We fit our TDI engines with exhaust turbochargers featuring variable turbine geometry. This not only boosts power output and torque (pulling power), but also saves energy and reduces harmful emissions. The turbocharger compresses the air required for combustion, letting the engine draw in more air while its displacement and revs stay the same. A turbocharger is powered by the energy in the exhaust gas. It has two connected turbines. The turbine wheel in the exhaust stream drives the intake compressor, which sucks in air through the intake system. The compressed air is cooled by a charge air cooler before entering the combustion chamber. Because cool air is denser than hot air, more oxygen can be fed into the cylinder boosting the efficiency of the combustion process.

Article source: www.volkswagen.co.uk