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Late Great Engineers: Rudolf Diesel - Powering the modern world

With the development of his eponymous engine, Rudolf Diesel was to have a profound effect on the way industry, transportation and international freight shaped the 20th century. Written by Nick Smith.

Diesel engines play a part in the lives of us all. They generate electricity. Pump water and gas. Propel ships, trucks and buses. Power railway locomotives, farming, military and construction machinery. We may live in an age where the focus has shifted to the use of renewable energy and green fuels, but diesel engines are still with us, and they will be for years to come. In fact, the man behind the engine that powered the modern world was also a visionary who foresaw the use of sustainable fuels when he said: ‘The use of vegetable oils for engine fuels may seem insignificant today. But such oils may become in course of time as important as petroleum and the coal tar products of the present time.’ That man was of course Rudolf Diesel, the engineer whose name will be for ever linked with his sparkless compression-ignition engine that extracted the maximum amount of work from a given heat source. In his biography Rudolf Diesel and the Diesel Engine John F Moon, writing in the 1970s, claimed that the invention ‘has yet to be bettered commercially.’ Half a century on, and despite new and competing alternative technologies, that claim still has merit.

Rudolf Diesel: Image: Sueddeutsche Zeitung Photo / Alamy Stock Photo

Rudolf Christian Karl Diesel was born in Paris to Bavarian parents in 1858, at the height of what’s now called the First Industrial Revolution. It was the age of steam and iron production, and Europe’s economies were driven by them. Little was made, mined or moved without the influence of Thomas Newcomen and James Watt’s engines. And yet the boy who was to transform how the 20th century was powered, came from a distinctly pre-industrial parentage. A Bavarian émigré, his father Theodor was a bookbinder and leatherworker, while his mother Elise was the daughter of a Nuremberg merchant (which is why Diesel is usually referred to as German or sometimes as French-German). Following a complex early childhood that saw the young Rudolph temporarily fostered by a French farming family and that was overshadowed by his father’s debts, he helped in the leather business before attending a Protestant school where he became interested in technology.

On the outbreak of the Franco-Prussian War the family fled from Paris, first to London and then Germany to live with relatives. Rudolf became fluent in German and studied at the Königliche Kreis-Gewerbeschule (Royal County vocational College) where, influenced by his uncle (who taught mathematics at the college) he recognised his desire to become an engineer, accepting a scholarship at the Royal Bavarian Polytechnic of Munich, much against his parents’ wishes, who would have preferred him to get a job. While in Munich he established his credentials as a first-class engineer and became a protégé of the refrigeration engineer and industrialist Carl von Linde, whose Paris firm he joined in 1880.

While working for Linde, Diesel devoted much of his time to developing an internal combustion engine that would approach the theoretical efficiency of the Carnot cycle (a theoretical construct that provides an upper limit for the conversion of heat into work in any classical thermodynamic engine). In 1890, he relocated to Berlin to take up a new position in the Linde organisation, where he conceived the idea for what would become known as the ‘Diesel engine’ and obtained a German development patent in 1892. During his time with Linde, Diesel spent many months in hospital following a near-fatal explosion of a high compression cylinder in an ammonia vapour steam engine he was testing.

The automobile engine will come, and then I will consider my life’s work complete

Rudolf Diesel (1858-1913)

1893 was a big year for Diesel, in which he published his treatise Theorie und Konstruktion eines rationellen Wärmemotors zum Ersatz der Dampfmaschine und der heute bekannten Verbrennungsmotoren (or ‘Theory and construction of a rational heat motor with the purpose of replacing the steam engine and the internal combustion engines known today’). Put succinctly, it was his musings on how to create an alternative technology for what he saw as the woefully inefficient steam engine and early internal combustion engines which, at the time Diesel was writing his paper (that was largely dismissed by the academic establishment), converted as little as 10 percent of their heat into useful work. Then there was equine power. Horses were a problem in the industrial world’s growing cities. As Tim Harford notes in his article How Rudolf Diesel’s Engine Changed the World: ‘A city of half a million people might have 100,000 horses. Each one liberally coated the streets with 15kg of manure and 4 litres of urine every day. An affordable, reliable, small-scale engine that could replace the horse would be a godsend.’

After realising that there were errors in his rational heat motor theory, Diesel rewrote his paper, applied for another patent and spent the following four years testing his ideas under the patronage of Heinrich von Buz, director of Maschinenfabrik Augsburg (today known as MAN) and Krupp. He produced a series of increasingly successful models, culminating in his demonstration in 1897 of a 25-horsepower, four-stroke, single vertical cylinder compression engine that can be seen to this day at the German Technical Museum in Munich.

Rudolf Diesel's engine. Image: INTERFOTO / Alamy Stock Photo

With the successful trials of his engine completed, the German engineer became rich. With his newly acquired wealth he moved his family into a luxury apartment in Munich, where he also found himself famous. As Moon explains, this renown had not so much to do with the fact that he was a brilliant engineer that had single-handedly invented a rational heat engine; more that the innovation that was dominating the headlines bore his name. Early in the development Diesel had realised that the machine’s name (as well as that of his now famous treatise) was too long and complicated, and had toyed with the idea of calling it either Delta or Beta. But his wife Martha overruled such modesty with the suggestion that the obvious designation for the engine was ‘Diesel’: ‘and this is the name that has stayed with this type of compression-ignition engine.’

Despite its high efficiency and simplicity of design making the engine an immediate success, Diesel was not able to enjoy fame and wealth for long. For all the acclaim – engineers reportedly travelled from all parts of the globe to get a glimpse of ‘the Diesel’– he was also forced to deal with with objections to his claim to have invented the machine. These would embroil Diesel in costly legal struggles for the remainder of his life. Not only that, his engine was also plagued by reliability problems. According to Harford: “Unfortunately for Rudolf, in early versions these efficiency gains were outweighed by reliability issues. He faced a steady stream of refund demands from unhappy customers. This dug the inventor into the financial hole from which he could not escape.”

While the diesel car boom, that once peaked at almost 50 percent of all vehicle registrations in Europe, might be fast heading towards the pages of history, there can be little doubt over the influence Diesel’s innovation had on both domestic and commercial transportation in the 20th century. As electric vehicle registrations in Europe start to eclipse diesel-powered passenger cars, global freight movement by road, rail and sea still relies almost exclusively on a technology that was – and still is – a prime mover of globalisation. None of which could have ever been imagined by the engineer who died decades before the first production model diesel-powered car rolled off the assembly lines at Mercedes-Benz in 1936.

Although conspiracy theorists support the colourful notion that Diesel was murdered by industrialists involved in competing technologies, the balance of probability is that while travelling from Belgium to Britain, Diesel committed suicide by jumping overboard into the English Channel. A bag of documents he had given to his wife just before he set sail (and only to be opened in the event of his death) confirmed that the engineer was swamped by debt to the point where he could not even service the interest. While Wikipedia includes Rudolph Diesel on its list of ‘unsolved deaths’, the editors of Encyclopaedia Britannica prefer a more neutral interpretation of events, suggesting: ‘Diesel disappeared from the deck of the mail steamer Dresden en route to London and was assumed to have drowned.’ The probable day of his death – 29th September 1913 – is marked in Diesel’s diary with an ‘X’, and his body was found floating in the North Sea ten days later. As his biographer says: ‘the world had lost a genius, but had gained economical power that was to revolutionise all forms of transport, and was to carry the name of its inventor for all to remember.’