The new inline six cylinder Twin-Turbo gasoline engine forms the pinnacle of BMW's wide range of straight-six power units, developing maximum output of 300hp and a peak torque of 300 lb-ft with a displacement of 3.0 litre. Using two turbochargers in combination with the new BMW High Precision Fuel Injection leads to a responsive build-up of torque and to an impressive development of power over a wide engine speed range.
This paper gives a detailed overview of the turbocharger-and the injection system and describes the effect of both systems on power and torque, as well as on fuel consumption and emission. The big advantage of using two small turbochargers is their low moment of inertia, even the slightest movement of the accelerator pedal by the driver's foot serving to immediately build up superior pressure and power. This puts an end to the turbo “gap” previously typical of a turbocharged power unit. Therefore, the new Twin-Turbo power unit offers the same muscle as a much larger normal-aspiration engine, the 3.0-litre developing 300 lb-ft consistently throughout the engine speed range from 1,300 to 5,000 rpm, with the engine continuing to rev up to a speed range of 7,000 rpm.
To combine a thrilling driving experience with a standard of fuel economy appropriate in this day and age (e.g. 27,4 mpg for BMW 335i) , this Twin-Turbo is equipped with a direct gasoline injection and an all-aluminum crank-case. High Precision Fuel Injection performs the key function in this concept for maximum fuel efficiency: With even more exact dosage of fuel as well as a higher compression ratio (10,2:1) the new generation of BMW's direct gasoline injection power units meets all expectations also in practice in terms of fuel economy, without requiring any compromise in the engine's dynamic qualities. This is made possible by the central position of the piezo-injector between the valves. In this position the innovative injector opening up to the outside is able to distribute fuel in a conical, particularly consistent spread throughout the combustion chamber. Operating within a wide range of fuel pressure the system can perform up to three injection pulses per cycle to optimize the combustion process under its specific conditions. For a quick catalyst light-off for example a two pulse injection mode is used, leading to excellent combustion stability with very low hydrocarbon emission level.
Putting it all together this paper analyzes the properties of the turbocharger- and the injection system and shows their contribution to the dynamics, the fuel efficiency and the emission level of the new BMW Twin-Turbo engine.