The old perception that diesel engines are noisier, slower and dirtier than their petrol equivalents no longer holds true. The black pump is no longer a 'social pariah' and diesels are no longer slow and unrefined. Are we entering the age of the diesel? Arnold Clark looks at the facts.
Development of the pre-ignition systems, whereby a tiny quantity of fuel is injected into the chamber and ignited before the primary combustion takes place, minimises the harsh rattle or knocking sound traditionally associated with diesel engines.
According to BMW, the diesel engine transforms the chemical energy contained in diesel into mechanical energy. While petrol engines compress a mixture of air and fuel and ignite it with a sparkplug (externally-supplied ignition), diesel engines first compress pure air, which causes it to heat up. The fuel is later injected directly into the combustion chamber and ignites itself (self ignition). The direct injection with common rail technology enables the precise control of the ignition process (unlike in older diesel engines), an even increase in pressure and the targeted burning of remaining soot particles by post injections. This minimises burning noises, makes running smoother and reduces emissions.
According to BMW, the small letter ‘d’ in the BMW model names "stands for a difference with big results: every BMW diesel engine – whether four, six or eight-cylinder – delivers refined power and superb fuel efficiency".
The petrol-powered BMW 530i and the diesel 530d cost a similar amount. The 530i has more power (258bhp vs 218bhp) but the diesel has a huge torque advantage (369lb ft vs 221 lb ft). In real world driving conditions, it’s the 530d that’s the faster and more engaging. On top of this, the 530d achieves an average of 40.9mpg, 8.8mpg more than the 530i. It appears that, in this case, the diesel 5-series is not just more enjoyable to drive but it’s also cheaper to run.
German BMW performance manufacturer Alpina has released the new D3 Bi-Turbo – a tuned version of the BMW 3 series. The car hits 62 mph (100 km/h) in 4.6 seconds, and has an impressive top speed of 173 mph (278 km/h) top. Alpina claims that this makes it the fastest diesel production car in the world.
Some commentators have suggested that we’re entering the age of the diesel, although much of the technology that’s being used to such good effect in modern turbodiesels is also beginning to filter into petrol engines. The Volkswagen group, for example, already offers a range of direct injection petrol engines that offer improved fuel economy and lower exhaust emissions. Audi’s Le Mans winning R8 was powered by a direct injection petrol engine, and a more affordable derivative is employed to fine effect in the Volkswagen Golf GTi.
Diesels are gaining momentum though, whichever way you look at it. Even in the traditionally diesel-hostile USA, diesel vehicle sales are due to explode in the next few years, hitting as much as 10% of new vehicle sales by 2018, according to a USA Today expert panel.
For many, the point is not that diesel is about to replace petrol but that, for the first time, we have a genuine choice – which can only be a good thing.
Where do you stand in the petrol vs. diesel debate? Are we living in the diesel renaissance? Share your comments below.