Audi breaks new ground once again with the electric biturbo, which makes a secondary compressor give the main turbocharger a boost at lower engine speeds. Almost 25 years ago, Audi decided to focus on international diesel engineering. Audi introduced the first diesel with direct fuel injection, turbocharging and electronic control in the Audi 100 in 1989. Since that time, the TDI has been successful. When used with diesel engines, turbocharging improves the performance and significantly cuts fuel consumption and emissions – much more than what naturally aspirated engines are capable of. With regards to the displacement, the TDI engines can reach power gains of more than 100% and torque increases of 70% since 1989. Emissions also dropped by 95% since then.
Audi’s latest development stage is a biturbo version of the 3.0 TDI, which can deliver 230 kW (313 hp) and a maximum torque of 650 Nm (479.42 lb-ft) between 1,450 and 2,800 rpm. For each liter displacement, there’s a specific power output of 77.5 kW (105.5 hp). But then, the A6’s combined fuel consumption is just 6.4 liters of fuel per 100 km (36.75 US mpg), and with CO2 emissions of 169 grams per km (271.98 g/mile).
What all turbocharged engines all share is that energy from the exhaust is driving the turbocharger. This means that beginning with very low revs, the increase in boost pressure and torque gets increasingly greater as the exhaust energy increases. Audi is working on the electric biturbo as a new development stage. This enables the quick building-up of charge pressure and the achievement of high levels of torque even at very low revs. These are accomplished independently of the available exhaust energy.