The Efficiency Principle

The revolutionary effect that the TFSI engines are having on petrol engine construction – comparable to the impact that TDI technology had on diesels in the past – is due to a whole series of innovations. For a long time turbocharged petrol engines were not really fuel-efficient, but this changed with the development of direct fuel injection for petrol engines. Whereas conventional engines inject the fuel into the inlet tube, from where the final mix of fuel and oxygen travels to the combustion chamber, direct injection technology uses a valve in the combustion chamber to inject the fuel into the inflowing air. The advantage of this approach is obvious: the fuel supply can be managed more precisely, making for enhanced combustion control. In addition, the fact that the fuel is vaporized in the combustion chamber improves chamber filling and reduces knocking. Components such as the Audi Valvelift System increase the efficiency of the engines even further.

The principle of downsizing has now been applied to a large proportion of the engine range. At the lower end is the 1.4 TFSI. Offering 125 PS (92 kW) and a torque of 200 newton meters, starting at 1,500 revolutions per minute, the engine sets new standards for both power and fuel efficiency: with an average fuel consumption of a mere 5.9 liters and CO2 emissions of only 140 grams per kilometer, the smallest TFSI is one of the most fuel-efficient and cleanest engines in its class today. The next engine in the TFSI series is the 1.8 TFSI, with 160 PS (118 kW). At a technical level, this is essentially based on the somewhat larger 2.0 TFSI, but offers a further reduction in fuel consumption.

Altogether extremely fuel-efficient

Audi engineers take a top-down approach to their cars, looking at them as end-to-end energy systems when working out the best way to reduce fuel consumption. This approach has allowed them to identify a large number of areas to tweak so they can improve efficiency, including innovative drive and gearbox components, chassis made out of light yet extremely strong materials, and more efficient auxiliary units and driver assistance systems. All are contributing to the ongoing process of making vehicles of the Audi brand more and more fuel-efficient.

Audi is also successfully applying the principle of downsizing at the upper end of the engine range. “The larger the engine capacity, the greater the potential savings offered by the new technologies”, says Eiser. For example, the new Audi S4 has a three-liter V6 motor with 333 PS (245 kW), whereas its predecessor relied on a 4.2 liter V8 engine. The new model has a minor sensation tucked away snugly between its banks of cylinders: a mechanical supercharger that gives the engine a real boost. Despite having 11 PS less, the new engine outguns its S4 predecessor by several tenths of a second in terms of both acceleration and elasticity – thanks to an additional 30 newton meters of torque. According to Eiser, Audi uses a compressor instead of a turbocharger for this engine, which is also used in the A6 but with somewhat different performance data, because of the features of the cars concerned: “The V6 is basically used for larger, heavier cars, where we need a particularly high torque at low engine speeds to ensure powerful acceleration. This is what the compressor does.” Since it is driven directly via the crankshaft, it responds more quickly than a turbocharger, which is powered by the exhaust gas flow. At 9.7 liters per 100 kilometers in the 300 PS class, the S4 has a fuel consumption to be proud of. In comparison to the V8 engine used by its predecessor model, the engine uses around 27 percent less fuel on average. Something that is not only extremely efficient but also a source of great pleasure for Audi customers.


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