Rochas

The four-stroke cycle of an internal combustion engine is the cycle most commonly used for automotive and industrial purposes today (cars and trucks, electrical generators, etc). more...

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The Thermodynamics cycles used in internal combustion reciprocating engines are the Otto Cycle (the ideal cycle for spark-ignition engines) and the Diesel Cycle (the ideal cycle for compression-ignition engines). The Otto Cycle consists of adiabatic compression, heat addition at constant volume, adiabatic expansion and rejection of heat at constant volume. It was conceptualized by the French engineer, Alphonse Beau de Rochas in 1862 and independently, by the German engineer Nicolaus Otto in 1876. According to recent historical studies, Otto copied faithfully the plans of the engine patented in London in 1854 (patent number 1072) by the Italian inventors Eugenio Barsanti and Felice Matteucci: the Otto and Langen engine was very similar to Barsanti and Matteucci's, reproducing its function, many technical solutions and even aesthetic features as one can note from a profound examination of the patent sketches and comparing them to the ones relative to the engine built at the Benini Foundry in 1856.

A rack and a toothed pinion constituted the mechanical system, which transformed the alternating motion of the piston to the circular motion of the flywheel, with jack, that is, identical to the mechanism used by Barsanti and Matteucci. The four-stroke cycle is more fuel efficient and clean burning than the two-stroke cycle, but requires considerably more moving parts and manufacturing expertise. (In fact, 2-cycles are not inherently inefficient or \"dirty\". Their simplicity of manufacture has lead them to be the preferred engine for extremely inexpensive applications. Thus, the 2-cycle engines familiar to most are designed for ease of manufacture at the cost of all other features.) Moreover, it is more easily manufactured in multi-cylinder configurations than the two-stroke, making it especially useful in high-output applications such as cars. The later-invented Wankel engine has four similar phases but is a rotary combustion engine rather than the much more usual, reciprocating engine of the four-stroke cycle.

The Otto cycle

The Otto cycle is characterized by four strokes, or straight movements alternately, back and forth, of a piston inside a cylinder:

intake (induction) stroke; compression stroke; power (combustion) stroke; exhaust stroke;

The cycle begins at top dead centre (TDC), when the piston is furthest away from the crankshaft. On the first stroke (intake) of the piston, a mixture of fuel and air is drawn into the cylinder through the intake (inlet) port. The intake (inlet) valve (or valves) then close(s) and the following stroke (compression) compresses the fuel-air mixture.

Read more at Wikipedia.org