Recent articles in the press have

raised the specter of another

possible energy crisis (see

sidebar on pg. 2). In addition, concern

is growing about the air quality issues

resulting from vehicle exhaust emissions and about global climate change

from greenhouse gases such as carbon dioxide. Despite these concerns,

we still have an economic imperative

of continuing to produce and transport goods, and of providing services

important for economic growth.

Figure 1 shows the correlation

between gross domestic product 

(and hence, economic activity and

growth) and freight transport (in 

ton-miles of travel). Meeting energy 

demands for moving goods is, therefore, critical to the economy. Freight

transport is expected to continue

growing, and with it, the amount of

energy used by heavy-duty trucks.

Projections by the Energy Information Administration (EIA) show

that by the year 2010, if current

trends continue, heavy vehicles

(trucks of all classes including the

heavy-duty Class 7 and 8) will be

consuming as much fuel as automobiles (Figure 2). Truck energy use is

less discretionary, even essential for

maintaining economic growth. The

question, then, is how can we sustain

this continuing expansion of economic

activity in an environmentally sound

manner?

The Importance of Efficiency

The diesel cycle (compressionignition) engine is the engine of

choice for heavy-duty freight transport, where efficiency and low-speed

power requirements are important. 

In conjunction with industry partners,

the DOE Office of Heavy Vehicle

Technologies is funding research 

and development of advanced lowemissions, 55% efficient (known as 

LE-55) diesel engine technologies to

enable heavy-duty trucks to continue

operating efficiently, plus meet EPA

emissions standards proposed for

2004. Research to date indicates that

the heavy-duty diesel is well on its

way to being an environmentally

sound engine. Indeed, three Cummins

Diesel engines running on natural 

gas have been certified as meeting

the California Air Resources Board 

(Continued on pg. 2)

Volume 6, Number 2

Future Fuels for Heavy-Duty Trucks

by James J. Eberhardt, Director, Office of Heavy Vehicle Technologies, Energy Efficiency and Renewable Energy,

U. S. Department of Energy (DOE)

INSIDE THIS ISSUE

LNG Tax Relief......................4

The Status of the Federal

Clean Fuel Fleet Program....4

Cummins Engine Successfully

Meets EPA and CARB

Standards...............................7

Z1-B155402

1950 1955 1960 1965 1970 1975 1980 1985 1990

GDP (billions of 1987 $)

1,000

0

2,000

3,000

4,000

5,000

6,000

1,000

0

2,000

3,000

4,000

5,000

6,000

Billions of ton-miles of travel

Ton-miles of travel

Gross domestic product

Figure 1. Gross domestic product correlated with freight transport
(CARB) and EPA 1998 on-highway

heavy-duty truck and bus emissions

standards without using exhaust 

aftertreatment catalysts. 

Comparable efficiency and emissions

levels have been achieved in diesel

engines running on dimethyl ether

(DME) with exhaust gas recirculation

(EGR). DME is a fuel with physical

properties close to those of propane

but with excellent compression

ignitability.

As important as efficiency is to profitability and to emissions reductions,

efficiency improvements alone are

not enough to greatly reduce petroleum consumption for heavy-duty

transport.

Perhaps the most significant barrier

to the use of alternative fuels for

heavy-duty trucks is the lack of a 

fuel production and distribution

infrastructure. Commercial transport

operators depend on the ready availability of cost-competitive fuel for

seamless operation and for profitability. In addition, the cost and

expected service life of engines in

commercial applications (for example, one million miles or more are

expected of diesel engines in tractortrailer combinations) preclude these

operators from investing in alternative fuel engines for which the fuel 

production and distribution infrastructure is limited or nonexistent. 

Research has demonstrated that

diesel engines can run on natural gas,

DME, diethyl ether, methanol, ethanol, and biodiesel. These dedicated

alternative fuel engines, however,

have not made significant inroads

into the heavy-duty transport market,

for the reasons outlined above. In

addition, the alternative fuel engines

have needed extensive tuning. Moreover, running such engines on fuels

requiring ignition assist (e.g., spark,

glow plug, or pilot injection) results

in efficiencies lower than those

achieved with petroleum-based 

(compression-ignitable) diesel fuel.

Future Fuels Strategy

To design a stategy for future fuels, it

makes sense to focus on fuel properties that are suitable for the heavyduty diesel cycle engine and use

plentiful feedstocks to produce the

fuel with these properties. The current feedstock is almost exclusively

petroleum. However, if other feedstocks such as natural gas, coal, and

biomass can be converted cost effectively into fuels appropriate for the

diesel engine, they can be dispensed

using the existing fuel infrastructure,

and then used by a single energy

conversion system, the diesel cycle

engine. These future fuels from alternative, non-petroleum resources

could then find significant penetration into the heavy-duty transport

market. The DOE Office of Heavy

Vehicle Technologies envisions the

diversity-of-feedstocks strategy

shown in Figure 3.

What fuel properties are required by

the diesel engine? Cetane number 

has traditionally been an empirical

measure of fuel ignitability. Fuels

lternative Fuels In Trucking — Volume 6, Number 2 2 Z1-B155401

Class 3-8 trucks

Class 1-2 trucks

Automobiles

10

8

6

4

2

0

1970 1975 1980 1985 1990 1995 2000 2005 2010

Energy use (Mbbl/day)

Actual Projected

Figure 2. Actual and projected fuel use by cars and by trucks

Relevant Publications

• Hodel, D., Crisis in the Oil Patch:

How America's Energy Industry is 

Being Destroyed and What Must be

Done to Save It, Washington, D.C.,

Lanham, MD: Regnery, 1993.

• Romm, J.J. and C.B. Curtis, "Mideast Oil Forever?" The Atlantic 

Monthly, April 1996.

• Romm, J.J. and C.A. Ervin, "How 

Energy Policies Affect Public 

Health," Public Health Reports,

September/October 1996.

• "Development of a ProductionFeasible Common Rail Fuel 

Injection System for Liquid 

Dimethyl Ether (DME) for Use 

in Heavy-Duty Vehicles," Golden,

CO: National Renewable Energy 

Laboratory, 1996, http://www.afdc. 

nrel.gov/fuelutil/engoptim96.html

• Fritsch, P., "Exxon Project to 

Expand Use of Natural Gas," The 

Wall Street Journal, October 30,

1996.
with a cetane number of 50 or higher

are suitable for compression ignition

in diesel engines. Table 1 shows the

properties of some of the alternative

fuels that have been tested as well as

those of petroleum-based diesel fuel.

Comparing cetane numbers, we can

see why certain fuels do not perform

very well in diesel cycle engines.

It is possible for the nation to take

advantage of its indigenous feedstock resources (coal, natural gas,

and biomass) to produce high-quality 

fuels for heavy-duty diesel engines.

Since World War II, we have known

that coal can be converted to diesel

fuels through the synthesis gas route,

commonly called Fischer-Tropsch

(FT) synthesis. Not so widely recognized is that the same process can be

used to convert methane (natural gas)

to FT diesel fuel as well. Last but not

least, biomass can be "gasified"

(turned into a mixture of carbon

monoxide and hydrogen called 

synthesis gas or syngas). From syngas, a number of high-quality fuels

appropriate for compression ignition

engines can be made, including 

DME and FT diesel.

DME has physical properties akin to

propane (see Table 1) for which a

distribution infrastructure already

exists. In Canada, for example,

significant numbers of propanepumping stations are available at

gasoline retail outlets. FT diesel is

compatible with the current diesel

fuel infrastructure. Indeed the first

usage of FT diesel is likely to be as 

Alternative Fuels In Trucking—Volume 6, Number 2 3 Z1-B155403

Diversity of

feedstocks

• Petroleum

• Natural gas

• Coal

• Biomass

Petroleum

refining

Synthesis

gas

A common

diesel fuel

specification

One energy

conversion

system

Uses existing fuel

infrastructure

• Cetane number

• Energy density

• Emissions characteristics

• Cost competitive

•

•

Diesel cycle engine

Figure 3. A diversity-of-feedstocks strategy

Table 1. Selected Properties of Potential Diesel Engine Fuel(s)

Property DF-2 Diesel Fischer- Biodiesel CNG Propane Methanol Ethanol DME Diethyl ether

Tropsch HD-5

Formula Hydrocarbons Various oils Principally Principally

C10-C21 and esters CH4 C3H8 CH3OH CH2H5OH CH3OCH3 C2H6OC2H6

Boiling point (%F) 370–650 350–670 360–640 -258.5 -43.9 149 172 -13 94

Vapor pressure (psi @ 100°F) <0.2 n/a n/a n/a 170 4.6 2.3 116 16.0

Cetane number 40–55 >74 >48 low low low <5 >55 >125

Auto-ignition temp. (°F) ~600 ~600 – 990 870 867 793 662 320

Stoichiometric air-fuel ratio (wt) 15.0 15.2 13.8 16.4 15.7 6.45 9.0 8.9 11.1

Lower heating value (Btu/lb) 18,500 18,600 16,500 20,750 19,940 8570 11,500 12,120 14,571

Specific gravity (60°F) 0.860 0.783 0.880 – 0.506 0.796 0.794 0.66 0.714
lternative Fuels In Trucking — Volume 6, Number 2 4

a blend for petroleum-derived diesel

fuels to upgrade their cetane number

and lower their sulfur and aromatics 

content.

In addition to being gasifiable, the

renewable biomass feedstock has 

two additional routes to provide 

additional fuels for heavy-duty

diesels. Biodiesel can be made from

vegetable oils by a simple esterification process. Reaction of soybean or

canola oils high in carboxylic acids

with methanol (or ethanol) produces

the dimethyl or diethyl ester of these

carboxylic acids. Both have good

properties for diesel fuel. Indications

are that biodiesel formulations may

be useful in blends to upgrade

petroleum-based diesel fuels. 

Conclusion

The diesel cycle engine has already

been established as the engine of

choice for the heavy-duty transport

industry because of its fuel efficiency,

durability, and reliability. In addition,

it has proven to be capable of using

alternative fuels, albeit at efficiencies

lower than those achieved with petroleum-derived diesel fuel. Alternative

fuel dedicated engines have not made

significant inroads into the heavyduty truck market because truck fleet

operators need a cost-competitive

fuel and a reliable supply and fueling

infrastructure. In lieu of forcing

diverse fuels from as many diverse

domestic feedstocks onto the end

users, the Office of Heavy Vehicle

Technologies envisions a future fuels

strategy for the heavy-duty transport

sector where the diverse feedstocks

are utilized to provide a single fuel

specification (dispensed from the

existing fueling infrastructure).

Under this scenario, this fuel would

run efficiently in a single highefficiency energy conversion device,

the diesel cycle engine. This strategy

may also allow the U.S. commercial

transport industry to gain a measure

of security from rapid fuel price

increases by relying less on a single

feedstock source to meet its increasing fuel requirements.

On May 22, 1997, the EPA

announced a 1-year delay for nonattainment areas subjected to the Clean

Fuel Fleet Program (CFFP), but it is

not yet clear if this delay is voluntary. With this delay, covered fleets

must begin purchasing clean fuel

fleet vehicles (CFFVs) in model year

1998 (MY 98). The CFFP provisions

are part of the Clean Air Act Amendments of 1990, in which Congress

chose to create a market for lowemission vehicles (LEVs) by requiring fleet operators to purchase these

vehicles. They mandated that metropolitan areas with 1980 populations

greater than 250,000, which either

(1) the EPA has designated "serious,"

"severe," or "extreme" for ozone, or

(2) have a design value of 16.00 

parts per million for carbon monoxide, implement a Clean Fuel Fleet

Program starting in MY 98. However,

the provisions of the CFFP prohibit

the EPA from ordering vehicle manufacturers to produce clean fuel fleet

vehicles.

Liquefied Natural Gas (LNG) Tax Relief

The Status of the Federal Clean Fuel Fleet

Program

As a result of the Revenue Reconciliation Act of 1997, the federal

excise tax on LNG will be reduced

from 18.3 cents per gallon to 11.9

cents per gallon as of October 1,

1997. Because of the difference in

energy content of LNG compared

with diesel fuel, the LNG federal

excise tax, which supports the

Highway Trust Fund, now stands 

at approximately 20.5 cents per

diesel equivalent gallon, down 

from 31.5 cents. Given that the federal excise tax on diesel itself is

24.3 cents per gallon, this tax rate

actually gives LNG a tax advantage

over diesel, the fuel with which it

competes most directly.
In a press release dated July 15, the

EPA announced the delay and that 

it will issue its final ruling later this

year. It will allow areas to start the

program this fall, although most

areas subjected to the program will

probably wait until model year 1999.

Initially, the EPA didn't expect any

problems with implementing its plan

as designed, but the agency was

unprepared for the concerns raised 

at a recent CFFP stakeholders meeting. Various air quality officials

raised issues about the lack of cleanfuel vehicle offerings, and participants at the meeting criticized the

EPA for waiting so long to take

action. EPA representatives assured

these participants that it intends to

work with the automakers, fuel

providers, and state providers to

make the program work. The EPA

intends to change its certification

program to make it easier for automakers to certify products to the

CFFV standards. The impact of 

using federal reformulated gasoline

in vehicles certified on California's

reformulated gasoline (CARFG) will

also be reviewed. The EPA wants to

determine whether vehicles currently

certified on CARFG can be operated

on federal gasoline within CFFV

standards.

Under original CFFP regulations,

30% of light-duty (<8500 gross 

vehicle weight) vehicles purchased

by covered fleet operators with 10 

or more centrally fueled vehicles in

MY 98 must use clean fuels—fuels

that burn more completely and meet

EPA emissions standards. For heavyduty vehicles, the requirements are

50% in MY 98. The EPA estimates

that in MY 98, the demand for cleanfuel fleet vehicles would be approximately 47,000 for light-duty vehicles,

and 12,000 for heavy-duty vehicles.

CFFP rules further require that in

1999, 50% of fleet vehicles purchased must use clean fuels, and 

this increases to 70% in the year

2000. The CFFP rules do not apply

to small fleets—fleets with less than

10 vehicles—nor does it apply to

emergency, law enforcement, or 

construction vehicles. 

The Clean Air Act (CAA) allows

states to opt out of the CFFP 

requirements if they can devise 

other methods of controlling the air

pollution problem in their nonattaining metropolitan areas. The CAA

also allows these areas to request a 

1-year delay in adopting the policies.

Originally, the Clean Air Act Amendments (CAAA) Clean Fuel Fleet

Program affected 22 metropolitan

areas. At present, Atlanta, Metropolitan Washington D.C., ChicagoGary-Lake County, MilwaukeeRacine, Denver-Boulder, and Baton

Rouge are the only six areas that

remain in the EPA program. 

Several nonattainment areas have

decided to opt out of the federal

CFFP program and have started 

their own programs for attaining 

the EPA's standards for air quality.

California, for example, has implemented its own Clean Fuel Fleet

Program by setting up the California

LEV program. This program, however, does not cover vehicles between

14,000 and 26,000 gvwr. It only

applies to lighter vehicles; that is,

Classes 1-3 trucks and cars. The 

sidebar lists the industry classification of trucks by weight.

Connecticut has also opted out of the

federal CFFP by adopting its own

CFFP. In addition, Connecticut chose

to achieve compliance by obtaining

further emission reductions through 

enhancing its inspection and mainte

nance (I/M) program in the areas not

affected by the state CFFP. Connecticut also gives tax benefits to fleets

that purchase electric vehicles, or

those that run on alternative fuels 

that burn cleaner and meet the EPA's

emissions requirements. Incentives

also apply to equipment purchased

for the purpose of converting trucks

to alternative fuels, and equipment

for compressed natural gas fueling

stations. 

As shown in Table 2, Massachusetts

and Rhode Island have also opted 

out of the EPA's CFFP program.

Both states have devised their own

programs for improving the air quality

of their metropolitan areas. Massachusetts has adopted the California

LEV program, and Rhode Island has

agreed to use reformulated gasoline,

and will probably implement a voluntary alternative fuel program as well.

The areas that have petitioned for a

1-year delay are: Chicago-Gary-Lake

Counties, Baton Rouge, Metropolitan

Washington D.C., and MilwaukeeRacine. These areas must have revisions to their State Implementation

Alternative Fuels In Trucking—Volume 6, Number 2 5 

Definitions of Trucks and Cars by

Weight

Class I: 6000 lb or less

Class II: between 6001 and 

10,000 lb

Class III: between 10,001 and 

14,000 lb 

Class IV: between 14,001 and 

16,000 lb 

Class V: between 16,001 and 

19,500 lb 

Class VI: between 19,501 and 

26,000 lb 

Class VII: between 26,001 and 

33,000 lb 

Class VIII: 33,001 lb and higher
Plans (SIPs) approved by the EPA,

which means they have to conform 

to the provisions established in

Section 246(c) of the Clean Air Act.

The areas asking for the delay have

to start phasing in their CFFPs by

MY 99. In all cases, if fleet operators

purchase CFVs under the current 

regulations earlier than the 1999

model year, they can earn credits.

Table 2 shows the status of the State

Clean Fuel Fleet Program as of May

1997.

The fleet operators who work under

the CFFP will have to deal with the 

increased costs of adapting their

fleets to use alternative fuels. Much

work has been done to develop

infrastructure for the alternative 

fuels so that fleets around the country

can use them, and the EPA allows

some added flexibility with its 1-year

delay option. This delay should make

it easier for fleet operators to make

necessary arrangements to adjust to

the mandates of the CFFP. This will

also allow for expanded certified

vehicle availability to meet these

requirements and the additional time

will allow fleets to learn their capabilities and integrate them, as well as

provide greater opportunity for truck

original equipment manufacturers to

market their alternative fuel vehicles.

lternative Fuels In Trucking — Volume 6, Number 2 6

State CFFP Covered Area Current Status

California Bakersfield Opted out of CFFP

Fresno

Los Angeles-Anaheim-Riverside

Sacramento

San Diego

Colorado Denver-Boulder Developed federal CFFP

Connecticut Greater Connecticut Opted out of CFFP

Delaware Wilmington-Trenton Plans to opt out of CFFP

District of Columbia Metro Washington D.C. Requested 1-year delay for CFFP

Georgia Atlanta Developed federal CFFP

Illinois Chicago/Gary Lake 1-year delay for CFFP granted 

via May 22 means

Indiana Gary 1-year delay for CFFP granted

via May 22 means

Louisiana Baton Rouge 1-year delay for CFFP granted

via May 22 means

Maryland Baltimore Plans to opt out of CFFP

New Hampshire Developed state CFFP

Pennsylvania Philadelphia Plans to opt out of CFFP

Rhode Island Providence Opted out of CFFP

Texas Houston-Galveston-Brazoria Developed state CFFP

El Paso

Beaumont-Port Arthur

Virginia Northern VA/Washington D.C. 1-year delay granted, 

developing state CFFP for

Richmond/Hampton Roads area

Wisconsin Milwaukee-Racine 1-year delay for CFFP granted

Table 2. Current Status of Federal CFFP in Nonattainment Areas
Alternative Fuels In Trucking — Volume 6, Number 2 7

In 1996, the Cummins Engine Company, Inc., introduced on the market

a natural gas engine that has been

recognized as one of the most technologically advanced and versatile

engines available today. The Cummins B5.9G engine has successfully

met both the EPA's 1998 emissions

requirements and the low oxides 

of nitrogen (NOx) standards set by

CARB. As a result, both of these

agencies certified the B5.9G engine

as of February 1997. 

The Cummins B5.9G engine is a

spark-ignited, six-cylinder, 5.9-liter

engine with closed-loop air/fuel 

ratio control, lean-burn technology,

advanced engine controls management, and integrated subsystems. It

also has altitude and fuel variability

compensation mechanisms that make

it very useful at high altitudes. The

lean-burn technology increases the

thermal efficiency of the B5.9G to 

up to 37% while decreasing its NOx

emissions, and it does not even need 

an exhaust catalyst to meet these

emissions standards.

Truck operators can use it in any number of vehicles, including school

buses, shuttle buses, recycling 

trucks, pickup and delivery trucks,

and sweepers. The engine is available

in 195 hp and 150 hp with 420 and

375 ft-lb torque peak ratings, respectively. A 230 hp, 500 ft-lb rating

should be available in January of

1998. Table 3 shows the B5.9G's 

original equipment manufacturer

(OEM) availability for use in trucks,

buses, and utility vehicles.

The Cummins B5.9G has already

attracted a significant customer, the

U.S. Postal Service (USPS). As part

of a joint venture between DOE and

USPS, the Freightliner Custom 

Chassis Corporation's plant in 

Gaffney, S.C. has been building 

two-ton mail trucks with the B5.9G

engine. The mail trucks will be used

and tested in Atlanta, GA; Denver,

CO; El Paso, TX; Huntington Beach,

CA; and New York City. 

The Gas Research Institute (GRI) has

also taken an active interest in the

Cummins B5.9G natural gas engine,

and will closely monitor the performance and efficiency of the mail

trucks that use it. GRI conducts 

performance evaluations on these

engines in heat and cold, humid and

dry weather, and sea-level to high

altitude environments at several 

EPA-certified testing facilities. The

natural gas engines are being compared to diesel engines under similar

environ-mental conditions. GRI plans

to make a final report on these tests

available to fleet operators in 1998.

With interest in natural gas engines

increasing because of the more stringent requirements of the Clean Fuel

Fleet Program, the Cummins B5.9G

engine has a very promising future.

This engine's strengths—cool burning combustion technology, utility 

in a wide variety of trucks, and 

double certification from the EPA

and CARB—are making it a popular

choice for the trucking industry's

many medium-sized vocations.

Cummins Engine Successfully Meets EPA and

CARB Standards 

School/Shuttle/Transit Medium-Duty Truck Refuse

Blue Bird Elgin-sweeper Crane Carrier

Cespel/EAG (Europe) ERF (UK) ERF (UK)

Champion Coach Freightliner Custom Chassis

Chance Coach Leyland-DAF (UK)

Dennis Specialty (UK) Ottawa Truck-yard spotter

El Dorado National SISU (NA)-yard spotter

Goshen Coach

Matthews Bus

North American Transit

Neoplan (Europe and NA)

Optare (UK)

Orion Bus

Metrotrans

Spartan

Specialty Vehicles

Thomas Built

Table 3. The B5.9G's Availability
Volume 6, Number 2

René Howard, Editor

Jim Miller, Graphic Designer

Alternative Fuels in Trucking is published quarterly

by the National Renewable Energy Laboratory

(NREL), a U.S. Department of Energy (DOE) 

national laboratory. The newsletter is written by 

the American Trucking Association Foundation’s

(ATAF’s) Trucking Research Institute.

The aim of Alternative Fuels in Trucking is to

inform fleet owners and operators, equipment suppliers, government officials, and other interested parties

about important developments in the use of alternative

fuels in heavy-duty trucks. Suggestions and comments

are welcome and may be directed to the National

Alternative Fuels Hotline at 800-423-1DOE. Views

expressed by guest authors are their own, and not

those of ATAF, DOE, or NREL.

NREL/BR-540-23440

October 1997

Printed with a renewable-source ink on paper

containing at least 50% wastepaper, including

20% postconsumer waste

UNITED STATES OF AMERICA

• DEPARTMENT OF ENERGY •

U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

Office of Transportation Technologies

How to Reach Us

• The AFDC World Wide Web 

address is 

http://www.afdc.doe.gov

• The Alternative Fuels in

Trucking newsletter is available

on the WWW at http://www.

afdc.doe.gov/1/trknews It is

available on-line 2 or 3 weeks

before the newsletter is mailed.

To speak to a human

being, call the

National Alternative

Fuels Hotline at 

800-423-1DOE.