Mercedes' History of the Diesel Engine 3/9 - E.U. Official Press Release

MERCEDES-BENZ Europe: Official Press Release

Prosper L’Orange and the Modern Diesel Engine

From Ship to Road

The diesel engine was not ready for the step from stationary and marine use to installation in the automobile until after 1920. The engineering achievement which this development represents was the work of Prosper L’Orange, an engineer working for Benz & Cie since 1908. In Mannheim he devoted himself to making Rudolf Diesel’s dream reality: the compact, high-speed diesel engine as an automotive power unit. L’Orange developed prechamber injection, the pintle-type injection nozzle, the funnel prechamber and the variable injection pump – milestones on the compression-ignition engine’s way into the automobile and at the same time the basis for the first vehicle diesel engines.

A Life for Engine Technology

Prosper L’Orange was born on 1 February 1876, in Beirut, in the then Ottoman Empire. He grew up in Germany after 1890. The boy was very enthusiastic about the technology of internal combustion engines and decided to attend the Technical University in Berlin-Charlottenburg. He passed his diploma examination cum laude and became an assistant to Privy Councilor Emil Josse in the university’s heat technology laboratory.

L’Orange went from there to Gasmotorenfabrik Deutz, where he became head of the testing department in 1906. Here he worked mainly on a diesel engine variant which did not have a compressor for air-injection of the diesel oil. He planned to transfer the principle of this internal combustion engine to smaller engines: compact units with outputs of around 26 kW (35 hp) would make ideal power plants for automobiles. However, L’Orange realised that the engine first had to be cured of the “lack of restraint of its fuel feed.” He intended to devise a solution which would enable controlling fuel atomisation, and thus combustion, more accurately than before.

Similar projects were pursued by other engineers too, but Prosper L’Orange took the most forward-looking approach with his injection pump. This precision-controlled instrument delivered fuel to the combustion chamber under 50 atmospheres of pressure. The engineer then turned to the shape of the compression space to improve the mixing of compressed air and fuel spray: in 1908 L’Orange took out a patent on a so-called afterchamber, a space before the cylinder in which air and fuel could swirl. The uncooled, spherical chamber was placed opposite the combustion chamber, with inlet and outlet valves arranged between the two. After the fuel was injected, a small amount of diesel fuel was ignited in the afterchamber; this ensured good swirling of the remaining fuel in the compressed air of the combustion chamber proper. Compared with the usual solution up to then – the use of a compressor to inject atomised fuel – L’Orange's new engine with injection pump and afterchamber was appreciably more compact. But the Deutz diesel engines still were too heavy for fitting in vehicles.

After moving along to Benz & Cie. in Mannheim, with a series of innovations between 1908 and 1922 Prosper L’Orange developed the heavy oil engine further into a high-speed power unit for vehicles. The engineer’s most important improvements during this period were the prechamber principle, the funnel prechamber, the pintle-type injection nozzle, and finally the variable injection pump. However, L’Orange left Benz & Cie. in 1922 before the first diesel truck was introduced, becoming the head of stationary engine manufacture at Motoren-Werke Mannheim (MWM), which had emerged from Benz & Cie. From 1926 he worked as a free-lance engineer, and in 1927 he took over the management of the firm REF-Apparatebau GmbH in Stuttgart-Feuerbach. In 1932 REF-Apparatebau went bankrupt. In September 1933 Prosper L’Orange’s son Rudolf set up Gebrüder L’Orange Motorzubehör GmbH, today an enterprise of the Tognum Group. His father was honoured for his lifework in 1939 with an honorary doctorate from Karlsruhe Technical University. Prosper L’Orange, pioneer of the modern diesel engine, died on 30 July 1939 in Stuttgart.

1909 – The Prechamber

In 1908 Prosper L’Orange was hired by Benz & Cie. as head of engine testing. In Mannheim the engineer’s aim was mainly to improve the diesel principle, as he had done at Deutz. With his afterchamber diesel he had already taken a first step towards splitting mixture formation and the combustion chamber. Now he experimented on an improvement to the shape of the cylinder head. For this work L’Orange designed a test engine that could be fitted with different cylinder heads.

On this engine he also tried out a variant in which a semispherical chamber was arranged between the injection nozzle and the cylindrical combustion chamber. In this space, which occupied 20 percent of the total cylinder volume, after injection a small portion of the diesel fuel burnt upon contact with the hot chamber wall. This created an extremely high pressure in the prechamber, driving the remaining diesel-air mixture into the cylinder and ensuring very good mixing there due to the turbulence of the compressed intake air. Pressure and mixing enabled rapid combustion at high temperatures. With the prechamber diesel, therefore, appreciably higher engine speeds were possible than with older forms of the compression-ignition engine.

In a first test run, the prechamber diesel proved robust, reliable, and above all economical. The engine continued to cause problems for its designer, not the smallest of which was that it was still too big to be installed in an automobile. But Prosper L’Orange knew he was on the right track in his work: on 14 March 1909 he submitted a patent application for the prechamber system (DRP 230 517). L’Orange was rewarded for his success by Benz & Cie. by being given the position of an authorised officer in the stationary engine construction unit in 1910.

1919 – Funnel Prechamber, Pintle-Type Injection Nozzle and Variable Injection Pump

The First World War put a stop to the further development of diesel technology at Benz & Cie. In 1915 the Mannheim people even gave up the prechamber patent entirely. So when L’Orange resumed the work on a modern diesel engine after the war’s end, he not only remembered his own groundwork, but also examined other new concepts. He happened upon the Swedish Ellwe diesel engine with semispherical prechamber and bores connecting it with the combustion chamber.

Spurred by the competitor’s development, L’Orange continued improving his own prechamber. With a funnel-shaped insert between prechamber and combustion chamber he changed its shape to achieve reliable ignition and good combustion under different loads. Among other things, the new shape improved the vaporisation of the diesel oil and reduced the risk of carbon deposits. He applied for a patent on this modification on 18 March 1919 (DRP 397 142). Parallel to this he was working on a new injection nozzle that worked much better than earlier variations. Prosper L’Orange also introduced this pintle-type injection nozzle in 1919.

In 1921 a variable injection pump for the diesel engine followed. Its delivery quantity could be infinitely varied, and it finally enabled the engineer to regulate the power output of the engine with the precision required for use in automobiles. The first installation of a high-speed diesel power unit in a vehicle was now only a matter of time.