History (TDI)

The first Volkswagen Group TDI engine was the Audi-developed 2.5 litre R5 TDI – an inline five-cylinder engine (R5), introduced in the Audi 100 in 1989 – and this exact variant is still in use today, in Volkswagen Marine applications. The TDI arrangement has been enhanced through various stages of evolution – by improving the efficiency of the turbocharger, increasing the pressure at which fuel can be injected, and more precisely timing when the injection of fuel takes place. There have been a few major 'generations', starting with what are known as "VE", and "VP" (German: VerteilerPumpe) engines, which use a distributor-type injection pump. In 2000, the Pumpe Düse (PD, variously translated "pump nozzle", "unit injector", "pump injector") TDI engine^[1] began to appear in Europe, eventually coming to North America a few years later.
The Pumpe Düse design was a reaction to the development of high-pressure common rail fuel injection systems by competitors - an attempt by Volkswagen Group to create an in-house technology of comparable performance that would not require any royalties to be paid.^{[citation needed]} While Pumpe Düse engines had a significantly higher injection pressure than older engines, they are slightly less refined when compared to the very latest common rail,^{[citation needed]} and with the original solenoid-operated unit injectors, weren't able to control injection timing as precisely (a major factor in improving emissions).^{[citation needed]} Some current PD TDI engines now utilise piezoelectric unit injectors, allowing far greater control of injection timing and fuel delivery. Furthermore, appearing in 2009 model year, Audi and Volkswagen TDI engines are starting to use the common rail (CR) technique, again with piezoelectric injectors, and CR TDI engines are starting to appear in models from other marques of the Group.^[1]