The A4 model series has a particularly broad engine lineup with 13 powerplants. All of them feature direct-fuel injection and, with the exception of the most powerful 3.2 FSI engine, are also turbocharged. The V6 and the 2.0 TFSI feature different versions of the Audi valvelift system, which uses two-stage variable valve lift to increase torque. A start-stop system is standard with many of the engines; all come standard with a recuperation system. The most efficient model in the A4 lineup is the 2.0 TDI with 100 kW (136 hp). In the sedan, the four-cylinder diesel producing 320 Nm (236.02 lb-ft) of torque consumes just 4.4 liters of diesel per 100 km (53.46 US mpg) on average, a CO2 equivalent of just 115 grams per km (185.07 g/mile). The model features the know-how from Audi's modular efficiency platform. Two other particularly environmentally compatible engines join the 2.0 TDI in the A4 lineup. A sophisticated purification system in the A4 3.0 TDI clean diesel quattro largely eliminates nitrides of oxygen so that the V6 diesel satisfies all U.S. emission standards and also the future Euro 6 standard. The A4 2.0 TFSI flexible fuel is also designed for operation on bioethanol E 85.