Audi Introduces Compressor Supercharging

The new 3.0 TFSI engine of Audi's V6 engine range combines two technologies: gasoline direct injection and compressor supercharging. The 3.0 TFSI develops 213 kilowatts and delivers its maximum 420 Newtonmetres at 2500 revolutions per minute and maintains this constantly until 4850 revolutions per minute. The crankcase of the three-litre version is made of cast aluminium/silicon, and tips the scales at 33 kilograms. The entire engine, including the compressor, weighs 189 kilograms. Later this year the new V6 will go into production.

The compressor of the engine is so compact that it fits inside the 90-degree V of the cylinder banks, in place of the intake manifold. Because it is driven by the engine via poly-V belt, its full thrust is available from idle speed upwards. The gas paths after the compressor are very short; this means that the torque is built up quickly, even more dynamically than on a naturally aspirated engine of the same displacement. The 3.0 TFSI revs up to the maximum of 6500 revolutions per minute, achieving its rated output of 213 kilowatts at under 5000 revolutions per minute.

The engine has a compression ratio of 10.5:1. The direct injection principle is once again the key, because the intensively swirled fuel cools the combustion chamber, reducing the tendency to knock. The compressor of the new 3.0 TFSI is what is known as a Roots blower. Inside it, two four-vane rotary pistons counter-rotate at a speed of up to 23,000 revolutions per minute, with an air gap between them measuring just a few thousandths of a millimetre. The rotors can deliver 1000 kilograms of air per hour and force it into the combustion chambers at a pressure of up to 0.8 bar.

Two water-to-air intercoolers made from aluminium and connected to a separate coolant circuit are integrated into the housing. Here, the compressed and therefore heated intake air is cooled down again in order to boost its oxygen content for the combustion process.

The crankcase of the three-litre engine is made of cast aluminium/silicon and tips the scales at 33 kilograms. The entire engine, including the compressor, weighs 189 kilograms. The bore measures 84.5 millimetres and the stroke 89.0 millimetres, producing a swept volume of 2,995 cubic centimetres. Also the crankcase has been adapted to the higher prevailing pressures, all components are frictionally optimised. The two intake camshafts can be adjusted through 42 degrees crankshaft angle. In the intake ports, tumble flaps induce movement in the incoming air to promote optimum mixture preparation.

The injection system is a new design also. A common rail system with six-hole injectors injects the fuel directly into the combustion chambers at a pressure of up to 150 bar. The injectors' dynamic response permits up to three fuel injections per operating cycle across an extensive range of the characteristic map.The new 3.0 TFSI will achieve an average fuel consumption of less then ten litres per 100 kilometres in virtually all longitudinally engined models of the car manufacturer, the concept for which it is envisaged. It is designed to run on either premium or regular gasoline and complies with the future emission standard Euro 5.

The car manufacturers technology of gasoline direct injection according to the FSI principle was what made this efficiency possible in the first place. Unlike conventional concepts, it allows the compressor to be located behind the throttle valve. In view of the low density of the intake air at loads below supercharging level and when coasting, its rotors are free-running and the amount of power required to drive them is low.