NECKARSULM, Germany - Audi will launch its new direct-injection V-6 turbodiesel on the aluminum-bodied A8 later this month.
Audi's is the first direct-injection turbodiesel with a V-6 layout and four valves per cylinder. The 2.5-liter unit delivers 150ps.
The engine will appear in the new A6 this fall and will probably be offered on the smaller A4 series and the Volkswagen Passat next year.
The engine has a similar configuration to Audi's existing 2.6-liter gasoline engine. The design is compact. The variable-geometry turbocharger and the injection pump are housed within the vee. This makes the engine workable in a range of mid-size and large models, according to Audi engineers.
The four-valve cylinder head layout allows optimum swirl and distribution of fuel in the combustion chambers, said Audi. This allows high power output and torque, and cleaner emissions.
At 150ps the Audi V-6 is one of the most powerful passenger car diesels. Only the 177ps, 3.0-liter Mercedes straight six is more powerful. The maximum torque of 310Nm is achieved at a low 1,500rpm and is maintained through 3,200rpm.
The engine block is cast iron. The induction-hardened crankshaft is balanced by a counter-rotating balance shaft in the oil pan to make the engine run smoother.
To reduce noise the V-6 has dual-rate springs in the injector nozzles. The softer spring allows a small amount of fuel into the combustion chamber before the harder spring allows the remaining fuel to enter.
Audi's V-6 uses the new Bosch VP44 radial piston distributor pump.
The engine has charge-air intercooling, and uses electronics to control several functions. Electronics control not only the fuel injection, but also the turbocharger, boost pressure and exhaust gas recirculation rate.