At the annual Vienna Motor Symposium recently, Audi revealed a brand new four-pot petrol engine which promises a near-diesel like fuel efficiency levels and will find its way into the next-generation Audi A4.
The engine is specified as a TFSI four-cylinder with a capacity of 2.0-litres with turbocharging and direct-injection, producing 190hp and 320Nm of torque. However, although it may produce less power than the current 2.0 TFSI (225hp/350Nm), the new powerplant is capable of returning a NEDC combined fuel consumption figure of 5.0 litres per 100km according to Audi.
That’s 1.7 litres per 100km less than the current Audi A4 you can buy in Malaysia today and will certainly take the fight to competitors like Mercedes-Benz, BMW, and Jaguar. Not only that, the new engine weighs in at just 140kg.
Utilising a new combustion method that is comparable to the Miller cycle, Audi engineers have managed to increase the “efficiency and performance characteristics across the entire engine speed range.”
So how does it work?
The Miller cycle was patented by Ralph Miller in 1957 and operates in a similar manner to the Atkinson cycle but tags on force induction (turbocharging or supercharging).
An Atkinson and Miller cycle engine leaves the intake valve open during the compression phase longer than a normal engine on the traditional Otto cycle. However, this results in lower engine compression. With the Miller cycle, forced induction makes up for that loss in engine compression.
Audi’s new 2.0-litre TFSI engine employs this combustion method while applying other bits of technology to improve efficiency.
Audi also changed the engine’s intake period by shortening the crank angle to 140 degrees from around 190 or 200 degrees. The intake valves also close earlier, before the bottom dead centre of the crankshaft’s rotation is reached. This lowers the medium cylinder pressure, allowing for a higher compression ratio provided by the turbocharger on the inlet side, translating to higher energy levels from each combustion cycle.
During partial loads, Audi says the engine will deliver an extra fuel-injection burst from its indirect fuel-injection system (in the intake manifold) before the fuel-air mixture reaches the combustion chamber.
Using Audi’s variable Valvelift system on the inlet side, it allows a short intake time during partial loads but when high performance is required on heavy loads, the intake time is extended up to 170 degrees on the crank angle.
This allows a high torque output across a wide rev range – 1,450 to 4,400 rpm.
Also part of Audi’s ‘rightsizing’ approach, the exhaust manifold is integrated in the cylinder head. Together with the controlled coolant flow, engine warm-up time is shortened. Low friction 0W-20 lubricant is also used to minimise internal friction.