Compressor and direct injection – a compelling duo
213 kW (290 hp), 420 Nm and outstanding efficiency
Superb power from idle speeds up, spontaneous torque buildup
Powerful, spontaneous and ultra-efficient: this is the new top version in Audi's V6 engine range. The 3.0 TFSI develops 213 kW (290 hp) and a huge 420 Nm (309.78 lb-ft) of torque. It combines two state-of-the-art technologies in perfect style – gasoline direct injection and compressor supercharging. The hi-tech V6 will go into production later in the year.
The brand with the four rings has a long tradition of supercharged engines. The legendary Grand Prix racing cars built by Auto Union back in the 1930s already featured compressors, which coaxed as much as 440 kW (around 600 hp) out of the mighty 16-cylinder and 12-cylinder engines. From the late 1970s on, Audi focused its attention on the exhaust turbocharger, which helped it to a succession of noteworthy triumphs in the world of motor sport. It was at this time that Audi's turbo engines began to enjoy resounding market success.
The compressor is now staging a comeback. It is the ideal supercharging technology for the new three-liter V6, the 3.0 TFSI; the T in Audi engine designations consequently no longer exclusively denotes turbo versions.
Extensive comparative tests revealed the mechanical supercharger to be superior to a biturbo concept for this engine. In conjunction with direct injection, its packaging, starting performance and dynamic response were far superior.
The compressor is so compact that it easily 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 huge pulling power when driving off. The 3.0 TFSI delivers its maximum 420 Nm (309.78 lb-ft) at only 2,500 rpm and maintains this constantly until 4,850 rpm.
The gas paths after the compressor are very short; this means that the torque is built up extremely quickly, even more dynamically than on a naturally aspirated engine of the same displacement. The 3.0 TFSI responds sportily to the throttle, with exceptional agility and bite. And it revs up to the maximum of 6,500 rpm with playful ease, achieving its rated output of 213 kW (290 hp) at just under 5,000 rpm.
Top marks for fuel efficiency
The 3.0 TFSI without question earns top marks for fuel efficiency, too. And its pulling power enables it to extend the transmission ratio, further adding to its already superior efficiency. The new 3.0 TFSI will achieve an average fuel consumption of well under 10 liters per 100 km (23.52 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 – a question of honor for every new Audi engine.
The Audi technology of gasoline direct injection according to the FSI principle was what made this trailblazing 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.
The engine's high compression ratio of 10.5:1 also plays a big part in its efficiency. 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 rpm, with an air gap between them measuring just a few thousandths of a millimeter. The rotors can deliver 1,000 kilograms (2204.62 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. An extensive package of measures reduces the level of noise generated by the compressor to a minimum.
The engine itself belongs to Audi's family of ultramodern V engines. In addition to the standard cylinder angle of 90 degrees, their attributes include systematic lightweight construction – the three-liter version's crankcase, which is made from cast aluminum/silicon, tips the scales at just 33 kilograms (72.75 lb). The entire engine, including the compressor, weighs 189 kilograms (416.67 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.
Reinforcements on the crankcase
Audi has included a whole array of refined hi-tech features on the 3.0 TFSI. 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. They, too, optimize the combustion process and therefore contribute to the impressive performance of the new 3.0 TFSI.