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Final Results from the National Renewable Energy Laboratory Vehicle Evaluation Program


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Produced for the U.S. Department of Energy (DOE)

by the National Renewable Energy Laboratory (NREL),

a U.S. DOE national laboratory

BUS STOP Transit BusesAlternative

FuelAlternative

Fuel

Produced by the Center for Transportation Technologies and Systems at the National Renewable Energy Laboratory (NREL), a U.S. Department of Energy national laboratory

NREL 1617 Cole Blvd. Golden, CO 80401-3393

NREL/TP-425-20513 DE96013097 October 1996

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

Final Results from the National Renewable Energy Laboratory (NREL)Vehicle Evaluation Program

by

Robert Motta, Paul Norton, and Kenneth Kelly, NRELKevin Chandler, BattelleLeon Schumacher, University of MissouriNigel Clark,West Virginia University

October 1996

The authors wish to thank all the transit agenciesthat participated in this program.

World Wide Web: http://www.afdc.doe.govAlternative Fuels Hotline: 1-800-423-1DOE

A lternative Fuel Transit Buses

iii

Alternative FuelTransit Buses

Final Results

Table of Contents

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

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Program Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Program Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Data Collected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Reliability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Liquefied Natural Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Compressed Natural Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Reliability Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Fuel Economy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Liquefied Natural Gas—Houston Dual-Fuel Buses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Liquefied Natural Gas and Compressed Natural Gas—Dedicated Spark-Ignited Engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Fuel Economy Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Operating Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Capital Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Emissions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Compressed Natural Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Emissions Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Other Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Lessons Learned . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Future Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Numbers, Numbers, Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

1

Transit buses represent one of the bestapplications for alternative fuels, whichhave already made significant inroads intothe transit bus market. As of January 1996,approximately 4% of the more than 50,000transit buses in the United States surveyedby the American Public Transit Associationran on an alternative fuel such as ethanol,methanol, compressed natural gas (CNG),or liquefied petroleum gas (LPG). Evenmore significant, 1 out of every 5 newbuses on order is an alternative fuel bus.These numbers do not include electrictrolley buses.

The National Renewable Energy Laboratory,with funding from the U.S. Department ofEnergy, initiated a program to study the per-formance, reliability, costs, and emissions of alternative fuel transit buses versus conventional diesel buses (controls). The program involved collecting detailed opera-tional and maintenance data from morethan 100 buses at eight transit agenciesacross the country. A program goal was tohave 10 test buses of each alternative fueltype, with 10 controls, split between twoagencies, operating for 18 months.WestVirginia University used its transportablechassis dynamometer to measure the emis-sions from the buses using a CentralBusiness District (CBD) driving cycle.

Transit properties involved in the program,and their alternative fuel buses, were:

• Houston Metro, in Houston,Texas (10 liquefied natural gas [LNG] buseswith Detroit Diesel 6V92 pilot ignitionnatural gas engines)

• Tri-Met, in Portland, Oregon (eight LNGbuses with Cummins L10 dedicatedspark-ignited engines)

• Metro Dade, in Miami, Florida (fivemethanol buses with Detroit Diesel 6V92 engines and five CNG buses with Cummins L10 engines)

• Triboro in New York, New York (fivemethanol buses with Detroit Diesel 6V92 engines, and five CNG buses with Cummins L10 engines)

• Pierce Transit in Tacoma,Washington (10CNG buses with Cummins L10 engines)

• Metropolitan Transit Commission,Minneapolis/St. Paul, Minnesota (five ethanol buses with Detroit Diesel 6V92 engines)

• Greater Peoria Transit in Peoria, Illinois(five ethanol buses with Detroit Diesel6V92 engines)

• Bi-State in St. Louis, Missouri (five 20%biodiesel blend buses with Detroit Diesel 6V92 engines)

The alternative fuel engines in this programhave only a few years of product develop-ment, versus decades for the diesel engine;however, the results show they are compet-ing very well with diesels in many areas:

Vehicle Reliability. Road calls experi-enced per 1,000 miles of operation con-stitute one measure of a bus’s reliability.A road call is defined as any event thatprevents a driver from completing his or her route and results in a call for abackup bus. The program studied totalroad calls and those attributable toengine/fuel system-related componentsonly—the areas most likely to be affectedby alternative fuel use. The number ofengine/fuel system-related road calls forthe Tacoma CNG buses is the same as forthe diesel buses. Most other sites showsome reliability penalty, but in many

Executive Summary

2


Final Results

cases the causes are either rela-tively minor (the buses runningout of fuel because the driver isunfamiliar with the vehicle), orappear solvable (fuel filter plug-ging because of fuel quality prob-lems at the alcohol sites).

Operating Costs. Operating costsof the buses are largely driven bythe fuel cost. Fuel cost differ-ences versus diesel far outweighany differences in maintenancecosts between the alternative fueland diesel buses. Operating costsare lowest for the CNG buses,which are approximately equal to diesel bus operating costs.Operating costs are the highestfor the alcohol and biodieselbuses because of high fuel prices.

Capital Costs. Capital costs con-sist of the extra cost to purchasean alternative fuel bus, and theextra cost (if any) to modify thefacilities to fuel, service, and main-tain them. Capital costs are thehighest for CNG and LNG buses,and lowest for the alcohol andbiodiesel buses—inverse to theoperating costs. In the future,alternative fuel engine prices areexpected to decrease as volumesincrease, although whether theywill be equal to or lower thandiesel is unclear.

At the present time, no alterna-tive fuel combines a low operat-ing cost with a low up-frontcapital cost.

Vehicle Emissions. Emissionswere measured on a transportablechassis dynamometer using theCBD driving cycle.

Natural gas and alcohol buseswere shown to have the potentialto significantly lower particulatematter (PM) and oxides of nitro-gen (NOx) emissions. With natural gas, PM emissions werevirtually eliminated.

Test results also showed highvariability in the emissions resultsfrom the alternative fuel vehicles.This probably results from the relative immaturity of the tech-nology and from the differentmaintenance requirements of the alternative fuel engines.Investigative emissions testingshowed substantial reductions in high-emitting vehicles aftertune-ups and parts replacements.

Both diesel and alternative fuel technologies have changedsubstantially since we ran ouremission tests. Newer generationCNG engines often feature closed-loop feedback control of air:fuelratio, which should significantlyreduce emissions variabilitybetween engines. Newer dieselengines are electronically man-aged and have lower PM emis-sions to meet the latestEnvironmental Protection Agencystandards. We plan to test bothtypes of engines in the future.

Looking to the future, newer, signifi-cantly more advanced alternativefuel engines than those in this pro-gram continue to be introduced,and they promise even better performance.

3


Final Results

Introduction

Background

The National Renewable EnergyLaboratory (NREL) is a U.S.Department of Energy (DOE)national laboratory; this project wasfunded by DOE.

One of NREL’s missions is to objec-tively evaluate the performance,emissions, and operating costs ofalternative fuel vehicles so fleetmanagers can make informed deci-sions when purchasing them.Alternative fuels have made greaterinroads into the transit bus marketthan into any other. Each year, theAmerican Public Transit Association(APTA) surveys its members ontheir inventory and buying plans.The latest APTA data show thatabout 4% of the 50,000 transitbuses in its survey run on an alter-native fuel. Furthermore, 1 in 5 ofthe new transit buses that membershave on order are alternative fuelbuses. This program was designedto comprehensively and objectivelyevaluate the alternative fuels in usein the industry.

In designing a program of this type,our most challenging problem wasproviding information on the latestproducts in a short period of time.Once a new product is introduced,we must find a suitable fleet thathas ordered the vehicles, along withsimilar diesel controls. Next, wemust collect, analyze, and report on18 months of data. Because alterna-tive fuel products are being rapidlyimproved, the information we pre-sent is often not on the latest gener-ation of the engine or vehicle.

Nevertheless, this information is farsuperior to none, and often revealstrends that continue to be trueeven with newer technology.

Some people may wonder why weincluded data on alcohol engines inthis report, as the ethanol andmethanol engines had been discon-tinued from production at the timeof this writing. Because this is theonly study of its kind, we decided toinclude the information to presentan across-the-board comparison ofalternative fuels. We believed thatdocumenting the experience withall the fuels in one report wasimportant. We also recently learnedthat one transit authority placed anorder for the ethanol 6V92 engine,so this engine may again becomeavailable. The ethanol informationmay therefore be more relevantthan we anticipated.

This report has data and results thatare significantly updated from ourprevious reports, in which we stat-ed that in some cases (such as withMiami) the diesel buses started theprogram at a higher mileage(odometer) reading than the alter-native fuel buses. The data availableto us were therefore not for compa-rable periods in the buses’ life. Wehave since received back data on allthe sites, so comparisons at eachsite are now made between buseswith similar mileage accumulation.

Finally, we received valuable feed-back—including written com-ments—on our last report. Weappreciate the comments, andwherever possible have incorpor-ated your suggestions.

4


Final Results

FIGURE 1. Buses were tested

in eight metropolitan areas

across the country.

Program Objective

The objective of the program wasto comprehensively and objectivelyevaluate the reliability, operatingcosts, and emissions levels of allalternative fuels currently in use inthe transit bus industry. This includ-ed compressed natural gas (CNG),liquefied natural gas (LNG), 95%and 93% ethanol (E95 and E93),100% methanol (M100), and a mixture of 80% diesel and 20%biodiesel (BD-20). Each fuel isbriefly described in the sidebar on page 6. A future study will lookat liquefied petroleum gas (LPG)-powered buses, which are not yetin production.

Program Design

The program was set up with thefollowing guidelines:

• A program target was to evaluate10 buses of each alternative fuelwith 10 controls split betweentwo sites. This would provide a

sufficient sample size to drawconclusions and ensure that we did not “put all our eggs inone basket.”

• We attempted to find transit agencies with the latest tech-nology buses.

• Each transit agency had to havediesel control buses similar to the alternative fuel buses.

• Each transit agency had to haveexcellent maintenance recordsand be willing to supply detaileddata on the vehicles for about 18 months.

Using these criteria, we testedbuses in eight metropolitan areas:Houston,Texas; Miami, Florida;Minneapolis, Minnesota; New York,New York; Peoria, Illinois; St. Louis,Missouri;Tacoma,Washington; andPortland, Oregon (see Figure 1).

NREL contracted with Battelle tomanage the program at each site,collect the detailed information,analyze the data, and write a reporton the conclusions. Battelle per-formed this function for all sites,except one. The University ofMissouri was contracted to performsimilar functions for the biodieselsite at St. Louis.

Engines in the program included:

• Cummins L10-240G and L10-260Gengines running on CNG

• Cummins L10-240G engines run-ning on LNG

• Detroit Diesel Corporation (DDC)6V92TA methanol engine

• DDC 6V92TA ethanol engine

• DDC 6V92TA pilot ignition natur-al gas (PING) dual-fuel engine

• The biodiesel buses use biodieselfuel in an unaltered DDC 6V92TAdiesel engine.

MCTO, Minneapolis E95

Houston Metro, Houston LNG dual-fuel

Metro-Dade, Miami M100 and CNG dedicated

Triboro, N.Y. M100 and CNG dedicated

GP Transit, Peoria E93/E95

Bi-State, St. Louis BD-20

Pierce Transit, Tacoma CNG dedicated

Tri-Met, Portland LNG dedicated

M70

-B10

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Final Results

In a follow-up program being con-ducted now, we are evaluating theemissions performance of the newCummins L10-280G or CumminsL10-300G, as well as the latest ver-sion of the DDC Series 50G.

A complete list of all sites, technolo-gies evaluated, engine models, andbus models in the program appearsin Table 1. For the New York M100test fleet, the diesel control busesuse the new DDC Series 50 engine,

not a 6V92 engine. When New Yorkordered its 6V92 M100 engines, the6V92 diesel engine was beingphased out, so it ordered Series 50diesel engines instead. We believethat even though the alternativefuel and control engines differedsignificantly at this site, this was stilla valid comparison, because this isthe realistic choice any transitagency would have to make.

Table 1. Participating Transit Agencies, Engines, and Alternative Fuels

Engine Model Year AF ControlTransit Agency City Bus Engines Alt. Fuel (AF)/Diesel AF Buses Buses

Houston Metro Houston, TX 40-ft Stewart DDC dual-fuel 1992/1992 LNG 10 5& Stevenson 6V92TA PING1

Tri-Met Portland, OR 40-ft Flxible Cummins L10-240G 1993/1992 LNG 8 5

Metro-Dade Transit Miami, FL 40-ft FlxibleCummins L10-240G 1991/1990 CNG 5 5

Authority (MDTA) DDC 6V92TA 1992/1990 M100 5 5

Pierce Transit Tacoma, WA 40-ft BIACummins L10-240G 1992/1991 CNG 5 5

Cummins L10-260G2 1994 CNG 5 —

GP Transit Peoria, IL 35-ft TMC DDC 6V92TA 1992/1992 E95/E935 5 33

Metropolitan Council Minneapolis/ 40-ft Gillig DDC 6V92TA 1991/1991 E95 5 5of Transit Operations St. Paul, MN(MCTO) 52,3

Triboro CoachDDC 6V92TA 1993/1993 M100 5 5

Company (NYCDOT)New York, NY 40-ft TMC DDC Series 504

Cummins L10-260G2 1993 CNG 4

Bi-State St. Louis, MO 40-ft Flxible DDC 6V92TA 1988 &1989 BD-20 5 5Development Agency

Note: BIA = Bus Industries of America (now Orion Bus), TMC = Transportation Manufacturing Company (now NOVABus), DDC = Detroit Diesel Corporation.

1 PING - pilot ignition natural gas. This engine is a dual-fuel engine, which operates on diesel and natural gas fuels in normal opera-tion, but can also operate on diesel fuel alone if needed.

2 Used for emissions testing only.3 Equipped with particulate trap.4 The Series 50 engine was used for the diesel control vehicles in New York because the diesel 6V92TA was being phased out and

was not available for new vehicles. The alcohol 6V92TA engine was the only methanol engine available for new vehicles.5 GP Transit switched from E95 to E93 in early 1994 for fuel cost savings.

Data Collected

The data collected in the programincluded:

• Records of all fuel and oil addi-tions to the buses

• All maintenance records for thebuses (the biodiesel site is anexception—only engine/fuel system-related data were collect-ed because of the age of the buschassis)

• Records of all road calls thatresulted from a breakdown whilethe bus was in service

• Emissions data. West VirginiaUniversity (WVU) staff visitedeach site and used the university’stransportable chassis dynamome-ter to conduct emissions tests onthe buses.

• Capital cost information. Adescription of the alternative fuelfacilities and facility cost was col-lected from each site. The incre-mental cost of the alternative fuelbuses was also recorded.

A program goal was to collectapproximately 18 months of dataon each site. Figure 2 shows thetotal mileage accumulation on thealternative fuel buses at each site.Data collection from all sites is nowcomplete, and the following sec-tions present the data analysis.

During the program, the biodieselsite encountered a problem that ledus to exclude most of those datafrom the detailed analysis. Whenthe site started up, biodiesel anddiesel were splash blended in theon-site tank and agitated with apump. After a few days, numerousproblems occurred with clogged filters because contaminants werestirred up from the bottom of thetank. The agitation was stoppedand the program continued. Latertesting of fuel samples revealed thatthe biodiesel was not blending withthe diesel during splash blending,but was forming a layer on the bot-tom that would cause the buses torun on blends other than the targetblend of BD-20. Additional prob-lems were uncovered: the fuel sup-plier was mixing one part biodieselto five parts diesel (a 17% blend)instead of one part to four. Theproblems were rectified in October

6


Final Results

The Alternative Fuels Being Tested

Methanol. An alcohol produced primarily from natural gas. Because it can alsobe derived from biomass or coal, the domestic resource base for methanol isvast. The methanol buses in this program run on 100% methanol.

Ethanol. An alcohol derived from biomass (corn, sugar cane, grasses, trees, andagricultural waste). The ethanol used in the test buses was E93 (93% ethanol,5% methanol, and 2% kerosene) or E95 (95% ethanol and 5% unleaded gasoline).

Biodiesel. Can be produced from any plant- or animal-derived oil product. Thebiodiesel blend used in the test buses was 20% biodiesel (from soybeans) and80% diesel fuel.

Natural Gas. Composed primarily of methane. It can be stored on the vehicle aseither a compressed gas or a cryogenic liquid. The program is collecting dataon vehicles that use both types of storage.

Pierce Transit in Tacoma,

Washington, has had

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Final Results

1995 and the program continued.Unfortunately, these problems pre-vented us from having enough datato conduct a detailed maintenanceand reliability analysis. We havetherefore included only that infor-mation we believe is reliable fromthat site. WVU reran the emissionstests after the problem was correct-ed, and the results are discussed inthe emissions section. Also not tobe overlooked is the lesson thatsplash blending biodiesel blendswith diesel fuel is not effective. Thefuel must be properly blended,preferably before delivery.

FIGURE 2. Mileage accumulation

on the alternative fuel buses

by site

1 206,000 miles accumulated on E95,119,000 miles on E93

West Virginia University

is able to transport this

chassis dynamometer

from site to site.

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100

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200

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350

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Number of alternative fuel buses

in fleet

St. Lou

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New Yo

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M10

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Minn

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Peoria

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IX 0

4112

8


Final Results

Reliability

One measure of the reliability of abus is the average number of roadcalls. When the driver cannot com-plete his or her route and calls for areplacement bus, a road call (whichencompasses events from enginefailure to running out of fuel) isrecorded. For analysis, we dividedthese calls into two categories: (1)all road calls, including thosecaused by engine shutdowns, doorfailures, wheelchair lift failures orany other problem; and (2) callsthat involve only the engine/fuelsystem-related components (specifi-cally the engine, fuel system, electri-cal, ignition, engine cooling system,and exhaust systems). These arethe systems most likely to show dif-ferences caused by the alternativefuel. We included “out of fuel” roadcalls in this group (even thoughthese may not be caused by anymechanical or other problem withthe alternative fuel system) becausewe believe this is a real issue beingexperienced as a result of alterna-tive fuel use.

Figure 3 shows the road calls per1,000 miles for the buses in the testprogram, displayed according to thetwo categories above. Below thechart is a schematic that shows thetotal mileage accumulation on thealternative fuel buses at that site.This helps provide a “weighting factor” for weighting the relativestrength of the data from a sitebased on the number of miles accumulated.

Liquefied Natural Gas

Houston Pilot Ignition NaturalGas Dual-Fuel Engine

This figure indicates that the dual-fuel buses in Houston, which runon LNG and diesel, experiencedconsiderably more road calls thanthe diesel controls. Comparing onlyroad calls related to the engine/fuelsystem, there are about .39 roadcalls per 1,000 miles for the LNGbuses, versus only .06 for the diesel,a ratio of greater than 6:1. The highrates are due mainly to either thebuses running out of fuel (59 out of210 calls), or the monitoring systemdetecting a fuel leak and shuttingdown the bus (24 calls). The dual-fuel buses have a very small dieseltank. If a fuel problem developswith the LNG system, the dual-fuelengines are designed to run ondiesel as a backup. In this case, thebus would run out of diesel in ashort time—the diesel fuel tankalone is not adequate to run the busindependently for long. The dual-fuel buses experienced nearly 15times the rate of road calls for “outof fuel” as did the diesel controls.This engine is no longer in produc-tion, and to determine whetherother sites using LNG were havingsimilar problems, we addedPortland, Oregon, as a site. Portlandis running dedicated Cummins L10-240G engines in its LNG buses.

Portland Dedicated Spark-Ignited Engine

Portland is experiencing more roadcalls with its LNG buses than withits diesel buses, but the problems

9


Final Results

FIGURE 3. Number of road calls

by site and category

are much less severe. The LNGbuses are having road calls causedby the engine/fuel-related systemsat a rate of .22 per 1,000 miles ver-sus .15 for diesel, a 50% increase.Most alternative fuel-related roadcalls on the LNG buses are causedby the fuel leak detection systemand/or fuel leaks (16 of 172 totalcalls), or the buses running out offuel (6 out of 172 total calls). If thefuel leak detection system senses aleak, the bus is automatically shutdown. However, a fuel leak wasactually found in only 4 of the 16cases. The reliability of the fuel sen-sors has been a problem, andPortland has reported much betterperformance with a new sensordesign recently installed.

The drivers’ unfamiliarity with thevehicle range probably results inmost cases of the buses running out of fuel. This problem generallydiminishes rapidly with time.

Looking at the bigger picture of allroad calls at Portland, the LNGbuses experienced even more thanthe diesel buses. The largest catego-ry of road calls for the LNG buses,however, related to body systems,(including the doors not working),rather than the alternative fuel sys-tem. This shows the importance oflooking at the alternative fuel sys-tem in perspective of the entirevehicle. Overall the engine/fuel sys-tem reliability appears much betterthan that of Houston’s buses, andnot out of line with other systemson the buses.

0

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0.8

0.9

New York M100

Miami M100

Minneapolis E95

Peoria E95/E93

Tacoma CNG

Miami CNG

LNG CNG Ethanol Methanol

Road

cal

ls p

er 1

000

mile

s

Total road calls

Engine/fuel system- related road calls only

Alternative fuel

Diesel control

Portland LNG

Houston LNG/Diesel

Miles on alternative fuel buses

(1 bus = 100,000 miles)

M70

-B10

4903

10


Final Results

Compressed Natural Gas

Buses that ran on CNG in Miamihad about four times as many alter-native fuel system-related road callsper 1,000 miles as their dieselcounterparts. Most were engine orfuel system-related, including 9 outof 81 for running out of fuel. Asshown in Figure 3, these buses havevery low mileage because there isno convenient fuel station on thepremises. In contrast, the buses atTacoma have more than four timesthe mileage accumulation as the Miami buses. The Tacoma enginesare also one model year newer.Their road call rates are identicalfor CNG and diesel. Because of the much greater mileage on theTacoma buses, and the later modelyear engine, we have placed greaterweight on these data. Overall, wecan conclude that CNG buses arepotentially as reliable as diesels. Itis important to note that the manu-facturer is now selling newer, moreadvanced CNG engines than theones used at Miami or Tacoma.

Alcohol

All the alcohol sites had similarexperience with road calls. Atevery site, fuel-quality problemswere a significant issue, andaccount for a major portion of the difference observed betweenthe alcohol and diesel controlbuses. Fuel filter plugging on thealcohol buses resulted in 5 of 61total road calls in Peoria, 4 of 21 in

Minneapolis, 18 of 123 in Miami,and 4 of 47 in New York. In addi-tion, a few of these sites experi-enced many engine-related roadcalls, most of which were for lackof power and engine stalling. Webelieve these two problems are inmany cases directly related to filterplugging, but were not recorded assuch. These problems appear relat-ed to lingering material compatibili-ty problems with the alcohol fuelsthat are probably occurring in thefuel delivery system, not on thebuses.

Reliability Summary

In summary, except for Tacoma’sCNG buses, all sites showed roadcall rates for the engine/fuel-relatedsystems on the alternative fuelbuses to be higher than on thediesel buses by varying degrees.Most of the problems are not insur-mountable and are expected withrelatively new technology. Theycan be divided into a few generalcategories: running out of fuel—afairly minor issue, and one thatseems to be largely concentrated inthe first few months of operation;fuel leaks and leak detection shut-downs on the LNG buses—a prob-lem that appears correctable withnew improved leak detection sen-sors; and fuel filter plugging on thealcohol buses—a problem probablyrelated more to fuel delivery to thebuses than to what is happening onthe bus.

11


Final Results

0

1

2

3

4

5

6

New York M100

St. Louis BD-20

Miami M100

Minneapolis E95

Peoria E95/E93

Tacoma CNG

Miami CNG

Portland LNG

(Dedicated)

Houston LNG/Diesel

(Dual-fuel)

LNG CNG Ethanol BiodieselMethanol

MPG

(die

sel #

2 eq

uiva

lent

)

Alternative fuel

Diesel control

E95

E93

Fuel Economy

Fuel economy and fuel costs arevery important to transit agenciesbecause they represent a significantpart of the operating cost of a tran-sit bus. Figure 4 shows the repre-sentative fuel economy for each siteexpressed as miles per diesel equiv-alent gallon, the quantity of alterna-tive fuel that has the same energycontent as one gallon of diesel fuel.The representative fuel economy isnot always based on the total fuelconsumed during the total data col-lection period. We selected a periodof operation when we had gooddata and could accurately calculatethe fuel economy. In the case of theHouston dual-fuel buses, we used aperiod of operation when the alter-native fuel buses ran consistently onLNG (as opposed to running in theirbackup mode of diesel only). Forcomparison purposes, we haveexpressed all fuel economy in termsof #2 diesel equivalent gallons.

Liquefied Natural Gas—Houston Dual-Fuel Buses

The buses at Houston use PINGengines, which operate on a com-pression-ignition cycle that usesdiesel as the pilot ignition source toignite the natural gas. The averagefuel economy for these buses wascalculated by adding the amount ofLNG (in diesel equivalent gallons)and diesel burned in the buses overtime, and dividing that sum by thetotal miles logged. The average fueleconomy for the LNG buses (3.1miles per diesel equivalent gallon)was approximately 13% less thanthat of their diesel counterparts. Asmall part of this reduction is dueto the approximately 860 poundsof extra weight of the LNG/dieseldual-fuel buses, but the largest partis most likely attributable to theengine design, engine operating

FIGURE 4. Fuel economy by site

M70

-B10

4904

12


Final Results

problems (see Reliability section),differences in driving cycles, orLNG measurement inaccuracies.

Liquefied Natural Gas andCompressed Natural Gas—Dedicated Spark-IgnitedEngines

The natural gas engines that operat-ed in Portland, Miami, and Tacomawere spark-ignited throttledengines; the diesel engines wereunthrottled compression-ignitionengines. When a diesel compres-sion-ignition engine is redesignedinto a spark-ignition engine to runon natural gas (the case with all nat-ural gas engines in the program),there is an inherent loss of efficien-cy because of pumping losses.Pumping losses represent theamount of energy required for theengine to draw in air during theintake cycle. An unthrottled dieselengine has minimal pumping losses,whereas a spark-ignited engine witha throttle has significant pumpinglosses. In addition, natural gasengines have a lower compressionratio than their diesel counterparts(10.5:1 for natural gas engines ver-sus 16.3:1 for diesel engines), whichalso tends to lower efficiency.

An added disadvantage for CNGbuses is their weight—as much as3,900 pounds more than their dieselcounterparts. This weight penalty is largely due to the weight of theCNG tanks, and increases the curbweight by about 15% (the dieselcontrol buses have a curb weight of approximately 27,000 pounds).Newer design all-composite tanksreduce this weight penalty signifi-cantly, but these tanks were notused on the buses in the program.These factors led to the expectation

that energy efficiency might be significantly reduced.

At the two CNG sites, the fuel econ-omy of CNG buses was reduced by3% and 23% compared to dieselbuses. At the Portland LNG site,the fuel economy was 30% loweron LNG buses than on diesel,greater than expected for this typeof engine. This may be due togreater idling time for LNG buseson the weekends, because Portlandpersonnel believed that this wasnecessary to control pressurebuildup and venting of the tanks.

Alcohol

The alcohol buses also have weightpenalties—1,000 to 1,500 pounds,depending on the fuel tank capaci-ty. Also, the alcohol buses at theMiami site have an additionalweight penalty of 1,200 pounds,which is attributed to options andspecifications unrelated to the alco-hol fuel engine. This extra weightwas expected to reduce the fueleconomy of the alcohol buses.

The alcohol buses also have veryhigh compression ratios (more than 20:1), which were expected to lower fuel economy because ofhigher friction losses such as pistonside loading. The results to date,however, indicate that the alcoholbuses at all sites are performingvery well, delivering fuel economycomparable to that of the diesels onan equivalent energy basis. (Twonotes: first, the diesel control busesat Peoria are equipped with particu-late traps, which lower fuel econo-my slightly; and second, the dieselcontrol buses at New York areSeries 50 4-stroke diesel engines,not 6V92s.)

13


Final Results

Cost

The cost of operating alternativefuel buses versus the diesel controlscan be broken down into operatingand capital costs. Capital costs con-sist of the additional cost of thealternative fuel bus and the cost ofmodifying the facilities for alterna-tive fuel use.

Operating Costs

Figure 5 shows the breakdown ofoperating costs for the transit agen-cies in the program. The costs like-ly to be affected by the use of analternative fuel include fuel andlubricant costs and vehicle mainte-nance costs. Together these com-prise one-fourth of the totaloperating costs.

The vehicle maintenance costs(shown as 21% of the total) includethe costs not only to perform actualrepairs and maintenance on thebuses, but also to staff the partsdepartment, paint shop, body shop,vehicle cleaning facility, and fuelingfacility. In this study we recordedonly the maintenance costs directlyassociated with the bus—repairsand maintenance on the buses,

rebuild costs, and inspections, butnot supporting activities such ascosts associated with running thetire, paint, body, or parts shops.Finally, to calculate maintenancecosts we used a standard mechaniclabor rate of $25/hour for everysite, and multiplied this by thehours spent on each job. This rep-resents a typical mechanic’s wageplus overhead costs of approxi-mately 50%.

Biodiesel

On a diesel #2 equivalent gallonbasis, biodiesel buses exhibitedapproximately the same fuel econo-my as the diesel control buses.

Fuel Economy Summary

In summary, the fuel economyresults are in line with expectationsfrom the various engine technolo-gies, with the possible exception of the LNG dual-fuel engine.

Vehicle maintenance (including mechanic labor & parts): 21%

Fuels and lubricants: 4%

Other: 2%

Facility maintenance: 4%

General administration: 16%

Driver labor: 53%

FIGURE 5. Operating costs

for the transit agencies by

categoryM

70-B

1049

05

14


Final Results

0

100

200

300

400

500

600

700

New York M100

St. Louis BD-20

Miami M100

Minneapolis E95

Peoria E95/E93

Tacoma CNG

Fuel cost per diesel #2

equivalent gallon

Miami CNG

Portland LNG

(Dedicated)

Houston LNG/Diesel

(Dual-fuel)

LNG CNG Ethanol BiodieselMethanol

Dol

lars

per

100

0 m

iles

Alternative fuel

Diesel control

E95

E93

0.80/0.61 0.93/0.55 0.69/0.64 0.52/0.65 1.83/1.21/0.61 1.80/0.65 1.72/0.64 1.31/0.51 1.32/0.56

Fuel Costs

Fuel costs per 1,000 miles of opera-tion for each transit agency areshown in Figure 6. These costswere calculated based on the repre-sentative fuel economy of the busesat the site and the prices paid for the fuel during the data collectionperiod.

At the bottom of the figure, the fuelcosts used to make these calcula-tions are shown. In general, theprices of alternative fuels have been

more variable than those of dieselfuel, both regionally and over time.For example, CNG prices differ sig-nificantly from region to region andmethanol prices nationwide havebeen very volatile. The LNG pricesat Portland are relatively high. LNGprices in other locations across thecountry are lower, in some casesmuch lower.

Maintenance Costs

Maintenance costs were tracked onall the buses. Each transit agencyprovided copies of all work ordersand lists of parts replaced. Thework performed and parts replacedwere coded by type of work (sched-uled maintenance, unscheduledmaintenance, road calls, and config-uration changes to the buses), aswell as by vehicle subsystem.

To show the effects of the alterna-tive fuel system on costs, Figure 7shows the maintenance costs forthe engine/fuel-related systems only,

FIGURE 6. Fuel costs per

1,000 miles of operation

What Are the Fuel Prices in Your Area?

Fuel prices have a dramatic effect on operating costs. The fuel prices used tocalculate operating costs in this report were the prices actually paid by theagencies while we were collecting data. For example, Pierce Transit was paying$0.52 per diesel #2 equivalent gallon for CNG and $0.65 for diesel. Since that time,the prices have changed significantly. Pierce Transit now pays $0.29 per gallonfor CNG (because the agency buys it directly from the wholesaler as a commodi-ty) and $0.76 for diesel, changing the economics considerably in favor of CNG.You might want to check on the fuel prices in your area to see what the currenteconomics would be for your fleet.

M70

-B10

4906

15


Final Results

0

100

200

300

400

500

New York M100

Miami M100

Minneapolis E95

Peoria E95/E93

Tacoma CNG

Miami CNG


Dol

lars

per

100

0 m

iles

Total costs

Maintenance costs due to engine/fuel

system repairs only

Alternative fuel

Diesel control

Portland LNG

Houston LNG/Diesel

Miles on alternative fuel buses

(1 bus = 100,000 miles)

and total maintenance costs for theentire bus. Engine/fuel-related sys-tems include the engine, fuel sys-tem, electrical, ignition, enginecooling system, and exhaust sys-tems. Total maintenance costsinclude work on all vehicle systems,including, for example, the engineand fuel system, body hardware, air conditioning and heater systems,suspension, and door systems.

We must keep the costs related tothe engine/fuel system on the alter-native fuel buses in perspective.For example, in some cases, costsrelated to these systems on thealternative fuel buses are signifi-cantly higher than on the dieselbuses. However, these increasesoften are not driving factors whenyou consider the total bus mainte-nance costs. In other words, repairsto systems totally unrelated to alter-native fuel use, such as the air con-ditioning system, often outweigh

costs associated with using a differ-ent fuel. In addition, these costs areonly a relatively small part of thetotal bus operating costs shown inFigure 5.

The maintenance cost data present-ed do not include warranty workperformed on the buses becausethe agencies do not bear the cost of this work (except for the in-house labor costs for warrantyrepairs—these are generally paid bythe transit agencies and are includ-ed in the maintenance costs pre-sented in this report). Maintenancecosts for the biodiesel buses are notshown because of insufficient data.

Comparisons of maintenance databetween agencies should not bemade because each agency has adifferent system for maintaining itsbuses. Alternative fuel buses shouldonly be compared with diesel con-trol buses at the same site.

FIGURE 7. Maintenance costs

for the buses in the program

M70

-B10

4907

16


Final Results

Liquefied Natural Gas—Houston DDC Dual-Fuel EnginesMaintenance costs for the engine/fuel-related systems on the LNGbuses have been more than threetimes those of the diesel buses.Significant problems occurred with the engine gas injectors. It is believed that contaminants in the fuel, possibly in combinationwith other problems, caused theinjectors to stick open. The engine manufacturer has worked on theproblem under warranty, but inter-nal labor costs at Houston Metrowere still significant. Fuel systemleaks and “false alarms” by the leakdetection system have also been asource of cost in the LNG buses.

Liquefied Natural Gas—Portland Dedicated EnginesMaintenance costs for the engine/fuel-related systems on the LNGbuses were approximately 50% high-er than those for the diesel controlbuses. Higher costs are largelyattributable to fuel leaks (or appar-ent fuel leaks) that caused the sen-sors to signal a leak, and to replacingcryogenic pumps and related hard-ware. In all, 11 cryogenic pumpsand 8 hydraulic driver pumps werereplaced on the buses during theprogram. The cryogenic pumps are very expensive, costing about$1,500 for a remanufactured one,or $6,000 for a new one. The partscost for these pumps was coveredunder warranty, but a significantamount of the labor to diagnose and replace them was not. OtherLNG designs that do not require afuel pump are now on the market.Other things being equal, thesedesigns should be more reliable.

Compressed Natural GasIn Tacoma, the engine-related main-tenance costs for CNG buses werewithin 16% of the diesel controls.No major problems or trouble areaswere encountered on the CNGbuses. Most of the cost differenceis attributable to the extra tune-upsrequired for the spark-ignited CNGengines—spark plugs, plug wires,and other tune-up costs.

In Miami, the engine-related mainte-nance cost for buses running onCNG was about double that fordiesel buses. The Miami buses,however, were only used in “trip-per” service and have accumulatedonly 95,000 miles on CNG, versusmore than 400,000 miles for theTacoma buses that were used in full service against their dieselcounterparts. The engines are alsoone model year newer at Tacoma.We therefore place significantlymore weight on the Tacoma data.

EthanolThe ethanol-powered buses inPeoria had engine/fuel system-relat-ed maintenance costs about 75%higher than those of the dieselbuses. The cost of maintaining the fuel system contributed most to the overall maintenance cost,and was due primarily to the cost of ethanol fuel filters. The primaryand secondary fuel filters togethercost nearly $105 for ethanol com-pared to about $6 for diesel. Thehigher cost, coupled with a higherreplacement rate—caused by mater-ial incompatibility problems in thefuel station—results in significantlyhigher overall fuel system costs. Thematerial incompatibility has sincebeen rectified. Electrical systemmaintenance costs were also higherfor the ethanol buses because of the

17


Final Results

FIGURE 8. Total fuel and

maintenance costs per mile

traveled

0

100

200

300

400

500

600

700

800

900

New York M100

Miami M100

Minneapolis E95

Peoria E95/E93

E95

E93

Tacoma CNG

Miami CNG

Portland LNG

(Dedicated)

Houston LNG/Diesel

(Dual-fuel)

Dol

lars

per

100

0 m

iles


Total costs

Maintenance costs only

Alternative fuel

Diesel controlhigher replacement rate of starters,

batteries, and glow plugs.

Minneapolis experienced similarissues, with engine/fuel system-relat-ed costs almost four times higherthan those for the diesel buses.

MethanolMiami and New York methanolbuses experienced issues similar tothe ethanol buses. At both Miamiand New York, engine/fuel system-related costs were almost fourtimes as high on the methanolbuses as on the diesel controlbuses. The largest cost increasesoccurred in the fuel system andelectrical area, with fuel filter andelectrical problems similar to theethanol buses.

BiodieselAs a result of the problems with theinadequate mixing of the biodieseland diesel discussed earlier, we

decided there were insufficient dataafter the fuel “clean point” (whenwe knew the fuel had been proper-ly mixed) to analyze maintenancecosts. At least one issue did arisethat is worth mentioning. Some ofthe older buses had elastomer mate-rials in the fuel pumps (a sealaround the shaft) that were incom-patible with the biodiesel blend.Later in the program these werechanged to a synthetic material(Viton®) that is compatible withbiodiesel. Newer fuel pumps soldby the manufacturer comeequipped with the synthetic seal.

Cost per Mile Traveled

Figure 8 shows the total fuel andmaintenance costs per mile trav-eled. In all cases the oil cost wasinsignificant compared to the fueland maintenance costs. The fuelcost per mile was calculated usingthe average in-use fuel economy

M70

-B10

4908

18


Final Results

and the actual fuel cost paid by thetransit agencies. The fuel and main-tenance cost per mile for test busesrunning on CNG has been aboutthe same as those for buses runningon diesel fuel. However, the analo-gous costs for all buses that usealcohol fuel have been up to twiceas high as the costs for buses usingdiesel. The costs for LNG buseshave been 35% to 80% higher thantheir diesel counterparts.

This figure shows clearly that main-tenance costs are the smaller partof the cost equation, and that fuelcosts are the determining factor forcosts directly related to operatingthe bus (excluding driver laborcosts).

Capital Costs

Adding alternative fuel buses to afleet requires not only the acquisi-tion of alternative fuel buses, but inmost cases also requires changes inthe refueling, maintenance, andstorage facilities at the site.

Additional Bus AcquisitionCosts

At this time, buses that run on alter-native fuels are more expensive topurchase than those that run ondiesel. Higher engine costs, drivenby low production volumes, addabout $15,000 to $30,000 to theprice of the bus. As volumesincrease, the cost of alternative fuel engines should approach thatof their diesel counterparts. Someknowledgeable people believe thatthey will be equal to diesel in thenot-too-distant future.

Biodiesel buses are the exception.Because the buses that ran on BD-20 in this program use conven-tional diesel engines, there was no additional acquisition cost.(However, biodiesel has not yetbeen approved by most enginemanufacturers as a diesel substitute.Because the use of biodiesel mayaffect engine warranty claims, atransit agency should check withthe engine manufacturer beforeusing the fuel.)

The fuel tanks of alternative fuelbuses are also generally moreexpensive than diesel fuel tanks.These additional costs can run from$5,000 for a bus that operates onE95 to about $20,000 for one thatoperates on CNG. Again, fuel tanksrepresent no additional expense forbuses running on biodiesel. Table 2presents estimated incrementalcosts (over and above a diesel-fueled bus) for new alternative fuel40-foot transit buses. The incremen-tal costs for an LPG-fueled bus havebeen included because we willstudy LPG buses as they becomeavailable. These prices are only forcomparison purposes; actual busprices will vary with each transitproperty because of variations in

Table 2. Incremental Capital Costs of40-Foot Buses by Fuel Type (1994 $). (The base price for a diesel bus is $215,000.)

Fuel Type Incremental Cost

Diesel Base

LNG $55,000

CNG $50,000

Ethanol $20,000

Methanol $20,000

Biodiesel $0

Propane $40,000

Source: Battelle

19


Final Results

vehicle specifications and the sizeof the order.

We obtained these cost estimatesfrom transit agency bus bids and inconversations with bus manufactur-ers. They reflect market pricesafter a few years of alternative fuelbus production, with relatively lowproduction volumes. As volumesincrease, prices should decrease.

Facilities Costs

Transit buses are stored and refu-eled centrally in facilities ownedand operated by transit agencies.As a result, the capital and operat-ing costs for any changes made to afacility to accommodate alternativefuel buses are important to consid-er when calculating the overall costof operating with alternative fuels.

The capital and operating costs for new facilities or modifying facili-ties vary considerably, even for onetype of alternative fuel. Necessarychanges can include installing newrefueling equipment or installingmonitoring and ventilation equip-ment in maintenance and storagefacilities.

Table 3 lists the typical modifica-tions needed for transit bus mainte-nance and storage facilities for eachtype of alternative fuel. For alcoholfuels and propane, ventilation andelectrical designs for gasoline facili-ties are often acceptable to the firemarshal or other local officials.However, both CNG and LNGrequire modifications to bus main-tenance facilities and indoor storageareas. In all cases, you should

Table 3. Maintenance and Storage Facility Modifications for Alternative Fuel Transit Bus Fleets

Fuel Ventilation Electrical Heating Other Comments

Natural gas At ceiling No overhead No open flame — Requires sensors for(CNG and LNG) highest points sparking contacts heaters overhead combustible fuel detection

Ethanol No change1 Unclassified electrical No change1 Requires cistern No ignition sources in 18 inches above finished for drain to trap floor area (18 inchesfloor, no change1 fuel leakage and lower)

Methanol No change Unclassified electrical No change1 Requires cistern No ignition sources in 18 inches above finished for drain to trap floor area (18 inchesfloor, no change1 fuel leakage and lower)

Biodiesel blend No change No change No change — —

Propane Forced Unclassified electrical No change1 — No ignition sources in (LPG) ventilation 18 inches above finished floor area (18 inches

within 18 floor, no change1 and lower).inches of floor See also Note below.

1 If facility is certified for gasoline fuel. Source: Battelle

Note: Additional considerations for propane facilities: Propane fuel tanks should never be overfilled, because thermal expansion of the fuel can actuate the tank relief valve. However, both facility codes and design practices often make some allowance for this contingency. Thus, the installation of propane gas detection systems in areas where propane-fueled vehicles are parked or maintained may be required by local authorities or considered to be good practice by facility design engineers. Increasedventilation to handle possible propane releases may also be included in the facility design. Often, the operation of suchincreased ventilation is tied to the gas detection system.

20


Final Results

check with local authorities forrequirements in your area.

The costs of maintaining and modi-fying storage and refueling facilitiesalso depend on the size of theagency, as well as on state and localbuilding codes. Table 4 lists thetypes of refueling facilities requiredfor each alternative fuel, and showsestimates of the cost range for arefueling facility capable of refuel-ing 80 to 160 alternative fuel buses.

For each alternative fuel, we alsoestimated the total costs of the nec-essary modifications to the fuelingand maintenance facilities for a busfleet of 160 alternative fuel buses.We estimated the costs of upgrad-ing the building, mechanical sys-tems, and electrical systems, and of acquiring new equipment.Estimates included contractor over-head and profit (assumed to be17%), and contingency (assumed tobe 25%). We assumed the facilitieswere converted in three phases toallow normal operations to contin-ue and to serve a mix of diesel,gasoline, and alternative fuel vehi-cles. Table 5 shows the cost esti-mates for converting a 160-busfacility with 84,850 square feet ofindoor storage, 19,250 square feetfor the maintenance area, and a9,120-square-foot fueling area.

At this time, CNG and LNG facilitieshave the highest capital costs.

Each alternative fuel facility mustbe custom designed to meet thespecific needs of the transit agency.The cost of the facility can vary sig-nificantly. The cost estimates pre-sented above should be viewed asrepresentative for typical facilities.You should consult architecturaland engineering firms experiencedin alternative fuels for cost esti-mates for your particular site.

Table 4. Refueling Facilities for a Fleet of 80 to 160 Alternative Fuel Buses

Inventory Range ofAlternative Storage Incremental OperatingFuel Options Capital Cost Cost Comments

Diesel1 Underground Baseline Low Tank insurance(Baseline) tank would be needed.2

LNG Above-ground $750,000 to Lowtank $900,000

CNG Small high $750,000 to Low to Compressors would(fast-fill) pressure $1,500,000 Medium require noise

accumulator suppression.tank & buffer

CNG No storage $600,000 to Low Noise suppression(slow-fill) needed $900,000 measures required

for night operation.

Ethanol1 Underground $50,000 to Low Tank insurance tank $100,000 would be needed.2

Methanol1 Underground $50,000 to Low Tank insurance (M100 or M95) tank $100,000 would be needed.2

Biodiesel Underground $0 Low Tank insuranceblend1 tank would be needed.2

Propane Above-ground $100,000 to Low Fire suppressiontank $150,000 system required.

1 Mobile fueling could be used, which eliminates capital costs, inventory costs, insurance costs, and is generally allowed by current codes/regulations.

2 Tank insurance is insurance that covers fuel spills from the tank.

Table 5. Incremental Facility Costs for a Fleet of 160 Alternative Fuel Buses (in millions of 1994 $)

LNG CNG Alcohols1 Biodiesel Propane

Fueling Facility $0.90 $1.50 $0.10 N/C $0.15

Maintenance Facility $1.17 $1.08 N/C N/C N/C2

Bus Storage Facility $1.44 $1.17 N/C N/C N/C2

Total $3.51 $3.75 $0.10 N/C $0.15

N/C = No change if facility is certified for gasoline Source: Battelle1 Methanol and ethanol2 See Note to Table 3.

21


Final Results

Emissions

WVU conducted emissions testingon the buses with its transportablechassis dynamometer, which wastransported to each transit agencyin the program. In performing thechassis dynamometer emissionstests, buses were driven accordingto the CBD driving cycle, which wasdesigned to simulate the speeds,loads, and conditions experiencedby buses during a typical routethrough a city’s central business district. Buses were tested with thefuel in the bus at the time. Most ofthe buses were tested in two con-secutive years—1994 and 1995.

Compressed Natural Gas

The results of chassis dynamometeremissions tests on CNG and dieselbuses powered by Cummins L10engines are summarized in Table 6and shown in Figure 9. The fiveCNG buses tested in Miami and fiveof the buses tested in Tacoma wereequipped with early versions of theCummins L10 engine (referred to asL10-240G) that did not require cer-tification by the U.S. EnvironmentalProtection Agency (EPA) or theCalifornia Air Resources Board(CARB). In 1994, Cummins madeseveral enhancements to theengine. The later versions of thisengine (referred to as L10-260G)have been certified by CARB. Fivebuses with the newer engines weretested in Tacoma, and five were test-ed in New York City.

There is a substantial amount ofscatter in the data, but we can draw

several general conclusions. Themost obvious result is that the PMemissions levels are reduced tonearly zero with CNG. Figure 9shows that all CNG buses tested(including vehicles with mileagegreater than 150,000 miles) had PM levels an order of magnitudelower than the diesel buses.

It is important to note that theCummins diesel engines tested thusfar were 1992 model year or older.Since 1992, the EPA heavy-dutyengine emissions certification stan-dard (measured in grams [g] perbrake horsepower hour [bhp-hr])for PM in urban buses has beenreduced by a factor of five (from0.25 to 0.05 g/bhp-hr). Likewise,substantial improvements havebeen made in PM emissions fromdiesel engines. Although a directcorrelation between dynamometercertification emissions and in-usechassis dynamometer emissionsdoes not exist, recent engine certifi-cation data from the latest CNG anddiesel engines suggest that the gapbetween CNG and diesel PM hasbeen narrowed considerably.

Figure 9 also shows that busesequipped with the newer CARB-certified CNG Cummins L10-260Gengines exhibited lower carbonmonoxide (CO) and oxides of nitro-gen (NOx) emissions than eitherthe original CNG demonstration or the diesel control buses. TheL10-260G tests were performed at 20,000 miles or less. The totalhydrocarbon (HC) emissions levelsfrom the CNG buses are higher

22


Final Results

than those from the diesel buses.However, HC emissions from CNGvehicles are typically composed ofmore than 95% methane. EPA andCARB regulations are written interms of non-methane hydrocar-bons (NMHC) because methane isconsidered to be nonreactive in theatmosphere. The NMHC levels fromthe CNG buses were not directlymeasured, but can be projected tobe at similar or lower levels thanthose from the diesel buses.

To investigate the causes of highemissions observed on some buses,we diagnosed, repaired, and retest-ed three of the L10-240G buses inTacoma with higher-than-expectedCO emissions. The repairs includedreplacing air:fuel mixing valve com-ponents and adjusting the air:fuelratio. All three buses showed reduc-tions in CO that averaged approxi-mately 93% (an average of 30 g/mibefore repairs to 2 g/mi afterrepairs). A complete description of this work will be available in aseparate short report published byNREL. Call our hotline or check

our web site for a copy. (Our webaddress and hotline phone num-ber are given at the front of thisreport.)

Cummins has recently begun toproduce even newer versions ofthe Cummins L10 CNG engines—the L10-280G and L10-300G. Theseengines use closed-loop feedbackcontrol to provide much bettercontrol of the air:fuel ratio, whichshould make emissions much moreconsistent from bus to bus andfrom test to test.We are now look-ing for sites that have these busesfor future testing.

Alcohol

The results of chassis dynamometeremissions testing on ethanol andmethanol buses powered by DDC6V92TA engines are summarized inTable 7 and illustrated in Figure 10.In 1994 and 1995, 10 buses inPeoria and Minneapolis were testedon ethanol, and 10 were tested onmethanol in Miami and New York.Additionally, 17 diesel control buses

Table 6. Average Chassis Dynamometer Emissions Results for CNG (g/mi) - Cummins L10 Engines

Engine Test Number Number OdometerCity Model* Fuel of Buses of Tests Minimum Maximum PM NOx HC CO

Miami L10-240G CNG 5 7 8,000 52,000 0.01 29 20.6 15.8

Tacoma L10-240G CNG 5 10 97,000 170,000 0.01 30.4 9.3 21.8

New York L10-260G CNG 5 10 3,000 20,000 0.03 12 16.1 1.6

Tacoma L10-260G CNG 5 5 10,000** 10,000** 0.02 11.2 15.5 0.7

Miami L10 Diesel 6 7 153,000 250,000 1.99 22.0 1.9 23.5

Tacoma L10 Diesel 5 9 144,000 220,000 1.74 24.6 2.4 11.2

* L10-240G is a non-emissions-certified demonstration engine. L10-260G is the CARB-certified version.** Estimated odometer reading at the time

23


Test Odometer

50

40

30

20

10

00 50000 100000 150000 200000 250000

Test Odometer

50

40

30

20

10

00 50000 100000 150000 200000 250000

Test Odometer

4

3

2

1

00 50000 100000 150000 200000 250000

L10-Diesel

Test Odometer

80

70

60

50

40

30

20

10

00 50000 100000 150000 200000 250000

Carbon Monoxide

L10-240G (CNG) L10-260G (CNG)

L10-Diesel L10-240G (CNG) L10-260G (CNG)



Tota

l Hyd

roca

rbon

s - T

HC

(g/m

i)Pa

rtic

ulat

e M

atte

r - P

M (g

/mi)

Oxi

des

of N

itrog

en -

NO

x (g

/mi)

Carb

on M

onox

ide

- CO

(g/m

i)Total Hydrocarbons

Particulate Matter Oxides of Nitrogen

Final ResultsFIGURE 9. Chassis dynamometer emissions from buses with Cummins L-10 engines

were tested in Peoria, Minneapolis,and Miami. Of the 17 diesel con-trol buses, 8 were originallyequipped with particulate traps.The buses with particulate trapswere tested with the traps in place in 1994, and with the traps removed in 1995.

Figure 10 shows the test resultsplotted against odometer reading.This figure shows the range andvariation of individual test resultsfor a population of buses at variousodometer readings, but is notintended to represent how emis-sions from a single bus deteriorateover time. Table 7 indicates therange of odometer readings forwhich buses were tested at a givensite during the 2-year period.

Results from the alcohol buses varyconsiderably from site to site andfrom bus to bus. In general, thebuses tested on ethanol andmethanol appear to emit PM levelssimilar to diesel buses equipped

with particulate traps, and signifi-cantly less PM than diesel buseswithout traps. Although the partic-ulate traps effectively reduced PMlevels from diesel vehicles, theywere removed because of mainte-nance and durability problems.However, recent diesel engine emis-sions certification data show thatPM levels from diesel engines havebeen reduced substantially in orderto meet tougher EPA PM standards.Most ethanol- and all methanol-powered buses emitted lower NOxlevels, and had significantly higheramounts of HC and CO, than thediesel controls. However, newermethanol buses with DDC 6V92TAengines (with odometer readingsbetween 6,700 and 42,000) testedin New York City had consistentlylower CO and HC emissions thanthe older alcohol-fueled buses. Theemissions levels from the newermethanol engines were similar tothe diesel control levels.

24


Final Results

Table 7. Average Chassis Dynamometer Emissions Results for Alcohol (g/mi) - DDC 6V92 Engines

ParticulateTest Trap Number Number Odometer

City Fuel (Diesels only) of Buses of Tests Minimum Maximum PM NOx HC CO

Peoria Ethanol 5 8 60,000 104,000 0.63 13.4 8.9 37.1

Minneapolis/St. Paul Ethanol 5 8 28,000 43,000 0.49 22.0 15.4 41.9

Miami Methanol 5 9 38,000 87,000 0.39 11.6 37.5 25.1

New York Methanol 5 10 6,700 42,000 0.11 6.8 2.1 8.4

Peoria Diesel No 3 6 89,000 108,000 0.72 25.3 2.7 7.5

Diesel Yes 3 3 58,000 69,000 0.44 – – –

Minneapolis/ Diesel No 5 9 107,000 151,000 1.05 25.3 3.4 9.5St. Paul Diesel No 5 10 43,000 69,000 0.81 26.4 2.1 6.7

Diesel Yes 5 5 26,000 41,000 0.34 – – –

Miami Diesel No 4 6 181,00 256,000 2.53 26.7 2.1 16.0

25


70

60

50

40

30

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10

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Test Odometer

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Test Odometer

45

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Carbon Monoxide

Diesel Ethanol Methanol

Test Odometer

Diesel Ethanol Methanol

Diesel Ethanol MethanolEthanol MethanolDiesel w/TrapDiesel

Total Hydrocarbons

Particulate Matter

Tota

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(g/m

i)

5

4

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0 50000 100000 150000 200000 250000 300000

Test Odometer

Oxi

des

of N

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x (g

/mi)

Carb

on M

onox

ide

- CO

(g/m

i)

Oxides of Nitrogen

Final ResultsFIGURE 10. Chassis dynamometer emissions from buses with DDC 6V92 engines

The EPA engine certification datafrom the methanol DDC 6V92TA(ethanol has not been certified)have shown emissions reductionsin all four components (HC, CO,NOx, and PM) versus the diesel6V92TA. To investigate the reasonfor the relatively high emissions onsome engines, two buses in Peoriathat showed high CO and HC emis-sions were diagnosed, repaired, andretested. Several repairs, whichincluded adjusting blower bypassvalve settings and replacing fuelinjectors or catalytic converters,were performed.

Tests on both buses performedbefore and after the catalytic con-verters were replaced showed COreductions of approximately 85%(approximately 40 g/mi to 6 g/mi)and HC reductions of approximate-ly 67% (approximately 11 g/mi to 4 g/mi). A complete description of this work will be available in aseparate short report published byNREL. Call our hotline or checkour web site for a copy. (Our web address and hotline phonenumbers are given at the front of this report.)

Biodiesel

Tests were run on buses using bothBD-20 and straight diesel back-to-back. The results are shown in

Table 8. With the limited number of buses run (four), and the relativescatter in the data, we were unableto draw any conclusions. BD-20 isgenerally believed to have a relative-ly small effect on exhaust emissions.This type of change is probably bestevaluated on an engine dynamome-ter where it is possible to havemuch better control of the test vari-ables and measure smaller changesin emissions levels.

Emissions Summary

The CNG and alcohol buses appearto be particularly well suited toreducing PM and NOx emissions.This feature is quite important, asthe federal emissions standards forPM and NOx are becoming morestringent. Diesel technology hasbeen developed to meet thesemore stringent PM standards,thereby narrowing the gapbetween alternative fuels anddiesel. However, virtually all cur-rent engine certification data stillshow CNG with an advantage.

Results from chassis dynamometeremissions testing have also shownhigh variability in some emissionslevels from these early generationCNG and alcohol engines com-pared to the diesel control engines(which have decades rather thanonly a few years of development).

26


Final Results

Table 8. Average Chassis Dynamometer Emissions Results for 20% Biodiesel Blend (g/mi) - DDC 6V92 Engines

Test Number Number OdometerCity Fuel of Buses of Tests Minimum Maximum PM NOx HC CO

St. Louis BD-20 4* 4 n/a 238,702 0.89 54.5 2.2 9.6

St. Louis Diesel 4* 4 n/a 238,702 0.85 52.4 2.6 9.6

* Note: The same four buses were tested on both fuels.

Both the engine certification andthe chassis dynamometer testinghave shown that CNG and alcoholengines have the potential to sub-stantially reduce emissions levels,but emissions are also highlydependent on the engine technolo-gy and the condition of the vehicle.Testing showed that some enginesin the program exhibited high HCand CO emissions. In cooperationwith the engine manufacturers, wediscovered that many of thesebuses were either improperly tuned or had problems with fuelinjectors, catalytic converters, mix-ing valves, and other engine compo-nents. Correcting these problemsresulted in dramatic reductions inemissions, and shows the impor-tance of proper maintenance inachieving low emissions, as well as the need for technology that is

more robust in maintaining opti-mum air:fuel ratio.

NREL and WVU have attempted toselect the latest technologies avail-able; however, many vehicles testedduring the past several years repre-sent early versions of alternativefuel engines. Technology is chang-ing rapidly in this industry, andmore advanced designs appearalmost yearly. Newer CNG enginedesigns that feature closed-loopfeedback control should providemuch better control of the air:fuelratio, and hence more consistentemissions. However, diesel enginesalso continue to improve and pro-vide tough competition for alterna-tive fuels. As these newer designsbecome available for testing, wewill test and report on them.

27


Final Results

All alternative fuels, exceptbiodiesel, add to the curb weight ofthe bus. Table 9 shows the approxi-mate increase in curb weight of a40-foot bus as a result of the alter-native fuel option.

Because of tank weight, CNG hasthe greatest weight penalty. Thelower number in Table 9 representsthe weight penalty with the latestdesign composite tanks.

Most municipal, state, and federalhighways have axle loading limitsto prevent excessive damage to the roadways. As a result, addingthe CNG option often substantiallyreduces maximum passenger

loading. If enforced, this willrestrict the utility of the bus.

The other alternative fuels havesubstantially lower weight penal-ties. Biodiesel has none.

Table 9. Approximate Increase in Curb Weight for a 40-ft Transit Bus(diesel curb weight of approximately 27,000 lbs)

Alternative Fuel Option Approximate Increase in Curb Weight (lbs)

LNG 860

CNG 2,500–3,900

E95/M100 1,000–1,500

Biodiesel 0

Other Considerations

During the course of this programwe learned numerous lessons thatdo not appear in the numbersabove. We have listed key oneshere:

• For alternative fuel buses to deliv-er the maximum benefit to theenvironment, proper maintenanceis very important, perhaps evenmore so than for diesels becauseof the relative immaturity of thetechnology.

• If you use a biodiesel blend, don’tsplash blend on site. Require thatyour contractor deliver a properlypre-mixed batch of fuel. Youshould also check with theengine and fuel systemsupplier(s) to make sure that all

materials used in the system arebiodiesel-blend compatible.

• The one item that seems to haveseparated the truly successfulsites from the others is the com-mitment to the alternative fuel—from the top of the organizationdown. The successful sites’ atti-tude is “if you are going to do it,do it right.” Everyone has to becommitted to the project,resources have to be allocated totrain people up front, and fuelmust be on site or very readilyaccessible. We have a separatecase study that covers the successof Pierce Transit in accomplishingjust that. Call our hotline at (800)423-1DOE and ask for a copy.


Final Results

28

Lessons Learned

Future Plans

The program is now completeexcept for a few open items wewould like to address:

• Earlier versions of CNG engineswith open-loop control have hadinconsistent emissions in someareas. We plan to evaluate the lat-est closed-loop feedback enginesas they become available. Ideally,we are looking for a fleet that hasbuses with CNG feedbackengines with otherwise identicaldiesel buses for comparison. Ifyou have these types of alterna-tive fuel and control buses, andwould like to participate in this

program, please call us at (303)275-4482.

• We plan to evaluate LPG, whichhas the potential for relativelylow up-front costs and low oper-ating costs, as it becomes avail-able.

• We may look at one more LNGsite to investigate its operatingcosts and reliability on a systemthat has no cryogenic pump. Ifyou have these types of alterna-tive fuel and control buses, andwould like to participate in thisprogram, please call us at (303)275-4482.

Transit buses represent one of thebest potential applications for alter-native fuels, which have alreadymade significant inroads into thetransit bus market. The alternativefuel engines in this program haveonly a few years of product devel-opment—versus decades for thediesel engine—but the results showthey are competing very well withdiesels in many areas:

• In reliability, one site—Tacoma—is equal to diesel. Most othersites show some reliability penal-ty, but in many cases the causesare either relatively minor (thebus runs out of fuel because thedriver is unfamiliar with the vehi-cle), or appear solvable (fuel filterplugging at the alcohol sites).

• Operating costs of the buses aredriven by the fuel cost. In otherwords, fuel cost differences ver-sus diesel far outweigh any

differences in maintenance costsbetween the alternative fuel anddiesel bus. Operating costs arelowest for the CNG buses andhighest for the alcohol andbiodiesel buses.

• Capital costs are inverse to theoperating costs—they are highestfor CNG/LNG buses, and lowestfor the alcohol and biodieselbuses. At the present time, nofuel combines a low operatingcost with a low up-front capitalcost.

• Natural gas and alcohol buseshave the potential to significantlylower PM and NOx emissions.With natural gas, PM emissionsare virtually eliminated.

Newer, significantly more advancedalternative fuel engines than wereused in this program have alreadybeen introduced, and they promiseeven better performance.

29


Final Results

Summary and Conclusions

Numbers, Numbers, Numbers

The following tables summarize the key results of the transit bus program.

30


Final Results

31

Houston Portland Miami Tacoma Peoria Mpls/St. Paul Miami New York St. LouisFleet LNG LNG CNG CNG E95 E93 E95 M100 M100 BD-20

Number of buses AF 10 8 5 5 5 5 5 5 5DC 5 5 5 5 3 5 5 5 5

Mileage in program AF 367,174 297,065 93,570 407,778 324,668 120,941 203,206 181,134 102,307DC 278,409 349,930 327,491 451,337 173,609 344,472 376,070 217,355 105,761

Engine/fuel system-related AF 0.39 0.22 0.52 0.11 0.12 0.16 0.32 0.17 N/Aroad calls per 1,000 miles DC 0.06 0.15 0.13 0.11 0.07 0.14 0.26 0.07 N/A

Total road calls AF 0.57 0.58 0.87 0.21 0.19 0.18 0.61 0.26 N/Aper 1,000 miles DC 0.26 0.23 0.54 0.21 0.17 0.29 0.52 0.15 N/A

Representative MPG AF 3.1 3.0 3.4 4.5 3.6 3.3 2.9 3.4 2.6 4.0(per diesel #2 equivalent gallon) DC 3.5 4.2 3.5 5.8 3.6 3.4 3.1 3.5 3.0 4.0

MPG ratio (AF/DC) 0.87 0.70 0.97 0.77 1.02 0.96 0.94 0.99 0.87 1.01

Fuel cost per 1,000 miles AF $218 $313 $206 $116 $504 $369 $616 $504 $507 $329(per diesel #2 equivalent gallon) DC $172 $130 $184 $112 $173 $208 $185 $173 $142

Engine oil consumption cost AF $1 $9 $2 $3 $5 $4 $3 $5 $2per 1,000 miles DC $2 $2 $2 $2 $2 $1 $3 $1 $1

Engine/fuel system-related AF $115 $133 $134 $64 $56 $108 $154 $170 N/Amaintenance cost per 1,000 miles DC $33 $88 $69 $56 $32 $29 $42 $46 N/A

Total bus maintenance cost AF $321 $424 $335 $161 $215 $259 $324 $333 N/Aper 1,000 miles DC $227 $287 $270 $159 $171 $181 $194 $259 N/A

Total bus operating cost AF $540 $746 $542 $279 $713 $584 $879 $831 $845 N/Aper 1,000 miles DC $400 $419 $456 $273 $303 $423 $390 $382 $433 N/A

AF = Alternative Fuel, DC = Diesel Control

N/A = insufficient data

1. The engine/fuel system-related areas are: general electrical, charging, cranking, ignition, air intake, cooling, exhaust, fuel, and engine. The rest of the mainte-nance costs in the total bus maintenance cost are an average of $169 per 1,000 miles, which includes inspections, air conditioning, transmission, body, door systems, air system, brakes, wheelchair lifts, and other repairs. Mechanic hourly labor rate is assumed to be $25 per hour.

2. For Miami, the CNG is purchased from the Airport Authority and therefore includes the fuel cost, compressor station maintenance labor and parts, as well ascapital costs for the station. For Tacoma, the CNG cost includes maintenance labor and parts for the compressor station, but does not include capital costs.

3. For Houston, the fuel cost does not include a fuel loss due to storage over time and during transfer, which could be as significant as 25%. These are dual-fuel buses that were using 50%–70% diesel fuel during the period used to calculate fuel economy and cost.

4. At Portland, the LNG is purchased from the local utility. Therefore, the purchase price includes the fuel cost, maintenance labor, and parts for the station, as wellas capital costs for the station. Also, of the truck and bus operators in the United States using LNG, Portland pays the highest price for LNG.

Table 10. Summary of Program Results


Final Results

CNG Buses - Cummins L10-240G - Miami, FL

Vehicle Bus Engine Engine Engine Test Test Test Emissions Test Results (g/mi)

Number Make Make Model Year Date Odom Fuel PM NOx HC CO

MDTA-9201 FLX Cummins L-10 240G 1991 1/26/94 10000 CNG 0.00 27.4 14.3 46.1MDTA-9202 FLX Cummins L-10 240G 1991 1/28/94 9018 CNG 0.00 25.9 8.3 2.1MDTA-9202 FLX Cummins L-10 240G 1991 2/18/95 39670 CNG 0.00 17.1 14.5 0.6MDTA-9203 FLX Cummins L-10 240G 1991 1/26/94 7004 CNG 0.00 40.1 10.0 1.0MDTA-9204 FLX Cummins L-10 240G 1991 1/27/94 36973 CNG 0.00 29.0 17.5 41.4MDTA-9204 FLX Cummins L-10 240G 1991 2/20/95 52182 CNG 0.02 35.7 70.2 16.8MDTA-9205 FLX Cummins L-10 240G 1991 2/3/94 7944 CNG 0.02 27.8 9.3 2.4

Count 7 7 7 7Average 0.01 29.0 20.6 15.8

Max 0.02 40.1 70.2 46.1Min 0.00 17.1 8.3 0.6

CNG Buses - Cummins L10-240G - Tacoma, WA



PT-478 BIA Cummins L-10 240G 1992 8/12/94 104000 CNG 0.01 26.8 9.2 35.8PT-478 BIA Cummins L-10 240G 1992 7/4/95 160000 CNG 0.00 44.3 8.8 22.8PT-479 BIA Cummins L-10 240G 1992 8/5/94 109010 CNG 21.0 7.4 11.5PT-479 BIA Cummins L-10 240G 1992 7/5/95 170000 CNG 0.00 27.3 7.0 3.6PT-480 BIA Cummins L-10 240G 1992 8/9/94 96730 CNG 0.02 34.7 8.6 36.4PT-480 BIA Cummins L-10 240G 1992 7/6/95 150000 CNG 0.03 46.1 10.5 40.7PT-481 BIA Cummins L-10 240G 1992 8/11/94 100800 CNG 0.00 20.9 11.2 33.7PT-481 BIA Cummins L-10 240G 1992 7/7/95 150000 CNG 0.00 38.8 16.9 28.3PT-482 BIA Cummins L-10 240G 1992 8/15/94 108654 CNG 0.00 20.6 6.0 4.0PT-482 BIA Cummins L-10 240G 1992 7/8/95 160000 CNG 0.00 23.2 7.7 0.8

Count 9 10 10 10Average 0.01 30.4 9.3 21.8

Max 0.03 46.1 16.9 40.7Min 0.00 20.6 6.0 0.8

CNG Buses - Cummins L10-260G - New York, NY



CBC-4903 TMC Cummins L-10 260G 1993 12/9/94 8517 CNG 0.04 20.9 14.9 0.6CBC-4903 TMC Cummins L-10 260G 1993 7/25/95 18872 CNG 0.01 12.0 21.4 1.5CBC-4904 TMC Cummins L-10 260G 1993 11/20/94 6764 CNG 0.04 9.2 9.5 0.4CBC-4904 TMC Cummins L-10 260G 1993 7/25/95 18666 CNG 0.01 14.2 13.7 8.7CBC-4907 TMC Cummins L-10 260G 1993 11/29/94 9048 CNG 0.01 11.1 15.5 0.8CBC-4907 TMC Cummins L-10 260G 1993 7/26/95 20091 CNG 0.00 5.4 16.7 0.8TBCC-2051 TMC Cummins L-10 260G 1993 11/17/94 5223 CNG 0.05 6.9 16.7 0.6TBCC-2051 TMC Cummins L-10 260G 1993 6/24/95 10871 CNG 0.05 4.6 24.1 0.8TBCC-2054 TMC Cummins L-10 260G 1993 11/19/94 2774 CNG 0.03 20.4 11.7 0.5TBCC-2054 TMC Cummins L-10 260G 1993 6/23/95 11993 CNG 0.02 15.5 16.5 0.9

Count 10 10 10 10Average 0.03 12.0 16.1 1.6

Max 0.05 20.9 24.1 8.7Min 0.00 4.6 9.5 0.4

Table 11. Summary of Emissions Results

32

33


Final Results

CNG Buses - Cummins L10-260G - Tacoma, WA


Number Make Make Model Year Date Odom* Fuel PM NOx HC CO

PT-803 BIA Cummins L-10 260G 1994 7/10/95 10000 CNG 0.03 11.6 9.7 0.7PT-804 BIA Cummins L-10 260G 1994 7/12/95 10000 CNG 0.01 6.6 16.1 0.4PT-806 BIA Cummins L-10 260G 1994 7/10/95 10000 CNG 0.03 15.6 17.2 0.6PT-807 BIA Cummins L-10 260G 1994 7/14/95 10000 CNG 0.00 11.6 23.3 0.9PT-811 BIA Cummins L-10 260G 1994 7/13/95 10000 CNG 0.01 10.6 11.1 1.1

Count 5 5 5 5* Estimated odometer reading at time of test Average 0.02 11.2 15.5 0.7

Max 0.03 15.6 23.3 1.1Min 0.00 6.6 9.7 0.4

Diesel Buses - Cummins L10 - Miami, FL



MDTA-9001 FLX Cummins L-10 1990 2/7/94 204000 D2 2.83 18.4 2.1 40.9MDTA-9001 FLX Cummins L-10 1990 2/24/95 250000 D1 3.10 20.2 4.9 26.6MDTA-9003 FLX Cummins L-10 1990 2/7/94 153000 D2 1.68 22.9 1.0 23.8MDTA-9004 FLX Cummins L-10 1990 2/8/94 174000 D2 2.19 24.0 1.0 27.1MDTA-9081 FLX Cummins L-10 1990 2/8/94 167000 D2 1.20 24.3 1.5 16.0MDTA-9082 FLX Cummins L-10 1990 2/9/94 172000 D2 1.26 21.2 1.5 11.3MDTA-9083 FLX Cummins L-10 1990 2/9/94 159000 D2 1.66 23.2 1.6 19.0

Count 7 7 7 7Average 1.99 22.0 1.9 23.5

Max 3.10 24.3 4.9 40.9Min 1.20 18.4 1.0 11.3

Diesel Buses - Cummins L10 - Tacoma, WA



PT-464 BIA Cummins L-10 1991 7/3/95 200000 D2 1.48 27.9 1.9 13.1PT-465 BIA Cummins L-10 1991 8/18/94 164006 D2 2.29 20.0 3.2 12.5PT-465 BIA Cummins L-10 1991 7/15/95 220000 D2 1.83 26.3 2.6 9.5PT-466 BIA Cummins L-10 1991 8/19/94 107943 D2 1.91 21.9 2.6 11.7PT-466 BIA Cummins L-10 1991 7/17/95 210000 D2 1.44 27.2 2.1 9.2PT-467 BIA Cummins L-10 1991 8/20/94 155815 D2 1.68 23.8 2.3 13.0PT-467 BIA Cummins L-10 1991 7/18/95 220000 D2 1.32 29.3 1.9 12.8PT-468 BIA Cummins L-10 1991 8/22/94 144051 D2 2.05 19.5 2.5 11.1PT-468 BIA Cummins L-10 1991 7/20/95 200000 D2 1.67 25.1 2.2 8.1

Count 9 9 9 9Average 1.74 24.6 2.4 11.2

Max 2.29 29.3 3.2 13.1Min 1.32 19.5 1.9 8.1

34


Final Results

Ethanol Buses - Peoria, IL



GPT-1504E TMC DDC 6V-92TA 1992 4/19/94 59925 E93 0.61 13.4 12.7 44.1GPT-1504E TMC DDC 6V-92TA 1992 4/18/95 94999 E93 0.33 11.9 6.1 27.6GPT-1506E TMC DDC 6V-92TA 1992 4/25/94 66567 E93 0.82 8.9 9.0 55.6GPT-1506E TMC DDC 6V-92TA 1992 4/10/95 103481 E93 0.72 12.2 9.2 31.6GPT-1507E TMC DDC 6V-92TA 1992 4/21/94 63588 E93 0.71 15.0 7.6 39.1GPT-1507E TMC DDC 6V-92TA 1992 4/6/95 102819 E93 0.88 15.2 10.1 33.8GPT-1508E TMC DDC 6V-92TA 1992 4/10/95 88049 E93 0.72 8.7 10.2 32.5GPT-1516E TMC DDC 6V-92TA 1992 4/20/94 84911 E93 0.22 21.6 6.0 32.3

Count 8 8 8 8Average 0.63 13.4 8.9 37.1

Max 0.88 21.6 12.7 55.6Min 0.22 8.7 6.0 27.6

Ethanol Buses - St. Paul, MN



MTC-8000 GLG DDC 6V-92TA 1991 10/5/94 27605 E95 0.44 24.5 22.2 61.3MTC-8000 GLG DDC 6V-92TA 1991 5/21/95 39609 E95 0.63 22.8 27.6 55.5MTC-8001 GLG DDC 6V-92TA 1991 10/1/94 29694 E95 0.40 21.6 10.2 31.2MTC-8001 GLG DDC 6V-92TA 1991 5/22/95 41979 E95 0.45 20.4 10.7 33.8MTC-8002 GLG DDC 6V-92TA 1991 5/25/95 33831 E95 0.55 14.2 20.8 43.2MTC-8003 GLG DDC 6V-92TA 1991 10/4/94 28722 E95 0.46 33.5 10.2 18.7MTC-8003 GLG DDC 6V-92TA 1991 5/25/95 42581 E95 0.59 24.3 13.7 43.2MTC-8004 GLG DDC 6V-92TA 1991 10/5/94 29119 E95 0.41 15.0 8.1 48.1

Count 8 8 8 8Average 0.49 22.0 15.4 41.9

Max 0.63 33.5 27.6 61.3Min 0.40 14.2 8.1 18.7

Methanol Buses - Miami, FL



MDTA-9211 FLX DDC 6V-92TA 1992 1/21/94 42283 M100 0.24 9.6 55.9 30.9MDTA-9211 FLX DDC 6V-92TA 1992 2/14/95 87000 M100 0.23 13.1 20.9 34.9MDTA-9212 FLX DDC 6V-92TA 1992 1/22/94 37745 M100 0.50 9.7 39.3 23.9MDTA-9212 FLX DDC 6V-92TA 1992 2/15/95 72364 M100 0.78 13.0 83.2 27.3MDTA-9213 FLX DDC 6V-92TA 1992 1/24/94 39500 M100 0.56 14.2 37.5 22.7MDTA-9213 FLX DDC 6V-92TA 1992 2/14/95 67697 M100 0.15 12.7 1.9 17.1MDTA-9214 FLX DDC 6V-92TA 1992 1/25/94 65450 M100 0.48 12.5 61.8 31.0MDTA-9215 FLX DDC 6V-92TA 1992 1/24/94 43800 M100 0.54 8.8 32.2 27.8MDTA-9215 FLX DDC 6V-92TA 1992 2/16/95 75000 M100 0.06 11.3 4.5 10.3

Count 9 9 9 9Average 0.39 11.6 37.5 25.1

Max 0.78 14.2 83.2 34.9Min 0.06 8.8 1.9 10.3

35


Final Results

Diesel Buses without Particulate Traps - St. Paul, MN



MTC-2207 GLG DDC 6V-92TA 1991 9/13/94 116911 D1 1.16 24.6 3.7 12.5MTC-2207 GLG DDC 6V-92TA 1991 5/19/95 142835 D1 1.01 25.6 3.6 6.6MTC-2208 GLG DDC 6V-92TA 1991 5/17/95 140678 D1 1.23 25.6 3.2 7.7MTC-2209 GLG DDC 6V-92TA 1991 9/15/94 126622 D1 0.94 24.4 3.2 12.2MTC-2209 GLG DDC 6V-92TA 1991 5/17/95 144612 D1 1.27 26.4 3.2 9.9MTC-2210 GLG DDC 6V-92TA 1991 9/17/94 122545 D1 1.13 24.3 3.2 12.8MTC-2210 GLG DDC 6V-92TA 1991 5/16/95 151201 D1 1.06 23.7 3.0 9.2MTC-2211 GLG DDC 6V-92TA 1991 9/16/94 107614 D1 0.92 26.5 3.5 9.1MTC-2211 GLG DDC 6V-92TA 1991 5/17/95 128418 D1 0.74 26.8 3.6 5.2

Count 9 9 9 9Average 1.05 25.3 3.3 9.5

Max 1.27 26.8 3.7 12.8Min 0.74 23.7 3.0 5.2

Methanol Buses - New York City



TBCC-2136 TMC DDC 6V-92TA 1993 11/12/94 22582 M100 0.16 6.4 4.0 9.6TBCC-2136 TMC DDC 6V-92TA 1993 6/19/95 42100 M100 0.05 5.9 0.5 4.8TBCC-2137 TMC DDC 6V-92TA 1993 11/16/94 9484 M100 0.15 7.5 3.7 12.5TBCC-2137 TMC DDC 6V-92TA 1993 6/19/95 17854 M100 0.07 6.1 1.1 6.6TBCC-2138 TMC DDC 6V-92TA 1993 11/14/94 6674 M100 0.16 7.4 1.5 10.4TBCC-2138 TMC DDC 6V-92TA 1993 7/11/95 16067 M100 0.04 6.7 0.2 3.8TBCC-2139 TMC DDC 6V-92TA 1993 11/15/94 7979 M100 0.11 8.0 2.5 11.5TBCC-2139 TMC DDC 6V-92TA 1993 6/21/95 20765 M100 7.3 0.8 5.9TBCC-2140 TMC DDC 6V-92TA 1993 11/17/94 15561 M100 0.14 7.1 6.1 16.7TBCC-2140 TMC DDC 6V-92TA 1993 6/21/95 23036 M100 6.0 0.5 2.2

Count 8 10 10 10Average 0.11 6.8 2.1 8.4

Max 0.16 8.0 6.1 16.7Min 0.04 5.9 0.2 2.2

Diesel Buses with Particulate Traps (traps removed prior to 1995 test date) - Peoria, IL


Number Make Make Model Year Date Odom Fuel PM1 PM2 NOx HC CO

GPT-1501 TMC DDC 6V-92TA 1992 4/15/94 68721 D1 0.14 27.0 2.8 10.4GPT-1501 TMC DDC 6V-92TA 1992 4/4/95 107954 D1 0.84 24.2 2.8 3.4GPT-1502 TMC DDC 6V-92TA 1992 4/15/94 59373 D1 0.70 25.1 2.5 10.7GPT-1502 TMC DDC 6V-92TA 1992 4/18/95 95032 D1 0.69 24.0 2.5 4.6GPT-1503 TMC DDC 6V-92TA 1992 4/27/94 58287 D1 0.48 24.6 2.8 12.6GPT-1503 TMC DDC 6V-92TA 1992 4/19/95 88913 D1 0.64 26.7 2.5 3.0

Count 3 3 6 6 61 PM results with particulate traps Average 0.44 0.72 25.3 2.6 7.52 PM results without particulate traps Max 0.70 0.84 27.0 2.8 12.6

Min 0.14 0.64 24.0 2.5 3.0

36

Alternative Fuel / Transit Buses Final Results

Diesel Buses without Particulate Traps - Miami, FL



MDTA-9067 FLX DDC 6V-92TA 1990 1/18/94 181385 D2 2.68 20.7 1.9 9.9MDTA-9067 FLX DDC 6V-92TA 1990 2/6/95 231619 D1 2.31 21.7 2.1 13.2MDTA-9068 FLX DDC 6V-92TA 1990 1/19/94 206506 D2 1.85 27.5 1.7 12.6MDTA-9068 FLX DDC 6V-92TA 1990 2/23/95 256087 D1 2.53 27.6 1.8 23.2MDTA-9070 FLX DDC 6V-92TA 1990 2/22/95 250000 D1 2.14 38.9 2.5 13.4MDTA-9071 FLX DDC 6V-92TA 1990 2/22/95 245674 D1 3.66 23.6 2.3 23.8

Count 6 6 6 6Average 2.53 26.7 2.1 16.0

Max 3.66 38.9 2.5 23.8Min 1.85 20.7 1.7 9.9

Diesel Buses with Particulate Traps (traps removed prior to 1995 test date) - St. Paul, MN


Number Make Make Model Year Date Odom Fuel PM1 PM2 NOx HC CO

MTC-2222 GLG DDC 6V-92TA 1993 9/23/94 36670 D1 0.23 27.1 2.5 10.8MTC-2222 GLG DDC 6V-92TA 1993 5/18/95 62561 D1 0.72 25.9 1.7 2.8MTC-2223 GLG DDC 6V-92TA 1993 9/26/94 34101 D1 0.79 25.8 2.7 9.9MTC-2223 GLG DDC 6V-92TA 1993 5/19/95 60000 D1 0.87 24.6 1.4 2.9MTC-2224 GLG DDC 6V-92TA 1993 9/27/94 40812 D1 0.20 27.0 2.9 10.5MTC-2224 GLG DDC 6V-92TA 1993 5/20/95 68890 D1 0.71 27.3 1.6 2.6MTC-2225 GLG DDC 6V-92TA 1993 9/28/94 33720 D1 0.31 28.4 2.9 9.2MTC-2225 GLG DDC 6V-92TA 1993 5/12/95 71583 D1 0.83 22.8 1.3 2.8MTC-2226 GLG DDC 6V-92TA 1993 9/29/94 26370 D1 0.18 26.9 2.8 12.8MTC-2226 GLG DDC 6V-92TA 1993 5/15/95 43043 D1 0.92 28.3 1.4 2.5

Count 5 5 10 10 101 PM results with particulate traps Average 0.34 0.81 26.4 2.1 6.72 PM results without particulate traps Max 0.79 0.92 28.4 2.9 12.8

Min 0.18 0.71 22.8 1.3 2.5

Diesel Buses tested on Biodiesel Blend - St. Louis, MO



SL-010BFD FLX DDC 6V-92TA 1988 04/24/96 22582 BD20 0.82 57.3 2.2 13.3SL-003BFD FLX DDC 6V-92TA 1988 04/15/96 36457 BD20 0.98 52.5 2.2 5.3SL-007BFD FLX DDC 6V-92TA 1988 04/13/96 238065 BD20 0.76 51.9 2.1 7.2SL-001BFD FLX DDC 6V-92TA 1988 04/12/96 140966 BD20 0.98 56.3 2.3 12.4

Count 4 4 4 4Average 0.89 54.5 2.2 9.6

Max 0.98 57.3 2.3 13.3Min 0.76 51.9 2.1 5.3

Diesel Buses (the same buses were tested on Biodiesel Blend) - St. Louis, MO



SL-010BFD FLX DDC 6V-92TA 1988 04/24/96 22592 D2 0.96 58.8 2.4 17.4SL-003BFD FLX DDC 6V-92TA 1988 04/22/96 37224 D2 0.73 51.6 2.6 6.9SL-007BFD FLX DDC 6V-92TA 1988 04/22/96 238702 D2 0.53 53.1 2.7 6.3SL-001BFD FLX DDC 6V-92TA 1988 04/20/96 141193 D2 1.16 46.0 2.9 7.8

Count 4 4 4 4Average 0.85 52.4 2.6 9.6

Max 1.16 58.8 2.9 17.4Min 0.53 46.0 2.4 6.3

35th St.

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Produced for the U.S. Department of Energy (DOE)

by the National Renewable Energy Laboratory (NREL),

a U.S. DOE national laboratory

BUS STOP Transit BusesAlternative

FuelAlternative

Fuel

Produced by the Center for Transportation Technologies and Systems at the National Renewable Energy Laboratory (NREL), a U.S. Department of Energy national laboratory

NREL 1617 Cole Blvd. Golden, CO 80401-3393

NREL/TP-425-20513 DE96013097 October 1996

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

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