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History of Diesel Engine

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The history of diesel engine started with Herbert Akroyd-Stuart or Rudolf Diesel, who contributed most to the instigation and evolution of the high-speed compression-ignition (C.I.) engine burning heavy fuel oil. A brief summary of the background and achievements of these two pioneers is as follows.

Herbert Akroyd-Stuart, born 1864, was trained as an engineer in his father's works at Fenny Stratford, England. Between 1885 and 1890 he took out several patents for improvements to oil engines, and later, in conjunction with a Charles R. Binney of London, he took out patent number 7146 of 1890 describing the operation of his engine. Air alone was drawn into the cylinder and compressed into a separate combustion chamber (known as the vaporiser) through a contracted passage or bottleneck. A liquid fuel spray was then injected into the compressed air near the end of the compression stroke by means of a pump and a spraying nozzle. The combination of the hot chamber and the rise in temperature of the compressed air provided automatic ignition and rapid combustion at nearly constant volume - a feature of the C.I. engines of today.

These early engines were of low compression, the explosion taking place mainly due to the heat of the vaporizer chamber itself so that these engines became known as 'hot-bulb' or 'surface-ignition' engines. At starting, the separate combustion chamber was heated externally by an oil-lamp until the temperature attained was sufficient to ignite a few charges by compression. Then the chamber was maintained at a high enough temperature by the heat retained from the explosion together with the heat of the compressed air.

Rudolf Diesel was born in Paris in 1858, of German parents, and was educated at Augsburg and Munich. His works training was with Gebru¨-der Sulzer in Winterthur. Dr Diesel's first English patent, number 7421, was dated 1892 and was for an engine working on the ideal Carnot cycle and burning all kinds of fuel - solid, liquid, and gas - but the practical difficulties of achieving this ther-modynamic cycle proved to be far too much. A reliable diesel oil engine was built in 1897 after four years of experimental work in the Mashinen-fabrik Augsburg Nu¨rnberg (MAN) workshops.

In this engine, air was drawn into the cylinder and was compressed to 35-40 bar. Towards the end of the compression stroke, an air blast was introduced into the combustion space at a much higher pressure, about 68-70 bar, thus causing turbulence in the combustion chamber. A three-stage compressor driven by the engine (and consuming about 15% of the engine's gross power) supplied compressed air which was stored in a reservoir. This compressed air served both for starting the engine and for air-injection into the compressed air already in the cylinder - that is, for blasting air to atomize the oil fuel by forcing it through perforated discs fitted around a fluted needle-valve injector. The resulting finely divided oil mist ignites at once when it contacts the hot compressed cylinder air, and the burning rate then tends to match the increasing cylinder volume as the piston moves outwards - expansion will therefore take place at something approaching constant pressure.

A summary of the combustion processes of Akroyd-Stuart and Diesel is that the former inventor used a low compression-ratio, employed airless liquid-fuel injection, and relied on the hot combustion chamber to vaporize and ignite the fuel; whereas Diesel employed a relatively high compression-ratio, adopted air-injection to atomize the fuel, and made the hot turbulent air initiate burning. It may be said that the modern high-speed C.I. engine embraces both approaches in producing sparkles automatic combustion - combustion taking place with a combined process of constant volume and constant pressure known as either the mixed or the dual cycle.