OIL ENGINES
The small oil engine is practically the same as the gas engine, with the addition of a vaporiser for converting the oil into gas, or vapour, to be exploded in the cylinder; consequently the one may be converted into the other in many cases without much trouble. The difficulty of producing an efficient oil engine lies principally in devising a satisfactory and reliable vapouriser—one which will work equally well under all loads. The heat supplied to the chamber must be sufficient to vaporise the oil, but not great enough to decompose it. There are various methods of vaporising the oil, and many types of vaporisers are employed to attain the same end. There are some in which a charge of oil is drawn by suction into a hot chamber in which it is converted into vapour and at the same time mixed with a small quantity of hot air; this rich mixture is then passed into the combustion chamber of the engine, in the same manner as coal-gas would be, where it is further diluted with more air drawn in through the air valve. Other arrangements cause a jet of oil to be injected into a chamber containing hot air, in the form of spray, which immediately converts the oil into vapour, and is then passed into the cylinder, compressed, and fired. Then, again, we can pump oil through a spraying nipple into the vapouriser (which is kept at a suitable temperature) whilst the cylinder is being filled with air on the suction stroke. On the following compression stroke the air is driven into the vapouriser, which communicates with the cylinder through a narrow neck, and mixes intimately with the oil vapour. Gradually, as the pressure rises, due to compression, the charge becomes more and more explosive, until at the completion of this stroke it has attained the proper proportions of air and oil vapour, and is fired by the temperature of the vapouriser and that caused by a high compression; that is, the charge is fired automatically; and once the engine is running, no heating lamp is required to keep the vapouriser at the correct temperature. It is necessary, however, to raise it to the workable temperature at starting. This is known as the Hornsby-Akroyd method.
Capel's arrangement is also simple and efficient, and has the additional advantage of being capable of being fitted to their existing gas engines, the conversion being made in a very short time. This vapouriser consists primarily of a tubular casting A, on the outside of which are formed a series of vertical ribs, shown in plan, fig. 46, running to within a short distance of the flange at one end, as shown in the section, fig. 45, thus providing an annular space C between the upper ends of the ribs and the flange. This casting is enclosed by an outer casing B, which fits well over the inner tube. It has also a number of small holes drilled near the lower end communicating with the channels between the ribs. Thus it will be seen that when the gas valve is opened and suction takes place, air is drawn in through these holes, passes up into the annular space C below the top flange, from there travels to the opposite side of vapouriser, and mixes with the oil which is also being drawn in through a small nipper at N, fig. 45. Both then pass between a series of pegs, where they become thoroughly mixed, and finally pass on to the inlet valve V, fig. 47, and so into the cylinder, where the complete charge is mixed up and compressed and fired in the usual manner. Iron ignition tubes may be used, and one heating lamp serves a double purpose in keeping the tube and vapouriser hot at the same time. This lamp is fed by means of a pump actuated from the side shaft. The plunger of the pump is loaded with a spiral spring, which may be adjusted to give any desired pressure, and is kept constant and steady by means of an air vessel. This pump is shown in fig. 48. It is actuated by means of a rod and lever from the side shaft of engine. The plunger P works in a barrel B, which is carried by a small reservoir R, the latter being in communication with the main oil tank by means of the pipe H.
Fig. 46.
Fig. 45.
Fig. 47.