1926 – The early history of the Mercedes-Benz 260 D
Mercedes-Benz held a sensation in store at the February 1936 International Automobile and Motorcycle Show in Berlin: in the model 260 D (W 138 series) the diesel engine swept into the passenger car world. In the year of the Olympic Games the Stuttgart company introduced this model as the world’s first production diesel car. It was equipped with a four-cylinder engine with a Bosch injection pump which permitted higher engine speeds and speedier fuel supply. The 2.6-litre unit had a compression ratio of 20.5:1 and delivered 33 kW (45 hp) at 3200 rpm.
The first diesel car in the world was the result of intense research which began upon the merger of DMG and Benz & Cie. in 1926. The first thing done by the young Daimler-Benz AG was to design a new six-cylinder diesel engine for trucks. The power plant was steadily improved. Its output and engine speed rose: in the early 1930s, the diesels already managed 2000 rpm.
Over the coming decades the engine speed especially of car diesel engines would be continuously boosted. However, compared with the spark-ignition petrol engine the compression-ignition engine has a physically determined speed limit of around 5500 rpm – a result of the delayed ignition of the fuel. The time that passes between injection and ignition is appreciably less with modern-day diesel fuels than with the earlier diesel oil, which was chemically identical with fuel (heating) oil. The cetane rating indicates the quality of the diesel fuel. The higher it is, the quicker the fuel ignites.
1934 – Four-cylinder diesel for cars
A high engine speed was an important condition for adopting the diesel in cars. For its premiere the compression-ignition engine had to come as close as possible to the petrol engine. However, diesel engines were still much heavier and less smooth than petrol engines. And so the first test diesel engine for a car, a 3.8-litre six-cylinder developing 60 kW (82 hp) at 2800 rpm, promptly proved too rough for the chassis of the test car because of its strong vibrations.
It was followed by several test engines, such as the OM 134 – a water-cooled three-cylinder diesel with 22 kW (30 hp) – which was installed in the Mercedes-Benz 160 V car in 1934. The six test cars (W 134 series) received the model designation Mercedes-Benz 175 D and were available with saloon as well as convertible B and C bodies. However, the vibration problems of the three-cylinder proved to be uncontrollable. In the same year, therefore, four test cars of the 175 DX model (W 141 series) were set up and fitted with four-cylinder engines (OM 141, 26 kW/35 hp). The engineers undertook further diesel tests in models which included the Mercedes-Benz 130 H and the Mercedes-Benz “Mannheim.”
In November 1934 the Mercedes-Benz engineers then opted for a different approach and, instead of an entirely new development, banked on modifying the proven six-cylinder of commercial vehicle provenance. For operation in passenger cars the engine was reduced to the size of a four-cylinder with a displacement of 2.6 litres. The smooth combustion permitted by the prechamber principle meanwhile had been perfected, among other things through the use of a four-plunger injection pump from Bosch. The four-cylinder already had overhead valves, a very modern feature, and developed its maximum output of 33 kW (45 hp) at 3000 rpm. A crankshaft running in five bearings contributed effectively to vibration damping and, in addition, permitted high revolving speeds. The engineers had finally reached their goal.
1936 – Darling of taxi operators
Assembly-line production of model 260 D began in 1935. The OM 138 was installed in the chassis of the Mercedes-Benz W 21 series. The resultant Mercedes-Benz 260 D consumed an average of 9.5 litres of diesel fuel per 100 kilometres – the closely related model 200 guzzled 13 litres of petrol over the same distance. The 260 D travelled 450 – 500 kilometres on one tank filling – quite an asset given the rather wide-meshed gas station network at the time. What’s more, a litre of diesel cost 24 pfennigs in Germany – clearly less than a litre of petrol for which 39 pfennigs had to be paid. And anyone working as a taxi driver with a passenger transport license was able to buy diesel at a reduced price of 19 pfennigs per litre. With a top speed of 90 km/h, despite all economy the Mercedes-Benz 260 D travelled at a fairly brisk pace – even the 200 managed only 98 km/h.
The world’s first diesel passenger was built on the chassis of the W 21-series landaulet (Mercedes-Benz 200 and 230). The sales brochure proudly extolled the combination of modern passenger car and diesel technology: “It is natural that
Daimler-Benz A.G., in view of its great successes in the fields of passenger car and diesel commercial vehicle manufacture, also deeply concerned itself with the question of the passenger car diesel engine. The result is the Mercedes-Benz model 260 D […], which combines the great advantages of the diesel engine with the obvious comforts of the swing-axle passenger car.”
The first 170 vehicles already were delivered in autumn 1935 before actual series production began in 1936. The 260 D quickly gained acceptance as the ideal taxi. Cheap to maintain, robust and long-lived engines, a spacious body (also in a special taxicab version with up to seven seats): these were the arguments with which the new Mercedes-Benz convinced the taxi trade. Engine-powered cabs based on the 260 D were still widespread far into the 1950s. Also, the 33 kW (45 hp) 2.6-litre diesel powered the van models L 1100 to L 1500, which were built in Stuttgart and Mannheim.
1937 – Diesel cars for private customers
Contemporaries were favourably impressed how quiet this diesel car was. Private customers too let themselves be convinced by the virtues of the Mercedes-Benz 260 D and bought the car with the compression-ignition engine – especially after the engine was worked over in 1937 and the model got a new body.
The Mercedes-Benz W 143 series served the 260 D as new chassis beginning in 1937. Two- and four-door convertibles and an open touring car were added to the landaulet and Pullman limousine. Through 1940 some 2000 units of the world’s first diesel car were built – not a large number, but enough to make the diesel-powered car acceptable and smooth its way in the post-war period. Thanks to the farsightedness of its creators and above all the continuity of its further development, the diesel car has captured a firm spot in the Mercedes-Benz model range.
1949 – New beginning with the 170 D
Following the end of the Second World War, economical automobiles were more than ever in demand. Mercedes-Benz again included a four-cylinder car diesel engine in the model range in the form of the model 170 D (W 136 series). The 170 was largely identical with the Mercedes-Benz 170 V built from 1936 to 1942. The diesel variant launched in 1949 was powered by the 1.8-litre OM 636 I engine, an in-line four-cylinder diesel developing 28 kW (38 hp) at 3200 rpm. As early as 1950 Mercedes-Benz introduced a modified power plant that now had an output of 29 kW (40 hp). The saloon’s top speed increased from 100 km/h to 105 km/h.
The first 170 D was handed over to its buyer on 1 August 1949. In the following years many more customers in industry, the trades and the public sector, but also private individuals, chose the first post-war Mercedes diesel. From 1949 to 1953 a total of 33,822 units of the model were built, including chassis and half-ton panel vans.
In addition to the 170, there was also a diesel-powered variant of the 170 S, the first special-class car from Mercedes-Benz since the war. The Mercedes-Benz 170 DS (W 136 VIII D series) came out on the market in 1953 and was built until 1955. The 170 DS was equipped with the 29 kW (40 hp) OM 636 VIII. To cut the higher production price of this diesel engine versus the petrol drive, the OM 636 was manufactured in very large numbers and not only used in models 170 D and 170 DS, but also in the Unimog. Daimler-Benz AG also sold the unit as a stationary engine.
1954 – “Ponton” Mercedes with diesel engine
Models 180 D (W 120 series) and 190 D (W 121 series) put the diesel drive in the wrappings of the “Ponton” (a self-supporting chassis-body structure) design introduced in 1953: aerodynamically optimised and featuring a unitary body. The familiar 29 kW/40 hp engine powered the 180 D on its debut in March 1954; in 1955 the output was raised to 32 kW (43 hp) at 3500 rpm. In 1958 Mercedes-Benz then introduced the new OM 621 engine. As a 1.9-litre diesel power unit it developed 37 kW (50 hp) at 4000 rpm in model 190 D; from 1961 it also propelled the 180 D with 35 kW (48 hp) developed at 3800 rpm. In all, 235,000 units of the two models were built.
The Mercedes-Benz “Ponton” with diesel engine also was exported to North America. To create awareness of the design, in 1954 journalist Bill Carroll undertook a test drive across the USA in a Mercedes-Benz 190 D. Mercedes-Benz diesel cars repeatedly have provided such demonstrations of reliability. In addition to long, strenuous journeys, records and outstanding sporting achievements have moulded the diesel history of Mercedes-Benz. In 1955, for example, three Mercedes-Benz 180 D were the winners in their class in the Mille Miglia. Mercedes racing manager Karl Kling personally showed that the diesel drive is good for sporty performance. In a model 190 D he won the 1959 Africa Rally over 14,045 kilometres from Algiers to Cape Town at an average speed of 80.6 km/h.
1961 – Tailfin 190 D and 200 D
In the “tailfin” (W 110 series) the diesel further emancipated itself from its origins in the commercial vehicle. The two-litre diesel presented in 1961 was still called the 190 D. But when Mercedes-Benz introduced the new model 200 in 1965, the compression-ignition variant also was renamed 200 D to match it, though its displacement and output (44 kW/55 hp at 4200 rpm) remained the same. In addition to a five-bearing crankshaft the OM 621 four-cylinder diesel engine got better sound insulation than its predecessor and, as a high-speed diesel, propelled the car to a top speed of 130 km/h. On the other hand, accelerating from standstill to 100 km/h still took 28 seconds.
From 1965 to 1968, 159,365 200 D saloons were built, plus units of the 200 D Universal estate and the 200 D with long wheelbase (3350 millimetres instead of 2700 millimetres) and eight seats. The diesel had become well established in the mid-sized range of Mercedes-Benz. This is shown by the sales figures and the model range diversification which took place in the late 1960s. And diesel-powered cars long since had ceased to be austere in their appointments: as an optional extra the compression-ignition models of Mercedes-Benz were now even available with an automatic gearshift.
1974 – Five-cylinder diesel in the Stroke Eight
In 1968, for the first time two new diesel models were introduced simultaneously, the 200 D and the 220 D, in the W 115 series. In 1973 the 240 D was added to the range, and in July 1974 the 240 D 3.0 appeared as the top-of-the-line model. It was powered by the world’s first five-cylinder passenger car diesel engine. Even the injection pump and its controls were new on this new engine developed on the basis of the OM 616.
With a swept volume of 3005 cubic centimetres, the OM 617, designed as an in-line five-cylinder, generated 59 kW (80 hp) at 2400 rpm and had a respectable top speed of 148 km/h. With acceleration from standstill to 100 km/h in 19.9 seconds, the new top diesel model from Stuttgart was the liveliest and fastest diesel car in the world and featured impressive smoothness and economy. 53,690 units of the 240 D 3.0 were manufactured; in all Mercedes-Benz sold 945,206 W 115-series diesel cars.
The starting equipment of the five-cylinder diesel also was innovative: instead of the mechanical shutoff device of the 2.4-litre engine only a pneumatic device was used, so that the engine could be shut off with the ignition key. Starting was also by a turn of the key in the 240 D 3.0 and not, as previously was the case, by pulling a lever: when the driver turned the ignition key, preglowing was initiated and an indicator lamp lit up. When the light went out after a bit, the engine could be started in the normal way with a key. What now appears the most natural thing in the world was appreciated as a new comfort feature in 1974, which has since gradually found its way into all diesel cars of the brand and beyond.
1976 – Four diesel engines for the 123 series
The new mid-sized series took the start with four diesel variants in 1976. The W 123 came out as 200 D, 220 D and 240 D with four-cylinder engines and as 300 D with the in-line five. With that Mercedes-Benz took the entire, extremely successful diesel programme of the Stroke Eight into the new model. For use in the W 123 the engines were thoroughly worked over. Among other things they were given new cylinder head gaskets made of a material called Ferrolastic®; in addition, oil changes were made simpler; the exhaust system was improved and the oil and fuel filters modified.
In view of the big demand for diesel models both from the new series and the W 115 series, the compression-ignition Stroke Eight models continued to be built for one year parallel to the W 123. How popular the diesel model had become in the meantime is shown in the statistics: the biggest-selling saloons of the 123 series were the 240 D (448,986 units) and 200 D (378,138 units).
1977 – A diesel coupé improves CAFE
In autumn 1977 the 300 CD diesel coupé was added to the 123 series. The engine of the two-door car was the same fitted in the 300 D Saloon: the three-litre five-cylinder diesel OM 617 with its output of 59 kW (80 hp) at 4000 rpm. However, the elegantly styled diesel was manufactured exclusively for the North American market. The object was to improve the Corporate Average Fuel Economy of Mercedes-Benz automobiles in the US and Canadian markets.
CAFE describes the average fuel consumption of all models of a brand. Under a regulation issued by the US government, by 1985 the average consumption of all models of a car brand sold in North America had to be less than the equivalent of 8.55 litres per 100 kilometres. The number of units of each model sold was not important. CAFE was computed simply by adding up the average consumption of all variants on offer and dividing up this figure by the number of variants. Innovative concepts like the economical diesel engine in the 300 CD therefore made their mark on the consumption statistics.
1977 – A turbodiesel for the S-Class
Another diesel model presented by Mercedes-Benz specifically for the American market caused a stir at the 1977 Frankfurt International Motor Show (IAA): the 300 SD was the first S-Class (W 116 series) from Stuttgart to be equipped with a compression-ignition engine. An exhaust-gas turbocharger provided for performance appropriate to the luxury saloon, boosting the output of the five-cylinder diesel familiar from the 123 series to 85 kW (115 hp).
In May 1978 production of the model based on the US version of the W 116 series began. The three-litre diesel was fitted with a Bosch injection pump and a Garret exhaust-gas turbocharger and provided the 1.8-ton saloon with respectable performance: the top speed was 165 km/h; the S-Class Turbodiesel sprinted from standstill to 96 km/h (= 60 miles per hour) in 14 seconds. The diesel cousin could not match the unbelievable performance of the 450 SEL 6.9 of the W 116 series. But it made up for it with an average consumption of only 14 litres of diesel per 100 kilometres, while the S-Class with the M 100 V8 engine required 22 litres of premium petrol for the same distance – albeit a very common consumption figure in those days.
1980 – Turbodiesel in the 123 series
The American CAFE standards were further toughened in the late 1970s. Accordingly, in 1981 Mercedes-Benz replaced the 300 CD and 280 C coupés from the 123 series with the new 300 CD Turbodiesel and also offered the 300 D Turbodiesel as a parallel model. Whereas these new models again were reserved for the North American market, the Mercedes-Benz 300 T Turbodiesel launched in 1980 was also sold in Germany. Like the saloon and the coupé, this estate had the three-litre in-line five-cylinder under its bonnet, boosted by a Garrett exhaust-gas turbocharger. After debuting in the S-Class the engine now developed 92 kW (125 hp) at 4350 rpm and was good for a top speed of 165 km/h and acceleration from standstill to 100 km/h in 15 seconds. In all, 28,219 units of the first Mercedes-Benz turbo-diesel car for the German market were sold between 1980 and 1986.
With the turbodiesel models from the 123 series, the turbocharged compression-ignition engine returned to its origins in the test shops of Mercedes-Benz: the first turbodiesel engine designed by the Stuttgart engineers, with an output of 132 kW (180 hp), was installed in a 123 chassis for test driving. Following the successful tests with the prototype it was decided to pursue the concept further and develop a five-cylinder turbodiesel for the S-Class.
1983 – Whisper diesel in the new compact class (W 201 series)
As third car series, Daimler-Benz put the compact class on the market in 1982. The small Mercedes got a new two-litre diesel (53 kW/72 hp at 4600 rpm) in 1983 and was called the 190 D. The engine was designed as a lightweight, economical, agile unit. Above all, the engine was completely encapsulated, reducing the noise it generated by half. The OM 601 became known as the “whisper diesel.” Mercedes-Benz supplemented this four-cylinder in 1985 with an in-line five-cylinder (66 kW/90 hp at 4600 rpm) installed in the 190 D 2.5. The top speed of the 190 D was 160 km/h, while the more powerful 190 D 2.5 now did 174 km/h.
Once again, models specifically intended for the North American market were created: the 190 D 2.2 of 1983 had a modified four-cylinder diesel engine, the 190 D 2.5 Turbo was based on the in-line five-cylinder of the 190 D 2.5. Exhaust gas turbocharging ensured an output of 90 kW (122 hp) at 4600 rpm, the top speed was around 192 km/h. Starting in 1986, 20,915 units of this most powerful of the diesel models from the W 201 series were built in all. Originally designed as an export model, the 190 D 2.5 Turbo also was available in Germany from September 1987 on.
1985 – Six-cylinder compression-ignition engine in the 124 series
For the first time the mid-sized 124 series offered an in-line six-cylinder diesel engine in a Mercedes-Benz passenger car. At the presentation of the new models in December 1984, the Stuttgart automakers introduced the 200 D with four-cylinder power plant (53 kW/72 hp at 4600 rpm), the 250 D with five cylinders (66 kW/90 hp at 4600 rpm), and finally the 300 D with an in-line six-cylinder (80 kW/109 hp at 4600 rpm). The two-litre four-cylinder of the 200 D was known from the compact class. The 300 D was distinguished externally from the smaller models by additional air intake slots in the front apron.
In 1985 Mercedes-Benz launched the 300 D Turbo as an estate, reserving it for export to North America until September 1987. The turbocharged in-line six-cylinder had an output of 105 kW (143 hp) at 4600 rpm, which was increased to 108 kW (147 hp) in 1988. The saloon of the same model was shown in 1987 in Frankfurt/Main at the International Motor Show; in addition to the 300 D Turbo with rear-wheel drive there was now also the 300 D Turbo 4MATIC with four driven wheels. Additional air intake gills in the right fender distinguished the Turbo version from the 300 D.
A second 124-series turbodiesel was put on display in September 1988 at the Paris Motor Show. The 250 D Turbo was powered by a turbocharged 2.5-litre OM 602 engine, the one also used in the compact class. However, the unit used in the 124 series was a modified version developing 93 kW (126 hp) at 4600 rpm; the top speed was around 195 km/h. The engine design was revised with the aim of improving the combustion process to reduce particulate emissions.
The most important means of achieving this was the use of a new prechamber featuring oblique fuel injection. This ensured more efficient combustion and also boosted output by 2.9 kW (4 hp). Together with the 250 D Turbo, the 300 D Turbo also had its three-litre engine revised. Finally, in 1989, in connection with the “Diesel ’89” initiative, the non-turbocharged diesel cars also were fitted with revised engines. The improved models gave off 40 percent less particulates than their predecessors and thus met the stringent US standards even without a particulate filter.
From October 1990 onwards, as an optional extra Mercedes-Benz additionally offered an emission control system featuring an oxidising catalytic converter and exhaust-gas recirculation. Initially an option for conventional diesel engines, it also became available for turbodiesels at the start of 1991.
1993 – Diesel refinement in the S-Class
Diesel engines have been available for the S-Class of Mercedes-Benz since the 300 SD model from the W 116 series (1978 to 1980). The compression-ignition engine also found its way into the 126 series in the 300 SD Turbodiesel (1980 to 1985) and 350 SD Turbodiesel (1990 to 1991). What these specimens of the Stuttgart luxury class had in common is that they were sold only in North America. The story of the
Mercedes-Benz 300 SD of the 140 series, which was exported exclusively to the USA and Canada from 1991 to September 1992, also begins this way.
From autumn 1992 on, however, an S-Class car equipped with a 3.5-litre turbodiesel also could be had in Europe: the compression-ignition engine finally had arrived in the international luxury automobile segment. The car developed 110 kW (150 hp) and, with a top speed of 185 km/h, was content with an average 9.7 litres of diesel fuel. Standard equipment included an exhaust-gas turbocharger and an emission control system with oxidising catalytic converter.
1993 – New names, new models
Appropriate to its displacement, the model was renamed in June 1993, now being designated the S 350 Turbodiesel. The diesel models of the mid-sized 124 series also got new designations in 1993. They were now called E 200 Diesel, E 250 Diesel, E 250 Turbodiesel, E 300 Diesel, E 300 Turbodiesel and E 300 Turbodiesel 4MATIC.
The S 350 Turbodiesel was replaced in 1996 by the S 300 Turbodiesel. The new diesel model in the S-Class had a turbocharged engine with four-valve-per-cylinder design and intercooling; with 130 kW (177 hp) developed at 4400 rpm its output was 20 kW (27 hp) higher than its predecessor’s. The engine had high torque over a very broad engine speed range; its pollutant emissions and fuel consumption were far less than the S 350 Turbodiesel’s owing to optimised combustion. On top of that the top speed climbed to 206 km/h. The S-Class with diesel engine met with increasing interest everywhere in the world: of the total 406,532 saloons from the 140 series sold, 28,101 had compression-ignition engines.
1993 – Four-valve-per-cylinder diesel and emission control as standard
In 1993 the diesel technology in several Mercedes-Benz models underwent a decisive change: as a world first, four valves per cylinder were used in the diesel. Four instead of two valves per cylinder enabled increased torque and output over an appreciably enlarged engine speed range and cut fuel consumption under full load by as much as eight percent. Owing to an improved process of combustion the particulate emissions simultaneously were reduced by about 30 percent.
Initially, only the five- and six-cylinder naturally aspirated engines were converted to four-valve technology. The two-litre four-cylinder and the turbocharged engines retained their two valves per cylinder for the time being. The new engines for the C- and E-Class developed 70 kW (95 hp, 2.2-litre displacement), 83 kW (113 hp, 2.5-litre displacement) and 100 kW (136 hp, three-litre displacement) – and were all equipped with exhaust-gas recirculation and oxidising catalytic converter as standard.
1995 – Three diesels and four eyes
In 1995 the new 210 mid-series made its debut. The distinguishing external feature of the new E-Class was the front end with its four elliptical headlamps. The model range initially comprised three diesel models. The E 290 Turbodiesel, its four-stroke diesel engine featuring direct injection, exhaust-gas turbocharger with intercooler, plus emission control system with oxidising catalytic converter, caused quite a stir. Its in-line five-cylinder OM 602 DE 29 LA engine offered the combination of diesel technology and direct injection for the first time in a Mercedes-Benz car. Compared with the naturally aspirated three-litre engine with prechamber injection in the E 300 Diesel, which practically had the same displacement, the new design impressed observers with appreciably higher torque and lower fuel consumption. The new engine was the first step of Mercedes-Benz towards the introduction of direct-injection car diesel engines.
1997 – With CDI into the future: Premiere in the C-Class
The future of diesel drive became reality at the International Motor Show in Frankfurt am Main in September 1997: in the C 220 Turbodiesel Estate Mercedes-Benz presented a direct injection system based on a new principle, “Common Rail Direct Injection” (CDI). In keeping with the designation of the new engine technology, which Mercedes-Benz and Bosch developed together, the vehicle came out on the market in December 1997 as the C 220 CDI.
While conventional injection systems have to generate the pressure for each injection operation individually, the new CDI engines operate with a common pressure reservoir for all cylinders, the so-called common rail. Regardless of engine speed, this reservoir continuously maintains an optimum pressure of 1350 bar for all cylinders; by means of solenoid valves, the ideal quantity of diesel fuel for each driving state is distributed to the injection nozzles and injected into the combustion chamber. The engine electronics individually calculate the requirements of every single cylinder dependent on the driving situation. The variable control of the injection process makes for appreciably improved mixture preparation and in effect results in lower fuel consumption and reduced pollutant emissions.
The CDI engine of Mercedes-Benz also impresses with its unusually smooth running, which can be put down mainly to so-called pilot injection. A few milliseconds before fuel injection proper, a small amount of diesel is sprayed into the cylinder, ignites, and ensures preheating of the combustion chambers. Owing to this preheating, during the main injection the pressure and temperature no longer rise so sharply, and the engine runs quieter.
The 92 kW (125 hp) four-cylinder OM 611 engine of the C 220 CDI is a four-valve-per-cylinder design and develops remarkable torque of 300 Newton metres from an engine speed as low as 1800 rpm. A comparison with the predecessor model is very interesting: 30 percent more power, double the torque, ten percent less consumption. CDI thus set new standards for diesel cars and changed the image of the diesel engine for good. Now the compression-ignition engine no longer is considered just a miracle of economy, but also an agile and sporty performer.
1998 – CDI in the E-Class
New CDI diesel engines featuring common rail direct injection and turbocharger brought the new technology to the E-Class too in June 1998. The E 200 CDI got 75 kW (102 hp) out of its turbocharged two-litre four-cylinder and sprinted to a top speed of 187 km/h. The E 220 CDI developed 92 kW (125 hp) and reached the 200 km/h mark. Yet the new models needed an average of only 6.3 litres of diesel per 100 kilometres.
The 1999 model refinement package fully established CDI technology in the E-Class: the five-cylinder of the E 270 CDI developed 125 kW (170 hp) and maximum torque of 370 Newton metres from 1600 rpm. But the most powerful diesel of the model range ran on six cylinders in the new E 320 CDI. The 145 kW (197 hp) direct-injection diesel got its maximum torque of 470 Newton metres at 1800 rpm and held it to 2600 rpm. This 3.2-litre engine took full advantage of the big torque that is the hallmark of the diesel. Compared with the previous six-cylinder diesel of the E-Class the torque increased by 42 percent. And yet the six-cylinder OM 613 DE 32 LA engine (direct injection, exhaust-gas turbocharger with intercooler, plus emission control system with oxidising catalytic converter) consumed on average only 7.8 litres of diesel fuel per 100 kilometres; its speed topped out at 230 km/h.
Like the new engines, the two four-cylinder CDI units introduced in 1998 also got new turbochargers with variable turbine geometry as part of the 1998 refinement package. This increased their output by up to 14 percent: The E 200 CDI now developed 85 kW (115 hp), the E 220 CDI 105 kW (143 hp).
2000 – The strongest diesel for the S-Class
The new S-Class W 220 debuted as a diesel in 1999 in the form of the S 320 CDI. Its in-line six-cylinder delivered 145 kW (197 hp) at 4200 rpm. The torque was 470 Newton metres, obtained in a range from 1800 to 2600 rpm. The luxury saloon got up to 230 km/h with the 3.2-litre compression-ignition engine and sprinted from standstill to 100 km/h in 8.8 seconds.
By far the most powerful diesel engine in a Mercedes-Benz car made its arrival in the
S-Class in the year 2000. From a displacement of four litres, the light-alloy V8 OM 628 DE 40 LA developed 184 kW (250 hp) at 4000 rpm. It delivered torque of 560 Newton metres at 1800 to 2600 rpm. A top speed of 250 km/h and 7.8 seconds for accelerating to 100 km/h illustrate the role of the S 400 CDI as first among the Mercedes-Benz diesel models.
2002 – The diesel returns to the coupé
Since the C 123 series of the 1970s there had been no more Mercedes-Benz coupés with diesel engines. In 2002 the CLK 270 CDI (C 209 series) was introduced. The four-stroke diesel (electronically controlled common rail direct injection, Bosch three-plunger high-pressure pump and exhaust-gas turbocharger with intercooler) was an engine that met the demands on a sporty vehicle yet operated economically. 125 kW (170 hp) at 4200 rpm were good for a top speed of 230 km/h and standstill to 100 km/h acceleration in 9.2 seconds.
Also in 2002 Mercedes-Benz presented the second generation of CDI technology. These new engines once again improved performance, consumption, comfort and emissions. To achieve this, among other things the Mercedes engineers raised the ignition pressure from 145 bar to 155 bar to optimise the gas cycle. The result is greater pulling power and flexibility. The injection pressure of now 1600 bar, in conjunction with the newly developed seven-hole injection nozzle, permitted finer distribution of the fuel in the combustion chambers, better mixture formation, and more homogeneous combustion.
New V6 engine for greater dynamism
The development of innovative features for the diesel engine continues unabated. An outstanding example from the long list of novelties is the six-cylinder V-engine which Mercedes-Benz presented in December 2004 and has been offering since the spring of 2005 in different model series where this engine replaced the previous five- and six-cylinder in-line units. The new engine made its debut in the C-Class, giving the saloon and estate models a highly agile character with a decidedly sporty touch. The saloon accelerates from standstill to 100 km/h in just 6.9 seconds. It is therefore not surprising that these diesel-engined cars were also made available as “Sport Edition” versions, among other things with a visual enhancement package from AMG. The “Sport Edition +” documents the dynamic nature of the modern compression-ignition engine with an even wider range of features including sports suspension.
The V6 diesel engine with direct injection develops 165 kW (224 hp) and a torque of 510 Newton metres, which is on tap from 1800 rpm and remains constant up to an engine speed of 2800 rpm. The engine complies with the Euro 4 emission norm and has been featuring a particulate filter as standard equipment ever since its market launch. Weight is reduced by a crankcase made of aluminium with cast-in grey-iron cylinder liners – an absolute novelty in this displacement and performance category. As a result, the new six-cylinder weighs in at just 208 kilograms and is thus only insignificantly heavier than the previous five-cylinder engine. And the very compact dimensions of this engine with all its ancillary components allow it to be combined with four-wheel drive which, for lack of space, was not available for any six-cylinder diesel engine before.
The equally newly developed electronic control unit monitors all the engine functions – from the Instant Start System and the automatic start function through to the high-pressure pump. The VNT (Variable Nozzle Turbine) turbocharger with electrically adjustable guide blades, the exhaust-gas recirculation with control valve and the intake air throttling system are controlled to match the situation at any given point in time, on the basis of up-to-date measurements. What’s more, the computer exchanges data with the seven-speed automatic transmission – if specified by the customer – and the Electronic Stability Program ESP®.
This new high-tech V6 diesel engine marks the beginning of the third generation of CDI technology at Mercedes-Benz. Owing to new materials and optimisation of the entire unit, the new CDI engines attained even higher combustion pressures than before – the engineers aimed at up to 200 bar and intended to boost the injection pressure too in future, to as high as 2000 bar. In addition, the complex CDI technology was further refined. The fuel is no longer injected all at once, but in as many as five portions. Special actuators (piezo crystals) take over the control of the injection nozzles: with electric pulses the atomic structure of the crystals can be expanded several hundred thousand times per second if required. With this sophisticated injection system, not only were the emissions further reduced; the working noise of the engine was also diminished once more.
Premiere: The torquiest eight-cylinder diesel engine
The Mercedes-Benz engineers also made us of the V6 engine’s technology in the world’s torquiest V8 passenger-car diesel engine (OM 629), which went into production in autumn 2005 in the E-Class and was available for other model series at a later stage. The 231 kW (314 hp) V8 with an aluminium crankcase, cooled exhaust gas recirculation and electric intake air throttling generates its maximum torque of 730 Newton metres at an engine speed as low as 2200 rpm. As a result, the E 420 CDI accelerates from standstill to 100 km/h in just 6.1 seconds and reaches a top speed of 250 km/h. In terms of dynamism and smooth running characteristics, this eight-cylinder represents the benchmark in its market segment. The combined fuel consumption is 9.3 litres per 100 kilometres. The standard specifications of the E-Class with this engine include a maintenance-free particulate filter, seven-speed automatic transmission and AIRMATIC air suspension.
2003 – Maintenance-free particulate filter and Euro 4 norm
Mercedes-Benz made a major advance in respect of the environmental compatibility of the diesel drive in autumn 2003. As first automobile brand in the world the company introduced diesel passenger cars built to the Euro 4 norm and featuring a maintenance-free particulate filter. Mercedes-Benz offered the first filters for export to California as early as in 1985.
2005 – Particulate filter as standard in more than 30 Mercedes-Benz models
Since the early 1990s through 2005, technologies like the common rail system developed by Mercedes-Benz had reduced the fuel consumption of diesel cars by more than 25 percent. The CDI, state of the art of Mercedes-Benz diesel technology, meanwhile is represented in all the vehicle classes marketed by the brand: from the
A-Class through the GL-Class to the S-Class.
More than 30 different models were affected when Mercedes-Benz began fitting all diesel cars from the A-Class to the S-Class with diesel particulate filters as standard in Germany, Austria, the Netherlands and Switzerland in the summer of 2005.
Mercedes-Benz had been offering its innovative particulate filter system, which operates maintenance-free and makes do without additives, since 2003.
Owing to economical, optimised engines, in combination with the filter, the particulate emissions are more than 90 percent less than those of earlier engines. In view of this success a retrofit solution for car particulate filters was made available from autumn 2005, initially for vehicles of the C-Class and E-Class. Dr Thomas Weber, member of the Board of Management of Daimler AG, responsible for Corporate Research and Mercedes-Benz Cars Development, emphasised: “Our retrofit solution for particulate filters is further proof of the high level of our diesel expertise and a consistent step towards environmentally compatible, fuel-saving vehicles.”
Unique change of character
At the Geneva Motor Show in 2005, Mercedes-Benz not only announced the incorporation of particulate filters in the standard specifications but also reviewed 70 years of diesel competence in the passenger car – the first 260 D had, after all, come off the assembly line in 1935. For decades, the diesel engine had been regarded merely as the epitome of longevity. It was known to be reliable and sound, but also somewhat sedate. In the course of time, it has lost this trait and acquired a completely new image. Today, sporty dynamism, agility, ride comfort, motoring pleasure and, not least, environmental compatibility rank among the attributes boasted by modern diesel engines. And the engineers at Mercedes-Benz have contributed to this change in no insignificant measure. This remarkable development is verified most clearly by figures: the world’s first passenger-car diesel engine in the Mercedes-Benz 260 D developed just 33 kW (45 hp), corresponding to a power-to-swept-volume ratio of 13 kW/litre (17.8 hp/litre). In the C 320 CDI, the V6 diesel engine presented in December 2004 develops an impressive output of 165 kW (224 hp) from a displacement of three litres – boasting a power-to-swept volume ratio of 55.2 kW/litre (75 hp/litre), more than four times the ratio of the 260 D.
Torque ratings – the decisive factor for tractive power from low engine speeds – rose just as dramatically, from 98 Newton metres in the 170 D of 1949 to 510 Newton metres in the C 320 CDI. In other words, some 55 Newton metres per litre of displacement in 1949 are pitted against more than three times this figure – 170 Newton metres - today.
Future development trends of the diesel engine were outlined by Mercedes-Benz at the 2005 Geneva Motor Show, among other things by means of two roadsters. In the Vision SL 400 CDI show car, a new V8 diesel engine develops 231 kW (315 hp) and transmits an enormous torque of 730 Newton metres to the crankshaft of the eight-cylinder unit.
From a displacement of three litres, the engine of the SLK 320 Triturbo develops remarkable 210 kW (286 hp) and a torque of 630 Newton metres – 70.3 kW and 211 Newton metres per litre of displacement. The triturbo engine is based on the modern V6 diesel. The show car is clad in the self-assured guise of the SLK 55 AMG. The car sprints from standstill to 100 km/h in 5.2 seconds; its top speed is limited to 250 km/h. It combines this impressive performance with excellent fuel economy: 7.5 litres of fuel per 100 kilometres (overall NEDC consumption).
Into the future with just a tenth of the first diesel’s consumption
The economy of modern CDI engines, 70 years from the premiere of the diesel-powered car, is astounding. Whereas the world’s first passenger car diesel engine in the 260 D consumed 0.3 litres of fuel on 100 kilometres to generate an output of one kilowatt, in 2005 the C 320 CDI made ends meet with just 0.04 litres per kilowatt over the same distance. This is a reduction by unbelievable 90 percent or, in other words, fuel consumption reduced by a factor of almost ten.
Innovations like this from Mercedes-Benz for the diesel drive not only conserve resources, but also reduce the burden on the environment, for as fuel consumption decreases, so too do exhaust-gas emissions – a tendency which has been amplified since 2005 mainly by innovative technologies like the BlueTEC emission control system and comprehensive concepts for environment-friendly vehicles such as BlueEFFICIENCY. Mercedes-Benz introduced BlueTEC for passenger cars in October 2006. In the commercial vehicle sector this technology, spelled “BlueTec”, has been employed since 2005.
The world’s smallest direct-injection diesel engine
Parallel to BlueTEC development, conventional diesel engines continue to be improved, one outstanding example being the diesel engine of the second-generation smart fortwo (451 series) introduced in 2007. With an NEDC consumption of just 3.3 litres per 100 kilometres and 88 grams of carbon dioxide emissions per kilometre, the smart fortwo cdi is the world’s most economical production car and, at the same time, the one with the lowest carbon dioxide emissions. With a tank filling of 33 litres, the two-door car with 33 kW (45 hp) engine has a range of some 1000 kilometres – in theory, that’s the distance from Berlin to the outskirts of Paris without a refuelling stop. The smart engineers further developed the predecessor model’s proven cdi engine and made it fit for the future. They boosted output and torque by ten percent each and reduced fuel consumption by some 13 percent.
At the time of its premiere, this engine was the world’s smallest direct-injection diesel unit – and a masterpiece of engine development with the most progressive engineering – normally the preserve of significantly larger engines – accommodated within highly compact dimensions. This includes a common rail direct injection system which produces high injection pressure ratings of up to 1600 bar (previously 1350 bar) even at low engine speeds, and feeds the fuel into the combustion chambers by means of newly developed six-hole injectors. Together, these two features account for an even more efficient combustion process. Turbocharger, charge air cooling, electrically operated and cooled exhaust gas recirculation, hydraulic valve clearance compensation and lightweight design are additional features which distinguish the smart’s cdi engine as a high-technology package.
Eight-cylinder power for the S-Class
In December 2006, Mercedes-Benz added another diesel variant to the S-Class range (W 221), the S 420 CDI. The eight-cylinder car has a modern V8 CDI engine with a displacement of four litres which delivers 235 kW (320 hp) and a torque of 730 Newton metres. For efficient and smooth power transmission, the 7G-TRONIC is installed as standard. Fuel consumption (NEDC) is as low as 9.4 to 9.6 litres per 100 kilometres and thus under the magical ten-litre line.
Mercedes-Benz diesel engines: Fit for climate protection
In 2007 piezo injectors on diesel engines formed part of the technologies Mercedes-Benz applied with the aim of systematically improving fuel economy and emissions. The Stuttgart-based brand provided evidence of this with the publication of its 2007 Sustainability Report which focuses on climate protection.
Future progress will continue to be based on internal combustion engines – as well as on research into alternative propulsion systems. Professor Herbert Kohler, Vice President with responsibility for Corporate Research and Advanced Vehicle/Powertrain Engineering as well as Chief Environmental Officer of Daimler AG: “Our research and development work therefore focuses not only on alternative propulsion systems but also, and above all, on the ongoing improvement of internal combustion engines. Our aim is to make the petrol engine as efficient as the diesel engine, and the diesel engine as clean as the petrol engine.”
Among other things, the company works on a new engine concept which combines the advantages of the two systems. Over and above this, all cars are developed so as to permit the option of hybrid drive. By combining an efficient internal combustion engine with a hybrid module, the optimum powertrain can be configured, matched to operating conditions and the customer’s preferences. One result of this work is the first diesel hybrid passenger car from Mercedes-Benz presented in March 2010, the E 300 BlueTEC HYBRID, which comes onto the market in 2011.
DIESOTTO: Combining the advantages of diesel & petrol engines
Mercedes-Benz presented the first results of research on a new internal combustion engine combining the advantages of diesel and petrol units at the 2007 Frankfurt International Motor Show: The DIESOTTO engine has the performance of a petrol engine as well as the high torque and fuel economy of a modern diesel – and it is extremely clean. Among other things, the novel high-technology package includes direct injection, turbocharging and variable compression. At the core of this innovation lies homogeneous charge compression ignition, permitting a highly efficient combustion process similar to that of a diesel. In contrast to comparable developments, the Mercedes-Benz system has the crucial advantage that it requires no synthetic fuels but can be operated using conventional petrol.
Upon being started and under full load, a spark plug is used for causing the petrol/air mixture to explode – as in a conventional spark-ignition engine. The DIESOTTO automatically switches to controlled auto-ignition (homogeneous combustion) within one power stroke in the part-load range, i.e. at low and medium engine speeds. This homogeneous combustion at reduced reaction temperatures results in very low nitrogen oxide emissions. A standard three-way catalytic converter takes care of emission control in the DIESOTTO engine. In addition, a highly efficient engine management system is used to network the individual systems into an integrated configuration.
Diesel milestones for the future of the combustion engine
By optimising the diesel engine, Mercedes-Benz has time and again been setting new milestones for the future of the internal combustion engine. With BlueTEC and CDI BlueEFFICIENCY models , in particular, Mercedes-Benz engineers have succeeded in recent years in making the powerful and economical diesel engine as clean as the petrol engine. In 2010 all CDI BlueEFFICIENCY E-Class models with six-cylinder diesel power plant, for example, already meet the EU5 emission standard, and the BlueTEC model E 350 BlueTEC with urea injection even meets the future EU6 standard. Diesel-hybrid vehicles like the E 300 BlueTEC HYBRID now represent a further step towards the future of the diesel engine. Read more about the latest diesel technology from Mercedes-Benz in the chapter “BlueTEC, CDI BlueEFFICIENCY and BlueTEC HYBRID – The future of the compression-ignition engine“.