NATURAL GAS FOR CARS AND TRUCKS: OPTIONS AND CHALLENGES - Natural Gas-powered Cars and Trucks: Options and Issues - page 9

Propane Autogas

Propane accounts for about 2% of the energy used in the United States. It
is stored and transported in compressed liquid form, but it is vaporized into a
gas for final use when released from a pressurized storage container. 35 Propane
is commonly used for home and water heating, cooking, and refrigeration,
especially in rural areas without natural gas. In addition, the chemical industry
uses propane as a raw material.
Propane's relatively high energy density 36 and clean-burning attributes
have made it attractive for some types of transportation. It is known as autogas
or liquefied petroleum gas (LPG) when used as a motor vehicle fuel. 37 Only a
very small part of the propane manufactured each year is used for
transportation. 38 Stored in a vehicle tank pressurized to about 150 pounds per
square inch, it becomes a liquid with an energy density 270 times greater than
the gaseous form. Because its Btu rating is lower than gasoline, it takes more
fuel to drive the same distance. As with CNG, vehicles are produced as
dedicated propane or bifuel, with separate fueling systems permitting use of
either propane or gasoline. General Motors offers the only light-duty propane
vehicles now on the market, the Chevrolet Express and GMC Savana vans. 39 It
is estimated that about 157,000 propane vehicles are on U.S. roads, most of
them school buses, police cars, and other fleet vehicles. 40

Other Natural Gas Fuels

Natural gas can be processed into a number of other fuels that are suitable
for use in motor vehicles:

 DME is a colorless gas that can be derived from renewable materials

and fossil fuels like natural gas and coal. When liquefied under
pressure, it has properties similar to propane. It can also be used as a
replacement fuel in diesel trucks. 41 China accounts for about 90% of
global DME consumption, using it for residential heating and cooking
but also increasingly as a truck and bus fuel. 42 A privately funded U.S.
pilot program for trucks is underway.

 Using gas-to-liquids technology (GTL), natural gas can be converted

into synthetic base oil with fewer impurities than petroleum, resulting
in less wear of equipment and greater fuel efficiency. GTL products
can be used as replacements for motor oil and diesel fuel (or blended