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The Diesel engine is as old as any form of internal combustion engine yet is still little understood.

More and more cars are sold which use the more efficient - and more environmentally acceptable - alternative fuel.

In the last few years, diesel has become much more attractive as an engine option. The increasing sophistication and cost effectiveness of such engines has almost entirely removed the commonly perceived disadvantages - smell, vibration, noise and lack of power.

Notable among the increasingly desirable plus points of diesels are far better fuel consumption, typically 25%-30% better than an equivalent petrol engine, and more environmental acceptability as diesels run cleaner than petrol engines.

The latest generation of small capacity diesels and turbo diesels are simply more reliable than petrol engines being capable of very high mileages with minimal repairs.

All of these factors explain the rapid increase in sales of diesel powered cars in the U.K. in the last few years, now to nearly 15 per cent of total car sales, a figure which is still half of that for most European countries where the fuel cost differential has long been even more favourable to diesels.

So, how do diesel engines work?

Diesel is a less explosive fuel than petrol and only combusts when subjected to great pressure. A diesel engine's additional weight is, therefore, a function of the need to contain much higher operating pressures than a petrol engine.

A fine spray of diesel is injected directly into the cylinder head which is already filled with highly pressurised, and thereby, very hot, air and the fuel, entering this high pressure area, spontaneously combusts.

The great environmental benefit of diesel is that the fuel combusts far more cleanly than petrol by mixing it with a greater quantity of air than is actually needed so ensuring that all of the fuel is burnt.

As to those perceived disadvantages:
  • Yes, the diesel engine is a bit noisier on start up or when idling but this is improving steadily.
  • Smellier?  Not any more.
  • More vibration? Not in the latest generation of such engines
  • Less powerful?  The latest turbo diesel engines can produce 95% - or more - of the power of an equivalent petrol engine without sacrificing any of the other diesel benefits.

Article © Graham Benge

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