Mercedes-Benz Diesel Engines: A Success Story

Genf, Feb 25, 2005
  • Mercedes-Benz, inventor of the diesel engines in passenger cars shows the future of modern diesel technology in Geneva
The story of Mercedes-Benz diesel technology for passenger cars is one of heritage, character and ability. An overview:
1892 - The birth of an idea
In 1892 Rudolf Diesel is granted the patent for his ”engine with compression ignition” — and the diesel engine is born. One year later the engineer realizes his first goal: a fully operational self-ignition engine that uses an injection compressor to feed highly compressed fuel into its combustion chamber. But the very large engine is suitable only for stationary applications and marine propulsion. In 1913, the year of his death, Diesel writes that ”the automobile engine will come, and then I will consider my life’s work complete.”
From 1909 - The technical basis
Prosper L’Orange, an engineering genius with a passion for the diesel engine and an employee of Benz & Cie. from October 1, 1908, dedicates all of his skills and energy to Rudolf Diesel’s dream of creating fast-running, more compact diesel engines that are suitable for use as motor vehicle drive systems. In 1909, L’Orange invents the prechamber injection process and patents the prechamber diesel engine. In the following years, L’O range achieves three further breakthroughs — the funnel prechamber, the needle injector nozzle and the adjustable fuel-injection pump. These advances form the basis for the first diesel engines in motor vehicles, which will be produced by Benz & Cie. in Mannheim between 1919 and 1921.
1923 - The first diesel truck
In 1923, Benz builds the world’s first diesel-powered truck — the 5K3. The five-ton vehicle is equipped with a four-cylinder, 8.8-liter-displacement prechamber diesel, which can deliver 45 to 50 hp at 1,000 rpm. It required approx. 25 percent less fuel than a comparable five-tonner with a gasoline engine. From 1926, after the merger with Daimler-Motoren-Gesellschaft, the prechamber principle developed at Benz & Cie. was the basis for production of truck diesel engines by the new Daimler-Benz corporation.
But the competition counters almost immediately. In Berlin-Marienfelde, engineers at Daimler-Motoren-Gesellschaft (DMG) develop an almost equally powerful air injection diesel for trucks, and Maschinenfabrik Augsburg-Nürnberg (MAN) presents a vehicle diesel engine with direct fuel injection. With these developments, the automotive sector has three competing diesel concepts to choose from.
1936 - First use in a passenger vehicle
Following the 1926 merger between Benz & Cie. and DMG — into Daimler-Benz AG — the more promising prechamber injection principle wins the upper hand. In 1936, the year of the Olympics, the carefully prepared Mercedes-Benz 260 D appeared at the Berlin Motor Show - the world's first diesel-engined production car. It was an absolute sensation. The 260 D’s four-cylinder engine delivers 45 hp at 3,200 rpm and is equipped with a Bosch injection pump, which means higher rpms and a faster fuel supply system.
The diesel engine's long road to success
The diesel engine's road to success in passenger cars was a long one – and paved with disappointments. In 1926, Daimler-Benz, still a young company at the time, began designing a six-cylinder diesel engine for trucks; this was to have a higher power output and a therefore a higher engine speed: 1,300 revolutions in the six-cylinder vs. 1,000 revolutions in the four-cylinder.
The first tests were rather discouraging: the pistons failed under the extreme stresses at higher engine speeds, and fuel supply also caused concern. It was not before Mahle provided newly developed pistons and Bosch a high-precision diesel injection pump that the much-longed-for breakthrough was achieved. In the course of the years, engine speed was raised in several development steps to 2000 revolutions per minute in the early thirties, with the resulting boosting effect on output.
Development of the diesel engine for passenger cars began in 1933. While already being state of the art in trucks at that time, its output and engine speed had to come as close as possible to those of a petrol engine in the opinion of its design engineers to become an interesting proposition for cars. A utopian aim, as the Mercedes engineers had to realise after the first test runs. Because of the diesel's significantly higher compression ratio compared to its petrol counterpart, the engine had to be more robust and therefore heavier. The higher weight, in turn, produced greater inertia forces, resulting in anything but smooth engine characteristics, with extremely adverse effects on the entire car's running.
The first passenger car diesel test engine – a 3.8 litre six-cylinder – developed an impressive output of 82 hp at 2,800/min. Not bad for a diesel – the drawback, however, was that the test car's chassis did not withstand the engine's vibrations. This was not the way to success.
The solution: four cylinders
In November 1934, the decisive idea was conceived, namely to reduce the six-cylinder to a four-cylinder with a displacement of 2.6 litres. The Mercedes-Benz pre-chamber combustion system – splitting combustion into two stages and thereby making it "soft" – proved to be par-ticularly favourable for the diesel-engined car; mixture formation was performed by a four-plunger injection pump from Bosch. The four-cylinder already had overhead valves – a modern feature – and developed 45 hp at 3,200/min.
Installed in the chassis of the petrol-engined 200, the diesel engine behaved itself from then on. Its average fuel consumption was around 9.5 litres per 100 kilometres – clearly less than the 13 litres of its petrol-powered counterpart. The car reached a top speed of 90 kilometres per hour.
Taxi drivers become friends of the diesel
It is therefore not surprising that this car became the taxi drivers' favourite right from the start – and has remained their favourite to this day. The car's low operating costs, the engine's above-average service life and the robust bodies – especially the spacious landaulet body-work in a special taxi cab version with up to seven seats – more than compensated for the higher purchase prices.
Other gratifying features: the car engines emitted neither smoke nor diesel smell, and they were also relatively quiet – fears that had been popularly voiced time and again. A close community of diesel car owners developed – and they didn't mind that the 260 D was not as smooth-running and quiet as a petrol-engined car. All that counted for them was economy and longevity. The 260 D remained a familiar sight at taxi ranks well into the fifties.
Once the diesel had proved itself in tough taxi operation, it soon began to attract private customers. To meet their wishes, the engine was revised in 1937, improving its smooth-running characteristics and refinement. Also for the benefit of private customers, the range of body-work versions was expanded. The diesel engine even made friends in two-door and four-door cabriolets and in an open-top touring car.
Quite a few diesel taxis survived World War II because they hadn't been requisitioned by the armed forces. Their drivers, however, were at the front, so their wives had to take over, evacuating people, carrying supplies and performing transport assignments according to strict rules: private journeys were prohibited.
A good illustration of this is Else Holl from Nürtingen near Stuttgart. Between 1938 and 1951, she drove more than 1.3 million kilometres in her 260 D; during the war, she transported cattle to the Stuttgart slaughterhouse in a heavy-duty trailer. During all those years, the rear axle had to be replaced after 600,000 kilometres, and the engine had to be overhauled three times.
Some 2,000 units of the world's first diesel-engined car were built until 1940 – not a big volume but big enough to make the diesel-engined car socially acceptable and to prepare the ground for the post-war diesel market. Thanks to the farsightedness of its creators and ongoing development, the diesel car conquered a firm place in the Mercedes-Benz model range.
After the war, economy was an even greater issue than ever. The four-cylinder passenger car diesel engine achieved one success after another at Mercedes-Benz, from 1949 in the 170 D, and from 1952 in the 170 DS. These were followed by the 180 D and 190 D – in the three-box body of 1953. Unit figures rose rapidly as the diesel engine was used in the "tail fin", the "/8" and subsequent models. And what would the Mercedes mid-series, today's E-class, have been without its diesel engines? Ongoing improvements, larger displacements and increasing performance - already 2.4 litres and 72 hp by 1973 - meant that it was constantly adapted to meet customer demand. Slowly but surely the competitors also acquired a taste for it.
Kick: With turbocharger
With its three-litre five-cylinder launched in 1974, Daimler-Benz offered its power-hungry diesel drivers 80 hp and a new dimension in terms of smooth running. A further eight hp were added to this in 1979. Being fitted with an exhaust gas turbocharger, a first in a Mercedes-Benz diesel passenger car, and with an output of 115 hp and 250 Nm torque, the diesel passenger car made the leap into the S-class in 1977 and also across the big pond. In the America of the late seventies, it was fashionable to drive a Mercedes S-class diesel, where it was known as the 300 SD TURBODIESEL – even coupé drivers got their way with a diesel in the Mercedes mid-series 300 CD and 300 CD TURBODIESEL. But only in the USA. In Europe, it took a few more years before a diesel-engined S-class became "acceptable".
1978 - Setting new world records
On April 30, 1978, the diesel-powered Mercedes-Benz C111-III research vehicle shows the world what a diesel can do when nine world speed records (irrespective of engine type and displacement) are broken on the 12-plus kilometers of the circuit at Nardo in southern Italy. The record-breaking car’s average speed over a 12-hour period is 315 km/h. And the vehicle’s fuel consumption might well have been record-setting too — just under 16 liters per 100 kilometers. The C111-III’s self-ignition drive system is essentially a series-production three-liter diesel engine. But equipped with its exhaust turbocharger and intercooler, the car delivers 230 hp of top performance. The record-smashing diesel racing engine generates 402 Nm of torque.
1983 - The ”whispering” engine
In late 1982, Daimler-Benz launched an entirely new model series onto the market, namely the "compact 190", the small Mercedes, or, as it was nicknamed by the press, the "Baby Benz", the predecessor of the C-class. Two petrol models and a new two-litre diesel – the 190 D - were launched in 1983. This lightweight, economical and punchy engine developed an impressive output of 75 hp with an impressively low noise level since it was totally encapsulated. The result was a new quality in terms of comfort through low noise in diesel passenger cars, both inside and out, since the encapsulation reduced the engine noise by around 50 percent. With this "whispering diesel", Mercedes once again set the pace, demonstrating that its pioneering spirit was still very much alive.
In 1984, the two-litre four-cylinder diesel in the new Mercedes mid-series was joined by a 90 hp 2.5 litre five-cylinder and a three-litre six-cylinder model with 109 hp. Thanks to turbochargers, the latter attained 126 and 143 hp, respectively. In 1993, the next diesel generation came along. It incorporated four-valve technology, higher torque, greater liveliness and impressively low emissions.
1993 - Four-valve diesel and Electronic Diesel Control (EDC)
In April 1993 the first car diesel engine with four-valve technology and electronic engine management, known as Electronic Diesel Control or EDC, appeared on the scene. Thanks to four-valve technology the new power unit not only developed more output and a higher torque, it was also even more economical than the preceding two-valve units and set new standards for a prechamber engine in terms of exhaust emissions.
EDC also played a decisive role in the 2.9 liter direct-injection diesel engine introduced in 1995. This 95 kW/129 hp five-cylinder unit was some 18 percent more economical than a comparable prechamber engine. This also meant 18 percent lower carbon dioxide emissions as a result of reduced thermal losses during combustion. In conjunction with the adapted emission control system this also reduced emissions of hydrocarbons and particulates in the direct-injection engine by more than one fifth versus conventional prechamber diesels.
1997 - Under high pressure
1997 saw the start of a new chapter in the history of passenger car diesel engines, once again with a four-cylinder unit. Its special feature was the direct injection system co-developed by Mercedes-Benz and Bosch on the basis of the common-rail principle. The magical abbreviation of this revolutionary development is "CDI", Common-Rail Direct Injection, which signifies higher performance, extremely low fuel consumption, minimal exhaust gas emissions and further reduced noise levels. Common-rail technology differs greatly from a conventional direct injection system which re-generates the pressure for each injection process as, for instance, in the Mercedes 2.9 litre direct injection engine of 1995. CDI makes use of a shared line, better known as the "common rail", in which high pressure is permanently stored and which, as a result, compresses the fuel at up to 1350 bar before feeding it into the variable, precision-controlled injector nozzles.
Fuel-efficient: Only 6.1 litres/100 km
The 2.2 litre four-cylinder delivered 92 kW/125 hp and, from as low an engine speed as 1800 rpm, generated an impressive torque of 300 Nm, remaining constant up to 2600 rpm. Offered for the first time in the form of the C 220 CDI in the C-class, this diesel car had the highest torque in its displacement category. It was equally impressive in terms of its fuel consumption and emissions. It used only 6.1 litres over 100 kilometres, allowing a 1,000 kilometre range on a single 62 litre tank. The exhaust gas emissions undercut the exacting German regulations.
2003 - Ready for the 21st century
Economy, comfort, high performance and low exhaust emissions — these are the characteristics that make diesel engine a promising drive system for the vehicles of the future. Thanks to its 0.8-liter, three-cylinder diesel, for example, the nimble little smart car consumes only about three liters of fuel per 100 kilometers. And the powerful 3-liter, five-cylinder diesel in the C 30 CDI AMG can generate 231 hp and 540 Nm. With its four-cylinder CDI engines in the Mercedes-Benz C- and E-Classes, DaimlerChrysler is the first automobile manufacturer to offer both Euro4 compliance and a particulate filter, which works without additives and has a very long service life.
2005 - New V6 engine continues the great diesel tradition
The new V6 motor, the third generation of common rail engines, continues the great diesel tradition of Mercedes-Benz. After a development and testing period of approximately 40 months a new CDI six-cylinder unit is entering series production, combining all the current and trailblazing technologies in diesel engine development – from the mechanical system and thermal/flow dynamics to the electronic engine management and emissions controls. This guarantees outstanding results in terms of output and torque characteristics, economy, exhaust emissions and refinement. Furthermore, the new V6 CDI is the first and only diesel power unit to be available in combination with a seven-speed automatic transmission.
With an output of 165 kW/224 hp the new power unit betters the existing five-cylinder engine by up to 38 percent and the in-line-six-cylinder by nine percent. In conjunction with 7G-TRONIC, the maximum torque is increased to 510 Newton meters and is available between 1600 an 2800 rpm. The inlet-metered high-pressure pump operates with a maximum injection pressure of 1600 bar.
The potential of DaimlerChrysler’s modern diesel engines has by no means been exhausted. Today’s systems operate with injection pressures of up to 1,600 bars. Following further fine adjustment and optimization of the injectors, the injection pressure will be increased to as much as 1,800 bars in modern CDI diesel passenger car engines and even 2,500 bars in those of commercial vehicles. This will enhance performance even further, while emissions and fuel consumption will be kept to a minimum.
Even in his fondest and most ambitious dreams, it’s hard to imagine that Rudolf Diesel could have foreseen what a spectacular future his namesake invention would one day have in the automotive industry.

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