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Alphonse Eugène Beau de Rochas (9 April 1815, Digne-les-Bains, Alpes-de-Haute-Provence - 27 March 1893) was a French engineer who originated the principle of the four-stroke internal-combustion engine.
His achievement lay partly in his emphasizing the previously unappreciated importance of compressing the fuel–air mixture before ignition.
He published his results in 1861, a year after Christian Reithmann was granted a patent in Germany and 16 years before Nicolaus Otto obtained his patent.
1862 January 16th. The concept of the four-stroke engine was patented
Extract from Internal Combustion Engines by Wallace L. Lind. Published 1920 Boston.
In the year 1862 M. Beau de Rochas, a French engineer, took out a patent setting forth, theoretically, the best working conditions for an internal-combustion engine, with a view to utilizing more completely the heat supplied. His cycle of operations was in all respects the same as that in use at the present day in the so-called Otto cycle engines. The following four propositions were embodied in his patents :
1. The largest cylinder capacity with the smallest possible cooling surface.
2. Maximum possible piston speed.
3. The greatest possible pressure at the beginning of the working stroke.
4. The greatest possible expansion.
To obtain the results which he laid down as being necessary for high efficiency, Beau de Rochas proposed to use a single cylinder and to carry out the cycle in four strokes as follows:
1. Drawing in the charge of gas and air on the first, or suction, stroke.
2. Compression during the following stroke.
3. Ignition at the dead point and expansion during the third stroke.
4. Forcing out the burned gases from the cylinder on the fourth and last, or return, stroke.