A case for diesel

Notwithstanding the hype surrounding the all-electric vehicle from Tesla and the record sales worldwide of the hybrid car Prius from the stable of Toyota, it appears the good old diesel car is not going to go away. In fact, it is undergoing a noiseless revolution to deliver a fuel economy even the best of hybrids cannot offer now. On fuel economy, it is reported that Prius hybrid is well below 19 other vehicles, all of which are clean diesels.

For most of us, our impression of passenger diesel cars, going back a decade or two ago, is that they were unsuited to comfort, since they were noisy, vibrated heavily and emitted thick exhaust fumes. They were not fit for the classes but may be all right for the masses, that is, for buses and trucks. We also knew, even if we didn’t own a diesel vehicle, that they have trouble starting, particularly in winter.

NEW TECHNOLOGY

But at the same time, engineers knew all along that diesel engines were

per se more efficient than petrol engines. However, in the US, which sets the trend in automobiles, the diesel route was abandoned because gasoline became cheaper in the 80s and the Oldsmobile brand folded up in 1985. General Motors gave up manufacture of the diesel vehicle after it gained notoriety for unreliability and anaemic performance. On the other hand, Europe, particularly Germany, pursued the diesel route unrelentingly and along with Japan is in the forefront of a Diesel Revolution in fuel economy and emissions.

In the 90s, the first significant breakthrough came with the development of the Common Rail Direct Injection System invented by Swiss engineers, nurtured along by Denso of Japan, perfected by Magneti Marelli in Italy and successfully commercialised by Bosch of Germany in the 1990s. The technology of electronic control made it possible to inject a small amount of diesel just before the main injection event, reducing its explosiveness, noise and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold starting and so on.

Reducing the compression ratio, as has been done now, may look marginal, but produces a virtuous cycle of extraordinary benefits.

Lower cylinder pressures mean all other parts of the engine can be lighter. Even the vehicle’s brakes, suspension components and bodywork need to be less rugged. All these weight savings translate into greater efficiency. According to Ricardo, an engineering consultancy, every 10 per cent reduction in a family car’s weight boosts its fuel economy by more than 4 per cent.

The lower compression ratio seems to do wonders for controlling emissions by completely burning the fuel .

The new range of diesel cars pose a challenge to the popularity of haute couture hybrids.

(The author is former Member, Ordnance Factories Board)