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What does the future hold for diesel engines?

For years the diesel engine has lived in the shadow of its cleaner-cut petrol cousin. While diesel boasts the more fuel efficient engine, it has had to bear the image of being a dirtier, noisier and higher polluting technology. However, with gradual development, diesel engines continue to make their mark on the passenger car market.

diesel engines

Fuel efficiency and technological development

With a higher energy density and lower refining requirements than petrol fuel, diesel engines are more efficient by 15%-20%; allowing motorists to generate significant cost savings over time.

Although diesel engines are typically £1000-£2000 more expensive than petrol engines, improved fuel efficiency provides significant payback for regular, long-distance motorists (upwards of approximately 11,000 miles a year). Asian manufacturers Honda and Hyundai are also seeing value in smaller diesel engines, suggesting there is a market for lower level use.

While petrol models are traditionally faster, smoother and quieter, Turbocharged Direct Injection (TDI) technology has allowed diesel cars to become quicker; further design advances have also reduced the trademark engine clatter. Many diesel cars are now indistinguishable from their petrol equivalents.


Following the recent economic crash, demand for diesel cars has been rising steadily; in July 2010, diesel cars took an all-time high of 50.6% of market share of new car sales in the UK. Demand for diesel fuel also appears to be on track to replace petrol as the most popular fuel; petrol sales since 2007 have fallen from 22.9bn litres to 17.4bn litres, while diesel has risen from 14.8bn to 16.7bn. Cost benefits from taxes and fuel efficiency means that businesses and fleet firms now consider diesel their preferred technology.

Environmental issues

The popularity of diesel cars has risen so far in London that the government recently amended its  Congestion Charge exemptions to discourage the purchase of such vehicles.

While this might be a cynical attempt to generate further revenue, it does raise questions about the long term environmental benefits of these engines. Diesel engines traditionally emit larger levels of nitrogen compounds (NOx) than petrol engines, leading to pollution like acid rain and smog. However, diesel also emits much lower levels of carbon dioxide; a huge advantage to a world hoping to reduce long term carbon emissions.

Although dirty diesel engines were difficult for consumers to digest in the 1980s, the addition of ultra-low sulphur diesel (ULSD), CRT particulate filters and catalytic converters now make their environmental impact lower than ever.

Long term technological shifts

The long term future of diesel technology will ultimately depend on continued improvements in electric technology. Electrics like the Nissan Leaf, however, are unlikely to provide long distance solutions just yet, requiring charging at regular intervals.

Diesel engines can now work on biodiesel fuel, synthesised from biological sources of energy, such as plants. Europe is currently the world’s largest producer of biodiesel, with the majority of fuel stations now set up to offer this type of fuel. With this in mind, it is important we take into consideration the environmental impact of obtaining fuel from food sources as the long term viability surrounding such processes are not necessarily secure.

The middle-term technological solution will continue to be hybrid vehicles, which can utilise electric and conventional fuel power. Hybrid technology currently favours petrol engines, although the world’s first diesel hybrid, the Volvo V-60, was recently released to rave reviews. The V-60’s price, at £40,000 inclusive of government subsidies, is currently prohibitive, although this is also in keeping with the majority of petrol hybrids.

As the technology progresses however, diesel hybrids will most likely provide the most fuel efficient alternative; combining the more fuel-efficient diesel combustion engine, for longer distance driving, with the ultra-low carbon electric alternative, for shorter journeys.

Fuel Price fluctuations

While diesel appears to be growing in popularity, fluctuations in prices continue to create an uncertain future. You only have to look at the American car market to see how pivotal taxes and relative prices are in determining the overall viability of the technology.

Fuel will continue to be a prime source of revenue generation for the government, and the relative popularity of petrol or diesel will ultimately depend on the respective rates of duty:

“Back in the ‘80s and ‘90s the duty, and price, of diesel was a lot lower than petrol. As popularity increased because of the lower price, the government saw fit to increase diesel duty on environmental grounds, with many arguing that this was merely a cynical attempt to build revenues. Whichever way you look at it, price uncertainty makes it very difficult to predict the future of diesel fuel,” said Robert Potts of RPM Fuels and Tanks.

China’s continued industrial boom has continued to push up the price of diesel, and other global economic shocks continue to play their part; forecourts often hike up the cost of diesel in order to support other petrol prices. While the economy has cooled for the moment, as growth sets in, demand for diesel will push its price up further.

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