Pump-nozzle fuel injection

A factor of key importance on a diesel engine is the fuel injection pressure. High pressure can achieve an optimal spray pattern in the combustion chamber, so that ignition takes place more rapidly and smoothly. More efficient combustion means higher power output, lower fuel consumption and therefore reduced exhaust emissions. The pump-nozzle injection system had its Audi premiere in 1999, when the 1.4 TDI began to be supplied with fuel at a maximum pressure of 2,050 bar. Each of the engine’s three cylinders was provided with a separate unit in which the pump and nozzle were integrated. A separate cam on the camshaft actuated a roller cam follower that moved the piston in the pump. The pressure built up in this way inside the pump was boosted hydraulically to more than 2,000 bar before the fuel reached the injector nozzle. The actual injection of fuel into the combustion chamber was controlled by a solenoid valve, with pre-injection made possible by a complex additional control system. Audi used the pump-nozzle injection principle on its three- and four-cylinder engines until it was discontinued in 2008