Contrary to modern belief that big business started small and then grew big, in many cases they started big before they were able to grow small, and diesel engines were no exception.

But before that,

From Wiki:

In 1689 Thomas Savery, an engineer and inventor, patented a machine that could effectively draw water from flooded mines using steam pressure.

François Isaac de Rivaz invented a hydrogen powered engine, the first successful internal combustion engine, in 1806.

Then Engineer Nicolaus August Otto invented the first practical alternative to the steam engine. Born in Holzhausen, Germany, Otto built his first gas engine in 1861, 3 years after Rudolf Diesel was born.

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This from an independant source dieselnet.com

Rudolf Diesel, who is best known for the invention of the engine that bears his name, was born in Paris, France in 1858. His invention came while the steam engine was the predominant power source for large industries.

In 1885, Diesel set up his first shop in Paris to begin development of a compression ignition engine. The process would last 13 years. In the 1890s, he received a number of patents for his invention of an efficient, slow burning, compression ignition, internal combustion engine [Diesel 1895][Diesel 1898][Diesel 1892][Diesel 1895a]. From 1893 to 1897, Diesel further developed his ideas at Maschinenfabrik-Augsburg AG (later Maschinenfabrik-Augsburg-Nürnberg or MAN). In addition to MAN, Sulzer Brothers of Switzerland took an early interest in Diesel’s work, buying certain rights to Diesel’s invention in 1893.

At MAN in Augsburg, prototype testing began with a 150 mm bore/400 mm stroke design on August 10, 1893. While the first engine test was unsuccessful, a series of improvements and subsequent tests led to a successful test on February 17, 1897 when Diesel demonstrated an efficiency of 26.2% with the engine, Figure 2, under load—a significant achievement given that the then popular steam engine had an efficiency of about 10%. The first Sulzer-built diesel engine was started in June 1898 [USPTO 2000][Deutsches Museum 2013]. Additional details of Diesel’s early testing can be found in the literature [Diesel 1913][Mollenhauer 2010].

Development of Diesel’s invention needed more time and work to become a commercial success. Many engineers and developers joined in the work to improve the market viability of the idea created by Rudolf Diesel. He, on the other hand, became somewhat threatened by this process and was not always able to find common language with other engine designers developing his invention. Diesel’s attempts of market promotion of the not-yet-ready engine eventually led into a nervous breakdown. In 1913, deeply troubled by criticisms of his role in developing the engine, he mysteriously vanished from a ship on a voyage to England, presumably committing suicide [Lienhard 2000]. After Diesel’s patents started to expire, a number of other companies took his invention and developed it further.

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How information is passed down through time and how it is recorded as such does occasionally remain a mysery to me and this case is no exception. For in my case, this story was passed down and preserved by family members, and even though it is not the recorded truth, it has a ring of truth behind it that can not be denighed, but somehow never got published as such, but here is the published version straight up out of wiki,

Rudolf Christian Karl Diesel (English: /ˈdiːzəlˌ -səl/,[1] German: [ˈdiːzl̩] (listen); 18 March 1858 – 29 September 1913) was a German inventor and mechanical engineer who is famous for having invented the diesel engine, which burns diesel fuel; both are named after him.

On the evening of 29 September 1913, Diesel boarded the GER steamer SS Dresden in Antwerp on his way to a meeting of the Consolidated Diesel Manufacturing company in London. He took dinner on board the ship and then retired to his cabin at about 10 p.m., leaving word to be called the next morning at 6:15 a.m.; but he was never seen alive again. In the morning his cabin was empty and his bed had not been slept in, although his nightshirt was neatly laid out and his watch had been left where it could be seen from the bed. His hat and neatly folded overcoat were discovered beneath the afterdeck railing.[14]

Ten days later, the crew of the Dutch pilot boat Coertsen came upon the corpse of a man floating in the Eastern Scheldt. The body was in such an advanced state of decomposition that it was unrecognisable, and they did not bring it aboard because of heavy weather. Instead, the crew retrieved personal items (pill case, wallet, I.D. card, pocketknife, eyeglass case) from the clothing of the dead man, and returned the body to the sea. On 13 October, these items were identified by Rudolf's son, Eugen Diesel, as belonging to his father.[15][16]

There are various theories to explain Diesel's death. Some people, such as his biographers Grosser (1978)[4] and Sittauer (1978)[17] argue that Rudolf Diesel committed suicide. Another line of thought suggests that he was murdered, given his refusal to grant the German forces the exclusive rights to using his invention; indeed, Diesel boarded the SS Dresden with the intent of meeting with representatives of the British Royal Navy to discuss the possibility of powering British submarines by diesel engine;[18] yet he never made it ashore. But evidence is limited for all explanations, and his disappearance and death remain unsolved.

Shortly after Diesel's disappearance, his wife Martha opened a bag that her husband had given to her just before his ill-fated voyage, with directions that it should not be opened until the following week. She discovered 20,000 German marks in cash[19] (US$120,000 today) and a number of financial statements indicating that their bank accounts were virtually empty.[20] In a diary Diesel brought with him on the ship, for the date 29 September 1913, a cross was drawn, possibly indicating death.[14]

Afterwards, in the middle of 1950, Magokichi Yamaoka, the founder of Yanmar, the diesel engine manufacturer in Japan, visited West Germany, and learned that there was no tomb or monument for Diesel. Yamaoka and the people associated with Diesel began to make preparations to honour him. In 1957, on the occasion of the 100th anniversary of Diesel's birth and the 60th anniversary of the diesel engine development, Yamaoka donated the Rudolf Diesel Memorial Garden (Rudolf-Diesel-Gedächtnishain) in Wittelsbacher Park in Augsburg, Bavaria, where Diesel spent his childhood.

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Of course the whys are most important here and here is where my why differs, but the overall legal conclusion would still be the same.

And this is where the official narrative and this story differ, from the very beginning Roudolph had an assistant, one who was even more obsesed with firing a engine w/o a spark. We dont how many prototypes were used to get to the last one, but by the last one it was a hugh engine, one with a piston diameter of close to 10 inches, a single cylinder like the one pictured here.

The first design used coal dust as the propelant, it was a conveyer belt driven carb, the dust falling into the intake manifold. They must have used the cyntrifical force wheel as the starter, and then in theory once it got started, the power from piston would then keep the wheel turning.

Who knows what was occurring during experimentation as to amounts of dust and/or the speed of the belt, nor have I heard of any actual dates of occurrance, but on this one particular day, and it was a hopeful start to day, because just the right amount of both material and belt driven speed was achieved to begin to start this motor.

But Roudolph sensed that something was wrong, my belief was the noise it was making to raise enough concern that he excused himself temporarly from the room as the assistant kept at keeping the motor going. But too much dust had entered and this in turn created a catastrophic explosion that actually killed the assistant.

Upon returning and managing the aftermath, it was determined that a liquid fuel should be used from here going forward.

So my theory, and it holds as a legal one regardless of the public story's also. Is that once determined, (possibly taking decades), finally knowing that any significant financial gain would be not be forth comming due to the causes stemming from the accident, he simply did what he thought he had to do to further his family at that point in time. I really dont believe it was much more than that even though alot was going on at the time too.

So thats it, stories passed down by word of mouth differing from the official narrative, yet still have a ring of truth to them.