We will see that Rudolf Diesel's path to the engine that bears his name was anything but straightforward. Linde probably believed very much in young Diesel's talent. It wasn't the only thing, because he not only hired him in his ice cream machine company, but after a year he made him manager of the Paris branch. Then it was back where its development had started.

Just to put things in context: we are in the year 1880. Rudolf Diesel was 22 years old at the time. In 1883 he married. His three children were born in 1884 (Rudolf), 1885 (Helene) and 1889 (Eugen). In 1893 he signed the contract with the Maschinenfabrik in Augsburg and began work on the diesel engine. In 1897 there was a first operational engine. In 1913 Rudolf Diesel died at the age of 55.

Of the three areas of life after the training, we cover the first until 1893. So he was in Paris and, in addition to his main job, he also took the time to develop a steam engine based on ammonia, which worked as a motor through liquefaction or evaporation. The relationship to the refrigeration machine was noticeable, but further development into the superheated steam machine nullified the advantage of the possibly higher efficiency of its small motor.

Diesel approached the matter theoretically. With the newer steam engines, the higher efficiency was due to the superheating of steam. He made long considerations and calculations in order to be able to carry out the cycle process based on Carnot with ammonia as well. Then, at some point during his many studies, he came to the decisive realization that the properties of vapors do not differ from gases. The way led straight to the compression of air, ammonia is passé.

He was able to stay with Carnot in his quest for better efficiency, since Carnot had always acted on the assumption of air in his cycle. But that only existed in theory, based on very high pressures. It became one of Diesel's tasks to enforce this with the technicians, albeit certainly not to the required extent. But it wasn't time yet. It wasn't even the theory.

He had no objection to the high temperatures during combustion, but according to Carnot's principle he had to use the heat completely to increase the volume. That said his demand for isothermal change of state. So no heat was allowed to escape outside. You can clearly see the theoretical approach here.

Diesel didn't challenge that. He had the idea of being able to control combustion in such a way that every increase in temperature should be converted directly into an increase in volume, so to speak. So an increase in temperature should be avoided. We know today that such a slow and targeted control of heat is not possible. Ignition of an air-fuel mixture automatically entails a certain increase in temperature.

Of course, Rudolf Diesel described almost fantastic technology. It would be the almost complete utilization of the energy contained in the fuel, because this would be adapted to the temperature development in a kind of cyclic process. Of course, cooling would no longer be necessary, the archenemy of efficiency. And all this should be possible at approx. 250 bar and a compression temperature of 800°C.

These were just the assumptions about the working cycle. Carnot also requested similar ones for the compression stroke. Of course, lost heat reduces the efficiency always and everywhere. But anyone who has ever witnessed the 'birth' of a newly developed motor knows that it initially runs without fuel towed by an electric motor, i.e. it has no combustion of its own. It already reaches operating temperature. Diesel wanted to combat this with water to be injected.

We make a cut at this point, only mentioning that he wrote all these unfulfillable demands on the new engine and even more in his patent from 1892. To the credit of the Imperial Patent Office, after some back and forth it limited this to ignition initiated by high compression. However, the very slow addition of fuel to avoid excessive pressure or temperatures was retained.

After the patent application, the handwriting came: Theory and construction of a rational heat engine', then the showdown at a meeting with his boss in Berlin, where his main occupation had meanwhile also shifted. The needed some time, studied the handwriting, and also questioned another university colleague and they both came to an agreement relatively quickly.

Linde and his colleague praised Diesel's theoretical approach on the one hand, but were both convinced of its impracticability. They also questioned the efficiency of the new engine of 45 percent that Diesel was aiming for. Linde's estimate of a maximum of 25 percent, which was later achieved almost exactly by the first engine, is astounding, but still more than the double of the steam engines of the time. However, Linde and his company did not participate in the development.

The discussion in professional circles continued and the extremely lengthy search for sponsors or preparations for the construction of such an engine began. As might be expected, the high technical expectations presented almost insurmountable hurdles to success, but Rudolf Diesel seemed undeterred.