Automotive Engineer

BMW has developed a triple-turbo diesel engine. The 3.0-litre six cylinder develops 280kW and 740Nm and is the most powerful the firm has ever built. The engine appears in BMW M-developed versions of the X5 and X6 SUVs and the 5 Series sedan and estate.

The vehicles, which are all-wheel drive, offer similar performance to models such as the M5 but using a diesel instead of a gasoline engine means that carbon dioxide emissions are much lower: only 165g/km CO2 for the M550d xDrive sedan compared to the M5's 232g/km.

President of BMW M, Dr Friedrich Nitschke, said: “We are targeting our efforts at customers looking for more emotionality and more performance, but who don’t want to forgo the everyday usability of their cars.”

The engine uses two small variable-geometry turbochargers which operate in sequence at low engine speeds and loads. A large fixed geometry turbo cuts in at medium loads, and then provides all of the boost pressure at high loads.

This enables the engine to develop such high ratings without compromising launch performance or transient response: maximum torque is developed at 2,000rpm, but the engine will rev to 5,400rpm – very high for a diesel.

To match the increase in airflow, extra fuel is fed to the combustion chamber by increasing the commonrail pressure from 2,000 to 2,200bar. The piezo injectors deliver eight injections per cycle. Maximum cylinder pressures have risen from 185 to 200bar, although the cylinder block remains an aluminium casting.

This engine will take the X6 M50d SUV from 0-100km/h in 5.3s and to a 250km/h limited top speed. Consumption and emissions are 7.7-litres/100km and 204g/km CO2.