Diesel engines in Mercedes-Benz passenger cars: 1997 - 2006

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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/Main in September 1997: in the C 220 CDI Mercedes-Benz presented a direct injection system based on a new principle, “Common Rail Direct Injection” (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 1,350 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 engine of the C 220 CDI is a four-valve-per-cylinder design and develops remarkable torque of 300 Newton meters 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-liter four-cylinder and sprinted to a top speed of 187 km/h (116 mph). The E 220 CDI developed 92 kW (125 hp) and reached the 200 km/h (124.3 mph) mark. Yet the new models needed an average of only 6.3 liters of diesel per 100 kilometers (37.3 mpg).
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 meters 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 meters at 1800 rpm and held it to 2600 rpm. This 3.2-liter 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 oxidation-type catalytic converter) consumed on average only 7.8 liters of diesel fuel per 100 kilometers (30.1 mpg); its speed topped out at 230 km/h (143 mph).
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 meters, obtained in a range from 1800 to 2600 rpm. The luxury sedan got up to 230 km/h with the 3.2-liter 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 liters, the light-alloy V8 OM 628 DE 40 LA developed 184 kW (250 hp) at 4000 rpm. It delivered torque of 560 Newton meters at 1800 to 2600 rpm. A top speed of 250 km/h (155 mph) 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 coupe
Since the C 123 series of the 1970s there had been no more Mercedes-Benz coupes 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.
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 sedan and station wagon models a highly agile character with a decidedly sporty touch. The sedan 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 in-cluding sports suspension.
The V6 diesel engine with direct injection develops 165 kW (224 hp) and a torque of 510 Newton meters, which is on tap from 1800 rpm and remains constant up to an engine speed of 2800 rpm. The engine complies with the EURO IV emission norm and has been featuring a particulate trap as standard equipment ever since its market launch. Weight is reduced by a crankcase made of aluminum with cast-in gray-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 trans-mission – if specified by the customer – and the Electronic Stability Program.
Premiere: The torquiest eight-cylinder diesel engineIn the fall of 2005, production began of the torquiest V8 passenger-car diesel engine (OM 629), initially for the Mercedes-Benz E-Class and planned to be made available for other model series at a later stage. The 231 kW (314 hp) V8 generates its maximum torque of 730 Newton meters 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 (155 mph). In terms of dynamism and smooth running characteristics, this eight-cylinder represents the benchmark in its market segment. The combined fuel con-sumption is 9.3 liters per 100 kilometers (25.3 mpg). The standard specifications of the E-Class with this engine include a maintenance-free particulate trap, seven-speed automatic transmission and AIRMATIC air suspension.
Alongside the aluminum crankcase, cooled exhaust-gas recirculation and electric intake air throttling, third-generation common rail direct injection ranks among the technical tidbits of the new Mercedes-Benz eight-cylinder engine. This CDI system operates at an injection pressure raised to 1,600 bar and permits high-precision fuel apportionment – for the benefit of fuel economy and exhaust emissions.
2003 – Maintenance-free particulate trap and EURO IV norm
Mercedes-Benz made a major advance in respect of the environmental compatibility of the diesel drive in the fall of 2003. As first automobile brand in the world the company introduced diesel passenger cars built to the EURO IV norm and featuring a maintenance-free particulate trap. Mercedes-Benz offered the first traps for export to California as early as in 1985.
2005 – Particulate trap as standard in more than 30 Mercedes-Benz models
Since the early 1990s, technologies like the common rail system developed by Mercedes-Benz have 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 in summer 2005 began fitting all diesel cars from the A- to the S-Class with diesel particulate traps as standard in Germany, Austria, the Netherlands and Switzerland. Mercedes-Benz had been offering its innovative particulate trap system, which operates maintenance-free and makes do without additives, since 2003.
Owing to economical, optimized engines, in combination with the trap, 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 the fall of 2005, initially for vehicles of the C-Class and E-Class. Dr. Thomas Weber, member of the Board of Management of DaimlerChrysler AG, responsible for Research and Technology and Development in the Mercedes Car Group, emphasizes:
“Our retrofit solution for particulate taps 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 traps in the standard specifications but also reviewed over 70 years of diesel competence – 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/liter (17.7 hp/liter). 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 liters – boasting a power-to-swept volume ratio of 55.2 kW/liter (75 hp/liter), 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 meters in the 170 D of 1949 to 510 Newton meters in the C 320 CDI. In other words, some 55 Newton meters per liter of displacement in 1949 are pitted against more than three times this figure – 170 Newton meters - 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 meters to the crankshaft of the eight-cylinder unit.
From a displacement of three liters, the engine of the SLK 320 Triturbo develops remarkable 210 kW (286 hp) and a torque of 630 Newton meters – 70.3 kW and 211 Newton meters per liter 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 (155 mph). It combines this impressive performance with excellent fuel economy: 7.5 liters of fuel per 100 kilometers (overall NEDC consumption) or 31.3 mpg.
The economy of modern diesel engines is astounding. Whereas the world’s first passenger car diesel engine in the 260 D consumed 0.3 liters of fuel on 100 kilometers to generate one kilowatt, the C 320 CDI makes ends meet with just 0.04 liters per kilowatt over the same distance, equivalent to a reduction by unbelievable 90 percent or, in other words, fuel consumption reduced by a factor of ten. This is a development which not only saves natural resources but also reduces the burden on the environment. At the same time, exhaust-gas emissions have been reduced significantly, not least by state-of-the-art filter technology. And the next step towards even greater cleanliness has already been taken – its name is BLUETEC.
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