National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

Natural Gas Engine Development 

July 2003 — July 2005 

T.C. Lekar and T.J. Martin 

John Deere & Company 

Waterloo, Iowa 

Subcontract Report 

NREL/SR-540-39491 

March 2006 
Natural Gas Engine Development 

July 2003 — July 2005 

T.C. Lekar and T.J. Martin 

John Deere & Company 

Waterloo, Iowa 

NREL Technical Monitor: R. Parish 

Prepared under Subcontract No. ZCI-3-32027-04 

Subcontract Report 

NREL/SR-540-39491 

March 2006 

National Renewable Energy Laboratory 

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
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Table of Contents 

List of Tables...............................................................................................................................................v 

List of Figures .............................................................................................................................................v 

List of Photos...............................................................................................................................................v 

List of Acronyms and Abbreviations .........................................................................................................vi 

1.0 Executive Summary ..............................................................................................................................1 

2.0 Introduction ...........................................................................................................................................4 

2.1 Project Objective ...............................................................................................................................4 

2.2 Project Participants ............................................................................................................................4 

2.3 Project Design....................................................................................................................................5 

3.0 Task Specifications................................................................................................................................8 

3.1 Engine Design, Performance and Emissions (Task 3.1)....................................................................8 

3.1.1 Engine Specifications..................................................................................................................9 

3.1.2 Torque and Power Curves.........................................................................................................11 

3.1.3 Vehicle/Fleet Description..........................................................................................................19 

3.1.4 Duty Cycle Description.............................................................................................................19 

3.2 On-Road Engine Development (Task 3.2).......................................................................................19 

3.2.1 Description of Development Work ...........................................................................................21 

3.2.2 Fuel Economy and Mileage Accumulation...............................................................................21 

3.2.3 Future Plans for the Engine Model ...........................................................................................21 

3.3 FTP Results (Task 3.3) ....................................................................................................................22 

3.3.1 Commercial Engine Ratings .....................................................................................................22 

3.3.2 Commercial Engine Efficiency Map.........................................................................................23 

3.3.3 Narrative Description of Test Results .......................................................................................24 

4.0 Conclusions .........................................................................................................................................28 

5.0 Appendices ..........................................................................................................................................29 

Appendix A: Fleet Vehicle Specifications Form...................................................................................30 

Appendix B: Daily Test Log..................................................................................................................34 

iv
List of Tables

Table 1-1. Summary of Bus 2460 Fuel Economy during Field Test...........................................................2 

Table 1-2. New DF Factors Achieved.........................................................................................................2 

Table 1-3. Summary of Certification Testing Results.................................................................................3 

Table 3-1. Gas Composition for 280 hp Certification Testing ....................................................................8 

Table 3-2. Deterioration Factors................................................................................................................10 

Table 3-3. Target Values for Power Validation Test Conditions..............................................................10 

Table 3-4. Gas Composition for 250 hp Certification Testing .................................................................14

Table 3-5. Certification Results.................................................................................................................18 

Table 3-6. Certification Test Hardware....................................................................................................18 

Table 3-7. John Deere 6081 NG Engine Deterioration Factor Test Cycle................................................19 

Table 3-8. Field Test Data.........................................................................................................................21 

Table 3-9. Deterioration Factors................................................................................................................22 

Table 3-10. 6081HFN04 Engine Ratings .................................................................................................23 

List of Figures

Figure 3-1. Torque curve for 280 hp-900 lb-ft rating................................................................................12 

Figure 3-2. Summary of emission results for 280 hp rating......................................................................13 

Figure 3-3. Comparison of emission results versus targets for 280 hp rating ...........................................13 

Figure 3-4. Torque curve for 250 hp – 800 lb-ft rating ............................................................................14 

Figure 3-5. Summary of emission results for 250 hp rating.....................................................................15 

Figure 3-6. Comparison of emission results versus targets for 250 hp rating ..........................................15 

Figure 3-7. Torque Curve Comparison .....................................................................................................17 

Figure 3-8 John Deere 8.1 Engine Efficiency Map...................................................................................23 

List of Photos

Photos 3-1 and 3-2. John Deere 8.1L deterioration factor engine installed on laboratory dynamometer at 

SwRI............................................................................................................................................................9 

Photos 3-3 and 3-4. Views of John Deere 8.1 L engine installed in New Flyer Bus ................................20 

Photo 3-5. View of WMATA buses.........................................................................................................20 

v
List of Acronyms and Abbreviations 

CARB California Air Resources Board 

CO carbon monoxide 

CNG compressed natural gas 

DF deterioration factor 

DGE diesel gallon equivalent 

DOE U.S. Department of Energy 

EMS Electronic Microsystems 

EPA U.S. Environmental Protection Agency 

FTP Federal Test Procedure (for emission compliance) 

g/bhp-hr grams per brake horsepower-hour 

HHDD heavy heavy-duty diesel 

hp horsepower 

JDPS John Deere Power Systems 

kW kilowatt 

L liter 

LNG liquefied natural gas 

MHDD medium heavy-duty diesel 

mpg miles per gallon 

mph miles per hour 

NMHC Non-methane hydrocarbon 

NOx nitrogen oxides 

NREL National Renewable Energy Laboratory 

PEC John Deere Product Engineering Center 

PM particulate matter 

scf standard cubic feet 

SwRI Southwest Research Institute 

UB urban bus 

UEGO Universal Exhaust Gas Oxygen 

WMATA Washington Metro Area Transit Authority 

vi
1.0 Executive Summary

The U.S. Department of Energy (DOE) funds research and development that reduces U.S. 

dependence on imported petroleum and promotes better air quality. Natural gas vehicles help to 

diversify automotive fuel requirements. In addition, natural gas engines and vehicles have led 

the way to lower exhaust emission requirements. The work described in this report was 

supported through DOE’s National Renewable Energy Laboratory (NREL). 

NREL is the field manager for DOE’s Alternate Fuels Utilization R&D Program. NREL 

submitted a request for proposal number RCI-2-32027 for “Natural Gas Engine Development” 

in early 2002. The scope of this project was to develop natural gas engines that would be 

certifiable to emission levels below the 2004 federal standards (2.5 g/bhp-hr NOx + NMHC) and 

to be commercially viable. NREL awarded a contract to John Deere to further develop the onhighway, heavy-duty 8.1L natural gas engine in July 2003. 

The project outlined multiple technical objectives divided into three specific core tasks: 

• Task 3.1 Completion of Laboratory Engine Development 

• Task 3.2 On-Road Prototype Engine Development in Vehicles 

• Task 3.3 Perform Federal Test Procedure Testing / Commercialize Engine. 

The technical objectives of the program were met or exceeded in the execution of these tasks as 

follows: 

1) The contract called for laboratory development of the engine, specifically ECU development 

of the proprietary John Deere FOCUS controller. The laboratory and field development and 

production release of the FOCUS controller was completed by John Deere prior to signing a 

contract with NREL. However, during the course of completing the NREL contract minor 

engine recalibration work was conducted. Additionally, Deere conducted work 

independently and in parallel to the NREL contract, to address field performance issues. 

The work resulted in the elimination of several recurring nuisance fault codes as well as one 

significant system control strategy fault that caused engine down time. All of the work 

conducted during this phase enhanced the commercial viability of the engine and readied it 

for field and deterioration factor (DF) testing. 

2) The focus of the field test related to Task 3.2 was in the nation’s capital, Washington, D.C., 

within the Washington Metro Area Transit Authority (WMATA) fleet. A total of five New 

Flyer model CF-40 buses were repowered with John Deere 280 hp, 8.1L CNG engines 

(6081HFN04 model) as part of a marketing demonstration in December 2002 by Bell 

Power, a John Deere engine distributor. These vehicles went into service in March 2003 for 

field evaluation at WMATA. All five buses were used in day-to-day operation within the 

fleet and had satisfactory performance. One of the buses (bus 2460) was selected in April 

2004 for the Task 3.2 field program. The six-month duration test monitored and recorded 

engine performance, maintenance, fuel consumption, and mileage. 

1
Table 1-1. Summary of Bus 2460 Fuel Economy during Field Test 

 Miles Fuel (gal) Average Fuel Economy (mpg, DGE)

Overall 14546 6200 2.35

(For details, see Table 3-8 and Appendix B) 

3) The technical requirements of the proposal called for the achievement of emission levels 

below the 2004 federal standards of 2.5 g/bhp-hr for nitrogen oxide (NOx) + non-methane 

hydrocarbon (NMHC), and meeting the optional California Air Resources Board low 

emission levels of 1.8 g/bhp-hr for NOx+NMHC. Due to independent engine development 

that Deere pursued prior to signing a contract with NREL, the 1.8 gram target was achieved 

prior to the start of the program. It was therefore decided to lower the target to 1.2 g/bhp-hr 

for NOx+NMHC, which was successfully achieved with new DFs. The 1125 hour DF test 

was run from April to October 2004, and the test resulted in new, lower DFs for the 8.1L, 

which are listed below:

Table 1-2. New Deterioration Factors Achieved 

 MHD DF UB / HHD DF 

NOx 1.00 1.00 

PM 1.00 1.01 

CO 2.28 4.13 

NMHC 1.77 2.87 

In addition to the new DFs, the project also generated new certification results from testing that 

was completed in February 2005. The new certification results, along with the newly achieved 

DFs, allowed all of the John Deere 6081HFN04 model engine ratings to be certified at the 1.2 

gram NOx+NMHC target starting in October 2005. For the period of October through 

December 2005, a customer will be able to purchase engines at 1.2 gram, 1.5 gram, or 1.8 gram 

certification levels. Beginning in January 2006, Deere will only offer the 1.2 gram certification 

option, at which point, the Deere 8.1L will offer the lowest certification available in the CNG 

engine market, for the 250 and 280 hp ratings. Certification emission test results are listed in 

Table 1-3. 

2
Table 1-3. Summary of Certification Testing Results 

Certification Testing Results for 250 hp 

 NOx PM CO NMHC 

Composite: 0.874 0.003 0.026 0.059 

DF factors applied: 

NOx+NMHC = (.874*1)+(.059*1.77)=0.978 0.978 

PM = (.003*1.00) = .003 0.003 

CO = (.026*2.28) = .059 0.059 

Certification Testing Results for 280 hp 

 NOx PM CO NMHC 

Composite: 1.033 0.004 0.120 0.046 

DF factors applied: 

NOx+NMHC = (1.033*1)+(.046*2.87)=1.165 1.165 

PM = (.004*1.01) = .004 0.004 

CO = (.120*4.13) = .496 0.496 

3
2.0 Introduction 

The U.S. Department of Energy’s (DOE) FreedomCAR and Vehicle Technologies 

Program is advancing the development of gaseous-fueled internal combustion engines, 

which have the potential to reduce U.S. dependence on imported petroleum and improve 

air quality. Natural gas is a predominantly domestic energy source that can be used for 

transportation. With rising fuel prices, many companies are seeking alternatives to 

imported oil to help offset fuel costs. However, only a small portion of vehicles are 

powered by natural gas and mainly operated by local state municipalities. DOE’s 

National Renewable Energy Laboratory (NREL), led by the Center for Transportation 

Technologies and Systems (CTTS), has the goal to help industry introduce alternative 

fueled vehicles into the marketplace by working with public and private organizations to 

develop and demonstrate innovative technologies to help reduce the nation’s dependence 

on imported oil.

NREL submitted a request for proposal number RCI-2-32027 for “Natural Gas Engine 

Development” in 2002. The scope of this project was to develop on highway natural gas 

engines that would certify to emission levels below the 2004 federal standards [2.5 g/bhphr nitrogen oxide (NOx) + non-methane hydrocarbon (NMHC)] and to be commercially 

viable by meeting the optional California Air Resources Board (CARB) specification (1.8 

g/bhp-hr NOx + NMHC). 

2.1 Project Objective 

As a result of John Deere’s response to a competitive solicitation, NREL awarded a 

contract to John Deere to further develop the 8.1L on-highway, heavy-duty natural gas 

engine. At that time, the 8.1L engine was rated at 250 hp and 280 hp and was certified to 

the 2.5 g/bhp-hr standard. 

The project outlined three specific core objectives: 

• Task 3.1 Completion of Laboratory Engine Development 

• Task 3.2 On-Road Prototype Engine Development in Vehicles 

• Task 3.3 Perform Federal Test Procedure (FTP) Testing / Commercialize Engine. 

2.2 Project Participants 

From the onset, there were several subcontractors identified by John Deere as partners in 

achieving the project objective. These subcontractors were to be involved in the 

following portions of the project: 

• Both Task 3.1 and Task 3.3 were to be completed with the assistance of Electronic 

Microsystems (EMS) of Boerne, Texas, and Southwest Research Institute (SwRI) of 

San Antonio, Texas. EMS employees were to complete engine development on-site 

at the SwRI facility. This relationship was a natural one as the staff at EMS had been 

4
formerly employed by SWRI and had heavy involvement in past development of the 

John Deere compressed natural gas (CNG) engine. This subcontractor structure 

remained intact throughout the entire project. 

• Task 3.2 was to be completed with the assistance of ECOTRANS of Los Angeles, 

California, which had specialized for many years in the retrofit and repower of heavy 

duty vehicles with both liquefied natural gas (LNG) and CNG engines. Due to the 

bankruptcy of ECOTRANS, prior to the beginning of the project, changes were 

required. Task 3.2 was configured to consist of one bus with a test duration of six 

months. The support of the test was supplied by Deere employees. This change in 

task responsibility from an outside contractor to John Deere is noteworthy as it 

translated into a slight delay of the signing of the contract with NREL in the summer 

of 2003. 

In July 2003, Deere and NREL reached agreement and approved a Statement of Work for 

RFP No. RCI-2-32027. 

2.3 Project Design 

The project design was modified from the original agreement, not related to the project 

objectives, but rather with the order of completion and financial support related to the 

specific objectives. Initially, the project outlined a progression of Tasks 3.1 through 3.3 

from engine design and development in the lab (Task 3.1), followed by field test of the 

new engine (Task 3.2), and concluding with additional laboratory work for emission 

work (Task 3.3). As previously mentioned, the delay in achieving contract agreement 

with NREL forced Deere to move ahead with engine development activities. These 

activities were required commercially to meet the CARB optional 1.8 gram standard and 

to provide field support for the engines already produced. 

Briefly, in July 2003 production customers began experiencing a significant number of 

universal exhaust gas oxygen (UEGO) sensor failures, several repetitive instances of 

minor nuisance electronic error fault codes being displayed, and two front drive belt 

failures. Deere determined these issues had to be addressed before work on the NREL 

proposal could begin. An intense investigation was launched to determine root cause of 

each problem and to implement corrective action. This culminated in a new production 

software release in December 2003 that addressed the five separate control problems 

identified. Of these five problems, three were classified within the nuisance category, but 

the remaining two problems– new UEGO sensor faults and the Knock Module sensor 

faults – were considered significant. 

In fact, both problems required additional control system development through spring of 

2004. The knock sensor control strategy required additional development work for 

developing the ability to discriminate between actual combustion knock and structurally 

transmitted vibration. The work resulted in additional software code changes designed to 

5
enable the sensor to ignore the spurious mechanical vibration signals and prevent 

transmission of false codes. These changes were validation tested on a 12-bus fleet in 

California with 100% success. 

The UEGO Sensor control strategy required two additional changes in March 2004 to 

prevent false sensor failure codes. The two changes were validated on a three-week test 

on the same 12-bus fleet in California with a 100% success rate during the test period. 

During this time period, the original software with the December 2004 control system 

changes ran on the Washington Metro Area Transit Authority (WMATA) buses without 

any UEGO-related fault codes. 

The final FOCUS controller operating code release was delayed until the Controls Group 

completed new base code to correct upstream throttle pressure fault codes and subsequent 

engine power derates. The results from both laboratory and field test were combined into 

the final production version of the software that was released in April 2004. 

In the completion of the engine problem resolution and software development just 

described, Deere absorbed the full cost of the work. The optional low NOx standard of 

1.8 gram was maintained for the 280 hp ratings of the John Deere engine, with the 250 hp 

ratings maintaining an emission output of 1.5 gram. 

Due to this problem resolution and software development, the overall project was delayed 

further as neither fleet evaluation (Task 3.2) nor laboratory Deterioration Factor (DF) 

testing (Task 3.3) could be started until the new control system software was available in 

April 2004. At that point, with new production software available, one of the five 

WMATA buses previously repowered with the Deere 6081HFN04 model was selected as 

the test bed for Task 3.2, field test. A. Hageman from John Deere Power Systems (JDPS) 

traveled to Washington, D.C., April 13-16, 2004 to install the updated software. New 

oxidation catalysts with higher precious metal loading required to meet the 1.8 gram 

NOx+NMHC standard were also installed. (Note: The five engines when installed in 

December 2002 were originally certified to the 2.0 gram NOx+NMHC level). 

Additionally, Deere participated in the NREL sponsored mobile chassis dynamometer 

emission testing of in-use engines conducted by the University of West Virginia. 

Engines tested included three 280hp Deere 8.1L Natural Gas engines configured to meet 

1.8g/bhp-hr NOx + NMHC and three competitive diesel and natural gas engines. Bus 

2460, which was one of the three buses used in chassis dynamometer tests, was identified 

for use in the field test (Task 3.2). It began accumulating hours on April 19, 2004, 

marking the start of a six-month tracking period through November 18, 2004. During 

this period, maintenance and other information was collected and recorded on a monthly 

basis for this bus/engine combination (See Section 3.2.2). 

Work on Task 3.3 also began in April 2004. Approval had been previously secured from 

the U.S. Environmental Protection Agency (EPA) for the final version of the 1125-hour 

6
Deterioration Factor test sequence plan. The test engine RG6081HFN228450, was built 

September 18, 2003 at the John Deere Engine Works in Waterloo, Iowa. It was rated at 

280 hp @ 2200 rpm and 900 lb-ft peak torque at 1500 rpm. The engine was shipped to 

the test facility at SwRI, prepared for testing, and installed in an engine dynamometer 

cell. The official hour accumulation began at the end of April 2004 when the new 

production release software became available. The engine DF test required 

approximately six months to accumulate the planned 1125 hours. Emission data were 

collected at 125 hours (baseline), 375 hours, 750 hours, and at 1125 hours. The data 

collected allowed curve fit lines to be plotted through the data points, projecting emission 

output at the useful life limits. DFs were then calculated from the actual and projected 

emission data. 

Application of the new DFs showed the 280-hp rating certification could be reduced from 

its current 1.8 gram level to the 1.5 gram level. However, it was not possible with the 

existing engine calibration to achieve a 1.2 gram certification for either the 250-hp or 

280-hp ratings. Given the incipient 2007 on-road regulation requiring the 1.2 gram 

certification, Deere petitioned NREL to use the remaining funding from Task 3.1, 

Laboratory Engine Development, to create a new engine calibration. (The work originally 

planned for Task 3.1 had been skipped because Deere had already achieved the original 

1.8 gram program goal). The goal of the new calibration work was to enable the 8.1L 

engine, with the new DF factors, to meet the 1.2 gram certification level in all three 

[Medium Heavy-Duty Diesel (MHDD), Heavy Heavy-Duty Diesel (HHDD), and Urban 

Bus (UB)] use categories. In addition to recalibration, Deere further proposed that a 

shortened and modified Task 3.2 field test be conducted. 

The Task 3.1 laboratory engine work was completed in February 2005, with small 

calibration changes made to fueling and spark timing to obtain the needed emission 

reduction. In order to validate the software changes, Deere outlined a three-phase test 

and evaluation program at Deere-owned and external test sites. The Deere test site work 

included Society of Automotive Engineers test cycles on a test track; simulated school 

bus/ transit bus operating cycle of multiple start/ stop sequences with idle time; and an 

extended, over-the-road, high speed operation. All of these operations were successful 

with no fault codes generated. In addition, two external test sites (a school bus fleet and a 

transit bus fleet) were identified. Both sites were provided with experimental software 

for three existing John Deere 1.8 gram engines, which were then evaluated for several 

weeks. Again, no fault codes were generated with the new software version. The 

external testing of the 1.2 gram software continued through the end of July 2005, at 

which time the work associated with the project ceased. 

The software changes used to achieve the reduction to 1.2 gram NOx + NMHC were 

released to the Deere production system in August 2005, concurrent with applications for 

the lower certification levels with both EPA and CARB. Production is scheduled for 

October 2005, after the emission certification approvals have been received. 

7
3.0 Task Specifications

As noted earlier, JDPS contracted with several organizations through the project, 

primarily EMS and SwRI. All of the engine development was completed at SwRI 

institute, under the direction of EMS. Deere personnel communicated on a daily basis 

with both subcontractors during testing and also worked with the subcontractors on-site 

and in the field, as required during lab and the field test. There were several engines used 

during testing: engine serial number RG6081H228450 was evaluated on the 1125 hour 

DF test; and engine serial numbers RG6081H224392 and RG6081H256433 were used 

during development in the dynamometer test cell (software changes to achieve the 1.2 

gram emission target). The five engines that were installed for field evaluation in 

WMATA transit buses are still in service at that site. 

3.1 Engine Design, Performance and Emissions (Task 3.1) 

The goal of the project was to attain HFN04 engine certification levels below the 2004 

EPA standards of 2.5 g/bhp-hr (NOx+NMHC), and also at or below the optional CARB 

low-NOx emission standard of 1.8 g/bhp-hr (NOx+NMHC). Due to commercial 

imperatives, Deere obtained (and funded) certification to the 1.5 gram and 1.8 gram 

levels in Summer 2003. Consequently, very little Task 3.1 activity took place at the start 

of the project, and the original funding was still available in late 2004, when Task 3.2 and 

Task 3.3 were completed. This led to the proposal by John Deere to complete additional 

laboratory engine development with the remaining funds to potentially allow certification 

at 1.2 g/bhp-hr (NOx+NMHC). 

The Deere 8.1L CNG engine was installed in a transient-capable development test cell in 

the Emissions Research Department at SwRI in February 2005. A gaseous fuel blend 

that conforms to EPA and CARB specifications (composition shown in Table 3-1) was 

used for testing. 

Table 3-1. Gas Composition for 280 hp Certification Testing 

Component Formula 

 Mole 

Fraction 

(%) 

Methane CH4 90.42 

Ethane C2H6 4.04 

Ethylene C2H4 0.14 

Propane C3H8 2.05 

Nitrogen N2 3.32 

8
Photos 3-1 and 3-2. John Deere 8.1L deterioration factor engine installed on 

laboratory dynamometer at SwRI 

The certification data was obtained in compliance with the rules for dynamometer testing 

of heavy-duty, compression-ignition engines, as outlined in 40 CFR part 86, subpart N. 

The compression-ignition engine test cycle was used, since the base engine is a diesel 

engine. 

3.1.1 Engine Specifications 

(For detailed engine technical and design specifications, refer to Appendix A). Prior to 

testing, target emission levels for certification were determined. In particular, 

certification data were required for two power ratings: the 280-hp, 900-lb-ft-rating and 

the 250-hp, 800-lb-ft rating, which would be used to create emission families. For each 

rating, a target NOx value was calculated and used as a guide during the calibration 

process. This target NOx value was provided by John Deere and was based on a 

statistical analysis of emission results from prior tests on similar engines. The statistical 

analysis took into account the variability in emissions on an engine-to-engine basis. The 

emission targets also used newly developed DFs for the various combustion by-products. 

Since this engine is equipped with a catalyst, multiplicative DFs are used. Table 1 

summarizes the DF values used. 

9
Table 3-2. Deterioration Factors

Rating DF Type NOx DF NMHC DF PM DF CO DF 

280 hp UB / HHD DF 1.00 2.87 1.01 4.13 

250 hp MHD DF 1.00 1.77 1.00 2.28 

At the start of testing, the performance of the engine was verified by running a power 

validation test. During this test, the engine was operated at rated power with the inlet 

restriction, aftercooler pressure drop, and aftercooler outlet temperature set to target 

application values. The exhaust restriction was not set independently, since it is 

controlled by the restriction of the catalyst. The target values for these settings are shown 

in Table 3-3. 

Table 3-3. Target Values for Power Validation Test Conditions 

Parameter Value 

Intake restriction 2 kPa 

Exhaust restriction 10 kPa 

Aftercooler outlet temperature 52 °C 

Aftercooler pressure drop 7 kPa 

The engine power at 2200 rpm rated speed was found to be 280 hp [209 kilowatts (kW)], 

so the engine was deemed to be operating correctly. A wide-open-throttle torque curve 

sweep was then conducted, and the measured data was subsequently used by the test cell 

control computer to generate speed and torque set points for the transient cycle. A trial 

emission cycle was run to verify the ability of the engine to properly track the test cycle. 

The engine ran well through the trial cycle with good performance verified by the highregression coefficients produced by the cycle matching statistics. In particular, the torque 

correlation coefficient was 0.956, which is similar to that obtained with typical diesel 

engines. 

Since calibration modifications primarily affect NOx, the NOx output of the engine was 

used to control the overall NOx + NMHC level, and the catalyst was relied upon to 

eliminate as much NMHC as possible. The NOx measured during the trial test was higher 

than desired, so modifications were made to the engine calibration in an attempt to reduce 

NOx. These changes concentrated on the equivalence ratio and spark timing set-point 

tables. In general, a slightly leaner equivalence ratio was adopted over a large part of the 

engine map, and spark timing retard was also used in various regions. Some slight 

changes were made to the volumetric efficiency table used to estimate open loop fueling, 

and the maximum fuel table was modified accordingly to maintain the proper torque 

curve after the other calibration changes were made. 

The changes made were incremental based on test results, and analysis of the test cell 

data acquisition logs and data logs of relevant parameters from the engine controller. 

This process resulted in an engine calibration that produced a repeatable NOx and total 

hydrocarbon level that was expected to meet the targets set by John Deere. The final 

calibration had changes that were considered to be relatively minor from a driveability 

standpoint, and this view was confirmed by the good cycle-tracking performance seen 

10
during the trial cycles. A copy of this modified calibration information was compiled in a 

format compatible with the FOCUS controller and supplied electronically to John Deere. 

The results shown in the next section are with this modified calibration. 

The discussion in this section is all related to CNG fuel. Previous gas development 

experience has shown LNG calibrations can be directly derived from the engine CNG 

calibration. The only changes necessary are to customize the engine control software to 

provide the correct fuel delivery levels with the LNG fuel system hardware. Therefore, 

all development work in this project was conducted on CNG fuel, but is also applicable 

for the LNG models. 

3.1.2 Torque and Power Curves 

The certification data presented in this section are composite cold-start/hot-start results 

unless otherwise noted. Certification data were obtained after all calibration and engine 

changes had been made and trial cycles were run to verify the engine’s performance and 

emissions. Upon satisfactory completion of these cycles, the engine was shut down in 

preparation for a cold-start/hot-start sequence. The cold start was conducted on the 

following morning to ensure the engine was fully cooled to ambient conditions, followed 

by two hot starts. The second hot start was used to confirm repeatability of the first hot 

start. A 20-minute soak period with the engine shut down occurred between tests. The 

composite emission numbers were calculated from the cold start cycle data and the first 

hot start cycle data, using a weighted sum of the results for the two cycles (1/7 for the 

cold data, and 6/7 for the first hot-start data). In all cases, the data from the second hot 

start was found to repeat well with the first hot-start data, thereby verifying the 

repeatability of the engine. The following sections contain certification data for the 280-

hp/900-lb-ft rating and the 250-hp/800-lb-ft rating, respectively. 

280-hp/900-lb-ft CNG Rating 

A power validation test and a torque map were conducted with certification fuel using the 

280-hp/900-lb-ft rating. The power validation test confirmed this power rating. The 

engine full-load torque curve was then mapped, and the resulting torque curve is shown 

in Figure 3-1. 

11
Measured Torque Curve 

280 hp / 900 lb-ft Rating

0

100

200

300

400

500

600

700

800

900

1000

600 800 1000 1200 1400 1600 1800 2000 2200 2400

Engine Speed (rpm)

Torque (ft-lbs)

Figure 3-1. Torque curve for 280 hp-900 lb-ft rating 

Following the torque map generation testing, a preparation cycle was run to verify that 

the engine NOx emissions were in the correct range. The engine ran well through the 

preparation cycle, and it was shut down in preparation for a cold start and two hot starts 

the next day. The subsequent cold start test was invalidated by a fuel delivery problem 

with the gas trailer. The two hot starts were run, however, to help provide additional 

engine performance repeatability data. 

The subsequent cold-start and two hot-start tests were completed the next day. Emission 

results for these tests, which constitute the certification data for the 280-hp/900-lb-ft 

rating, are shown in Figure 3-2. Note that all of the composite emission numbers are well 

below the standards. Figure 3-3 shows a comparison between the certification test 

results and the standard (1.2 gram NOx+NMHC, and 0.01 gram PM). Note that the PM 

values in Figure 3-3 are multiplied by 100 to maintain a consistent y-axis and clarity in 

this plot. Also note that the carbon monoxide (CO) emissions were not included in 

Figure 3-3. CO emissions, even with the DF applied, are less than 4% of the standard 

and are of no concern for meeting the certification. The baseline NOx + NMHC level of 

1.079 is significantly lower than the CARB standard of 1.2 g/bhp-hr, but increases to 

1.165 when the DF factor is applied. This value is still well below both the EPA and the 

CARB standard. In the case of particulate matter (PM) with a DF of 1.01, the 

deteriorated value is essentially the same as the baseline result of 0.004 gram, well below 

the 0.01 gram standard. 

12
Composite FTP Emissions Results 

280 hp-900 lb-ft rating

1.033

0.046 0.004 0.120

0.000

0.200

0.400

0.600

0.800

1.000

1.200

NOx NMHC PM CO

Brake Specific Emissions

 (g/bhp-hr)

Figure 3-2. Summary of emission results for 280 hp rating 

Test Results vs. Certification Standards 

280 hp-900 lb-ft Rating

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Brake Specific Emissions 

(g/bhp-hr)

Standard

Results w/ DF

Baseline Results

Standard 1.200 1.000

Results w/ DF 1.165 0.400

Baseline Results 1.079 0.400

NOx+NMHC PM (x100)

Figure 3-3. Comparison of emission results versus targets for 280 hp rating 

13
250-hp/800-lb-ft CNG Rating 

Prior to certification testing of the 250-hp rating, additional fuel was required so a new 

fuel batch was blended. The composition of this fuel is shown in Table 3-4. This fuel 

was used for running the 250 hp validation and torque map as well as all of the 

certification test runs. 

Table 3-4. Gas Composition for 250 hp Certification Testing 

Component Formula 

 Mole 

Fraction 

(%) 

Methane CH4 90.33

Ethane C2H6 4.13

Ethylene C2H4 0.13

Propane C3H8 2.03

Nitrogen N2 3.37

To obtain data for the 250-hp certification, the ECU calibration tables were updated with 

the setting values for the 250-hp/800-lb-ft rating. The engine’s performance was verified 

by conducting a new power validation and torque map. The power validation data test 

confirmed the proper power and peak torque levels, and a torque map was generated. A 

plot of the torque curve generated at the 250-hp/800-lb-ft rating is shown in Figure 3-4. 

Measured Torque Curve 

250 hp / 800 lb-ft Rating

0

100

200

300

400

500

600

700

800

900

1000

600 800 1000 1200 1400 1600 1800 2000 2200 2400

Engine Speed (rpm)

Torque (ft-lbs)

Figure 3-4. Torque curve for 250 hp – 800 lb-ft rating 

14
Test Results vs. Certification Standards 

250 hp-800 lb-ft Rating

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Brake Specific Emissions 

(g/bhp-hr)

Standard

Results w/ DF

Raw Results

Standard 1.200 1.000

Results w/ DF 0.978 0.300

Raw Results 0.933 0.300

NOx+NMHC PM (X100)

The feed forward throttle map and test cell controller gains used with the 280-hp testing 

were reused for these tests due to the similarity of the ratings. The emission results for 

the 250-hp/800-lb-ft rating are shown in Figure 3-5. The results for these tests were quite 

good, with NOx emissions significantly lower than those obtained with the 280-hp, 900-

lb-ft rating. The other emissions were slightly lower but similar to the 280-hp rating. 

Figure 3-6 below illustrates that the baseline emissions of NOx+NMHC and also PM for 

the 250-hp rating were significantly below the CARB standards. (Again, please note that 

the PM values are shown multiplied by 100 to maintain consistent graph scaling). 

Composite FTP Emissions Results 

(250 hp- 800 lb-ft rating)

0.874

0.059 0.003 0.026

0.0

0.2

0.4

0.6

0.8

1.0

1.2

NOx NMHC PM CO

Brake Specific Emissions 

(g/bhp-hr)

Figure 3-5. Summary of emission results for 250 hp rating 

Figure 3-6. Comparison of emission results versus targets for 250 hp rating 

15
The maximum torque curve for each family (280-hp/900-lb-ft and 250-hp/800-lb-ft) was 

formulated during the emission certification process. It was now necessary to develop 

the alternative ratings in each family, namely the 275-hp/800-lb-ft and the 250-hp/735-lbft ratings. The calibration work that is listed next was related to the development of two 

additional ratings. The calibration process consisted of verifying the performance of the 

engine with the two existing calibrations and then modifying the appropriate fuel control 

table to produce a modified torque curve. 

The additional calibration work was conducted on a John Deere 8.1L natural gas engine, 

serial number RG6081H256433. The engine was mounted to an absorbing dynamometer 

in a steady-state test cell at SwRI. The test cell was equipped to measure speed, torque, 

and fuel flow; and the engine had a limited amount of pressure and temperature 

instrumentation installed on it. The engine was operated on pipeline natural gas and a 

conditioned air supply was used to maintain a nominal inlet air temperature of 25°C with 

a nominal dew-point temperature of 15°C. 

Prior to testing, the engine controller was reprogrammed with the newly developed low 

NOx calibration for the 280-hp/900-lb-ft rating. This particular calibration had been 

developed in the transient test cell during the certification process and represented the 

latest calibration for the maximum engine rating available. Test preparations consisted of 

warming the engine to operating temperature and setting exhaust back pressure at rated 

power. The performance of the engine at the 280-hp/900-lb-ft rating was verified by 

collecting full-load data at 100 rpm intervals from 2200 rpm to 800 rpm. After successful 

completion of these test runs, the low NOx calibration for the 250-hp/800-lb-ft rating was 

loaded, and the torque curve for this rating was also measured. The data obtained from 

these torque curves was found to be comparable to the torque curve data produced in the 

transient emissions test cell on the certification test engine, thereby verifying the 

performance of this engine. 

To produce the new torque curves, the 280-hp/900-lb-ft was used as the base calibration 

and changes were made to the fuel limiting table that governs the maximum fuel flow for 

a given speed. Iterative changes to the fueling amount were made in order to achieve 

torque levels similar to those of current engine ratings (torque curve data was supplied by 

John Deere to EMS for reference). When the match between the test data and the 

reference torque data were satisfactory, a full torque curve data set was collected. This 

procedure was conducted for the 275-hp/800-lb-ft rating and repeated for the 250-hp/735-

lb-ft rating. The resulting torque curve data for all four engine ratings is plotted in Figure 

3-7. 

16
Torque Curve Comparison

John Deere 8.1L CNG Engine with Low NOx Calibration

0

100

200

300

400

500

600

700

800

900

1000

600 800 1000 1200 1400 1600 1800 2000 2200 2400

Engine Speed (rpm)

Torque (ft-lbs)

280 hp - 900 lb-ft

250 hp - 800 lb-ft

275 hp - 800 lb-ft

250 hp - 735 lb-ft

Figure 3-7. Torque Curve Comparison 

The fuel table calibration changes were exported and used to prepare new parameter 

pages to communicate these changes to John Deere. The files were then used by John 

Deere to build new production software. 

 

In summary, transient emission testing confirmed the HFN04 engine platform can 

achieve the 1.2 g/bhp-hr combined NOx + NMHC standard at the 280-hp/900-lb-ft and 

250-hp/800-lb-ft family ratings. Calibration changes and the use of the 69X60449 

oxidation catalyst were required for the engine to achieve these ratings. In the 250-hp 

and 280-hp configurations, the engine NOx + NMHC emissions were below the CARB 

standards. PM emissions were significantly below the standard. Fuel economy for the 

1.2 gram calibration, as measured during the FTP test cycle, showed a small 

(approximately 2%) loss compared to the previous 1.8 gram calibration. 

17
Table 3-5. Certification Results

The required Cold/Hot/Hot 

FTP cycle sequences were 

run, which confirmed the 

calibration changes were 

successful in reducing the 

emission output. The results 

table indicates the baseline 

emission results from this 

testing, and also depicts the 

useful life output by 

applying the appropriate 

multiplicative DFs to each of 

the baseline constituent 

results. 

As evident in the results 

table, the calibration changes 

for both power ratings were 

successful in meeting the 

targeted level of 1.2 g/bhp-hr 

for NOx+NMHC. The 250-hp rating output at useful life is .978 g/bhp-hr for 

NOx+NMHC, and the 280-hp rating output at useful life is 1.165 g/bhp-hr for 

NOx+NMHC. The PM and CO results at both power ratings were well below the limits 

of .01 g/bhp-hr and 15.5 g/bhp-hr. 

With confirmation that no further calibration changes were necessary, the engine was 

removed from the test lab. Both the certification engine and DF engine were returned to 

John Deere for storage. 

Table 3-6. Certification Test Hardware 

Certification Testing Results for 250 hp rating: 

 NOx PM CO NMHC 

Cold Start: 0.824 0.005 0.070 0.061 

Hot Start: 0.883 0.003 0.018 0.059 

Hot Start: 0.909 0.004 0.007 0.045 

Composite: 0.874 0.003 0.026 0.059 

DFs applied: 

NOx+NMHC = (.874*1)+(.059*1.77)=0.978 

PM = (.003*1.00) = .003 

CO = (.026*2.28) = .059 

Certification Testing Results for 280 hp rating: 

 NOx PM CO NMHC 

Cold Start: 0.946 0.004 0.158 0.060 

Hot Start: 1.048 0.004 0.114 0.044 

Hot Start: 1.031 0.004 0.099 0.044 

Composite: 1.033 0.004 0.120 0.046 

DFs applied: 

NOx+NMHC = (1.033*1)+(.046*2.87)=1.165 

PM = (.004*1.01) = .004 

CO = (.120*4.13) = .496 

Component 

Description 

Part 

Number 

Serial 

Number 

Engine n/a RG6081H224392 

ECU RE520420 100201 

UEGO Sensor RE519691 1817 

Humidity Sensor RE508476 FR-A146 

Catalyst Muffler 69X60449 SwRI 11-29-04 

18
3.1.3 Vehicle/Fleet Description 

See Appendix A for Fleet Vehicle Specification Form. 

3.1.4 Duty Cycle Description 

Actual vehicle testing has shown an average speed of 33 mph (100,000 miles in 3000 

hours of driving) and an average load factor (actual fuel usage divided by fuel usage at 

rated power) of 28%. The required cycle set-up for the DF test has a load factor of 84%—

a factor of 3.0 times the typical customer load factor of 28%. 

Table 3-7. John Deere 6081 NG Engine Deterioration Factor Test Cycle 

2400 

198 NM 

2200 49.7 kW

770 NM

177 kW

Speed 650 

Torque 0 NM 

Power 0 kW 

Slow Full Load Fast 

Idle Rated Speed Idle 

STEP 1 2 3 

Step Duration 

(minutes) Condition 

1 0.5 NO LOAD SLOW IDLE – 650 RPM 

2 29 85% LOAD RATED SPEED - 2200 RPM 

3 0.5 50% LOAD OVERSPEED - 2400 RPM 

* Note: Small adjustments in the cycle may be necessary to achieve the target load factor of 84%

3.2 On-Road Engine Development (Task 3.2) 

As previously mentioned, the field test was completed at the nation’s capital, 

Washington, D.C. within a large transit fleet, WMATA. A total of five New Flyer buses 

were repowered with John Deere 280 hp, 8.1L CNG engines (6081HFN04 model) in 

December 2002 by Bell Power, a John Deere engine distributor. These vehicles went 

19
into service in March 2003 for field evaluation at WMATA. All five buses were used in 

day-to-day operation within the fleet, and had satisfactory performance. 

Photos 3-3 and 3-4. Views of John Deere 8.1 L engine installed in New Flyer Bus 

Photo 3-5. View of WMATA buses

20
3.2.1 Description of Development Work

The only development work associated with Task 3.2 was loading the 1.8 gram software, 

changing the catalyst, and then a relatively short test drive before putting the bus back 

into service. 

3.2.2 Fuel Economy and Mileage Accumulation 

One of the five buses (bus 2460) was selected for evaluation over a six-month period, 

spanning from April 19 to October 18, 2004, during which engine performance was 

monitored and fuel consumption and mileage were recorded. The bus operated 

successfully in normal daily service at WMATA over the six-month period, accumulating 

14,546 miles without any engine related problems. A summary of the monthly test 

reports is shown below. Details of the daily test log are listed in Appendix B. 

Table 3-8. Field Test Data 

Summary of data 

 Miles Gals Fuel Average Monthly Fuel Economy(mpg, DGE)

April 1212 422 2.87

May 3758 1554 2.42

June 2328 1007 2.31

July 2137 955 2.24

August 2136 865 2.47

September 1302 712 1.83

October 1673 685 2.44

Overall 14546 6200 2.35

3.2.3 Future Plans for the Engine Model 

Given that the project timeline more than doubled for the various reasons already 

discussed, most of the originally conceived “future plans” have already been 

accomplished. The plans for commercialization of the 6081HFN04 engine at reduced 

emissions level have already occurred with the release of the 1.5 gram /1.8 gram 

software, which was completed in September 2003. Engines have been successfully 

installed into multiple applications since that time including school buses, industrial 

trucks, and transit buses with multiple OEM customers. The initial introduction of the 

John Deere engine into the New Flyer chassis (repower) during the field demonstration 

led to a production build of New Flyer buses powered by John Deere CNG engines in 

Spring 2005. Additional builds with New Flyer are scheduled for Fall 2005, and a large 

build is scheduled with Orion for 100 WMATA buses during late 2005 into 2006. 

Depending on contract details and engine order dates, the 1.2 gram software could be 

programmed in engines for either of the two customers just mentioned. Beginning in 

2006, all John Deere CNG engines will be built with the 1.2 gram software, available in 

either CNG or LNG versions. 

21
3.3 FTP Results (Task 3.3) 

The John Deere 6081HFN04 engine model is offered with 3 power levels: 250 hp, 275 

hp, and 280 hp. The engine is certified at 250 hp for the medium heavy-duty class with a 

useful life of 185,000 miles at 275 hp; and 280 hp for the heavy heavy-duty class with a 

useful life of 435,000 miles at 250 hp, 275 hp, and 280 hp for the urban bus duty class 

with a useful life of 435,000 miles. The DF test was completed at the 280 hp rating, and 

it was intended to achieve lower DFs for all three engine classifications. 

A DF test, consisting of overall hour accumulation of 1125 hours was completed, with 

emission testing at 125 hours, 375 hours, 750 hours, and 1125 hours. The 1125 hours of 

dynamometer testing on the DF test cycle corresponds to 3375 hours of actual operation, 

which equates to 111,375 miles in a vehicle application. The data from the DF test is 

then extrapolated, as necessary, to obtain additive and multiplicative DFs at 185,000 and 

435,000 miles. The DF test was run from April to October 2004. 

DFs were calculated by plotting hot test data for each of the exhaust constituents of NOx, 

PM, CO, and NMHC. Initially (at 125 hours and 250 hours) six sets of data for each of 

the constituents were plotted. However, due to variability (instrumentation repeatability) 

in measuring the very low levels of PM, starting at 750 hours, the test plan was modified 

with CARB approval to take 18 data points at 750 hours and 1125 hours. The 18 data 

points were then reduced to six by averaging the six sets of three data points. 

Once data points have been plotted for the emission results from 125, 375, 750, and 1125 

hours, a curve fit line was established through the data points. A data outlier test was 

conducted to ensure that none of the data points were excessively deviant of the overall 

plot pattern. Using the curve fit line’s equation, the engine emission results were 

projected out to the appropriate useful lives for the respective engine classifications 

(again 185,000 miles for MHD classification, and 435,000 miles for HHD and UB 

classifications). The results of the DF test were new lower, DFs for each of the exhaust 

constituents; the newly obtained DFs are listed below: 

Table 3-9. Deterioration Factors 

 Slope Offset MHD DF UB / HHD DF 

NOx -0.0003 1.8351 1.00 1.00 

PM 0.0000 0.0090 1.00 1.01 

CO 0.0000 0.0097 2.28 4.13 

NMHC 0.0000 0.0409 1.77 2.87 

3.3.1 Commercial Engine Ratings 

The 6081HFN04 model engine has three power ratings of 250 hp, 275 hp, and 280 hp; 

there are also three different peak torque levels of 735 lb-ft, 800 lb-ft, and 900 lb-ft. The 

specific ratings and their appropriate engine classifications are listed in Table 3-10: 

22
Table 3-10. 6081HFN04 Engine Ratings 

Rated Power / Peak 

Torque Specifics 

250 hp - 735 lb-ft 250 hp 735 lb-ft, MHD rating and UB rating 

250 hp – 800 lb-ft 250 hp 800 lb-ft, MHD rating 

275 hp – 800 lb-ft 275 hp 800 lb-ft, HHD rating 

280 hp – 900 lb-ft 280 hp 900 lb-ft, HHD rating and UB 

3.3.2 Commercial Engine Efficiency Map 

Figure 3-8 John Deere 8.1 Engine Efficiency Map 

23
3.3.3 Narrative Description of Test Results

April 2004 

The DF test officially started April 29, when the engine setup was complete and hour 

accumulation began. The engine, serial number 6081HFN228450, was programmed at 

the 280 hp / 900 ft-lb rating. During the month of April, the engine accumulated 20 

hours. 

 

May 2004 

The DF test accumulated hours during May in preparation for the baseline emission test 

sequence after 125 hours. During the break-in test, the steady-state engine emissions 

were checked every 10 hours to document the emissions break-in characteristics of the 

engine and the oxidation catalyst. On May 10 at 70 engine hours, the engine suffered a 

spark plug failure in cylinder No. 6. Permission was received from EPA/CARB to 

replace the spark plug and the test continued. On May 24, the engine again developed a 

misfire in No. 6 cylinder. Again, the plug was replaced. However, as part of the 

continuing investigation, it was found that damage to the No. 6 spark plug wire was 

actually root cause of the failure, allowing arcing that caused the apparent misfiring of 

the spark plug. (Detailed investigation showed that when the spark plugs were installed 

at SwRI prior to the start of test, the di-electric grease specified for boot assembly was 

omitted, leading to the spark plug wire boot being damaged.) The engine reached the 125 

hour break-in point on May 25 and was removed from the development cell in 

preparation for baseline emission tests. 

June 2004 

Due to SwRI’s schedule at the time being very busy, the actual baseline test wasn’t run 

until June 11. The DF test engine ran the 125-hour, break-in point baseline test from 

June 11 – 15 and was then put back on the life test portion of the test. By June 30, the 

engine accumulated a total of 283 hours with no problems. 

July 2004 

The DF test engine continued to accumulate hours at SwRI during July without problems. 

The engine began the month at 283 hours and ended the month at 557 hours, for a 

monthly accumulation of 274 hours. The engine was ready for the 350-hour emission 

test on July 13, but again due to workloads at SwRI, the test wasn’t started until July 19. 

The engine was put back on the DF test starting July 23. At the 350-hour point, the 

engine emissions (NOx, NMHC, PM, and CO) had remained the same as at the 125-hour 

baseline test or actually slightly declined. 

August 2004 

The DF test engine continued to accumulate hours at SwRI during the initial portion of 

August without problems. The engine began the month at 557 hours and reached the next 

emissions checkpoint of 750 hours on August 9. Again, due to workloads at SwRI, the 

24
emission test wasn’t conducted until August 17. At the 750-hour point, the engine 

emissions (NOx, NMHC, and CO) had remained roughly the same as at the 375-hour 

point or actually slightly declined. A very slight trend of increased PM caused concern, 

as it would calculate a DF factor >1. Due to this concern an engine analysis and 

inspection program of the DF engine was executed. It included: 

• Visual inspection of valve guide seals for damage 

• Visual inspection (borescope) of the power cylinders, including the valve face and 

tulip areas for deposits 

• Visual inspection of spark plugs for deposits 

• Twelve additional hot FTP tests, six per day, were run. The tests were conducted on 

a Friday and Tuesday purposely to provide a 72 hour separation between the test 

events to allow check for test stability, or “drift.” 

• Elemental analysis of the PM matter collected during the 12 additional FTP tests. 

The apparent cause of the increase in the PM measurements between 375 hours and 750 

hours is in test stability or drift. This is proven by the results of the three sets of FTPs 

conducted at 750 hours: 

 PM Average

 Test 1 .011 gram 

 Test 2 .0083 gram 

 Test 3 .0085 gram 

This shows the average =.0093 gram under the same test conditions on different days, so 

the PM test stability is not zero. In fact, there is “drift” in the results, and all of the tests 

are equally valid. Considerable effort was expended to identify the cause of the PM 

increase, including engine mechanical inspection; emission measurement equipment 

calibration and validation by SwRI; and engine performance validation. There were no 

conditions or changes found that could have caused the increase observed. 

Based on previous experience by both Deere and SwRI, the leading suspect became 

stability (or drift) of the PM measurements during the hot FTP tests. This means that 

minor changes in test conditions, while remaining within specification, can cause changes 

in the amount of PM measured. Because the CARB 0.01 gram PM spec the engine is 

attempting to meet is so low, even very minor measurement variation can cause a 

significant upturn in the slope of the regression line of the measurements. This in turn 

can, when extrapolated out to the 435,000 mile HHDD/Urban Bus useful life point, cause 

the engine to not meet the 0.01 gram spec. 

This information was submitted to and discussed with CARB with a request to continue 

the DF test and use the grand average of all the FTP PM results for use in calculating the 

DF factor; the request was approved. 

25
September 2004 

The PM measurement problem investigation started in August and continued through 

September. 

October 2004 

CARB, after a considerable length of time, agreed on October 8 with the Deere request to 

run two additional FTP tests at 750 hours and 1125 hours, and average the results for PM. 

The DF engine was put back into the dyno to resume hour accumulation on October 11. 

Upon restart, the engine wasn’t able to run the durability cycle without a noticeable 

misfire; it was necessary to change out spark plugs and wires due to damage incurred on 

the ignition components at the last transient emission test point. The engine also had 

ignition components serviced on October 20 (No. 6 spark plug and wire) and October 27 

(#2 spark plug and wire). In both cases, misfire was noticed by lack of engine power. 

Subsequent diagnostic work identified a specific cylinder miss in both cases, and service 

work was completed. The engine reached 1125 hours on October 31 and was shutdown, 

and required maintenance was completed. The ignition component service was approved 

by CARB. 

November 2004 

The engine underwent the 1125 hour emission testing from November 15-17. As was 

discussed previously, the extra data collected included 18 data points from hot FTP 

cycles, and then the 18 points were averaged in sets of three down to 6 data points. 

Following completion of the last emission data collection for the DF, the 1125 hour data 

was plotted along with data collected at 125, 375, and 750 hours and a curve fit line was 

established through the data points. The final curve fit lines were then evaluated to 

obtain the slope of each line. In turn the calculations were carried out to project emission 

levels at the useful life for both medium heavy-duty (185,000 miles) and heavy heavyduty (435,000) ratings. 

The DFs calculated were an improvement to the previous DFs, with the improved 

software control strategy utilized on the HFN04 model engine and improved engine oil 

control as the main contributors. 

December 2004 

Initial calculations were made with the new DFs and the certification results from 

Summer 2003 (1.5 gram/ 1.8 gram software) to determine if the new DFs would allow 

certification down to 1.2 g/ bhp-hr for NOx +NMHC. These calculations showed that 

although emission levels with the new DFs were very close to the 1.2 gram target, they 

were not under the target. It was therefore planned to go back onto the engine 

development dynamometer to make base engine calibration adjustments. 

January 2005 

No engine lab development was completed due to lack of test cell availability at SwRI 

during this month. Emission targets to achieve the 1.2 gram target, with satisfactory 

26
margin were set and provided to EMS in preparation for upcoming engine calibration 

work. 

February 2005 

The development engine, RG6081H224392, was installed in the test cell, and engine 

testing was completed. New calibrations (slight changes in spark timing and fueling) 

were established. 

March 2005 

The calibration changes were evaluated in the lab for each of the four power ratings for 

the 6081HFN04 model engine. This lab work confirmed that power output was 

unaffected by changes, and yielded power output at the specified levels. 

The calibration changes were then compiled into experimental software. This software 

was then loaded into a test vehicle on-site at the John Deere Product Engineering Center 

(PEC), and the test vehicle was evaluated on multiple cycles. These cycles included short 

internal test track and external routes around the PEC site, extended stop-start sequences, 

and a long distance route. The experimental software performance was satisfactory, so 

the experimental software was made available for external evaluation. 

April 2005 

Experimental software was provided to the first test site, Poway Unified School district in 

Poway, California. This test site is a school district with multiple CNG-powered buses. 

Six engines were identified to be programmed with the experimental 1.2 gram software. 

These engines were programmed on April 25-26. The engines performed well with the 

software, and no fault codes were generated due to the software. 

May 2005 

A trip was taken from May 23-26 to the second test site, Placer County Transit in 

Auburn, California. This test site is a transit bus operation with multiple CNG-powered 

buses. Three engines were programmed on May 24 and then monitored as the buses were 

placed into route operation. The engines performed well with the software, and no fault 

codes were generated due to the software. 

June 2005 

The first field evaluation of the school bus fleet at Poway Unified School district fleet 

(Poway, California) ran from April to June 2005. The second field evaluation ran from 

May to June 2005 at Placer County Transit in Auburn, California. Both field tests 

yielded good performance with the 1.2 gram software in place; there were no engine 

problems associated with the new 1.2 gram software. 

27
July 2005 

John Deere Engine Engineering prepared the internal documentation to release the 1.2 

software for production; the new release will offer a 1.2 gram performance option along 

with the current 1.5 gram/1.8 gram options through the end of 2005. At the end of the 

year, the 1.5 bram/1.8 gram performance options will be cancelled, with only the 1.2 

gram performance option available starting in January 2006. Given the release internal 

option code processing time, it is projected to have the 1.2 gram option available on 

production engines by October 2005. Concurrently emission certification applications to 

1.2 gram were submitted to both EPA and CARB (July 14). Past experience had shown 

that 6-8 weeks are required to receive certificates back, which will meet the October start 

of production target. 

4.0 Conclusions

• The Deere 8.1L - HFN04 model successfully completed a 1125 hour deterioration 

factor test as part of Task 3.3, achieving critical reductions, especially in the NOx

level. 

• The engine performance development work in Task 3.1 was successful in providing 

new calibrations for both the 250 hp and 280 hp levels. 

• The new, lower DFs combined with the new calibrations allow the 8.1L - HFN04 

model to be certified to the CARB optional 1.2 gram NOx + NMHC standard for the 

MHDD, HHDD, and Urban Bus classes. 

• The 8.1L - HFN04 model successfully completed a six-month field test in a New 

Flyer transit bus in Washington, D.C. (WMATA) as part of the project. The bus 

performed without fault during the six-month test, covering 14,500 miles at an 

average fuel economy of 2.35 mpg (diesel equivalent). Additionally, the HFN04 

model when compared to three other competitor diesel and natural gas engines using 

the West Virginia University mobile chassis dynamometer, obtained higher fuel 

economy ratings. (Testing was conducted under NREL contract in March 2004; 

pending NREL document “Heavy Duty Vehicle Emission Testing.”) 

• A separate, abbreviated three-phase driveability field test was conducted to evaluate 

the final 1.2 gram calibration before production release. Phase 1, using captive Deere 

vehicles, was conducted in Waterloo, Iowa. Phases 2 and 3 both took place in 

California, using public school bus and transit bus fleets. No driveability faults were 

found in any of the phases, demonstrating the commercial viability of the new 

calibrations. 

• Due to earlier Deere development work, little work was required to the ECU and/or 

the control system strategy overall. The only real changes required to achieve the 1.2 

gram calibrations were to the end-of-line files regarding spark timing, fuel quantities, 

etc. 

• The 1.2 gram calibration will be available for commercial application as soon as the 

certification documents are received from EPA and CARB. This is anticipated to be 

in October 2005. 

28
5.0 Appendices

29
30

Appendix A: Fleet Vehicle Specifications Form

FLEET VEHICLE SPECIFICATIONS 

Revised 1/12/96 

HDV_VEH Table Vehicle ID Number (VIN) Vehicle identification number 

Fleet_Veh_ID Vehicle identification number used by fleet Vehicle_Make Name of vehicle manufacturer Vehicle_Model Truck model number Vehicle_Year Year vehicle was manufactured Service_Date Date vehicle was put into service by fleet 10/25/02 (Start_Mileage Mileage on vehicle at the start of the fleet demonstration 1630 miles (when repower wActivity_Code Type of activity vehicle is used for (Code 1 from VMRSH) NA; doesEquipment_Category_Code Type of optional equipment installed on vehicle Body_Mfgr_Code Name of body manufacturer Body_Descr_Code Type of body attached to cab (Code 48 from VMRSH) Engine_Serial Serial number of the engine 

HDV_ENGINE Table OEM_Retrofit Is the engine OEM or a retrofit? 

Eng_Mfgr_Code Name of engine manufacturer Eng_Model Engine model number Eng_Config_Code Engine Configuration Code (Code 35 from VMRSH) CoEng_Cu_In Engine size in cubic inches Num_Cylinders Number of cylinders Eng_Year Year engine was manufactured Cycle Is the engine 2 cycle or 4 cycle ? 
31

Compr_Ratio Compression ratio 

Ignition_Aid_Type Type of ignition aids used EPA Certified (Y/N) Is the engine configuration EPA certified Maximum bHp Rated maximum brake horsepower of engine Rpm of Max bHp Rpm at rated maximum brake horsepower Maximum Torque (ft-lbs) Rated maximum torque of engine Rpm of Max Torque Rpm at rated maximum torque Oil Capacity (qts) Oil capacity in quarts Blower? (Y/N) Does the engine have a blower? Turbocharger? (Y/N) Does the engine have a turbocharger? 

HDV_FUEL_SYSTEMS Table Fuel_ Type_Code What type of fuel is engine designed for? 

Diesel Additives Type of additives used in diesel fuel Alt Fuel Additives Type of additives used in alternative fuel Mech_Elec For liquid fuel engines, are the injectors mechanically or 

electronically controlled? 

Injector Mfr Name of liquid fuel injector manufacturer Inj Model Liquid fuel injector model number Num of Injectors Number of liquid fuel injectors Liq-Fuel Filter Mfr Name of liquid fuel filter manufacturer Liq-Fuel Filter Model Liquid fuel filter model number Fuel_Induction For gaseous fuel engines, is it injection or fumigation? Air Intake Throttle (Y/N) Does the engine use an air intake throttle Gas Equip (OEM/Retrofit) Is the gas fuel system OEM or retrofit? Number of Alt Fuel Tanks Number of alternative fuel tanks Number of Diesel Tanks Number of diesel tanks AF Max Work Press (psi) Alternative fuel maximum working pressure in psi Amount of Useable AF Total useful alternative fuel in tank(s) Alt Fuel Units Units used for alternative fuel tank(s) useful volume S
Amount of Useable Diesel Total useful diesel fuel in tank(s) 

Diesel Fuel Units Units used for diesel fuel tank(s) useful volume AF Tank Manufacturer Name of alternative fuel tank(s) manufacturer General DynamiDiesel Tank Manufacturer Name of diesel fuel tank(s) manufacturer Alt Fuel Tank Model Alternative fuel tank(s) model number Diesel Tank Model Diesel fuel tank(s) model number Alt Fuel Empty Tank Wt Alternative fuel tank(s) empty weight Alt Fuel Tank Wt Units Units used for alternative fuel tank(s) empty weight Diesel Empty Tank Wt Diesel fuel tank(s) empty weight Diesel Tank Wt Units Units used for diesel fuel tank(s) empty weight HDV_TRANS Table Transmission Mfr Name of transmission manufacturer Trans Model Number Transmission model number Trans Year of Mfr Transmission year of manufacture Trans_Type_Code Type of Transmission (Code 7 from VMRSH) Code 2 (Forward Speeds Number of forward speeds Reverse_Speeds Number of reverse speeds 

HDV_AXLE Table Axle_Type_Code Type of axle configuration (Code 3 from VMRSH) 

Axle_Front_Weight Axle front weight Front_Tire_Size Size of front tire Rear_Tire_Size Size of rear tires Axle_Mfgr_Code Name of drive axle manufacturer (from VMRSH) Axle Model Drive axle model number Rear_Axle_Config_Code Rear axle configuration (Code 37 from VMRSH) Code 1 (Single SRear_Axle_Setup_Code Setup of rear axle configuration (Code 38 from VMRSH) Axle_Ratio_Low Low axle ratio 

32
Axle_Ratio_High High axle ratio 

Total GVW Wt (lb) Total gross vehicle weight in pounds Total Curb Wt (lb) Total weight with the truck in curb weight configuration Torque Converter Ratio Torque converter ratio Wheelbase Length of wheelbase HDV_EMISSION Table Cat_Conv Does the vehicle have a catalytic converter? Y or N Cat_Conv_Mfg Name of catalytic converter manufacturer. Johnson MatthCat_Conv_Model Model number of the catalytic converter. Johnson Matthey 3Dsl_Prt_Trap Does the vehicle have a diesel particulate trap? Y or N Trap_Mfg Name of the particulate trap manufacturer. Trap_Model Model number of the particulate trap. Trap_Regen_Type Type of trap regeneration process Trap_Conf Particulate trap configuration Num_Trap_Ele Number of particulate trap elements Trap_Sys_Wt Weight of the particulate trap system 

33
34

Appendix B: Daily Test Log 

Summary of data collected for task 3.2, WMATA bus 2460 

 Miles Fuel Average Monthly Fuel Economy(mpg, DGE) 

April 1212 422 2.87 

May 3758 1554 2.42 

June 2328 1007 2.31 

July 2137 955 2.24 

August 2136 865 2.47 

September 1302 712 1.83 

October 1673 685 2.44 

Overall 14546 6200 2.35 

Month Date Mileage Fuel Usage* Maintenance or Problem Log 

 (*Fuel usage is in gallon equivalent) 

Apr 19 30744 42.0 

 20 30744 0.0 Changed engine oil & filter on PMI (preventative 

maintenance interval) 

 21 30778 25.0 

 22 30824 22.0 

 23 30824 0.0 

 24 31160 67.0 

 25 31319 69.0 

 26 31465 50.0 

 27 31559 43.0 

 28 31626 36.0 

 29 31810 53.0 

 30 31956 57.0 Average for April: 2.87 mpg 

May 1 32105 59.0 

 2 32302 78.0 

 3 32451 62.0 

 4 32666 70.0 

 5 32862 84.0 

 6 32920 40.0 

 7 33026 40.0 

 8 33149 60.0 

 9 33267 57.0 

 10 33333 34.0 

 11 33490 56.0 

 12 33593 56.0 

 13 33649 25.0 

 14 33737 62.0 

 15 33737 0.0 

 16 33737 0.0 

 17 33753 37.0 

 18 33816 28.0 

 19 33973 47.0 

 20 34177 72.0 

 21 34391 88.0 

 22 34531 60.0 

 23 34701 73.0 

 24 34878 9.0 

 25 34952 34.0 

 26 35048 49.0 
35

Month Date Mileage Fuel Usage* Maintenance or Problem Log 

 (*Fuel usage is in gallon equivalent) 

 29 35526 79.0 

 30 35616 44.0 

 31 35714 35.0 Average for May: 2.42 mpg 

Jun 1 35714 35.0 

 2 35821 48.0 

 3 35938 63.0 

 4 36190 92.0 

 5 36190 0.0 

 6 36190 0.0 

 7 36294 38.0 

 8 36407 24.0 

 9 36544 48.0 

 10 36662 47.0 

 11 36672 45.0 

 12 36763 16.0 

 13 36763 0.0 

 14 36763 0.0 Changed engine oil, oil filter, pressure washed 

engine, replaced belt guard on PMI (preventative 

maintenance interval 

 15 36909 51.0 

 16 36948 19.0 

 17 37074 41.0 

 18 37268 94.0 

 19 37452 74.0 

 20 37452 0.0 

 21 37515 38.0 

 22 37668 52.0 

 23 37881 71.0 

 24 37881 0.0 

 25 37881 0.0 

 26 37881 0.0 

 27 37881 0.0 

 28 37889 38.0 

 29 37949 42.0 

 30 38042 31.0 Average for June: 2.31 mpg 

Jul 1 38110 41.0 

 2 38247 57.0 

 3 38247 0.0 

 4 38261 24.0 

 5 38261 0.0 

 6 38326 27.0 

 7 38543 64.0 

 8 38711 70.0 

 9 38849 52.0 

 10 38849 0.0 

 11 38849 0.0 

 12 38849 0.0 No power, check engine light on 

 13 38849 0.0 

 14 38902 42.0 

 15 39006 46.0 

 16 39223 79.0 

 17 39223 0.0 

 18 39223 0.0 
Month Date Mileage Fuel Usage* Maintenance or Problem Log 

 (*Fuel usage is in gallon equivalent) 

 21 39567 43.0 

 22 39685 59.0 rd tested, sluggish while driving, check engine light 

on - checked codes "fuel derate codes" no other 

problem 

 23 39773 48.0 

 24 39773 0.0 

 25 39773 0.0 

 26 39876 52.0 

 27 39928 31.0 

 28 39988 31.0 

 29 40124 53.0 

 30 40179 34.0 

 31 40179 0.0 Average for July: 2.24 mpg 

Aug 1 40179 0.0 

 2 40324 41.0 

 3 40461 54.0 

 4 40660 59.0 

 5 40660 0.0 

 6 40660 0.0 

 7 40660 0.0 

 8 40752 33.0 

 9 40828 42.0 

 10 40899 26.0 

 11 40910 16.0 

 12 40936 12.0 

 13 40969 22.0 

 14 41156 27.0 

 15 41308 62.0 

 16 41308 0.0 

 17 41430 54.0 

 18 41540 37.0 

 19 41682 65.0 

 20 41733 25.0 

 21 41733 0.0 

 22 41733 0.0 

 23 41766 23.0 

 24 41769 10.0 

 25 41857 42.0 

 26 41923 33.0 

 27 42012 45.0 

 28 42024 16.0 

 29 42093 36.0 

 30 42270 58.0 

 31 42315 27.0 Average for August: 2.47 mpg 

Sep 1 42420 60.0 

 2 42464 29.0 

 3 42576 54.0 

 4 42576 0.0 

 5 42576 0.0 

 6 42576 0.0 

 7 42615 47.0 

 8 42752 60.0 

 9 42889 47.0 

36
Month Date Mileage Fuel Usage* Maintenance or Problem Log 

 (*Fuel usage is in gallon equivalent) 

 12 42998 32.0 

 13 43054 44.0 

 14 43077 23.0 

 15 43146 29.0 

 16 43235 21.0 

 17 43235 0.0 

 18 43235 0.0 

 19 43235 0.0 

 20 43257 19.0 

 21 43257 0.0 

 22 43262 6.0 

 23 43343 62.0 

 24 43435 35.0 

 25 43435 0.0 

 26 43435 0.0 

 27 43504 65.0 

 28 43561 19.0 Check for idle low, cleared codes, rd tested 

 29 43561 0.0 

 30 43617 38.0 Average for September: 1.83 mpg 

Oct 1 43686 23.0 

 2 43686 0.0 

 3 43686 0.0 

 4 43872 62.0 

 5 43989 39.0 

 6 43992 79.0 

 7 44118 42.0 

 8 44292 58.0 

 9 44433 47.0 

 10 44433 0.0 

 11 44433 0.0 

 12 44553 40.0 

 13 44655 34.0 

 14 44805 50.0 

 15 44928 41.0 

 16 45048 40.0 

 17 45285 79.0 

 18 45290 51.0 Average for October: 2.44 mpg 

37
F1146-E(12/2004) 

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services and Communications Directorate (0704-0188). Respondents 

should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a 

currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

March 2006 

2. REPORT TYPE

Subcontract Report 

3. DATES COVERED (From - To)

July 2003 - July 2005 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Natural Gas Engine Development 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/SR-540-39491 

5e. TASK NUMBER

FC05.9000 

6. AUTHOR(S)

T.C. Lekar and T.J. Martin 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

John Deere & Company 

3800 Ridgeway Ave. 

Waterloo, IA 50704-8000 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

ZCI-3-32027-04 

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

NREL/SR-540-39491 

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES

NREL Technical Monitor: Richard Parish 

14. ABSTRACT (Maximum 200 Words)

This report provides information and data on a project to develop natural gas engines that would be certifiable to 

nitrogen oxide and nonmethane hydrocarbon emission levels below 2004 federal standards. 

15. SUBJECT TERMS

natural gas engines; natural gas vehicles, natural gas engine emissions; natural gas vehicle emissions 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

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