Born in Paris of German parents, Rudolph and his family left for London when the Franco-Prussian war of 1870 began but he soon moved to Germany to continue his education, eventually studying at the Munich Polytechnic.
From 1880–90 he worked on refrigeration plant, but his interest was in engines. He realized that on thermodynamic principles an internal combustion engine should desirably operate with a large temperature range, which implies a high pressure. His patent of 1893 and his engines produced in the late 1890s use a four-stroke cycle like the Otto engine (induction, compression, combustion, exhaust) but in the Diesel engine a higher-boiling petroleum fraction is used. In the induction stroke, air alone is drawn into the cylinder.
On the compression stroke this air is compressed by up to 25:1 (unlike the 10:1 compression of the petrol:air mixture in a petrol engine) and this raises its temperature to near 600°C. Then an injector admits a fine spray of fuel into the heated air; it ignites spontaneously, and the combustion stroke provides power. An exhaust stroke to remove the burned gas completes the cycle. Diesel prospered, but in 1913 he vanished from the Antwerp–Harwich mail steamer and was presumed drowned; his body was never found.
Diesel engines are more efficient than petrol engines and were used in the First World War in submarines, and later in ships and rail locomotives. The smaller units for buses, tractors, trucks and small electrical generators were developed in the 1930s, with important design contributions by two British engineers, C B Dicksee (1888–1981) and H R Ricardo (1885–1975); by the 1980s larger commercial vehicles were normally powered by high-speed compression- ignition units.
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