Gas and Oil Engines, Simply Explained.
by Walter C. Runciman.
PREFACE
My object in placing this handbook before the reader is to provide him with a simple and straightforward explanation of how and why a gas engine, or an oil engine, works. The main features and peculiarities in the construction of these engines are described, while the methods and precautions necessary to arrive at desirable results are detailed as fully as the limited s.p.a.ce permits. I have aimed at supplying just that information which my experience shows is most needed by the user and by the amateur builder of small power engines. In place of giving a mere list of common engine troubles and their remedies, I have thought it better to endeavour to explain thoroughly the fundamental principles and essentials of good running, so that should any difficulty arise, the engine attendant will be able to reason out for himself the cause of the trouble, and will thus know the proper remedy to apply. This will give him a command over his engine which should render him equal to any emergency.
WALTER C. RUNCIMAN.
LONDON, E.C.
GAS AND OIL ENGINES
SIMPLY EXPLAINED
CHAPTER I
INTRODUCTORY
The history of the gas engine goes back a long way, and the history of the internal combustion engine proper further still. It will be interesting to recount the main points in the history of the development of the cla.s.s of engine we shall deal with in the following pages, in order to show what huge strides were made soon after the correct and most workable theory had been formulated.
In 1678 Abbe Hautefeuille explained how a machine could be constructed to work with gunpowder as fuel. His arrangement was to explode the gunpowder in a closed vessel provided with valves, and cool the products of combustion, and so cause a partial vacuum to be formed. By the aid of such a machine, water could be raised. This inventor, however, does not seem to have carried out any experiments.
In 1685 Huyghens designed another powder machine; and Papin, in 1688, described a similar machine, which was provided with regular valves, as devised by himself, in the _Proceedings of the Leipsic Academy_, 1688.
From this time until 1791, when John Barber took out a patent for the production of force by the combustion of hydrocarbon in air, practically no advancement was made. The latter patent, curiously enough, comprised a very primitive form of rotary engine. Barber proposed to turn coal, oil, or other combustible stuff into gas by means of external firing, and then to mix the gases so produced with air in a vessel called the exploder. This mixture was then ignited as it issued from the vessel, and the ensuing flash caused a paddle-wheel to rotate. Mention is also made that it was an object to inject a little water into the exploder, in order to strengthen the force of the flash.
Robert Street"s patent of 1794 mentions a piston engine, in the cylinder of which, coal tar, spirit, or turpentine was vaporised, the gases being ignited by a light burning outside the cylinder. The piston in this engine was thrown upwards, this in turn forcing a pump piston down which did work in raising water. This was the first real gas engine, though it was crude and very imperfectly arranged.
In 1801 Franzose Lebon described a machine to be driven by means of coal-gas. Two pumps were used to compress air and gas, and the mixture was fired, as recommended by the inventor, by an electric spark, and drove a piston in a double-working cylinder.
The atmospheric engine of Samuel Brown, 1823, had a piston working in a cylinder into which gas was introduced, and the latter, being ignited, expanded the air in cylinder whilst burning like a flame. The fly-wheel carried the piston up to the top of its stroke, then water was used to cool the burnt gases, which also escaped through valves, the latter closing when the piston had reached the top of its stroke. A partial vacuum was formed, and the atmospheric pressure did work on the piston on its down stroke. A number of cylinders were required in this engine, three being shown in the specification all connected to the same crank-shaft. According to the _Mechanic"s Magazine_, such an engine with a complete gas generating plant was fitted to a boat which ran as an experiment upon the Thames.
A two-cylinder engine working on to a beam was built in Paris, but no useful results were obtained.
Wright"s engine of 1833 used a mixture of combustible gas and air, which operated like steam in a steam engine. This engine had a water-jacket, centrifugal governor, and flame ignition. In 1838 Barnett applied the principle of compression to a single-acting engine. He also employed a gas and air pump, which were placed respectively on either side of the engine cylinder, communication being established between the receiver into which the pumps delivered and the working cylinder as the charge was fired. The double-acting engines which Barnett devised later were not so successful.
From this time to about 1860 very few practical developments are recorded. A number of French and English patents were taken out, referring to hydrogen motors, but are not of much practical value.
Lenoir"s patent, dating from 24th January 1860, refers to a form of engine which received considerable commercial support, and consequently became very popular. A manufacturer, named Marinoni, built several of these engines, which were set to work in Paris in a short time. Then, due to sudden demand, the Lenoir Company was formed to undertake the manufacture of these engines. It was claimed that a 4-horse-power engine could be run at a cost of 34 shillings per day, or just one half the cost of a steam engine using 99 pounds of coal per horse-power per hour. Many similar exaggerated accounts of their economy in consumption were circulated, and the public, on the strength of these figures, bought.
It was understood that 176 cubic ft. of gas were required per horse-power per hour, but it was found that as much as 105 cubic ft.
were often consumed. The discrepancy between the stated figures and the actual performance of the engine was a disappointment to the using public, and, as a result, the Lenoir engine got a bad name.
Hugon, director of the Parisian gas-works, who, together with Reithmann, a watchmaker of Munich, hotly contested Lenoir"s priority to this invention, brought out a modification of this engine. He cooled the cylinder by injecting water as well as using a water-jacket, and used flame instead of electric ignition. The consumption was now brought down to 875 cubic ft.
At the second Parisian International Exhibition, 1867, an atmospheric engine, invented by Otto & Langen about this time, was shown. In this engine a free piston was used in a vertical cylinder, the former being thrown up by the force of the explosion. The only work done on the up-stroke was that to overcome the weight of the piston and piston rod, and the latter being made in the form of a rack, engaged with a toothed wheel on the axle as the piston descended, causing the fly-wheel and pulley to rotate.
Barsanti and Matteucci were engaged in devising and experimenting with an engine very similar to this some years before, but Otto & Langen, no doubt, worked quite independently. Barsanti"s engine never became a commercial article; while Otto & Langen"s firm, it is said, held their own for ten years, and turned out about 4000 engines. In 1862 the French engineer, Beau de Rochas, laid down the necessary conditions which must prevail in order to obtain maximum efficiency. His patent says there are four conditions for perfectly utilising the force of expansion of gas in an engine.
(1) Largest possible cylinder volume contained by a minimum of surface.
(2) The highest possible speed of working.
(3) Maximum expansion.
(4) Maximum pressure at beginning of expansion.
These are the conditions and principles, briefly stated, that combine to form the now well-known cycle upon which most gas engines work at the present time.
It was not until 1876, fifteen years after these principles had been enumerated, that Otto carried them into practical effect when he brought out a new type of engine, with compression before ignition, higher piston speed, more rapid expansion, and a general reduction of dimensions for a given power. Due to this achievement, the cycle above referred to has always been termed the "Otto" cycle.
CHAPTER II
THE COMPONENT PARTS OF AN ENGINE
Having recounted very briefly the chief points in the development of the gas engine from its beginning, we may proceed to deal with matters of perhaps more practical interest to those who we are a.s.suming have had little or no actual experience in making or working internal combustion engines.
The modern gas engine comprises comparatively few parts. Apart from the two main castings--the bed and cylinder--a small engine, generally speaking, consists of four fundamental members, viz., the valves and their operating mechanism, the cams and levers; the ignition device for firing the charge; and the governing mechanism for regulating the supply and admission of the explosive charge. There are innumerable designs of each one of these parts, and no two makes are precisely alike in detail, as every maker employs his own method of achieving the same end, namely, the production of an engine which comprises maximum efficiency with a minimum of wear and tear and attention.
Therefore, before dealing with each of these primary parts in an arbitrary manner, and with the cycle of operations in detail, we propose to make the reader familiar with the general arrangement and method of working which usually obtains in the smaller power engines. In the following ill.u.s.trations these parts are shown. A (fig. 1) is the ignition device which carries the ignition tube to fire the charge. H and I (fig. 2) are the main valves, and GC (fig. 1.) is the gas-c.o.c.k.
The side or cam shaft N (sometimes called the 2 to 1 shaft), the cams which move the levers M, the latter in turn operating the valves, and causing them to open and close at the proper time, are shown in fig. 11.
A bracket bolted up to the side of cylinder forms a bearing for one end of the side shaft, and also carries a spindle at its lower end on which the levers oscillate, transmitting the motion imparted to them by the cams to the valves. The main cylinder casting and the bed need no description. In some cases the bed is in two portions, though now a great many makers are discarding the lower portion altogether, having found that it is cheaper, and quite as satisfactory, to use a built-up foundation instead, and, if necessary, to cut a trough for the fly-wheel to run it. This arrangement, however, only obtains where larger engines are concerned. A half-compression handle by which the exhaust cam is moved laterally on the side shaft as required is not needed on very small engines.
[Ill.u.s.tration: FIG. 1.--General Arrangement of a Gas Engine and Accessories.]
Further reference will be made to this in another chapter, and, although this is not a necessity on a _small_ engine, it is always employed on engines over 2 B.H.P. In fig. 1, HW is the cooling water outlet and CW the inlet. A small drain c.o.c.k is shown at DC, through which the water in the cylinder water-jacket may be drawn off when required. The pipes leading to the inlet and outlet of this supply are connected to the cooling water tank by means of a couple of broad, flat nuts and lead washers, one inside and the other outside the tank, the latter, when clamped up well, making a perfectly water-tight joint. The outlet pipe making an acute angle with the side of tank, the washers used there should be wedge-shape in section. It is also desirable to fit a stop-c.o.c.k SC, so that the pipes can be disconnected from the engine entirely, or the water-jacket emptied without running the whole of the water out of the tank. The exhaust pipe EP is made up of gas-barrel. It should lead from the engine to the silencer or exhaust box (if one is found to be necessary) as directly as possible, _i.e._, with no more bends than are needed, and what there are should not be acute. The silencer can be inside or outside the engine-room, whichever is most convenient; but both it and the exhaust piping should be kept from all direct contact with wood-work, and at the same time in a readily accessible position.
Beyond the exhaust-pipe and box and the water-tank, the gas bag GB and gas meter (where small powers are concerned, the ordinary house or workshop lighting meter may be used without inconvenience) are the only other accessories which are included in a small installation.
[Ill.u.s.tration: FIG. 2.--A Section of a Gas Engine.]
Fig. 2 gives a sectional view, showing the cylinder and liner. The latter is a very desirable feature in any type of gas engine, but especially in the larger sizes; for at any future time, should it be found necessary to re-bore the liner, it can be removed with comparative ease, and is, moreover, more readily dealt with in the lathe than the whole cylinder casting would be.
The liner is virtually a cast-iron tube, with a specially shaped f.l.a.n.g.e at either end. At the back end the joint between it and the cylinder casting has to be very carefully made. This is a water _and_ explosion joint; hence it has not only to prevent water entering the cylinder from the water-jacket, but also to be sufficiently strong to withstand the pressure generated in the cylinder when the charge is fired. For this purpose specially prepared coppered asbestos rings are used, which will stand both water and intense heat. Sometimes a copper ring alone is employed to make the joint. At the front end the liner is just a good fit, and enters the bed easily, and a couple of bolts fitted in corresponding lugs on the liner, pa.s.s through the back end of cylinder casting, so that by tightening up these the joint at back end is made secure. A small groove is cut on a f.l.a.n.g.e, and a rubber ring, of about 1/4-in. sectional diameter, is inserted here when the liner is fitted into the cylinder casting. This makes the water-jacket joint at the front end.
[Ill.u.s.tration: FIG. 3.]
[Ill.u.s.tration: FIG. 5.]