Gaseous Fuels For Engine Use

By Staff

Annandale, Virginia 22003

Gas fuels for engines have been in use since the earliest days
of the internal combustion engine. One of the earliest gas engines
to be manufactured for commercial use was the Lenoir engine, built
in France between 1860 and 1865. The earliest gas fuels were
illuminating gas and natural gas. These two fuels are similar, but
illuminating gas contains more carbon and impurities than does
natural gas. Even after gasoline became popular in the late 1800s,
gas fuels continued to be and still arepopular for use with
stationary engines. Over the years LP-gas has become the most
popular engine fuel, with natural gas the second-most popular.

LP-gas is the abbreviation for liquified petroleum gas which can
be either BUTANE (C4H10), PROPANE
(C3H8) or a mixture of the two. LP-gas first
began to gain recognition around 1890. Around 1903 Herman Blau
liquefied a very high pressure gas known as Blaugas, which
contained propane, butane and ethane. Around 1910, A. N. Kerr began
experimenting with the compression and storage of LP-gas as a fuel.
In 1912 Frank P. Peterson is claimed to have driven a car powered
by LP-gas in New York City. Between 1922 and 1928 improved
processes were introduced to separate propane from butane and
propane became the most popular of the LP-gasses. In the 1940s
propane became popular as a tractor fuel and in the 1950s propane
gained widespread use as an automotive fuel.

Gas fuels are desirable for several reasons, the two main
reasons being cleanliness and low cost compared to other fuels. A
gaseous fuel will always mix with air much better than a vaporized
liquid fuel such as gasoline; therefore, combustion is more
complete and fuel distribution more efficient in a gas engine. With
an improved fuel-air mix and improved fuel distribution, combustion
in each cylinder will be complete and uniform; therefore a properly
tuned gas engine will produce far less exhaust emissions than will
a properly tuned gasoline engine. Also, a gas fuel mix cannot
dilute cylinder wall lubricating oil, (a gasoline fuel mix
always dilutes some oil) so piston rings and pistons
receive excellent lubrication. Combustion of a gaseous fuel does
not produce acid and lead contaminants, so the crankcase oil also
stays clean and sludge formations are greatly reduced or completely
eliminated. A perfect example of this is the fact that the oil in a
gas engine has to be changed regularly because the oil gets thicker
instead of thinner and dirty as in a gasoline engine. Low operating
cost is due to the fact that the gas itself is usually lower in
cost than other fuels along with the fact that engine life is quite
long and the need for tune-ups and oil and filter changes is

Unfortunately, there is one area of the engine that can be
adversely affected by gas fuels; that area is the valves and valve
seats. The type of problem usually encountered is short valve
stem/guide life and short valve face/seat life. Gas fuels contain
no lead or other additives, therefore, unless adequate oil supply
is provided, valve stem and guide wear can occur. Valve seat and
face life is also thought to be a factor of the lead content of the
fuel. Some LP-gas carburetion experts feel that the lead forms a
microscopic layer on the valve and seat and actually keeps the two
parts from touching each other. This lack of direct contact would
keep small metal particles from sticking to one piece and being
pulled off of the other piece at high temperatures. In actual
practice, however, valve problems are usually encountered in
high-revving, heavy duty engines that are constantly being run at
their peak endurance levels. With show engines or family cars and
trucks that are rarely, if ever, pushed to their limits, valve
trouble is not likely as long as the valve stems have a good oil
supply. Engines with hard (stellite) valves and seats should not
encounter valve troubles. For older engines designed for leaded
gasoline, valves and seats should both be ground to 45° (do not
grind an interference angle) and the seats can be left slightly
wider than for gasoline. Valve clearance should also be slightly

Converting an engine to gas is quite easy, although the work
should be carried out by people who are familiar with correct
gas-handling methods and have a basic understanding of gas

For clarity of text, only the two types of LP-systems will be
described here. The two systems are Liquid Withdrawal and Vapor
Withdrawal. The liquid withdrawal system is used on engines with a
high fuel demand such as a car, truck or tractor. The vapor
withdrawal system is used on engines with a low fuel demand such as
small engines. A liquid withdrawal system draws liquid fuel from
the bottom of the tank, the fuel travels through the fuel line as a
liquid and is then changed back into a gas at the
vaporizer/regulator. A vapor withdrawal system draws gas from the
top of the tank and does not involve a vaporizer. The main
components of both LP gas systems are very similar to each other.
Both systems utilize a flexible high pressure fuel line, fuel
filter, primary regulator, secondary regulator and carburetor. For
automotive use a positive shut-off solenoid is used on the fuel
line. The functions of the primary regulator is to reduce the tank
pressure to about 5-6 pounds per square inch before it enters the
secondary regulator. The secondary regulator then meters the fuel
according to carburetor venturi vacuum. With liquid withdrawal
systems, a vaporizer (converter) is added ahead of the primary
regulator. The vaporizer is simply a chamber where the liquid
LP-gas expands and changes back into a dry gas; to offset the
freezing action of this expansion vaporizers are heated by water
from the engines cooling system, or in the case of air cooled
engines the vaporizer is heated by cooling air or exhaust. The two
regulators and vaporizers (if used) are usually combined into one
compact unit.

Carburetors for gas engines work on the same principle as
carburetors for gasoline engines, however, some gas carburetors
have an integral secondary regulator or are of the variable venturi
design. A carburetor adaptor is a single venturi which is mounted
on top of the gasoline carburetor, beneath the air filter. A
carburetor adaptor is usually used on cars and trucks so that the
original gasoline fuel system can be left intact for emergency

Natural gas, Methane (CH4) and Hydrogen (H) are
sometimes used as engine fuels. Natural gas and methane are often
used as fuels for stationary engines and have also been used as
automotive fuels. Hydrogen has been used as an automotive fuel on
an experimental basis.

When running with natural gas, methane, or hydrogen the
engine’s horsepower output must be de-rated due to the low heat
content of these fuels; when using propane or butane, the engines
power will be the same as for gasoline as long as a good grade of
fuel is used. HD-5 is the recommended grade of propane; it is 95%
pure propane only.

In conclusion, in addition to their desirability, gaseous fuels
are quite safe. LP-gas has been proven to be safer than gasoline
due to the strength and durability of the components. LP-gas motor
fuel tanks for engine applications are made of heavy-gauge steel
and all fuel system components must be U.L. approved.

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