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Clean diesel: A viable driver for the future of motoring

Motors | Published:

Comment by Peter Tabb

(27349709)

EVERY reader will already be familiar with the diktat that advises that from 2035 (or possibly, according to some sources, three years sooner) vehicles propelled by the internal combustion engine will no longer be able to be sold.

They will be replaced by electrically propelled vehicles relying on rechargeable batteries to do what today is done by petrol-, diesel- or liquefied-petroleum-gas-fuelled internal combustion engines.

At the dawn of motoring as we know it, electrical power vied with oil-derived fuels and even steam as the means of replacing the horse as a prime mover. Indeed, a curiously rocket-like car, La Jamais Contente, created and driven by one Camille Jenatzy, was, in 1899, the first vehicle to exceed 100kph. However, then as now, it was the battery required that was that concept’s weakness and ultimately internal combustion triumphed in the shape of the petrol and diesel engine. The former invented in 1876 by Nikolaus Otto and the latter by Rudolf Diesel in 1892.

Since then the two fossil fuels have competed with each other in popularity. Petrol relies on a spark to make it burn, whereas diesel relies on compression to cause it to explode. The energy released has the same effect, pushing a piston down to turn a crank.

Petrol engines can be light with low compression, but there is a finite size to the cylinder in which the piston moves, whereas there is almost no limit on the size of the cylinder for a diesel engine. But in order to cope with the continuous explosions, and the compression needed to cause the explosions in the first place, diesel engines are heavy. This is largely why diesel engines are used by commercial vehicles, railway trains and ships, where power rather than performance is the main requirement and their sturdy construction means that diesels tend to last much longer than their petrol counterparts.

What has all this foregoing, you are asking, got to do with 2035?

There was a time when for everyday motor vehicles, diesel was perceived to be the better option – it was more economical to use and with turbo-charging performance was not dissimilar to petrol engines. Governments embraced diesel and gave incentives to motorists to adopt diesel fuel, which required much less refinement than petrol and gave many more miles to the gallon. It had always been recognised that diesel exhaust was sootier than the fumes from petrol, but the impact on the environment was either not understood or largely ignored.

Diesel engines took a huge hit when one manufacturer was exposed for installing software on its vehicles designed to cheat emissions tests and since then much greater attention has been given to creating a genuinely much cleaner diesel.

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Due to advances in technology, more vehicles are switching to clean-diesel engines.

So what is clean diesel and why is this so important?

Today, the diesel engine in a car produces 99% less nitrous oxide emissions and 98% less soot than the diesel engines of 20 years ago. Their fuel economy and performance are also much better. The technology that makes all the difference is common rail fuel injection at very high pressures and frequencies. Clean diesels typically use piezo injectors that can cycle as many as five to eight times during injection to allow very precise control over the combustion to reduce noise and improve efficiency. Clean diesels are designed to run on ultra-low sulphur fuel and bio-fuels, which are increasingly becoming available. Constant research is undertaken to find higher blends of bio-diesel fuel.

Current technology has also introduced diesel exhaust after-treatment to clean up soot and other pollutants, with particular particulates being trapped in special filters.

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Traditionally, diesel engines have always been more fuel-efficient than their petrol counterparts due to their ability to run on very lean fuel mixtures and high compression ratios which ensure that there is no unused fuel to mingle with the exhaust, a common condition with many petrol engines as they wear. Diesel also has more heat energy per litre than petrol.

In many respects the newest diesel engines are actually cleaner than petrol engines and their visible emissions less dangerous than the invisible ones sneaking out of petrol engines.

There are still significant advantages in choosing a diesel. Fuel costs, mile for mile, are around 30 per cent lower than for petrol engines. Diesel fuel contains about 12% more energy per litre than ordinary petrol. A diesel can also run twice as long as a petrol engine before demanding serious service. Because diesels are more efficient, they do in fact emit less carbon dioxide than petrol engines.

In many minds diesel vehicles have fallen out of favour and, along with petrol and hybrids, they are threatened with being unavailable after 2035.

In the short term the modern clean diesel makes a lot of sense and, despite an occasionally tarnished reputation, is the more friendly option for the environment.

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