Rudolf Diesel, the inventor of the Diesel engine

Making the internal combustion engine as efficient as possible was the aim of many an engineer since the end of 19th century

Few inventors take a direct route to their final achievement and Rudolf Diesel was no different. He first worked as a refrigeration engineer before beginning his crusade to improve the combustion engine.

Although born in France, he spent most of his formative years in Germany, Austria and the UK. He studied at the Industrial School of Augsburg in southern Germany before winning a scholarship to study at the Royal Bavarian Polytechnic in Munich, graduating in 1880.

While at the polytechnic his relationship with one of the professors blossomed into a business opportunity. Diesel helped Carl von Linde to develop a refrigeration plant, where he would later become the director.

Although his enthusiasm for his work would see Diesel claim many patents for the refrigeration business, he began to look at other areas where he could put his knowledge to use.

One of them was motive power. Diesel was aware of the inefficiencies inherent in the powertrains of the day. Steam engines were only 6% thermodynamically efficient and the gasoline engine, while better, could still manage only 12%.

He first looked at improving steam power, using ammonia vapour in his design – a near-fatal mistake as he was seriously injured when the test engine suddenly exploded.

Undeterred, after his recovery Diesel set about developing a new system, based on a combustion process for a four-stroke gasoline engine but working to the theory that the air should be highly compressed to allow for a more effective combustion process.

In 1885 he established a laboratory to develop his engine technology. It took eight years for the determined engineer to construct his first fully working engine – a 10ft iron cylinder with a huge flywheel.

8 years of determination

Diesel patented the design in 1894 and companies quickly saw the advantages. MAN AG helped him to improve the technology, giving him time, money and resources. Two years later, his refined powertrain had a theoretical efficiency of more than 75%.

In 1898, Diesel was granted patent number 608,845 from the United States Patent Office. His application laid out his innovation: “My invention has a reference to improvements in internal combustion engines . . . The process consists in first compressing air or a mixture of air and a neutral gas or vapour to a degree producing a temperature above the igniting point of the fuel to be consumed, then gradually introducing the fuel for combustion in the compressed air while expanding against resistance.”

Diesel’s engine has since been put to use in a multitude of applications – from ships and submarines to trains and, in more recent times, the automotive industry.

While his theoretical efficiency of 75% has not materialised in practical use, the powertrain has managed to reach thermal efficiency figures of approaching 40%. 

That’s because of the higher compression ratios and the longer combustion process, allowing more of the heat to be converted into mechanical work.

The number of diesel engines in passenger vehicles has grown steadily across Europe. Tighter emissions legislation may force OEMs to invest more heavily in the technology, but Diesel’s groundbreaking work will remain an integral part of the automotive industry.

Motive power
tags: Sept 2010 Powertrain