Campbell gas engine.—Fig. 29 shows a very compact engine, built by the Campbell Gas Engine Co. There are only three valves; the admission valve is regulated by a centrifugal governor. The petroleum is gasified in a vaporizer heated by a lamp. The speed is very constant and the motor easily started.
Fig. 29.—Campbell Oil Engine.
Grob motor.—This engine is constructed in Leipzig and uses the Otto cycle, and, like the motors already described, works well with ordinary petroleum. The arrangement (Fig. 30) is vertical; the cylinder and valve gear are supported on a hollow cast-iron column, which in turn is bolted to a circular bed-plate. The shaft has on one side a fly-wheel and on the other a pulley. The working valve parts are all situated on the outside so as to be easily got at. The oil-pump marked in the figure drives, the petroleum into a vaporizer, where it is broken up into very minute drops. This oil spray becomes mixed with air, and passes through a vaporizing tube heated by a flame. In the state of vapour the explosive mixture passes into the cylinder, where it is ignited at the right moment by a red-hot tube. In consequence of the compression during a quarter of the cycle, the combustion is very rapid, the power of these engines being very great for their size. Ignition, and therefore the explosion, only takes place when the speed falls below the normal. This regulation is obtained by a pendulum governor, and ensures a very constant speed. The cylinder walls are warm enough to make sure of ignition happening.
Fig. 30.—Section of a Grob Motor.
All heat engines based on the principle of the explosion of a volume of gas require an arrangement for drawing superfluous heat from the cylinder, otherwise it would soon become red-hot. This cooling is obtained in small engines by the circulation of air about a large surface especially attached to the cylinder walls, but in larger engines this means is insufficient, and it becomes necessary to use water as a cooling agent. If water is laid on there is no difficulty about this, but it occasionally happens that water is too expensive, or that it is unobtainable; in such cases it is usual to erect a large cylindrical reservoir of galvanized iron holding about ten litres of water per horse-power of the engine. This reservoir is connected by two pipes from the top and bottom to the water jacket of the engine cylinder, and circulation takes place by the difference of density of hot and cold water. In the Grob motor a somewhat different device is resorted to. The water arriving from the jacket at a temperature of about 70° C. is divided into a number of fine streams, which pass up through a network inside the reservoir. At the same time a small centrifugal pump driven by the engine forces in addition a stream of air through the water; the effect is to cool the water before it returns to the jacket to a temperature of from 80° to 90° Fahrenheit. The Grob motor is built in the same manner as the Capitaine engine, which we shall describe next, but it does not work either as smoothly or efficiently as the latter engine. It possesses, in addition, other faults which are objectionable. The vaporizing apparatus is particularly troublesome, for the result of gasifying petroleum at such a high temperature is very often to decompose it, and thereby foul the cylinder and valve mechanism.
Fig. 31.—Exterior View of Grob Oil Motor.
Capitaine petroleum motor (Figs. 32, 33, 34).—More than seventeen years have elapsed since Emile Capitaine, already well known for his experiments on gas engines, first tried his hand at oil motors. His first patent dates from the year 1879, and since that time he has continuously worked at the subject, expending much patience and money in order to produce a high-speed motor capable of using ordinary petroleum of ·88 specific gravity. The result of his labours is a machine which is excellent in all respects, requiring no igniting or heating apparatus. In the earlier type it was found that the motor would not work at less than three-quarters of its full load, because when it was doing less work the vaporizer became cooled in the intervals which occurred between the rarer explosions. This motor could only work under certain conditions, and after further trials and experiments Capitaine brought out a motor which worked at small loads as well as full loads, and which only consumed fuel in proportion to the power developed. This machine was considered too complicated, and a fresh type was brought out.