Diesel engine
An internal combustion engine that compresses air alone until it is hot, then injects fuel, which ignites by itself. It is more efficient than a spark-ignited petrol engine.
Rudolf Diesel started from Carnot's theory. Reasoning that efficiency rises if heat is taken in at a high temperature, he devised a scheme that compresses air hard enough to reach several hundred degrees and then injects the fuel[1]. A working engine followed in 1897 and proved far more efficient than the petrol engines of the day.
Because it compresses air rather than a fuel mixture, it can use high compression without fear of knocking, and that is where the efficiency comes from. It became the mainstay of lorries, ships and generators. It also tends to emit nitrogen oxides and soot, which are troublesome and costly to clean up. After the emissions-test cheating exposed in 2015, its share of European passenger cars fell rapidly.
Related terms
- Internal combustion engineAn engine that burns fuel inside its cylinders and uses the pressure to push pistons. Petrol and diesel engines are both of this kind.
- Carnot's theoremThe law that any engine producing work from heat has an efficiency ceiling set only by the temperatures of its hot and cold sides.
- KnockingAbnormal combustion in an engine in which the fuel-air mixture explodes before the spark ignites it, with a metallic knocking sound.