When it comes to choosing the right car, it used to be an easy decision; if you were driving lots of miles, or longer overall distances, you drove a diesel-fueled car.

The economic difference that these engines made was simple. The fact that they didn’t perform as well as petrol cars was of little consequence when the cost of getting there was so much lower. However, things haven’t gone well for diesel over the last couple of years and data from the Society of Motor Manufacturers and Traders (SMMT) shows that there has been a steady decline in the sale of new diesel cars, while petrol and “alternative-fueled” car sales have been on the rise.

Is the diesel engine declining in popularity?

While these simple and efficient engines have been hit by scandals and charges of being dirty, is the decline in sales likely to continue? Have has the diesel engine had its day? Is the motoring world now the domain of petrol and, ultimately, hydrogen fuel-celled or electric battery cars?

Power and performance

Diesel engines have been around for well over a hundred years and have long been the engine of choice for many motorists. On paper, they win hands down against their petrol brethren, being more efficient, generally having a higher torque output for the same engine size and needing less servicing overall. In the past, they have been saddled with a slightly unfair label of having lower performance, but the turbo-diesels fitted to modern engines more than match the performance of petrol engines, something which has tipped the balance for buying a diesel fuel engine in recent years.

: Diesel engines have been used to make some popular and powerful cars, such as the Audi A7.

With performance sorted, the main argument against diesel cars dies. As far as any environmental concerns go, tes, diesel might produce larger amounts of nitrogen oxide and sulphur dioxide, but they also produce lower amounts of the carbon dioxide, carbon monoxide and associated hydrocarbons produced by a petrol engine. So, when it comes to affecting the environment, diesel is not as bad as it is assumed to be.

Furthermore, diesel engine manufacturers are making greater efforts to keep emissions down by fitting particulate filters and designing engines to burn more efficiently. Diesel vehicles are now nearly as clean as petrol engines and, with their obvious better fuel economy, why is it that sales are in decline?

Trust issues

The main reason for the current drop in sales is more to do with the notion that diesels aren’t as clean as the manufacturers make out, especially following the recent admission by Volkswagen that software, used on up to eleven million of its vehicles, has been used to defeat emissions checks by detecting when testing was taking place and switching on full emissions control.

The admission in, first uncovered in 2015, had a serious impact on the company’s sales of diesel cars, as well as impacting the sale of diesel cars by other manufacturers. It seemed that the general public has become wary of what results are real and whether official figures can still be believed.

Many people now question the level of diesel emissions.

Now, over a year later, the effects of this deceit are still being felt by the industry, as the drop in sales figures clearly demonstrates, but does this mean we are facing eventual end of diesel cars? While the current trend doesn’t look good - Volkswagen have suspended the sale of future diesel cars in America, for example - it’s not all doom and gloom.

After all, these types of engines are too useful to many motoring sectors, particularly for those undertaking longer road journeys and, of course, Heavy Goods Vehicles, which benefit from the extra torque that a diesel engine produces. It is this last sector in particular that is likely to remain, even when hydrogen fuel cells – whose only emission is pure water – become commonplace for cars, simply because the hydrogen cells can only hold a relatively small amount of energy and would become prohibitively expensive for powering trucks.

It’s also worth mentioning, of course, that many hybrid engines favour a diesel engine, rather than a petrol one, as it is often used for higher speeds and long distance driving.

Alternative fuels

Alongside hydrogen, the same can also be said for electric vehicles, as the current range anxiety of power limits ensure that such powerful engines can’t be produced without being costly. For now, at least, diesel engines represent a viable option that can be manufactured under budget, but it won’t be long until alternative sources are able to compete.

LPG, electric and hybrid vehicles all represent major competitors to traditional petrol and diesel cars.

The other threat to both diesel and petrol engines is Liquid Petroleum Gas (LPG). These vehicles perform as well as petrol cars but are notably lower on emissions, since the fuel source is more highly refined. While LPG isn’t a direct replacement for diesel, that fact that it is cleaner than petrol and more efficient is likely to spell a death knell for dirtier and worse performing diesel cars.

One only has to look to Europe to see more extreme situations. Norway, for example, wants to sell only 100% electric cars by 2025, eliminating petrol, diesel, hybrids and LPGs all together. Germany, likewise, has a similar goal, aiming to only register emissions-free cars by 2030. While the UK has no goals of its own in this manner, it’s safe to say that car manufacturers are likely taking note.

Changing car preferences

This shift in fuel types also becomes more noticeable as cars get smaller. Many manufacturers have already stopped offering a diesel option on their smaller ‘A’ sized cars and it is predicted by many industry commentators that a further stiffening of Euro 6 Emissions rules, coming in 2020, will also push diesel engines out of the small-to-medium sized ‘B’ category, too. With the sales of those cars increasing, the actual market share of diesel will drop overall, in terms of revenue, giving a progressively smaller margin on the remaining larger sized cars (and HGVs) using the fuel, eventually making them unviable to manufacture and support.

In other words, the death of diesels will come with a quiet whimper, rather than a bang.



No one denies that diesel engines will eventually be phased out, but their current worth is too great for them to be ignored, and it is possible they will be with us for a good couple of decades to come, so don’t put off buying that new diesel car just yet.