shows that the engine

rpm, engine load, and NOx emissions are affected by the
air conditioner com pressor load. The NOx, rpm, and

load spikes and peaks appear to occur at the same time.
These spikes and peaks produce an additive effect on th e NOx emission rates. As discussed in the June 2001

data sec t ion, higher rpm’s will produce higher emissions
and fuel consumption rates as evidenc ed in the data presented in Table 6.

Figure 8 shows all of the average NOx data in grams per

hour for the 2002 tests. Note that there is a general
trend where NOx increases wit h chamber temperature
and RPM. The data in Figure 8 are also presented in
Table 6. The occasional low NOx values are from the 1992 Ford Truck wi th a Caterpillar engine. This truck

appears to have the lowest NOx va lues and seems least
affected by engine RPM or ambient t e mperature or accessories active.

Clearly, air conditioning tests will pr oduce higher NOx values, especi ally with the additive cyclical NOx emission patterns and higher engine load from the air conditioner

compressor.

The matrix of tests run during 2002 showed a wide range of fuel consumption and emissions result s by varying engine age, engine rpm , and ambient temperature (accessories on or off). Table 7 summarizes the high, low, and average values.Page 9 of 10 Table 7: High, Low, and Average Emissions and Fuel Consumption Rates for 2002 Test Data

NOx (g/hr) CO 2 (g/hr) gal/hr

ARITHMETIC MEAN FOR ALL TESTS

High Value 329 16,578 1.65

LowValue 55 3,915 0.39

Average Value 144 8,224 0.82

Standard Deviation 72 3571 0.40

Coefficient of Variation 0.5 0.43 0.43

Low RPM avg. (600 - 800 rpm) 114 5805 0.58

High RPM avg. (1000 - 1200 rpm) 190 11815 1.18

WEIGHTED AVERAGE VALUES (60% High RPM, 40% Low RPM):

Weighted Average Value: 160 9411 0.94

WEIGHTED AVERAGE VALUES (70% High RPM, 30% Low RPM):

Weighted Average Value: 167 10012 1.00

As it turn s out, the average fuel consumption rate is the

same as the highest rate obtained from the 2001 t esting.
The average NOx of 144 g/hr, howe ver is somewhat higher than the 112 g/hr obtained from the 2001 testing,
which seems reasonable considering tests at higher

rpms such as 1200 rpm were performed. One should

k eep in mind that the aver age values in Table 7 are
calculated with over 30 unique test scenarios that span

extreme ambient temperatures, engine rpms, and parasitic l oads (A/C and heating) , which would explain the coefficients of variation in the 0.4 to 0.5 range.

It is general practice to idle the engin e at 1000 rpm or higher when heavy accessory load s are present.
Truckers can reason ably be expected to operate their
heaters on days when the tem perature drops below 50 o F
and to operate their air conditioning on days when temperatures exceed 70 o F. National Oceanic and Atmospheric Administratio n (NOAA) temperature data indicate that these temperature ranges can be expected
to occur nationwide between four and nine months of the

year (NOAA, 2000). Operation of accessory loads would occur during these months.

With that said, for illustration purposes only, weighted

average valu es were calculated in addition to the overall
arithmetic mean values, to reflec t use of accessory
loads. Table 7 shows that with the high rpm tests weighted at 60% and low rpm tests weighted at 40%, the weighted average NOx value is 160 g/hr. If the high rpm weighting factor is increased to 7 0% high rpm, with a

30% low rpm, the weight ed NOx is 167 g/hr. These are only example weighted averages. However, EPA staff conservatively estimate that on average, an idling class-8 truck can emit 144 g/hr of NOx based on the data collected in this study.

Emissions and Fuel Consumption Reductions Achievable by Using Idle Reducing Devices

Several types of technologi es exist that will effectively
reduce long-duration idling. EPA maintains a list of idle

r eduction technologies that can be accessed at the following website: http://www. epa.gov/otaq/retrofit/ idlingte c h.htm

. EPA makes no claims as to the
effectiveness or operation of these products, and the list
is for in formational purposes only. Two idle technologies

were selected to determine the emissio ns associated

with these products, and their potential emission reductions when compared to baseline idling emissions
from the test vehicles. One technology, an auxiliary

power unit by Pony Pack, I n c. has the ability to provide heat, air conditioning, and electrical power. The other technology is a direct fired heater by Espar, Inc., which provides heat only. These two products were selected for their ability to provide air conditioning and/or heat.

While other similar products ex i st on EPA’s list of technologies, these two were selected arbitrarily.

The fol lowing discussion compares the idle reduction
device to the tr uck to which that device is attached. For
the direct fired heater (DFH), NOx emission rates and
fuel consumption rates from the 1997 International Truck

with Caterpillar engine are compared to the DFH. With

the DFH producing 0.21 g/hr of NOx and the Caterpillar engine emitting 137 to 197 g/hr (700 to 1100 rpm, respectively at a chamber temperat u re of 0 o F with the
main engine heater on), a 99% reduction in NOx appears

to be ac hievable. Similarly, Table 8 shows percent
reductions achievable from a DFH or an APU.

The data from the May 2002 testing shows results comparable to those obtained in June 2001. The 1995
APU was capable of reducing NOx by 88% and CO 2 by 50%, whereas a 2000 APU was capable of reducing NOx by 89 to 96% and CO 2 by 52 to 81%.

Although the data o btained from June 2001 provided a glimpse of the idling d ata characteristics, EPA staff

ba sed their data analyses and emissions estimates on the May 2002 data, which provided a more comprehensive and consistent set of data. Nevertheless, the d ata from 2001 and 2002 are comparable.Page 10 of 10 Table 8: Percent Reductions Achievable with the Use of an Idle Reducing Device

1997 International Truck with Caterpillar Engine with the **truck**

**heater on**

gal/hr NOx (g/hr) CO 2 (g/hr)

Truck @ 700 rpm 0.71 137 7100

Truck @ 1100 rpm 1.02 197 10232

**DFH 0.04**  **0.21 402** 

Percent Reduction 94-96% 99% 94-96%

2001 Freightliner Truck with Detroit Diesel Engine with the **truck**
**heater on**

gal/hr NOx (g/hr) CO 2 (g/hr)

Truck @ 600 rpm 0.69 136 6848

Truck @ 1200 rpm 1.07 194 10640

**APU w/ heater on 0.20**  **7.3 2053** 

Percent Reduction 71-81% 94-96% 71-81%

2001 Freightliner Truck with Detroit Diesel Engine with the **truck air conditioning on** 

gal/hr NOx (g/hr) CO 2 (g/hr)

Truck @ 600 rpm 0.48 95 4787

Truck @ 1200 rpm 1.21 174 12090

**APU w/ AC on 0.23**  **10.0 2353** 

Percent Reduction 52-80% 89-94% 52-80%

Using the data in Tables 7 and 8 it is possible, with some

a ssumptions about the idling characteristics of the fl eet, to make estimates of the idling emissions of the nation’s
truck fleet. As an example, if the fleet consists of 500,000 trucks and those tr ucks idle 8 hours per day,

300 days per yea r while consuming 0.8 gal of fuel per

hour then those trucks produce 10.9 million tons of CO2

per year (21.7 tons/year pe r truck) and 190,476 tons of
NOX per year (0.38 tons/year per truck). Under this example, those trucks would consume 960 million gallons of diesel fuel while idling.

**CONCLUSION**

The purpose of EPA’s idling test program was to c losely
examine long-duration idling emissions on a diverse

group of heavy duty trucks under various engine speeds, ambient temperatures, and accessory loads. Prior to this

test program, long-duration idling tests had not bee n conducted. EPA and other organizations and institutions
have examined idlin g for brief periods of time, but these

tests did not reflect the more realistic long -duration idling periods.

Based on the emission s and fuel consumption data generated from this study, th e test data showed that (a)

on average, a class-8 truck could emit 144 g/hr of NOX

and 8224 g /hr of CO 2 , and could consume about 0.82

g al/hr of diesel fuel and (b) the use of idle redu ction technologies can reduce fuel consumption and emissions significantly.

The idling test progra m supports EPA’s continued
commitment in working with the trucking industry and its
stakeholders to reduc e idling. To date, EPA has organized workshops, funded demonstrat i on projects,
and created a grant program to a ssist trucking companies. Future plans include identifying idling

emissions within mobile models and inventories, and creating incentives for states to reduce idling.

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Brodrick, C.J. et al, Potential Benefits of Utilizin g Fuel Cell Auxiliary Power Units in Lieu of Heav y Duty Truck Engine Idling, Institute of Transport ation Studies , University of California - Davis, 2001.

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National Energy Policy Development Group, National Ene rgy Policy , President of the United States of America, May 2001.

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Stodolsky, Frank, Linda Gaines et al, Analysis of Technology Options to Reduce Fuel Consumption of Idling Trucks , Center for Transportation Research, Argonne National Laboratory, Paper No. ANL/ESD-43, 2000.

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