Practical Hand Book of Gas, Oil and Steam Engines / Stationary, Marine, Traction; Gas Burners, Oil Burners, Etc.; Farm, Traction, Automobile, Locomotive; A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel.

by John B. Rathbun

(8) Gaseous Fuels.

While the calorific values of the different gases given in the accompanying table are approximately correct for gases burning in the open air at atmospheric pressure they develop widely different values in the cylinder of an engine because of the effects of compression and preheating. The table serves, however, as an index to the relative values of the fuels under ordinary conditions without compression. While natural gas has nearly eight times the calorific value of producer gas in the open air, its actual heat value in the cylinder is only about 45 per cent greater. While acetylene has an exceedingly high calorific value and explodes five times as fast as gasoline gas, it develops only 20 per cent more power in the same cylinder. Another item affecting the value of a gas is the rate at which it burns, which is in part a characteristic of the fuel and partly a factor of the conditions under which it is burnt. This subject is treated of in the chapter devoted to the heat engine.

The calorific value of a gas may either be computed from its chemical composition or by burning it in an instrument known as a calorimeter. A gas calorimeter consists of a small boiler or heating tank which is carefully covered with some non-conducting material so as to prevent a loss of heat to the atmosphere. The gas under test is burned in the boiler whose extended surface catches as much of the heat as possible and transfers it to the water in the boiler. The weight of the water heated and its temperature are taken when a certain amount of the gas has been burned (say 100 cubic feet), and from this data, the heat units per cubic foot of gas are computed.

FUEL GASES.
GAS	B.T.U. per Cubic Foot	Cubic Feet of Air Required to Burn 1 Cubic Foot of Gas		Usual Compression Lbs. per Sq. Inch	Ratio of Gas to Air	Explosion Pressure in Lbs. per Sq. In.	Temperature of Combustion F°	Ignition Temperature F°	Weight per Cubic Foot, Lbs.	Candle Power	Mean Effective Pressure
		Actual	Theoretical
Natural Gas	1000.	12.60	9	130	1–12.6	375		1100	.0459		94.00
Natural Gas	1000.			110	1–6	245		1000			72.00
Coal Gas	650.	9.00	5.85	80	1–9	285		1200	.035	18.00	85.00
Producer Anthracite	140.	1.20	1.85	160	1–1.2	360		1450	.065		88.00
Producer Bituminous	160.	3.20	2.20					1350
Water Gas (Uncarb.)	290.	3.60	2.20						.044
Water Gas (Carb.)	500.	8.50	5.15		1.8					22.00
Blast Furnace Gas	94.	1.10	0.70	170				1560	.080		77.5
Acetylene	1500.	20.00	12.60
Gasolene Vapor	520.	See Table of Liquid Fuels		70	1.12	245	1865	1550			79.00
Gasolene Vapor	520.			70	1.8	360	2950	925			82.00
Gasolene Vapor	520.			70	1.6	410	3160	910			84.50
Kerosene Vapor				60	1.8	285		945			85.00
Coke Oven Gas	520.	7.	5.4						.042
Alcohol				180		450
The values given above are approximate, and vary not only with the engine used but also with the method used in producing the gas, and with the character of the fuel used. The figures will give an idea of the relative value of the gases in a rough way.

As a British thermal unit is the amount of heat required to raise the temperature of one pound of water through one Fahrenheit degree (at about 39.1° F.), the total heat per cubic foot of gas as observed by the calorimeter is equal to the weight of the water multiplied by its rise in temperature in degrees, divided by the number of cubic feet of gas burned in the calorimeter. Since a British thermal unit is equal to 778 foot pounds in mechanical energy, its mechanical equivalent is equal to the number of British thermal units multiplied by 778.

Another difference between the actual and theoretical results obtained is that due the perfect combustion in the calorimeter and the imperfect combustion in the engine. Since some gases require more air for their combustion than others, less of the first gas will be taken into the cylinder on a charge than the latter, which tends still further to balance the heating effect of rich and lean gases in the cylinder.