The new Mercedes-Benz E 420 CDI: the world’s highest-torque passenger car diesel engine

May 18, 2005
In autumn 2005, a new Mercedes-Benz E-Class model variant powered by the world’s highest-torque passenger car diesel engine will go into series production. The 231-kW/314-hp V8 powerplant develops maximum torque of 730 Newton metres at engine speeds as low as 2200 rpm. This allows the new E 420 CDI to accelerate from 0 to 100 km/h in just 6.1 seconds on its way to a top speed of 250 km/h. Combined fuel consumption stands at 9.3 litres per 100 kilometres. Among the standard features of Mercedes-Benz’ new flagship diesel model are a maintenance-free particulate filter, seven-speed automatic transmission and AIRMATIC air suspension.
The new eight-cylinder engine powers the E 420 CDI to the top of this market segment in terms of dynamics and smooth running characteristics - and offers exceptional diesel-powered driving pleasure. The imposing pulling power of the CDI engine sees to that, generating in excess of 700 Newton metres as low down 1950 rpm. The V8 reaches its maximum torque of 730 Newton metres at 2200 rpm, guaranteeing not only exemplary flexibility when overtaking and lightning-fast mid-range sprints, but also relaxed cruising in higher gears. The E 420 CDI requires a mere 5.4 seconds to power from 60 to 120 km/h in third gear.
Heading the list of technical innovations in the new Mercedes eight-cylinder powerplant – which also boasts an aluminium crankcase, cooled exhaust gas recirculation and electrically driven intake air throttling – is third-generation common-rail direct injection. This technology raises injection pressure to 1600 bar and allows particularly precise fuel metering, thus reducing both fuel consumption and exhaust emissions. As with all common-rail engines, the driver can count on high injection pressure at all times – even at low engine speeds.
An outstanding feature of the latest CDI technology are piezo injectors in place of solenoid valves. With a response time of just 0.1 milliseconds, piezo ceramic allows fuel injection to be adapted more quickly and precisely to suit changing loads and engine speeds than has previously been the case. This helps to cut emissions, fuel consumption and noise levels. To this end, Mercedes engineers have developed a dual pilot injection system which acts in just a few milliseconds and significantly reduces the combustion noise generated by the eight-cylinder engine. Added to which, double fuel post-injection helps to clean the residue away from the standard-fitted diesel particulate filter.
Improved charge air supply and cooling boosts power output
One particular focus for the Mercedes engineers was the air ducting either side of the turbochargers. Using airflow calculations and simulations, they were able to reduce the loss of pressure typically experienced in the charge air manifolds of turbochargers, leading to a sustained improvement in the supply of air to the engine. The pressure loss in the charge air manifolds has been cut by as much as 60 per cent compared to Mercedes-Benz’ previous eight-cylinder CDI engine. This means that an up to 15 per cent greater air mass can flow into the engine, and the V8 uses this to maximise power and torque development.
Improved charge air cooling allows further improvements along the same lines. The water-cooled intercooler in the new eight-cylinder CDI engine is integrated into a special low-temperature circuit with two water coolers. Here, the charge air is cooled by up to 120 degrees Celsius, pushing up air density under full load by as much as 25 per cent.
Modifications have also been made to the turbochargers with variably adjustable guide vanes. New vane geometry for the compressor and turbine wheels and the guide vanes makes the new engine more efficient than the previous eight-cylinder CDI unit. Another special development from the Stuttgart-based diesel experts are the hollow inserts in the intake lines, which increase the volume of the air before it enters the turbochargers. This raises torque output at lower engine speeds by some 15 per cent.
Standard-fitted particulate filter brings exhaust emissions below EU-4 limits
The new Mercedes-Benz eight-cylinder diesel engine is fitted as standard with two oxidizing catalytic converters and a maintenance-free particulate filter system, allowing it to keep below the stringent EU-4 exhaust-gas limits. The catalytic converters have the task of breaking down unburned hydrocarbons and carbon monoxide though a chemical reaction with oxygen (oxidation). The particulate filter does not require the use of additives and is cleaned as required whilst on the move through engine functions such as double fuel post-injection.
The new V8 compression ignition engine features a sensor in the oil sump which checks the level, temperature and quality of the oil. A display in the cockpit alerts the driver when the next oil change is due. Depending on how the car is driven, maintenance intervals of up to 40,000 kilometres are well within the range of the E 420 CDI.
The new eight-cylinder CDI engine will celebrate its series production premiere in the E-Class in autumn 2005 and will also be made available for other Mercedes-Benz passenger car model series in the future.