25 February 2021


It’s not over for combustion engines yet. As electrification gathers pace, advances in petrol and diesel motors will still contribute to cleaner vehicles.

Electrification of cars and vans has become inevitable, but petrol and diesel engine development has not come to halt. There are still many new technologies and advances to come that will reduce emissions and improve efficiency over the next decade.

Good Foundations

Efficiency targets are moving quickly, and that means there is still plenty of work to be done developing petrol and diesel engines. The EU is mandating a 37.5% reduction in average CO2 emissions for cars and vans between 2021 and 2030, while the UK will set out its post-Brexit framework later this year which could be even stricter. Combustion engines will still be available by that point, so continued improvement is necessary.

For example, Mazda’s new Skyactiv-X petrol engine uses compression-based ignition, similar to a diesel engine but assisted by a spark plug, with the resulting leaner-burn contributing to 30% improved fuel efficiency.

Hyundai Motor Group, meanwhile, recently introduced a system that varies the length of time the exhaust valves stay open. This can reduce the pumping effort under gentle driving for greater efficiency, while still offering performance when needed.  

Nick Molden, founder of research firm Emissions Analytics, says there’s still efficiency to be found: “Contrary to reports, there remain a number of potential technology improvements to the internal combustion, around compression, ignition and thermal management strategies, that could achieve many per cent of efficiency improvement.

Disappearing Technologies

The near-future change could be restricted choice. In the UK, diesel has fallen from a peak market share of 52.9% in 2013, to 16.0% in 2020, and it looks likely to be outsold by plug-in hybrid and electric vehicles this year. While several OEMs have already stopped offering diesel engines in cars, incoming Euro 7 regulations could see diesel moving mostly to commercial vehicles, with more efficient engines.

Light commercial vehicles will remain diesel, probably with bigger engines for emission controls for Euro 7,” comments Michel Forissier, chief engineer at vehicle tech company Valeo. “I don't believe that the small diesel engine will survive to Euro 7 - my guess is everything will be around 2.0-litres, so manufacturers that have [an engine of this size] will probably [continue to] develop.

Manual gearboxes are another likely casualty, and sales of these fell behind automatics for the first time in 2020, according to the Society of Motor Manufacturers and Traders (SMMT). Automatic transmissions allow for a wider spread of ratios tailored to efficiency or performance without requiring the driver to keep changing gear. They are also a foundation for electrification and assisted driving features, both of which will make three-pedal driving increasingly rare over the next decade.

Making More of Mild Hybrids

One in five diesel and one in eight petrol cars registered in the UK last year was a ‘mild hybrid’, according to SMMT data, and larger vehicles are often getting the technology as part of mid-life upgrades. These offer cost-effective efficiency improvements, integrating a small motor/generator and battery, which can either assist the engine under load or provide power to on-board systems while the car is ‘coasting’ or coming to a stop.  

However, it’s also a basis for other technologies. Engineering firm Vitesco Technologies has an electrically heated ‘e-catalyst’ for diesel vehicles which can be brought up to the correct operating temperature more quickly using energy from the 48-volt battery. The company claims it can reduce NOx emissions by 62% in a drive cycle simulating London traffic, and its first application – on a light commercial vehicle – is due next year.

This could also re-shape traditionally mechanical systems. British engineering company Aeristech has developed electric superchargers, and a Volkswagen Golf demonstration vehicle developed with Mahle Powertrain, an e-supercharger system produced 259bhp from 1.2-litre, three-cylinder petrol engine – similar performance to a 2.0-litre unit, but with 25% lower CO2 emissions.

Smaller, Simpler, Cheaper

Increased hybridisation is a double-edged sword; it adds cost and weight which need to be offset elsewhere, but the motor assistance potentially also makes this easier. Dr Mike Bassett, head of research at Mahle Powertrain believes this will steer development towards simplification.

[We see] the trend for downsizing continuing, as a hybrid powertrain’s electric power can support the engine’s performance in high-load events such as pulling away or overtaking,” he explains. “This means engines will become simpler, lighter and cheaper.

Synthetic Fuels

Engine development is only part of the picture. Porsche and Mazda have both recently voiced support for e-fuels, which combine green hydrogen from renewable energy with captured atmospheric CO2 to produce climate-neutral hydrocarbons.

Production is significantly less land-intensive than biofuels and it’s compatible with today’s engines and fuel stations without blending with fossil fuels, so could help decarbonise older and heavier vehicles too.

Want to know more about synthetic fuels? Read our article here.

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