There are two essential differences between the invention of the Otto-engine and the Diesel-engine. The latter was developed from a scientific theory. It is the cyclic-process of Sadi Carnot (1796 - 1832), which caused Rudolf Diesel to start thinking in the direction of an efficiency-optimised engine.

The principle of isotherms assumes an unusually small injection amount, in a large air-volume. Thereby, a combustion takes place, but no rise in temperature (iso = equal, therm = temperature). No cooling of the cylinder walls would be necessary, which is not conform with the highest possible efficiency anyway.

Unfortunately, the performance is then low, whereby, after the deduction of the natural losses, only a slightly positive, or in fact, even a negative result is left over. Even before the actual building of the engine, and with a large amount of participation from the scientific world, Rudolf Diesel corrected this error in his first patent. The later Diesel engine would work, in the power stroke, after the principle of changing the state of the isobars.

The second difference is the fuel itself. Otto, Daimler, Maybach and Benz could work with the available fuel, even if this was used, at the time for other purposes. Rudolf Diesel needed basically, a new fuel that was non-volatile but was, at the same time easily ignitable. All together, a good knowledge of the raw material, which was crude oil and also its processing was necessary. If one looks at the relatively simple end product, which was the Diesel engine, it is quite astonishing which round-about-ways Rudolf Diesel in 1888 had to go, to arrive at the basic principle, and in 1890, the possible construction of a high pressure engine. Years of testing with ammonia, which was known from the refrigeration technology, and its application in a complicated, externally fired engine was the fore-runner.

A 'difficult birth' is probably an appropriate description of the development of the Diesel engine. The problems were, by no means over, after the theoretical basics had been worked out. Thereby, it all started with very high hopes after Rudolf Diesel recieved a sort of scholarship in the shape of an annual salary of 30.000 Mark from the Krupp Company. He lived with his family in Berlin and carried out the practical testing, often for weeks on end, at MA(N) in Augsburg.

It is difficult to describe the development of such an object. A completely newly contrived engine runs for such a long time in the wake of, e.g., the electric motor, until all the defects occuring have been remedied. Is each independent movement of the crankshaft with fuel valid as a realisation of the the principle? A constant idling and delivery of performance is still a long way off.

Of course, one was constantly changing the adjustments and replacing defective parts. Thus, detours are also part of the agenda. Various oil products were tried out, either cold or heated, in the worst case, even electrically ignited, which for a Diesel engine, was pure nonsense. After four years Rudolf Diesel achieved a smooth running engine using petroleum, which ran for days on end after being started each morning.

This then, in 1897, is already the second, completely newly contrived test-engine. He achieved his target of about 33 bar final-compression thrust and followed the change in state of the isobars for a large part of the power stroke. It was probably never registered, from the word go until this point was reached, just how much scrap had been produced. 01/10