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.