January 2000 • NREL/SR-540-26758

California Energy Commission

Sacramento, California

Santa Barbara County Air Pollution Control District

Goleta, California

Demonstration of Caterpillar

C-10 Dual-Fuel Engines in

MCI 102DL3 Commuter Buses

National Renewable Energy Laboratory

1617 Cole Boulevard

Golden, Colorado 80401-3393

NREL is a U.S. Department of Energy Laboratory

Operated by Midwest Research Institute • Battelle • Bechtel

Contract No. DE-AC36-99-GO10337
January 2000 • NREL/SR-540-26758

Demonstration of Caterpillar

C-10 Dual-Fuel Engines in

MCI 102DL3 Commuter Buses

California Energy Commission

Sacramento, California

Santa Barbara County Air Pollution Control District

Goleta, California

NREL Technical Monitor: Paul Norton

Prepared under Subcontract No. ACI-6-15702-01

National Renewable Energy Laboratory

1617 Cole Boulevard

Golden, Colorado 80401-3393

NREL is a U.S. Department of Energy Laboratory

Operated by Midwest Research Institute • Battelle • Bechtel

Contract No. DE-AC36-99-GO10337
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i

Contents

CONTENTS.................................................................................................................................................................. i

FIGURES AND TABLES........................................................................................................................................... ii

APPENDICES ............................................................................................................................................................. ii

ACRONYMS AND ABBREVIATIONS ..................................................................................................................iii

INTRODUCTION....................................................................................................................................................... 1

PROJECT OBJECTIVE AND RESULTS SUMMARY ......................................................................................... 1

PROJECT DESCRIPTION AND TECHNICAL CONCEPT................................................................................. 3

VEHICLE OPERATIONS ................................................................................................................................................... 3

DESCRIPTION OF BUSES ................................................................................................................................................. 3

DUAL-FUEL ENGINE OPERATION .................................................................................................................................... 3

BUS ROUTE AND DRIVE CYCLES.................................................................................................................................... 6

DATA COLLECTION ........................................................................................................................................................ 6

FUELING FACILITY DESCRIPTION ................................................................................................................................... 6

RESULTS AND DISCUSSION.................................................................................................................................. 7

BUS OPERATIONS........................................................................................................................................................... 7

DISCUSSION OF OPERATING DATA ................................................................................................................................. 7

FUEL ECONOMY .............................................................................................................................................. 7

PERFORMANCE ................................................................................................................................................ 8

RELIABILITY .................................................................................................................................................... 8

CNG FUEL SUBSTITUTION............................................................................................................................... 9

NORMAL ENGINE OPERATIONS/"OUT OF RANGE" ENGINE PARAMETERS ...................................................... 10

ENGINE CNG SYSTEM DOWNTIME................................................................................................................ 10

FAILURE TO REFUEL BUSES WITH CNG......................................................................................................... 10

OIL CONSUMPTION AND OIL CHANGE INTERVALS ....................................................................................................... 11

DRIVER AND PASSENGER PERSPECTIVES ..................................................................................................................... 11

EMISSIONS TESTING............................................................................................................................................ 11

C-10 DFNG ENGINE IN DUAL-FUEL MODE VERSUS C-10 D ENGINE .......................................................................... 12

C-10 DFNG ENGINE IN DIESEL MODE VERSUS C-10 D ENGINE.................................................................................. 13

PROBLEMS AND RESOLUTION ...................................................................................................................................... 13

PROJECT ECONOMIC ANALYSIS ..................................................................................................................... 19

FIXED COST DIFFERENCES ........................................................................................................................................... 19

VARIABLE COST DIFFERENCES .................................................................................................................................... 19

POTENTIAL VALUE OF EMISSION REDUCTION CREDITS................................................................................................ 20

SUMMARY OF COSTS DURING DEMONSTRATION PERIOD ............................................................................................. 20

PROJECTED COSTS USING RETAIL DIESEL PRICES AND AN ONSITE CNG STATION ...................................................... 20

LESSONS LEARNED .............................................................................................................................................. 22

ALTOONA TESTING ...................................................................................................................................................... 22

ENCOURAGING BUS OPERATORS TO USE CNG............................................................................................................ 22

CONCLUSIONS AND RECOMMENDATIONS .................................................................................................. 23

CONCLUSIONS.............................................................................................................................................................. 23

PERFORMANCE .............................................................................................................................................. 23

EMISSIONS ..................................................................................................................................................... 23

RECOMMENDATIONS.................................................................................................................................................... 24
ii

Figures and Tables

FIGURE 1. CLEAN AIR EXPRESS BUS.......................................................................................................4

FIGURE 2. CNG BUS COMPONENTS ........................................................................................................5

FIGURE 3. C-10 DFNG ENGINE: MILES PER GALLON VERSUS DUAL-FUEL OPERATING TIME ..............9

FIGURE 4. EMISSIONS TEST RESULTS: EPA UDDC SCHEDULE D DRIVE CYCLE ................................14

FIGURE 5. EMISSIONS TEST RESULTS: WEST VIRGINIA UNIVERSITY CBD DRIVE CYCLE...................15

FIGURE 6. EMISSIONS TEST RESULTS: 55 MPH STEADY-STATE DRIVE CYCLE...................................16

TABLE 1. SUMMARY OF BUS OPERATING DATA ....................................................................................7

TABLE 2. EMISSIONS TEST RESULTS: DUAL-FUEL ENGINE IN DUAL-FUEL MODE

VERSUS DIESEL ENGINE .......................................................................................................17

TABLE 3. EMISSIONS TEST RESULTS: DUAL-FUEL ENGINE IN DIESEL MODE

VERSUS DIESEL ENGINE .......................................................................................................18

TABLE 4. ACTUAL ANNUAL OPERATING COST DIFFERENCES

DURING DEMONSTRATION PERIOD .......................................................................................21

TABLE 5. PROJECTED ANNUAL OPERATING COST DIFFERENCES

USING RETAIL DIESEL AND AN ON-SITE CNG STATION......................................................22

Appendices

APPENDIX A. DETAILED BUS SPECIFICATIONS

APPENDIX B. DETAILED BUS OPERATING DATA

APPENDIX C. EMISSIONS TEST RESULTS

APPENDIX D. CATERPILLAR C-10 DFNG AND D PERFORMANCE RATINGS

APPENDIX E. DIFFERENTIAL COST ANALYSIS REFERENCES
iii

Acronyms and Abbreviations

App. appendix

Avg. average

CARB California Air Resources Board

CAVTC Clean Air Vehicle Technology Center

CBD central business district

CEC California Energy Commission

CH4 methane

CNG compressed natural gas

CO carbon monoxide

CO2 carbon dioxide

D diesel

DFNG dual-fuel natural gas

DEG diesel equivalent gallon (135,000 Btu)

DF dual-fuel

EPA Environmental Protection Agency

ERC emission reduction credit

ft-lb foot-pound (torque)

g/bhp-hr grams per brake horsepower hour

gal gallon

GVWR gross vehicle weight rating

hp horsepower

incr. increase

LAMTA Los Angeles Metropolitan Transportation Authority

MCI Motor Coach Industries

mi miles

MPH miles per hour

NMHC non-methane hydrocarbons

NOx oxides of nitrogen

OEM original equipment manufacturer

PM particulate matter

PSA Power Systems Associates

psi pounds per square inch (pressure)

red. reduction

ROC reactive organic compound

rpm revolutions per minute

SBCAPCD Santa Barbara County Air Pollution Control District

scfm standard cubic feet per minute

THC total hydrocarbons

UDDC urban dynamometer drive cycle

WVU West Virginia University

yr year
1

Introduction

The purpose of this program was to demonstrate the Caterpillar C-10 Dual-Fuel Natural Gas

(DFNG) engine in an over-the-road bus application. Four Motor Coach Industries (MCI) 102DL3

buses were operated side-by-side on similar fixed-route revenue service for a 12-month

demonstration period from February 1998 through January 1999. Three of the buses were

equipped with Caterpillar C-10 DFNG engines and the fourth was equipped with a C-10 diesel

(D) engine. The buses were used as part of the Clean Air Express Commuter Bus Program in

Santa Barbara County, California.

The buses were obtained by the City of Lompoc through a grant from the Federal Transportation

Authority (through the Congestion Management and Air Quality Improvement Program). The

Santa Barbara County Air Pollution Control District (SBCAPCD) provided a 20% cost-share

toward the purchase of the buses. The base cost of the four buses was about $1,400,000

($350,000 each). The conversion of the buses to compressed natural gas (CNG) operation was

funded by the U.S. Department of Energy (DOE) through the National Renewable Energy

Laboratory (NREL), the California Energy Commission (CEC), and the Southern California Gas

Company. The buses were delivered from MCI with Caterpillar C-10 D engines. The cost to

retrofit the buses to dual-fuel operation was $180,000 ($45,000 per bus).

Project Objective and Results Summary

Project Objective

The objective of the project was to determine the benefits and problems encountered in

retrofitting and operating an over-the-road bus with the Caterpillar C-10 DFNG engine.

Specifically, this demonstration evaluated the retrofit costs and process, performance, reliability,

fuel economy, and emissions of the C-10 DFNG engine compared to a standard C-10 D engine.

Project Results Summary

All four buses performed well throughout the demonstration period. The dual-fuel buses

accumulated a total of 94,228 miles, or an average of 31,400 miles each, during the 12-month

operating period. The diesel bus accumulated 27,443 miles (this bus was removed from service

after 11 months to be converted to dual-fuel operation). No significant obstacles were

encountered in retrofitting the buses with the CNG components. Performance and reliability of

the dual-fuel buses were comparable to that of the diesel bus. The performance and reliability of

the C-10 DFNG engine was comparable to the C-10 D engine.

The C-10 DFNG engines averaged a 56% CNG-to-diesel substitution rate, on a total-energy-used

basis, during the demonstration period. This means 56% of the energy used to operate the buses

came from CNG. The remaining 44% was supplied by the diesel fuel. CNG use was primarily

affected by electronic engine controls (i.e., termination of CNG injection because of engine
2

operations outside allowable parameter ranges), failure of the bus operator to consistently refuel

the buses with CNG, and breakdown of the CNG station. The C-10 DFNG engines have an

electronic governor to reduce the available power when the engine is operated on diesel only.

The intent of the “reduced power mode” is to dissuade the operator from routinely operating the

engine in diesel-only mode, while still affording the opportunity to operate on diesel in an

emergency. For this demonstration, the reduction in power in diesel-only mode was not severe

enough to ensure consistent CNG use.

Although very few repairs were needed on either engine type during the demonstration period,

the C-10 DNFG engine had higher initial capital, fuel, fueling labor, insurance, and maintenance

costs than the C-10 D. On a 30,000 mile-per-year basis, the C-10 DFNG cost about $0.19 more

per mile to operate than the C-10 D, based on the results of this demonstration. Cost differences

between the C-10 DFNG and the C-10 D can vary greatly depending on the application. Fleet

operators should assess the cost differences based on their specific application.

At the conclusion of the 12-month demonstration period, the C-10 DFNG and C-10 D engines

were emissions tested on a chassis dynamometer using three drive cycles: the EPA Urban

Dynamometer Drive Cycle Schedule D (UDDC), the Central Business District (CBD) Drive

Cycle (West Virginia University [WVU] version), and a 55 Mile Per Hour (MPH) Steady State

Drive Cycle. The emissions tests were performed by the Los Angeles Metropolitan

Transportation Authority (LAMTA). The LAMTA test technician assured SBCAPCD that

appropriate EPA and California Air Resources Board (CARB) test procedures were used, but no

written documentation of the test methods, calibration procedures, or quality assurance

procedures was provided. This report simply presents the emissions test results as they were

provided by LAMTA. The C-10 DFNG engines in dual-fuel mode had lower emissions of the

following pollutants as compared with the C-10 D engine (ranges represent lowest/highest value

for all three drive cycles tested): NOx (27%–60%), PM (54%–64%), and CO2 (14%–19%), and

increases of CO (634%–860%) and non-methane hydrocarbons (NMHC) (697%–1,718%). In the

two variable load tests (EPA UDDC and the WVU CBD), the C-10 DFNG may have had higher

combined NOx and NMHC emissions. However, the smog-forming potential of these combined

emissions compared to diesel combined NOx and HC emissions cannot be quantified because

specific hydrocarbons vary in their ozone reactivity. Because the HC emissions were not

speciated in this study, the reactivity of the DFNG and diesel exhaust emissions cannot be

compared. Even so, the simple addition of NOx + NMHC emissions indicates a 17% increase

compared with the C-10 D engine for the variable load cycles. In contrast, on the 55-MPH Steady

State test, the C-10 DFNG engine had 42% lower NOx + NMHC emissions compared with the

C-10 D.

In comparing emissions from the C-10 DFNG engine in diesel mode with emissions from the

C-10 D, differences in NOx, CO2, and CO were too small (generally less than 3%) to allow any

meaningful conclusions. However, the C-10 DFNG engine in diesel mode had 25%–42% lower

PM emissions and 14%–18% lower NMHC emissions (depending on the drive cycle) than the

C-10 D diesel engine.
3

Project Description and Technical Concept

Vehicle Operations

The Clean Air Express Commuter Bus Service takes passengers from neighboring cities

(e.g., Santa Maria, Lompoc, Ventura, Santa Ynez) to Santa Barbara/Goleta to and from work

each day. The average one-way commute is about 60 miles. The purpose of the program is to

reduce air pollution from long-distance single-occupancy commuter automobiles by getting as

many as 55 people out of their cars and into one low-emissions bus.

The service currently uses 9 buses to serve approximately 350 commuters daily, 250 days per

year. The four buses used as part of this demonstration project were placed into service in early

1998 on the City of Lompoc to Santa Barbara/Goleta route. The buses were operated by Melni

Bus Company, which oversaw all aspects of vehicle operations, including maintenance, repairs,

fueling, and passenger booking.

Description of Buses

The buses used in this demonstration were brand-new 1997 MCI 102DL3 over-the-road coaches.

The buses were equipped by the original equipment manufacturer (OEM) with Caterpillar

C-10 D engines. The buses are 45 feet long, about 111⁄2 feet tall, and can carry 55 passengers.

They are equipped with wheelchair lifts, but not with restrooms. The bus gross vehicle weight

rating is 34,000 pounds.

Three buses were retrofitted with Power Systems Associates’ dual-fuel operating system. In the

dual-fuel mode, the C-10 DFNG engine is rated at 350 hp and 1,075 ft-lb of torque. Each bus was

fitted with 4 CNG cylinders for a total CNG capacity of 48 diesel equivalent gallons (DEGs) at

3,000 psi (58 DEGs at 3,600 psi). The buses had a range of approximately 460 miles in dual-fuel

mode (based on the average 56% CNG substitution rate and 5.34 miles/DEG obtained during the

demonstration period). Three cylinders were installed in the lower rear standard baggage

compartment, and one in the lower forward baggage compartment. The cylinders were hooded to

vent any leaks to the atmosphere, instead of into the baggage compartment. Also, pressure relief

valves and associated plumbing were installed to vent over-pressurization to the rear roof area of

the bus.

Figure 1 shows the Clean Air Express bus and the location of key CNG components. Figure 2

gives a detailed look at the various CNG components. Complete vehicle specifications are

included as Appendix 1.

Dual-fuel Engine Operation

Dual-fuel engines operate by introducing a small charge of diesel fuel into the combustion

chamber until the engine reaches idle. Beyond idle, natural gas is introduced as the engine load

increases. Dual-fuel engines operate simultaneously on natural gas and diesel. Some dual-fuel

engines operate on a mix of 80% CNG and 20% diesel fuel. The Caterpillar C-10 engine
4

Figure 1. Clean Air Express Bus
5

Figure 2. CNG Bus Components
6

demonstrated in this project is capable of operating on a mix of up to 85% CNG and 15% diesel

fuel. However, if natural gas fuel is depleted, the dual-fuel engine will operate in a reduced power

mode on diesel fuel until the vehicle is refueled with natural gas. Dual-fuel engines operating on

CNG and diesel fuel reduce harmful pollutants such as oxides of nitrogen and particulates. The

Caterpillar C-10 dual-fuel engine demonstrated in this project was certified to the California Air

Resources Boards alternative low-NOx standard of 2.5g/bhp-hr. This standard is 37.5% less than the

applicable standard for diesel trucks.

Bus Route and Drive Cycles

The buses make one round trip from the City of Lompoc to Santa Barbara each day, and operate

250 days per year. After boarding, the buses leave the City of Lompoc at approximately 6:30 a.m.

and travel about 60 miles to the Santa Barbara area. After delivering passengers to and around

Santa Barbara, the buses are turned off, except for refueling and maintenance operations, until the

return trip to Lompoc in the evening. More than 90% of the trip distance is on highways with posted

speed limits of 65 mph. The entire route is characterized by gently rolling hills and one significant

hill (approximately 2 miles long, 500 feet high [3%–7% grade]). The highway goes up then down

this hill, so the buses must traverse this grade on each segment of the trip (i.e., twice per round trip).

Aside from this grade, the entire route is less than 100 feet above mean sea level. The area is

characterized by a temperate climate, with daytime temperatures of 50o–90°F. Nighttime

temperatures occasionally reach freezing during the winter months.

Data Collection

Data collection was coordinated by SBCAPCD’s Innovative Technologies Group. The bus operator

maintained logs on routine maintenance, breakdowns, repairs, and fueling. Vendor receipts for both

CNG and diesel were recorded to allow cross-checking of operator fuel logs. Once each month, the

SBCAPCD downloaded engine operating data from each dual-fuel engine’s computer, including

total engine hours, engine hours in dual-fuel mode, amount of CNG used, and amount of diesel used

in dual-fuel mode. The C-10 DFNG does not record total diesel use.

Fueling Facility Description

A public-access CNG fueling facility was used to fuel buses during the demonstration program. The

facility was built and owned by the Southern California Gas Company; cost-share funding was

provided by SBCAPCD. The facility is equipped with 400 gasoline-equivalent gallons of storage

(at 3,000 psi), and a compressor rated at 170 scfm (approximately 1.3 DEGs per minute). Diesel fuel

was obtained at county-owned fueling facilities; however, when necessary, diesel was obtained from

commercial fueling sites.
7

Results and Discussion

Bus Operations

The buses were driven on similar routes in routine revenue service for 12 months. The three dualfuel buses logged a total of 94,228 miles, or an average of about 31,400 miles each; the diesel bus

logged 27,443 miles.1 The dual-fuel buses logged 2,682 engine hours, or an average of 894 hours

each. The diesel bus was not equipped with engine hour meter; however, because of the similarity in

routes and miles driven, the diesel bus probably operated a comparable number of hours. A

summary of the bus operations is presented in Table 1. Detailed monthly data for each bus are

included in Appendix 2.

Table 1.

Summary of Bus Operating Data

Operating Data Calculations

Bus

No.

Engine

Type

Engine

Time

(h)

DFNG

Time

(h) Miles

CNG

(DEGs)

Diesel

(DEGs)

Average

Miles/DEG

% CNG

when in

DF mode

% CNG

of total

fuel

% time in

DF mode

Air 11 DFNG 909 492 31,704 3,191 3,085 5.05 86% 51% 54%

Air 13 DFNG 866 483 32,600 3,192 2,667 5.56 87% 54% 56%

Air 14 DFNG 907 567 29,924 3,437 2,094 5.41 86% 62% 63%

Avg. DF Bus : 894 514 31,409 3,273 2,615 5.34 86% 56% 57%

Air 12 Diesel N/A N/A 27,443 N/A 4,580 6.00 N/A N/A N/A

Discussion of Operating Data

Fuel Economy

The following discussion of fuel economy is based on actual operating data from the buses during

the demonstration period. The amount of diesel fuel used was based on operator records, which

were cross-checked by SBCAPCD staff against county fueling records. CNG use was based on the

dual-fuel engine computer record and was cross-checked against Southern California Gas Company

billing records. Overall, the fuel economy of the dual-fuel buses averaged 5.34 miles/DEG. The fuel

economy of the diesel bus was 6.0 miles/DEG. Thus, the dual-fuel buses averaged about 11% fewer

miles per DEG than the diesel bus. Because the C-10 DFNG engine’s fuel efficiency is actually an

average efficiency based on part dual-fuel operation and part straight-diesel operation, the fuel

economy in dual-fuel mode is actually less than 5.3 miles per DEG. Assuming that the fuel economy

of the dual-fuel bus, when being operated in “diesel mode” is equivalent to that of the diesel bus

(6.0 miles/DEG), the fuel economy of the C-10 DFNG engine in dual-fuel mode is estimated to be

 

1 One reason for the lower miles on the diesel bus was that it was taken out of service approximately 1 month before the

end of the demonstration period for emissions testing and conversion to dual-fuel operation.
8

about 4.8 miles/ DEG,2 or about 20% lower than that of the diesel engine. This estimated fuel

economy of the dual-fuel engine is shown in Figure 3.

The fuel economy of the dual-fuel and diesel buses was also estimated during chassis dynamometer

emissions testing (see Appendix 3). The fuel economy estimates made during emissions testing

indicated that the dual-fuel engine had comparable, or better, fuel economy than the diesel engine.

However, the estimated fuel economy during emissions testing was not based on actual

measurement of fuel, but on a “carbon count” performed on the engine exhaust. The accuracy of this

method depends on an accurate analysis of the fuel composition. There is considerable uncertainty

associated with the fuel economy estimates obtained during the emissions testing for the dual-fuel

engine, as neither the composition of the CNG nor the blend ratio of CNG at the time of testing was

known.

Performance

Power output of the C-10 DFNG engines was comparable to that of the C-10 D diesel engine.

Although the bus drivers reported a slight but noticeable reduction in power in dual-fuel mode, the

C-10 DFNG engine’s power was more than adequate to perform the required duty. The C-10

DFNG engine has lower horsepower and torque than the C-10 D at the lower half of the rpm

operating range (see Appendix 4). For this demonstration, these differences were partially

compensated by reprogramming the shift points in the electronically controlled automatic

transmissions. Also, some drivers reported the C-10 DFNG engines had a slight delay in throttle

response.

The dual-fuel buses were equipped with an electronic governor to reduce the available engine power

when the buses were operated in diesel mode (see Appendix 4). This feature is designed to provide

enough power to “limp home,” yet reduce performance to such an extent that the driver is

discouraged from routinely operating without CNG. The reduced power mode was most noticeable

in hard accelerations and when traversing steep grades; otherwise, the C-10 DFNG engines

performed similarly (including maintaining highway cruising speeds) in both dual-fuel and dieselonly modes. During this demonstration, the reduced power mode alone was not sufficient to ensure

that the buses were consistently operated on CNG; the SBCAPCD had to play an active role in

ensuring CNG use.

Reliability

For the three C-10 DFNG engines, only three mechanical breakdowns were experienced during the

entire demonstration period. One consisted of water intrusion on two of the dual-fuel engine

computers; the other was a broken charge air cooler belt. Once new engine computers were

installed, the computers experienced no further water intrusion problems. The broken charge air

cooler belt was not related to dual-fuel operation; the belt could just as likely have broken on the

 

2

 Fuel Economy in DF-Mode

 Average Fuel Economy = 5.34 miles/DEG =

 = (Percent time DF) * miles/DEG (DF) + (Percent time diesel) * 6.0 miles/DEG (diesel)

 = ( 56% ) * “X” + 44% X 6.0 MPG

 Then, X = Fuel Economy in dual fuel mode = 4.82 miles/DEG
9

diesel base-case bus. Overall, the mechanical reliability of the dual-fuel buses was excellent. There

were no breakdowns on the diesel base-case engine.

CNG Fuel Substitution

Based on data retrieved from the C-10 DFNG engine computer, the CNG use averaged 86% when

the engine was operating in the dual-fuel mode. However, during the demonstration period, the

actual overall average CNG substitution rate was about 56% (on both a fuel-use and an operatinghour basis). Causes for the lower overall average CNG substitution rate were:

• Normal bus operations/“out of range” engine parameters;

• Bus CNG system downtime; and

• Failure to fuel the buses with CNG/breakdown of CNG station.

These issues are discussed more fully in the sections that follow.

The C-10 DFNG engines remained fully operational in the diesel mode, even when CNG was not in

use. This has the effect of making the overall CNG substitution rate lower than the ideal rate. When

comparing the fuel use of the C-10 DFNG engine to that of a dedicated CNG engine, consideration

Figure 3. C-10 DFNG Engine: Miles per Gallon 

versus Dual-Fuel Operating Time

4.6

4.8

5.0

5.2

5.4

5.6

5.8

6.0

6.2

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Time in Dual-Fuel Mode

Miles/DEG

12-month average 

for 1 diesel bus

12-month average

for Melni Bus Service

(1 DF bus)

3-week average for SB Air bus

(4 DF buses)
10

should be given to the amount of diesel used by replacement buses put into service when the

dedicated CNG engine was inoperable.

Normal Engine Operations/“Out of Range” Engine Parameters

The C-10 DFNG engine is designed to operate in diesel-only mode under certain normal conditions.

For example, the C-10 DFNG engine operates in diesel mode during idle and until the engine warms

up (even under power). Applications for which the C-10 DFNG engine is idled for extended

periods, driven in stop-and-go traffic, or used intermittently (when the engine is allowed to cool

down between trips) will have lower overall CNG substitution rates than applications involving

sustained highway driving.

According to Power Systems Associates (PSA), the C-10 DFNG engine computer is programmed to

terminate dual-fuel operation (and operate in straight-diesel mode) any time one of numerous

operating parameters strays outside an acceptable range. For example, if the CNG pressure drops too

low or the engine becomes too hot, the computer reverts back to the diesel-only mode. C-10 DFNG

engines regularly terminated dual-fuel operation because these “out of range” parameters were

detected. Apparently, the “allowable” engine operating parameter ranges have been confined to a

fairly narrow band to minimize the potential for damage to the engine. For increased CNG

substitution rates to be realized in real-world driving applications, the C-10 DFNG engine

computers need to be reprogrammed to allow wider ranges of allowable engine operating

parameters.

Another factor affecting CNG use is that once the computer terminated CNG operation, the engine

would typically not start using CNG again until the engine had been turned off, then on again. In

over-the-road buses and trucks, it is impractical (and potentially unsafe) to pull over and turn the

engine off and on to reset the computer. CNG use could be increased if the computer periodically

reassessed the engine operating parameters and reinitiated CNG injection if the parameters had

returned to within the allowable ranges.

Engine CNG System Downtime

CNG downtime can also be caused by mechanical failures of the CNG system. However, there were

no such physical failures of the CNG system during the demonstration period. The C-10 DFNG

computer failed on two of the buses because of moisture intrusion problems following heavy rains.

This computer controls the injection of CNG to the engine. More often, CNG downtime occurred

because of computer “glitches.” Although these breakdowns were from relatively minor causes, the

CNG downtime persisted for several days, and sometimes weeks, because of the logistics of having

a qualified mechanic repair the bus.

Failure to Refuel Buses with CNG

To complete their routes without running out of CNG, the dual-fuel buses had to be refueled with

CNG every other day. Sometimes the bus operator simply failed to fuel buses according to this

schedule. Fueling a bus (including driving to and from the fueling station) took almost an hour.

Consequently, this inconvenience served as a disincentive to consistently fill the buses with CNG.
11

In an effort to ensure consistent use of CNG, a system was implemented by which a special “fuel

person” refueled each bus during the bus layover in Santa Barbara each day.

There were several periods when the CNG station was inoperable during the 12-month

demonstration. Unfortunately, no convenient backup stations were available when the primary CNG

station was down. To minimize the amount of time the buses operate on diesel fuel during CNG

station downtime, a convenient backup facility should be available. For the Clean Air Express

buses, use of small “time-fill” compressors to fuel the buses overnight would have been ideal. The

public access CNG station could then have been used as the backup station when the time-fill

compressor unit was down, or for quick fill-ups as needed.

Oil Consumption and Oil Change Intervals

There was very little oil consumption on all four buses. Oil in all buses was changed every 7,500

miles. The used oil was not sampled and analyzed.

Driver and Passenger Perspectives

Aside from the need to obtain CNG fuel, operation of the dual-fuel buses was essentially

indistinguishable from that of the diesel bus. Engine noise and vibration were similar between the

two engines. As mentioned previously, the drivers felt that the dual-fuel buses had slightly less

power than the diesel bus, but the difference was very minor. Some drivers felt that the Caterpillar

engines, both the dual-fuel and the diesel, were louder during idle, and had higher turbine whine at

cruise than the Detroit Diesel 6V-92 DDEC engines that were familiar to them.

Emissions Testing

The CEC contracted with the Clean Air Vehicle Technology Center (CAVTC) to emissions test two

of the C-10 DFNG buses and the C-10 D diesel bus. CAVTC, in turn, arranged to have the testing

performed by and at LAMTA. The LAMTA test technician assured the SBCAPCD that appropriate

EPA and CARB test procedures were used, but no written documentation of the test methods,

calibration procedures, or quality assurance procedures was provided. This report simply presents

the emissions test results as they were provided by LAMTA.

The C-10 DFNG engines were tested in both dual-fuel and diesel modes. The buses were tested on

a chassis dynamometer using the following drive cycles: EPA Urban Dynamometer Drive Cycle

Schedule D, the WVU CBD, 55 MPH Steady State, and Idle. These drive cycles are intended to

provide a “snapshot” of the emissions from the buses under actual driving conditions.

A complete description of emission test results, including a description of test methods and drive

cycles, is included in Appendix 3. Figures 4–6 and Tables 2–3 summarize the testing results for

each loaded drive cycle.
12

C-10 DFNG Engine in Dual-Fuel Mode versus C-10 D Engine

When comparing the C-10 DFNG engines in dual-fuel mode to the base-case C-10 D engine, the

emissions differences followed consistent trends between the three loaded drive cycles. The

C-10 DFNG engines in dual-fuel mode had lower emissions of the following pollutants than the

C-10 D engine (ranges represent lowest/highest value for all three drive cycles discussed in Section

4.3): NOx (27%–60 %), PM (54%–64 %), and CO2 (14%–19 %), and increases of CO (634%–860

%) and NMHC (697%–1,718 %). Refer to Figures 4–6 and Tables 2–3 for a summary of the

emissions test results. NOx reductions were most pronounced in the 55 MPH Steady State drive

cycle. This may have been due to the C-10 D being equipped with a “defeat” device (see the

discussion in the following paragraph). Although NMHC emissions from the C-10 DFNG engines

in dual-fuel mode were expected to increase, the magnitude of the increase was surprising.

One interesting divergence in the emissions trends between the three tests was for NOx and NMHC

emissions combined (NOx and non-methane/non-ethane hydrocarbon emissions are considered

precursors to ground-level ozone). In the two variable load tests (EPA Urban Dynamometer Drive

Cycle and the WVU CBD), the C-10 DFNG had about 18% greater NOx and NMHC emissions

(combined) than the C-10 D; on the 55 MPH Steady State test, the C-10 DFNG engine had 42%

lower NOx and NMHC emissions (combined) than the C-10 D. Based on discussions with PSA, the

C-10 D engine computer is believed to operate the engine on one of two electronic “operating

maps” depending on whether the engine is operating in a variable load or a steady-state mode. This

type of system, commonly known as a “defeat device,” effectively results in the engine being

operated in a low-emissions mode when the engine is exposed to varying loads, as in city driving (or

emissions certification tests), and a higher emissions (and fuel economy) mode when the engine is

exposed to steady-state conditions, such as over-the-road highway driving. Although the C-10

DFNG engine has significantly lower NOx/NMHC emissions when operated in steady-state mode

than the C-10 D diesel engine (believed to be equipped with a defeat device), additional emissions

testing is needed to determine whether the C-10 DFNG has lower NOx/NMHC emissions than a

modern diesel engine that is not equipped with a defeat device.

If the dual-fuel engine is intended for use in reducing ozone precursor emissions (NOx and nonmethane/non-ethane hydrocarbons), the engine should be source-tested initially before use and

periodically over the life of the vehicle to verify assumptions made on ozone-precursor reductions.

Such testing should emphasize the accurate determination of the engine’s non-methane/non-ethane

hydrocarbon emissions. Also, air districts should be aware that the C-10 DFNG engines produce

significantly more CO emissions than the standard C-10 D diesel engine. Although high, the CO

levels could be within the standard and can be corrected by the use of oxidation catalysts.
13

C-10 DFNG Engine in Diesel Mode versus C-10 D Engine

Emissions from the C-10 DFNG engine in diesel mode were compared with emissions from the

C-10 D base-case engine. NOx, CO, and CO2 emissions were comparable (generally within 3%)

between the two engine types when using diesel fuel. However, NMHC and PM emissions averaged

about 17% and 33% lower, respectively, on the C-10 DFNG engine. Based on discussions with

PSA, there are no inherent engine operating differences between the C-10 DFNG engine operating

on diesel fuel and the C-10 D engine. No explanations for these emissions differences are offered in

this report. Because of the toxicity concerns with PM in diesel engine exhaust, additional PM testing

may be warranted to further explore whether the C-10 DFNG engine in diesel mode actually has

lower emissions of PM than the C-10 D diesel engine.

Problems and Resolution

At the beginning of the demonstration period, there was some difficulty in coordinating the CNG

fueling. The drivers were not used to fueling the buses every other day, as was necessary to ensure

continuous dual-fuel operation. The buses were filled with diesel fuel in Lompoc in the evenings;

however, because the CNG station was located in Santa Barbara, the buses had to be filled with

CNG during the day when the buses were between trips. Because the bus drivers were commuters

(i.e., they had other jobs during the day), the CNG fueling was difficult for them. One month into

the demonstration period, this issue was resolved by having one person (not a bus driver) fuel all the

buses with CNG during the day layover.

Because the C-10 DFNG engine had good power when used in diesel-only mode, there was little

incentive for the drivers to ensure the buses were fueled with CNG. Close supervision by the

SBCAPCD staff was necessary to ensure consistent use of CNG. Use of the dedicated fueling

person helped to minimize this problem.
14

Figure 3

EPA UDDC Schedule D Drive Cycle

x NMHC CO2 (/100) CO PM (X 10) NOx + NMHC

Figure 3.1 Emission Test Results 

EPA UDDC Schedule D Drive Cycle

iesel Control) Air 13 (DF in Diesel Mode) Air 14 (DF in Diesel Mode) Air 13 (DF in DF Mode) Air 14 (DF in DF Mode)

Figure 4. Emission Test Results

EPA UDDC Schedule D Drive Cycle
15

NMHC CO2 (/100) CO PM (X 10) NOx + NMHC

Figure 3.2: Emissions Test Results

Central Business District Drive Cycle (West Virginia University Version)

ntrol) Air 13 (DF in Diesel Mode) Air 14 (DF in Diesel Mode) Air 13 (DF in DF Mode) Air 14 (DF in DF Mode)

Figure 5. Emissions Test Results

West Virginia University

Central Business District Drive Cycle
16

NMHC CO2 (/100) CO PM (X 10) NOx + NMHC

Figure 3.3: Emissions Test Results

 55 MPH Steady State Test

ntrol) Air 13 (DF in Diesel Mode) Air 14 (DF in Diesel Mode) Air 13 (DF in DF Mode) Air 14 (DF in DF Mode)

Figure 6. Emissions Test Results

55 MPH Steady-State Drive Cycle
17

Table 2. Emissions Test Results:

Dual-Fuel Engine in Dual-Fuel Mode versus Diesel Engine

EPA UDDC Schedule D: Emissions units are grams/mile

Bus Description NOx NMHC

CO2

(/100)1 CO

PM

(x10)1

NOx +

NMHC

Air 12 Diesel Control 19.90 0.57 20.18 3.59 3.68 20.47

Air 13 DFNG in DF Mode 12.78 12.08 16.38 29.11 1.04 24.86

Air 14 DFNG in DF Mode 14.58 8.65 16.43 24.96 1.57 23.23

Avg. DFNG in DF Mode 13.68 10.36 16.40 27.04 1.31 24.04

Avg. % red. from DFNG engine 31% N/A 19% N/A 64% N/A

Avg. % incr. from DFNG engine N/A 1718% N/A 653% N/A 17%

WVU CBD: Emissions units are grams/mile

Bus Description NOx NMHC

CO2

(/100)1 CO

PM

(x10)1

NOx +

NMHC

Air 12 Diesel Control 22.41 1.19 25.71 4.03 4.90 23.60

Air 13 DFNG in DF Mode 15.21 13.99 21.99 42.99 1.76 29.2

Air 14 DFNG in DF Mode 17.51 8.90 22.23 34.40 2.39 26.41

Avg. DFNG in DF Mode 16.36 11.44 22.11 38.70 2.07 27.8

Avg. % red. From DFNG engine 27% N/A 14% N/A 58% N/A

Avg. % incr. From DFNG engine N/A 861% N/A 860% N/A 18%

55 MPH Steady State: Emissions units are grams/mile

Bus Description NOx NMHC

CO2

(/100)1 CO

PM

(x10)1

NOx +

NMHC

Air 12 Diesel Control 14.50 0.34 9.87 0.91 1.18 14.84

Air 13 DFNG in DF Mode2 5.06 3.41 8.28 7.92 0.44 8.47

Air 14 DFNG in DF Mode 6.64 2.02 8.38 5.43 0.64 8.66

Avg. DFNG in DF Mode 5.85 2.71 8.33 6.68 0.54 8.56

Avg. % red. From DFNG engine 60% N/A 16% N/A 54% 42%

Avg. % incr. From DFNG engine N/A 697% N/A 634% N/A N/A

1. CO2 and PM values in the tables are 1/100 and 10 times actual values, respectively.

2. Air 13 NMHC estimated based on Air 13 THC times the ratio of NMHC/THC for Air 14.
18

Table 3. Emissions Test Results:

Dual-Fuel Engine in Diesel Mode versus Diesel Engine

EPA UDDC Schedule D: Emissions units are grams/mile

Bus Description NOx NMHC

CO2

(/100)1 CO

PM

(x10)1

NOx +

NMHC

Air 12 Diesel Control 19.90 0.57 20.18 3.59 3.68 20.47

Air 13 DFNG in Diesel Mode 19.32 0.45 19.98 3.55 2.03 19.77

Air 14 DFNG in Diesel Mode 19.29 0.50 19.93 3.77 2.23 19.79

Avg. DFNG engine in Diesel Mode 19.31 0.47 19.95 3.66 2.13 19.78

Avg. % red. from DFNG engine 3% 18% 1% N/A 42% 3%

Avg. % incr. from DFNG engine N/A N/A N/A 2% N/A N/A

WVU CBD: Emissions units are grams/mile

Bus Description NOx NMHC

CO2

(/100)1 CO

PM

(x10)1

NOx +

NMHC

Air 12 Diesel Control 22.41 1.19 25.71 4.03 4.90 23.60

Air 13 DFNG in Diesel Mode 22.15 1.00 24.98 3.98 3.28 23.15

Air 14 DFNG in Diesel Mode 22.98 1.01 25.14 4.02 3.51 23.99

Avg. DFNG engine in Diesel Mode 22.57 1.00 25.06 4.00 3.39 23.57

Avg. % red. from DFNG engine N/A 14% 3% 1% 31% 0%

Avg. % incr. from DFNG engine 1% N/A N/A N/A N/A N/A

55 MPH Steady State: Emissions units are grams/mile

Bus Description NOx NMHC

CO2

(/100)1 CO

PM

(x10)1

NOx +

NMHC

Air 12 Diesel Control 14.50 0.34 9.87 0.91 1.18 14.84

Air 13 DFNG in Diesel Mode 13.48 0.28 9.45 0.85 0.77 13.76

Air 14 DFNG in Diesel Mode 13.79 0.29 9.75 0.93 1.02 14.08

Avg. DFNG engine in Diesel Mode 13.64 0.28 9.60 0.89 0.89 13.92

Avg. % red. from DFNG engine 6% 18% 3% 2% 25% 6%

Avg. % incr. from DFNG engine N/A N/A N/A N/A N/A N/A

1. CO2 and PM values in the tables are 1/100 and 10 times actual values, respectively.
Project Economic Analysis

Fixed Cost Differences

The difference in fixed costs between the C-10 DFNG and the C-10 D was limited to the capital

costs associated with the conversion of the C-10 D engines to dual-fuel operation ($45,000/bus).

This price included all parts and labor to convert the base diesel engine to the dual-fuel

configuration, and to install the CNG cylinders and plumbing. The Caterpillar engine was $1,300

per bus less than the original engine specified for the buses, a Cummins M11. However, for the

purposes of this report, only the cost difference between the C-10 DFNG and the C-10 D engine

is presented. If the buses had not already been equipped with the Caterpillar C-10 diesel engine,

additional costs would have been incurred to remove the original engine and replace it with the

Caterpillar engine, and from the need to modify any engine accessories (i.e., transmission,

radiators, and charge air coolers).

Variable Cost Differences

Variable cost differences between the dual-fuel and diesel buses included fuel, maintenance,

repairs, and insurance. Based on discussions with the insurance provider for the Clean Air

Express buses, collision insurance was more for the dual-fuel buses because the buses cost more

(because of the CNG hardware, not because of the use of CNG).

Cost for maintaining the dual-fuel buses was less for oil changes, because oil change intervals

could be extended approximately 100% longer than for the diesel bus. The dual-fuel buses have

an added cost in the maintenance of the CNG fueling system. All other maintenance costs are

estimated to be the same.

Fuel costs were higher for the dual-fuel buses. Fuel costs are functions of the cost of the fuel and

the efficiency of the engine (i.e., miles/DEG). During the demonstration period, the diesel was

obtained at a wholesale rate averaging $0.80/DEG; the CNG was obtained at a retail rate

averaging $0.90/DEG. Assuming a 56% CNG of the fuel used/total fuel blend in the C-10 DFNG

engines, the cost of “blended” fuel averaged $0.856/DEG. These costs are based on actual

invoices from fuel purchases during the course of the demonstration period. The dual-fuel buses

also used more fuel, because they averaged only 5.34 miles/DEG; the diesel bus averaged 6.0

miles/DEG.

Labor charges associated with fueling were higher for the dual-fuel buses. Because the dual-fuel

buses have less range than the diesel bus, they must be fueled more often. Also, the dual-fuel

buses had to be driven to two separate stations to obtain CNG and diesel, thereby increasing the

total time needed obtain fuel.

Based on reliability of the C-10 DFNG engine during the course of the demonstration period, the

cost of repairing the C-10 DFNG engines was assumed to be the same as for the standard diesel

engine. Because of the limited duration of this demonstration period, we could not determine

19
whether the C-10 DFNG engines will require more or fewer repairs during the lives of the

engines.

A summary of the differential costs of operating the C-10 DFNG engine compared to the C-10 D

diesel engine is presented in a later section.

Potential Value of Emission Reduction Credits

The CEC requested that SBCAPCD evaluate the potential value of Emission Reduction Credits

(ERCs) that could be generated through use of the C-10 DFNG engine. ERCs, once certified, can

be sold on the open market to sources needing to “offset” their emissions increases. In 1998, the

median purchase price for NOx, reactive organic compounds (ROCs), PM10, SOx, and CO ERCs

in California was $10,925/ton, $4,932/ton, $10,000/ton, $10,411/ton and $2,509/ton,

respectively.3

 The potential value of ERCs generated from use of the C-10 DFNG engine was not

determined because:

• Determining the overall value of ERCs from using the C-10 DFNG engine is complicated by

the fact that the value of NOx and PM reductions may be affected by the potentially

significant increases in NMHC (a possible concern in ozone nonattainment areas) and CO

(a concern in CO nonattainment areas) emissions.

• The quantity of ERCs generated can vary greatly depending on annual engine use, emissions

test results (new versus replaced engine), remaining life of the replaced engine or vehicle, and

the proximity of the source generating the ERCs to the source needing the ERCs.

• The cost to produce ERCs (and thus, the profit from selling the ERCs) can also vary greatly

depending on repower costs, differences in new versus old engine operating costs, and air

district compliance costs (permitting, emissions testing, reporting).

Summary of Costs during Demonstration Period

Based on the actual costs incurred during the demonstration period, the C-10 DFNG equipped

buses cost $6,150 more per year, or about $0.20 more per mile, to operate than the C-10 D

equipped bus. Table 4 summarizes the operating cost differential between the C-10 DFNG and

C-10 D engines. Only cost differences between the two engines are listed: costs that were the

same for both engine types are not listed. In this analysis, diesel was purchased at a wholesale

rate; CNG was purchased at a retail rate.

Projected Costs Using Retail Diesel Prices and an On-Site CNG Station

The cost of operating the C-10 DFNG and C-10 D engines can vary greatly depending on the

fleet application. The financial benefits of using CNG are optimized in cases where fleet

operators obtain diesel fuel from commercial retailers, and CNG can be obtained at a

“wholesale” rate by using an onsite CNG station owned by the fleet operator. An onsite CNG

station can also be equipped with “time-fill” stations to fuel the vehicles overnight where they are

 

3 California Environmental Protection Agency, Air Resources Board, “Emission Reduction Offset Transaction Cost

Summary Report for 1998,” April 1999.

20
parked, thereby reducing, or even eliminating, the labor costs associated with CNG refueling.

Table 5 summarizes the operating cost differential between the C-10 DFNG and C-10 D engine,

assuming the operator pays retail rates for diesel fuel and obtains CNG via an onsite CNG

station, and assuming an 80% CNG substitution rate. All other costs are assumed to be the same

as for the actual demonstration period (see Fixed Cost Differences and Variable Cost Difference

in this section). Based on this analysis, a C-10 DFNG engine is projected to cost approximately

$0.40/mile to operate. This is about $0.12/mile more than the projected cost of operating a

C-10 D engine in a similar application. If the vehicle operator did not have to pay for the capital

costs to convert the vehicle ($0.15/mile) to dual-fuel operation, the C-10 DFNG engine could

actually cost $0.03/mile less to operate than a diesel engine. Table 5 represents the presumed

optimum cost scenario for CNG use. Presumably, actual cost differences will fall somewhere

between the values presented in Tables 4 and 5. All fleet operators should assess the cost

differences based on their own specific application.

Table 4.

Actual Annual Operating Cost Differences during Demonstration Period

Item Description C-10 D C-10 DFNG Reference

Annualized Capital Cost $ 0 $ 4,500 Appn 5: Section 1.1

Fuel $ 4,000 $ 4,810 Appn 5: Section 1.2

Fueling Labor $ 342 $ 814 Appn 5: Section 1.3

Insurance $ 2,100 $ 2,370 Appn 5: Section 1.4

Maintenance—CNG System $ 0 $ 298 Appn 5: Section 1.5

Repairs $ 0 $ 0 Appn 5: Section 1.6

Maintenance—Oil Changes $ 400 $ 200 Appn 5: Section 1.7

Emission Reduction Credits $ 0 $ 0 Report Section 5.3

Total Cost per Year: $ 6,842 $ 12,992 Basis: 30,000 mi/yr

Cost per Mile: $ 0.23 $ 0.43

Incremental Cost for DFNG: $ 6,150/year or $ 0.20 mile

21
Table 5.

Projected Annual Operating Cost Differences Using Retail Diesel

and an On-Site CNG Station

Item Description C-10 D C-10 DFNG Reference

Annualized Capital Cost $ 0 $ 4,500 Appn. 5: Section 1.1

Fuel $ 5,500 $ 4,494 Appn 5: Sec. 1.2/2.1

Fueling Labor $ 342 $ 77 Appn 5: Sec. 1.3/2.2

Insurance $ 2,100 $ 2,370 Appn 5: Section 1.4

Maintenance—CNG System $ 0 $ 298 Appn 5: Section 1.5

Repairs $ 0 $ 0 Appn 5: Section 1.6

Maintenance—Oil Changes $ 400 $ 200 Appn 5: Section 1.7

Emission Reduction Credits $ 0 $ 0 Report Section 5.3

Total Cost per Year: $ 8,342 $ 11,939 Basis: 30,000 mi/yr

Cost per Mile: $ 0.28 $ 0.40

Incremental Cost for DFNG: $ 3,597 or $ 0.12/mile

Lessons Learned

Altoona Testing

Initially, the project team members tried to have MCI provide the buses equipped with the dualfuel components as an OEM installation. We envisioned that this would minimize the number of

purchase orders and contracts that would have to be issued to secure the buses. However, we

soon discovered that the Federal Transit Administration requires that all new over-the-road

chassis/engine combinations complete rigorous performance testing in Altoona, Maine. Having

the OEM deliver the bus in the dual-fuel configuration would have certainly triggered the

requirement for this testing. By having the buses delivered with the standard diesel engines, and

then sending them to be converted to dual-fuel operation as used buses, the Altoona testing was

not necessary.

Encouraging Bus Operators to Use CNG

Because the C-10 DFNG buses could operate satisfactorily on diesel fuel on the relatively flat

terrain characteristic of the routes, some oversight was necessary to ensure that the bus operator

consistently fueled the buses with CNG. If the buses had performed less satisfactorily in dieselonly mode, less oversight would have been necessary to ensure consistent CNG use (i.e., the

process would have been self-regulating).

22
Conclusions and Recommendations

Conclusions

The following conclusions are based on the performance of the three C-10 DFNG and one

C-10 D engines used in the Clean Air Express buses during the 12-month demonstration period.

Performance

• The performance and reliability of the C-10 DFNG engines were comparable to the C-10 D

engine. This conclusion may need to be reassessed after more prolonged CNG use and higher

mileage accumulation.

• When in dual-fuel mode, the C-10 DFNG engines used approximately 86% CNG and 14%

diesel. At an 86% CNG substitution rate, the C-10 DFNG engines averaged about 4.8 miles/

DEG, which is about 20% less than the C-10 D average of 6 miles/DEG.

• Averaged during the entire demonstration period, the C-10 DFNG engines operated about

57% of the time in dual fuel mode, and 43% of the time in diesel mode. The C-10 DFNG

engines averaged 5.34 miles/DEG overall, which is about 11% less than the C-10 D average

of 6.0 miles/DEG.

• When operating the C-10 DFNG engine in diesel mode, the reduced-power-mode feature

provided only minimal incentive for drivers to refuel with CNG. The C-10 DFNG engines

performed satisfactorily, even when fully loaded, in the reduced power mode.

• The lower-than-expected CNG substitution rate was the result of:

 Occasional failure of the vehicle operator to fuel the buses with CNG.

 Problems with the C-10 DFNG engine computer operating software.

 Breakdowns of the CNG refueling station.

• The C-10 DFNG-engine-equipped buses cost about $0.20/mile more to operate than the

C-10 D-engine-equipped bus.

Emissions

• Overall, the C-10 DFNG engine operating in the dual-fuel mode had lower NOx, CO2, and

PM emissions and higher CO and NMHC emissions than the C-10 D engine.

• The C-10 DFNG engine had higher NOx and NMHC emissions (combined) than the C-10 D

for the both the EPA UDDC and WVU CBD drive cycles. The C-10 DFNG engine had lower

NOx and NMHC emissions (combined) than the C-10 D for the 55 MPH Steady State drive

cycle.

23
• The C-10 DFNG engine demonstrated a greater percentage reduction in NOx emissions than

the C-10 D in the 55 MPH Steady-State drive cycle than in both the EPA UDDC and WVU

CBD drive cycles. This may be due to the C-10 DFNG engine having relatively lower NOx

emissions, or to the C-10 D having relatively higher NOx emissions (as would be expected if

the C-10 D engine computer was equipped with a defeat device), when operated in the

steady-state mode.

• When operated in the diesel mode, the C-10 DFNG engine had lower PM and NMHC

emissions than the C-10 D engine. Emissions of NOx, CO2, and CO from the C-10 DFNG

and C-10 D were similar when the engines were operated on diesel.

Recommendations

• Additional emissions testing may be warranted to:

 Verify the differences in NMHC emissions between the C-10 DFNG and C-10 D.

 Compare NOx emissions from the C-10 DFNG with those of a C-10 D engine that is not

equipped with a defeat device.

 Verify that the C-10 DFNG, when operating in diesel mode, has lower NMHC and PM

emissions than the C-10 D.

• Caterpillar should improve and refine the C-10 DFNG engine operating computer to increase

the overall CNG substitution rate under typical driving conditions.

• Differences between the C-10 DFNG and C-10 D operating costs (e.g., costs for dual-fuel

conversion, fuel, fueling labor, insurance, and engine repairs and maintenance) can vary

greatly depending on the fleet application. Cost differences between the C-10 DFNG and

C-10 D should be evaluated in detail for each specific application.

• Ongoing oversight of the vehicle operator may be needed if maximum CNG use is desired.

Alternatively, the power available when the C-10 DFNG engine is used in diesel-only mode

should be reduced to maximize the incentive for vehicle operators to consistently use CNG.

• A backup CNG station should be available to ensure maximum CNG use.

• If the C-10 DFNG engine is to be used for emissions mitigation purposes (e.g., to generate

ERCs), air districts should consider requiring that the C-10 DFNG engines undergo regular

emissions testing to verify any assumptions made on NOx and PM reductions and NMHC and

CO increases. Emissions testing should speciate hydrocarbon emissions to identify the nonmethane/non-ethane portion of the exhaust.

24
Appendix A:

Detailed Bus Specifications
A-2

Bus Specifications

unique alphanumeric code for each vehicle AIR 11 AIR 12 AIR 13 AIR 14

hicle identification number 1M8PDMVA6- 1M8PDMVA6- 1M8PDMVA6- 1M8PDMVA6-

WP050429 WP050430 WP050431 WP050432

hicle Identification number used by fleet 1729 1730 1731 1732

me of vehicle manufacturer MCI

uck model number 102DL3

ar vehicle was manufactured 1997

te vehicle was put into service by fleet 1/19/98

eage on vehicle at the start of the fleet demonstration 2568 2490 2589 2563

pe of activity vehicle is used for (Code 1 from VMRSH)

pe of optional equipment installed on vehicle

me of body manufacturer MCI

pe of body attached to cab (Code 48 from VMRSH)

rial number of the engine 2PN06582 2PN06563 2PN06580 2PN06570

he engine OEM or a retrofit? retrofit

me of engine manufacturer Caterpiller

gine model number C10

gine Configuration Code (Code 35 from VMRSH)

gine size in cubic Inches 629

mber of cylinders 6

ar engine was manufactured 1997

he engine 2 cycle or 4 cycle? 4 cycle

mpression ratio 16

pe of Ignition aids used none

he engine configuration EPA certified? no

ted maximum brake horsepower of engine 350

m at rated maximum brake horsepower 1500 - 2100

ted maximum torque of engine 1050

m at rated maximum torque 1200 - 1500

 capacity In quarts 30

es the engine have a blower? no

es the engine have a turbocharger? yes
A-3

Bus Specifications, continued

ernative fuel tank(s) model number A15.08436

mber of alternative fuel tanks 4

mber of diesel tanks 1

tal useful alternative fuel in tank(s) 48

its used for diesel fuel diesel fuel tank(s) useful volume U.S. gallons

its used for diesel fuel tank(s) useful volume U.S. gallons

hat type of fuel is engine designed for? CNG/Diesel

pe of additives used in diesel fuel nonepe of additives used in alternative fuel none

r liquid fuel engines, are the inj. mech. or electr. controlled electronic

tal useful diesel fuel in tank(s) 182 gallons

ernative fuel maximum working pressure in psi 3,600

me of alternative fuel tank(s) manufacturer CNG Cylinder

ernative fuel tank(s) empty weight 1,384

its used for alternative fuel tank(s) empty weight pounds

me of liquid fuel injector manufacturer Caterpillar

uid fuel injector model number 116-5414

mber of liquid fuel injectors 6

me of liquid fuel filter manufacturer Caterpillar

uid fuel filter model number 1Ro749

r gaseous fuel engines, Is it injection or fumigation? Injection

es the engine use an air intake throttle? no

me of diesel fuel tank(s) manufacturer MCI

esel fuel tank(s) model number 9L-6-108

esel fuel tank(s) empty weight 80

its used for diesel fuel tank(s) empty weight pounds

he gas fuel system OEM or retrofit? retrofit
Bus Specifications, continued

me of transmission manufacturer Allison

ansmission model number B-500 World

ansmission year of manufacturer 1997

pe of Transmission (Code 7 from VMRSH)

mber of forward speeds

6

mber of reverse speeds 1

pe of axle configuration (Code 3 from VMRSH)

e front weight 14,000e of front tire 12R22.5e of rear tire 12R22.5

me of drive axle manufacturer (from VMRSH) Rockwell

ve axle model number 61143HX 205

ar axle configuration (Code 37 from VMRSH)

tup or rear axle configuration (Code 36 from VMRSH)

w axle ratio none

gh axle ratio 4.56:1

tal gross vehicle weight in pounds 46,000

tal weight with the truck in curb weight configuration 48,000

rque converter ratio NA

ngth of wheelbase 279 inches

es the vehicle have a catalytic converter? Y or N

N

me of catalytic converter manufacturer -na

del number of the catalytic converter -na

es the vehicle have a diesel particulate trap? Y or N

N

me of the particulate trap manufacturer -na

del number of the particulate trap -na

pe of trap regeneration process -na

rticulate trap configuration -na

mber of particulate trap elements -na

eight of the particulate trap system -naA-4
Appendix B:

Detailed Bus Operating Data
B-1

Bus No. AIR 11 ( Dual Fuel )

Total Total Dual Fuel Mode Total

Reading Engine Dual-fuel Miles CNG Diesel Diesel

Month Date Hours1 Hours1 Traveled (DEG)1 (DEG)1 (DEG)2

February 3/2/98 45.1 23.8 2792 149.7 37.0 281.1

March 4/1/98 82.8 55.7 2702 358.7 55.9 189.5

April 5/4/98 88.1 61.3 2853 404.1 61.4 209.8

May 6/1/98 74.0 50.2 2419 339.2 49.7 218.0

June 7/1/98 79.0 44.8 2596 286.2 44.7 231.6

July 7/31/98 74.1 45.6 2437 272.5 46.3 178.4

August 9/2/98 83.1 4.7 2533 21.4 4.6 400.4

September 10/1/98 71.6 28.3 2494 192.6 29.6 415.5

October 11/2/98 79.5 58.2 2757 398.1 61.6 182.5

November 12/2/98 72.0 34.6 2272 215.0 34.6 325.8

December 12/31/98 93.0 41.1 3018 273.6 44.4 274.3

January 1/29/99 66.8 44.1 2831 279.9 46.0 178.5

Total 909.1 492.4 31704 3191.0 515.8 3085.4

Bus No. AIR 12 ( Diesel )

Total Total Total

Reading Engine Dual-Fuel Miles CNG Used Diesel Diesel

Month Date Hours Hours Traveled (DEG) (DEG) (DEG)2

February 3/2/98 NA NA 2059 NA NA 442.0

March 4/1/98 NA NA 2622 NA NA 374.6

April 5/1/98 NA NA 2534 NA NA 499.0

May 6/1/98 NA NA 2179 NA NA 349.6

June 7/1/98 NA NA 2506 NA NA 445.0

July 7/31/98 NA NA 2374 NA NA 430.3

August 9/1/98 NA NA 2805 NA NA 438.6

September 10/1/98 NA NA 2273 NA NA 377.9

October 11/2/98 NA NA 2679 NA NA 379.5

November 12/2/98 NA NA 2335 NA NA 295.0

December 12/31/98 NA NA 2503 NA NA 448.8

January (*) 1/29/99 NA NA 574 NA NA 99.7

Total 27443 4580

* This bus was taken out of service of January 11 for emissions testing and DF conversion.

1. This information was downloaded directly from the C-10 DFNG engine computer.

2. This information is based on operator fueling logs.
Bus No. AIR 13 ( Dual Fuel )

Total Total Dual-Fuel Mode Total

Reading Engine Dual-Fuel Miles CNG Diesel Diesel

Month Date Hours1 Hours1 Traveled (DEG)1 (DEG)1 (DEG)2

February 3/2/98 41.5 29.3 2364 170.6 41.3 345.0

March 4/1/98 79.8 58.7 2995 393.8 58.0 99.3

April 5/4/98 77.7 55.9 2775 407.1 56.3 198.2

May 6/1/98 68.9 47.1 2525 342.8 48.1 99.0

June * 7/1/98 53.8 6.0 2864 20.8 5.5 310.5

July 7/31/98 79.2 19.0 2753 126.2 18.8 423.9

August 9/2/98 83.6 44.4 3021 311.4 44.1 222.5

September 10/1/98 75.5 36.2 2632 262.2 38.9 260.8

October 11/2/98 86.9 65.2 2975 469.5 69.1 90.8

November 12/1/98 72.0 32.1 2208 211.0 30.6 240.0

December 12/31/98 78.1 49.9 3250 214.0 33.4 200.8

January 1/1/99 69.4 39.2 2238 262.1 41.4 176.1

Total 866.4 483.0 32600 3191.5 485.5 2666.9

* The engine computer was reset during CNG repairs, some of the month's data were lost.

Bus No. AIR 14 (Dual Fuel)

Total Total Dual-Fuel Mode Total

Reading Engine Dual-Fuel Miles CNG Diesel Diesel

Month Date Hours1 Hours1 Traveled (DEG)1 (DEG)1 (DEG)2

February 3/1/98 45.1 13.5 2267 77.5 21 391

March 4/1/98 80.8 43.6 2696 278.0 39.7 111.0

April 5/4/98 81.5 59.2 2690 377.9 60.0 89.7

May 6/1/98 70.0 49.7 2273 302.1 48.4 219.0

June 7/1/98 83.3 47.7 2642 306.0 46.2 207.1

July 7/31/98 77.4 44.8 2521 281.6 42.4 193.5

August 9/2/98 84.0 64.1 2739 398.4 60.3 112.0

September 10/1/98 73.5 49.6 2390 309.9 48.2 159.0

October 11/2/98 84.3 63.4 2727 381.1 62.0 164.4

November (*) 12/1/98 182.0

December 12/31/98 153.7 85.0 4988 487.5 81.6 191.0

January 1/29/99 73.3 46.4 1991 236.5 42.9 73.9

Total 906.9 567.0 29924 3436.6 552.7 2093.6

* Unable to download data due to faulty connection. November data included with December's.

1. This information was downloaded directly from the C-10 DFNG engine computer.

2. This information is based on operator fueling logs.

B-2
Appendix C:

Emissions Test Results
C-1

SUMMARY

EMISSIONS TESTING FACILITY

LOS ANGELES COUNTY

METROPOLITAN TRANSPORTATION

AUTHORITY

TEST BACKGROUND

Dynamometer :- Chassis (Road Load Model#57)

Vehicle I.D. :- Clean Air Express "Air 12"

Fuel :- Diesel (dedicated)

Engine Type :- Caterpillar C10 D

Vehicle Type :- MCI 45 ft., 55 passenger

Test Date :- 1/13/99

Test Inertia :- 38,555 lbs. (34,280 tare + 1/2 pass. load)

Eng. Mileage :- 030,276 miles

Project Description :- California Energy Commission

TEST DATA EPA UDDC SCHEDULE "D"

Test I.D. THC CO NOx CO2 PM Economy CH4

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile

T01955 0.565 3.59 19.90 2018.46 0.3684 5.02 nm

TEST DATA CYCLE:WEST VIRGINIA UNIV. CBD

Test I.D. THC CO NOx CO2 PM Economy CH4

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile

T01957 1.145 3.96 22.30 2559.99 0.4702 3.96 nm

T01958 1.181 4.05 22.59 2587.98 0.4904 3.92 nm

T01959 1.241 4.09 22.34 2565.63 0.5083 3.95 nm

Mean 1.189 4.03 22.41 2571.20 0.4896 3.94

Std. Dev. 0.05 0.07 0.16 14.80 0.02 0.02

TEST DATA CYCLE STEADY STATE:

Test I.D. THC CO NOx CO2 PM Economy CH4

T01960 0.0014 0.0044 0.041 2.05 0.00018 na nm

T01961 0.336 0.91 14.50 987.04 0.1181 10.28 nm

Comments: T01960 - Idle test, emissions data reported in grams/second.

T01961 – 55 MPH test, emissions data reported in grams/mile, economy in miles/gallon.

Legend: na = not applicable nm = not measured
C-2

SUMMARY

EMISSIONS TESTING FACILITY

LOS ANGELES COUNTY

METROPOLITAN TRANSPORTATION

AUTHORITY

TEST BACKGROUND

Dynamometer :- Chassis (Road Load Model #57)

Vehicle I.D. :- Clean Air Express Bus "Air 13"

Fuel :- CNG mode

Engine Type :- Caterpillar C10 DNFG

Vehicle Type :- MCI 45 ft., 55 passenger

Test Date :- 1/20/99

Test Inertia :- 38,555 lbs. (34,280 tare + 1/2 pass. load)

Eng. Mileage :- 034,556 miles

Project Description :- California Energy Commission

TEST DATA CYCLE: EPA UDDC SCHEDULE "D"

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile gm/mile

T01964 63.552 29.11 12.78 1638.02 0.1042 5.40 57.374 12.075

TEST DATA CYCLE: WEST VIRGINIA UNIV. CBD

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile gm/mile

T01966 91.940 44.15 15.25 2222.16 0.1761 3.94 67.276 14.325

T01967 84.206 41.67 15.21 2192.14 0.1777 4.03 62.709 13.327

T01968 89.346 43.14 15.16 2183.59 0.1728 4.01 67.512 14.322

Mean 88.497 42.99 15.21 2199.30 0.1755 3.99 65.83 13.99

Std. Dev. 3.94 1.25 0.05 20.26 0.00 0.05 2.71 0.58

TEST DATA CYCLE:STEADY STATE

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

T01969 0.0013 0.0059 0.026 1.96 0.00016 na nm nm

T01970 17.128 7.92 5.06 828.26 0.0442 11.37 nm nm

Comments: T01969 - Idle test, emissions data reported in grams/second.

T01970 - 55mph cruise test, emissions data reported in grams/mile, economy in miles/gallon.

Legend: na = not applicable nm = not measured
C-3

SUMMARY

EMISSIONS TESTING FACILITY

LOS ANGELES COUNTY

METROPOLITAN TRANSPORTATION

AUTHORITY

TEST BACKGROUND

Dynamometer :- Chassis (Road Load Model #57)

Vehicle I.D. :- Clean Air Express Bus "Air 13"

Fuel :- Diesel mode

Engine Type :- Caterpillar C10 DFNG

Vehicle Type :- MCI 45 ft., 55 passenger

Test Date :- 1/21/99

Test

Inertia

:- 38,555 lbs. (34,280 tare + 1/2 pass. load)

Eng. Mileage :- 034,556 miles

Project :- California Energy Commission

TEST DATA CYCLE: EPA UDDC SCHEDULE "D"

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile gm/mile

T01972 0.449 3.55 19.32 1997.84 0.2034 5.07 nm nm

TEST DATA CYCLE: WEST VIRGINIA UNIV. CBD

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile gm/mile

T01974 0.979 4.02 22.31 2518.64 0.3193 4.02 nm nm

T01975 0.994 3.93 21.98 2488.14 0.3310 4.07 nm nm

T01976 1.013 3.98 22.15 2487.75 0.3326 4.07 nm nm

Mean 0.995 3.98 22.15 2498.18 0.3276 4.05

Std. Dev. 0.02 0.05 0.17 17.72 0.01 0.03

TEST DATA CYCLE: STEADY STATE

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

T01977 0.0013 0.0044 0.040 2.02 0.00024 na nm nm

T01978 0.277 0.85 13.48 945.16 0.0774 10.74 nm nm

Comments: T01977 - Idle test, emissions data reported in grams/second.

T01978 - 55 MPH test, emissions data reported in grams/mile, economy is miles/gallon.

Legend: na = not applicable, nm = not measured
C-4

SUMMARY

EMISSIONS TESTING FACILITY

LOS ANGELES COUNTY

METROPOLITAN TRANSPORTATION

AUTHORITY

TEST BACKGROUND

Dynamometer :- Chassis (Road Load Model #57)

Vehicle I.D. :- Clean Air Express Bus "Air 14"

Fuel :- CNG mode

Engine

Type

:- Caterpillar C10 DFNG

Vehicle Type :- MCI 45 ft., 55 passenger

Test Date :- 1/27/99

Test Inertia :- 38,555 lbs. (34,280 tare + 1/2 pass. load)

Eng. Mileage :- 032,598 miles

Project :- California Energy Commission

TEST DATA CYCLE: EPA UDDC SCHEDULE "D"

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile gm/mile

T01990 43.906 24.96 14.58 1642.59 0.1568 5.59 40.588 8.646

TEST DATA CYCLE: WEST VIRGINIA UNIV. CBD

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile gm/mile

T01994 63.213 36.08 17.33 2226.56 0.2389 4.10 43.422 9.296

T01995 54.994 34.32 17.63 2224.82 0.2394 4.15 41.976 9.033

T01996 52.173 32.79 17.58 2218.65 0.2372 4.18 38.493 8.357

Mean 56.793 34.40 17.51 2223.34 0.2385 4.14 41.30 8.90

Std. Dev. 5.74 1.65 0.16 4.16 0.00 0.04 2.53 0.48

TEST DATA CYCLE: STEADY STATE

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

T01991 0.0021 0.0058 0.026 1.93 0.00031 na 0.0013 0.00078

T01992 10.128 5.43 6.64 837.56 0.0635 11.58 9.171 2.017

Comments: T01991 - Idle test, emissions data reported in grams/second.

T01992 - 55 MPH test, emissions data reported in grams/mile, economy in miles/gallon.

Legend: na = not applicable nm = not measured
C-5

SUMMARY

EMISSIONS TESTING FACILITY

LOS ANGELES COUNTY

METROPOLITAN TRANSPORTATION

AUTHORITY

TEST BACKGROUND

Dynamometer :- Chassis (Road Load Model #57)

Vehicle I.D. :- Clean Air Express Bus "Air 14"

Fuel :- Diesel mode

Engine Type :- Caterpillar C10 DFNG

Vehicle Type :- MCI 45 ft., 55 passenger

Test

Date

:- 1/26/99

Test Inertia :- 38,555 lbs. (34,280 tare + 1/2 pass. load)

Eng. Mileage :- 032,598 miles

Project :- California Energy Commission

TEST DATA CYCLE: EPA UDDC SCHEDULE "D"

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile gm/mile

T01981 0.498 3.77 19.29 1992.51 0.2233 5.09 nm nm

TEST DATA CYCLE: WEST VIRGINIA UNIV. CBD

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

(gm/mile) (gm/mile) (gm/mile) (gm/mile) (gm/mile) (mpg) gm/mile gm/mile

T01983 0.994 4.05 22.74 2503.11 0.3494 4.05 nm nm

T01984 1.023 4.03 23.13 2525.59 0.3428 4.01 nm nm

T01985 1.015 3.97 23.07 2514.02 0.3599 4.03 nm nm

Mean 1.011 4.02 22.98 2514.24 0.3507 4.03

Std. Dev. 0.01 0.04 0.21 11.24 0.01 0.02

TEST DATA CYCLE: STEADY STATE

Test I.D. THC CO NOx CO2 PM Economy CH4 NMHC

T01986 0.0013 0.0046 0.041 2.33 0.00021 na nm nm

T01987 0.292 0.93 13.79 974.61 0.1015 10.41 nm nm

Comment T01977 - Idle test, emissions data reported in grams/second.

T01978 – 55 MPH test, emissions data reported in grams/mile, economy in miles/gallon.

Legend: na = not applicable, nm = not measured
Appendix D:

Caterpillar C-10 DFNG and D

Performance Ratings
D-1

1997 C-10 DFNG and C-10 D

Torque (ft-lb) versus RPM

600

700

800

900

1000

1100

1200

1300

1000 1200 1400 1600 1800 2000 2200

Engine Speed (RPM)

Torque (ft-lb)

C-10 DFNG in DF m Mode

C-10 D

C-10 DFNG in Diesel Mode

Caterpillar C-10 DFNG and C-10 D 

Horsepower (bhp) versus RPM

150

200

250

300

350

400

1000 1200 1400 1600 1800 2000 2200

Engine Speed (RPM)

Power (bhp)

C-10 DFNG in DF Mode

C-10 D

C-10 DFNG in Diesel Mode
Appendix E:

Differential Cost Analysis References
E-1

Actual Costs During Demonstration Period

Annualized Capital Costs

The dual-fuel conversion costs were amortized over the expected life of the engines (12 years).

These conversion costs are representative of retrofitting a C-10 D equipped vehicle to dual-fuel

operation: if the engine has to be removed and replaced with a C-10 D engine before conversion,

total conversion costs would be considerably higher. The amortization formula uses a capital

recovery factor that reflects the time value of the funds used for the conversion. This

methodology is consistent with that recommended by CARB for the Carl Moyer Program.

C-10 DFNG Annualized Capital Cost (ACC) ($/yr) = CC * CRF

Where: CC = Conversion Costs = $45,000/bus

CRF = Capital Recovery Costs = [(1 + i)

n

 * i] / [(1 + i)

n

 - 1]

i = Interest Rate = 3%

n = Project Life = 12

Then: ACC = $45,000 * 0.10 = $4,500

C-10 D ACC = $0

Fuel Costs

The average cost of CNG fuel during the 12-month demonstration was $0.90/DEG (retail price);

the cost for diesel was $0.80/DEG (wholesale price). Using the 56% average CNG use actually

achieved in this demonstration, the “mixed” cost of CNG and diesel used in the C-10 DFNG

engine is $0.856/DEG.

C-10 DFNG fuel costs = 30,000 miles/yr/5.34 miles/DEG * $0.856/DEG

= $4,810

C-10 D fuel costs = 30,000 miles/yr/6.00 miles/DEG * $0.80/DEG

= $4,000

Fueling Labor Costs

Assumptions

• A dual-fuel bus requires 30 minutes (at a driver cost of $20/h) to fuel the bus with both diesel

and CNG fuel ($10/fillup). This includes driving time to/from the diesel and CNG stations.

Although the dual-fuel buses obtain less fuel per fillup than the diesel bus, the time per fillup

was assumed to be the same because the dual-fuel buses had to obtain both diesel and CNG,

and the CNG station was further away than the diesel station.

• For the dual fuel bus, the CNG and diesel tanks are fueled when the CNG tanks are 80%

empty, and the CNG-to-diesel substitution rate is 56% (max. CNG capacity 48 DEG: each

dual-fuel fillup obtains 38 DEG (80% of 48) and 31 DEGs of diesel).
E-2

• The driver needs 30 minutes at a rate of $20/h to fill a diesel bus ($10/fillup). This includes

driving time to/from the diesel station.

• The diesel tank is filled when the tank is 80% empty (maximum capacity 182 DEG:

80% of 182 = 146 DEG).

C-10 DFNG fueling labor costs = (DFL/CNG-D/fill-up) * (miles/yr/MPGDF)

Where:

DFL = dual fuel labor cost = $10/fillup

CNG-D/fillup = DEG/fill-up for DF engine = 38 DEG CNG + 31 DEG diesel (56% CNG ratio)

= 69 DEG total

mi/yr = 30,000 miles/year

MPGDF = miles/DEG for dual fuel engine = 5.34 miles/DEG

 

Then:

C-10 DFNG fueling labor costs = ($10/fill-up/69 DEG/fillup) * (30,000 miles/yr/

5.34 mi/DEG) = $814

C-10 D Fueling labor costs = (DL/D/fill-up) * (miles/yr/MPGD)

Where:

DL = diesel fuel labor cost = $10/fill-up

D/fillup = DEG/fillup for diesel engine = 182 * 0.8 = 146 DEG

mi/yr = 30,000 miles/year

MPGD = miles/DEG for diesel engine = 6.0 mi/DEG

 

Then:

C-10 D Fueling Labor Costs = ($10/fill-up/146 DEG/fill-up) / (30,000 miles/yr/

6.0 miles/DEG = $342

Insurance Costs

The following insurance quotes were obtained from Lancer Insurance Company:

Deductible Cost

$10,000 0.006 * insured value

$ 5,000 0.012 * insured value

$ 1,000 0.015 * insured value

Using the value quoted for a $10,000 deductible:

C-10 DFNG Bus Insurance Cost = $395,000 * 0.06 = $2,370

C-10 D Bus Insurance Costs = $350,000 * 0.06 = $2,100
E-3

Maintenance – CNG System

Costs for maintaining the CNG were provided by Caterpillar and are included in this appendix.

Costs were estimated for a 150,000-mile cycle to include all recurring maintenance costs.

Bus Miles Service Description Charge

15,000 15,000-mile service $110

30,000 15,000-mile service $110

45,000 45,000-mile service $155

60,000 15,000-mile service $110

75,000 15,000-mile service $110

90,000 45,000-mile service $155

105,000 15,000-mile service $110

120,000 15,000-mile service $110

135,000 45,000-mile service $155

150,000 150,000-mile service $165

Total cost per 150,000 miles = $1,490

Prorated cost for 30,000 miles = $298

There are no such costs for the C-10 D engine.

Repair Costs

Repairs on the C-10 DFNG engine were estimated to be the same as that of the C-10 D engine.

Maintenance Costs – Oil Changes

Oil changes for the C-10 DFNG engine were assumed to be needed every 15,000 miles, versus

7,500 miles for the C-10 D. The cost of each oil change was estimated by the Clean Air Express

operator to be about $100. Thus:

C-10 DFNG Oil Change Costs = 30,000 miles/yr/15,000 miles/change * $100/change

 = $200

C-10 DFNG Oil Change Costs = 30,000 miles/yr / 7,500 miles/change * $100/change

 = $400
E-4

Projected Costs using Retail Diesel Rates

and an Onsite CNG Station

Fuel Costs

The average retail cost per gallon of diesel fuel for the West Coast Region was estimated at

$1.10.1

 Based on discussions with Mr. Ron Smith (Southern California Gas Company), a

“ballpark” reasonable cost estimate for producing CNG at a fleet owner-owned onsite CNG

station was estimated at about $0.75/DEG. This price includes capital costs for the equipment,

electrical costs for compressor operation, pipeline natural gas costs, and maintenance station

costs. Actual costs can be higher or lower than this estimate depending on the CNG throughput,

utility costs, and type of station purchased. Assuming the Caterpillar technology can be refined

to achieved an 80% average CNG substitution rate, the “mixed” cost of CNG and diesel for the

C-10DFNG engine would be $0.80/DEG (0.2 *$1.10/DEG + 0.8 *$0.74/DEG).

C-10 DFNG fuel costs = 30,000 miles/yr/5.34 miles/DEG * $0.80/DEG

 = $4,494

C-10 D fuel costs = 30,000 miles/yr / 6 miles/ DEG * $1.10/DEG

 = $5,500

Fueling Labor Costs

Assumptions

• For a dual-fuel bus, CNG fueling takes place overnight (“time-filled”) where the vehicles are

parked overnight (i.e., there is no labor cost associated with CNG fueling). Diesel fueling for

the dual-fuel bus takes 30 minutes at a rate of $20/h (i.e., $10/fillup). This includes driving

time to and from the diesel station.

• Diesel has to be obtained less often for the dual-fuel bus because the bus runs on a

combination of CNG and diesel. The CNG-to-diesel substitution rate is 80%.

• The driver needs 30 minutes at a rate of $20/h to fill a diesel bus ($10/fillup). This includes

driving time to and from the diesel station.

• The diesel tanks on diesel and dual-fuel buses are fueled to completely full whenever they

are 80% empty (max. capacity 182 DEG; 80% of 182 DEG = 146 DEG). 

 

1

 National Energy Information Center, “On-Highway Diesel Fuel Price Survey,” for period from 4/13/98–4/5/99.
E-5

C-10 DFNG fueling labor costs = (DFL / D/fill-up) * (miles/yr/MPGDF)

Where:

DFL = dual fuel labor cost = $10/fill-up

D/fill-up = effective DEG per diesel-fill-up for DF engine = 146 DEG diesel + 584 DEG CNG 

= 730 DEG (80% CNG ratio)

mi/yr = 30,000 miles/yr

MPGD = miles/DEG for dual-fuel engine = 5.34 miles/DEG

 

Then:

C-10 DFNG fueling labor costs = ($10/fill-up / 730 DEG/fill-up) * (30,000 mi/yr /

5.34 mi/DEG = $77

C-10 D fueling labor costs = (DL / D/fill-up) * (miles/yr / MPGD)

Where:

DL = diesel fuel labor cost = $10/fill-up

D/fillup = DEG/fill-up for diesel engine = 182 * 0.8 = 146 DEG

mi/yr = 30,000 miles/year

MPGD = miles/DEG for diesel engine = 6.0 miles/DEG

 

Then:

C-10 D fueling labor costs = ($10/fill-up / 146 DEG/fill-up) / (30,000 miles/yr/6.0 miles/

DEG = $342
E-6

Dual-Fuel Engine – C-10 Engine (CNG Only)

(Earlier Model Fuel Management Module)

Maintenance Intervals/Customer Pricing

Recommended Service Interval Suggested List Price

Every 10,000 miles

Drain Coalescing Filter By Customer

Every 15,000 miles

Replace Coalescing Filter

Clean Last-hance Filter

Inspect Natural Gas Connections for Leaks

$110

Part # 3000072

Requires 1 hour labor ($70/h)

Every 45,000 miles

Replace Coalescing Filter

Replace Last-hance Filter

Inspect Natural Gas Connections for Leaks

$155

Part # 3000072

Part # 902112-1 (1/2" line size)

Requires 1 hour labor ($70/h)

Every 150,000 miles

Clean Natural Gas Injectors

Replace Injector Seals

Replace Coalescing Filter

Clean Last-hance Filter

Inspect Natural Gas Connections for Leaks

$365

Part # 3000072

Requires 4 hours labor ($70/h)

Parts Pricing

Part Number Description Customer List Price

3000072 Coalescing Filter $40.00

902112-1 Last-Chance Filter $45.00

Please verify the Fuel Management Module type with your Caterpillar Dealer prior to placing

filter order.

(pricing effective October 1998)
REPORT DOCUMENTATION PAGE Form Approved

OMB NO. 0704-0188

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 this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

January 2000

3. REPORT TYPE AND DATES COVERED

Subcontract report

4. TITLE AND SUBTITLE

Demonstration of Caterpillar C-10 Dual-Fuel Engines in MCI 102DL3 Commuter Buses

6. AUTHOR(S)

California Energy Commission (CEC)

Santa Barbara County Air Pollution Control District

5. FUNDING NUMBERS

C: ACI-6-15702-01

TA: FU913410

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

CEC, 1516 9th Street, Sacramento, CA, 95814

Santa Barbara County Air Pollution Control District, 26 Castilian Drive, B-23,

Goleta, CA, 93117

8. PERFORMING ORGANIZATION

REPORT NUMBER

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

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401-3393

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NREL/SR-540-26758

11. SUPPLEMENTARY NOTES

NREL Technical Monitor: Paul Norton

12a. DISTRIBUTION/AVAILABILITY STATEMENT

National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road

Springfield, VA 22161

12b. DISTRIBUTION CODE

1504

13. ABSTRACT (Maximum 200 words)

The purpose of this program was to demonstrate the Caterpillar C-10 Dual-Fuel Natural Gas (DFNG) engine in an over-theroad bus application. Three new Motor Coach Industries (MCI) 102DL3 buses, equipped with Caterpillar C-10 DFNG engines,

and one bus, equipped with a Caterpillar C-10 diesel engine, were operated side by side on similar fixed-route revenue service

for a 12-month demonstration period (February 1998 to January 1999). The buses were used as part of the Clean Air Express

Commuter Bus Program in Santa Barbara County, California. The performance and reliability of the DFNG engines were

similar to that of the diesel engine, but the emissions results were mixed.

15. NUMBER OF PAGES 14. SUBJECT TERMS

Dual-fuel natural gas engines, Caterpillar engines, Clean Air Express Commuter Bus

Program, alternative fuel vehicles, alternative fuel vehicle emissions 16. PRICE CODE

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

20. LIMITATION OF ABSTRACT

UL

 NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102