On Beau de Rochas’ Engines — Transcription from his 1862 handwritten mémoire
Keywords:Internal Combustion Engines, Beau de Rochas Cycles, 4-stroke cycle
The 1862 mémoire authored by Alphonse Beau de Rochas  is deemed as the earliest document that describes a piston-in-cylinder, 4-stroke engine operation with constant-volume combustion of a gaseous mass previously compressed and existing in one side of the piston—a cycle that gathers the defining features of what became widely known as the Otto cycle, especially outside of France—as well as exhaust burnt gases providing heat for vapor generation, as well as expanding water vapor lowering the atmospheric counter-pressure during the gas exhaust stroke—lesser known features of one of Beau de Rochas’ combined cycles from his Chapter 6, in which the 4-stroke engine operation is described in detail and in the context of some four engine variants. Moreover, on Chapter 7, two additional variants conceptually obtained by simplifying two engine configurations from Chapter 6 are briefly discussed, in which one design degenerates to a previously described, prototyped, and produced Lenoir engine, and the other, described under criticism by Mr. Beau de Rochas, being what is nowadays know as the proper gas-only, Otto-cycle engine, despite it’s perceived novelty by Mr. Beau de Rochas.
The mémoire—digitized and placed in the Public Domain by the National Library of France for non commercial, scientific, and academic purposes—is a handwritten, 19th century French language text that lacks most facilities of nowadays texts, including the ability of automated searching, and extracting text for further processing. Moreover, neither transcriptions nor translations of the digitized text seem to exist in searchable form, nor in other forms of publication, despite its historical relevance. In this work a manually made transcription from the handwritten French, with indications of illegible parts, is provided for Chapters 6 and 7 of Mr. Beau de Rochas mémoire, in which the 4-strokes and engine variants are enunciated aiming at recovering this part of the history of thermodynamics.
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