source: Helmut Hütten, "Motoren", Motorbuchverlag Stuttgart, Umschlag
Already early Rudolf Diesel (1858 - 1913) was interested in engines. In his youth he was fascinated by the engines of Lenoir and the steam engines that were usual at his time. During his study he learned of his teacher, professor Linde, a famous inventor, that the thermal engine could reach by far a better performance. He referred to the young Frenchman Sadi Carnot (1796 - 1832), who discovered the Carnot' cyclic process, a physical principle that describes the ideal process of the burn in an engine (read more about it in the physics section). Diesel was pursued from now on by the thought to build such an engine. 1890, Diesel had the crucial idea, how the cumbustion process could be improved: The engine takes in just air, which is to be compressed now to a pressure of about 200 bar. At this point, heavy fuel (such as crude oil or petroleum) gets injected by an injector in the air that is heated up because of the huge pressure. The high themperature leads immediately to the inflammation of the fuel by autoignition, which makes a spark plug unnecessary.
First diesel engine prototypes
This principle is not as simple as it sounds. The conversion into the practice was very problematic. Such high pressures and temperatures had never been used before, and the first experimental engine, built 1893 together with the Maschinenfabrik Augsburg (MAN) in Germany led to its destruction. Only a second engine, built 1896, could convince the engineers and performed an efficiency of about 25 percent, which was by far more than any other engine's performance at that time. But the engine was not after Diesel's requires yet: The compression ratio was still low and the max. pressure therefore small (about 30 bar), additionally a fuel injection was not yet possible. He had to use an air-injection, a procedure, which required many very complicated, expensive and heavy additional devices. This engine could become generally accepted only with many difficulties, because of economic problems - fuel oil and petroleum were very expensive - and disputes about patents delayed a successful introduction.
Grafic: Compression ratio
The compression ratio reflects, how strongly the content of the zylinder can be comprimated. In an otto engine, the compression ratio is smaller than in diesel engines, in which the air is compressed much more.
First diesel engine that worked, 1897. Source: Helmut Hütten, "Motoren", Motorbuchverlag Stuttgart, S. 19
Rudolf Diesel was pursued by patent quarrels, and scruplesless businessmen succeeded in acquiring rights for diesel's engine, so that he finally couldn't develop on his own engine any more. Only 1908, when the patents had run, he developed still smaller engines for the use in cars and trucks, together with the Swiss pioneer company Saurer. When he impoverished completely and didn't beleave any more in a successful advancement of his engine, he set an end to his life 1913 (see also biografie Rudolf Diesel).
Finally: Fuel injection pumps
About ten years after Diesel's dead, engineers succeeded in developing a pump which was able to inject heavy liquid fuel into highly compressed air directly. In the air-injection that was usual before, small fuel portions were hurled by compressed air into the cylinder.
Otto injection engines
Like the diesel engine, newer otto engines use injection pumps, too. The difference spark ignition - autoignion remains as distinguisher.
The company Bosch, Germany, was considerably involved in this development. 1927, Bosch produced a injection pump that was ready for the production. This brought finally the desired spreading of the diesel engine with itself. In the following animation a modern diesel engine is shown, which works with fuel injection.
The four stroke diesel engine
diesel engine: mode of operation
1. Suction stroke: Pure air gets sucked in by the piston sliding downward.
2. Compression stroke: The piston compresses the air above and uses therby work, performed by the crankshaft.
3. Power stroke: In the upper dead-center, the air is max. compressed: Pressure and Temperature are very high. Now the black injection pump injects heavy fuel in the hot air. By the high temperature the fuel gets ignited immediately (autoignition). The piston gets pressed downward and performes work to the crankshaft.
4. Expulsion stroke: The burned exhaust gases are ejected out of the cylinder through a second valve by the piston sliding upward again.
The diesel engine still uses above all heavy fuels such as fuel oil, which are a bit more expensive than gasoline. Because of this reason, cars with otto engines that are more harmful for the environment are often preferred to the ones using diesel engines. Only larger diesel engines are competitionsless. For example, in large ships or in older locomotives huge diesel engines with many cylinders are used for driving. The diesel two stroke engine, which can also be constructed, was less successful.
12 cylinder diesel in a ship, 1970. Power: 48'000 HP. Source: Helmut Hütten, "Motoren", Motorbuchverlag Stuttgart, S. 159