Audi has introduced a new top end to its V6 engine range: the 213 kW (290 hp) 3.0 TFSI with gasoline direct injection and compressor supercharging. The “T” in the Audi engine designation no longer exclusively denotes turbo versions. The new V6 will go into production later this year.
Audi, which has a long tradition of supercharged engines, said that comparative tests showed that the mechanical supercharger was a superior charging solution to a biturbo concept for the 3.0-liter engine. In conjunction with direct injection, the packaging, starting performance and dynamic response of the supercharger were superior.
The compact compressor—a Roots blower—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, producing large amounts of pulling power when driving off. The 3.0 TFSI delivers its maximum 420 Nm (310 lb-ft) at only 2,500 rpm and maintains this constantly until 4,850 rpm.
The compressor features two four-vane rotary pistons counter-rotating at a speed of up to 23,000 rpm, with an air gap between them measuring just a few thousandths of a millimeter. The rotors can deliver 1,000 kg (2,205 lb) of air per hour and force it into the combustion chambers at a boost pressure of up to 0.8 bar.
Two water-to-air intercoolers made from aluminum 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. A package of measures reduces the level of noise generated by the compressor to a minimum.
The gas paths after the compressor are very short; torque is built up extremely quickly, even more dynamically than on a naturally aspirated engine of the same displacement.
Gasoline direct injection technology enabled the use of the supercharger. Unlike in conventional applications, GDI allows the compressor to be located behind the throttle valve. With the low density of the intake air at loads below supercharging level and when coasting, the compressor rotors are free-running and the amount of power required to drive them is low.
The engine’s high compression ratio of 10.5:1 also contributes to its efficiency. The direct injection intensively swirls the fuel, cooling the combustion chamber and reducing the tendency to knock.
The crankcase has been adapted to the higher prevailing pressures and all components are frictionally optimized. 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 fundamentally new design. 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’ highly dynamic response permits up to three fuel injections per operating cycle across an extensive range of the characteristic map.
The entire engine, including the compressor, weighs 189 kilograms (417 lb). The bore measures 84.5 millimeters (3.33 in) and the stroke 89.0 millimeters (3.5 in), producing a swept volume of 2,995 cm3.
The pulling power of the 3.0 TFSI enables it to extend the transmission ratio, further augmenting its efficiency. The new 3.0 TFSI will achieve an average fuel consumption of “well under” 10 liters per 100 km (23.5 US mpg) in virtually all longitudinally engined Audi models, the concept for which it is envisaged. It is designed to run on either premium or regular gasoline and already complies with the future emission standard Euro 5.