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 (19,580 psi) 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 Nm (221 lb-ft) 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 l/100 km (37.33 mpg/US, 15.87 km/l) of diesel.
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 Nm (273 lb-ft) 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 Nm (347 lb-ft) 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 l/100 km (30.15 mpg/US, 12.82 km/l) of diesel fuel; 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 Nm (347 lb-ft), obtained in a range from 1800 to 2600 rpm. The luxury sedan got up to 230 km/h (143 mph) with the 3.2-liter compression-ignition engine and sprinted from standstill to 100 km/h (62 mph) 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 Nm (413 lb-ft) at 1800 to 2600 rpm. A top speed of 250 km/h (155 mph) and 7.8 seconds for accelerating to 100 km/h (62 mph) illustrate the role of the S 400 CDI as first among the Mercedes-Benz diesel models.
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 (143 mph) and standstill to 100 km/h (62 mph) acceleration in 9.2 seconds.