Henry C. Miller.

The increasing use of gas, gasoline, and oil engines for small powers, and the probability of a much greater development in the near future, make this subject worthy of considerable attention. The simplicity of construction, the low cost and ease of operation, and wide range of adaptability are the important factors contributing to this popularity. The many faults of the first engines were so objectionable that extended use was out of question. Continued experiment, however, gradually removed the objectionable features, until to-day such engines attain a high degree of efficiency. As an economical source of power for small manufacturing and lighting plants, nothing except water power can approach them. They are practically automatic; therefore the expense of constant attendance, as with a steam plant, is not necessary to their successful operation. Any intelligent person who will give proper attention to the instructions will have little or no difficulty in obtaining satisfactory results. The many avenues still undeveloped are plainly evident when we consider the hundreds of small hotels at seaside and country resorts that still use kerosene lamps for light, and do laundry work and freeze ice-cream by hand power. A still larger number of manufacturing plants using steam power, for which the cost of the engineer-fireman in charge is greater than for the fuel used; would find a change to gas-engine power of decided benefit. Many small country villages could establish a cooperative lighting plant and enjoy the benefits now reserved to larger places.

Accompanying this increase in plants will come a demand for competent men to take charge of them. The young men who are wise and energetic enough to study electrical and engine work now will have no difficulty in securing satisfactory positions when they become competent to fill them. These preliminary observations are inserted for the purpose of enabling the reader to appreciate the importance of the subject and influencing him to more extended study of it, should it prove to be of interest.

We will now consider how such engines are constructed and operated, gas engines being understood, in this article, to include those using both gas, gasoline, and kerosene. A gas engine utilizes the expansive force of the nitrogen in air resulting from the heat developed by combustion. A certain volume of hydrocarbon gas, together with a larger volume of air, are inclosed in a cylinder and exploded. The heat due to combustion expands the nitrogen of the air, and the watery vapor resulting from the union of the oxygen of the air and hydrogen in the gas, as well as the monoxide and dioxide, products of combustion formed by the union of the carbon in the gas and the oxygen in the air. This expansive force is exerted upon the piston and conveyed by the piston-rod to the crank and crank-shaft which revolves and becomes available for transmitting power by belt or other device. As compared with the steam-engine, it utilizes a larger proportion of the heat developed. The steam-engine converts into useful energy from 12 to 18 per cent, of the potential heat units of the coal. A gas engine secures from 18 to 25 per cent, or more.

The gas used in these engines may be the regular illuminating or fuel gas, or may be the vapor of gasoline, naphtha, kerosene, or petroleum. In the latter case the fluid is vaporized, previous to being admitted to the engine, in what is termed a carbureter. This is a device for applying sufficient heat to the fluid to convert it into vapor, and is automatically regulated to supply the vapor only as needed.

In some types of engines the gas or vapor is admitted to the cylinder, and there mixed with a suitable volume of air; in other types this union is effected before being admitted to the cylinder. The method of admitting the charge also varies. In one type, termed the two-cycle engine, the gas and air mixtures are drawn into the cylinder during a part of the outward stroke, exploded and expanded during the rest of the stroke, and the products of combustion exhausted during the re-turn stroke. This type of engine develops about 20 per cent, of the heat value of the gas used. Some engines of this type also compress the gas mixture on the last part of the inward stroke. The four-cycle engine admits the gas mixture on the first outward stroke of the piston, compresses it on the inward stroke, explodes it on the second outward stroke, and exhausts on the second inward stroke, an expansive impulse being given only with every other stroke. In this type of engine the compression of the mixture gives the explosion far greater expansive force than in the non-compression type, thus overcoming the loss due to the less number of explosions.

In all types of engines the explosions and consequent number of expansive impulses are as rapid as is mechanically possible. This means high piston speed, so that the expansive effort shall be exerted on the piston as often as possible. The exhaust should be quick, that the hot gases may not overheat the walls of the cylinder. The rapidly repeated explosions generate a high degree of heat, which is removed by radiation. In small engines this is generally effected by the air, the outside of the cylinder being covered with corrugations similar to a steam radiator, only deeper. With large engines and some small ones, the cylinder is surrounded with a water-jacket, which prevents the excessive heating of the cylinder that otherwise would follow. This is connected to a supply tank, the warm water being of less specific gravity, rising and being replaced by cooler water. A constant circulation is thus maintained, which serves to keep the cylinder at the right temperature. One of the important features of gas-engine design is the regulation of the water circulation so that the cylinder shall be kept at just the right degree of heat to most economically utilize the power developed.

There are several types of devices for firing the charges in gas engines. The direct flame ignition is through a hole in the cylinder wall, which is uncovered by the piston at the proper moment, and the flame admitted to contact with the gas mixture. It is protected so that the explosion will not extinguish the flame.

The tube igniter consists of a metallic tube, preferably platinum, externally maintained at a high heat by a burner of the Bunsen type, into which the gas mixture from the cylinder is admitted and fired, thus firing the mixture in the cylinder. Careful designing and adjustment of this type is necessary to successful working.

Electric ignition is secured by a spark between two platinum electrodes inside the cylinder. The current may be generated from either a primary or storage battery and induction coil, or by a permanent magnet generator driven from the engine shaft by a belt. This latter dispenses with the battery and its care, and also the induction coil, and is increasing in popularity. Some engines are equipped with both tube and electric ignition.

The lubrication of cylinders is a matter of much importance with engines of large size. The intense heat of the exploded gases has a tendency to thicken some kinds of oil and make a gummy deposit on the surface of the cylinder, which would seriously affect the smooth running of an engine. Mineral oils of a high grade should be used, and the oil-feed regulated to the minimum amount that will prevent wear.

The efficient governors now in use on gas engines afford close regulation of speed and allow freedom from constant personal attention. The type most generally used regulates by increasing or decreasing the supply of gas or gas vapor.

Regularity of piston movement is secured by heavy fly-wheels on the crank-shaft which, by the acquired momentum, overcome the violent increase in speed that would otherwise follow the explosions. A heavy bed is also necessary to secure steadiness. A firm foundation is desirable, as with all engines, to prevent vibration.

In the management of these engines cleanliness is the important desideratum. The cylinder, feed, and exhaust pipes should be regularly examined to see that they are in proper condition. The frequency with which this is done depends largely on the service being performed. In dusty workrooms, a separate enclosure would be advisable, otherwise the dust-laden air will cause a deposit of sediment that may be troublesome. When examining an engine see that it is freed from the gas mixture by giving it two or three turns. Do not open valves for examination with a lamp or gas flame near at hand until satisfied that no gas leakage is liable. An electric light may be used with more freedom. The special details of particular makes of engine are fully covered by instructions accompanying them.

The power of a gas engine should approximate that used, as engines largely in excess of requirements are not as economical as when correct power is used. The excessive cost is not prohibitive, but should be avoided if possible. The probability that Texas crude petroleum may soon be available at low cost may serve as an incentive to develop oil using engines. With cheap petroleum, an efficient oil engine would find many uses.