Oil Engines.
In some cases petroleum is the best available fuel for an engine, essentially much the same as a gas motor. A carburetor, or atomizer, blows the oil into a fine mist almost as inflammable as gas. In small sizes for launches, threshing machines, or work-shops of limited area, the petroleum engine is a capital servant. In sizes of 75 horse-power and upward the Diesel engine is not only the best oil engine but the most efficient heat-motor ever invented. It involves a principle as important as that of Watt’s separate condenser for the steam from his cylinder.
Fire Syringe.
To understand the Diesel principle let us begin by remembering that to the compression of a charge in a gas engine there is a moderate limit; if this be exceeded the heat of compression prematurely ignites the gases, so as to prevent due action. The air in a bicycle tire is compressed but moderately, and yet every man who has worked a bicycle air-pump with energy knows that soon its cylinder grows warm to the touch. On this very principle, that mechanical work is convertible into heat, our grandfathers had an ingenious mode of producing fire. In a syringe with a glass barrel they placed a piston fitting snugly. In a cavity of this piston they fastened a bit of cotton wool soaked in bisulphide of carbon. On forcing the piston suddenly into the cylinder, the air, quickly compressed, became hot enough to set the cotton wool on fire. The heat evolved in the compression of air is turned to account in the Diesel oil engine so as to make it the most economical converter of heat into work ever devised. First the mechanism compresses air alone to 500 pounds per square inch, then and then only the oil for combustion is injected, to take fire instantly from the heat of the compressed air. A governor regulates the period of burning; this is usually during one tenth part of the stroke, the expansion of the burned products completing the stroke. Because 500 pounds is a pressure out of the question for the compression of the mixed charge of air and combustible gas in an ordinary gas cylinder, the Diesel engine excels in economy any gas engine thus far built. At Ghent in 1903 a Diesel engine developed 165 brake horse-power from crude Texas oil with the extraordinary net efficiency of 32.3 per cent. At the St. Louis Exposition, 1904, three Diesel engines, using oil costing three cents per gallon, delivered for seven months, during eleven hours each day, at half-load, an average of 250 kilowatts at an expense for fuel of but three tenths of one cent per kilowatt hour on the switchboard, including all generator and line losses. Engineers of the first rank are convinced that the Diesel principle may be successfully embodied in gas engines. That done, with a success approaching the effectiveness of Diesel’s oil motor, we may expect steam engines and turbines to be largely dismissed from service.