At the recent Paris Motor Show car makers vied with each other to show small, economical cars. The tiny Volkswagen Lupo is billed as the world's first three-litre car. It is the first car capable of travelling 100 kilometres on three litres of fuel, or about 90 miles to the gallon. What makes this possible is a new kind of turbo charged direct injection (TDI) diesel engine. The same technology, which has already appeared in a BMW, is also hitting the road in a Mercedes, an Alfa Romeo and many others. Soon it will be common to all manufacturers models as an engine option, Suddenly, diesel is cool.