The 2007 Mercedes-Benz E-Class
THE MERCEDES-BENZ E320 BLUETEC
Heralded as the world’s most advanced diesel technology, BLUETEC combines several technologies to reduce exhaust emissions. BLUETEC is built on a foundation of advanced engine design that includes four valves per cylinder, centrally located piezo-electric injectors, the latest CDI direct injection, a turbocharger with variable nozzle turbine and exhaust gas recirculation.
Outside, the new Mercedes-Benz E320 BLUETEC looks just like other E-Class sedans. In fact, only the BLUETEC badge on the trunk lid identifies the new model. Inside, an additional warning light indicates glow plug operation. However, under the hood, its high-tech powerplant represents a dramatic step forward that seems destined to change people’s dated perceptions about diesels.
Farther, Faster, Cleaner
Like any diesel, the E320 BLUETEC will get improved fuel mileage and have increased cruising range (less frequent trips to the filling station) than a gasoline-powered car, but more important, it does it without the usual tradeoffs of diesel ownership.
Starting the E320 BLUETEC on a cold morning, you can hear a muted version of the characteristic diesel engine sound. However, as soon as the car warms up, most people would be hard pressed to hear any difference between this car and a gas-powered model. Under acceleration, the E320 BLUETEC feels faster than the gasoline-engine E320, a result of its whopping 400 foot-pounds of engine torque – the pulling power of a V8!
THE E320 BLUETEC ENGINE
Four-Valve V6 with Central Injectors
A new-generation 3.0-litre V6 diesel engine makes its Canadian debut in the E320 BLUETEC. The new 72-degree V6 diesel features four valves per cylinder, dual overhead camshafts and centrally located piezo-electric fuel injectors. Designed to spray diesel fuel directly into the centre of the combustion chamber, each injector is positioned in the aluminium cylinder head about where a spark plug might be found on a four-valve gasoline engine. This layout ensures even dispersion of fuel as its flame front spreads concentrically across the combustion chamber.
Based on an aluminium block with cast-in steel cylinders, the BLUETEC V6 engine has an 83 mm bore and 92 mm stroke, a ratio that automotive engineers refer to as “under-square.” While most Mercedes-Benz gasoline engines are over-square (bore is larger than the stroke), many diesels have a relatively long stroke, in part to produce the high compression needed to make intake air hot enough for ignition.
To neutralize vibration that’s inherent to V6 engines, a balance shaft located in the block between the cylinder banks counter-rotates at the same speed as the crankshaft. The intake and exhaust valves are operated by twin overhead camshafts in each cylinder bank, with the intake cams driven by a double chain that also drives the balance shaft. A gear on each intake cam, in turn, drives the exhaust camshafts.
VNT Turbocharging
Although many non-turbo diesel engines have compression ratios higher than 20:1, Mercedes engineers found that, in conjunction with the BLUETEC engine’s exhaust-driven turbocharger, the engine is most efficient with a compression ratio of 16.5:1. The turbocharger features variable turbine geometry called VNT (Variable Nozzle Turbine), which is integrated with the electronic engine management system. To vary the combustion air volume quickly, VNT adjusts the guide vanes electrically as load and engine speed conditions change.
Air-to-Air Intercooler
Electronic Throttle
Diesel engines usually operate without any throttle in the intake system, so that fuel delivery alone controls engine load and speed. However, Mercedes engineers found that, at light load, throttling one of the two diesel intake ports on each cylinder creates air turbulence that helps optimize the combustion process and further reduce fuel consumption and exhaust emissions. As a result, the BLUETEC engine makes use of electronic intake port deactivation that’s automatically managed by a sophisticate electronic control unit – the same one that determines everything from fuel injection quantity and timing to the vane angle of the VNT turbocharger and the quick-start glow-plug operation. This versatile microprocessor also networks with the 7G-TRONIC seven-speed automatic transmission and the Electronic Stability Program (ESP) systems.
