Gaseous Fuels For Engine Use

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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 reduced.

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 increased.

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 carburation.

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 use.

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.