Hornsby-Akroyd oil engine (Figs. 35, 36).—This interesting machine was invented by Messrs. Akroyd, Stuart and Binney; it works with ordinary petroleum, and without the help of a carburator uses oils varying greatly in specific gravity. The reservoir of fuel is situated in the bed-plate. The ignition is automatic, and an electric spark is unnecessary, in fact, the whole engine is of the simplest construction, in order that there may be no inconvenience due to breakdowns. Referring to Fig. 35, L is a special petroleum lamp situated at the back of the cylinder A. When starting this lamp is supplied with air from a rotary fan turned by hand; in a short space of time, by the help of this stream of high-pressure air, the cartridge C becomes sufficiently heated to ensure the ignition of the explosive mixture. This cartridge C is provided on its interior with radiating ribs, which greatly increase the surface. During the back-stroke of the piston it becomes filled with compressed air from the cylinder, and towards the end of this stroke a quantity of petroleum, exactly sufficient for the explosion, is squirted into it. To do this a small pump is provided, which is actuated by a cam driving the oil into the cartridge and brought back by a spring. The centrifugal governor G acts on the admission valve from this pump. The sudden injection of the oil into the middle of the heated chamber completely vaporizes it, forming with the air already present the necessary explosive charge, which immediately ignites in contact with the heated walls.
Fig. 35.—Hornsby-Akroyd Oil Engine (section).
When the vaporizing cartridge has been sufficiently heated a rapid turn of the fly-wheel by hand, so as to produce the first explosion, is sufficient to start it, after which the vaporizer keeps itself warm. The pump which keeps up the supply of oil will be seen in the right-hand bottom corner of Fig. 35. It is of the plunger pattern, and at every stroke of the piston draws in the right quantity of oil and injects it into the vaporizer through a valve. The illustration on page 91 shows the other side of the engine with the valve-shaft, which revolves once for every two revolutions of the crank, also driving the centrifugal Porter governor. If the speed should happen to exceed the normal, a steel finger moved by the governor closes the valve admitting oil to the vaporizer, which then returns to the reservoir, having failed to accomplish its object. As the ordinary Otto cycle is used, a heavy fly-wheel is necessary to maintain the speed constant between the explosions. After being once started very little attention is necessary, everything working automatically. A water jacket W cools the cylinder.
Fig. 36.—Exterior View of the Hornsby-Akroyd Oil Engine.
The specific gravity of the oil is usually about ·854, and of this the engine consumes about one pint per hour per B.H.-P., at a cost of 1½d. An additional advantage of the high speed is, that there is less chance of the cylinder becoming fouled by tarry products.
Vulcan motor.—This engine is in many respects a counterpart of the Akroyd motor. The cylinder is horizontal, and projects over the end of the bed-plate. Two fly-wheels are provided if very steady running is required. The lamp which vaporizes the petroleum at starting is removed when once the normal speed is attained. A water jacket prevents the cylinder from getting too hot. The most noticeable feature is the rather curious arrangement for governing by means of bent oscillating levers, which control both the admission and escape valves. The governor itself is situated inside the transmission pulley and keeps the speed within 1% of the normal; 600 grammes of petroleum per hour per horse-power is the usual consumption. The motor is rather too complicated, and can scarcely be said to have justified the expectations formed of it.
Ragot petroleum motor (Figs. 37, 38).—This engine, like the preceding ones, uses heavy petroleum and particularly schistic oil, which has a flashing-point above 77° Fahrenheit, and which may be bought very much more cheaply than naphtha, benzoline, or other artificial products of petroleum. Several different patterns of the engines are on the market, of which certain ones are of great value for electric lighting purposes, not only because of their steady running, but also because, by burning cheap oil, they allow the cost per horse-power to be reduced to a minimum. One high-speed pattern has been especially designed for coupling direct to dynamos, forming a very neat and compact plant. The latest developments in the construction of these engines tend to the simplification of the parts, and they are now so free from unnecessary mechanism, that persons with little or no knowledge of mechanics are quite capable of looking after them, and even taking them to pieces and putting them together again if a breakdown should occur, which is unlikely.
