Will synthetic fuels save the internal combustion engine?

Tristan Young

14 Jan 2022

Every car could become carbon neutral without going electric if we invested in fully-renewable synthetic fuels. So why aren’t we investing in this new technology?

We need a solution to the climate crisis and for cars and vans the plan is to go electric. Once the charging infrastructure and vehicles are up to the job this will work for new cars, but what about the existing parc of cars and vans, which in the UK stands at more than 35 million? What do we do about them?

One solution is to is to create carbon neutral synthetic fuels that can directly replace petrol and diesel. Doing this, would provide a way of decarbonising the existing car parc.

Take a step back and it could also mean we don’t need to go all-electric for new cars.

“Low-carbon and completely carbon-neutral fuels can help the existing global vehicle fleet play a role in achieving climate targets,” according to a Bosch spokesman. “Alternative fuels can complement electromobility where purely battery-electric powertrain solutions face economic or physical challenges, such as in heavy trucks.”


Science and technology is already capable of combining hydrogen and carbon to form a liquid hydrocarbon fuel that can be used in a conventional internal combustion engine. As long ago as 2015, Audi developed and produced synthetic diesel. Synthetic fuel can be produced by using green electricity, produced from a renewable source such as wind or the sun, to split water to produce the hydrogen this is then combined with CO2 captured atmosphere to make a hydrocarbon liquid fuel.

It's main downside, currently, is that because this process has yet to be scaled up, it’s yet to become cost effective; something that it shares with electric cars which are still more expensive to produce than ICE vehicles.


Fully synthetic fuels, as their name suggests, are fully man-made and shouldn’t be confused with biofuels. Biofuels are effectively distilled from organic bi-products of other industries and are then mixed with conventional petrol or diesel.

Synthetic fuels, sometimes called e-fuels, are 100% renewable if produced correctly and based on either methanol or ethanol, according to Professor James Turner from the Clean Combustion Research Center at the King Abdullah University in Saudi Arabia.

Turner points out that methanol, which is relatively energy dense, is liquid at room temperature, making it easy to store and transport. Methanol is poisonous, but no more so than petrol, he highlights.

Methanol, produced in other ways, “may be the world's most commonly traded chemical, because it's the basis for a lot of plastic”, says Turner.

Carbon neutral

So if synthesised, carbon-neutral, methanol or ethanol can be turned into a fuel that can be run in any petrol (or diesel) engine, why are car makers switching to electric cars rather than pushing for the use of e-fuels?

It’s all because taxation in road transport is all about tailpipe CO2 emissions, according to Turner, and synthetic fuels still produce CO2, even if that CO2 comes from the atmosphere, rather than non-renewable oil. As a result, there’s no incentive to develop, produce or sell e-fuels.

“As long as all your energy inputs are renewable, you've got an energy carrier [liquid fuel] that has no carbon footprint,” says Turner.

While there’s no incentive to produce these fuels for road transport, “we're going to have to do this sort of thing for aviation”, he adds.

“You'll have to make e-kerosene. And it's going to have to be carbon neutral, because we're not going to fly across the Atlantic on a battery powered plane. That's just not going to happen. Even Elon Musk doesn't say that. So we've got to do something to get the energy density up for the fuel in planes.

“The other thing, and this is to bring it back to something that's probably a bit more relevant to road car use, is that you cannot decarbonise the legacy fleet if you don't take the carbon out of the fuel they use. And that is just something that's not thought about. When governments talk about being net carbon neutral by 2050, they mean from that point going forward. They know there's going to be a load of stuff that still requires fossil fuels, but they're not being held to account about that. So the legacy fleet is a big issue.”

Taxing fuel

Taxation may be stopping e-fuels reaching road transport, but there’s also another, linked, hurdle.

“The stumbling block is scaling up, related to cost. But you could put a taxation regime in place, that would help,” claims Turner.

“My suggestion has always been that we need to tax units of energy [rather than volume of liquid fuel]. And then, we need to apply a multiplier, that's based on the fossil carbon impact of supplying that unit of energy. So for gasoline and diesel, they'd be the same. They'd all be put together. But if you could make a fully renewable fuel, you would have a lower carbon impact. You could say that the tax implication of a validated, zero-carbon-impact fuel, should be zero to begin with, so you don't pay any tax on it.”

In this way, there would be enough profit margin in e-fuels to cover the costs of scaling up production.

“But the important thing for the Exchequer is, you've got a mechanism for keeping the tax take the same, while favouring the fully renewable fuels. And if you had a fuel that was identical, in terms of how it performed in the engine, and it was 20% cheaper, because it was renewable, everyone would want it. You'd all rush over in that direction,” says Turner.

Turner believes it won’t be until either the taxation system changes that e-fuels will take off or it may trickle-down to road transport after it’s scaled up for aviation and possibly shipping.

He also admits that even if the cost of synthetic fuels can be brought down as production is scaled up, there are still issues with its efficiency in combustion engined cars compared to electric cars. Currently, if you start with wind-generated electricity, synthetic fuels are used in cars they’re around six times less efficient at powering a combustion engine car than driving an EV.

Until this efficiency and the cost of e-fuels is solved, it looks like EVs are here for the future.

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Tristan Young

14 Jan 2022