Classic cars accelerate along the road to sustainability

The UK, perhaps more than any other nation, loves old cars. There are upwards of 1.5 million historic vehicles registered in this country. And far from being a footnote, they support an industry employing more than 100,000 people and worth an estimated £18.3bn.

The long-term survival of this industry may eventually depend on its ability to decarbonise. While there is no imminent threat whatsoever to the availability of petrol, mainstream mobility is slowly turning its back on fossil fuels, as is public opinion. And even though the environmental impact of classic cars is negligible, there’s a genuine desire among owners to embrace sustainability.

A growing number of companies now offer electric conversions for classic cars, but manufacturing the batteries carries its own environmental penalty, and purists will question whether it still delivers an authentic classic car experience. For the small volumes involved, low carbon fuels may hold a better solution.

Until now, this technology has largely been the preserve of big-budget motorsport teams. Prodrive, for instance, set a record number of stage wins on this year’s Dakar Rally using a sustainable blend from Essex-based Coryton Fuels that cuts CO2 emissions by a full 80 per cent. A similar concept could potentially put classic car emissions on the road to net zero, while also addressing some of the other challenges posed by modern fuels.

Chief among these issues is the increasing amount of ethanol found in pump fuels. This can attack perishable materials used in older fuel systems; it traps moisture, which can lead to corrosion issues; and it burns at a slightly leaner air-to-fuel ratio, which can upset carburetion.

With this in mind, Coryton is developing a range of ethanol-free fuels based on sustainable hydrocarbons specifically for the classic market.

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“We take bio hydrocarbons from a range of sources and use those to create a liquid that behaves just like a high-octane pump fuel, but without the ethanol content, and with some very carefully-designed multifunction additive packages,” explains the company’s business development director, David Richardson.

The feedstocks for these second-generation bio hydrocarbons don’t compete with food production. They typically come from agricultural waste, such as starch slurries and the leftover stalks from corn harvesting.

Ironically, the first stage of the process is to ferment these feedstocks to produce ethanol, but this is promptly passed through a two-stage catalytic process to be broken down into its constituent parts, carbon, hydrogen and oxygen. The oxygen is released to the atmosphere, but the carbon and the hydrogen are reformed into a broad range of hydrocarbons, such as aromatics, olefins, naphthenes and isoparaffins.

This is essentially the same ‘tool kit’ of ingredients that fuel companies have traditionally taken from fossil sources. Consequently, the same amount of carbon dioxide is released during combustion. However, the crucial difference here is that it’s only releasing the CO2 that’s been absorbed during the growing of the feedstock. In fact, the final stage of the process is exothermic and can be used to power the plant – theoretically meaning it could be carbon negative.

“The process actually requires very little energy – it’s less than 3 per cent of the greenhouse gas emissions of the fuel – and there are some interesting synergies with other industries,” notes Richardson. “One of the plants that we work with, for instance, is attached to a bakery, so they use the leftover yeast as the feedstock and take waste heat from the ovens. The CO2 that’s released during the fermentation is then captured and used for the drinks industry.”

Hydrocarbon soup

Once these hydrocarbons have been obtained, they can be blended together to produce something that starts to resemble petrol. As with fossil-derived fuels, however, the blend lacks a number of key ingredients at this stage – notably the octane boosters that help to prevent knock. One of the additives used to raise the octane number on modern pump fuel is ethanol, while other components commonly used include MTBE (methyl tert-butyl ether) and ETBE (ethyl tertiary-butyl ether).

It’s theoretically possible to produce MTBE and ETBE from bio sources. At present, however, fossil-derived chemicals are an integral part of that process.

“We want to be open with the industry about what we’re doing and what’s actually achievable with sustainable fuels at the moment,” said Richardson. “The upper end of motorsport is spending millions in the pursuit of 100 per cent fossil-free fuels to be ready for the 2026 season, which is great news as motorsport is often a front runner for the wider automotive industry. But for now 80 per cent is more realistic.”

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There is a caveat here. The fossil-derived components can be written off to achieve a fuel that’s officially classed as fossil-free using a system known as mass balancing. Here, sustainable feedstocks and fossil feedstocks are co-processed in a known ratio. If, for instance, you had 100 litres of fuel taken from a mixed feedstock that was 90 per cent fossil-derived, the first 10 litres out of that tank could still be certified as fossil-free.

Initially this sounds like greenwashing, but it means that the fossil-derived portion can be reserved for non-fuel applications like paint or cosmetics, where its embodied carbon won’t be released into the atmosphere.

“We don’t believe mass balancing is the right thing for low-volume niche applications like classic cars, where you can control the supply quite easily,” comments Richardson. “However, it does make sense for mass market applications, like sustainable aviation. There, you want to be able to combine lots of different feedstocks together in one facility rather than creating a separate infrastructure for each one. Mass balancing allows the sustainable content to be progressively increased as the supply scales up.”

Additives

Other ingredients added to the fuel include oxidation stability improvers, metal deactivators and biocides to prevent the fuel degrading if it’s left for prolonged periods – for instance, if the car is laid up over the winter. Plus, a high-performance detergency package to prevent the build-up of deposits within the engine.

Equally significant is what’s been left out. Although it was withdrawn from mainstream fuels in 2000, some specialist blends continue to use tetraethyl lead to prevent valve seat wear in older engines, but Coryton is very much opposed to the idea.

“We fundamentally believe that adding lead is the wrong thing to do,” said Richardson. “It’s a very unpleasant chemical for the people who are using these fuels, and there are now alternative chemistries that you can use to achieve the same benefits.”

Modern lead substitutes can form unwanted deposits elsewhere in the engine, and they’re not generally compatible with the growing number of more recent classics fitted with catalytic converters.

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As such, Coryton has elected not to include a lead replacement additive in the fuel. There’s no reason why owners couldn’t add a third-party additive when they fill up, but Richardson points out that it’s now common practice for restoration companies to add hardened valve seats when they rebuild engines that could be affected by these issues.

On other projects, Coryton has also blended in e-fuel – a form of gasoline created by combining carbon captured directly from the atmosphere with hydrogen from electrolysis. However, bio hydrocarbons are currently available in greater quantities and production is easier to scale up, so the classic fuel range uses this technology.

For now, the bio components will continue to be combined with some fossil-derived content – the exact specifications won’t be confirmed until the range is launched in the summer - but blends that are up to 80 per cent renewable are understood to have been evaluated during the development.

The costs and volumes involved mean that renewable fuels are likely to be confined to niche applications – at least for the time being. For those designing new vehicles, competing technologies such as battery electric powertrains, fuel cells and hydrogen combustion are arguably a more practical way to reduce tailpipe emissions. But for those looking to preserve and enjoy our motoring heritage, sustainable fuels may well represent the best route to net zero.