Thus, the claimed benefits are similar to those of PSA's high pressure direct injection 2.0-litre engines developed to replace 1.9-litre and 2.1-litre turbodiesels in new Citroens and Peugeots, and also hailed as the way ahead for diesel. The technologies are similar, too. In brief, VW's PD achieves highly efficient combustion and 210lb-ft of torque at 1,900rpm by pumping the fuel to a pressure of 2,050 bar and then controlling its injection into the cylinders. HDI pumps up the pressure to 1,350 bar - less impressive than the German system but, nonetheless, much higher than in an 'old' turbodiesel - and holds it in a 'common rail' reservoir before sending it to computer-controlled injectors.
PD gets its UK launch in September, HDI has been available since the end of 1998, and there are common rail systems in BMWs, Rovers, Fiats, Alfa Romeos and Mercedes-Benz vehicles. General Motors and Ford are remaining tight-lipped about plans for new generation engines, but even though diesel sales continue to slide in the UK they are strong elsewhere in Europe, and it is clear that high pressure combustion is concentrating some of the highest minds in the motor industry.
Far from being the last words in oil-burning systems, common rail and pumpe duze are part of a new wave designed to bring diesel alongside petrol in terms of refinement and noise, and streets ahead of petrol in economy, torque and environmental cleanliness. The HDI is good, PD looks even better, but there's much more to come, including particulates filters.