Next Audi 2.0 TFSI detailed
BY DANIEL GARDNER | 8th May 2015
The fifth-generation A4 is due to arrive on Australian soil early next year and if the new engine is offered, it will better the fuel economy of the current version by a significant 2.0L/100km.
Critically though, Audi says the frugal 2.0-litre TFSI turbo four-pot will be the most efficient in its class, beating its two rivals, the BMW 3 Series and Mercedes-Benz C-Class.
In their most economical 2.0-litre petrol versions, the rival pair record combined consumptions of 6.0L/100km for the BMW 320i and 6.2L/100km for the C200.
The TFSI also ups the stakes in output too, beating the BMW by 5kW and 50Nm, while trumping the Merc by another 5kW and 20Nm.
Developments in valve-timing technology account for the significant step forward in efficiency with an operation similar to the Miller Cycle, which closes the inlet valve after the cylinder has reached bottom dead centre.
However, the Audi system alters the valve-timing depending on engine speed and load, and can close the valve before BDC under partial throttle conditions, reducing the time available for air to fill the cylinder and lowering the internal loading of the engine.
Under part load, the valve remains open for 140 degrees of crank rotation, but increases to 170 degrees under full load. The result is an engine that effectively changes its capacity.
The reduced induction time might normally reduce the amount of air filling the cylinder resulting in a reduction of power, but by increasing turbo boost pressure, the same volumetric efficiency is achieved.
Where turbocharged engines normally require a lowered compression ratio, the Audi system allows a higher ratio to be applied, further increasing combustion efficiency.
Audi describes the technology as “rightsizing” allowing the efficiency of a downsized small engine under low-load or a larger engine when more performance is required.
A similar system has previously been employed by Toyota with its Prius engine, but that system uses a fixed valve timing, giving the effect of an Atkinson cycle and at the cost of reduced power output.
The high-efficiency TFSI engine will make its debut in the new A4 range in Europe later this year, but will be applied to other models in the Audi line-up following the A4 launch.
