- Is it time to say goodbye to the black pump?

Does diesel have a future in our cars?

One minute it's the answer to our prayers, the next it's the root cause of urban pollution. What happens next?

7w ago

Like it or not, diesel in cars is seemingly on an unstoppable freefall towards its death - even ignoring the 2030 ban on new ICE cars. It's almost astounding at the rate it's happened, and I'm sure we can all remember when diesel was pushed heavily as the greener option. After all, that was only ten or so years ago.

And yet we now find ourselves at a place where diesel sales are projected to be overtaken by battery electric vehicles in the very near future. We find ourselves at a place where sales for diesel vehicles in the UK were 38% down in October 2020 compared to October 2019. So, what happened, and where does the short-term future lie?

The fuel that could do no wrong

It's a fact that diesel is physically more energy-dense and emits less carbon dioxide joule-for-joule compared to petrol. Rewind a couple of decades ago, and carbon dioxide was the pollution buzzword. It's a greenhouse gas that is a direct contributor to global warming, so of course, nobody was or still is wrong for wanting to cut down on CO2 emissions.

At the time, then, diesel seemed like the answer. Why drive a petrol car that emitted 180g/km of CO2 when you could drive an oil-burner emitting 130g? New Labour probably had the same thought, and in 2001 the then Chancellor Gordon Brown introduced a tiered vehicle excise duty (VED or road tax) system that we're still familiar with today. Quite simply, it was cheaper to tax cars that emitted less CO2 - which of course naturally favoured diesels.

"I wouldn't say that a CO2-based VED regime was designed to specifically incentivise the uptake of diesel per se," said Dr Johnathan Kershaw, a specialist in low-carbon automobility and self-confessed tree-hugging petrolhead. "I'd say it was designed to not-shut-out diesel vehicles at a time when carbon emissions were regarded as public enemy number one."

Some TDI engines such as the 1.9PD achieved legendary status as popularity grew in the 2000s

Some TDI engines such as the 1.9PD achieved legendary status as popularity grew in the 2000s

Regardless of motive, it worked: sales of diesel models increased consistently throughout the 2000s. Where just one-in-seven vehicles were diesel in 2000, sales were split more or less 50:50 between petrol and diesel in the first half of the 2010s. The incentive had worked, average CO2 emissions had fallen from vehicles - the world was healing, right?

Not quite.

Diesel's dirty secret

As you probably know, CO2 isn't the only thing that comes out of your car's exhaust. We also have major contributors such as nitrogen oxides, carbon particulates and hydrocarbons to deal with - diesel engines are major foul players with these emissions.

Compared to the equivalent petrol engine, diesel engines emit ten times as much nitrogen oxides, and almost uncountable times more particulate matter. Both of these can seriously play havoc on the respiratory system, especially in built-up urban areas where there are thousands upon thousands of diesel vehicles polluting away to air we breathe. "It's a pity that scant regard was given to other emissions associated with diesels," said Dr Kershaw.

Nobody wants that, of course, so diesel engines are heavily regulated with their emissions. Under the current Euro 6 rulebook, a diesel car cannot emit more than 0.08g/km of nitrogen oxides, 0.5g/km of carbon monoxide and a tiny 0.005g/km of particulate matter.

AdBlue is one way modern diesels keep emissions down

AdBlue is one way modern diesels keep emissions down

These regs ensure the damage caused by diesel cars is kept as low as technology allows, so long as everybody complies. But no company would be stupid enough to risk their massive reputations just to pollute a bit more...

Volkswagen: "Allow me to introduce myself."

Ah, yeah. Right. We can't forget 'dieselgate': the catastrophic embarrassment for VW in 2015 that quite literally changed the world's perception of the oily fuel.

It was all over the news, of course, but for the sake of a quick recap: VW fitted certain diesel models with 'defeat devices' that could tell when the car was under testing conditions and adjusted the engine mapping to comply with the tough regulations. As soon as the same car was out in the real world, the device would revert to 'normal' mapping and the emissions would be up to forty times above the limit. Yes, forty.

VW paid up $25 billion in fines, and the public focus moved on. The public's buying habits, however, did not move on. Not by coincidence, since 2015 sales of diesel cars have been falling rapidly in the UK. Market share, according to Statista, sat at 47% for diesel cars in 2016, but the preliminary numbers for 2020 put it at just 25%. That's half of the market share gone in just four years.

Diesel right here, right now

Much like a celebrity who's just been outed for tax evasion, diesel's reputation is tainted. "Certainly, the dieselgate scandal brought concern over diesel's other emissions to the fore," Dr Kershaw added. Even subliminally, the connotation for the once environmentally-friendly fuel is one that is dirty and dangerous.

Manufacturers have responded to the shift in demand by seriously reducing the number of diesel models on offer. In a recent analysis by Autocar, Volvo offered 21 diesel models in 2015 but can sell you just 8 today. It's not just them, either: in the same timeframe, Vauxhall has gone from 26 to 10, Mini has gone from 13 to 2, and Renault has gone from 10 to just one model, to name a few.

Not only is diesel tainted, but it's also now facing some serious competition in the form of alternative fuels. The main original pull of a diesel car was its low running cost - but modern hybrids and even some pure electric vehicles now offer similar or better running costs with a very little initial price premium. The result? EVs now have 10% of the market share, and it's a number that's rapidly increasing.

EVs are rapidly eroding diesel sales (y-axis: % share of UK sales)

EVs are rapidly eroding diesel sales (y-axis: % share of UK sales)

Where now?

Dr Kershaw doesn't see much in the way of a future of ICE cars in general, let alone diesel ones: "I personally wouldn’t advocate anyone buying a new diesel car today, if they don’t need to. The gap in emissions/fuel consumption between conventional petrol and diesel cars isn’t as marked as it once was, and the VED regime since 2017 hardly incentivises low or even zero-CO2 emissions as it once did. The combustion characteristics of diesel mean that the nasties emitted compared to petrol are still there, however, and will require ever more complex and expensive technology to mitigate them, and to meet ever more stringent emission regulations. It may even be that ICE, especially diesel ICE, has gone as far it can, technologically and economically."

In normal cars at least, it's tough to conclude that diesel cars have any real place in the next 5-10 years. Sure, they still offer superior motorway stamina today, but battery technology is rapidly evolving to match or even exceed traditional dinosaur juice range within the next decade or so. And with manufacturers across the world slowly reducing their diesel portfolio, we may truly have to say goodbye to the fuel that some love to hate, and some love to love in our everyday cars.

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Comments (12)

  • My Mercedes diesel (OM654) produces less NOx emissions than the vast majority of petrols out there having the latest diesel tech. Whilst most other manufacturers are extending the lives of their Diesel engines (which were originally designed 5-10+ years with mild improvements) these are not the clean ones and are soiling the reputation of the good ones.

    We need to differentiated the good from the bad and not vilify the breed.

      1 month ago
    • I agree. I have a 6 year old Merc with a 2.2L diesel. It’s Euro 6 compliant and my tax is a measly £30 per year. 0-60 in a smidge under 8s and 130mph top speed. Space for 5 people and a dog. I think it still makes sense.

        1 month ago
  • Thank Volkswagen

      1 month ago
  • I dunno... I know Audi has recently developed a new particle filter capable of capturnig 91% of the pollutant particles, so perhaps yes.

      1 month ago
  • Diesel generates more pollution than petrol, but diesel engine is more efficient and generates more torque than petrol engine. So it's complicated.

    And that's also why diesel engines are commonly used on buses, trucks and trains.

      1 month ago
  • Its politicaly dead

      1 month ago