Eleanor Norton. Audi. October 13th , 2017.
An important component of the B-cycle combustion process is the central position of the injectors in the combustion chamber. In the area around the inlet valve, this makes possible a geometry which, in interaction with the inlet ports, allows for targeted mixing up of the gas charge. The common-rail system injects the fuel into the combustion chamber with 250 bar of pressure - the high injection pressure ensures a homogeneous spray pattern and consequently a uniform propagation of the flame front.
The chain drive uses a new concept to reduce the drive power required: the crankshaft drives the balancer shaft via gears, with the shaft lying far down in the V of the cylinder banks. From here chains run to the four camshaft sprockets. These are trioval in shape, i.e. they have a slightly triangular shape, in order to compensate for peak forces. The balancer shaft rotates on roller bearings with particularly low levels of friction.
The front strut domes are made of highly integrated cast aluminum parts. Compared to sheet steel components made of many individual parts that are welded together, they are eight kilograms (17.6 lb) lighter. This construction allows a very stiff connection between the upper links and the body for the best-possible steering response - optimal conditions for dynamic handling.
In the classic Miller cycle, the reduced cylinder charge is detrimental to torque and power output. These aspects have been neutralized by Audi thanks to the implementation of turbocharging and the two-stage Audi valvelift system (AVS). The four camshafts of the 2.9 TFSI can each be adjusted by 50 degrees crank angle. At higher load and engine speed ranges, AVS closes the inlet valve later. The opening time increases from 130 to 200 degrees crankshaft angle, while at the same time the valve lift increases from 6.0 to 10.0 millimeters (0.2 to 0.4 in). Cylinder charging also increases considerably - the 2.9 TFSI revs up powerfully and delivers an impressive output.
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