Excerpted from Gas and Oil Engines
Sent to us by Richard D. Hamp, 1772 Conrad Avenue, San Jose, California 95 I 24-4501
A novel type conical rotating valve is employed in the Niel engine for controlling the whole distribution of the charge and the exhaust. By means of suitable gearing the valve is made to rotate once for every two revolutions of the crank, and during this period it effects successively the admission of the mixture to the cylinder, the ignition, compression, and expansion and finally the exhaust of the burnt gases. An ingenious arrangement ensures sufficient gas tightness and prevents the valve from sticking. Although the four-stroke cycle is used, suction only takes place during two-thirds of the forward stroke, and the quantity of gas drawn in is therefore less than the volume of the cylinder. From this there results a certain economy, as the expansion is not so great and the compression is less. The incandescent tube arrangement introduced by Leo Funck in 1883 is adopted for the ignition.
Although built by different makers, these engines, which work on the Otto cycle, differ from one another in unimportant details only. Considering also the absence of any novel features it is unnecessary here to do more than mention their names.
Mr. Lablin of Nantes devised what may be considered as the gas type of the Brotherhood steam engine, that is to say, an engine combining the greatest possible power with the minimum weight and size. To quote Mr. Lablin's words, the engine was devised with a view to increasing the 'dynamical density' of the gas engine, and he so far succeeded in being able to construct engines of half a horse power weighing only 88 lb. and engines of 8 HP weighing less than 3 tons with a consumption of 35 cu. ft. of town gas or 1 lb. of gasoline. The engine works on the Otto cycle but three cylinders arranged radially around one crank are used, and the system of working is such that an explosion takes place in each cylinder successively, there being thus three driving strokes per revolution of the common crank. A flywheel of the minimum proportions may then be used, as the driving effort is practically uniform. When the crank occupies the position shown in Fig. 344, and when the direction of motion is that indicated by the arrow, explosion occurs in cylinder A, and its piston drives the crank. Exhaust of the waste gases commences from cylinder B, and the piston of C finishes the suction stroke preparatory to the compression of the mixture. Between the end of one driving period and the commencement of the next the interval does not exceed one-sixth of a revolution. Firing of the mixture may be effected either by the use of a heated ignition tube or by an electric spark, the former method being usually adopted when the working substance is gas, and the latter for oil vapours. The speed of the engine was controlled by a centrifugal governor which acted upon the gas-admission valve.
Gas engines are built by the National Company in all sizes from the smallest of 1 HP to the largest units burning producer gas. Petrol engines are built by the same company for effective powers of from 1 to 10 HP. All of these engines, whether gas or oil, are provided with two large well-balanced flywheels which ensure uniformity of the rotational motion; but this uniformity is also partly due to the use of a novel form of centrifugal governor which materially reduces the consumption. Fig. 349 illustrates the outward appearance of the gas engine, and also with minor differences that of the oil engines, which are provided in addition with a vaporizer and lamp placed at the front and with an oil reservoir immediately above the cylinder. Special attention has been devoted to the reduction of the number of the parts, and the result has been a design of the simplest possible description. One cylinder alone is used for all engines of less than 50 HP. The starting gear has been much simplified, and the ignition arrangements are such that miss-fires rarely occur. Much skilled attention is not required to keep the engine in good condition and the lubrication is for the greater part done automatically.
Reference has already been made to the two-cycle non-compression engine first introduced by Mr. Forest, who has made the gas engine the subject of considerable research work. Two other interesting types of Forest engine, working on the four-stroke cycle, have also been introduced with considerable success. In one of these types, which is of a specially compact design, the cylinders
are open at both ends, and each contains two pistons, between which the charge is introduced. On the explosion of the mixture the pistons are driven in opposite directions, and their motions are transmitted to the crank, directly in the one case by means of connecting rods, and indirectly in the other through side levers. The second type, illustrated in Fig. 350, has two or more cylinders bolted together, and carried on columns over the crankshaft. By use of two cylinders the regularity of the running is much improved, as one driving impulse is obtained during each half revolution. For the driving of launches, Mr. Forest, in conjunction with Mr. Gallice, has succeeded in producing a very successful type of petrol engine, which has been adopted by the French government, and fitted by them to numerous boats of various sizes. By an ingenious and simple arrangement of the cams on the valve shaft, which controls the admission and exhaust, the motion of the engine may be reversed instantly and at will, which, for marine work, is a most important feature. Figs. 351 and 352 are external views of the front and back of one of these launch engines.
Mr. Charon sought to prolong the duration of the expansion by means less complicated than those devised in the first instance by Mr. Atkinson. His gear consists of a shaft having a double-stepped cam controlled from the governor.
One half of the double cam operates the admission, and the other half a special valve, through which a portion of the explosive mixture is driven into a large pipe or reservoir during the compression. The compression of the portion of the charge in the cylinder is thus reduced, while the expansion is more complete, and is, at the same time, entirely under the control of the governor. As a result of this increased expansion a very satisfactory consumption was obtained.
Messrs. Mollet Fontaine, of Lille, built the Letombe engine, which embodies several novel and interesting features. The engine is double-acting, and the stages in the action on the two faces of the piston follow one another at intervals of half a revolution, so that during each revolution of the shaft there is one driving impulse. As a result of this the uniformity of the motion is equal to that obtained with two-stroke cycle engines, and the economy is also increased to an important degree by the lengthening of the expansion, as in the Charon engine.
It is claimed for this engine that it is able to work equally well on gas or petroleum and that it works regularly without attention, and is not costly although strongly constructed. To a certain extent these claims are justified by results; but the mechanism is somewhat complicated, and the design is not carried out on well-proven lines. It is a four-cycle engine with electric ignition, the spark being produced by the interruption of the current from a small magneto machine driven by the engine itself, Fig. 368. Governing is done by throttling the gas supply at the admission valve, and the air supply is sucked directly by the piston over a sieve heated by a special arrangement in which the exhaust gases circulate. From this initial heating of the air a certain economy of gas results. The carburetor is automatic and self-regulating. It consists of a hermetically-sealed cylindrical vessel filled with the oil supply. On the surface of the oil there floats a mass of cork, into the centre of which the air to be carbureted is led through a pipe in the cover. The cork acts as a sponge and soaks in the volatile spirits which are thus brought into close contact with the air. The evaporation is always superficial, and the impurities remain in the bottom of the vessel. Petroleum having a specific gravity of about .7 is used, as it not only costs somewhat less than gasolene, but is also more readily procurable. As already stated, the one serious defect of the Durand engine consists in the number and the complication of the parts. In the case of gas engines, which are subjected to continual severe shocks, the fewer of the working parts the better, as otherwise the wear becomes very considerable and the difficulty of efficiently lubricating the working surfaces and the cylinder is increased.
Messrs. Bruhot, of Vierzon, have introduced a gas engine which can be run equally on the light volatile oils, and is particularly suitable for agricultural purposes. The engine, as arranged for town gas, differs from those already described in details alone. It works on a four-stroke cycle, and the firing of the mixture is done by means of a small battery, or by a magneto driven from the engine shaft. To make the engine suitable for running on oil vapour a carburetor and the necessary oil reservoirs are added. Air is sucked in by the motion of the pistons over the petroleum or other volatile mineral oils contained in the carburetor cylinder, and becomes charged with hydrocarbon vapours. In connection with the carburetor chamber is a tank containing a reserve supply of several pints of oil, and a special regulator keeps the level in the carburetor always constant, however variable the demands may be. The arrangement, which is both simple and strong, makes the engine particularly suitable for agricultural purposes.
This feature will continue in a future issue, when we will begin with the Capitaine, an oil engine.