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 class 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 AbbÉ 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 3·4 shillings per day, or just one half the cost of a steam engine using 9·9 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 17·6 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 MÜnich, 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 87·5 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.