1922 – Benz diesel for agriculture
The first land vehicle the Benz diesel engine saw use in was a tractor in 1922. The Mannheim firm developed the three-wheeled vehicle together with the Munich engine and tractor maker Sendling. Benz and Sendling displayed the prototype at a 1922 agricultural exhibition in Königsberg, today Kaliningrad, and immediately found buyers for this vehicle and two more preproduction series units. The machine was equipped with a two-cylinder diesel which developed 18 kW (25 hp) at 800 rpm. Bore and stroke: 135 x 200 millimetres. The tractor went into production in March 1923 as the Benz-Sendling S 6 motor plough with one driving wheel.
Benz & Cie. initially planned to manufacture 100 engines for Sendling tractors and motor ploughs. But by late 1924 they had already manufactured and sold 36 two-cylinders. Through 1931 the Mannheim people, later under the umbrella of Daimler-Benz, produced a total of 1188 of these engines. In addition to the three-wheeled tractor and motor ploughs, from 1923 on Benz-Sendling offered the four-wheeled BK diesel tractor model.
1923 – The world’s first diesel truck from Benz & Cie.
Benz & Cie. presented the world’s first diesel truck in 1923. The five-tonner was powered by a four-cylinder diesel designated OB 2, with 33 kW (45 hp) at 1000 rpm. In direct comparison with a petrol-powered truck of identical design, the diesel truck impressed right off with its economy: the compression-ignition power unit yielded fuel savings of 86 percent versus the spark-ignition engine.
Work on the new engine for the truck already began in 1922. In September of that year the first engine was running on a test bench. Initially, ten OB 2 engines were built. Test drives with the first production diesel were carried out from Gaggenau. The Benz engineers chose the Benz 5 K 3 truck as chassis, designed for a payload of five tons. The OB 2 made such a good showing in the road tests that the decision to build it in series was already taken on 14 April 1923. The world’s first series-built diesel truck finally debuted at the commercial vehicle show in Amsterdam in February 1924. By then the prechamber diesel engine OB 2 had an output of 37 kW (50 hp) at 1000 rpm.
Particularly impressive its low fuel consumption: running on tar oil distilled from brown coal, the OB 2 needed about a quarter less fuel than an equally powerful petrol engine. Due to the low price of tar oil compared with petrol, the result was sensationally low fuel costs. In addition to tar oil, the engine also could operate on “gas oil, kerosene, Texas oil as well as yellow or brown paraffin oil” – said a 1923 Benz & Cie. advertising blurb for the frugal power plant.
1923 – Air-injection diesel truck from Daimler
While Benz & Cie. were developing the diesel truck, in Berlin-Marienfelde Daimler-Motoren-Gesellschaft (DMG) was designing an almost equally powerful air injection diesel to be fitted in trucks. The Daimler engineers applied their knowledge from the manufacture of air-injection diesel engines for submarines to this engine and created a four-cylinder unit delivering 29 kW (40 hp) at 1000 rpm. The engine proved its practical suitability on a number of test runs in 1923. One very spectacular run was a long trip between two DMG plants: between 20 and 30 September 1923 a Daimler diesel truck drove from Berlin to Stuttgart and back.
1927 – The prechamber diesel prevails
However, after the merger of Benz & Cie. and DMG in 1926 the Benz prechamber principle prevailed over the air injection diesel. The first jointly developed prechamber engine was the six-cylinder OM 5 of 1927 (55 kW/75 hp from a displacement of 8.6 litres). The designation “oil motor” (OM) for diesel engines has survived since then in the Mercedes-Benz nomenclature.
The Mercedes-Benz L 5 truck operated alternatively with the new OM 5 (51 kW/70 hp at 1300 rpm) or an M 36 petrol engine (74 kW/100 hp at 2000 rpm). The five-tonner (a low-frame version called the N 5 also could be had) was the sole diesel-powered model in the new Mercedes-Benz commercial vehicle range presented in 1927. Both the 1.5-ton truck and the 3.5-ton truck initially were available only with petrol-fired carburettor engines – a Mercedes-Benz concession to the still considerable scepticism of customers towards the diesel engine.
The OM 5, regular production of which started up in 1928, was already fitted with the new Bosch injection pump. Robert Bosch began working on diesel injection pumps in 1922. With the systematically improved injection technology introduced in 1927, Bosch contributed to getting the diesel drive accepted. Bosch himself did not have to be convinced of the compression-ignition engine’s qualities: in 1924 he was one of the first customers to order a diesel truck from Benz & Cie.