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An advanced-technology ICE undergoes testing at the University of Wisconsin-Madison’s Engine Research Lab. (University of Wisconsin-Madison Dept. of Mechanical Engineering) 

Fuels to transition the global legacy fleet

The EV bandwagon has obscured potential solutions for decarbonizing the enormous global ICE legacy fleet.

Put the promise of mass vehicle electrification and its myriad challenges aside for a moment, and consider: What if most IC-engine vehicle owners don’t switch to EVs as the industry and regulators hope they will?

And how long will it take to alter the existing global vehicle parc, estimated at more than one billion mostly ICE-powered vehicles, to the extent its greenhouse-gas emissions are insignificant in the crusade to achieve net-zero (and thwart global warming) by 2050?

Some unavoidable truths: Simply ending sales of ICE vehicles, as some OEMs say they will do within the next decade, won’t solve the vehicle-emissions challenge, analysts and powertrain engineers tell SAE Media. In the U.S., the fleet is aging steadily. The average light-duty vehicle on the street today is 12.2 years old, according to forecasters S&P Global, up from 9.6 years in 2002. Engineered to last longer than ever, the roughly 15 million new gasoline-fueled cars and light trucks sold last year are expected to survive for 20 years or more, on average, as they’re cycled through successive owners. Thousands end up in foreign markets, bringing their worn valve guides and non-functioning exhaust aftertreatment with them.

Even optimistic EV-adoption scenarios concede that hundreds of millions of new ICE vehicles, increasingly hybrid-electric, will enter use worldwide by 2035 and beyond. Strategies already are being bandied by policymakers and enviro-NGOs for cleansing the global parc of its enormous piston-engine legacy. In discussion are out-of-reach tailpipe regulations, stiff CO2 taxes, trade-in “clunker” scrapping schemes and combustion-vehicle user fees.

The question isn't whether the transition to EVs can be done; “it's how fast can it be done," the Alliance for Automotive Innovation warned in a release in early April. The automaker trade group was anticipating the proposed EPA vehicle emission regulations for 2027-2032 and a new round of more aggressive fuel economy standards from the NHTSA, both of which are aimed at spurring the shift.

‘Green’ fuels
The EV may seem to be the forgone conclusion for a sustainable, carbon-free mobility future, but it’s not the only, nor necessarily the optimum way forward, argues SAE Fellow Kelly Senecal, co-author (with Felix Leach) of the book Racing Toward Zero: The Untold Story of

Driving Green, published by SAE. There is no ‘silver bullet;’ all propulsion technologies, from ICE and hybrids to BEVs and fuel cell EVs, impact the environment. Given the enormity of the gasoline- and diesel-powered vehicle parc, improving the ICE and its fuels must be a “main route on the road to zero emissions,” the authors assert.

The mobility future, as Senecal and Leach see it, requires a balanced approach. It’s not a matter of choosing between combustion or electrification; it’s a combination of the two. “The future is eclectic,” they maintain. Using the attributes of both technologies, including low-carbon fuels, will enable the industry to achieve net-zero goals as quickly as possible.

David Foster, professor emeritus at the University of Wisconsin-Madison’s Engine Research Center, is one of many engineers who see logic in a muti-mode approach to CO2 reduction. “As much as EVs as the ultimate solution are wonderful, the constraints surrounding their mass adoption – mineral resources, mining activities, charging infrastructure, battery cost – are delaying them,” he said. “And that means legacy vehicles will be around even longer, exacerbating CO2 emissions.

“EVs can be great – but they won’t be great for everything and everyone,” Foster observed. He and others support development and deployment of “green fuels” to help reduce the global legacy fleet’s emissions footprint during the long shift to EVs. Sustainable ‘green fuels’ encompass synthetic and so-called electrofuels (e-fuels) – liquid or gaseous fuels produced with electricity from renewables and/or biomass. Examples include synthetic natural gas (SNG), green methanol and green hydrogen. Green fuels are carbon-neutral when burned, emitting only the amount of CO2 absorbed during their production. So-called ‘drop-in gasoline’ contains constituents produced from biomass sources through a variety of biological, thermal, and chemical processes.

“If we look at making synthetic fuels, using the term in a broad sense, there is a very strong argument for engaging with the energy industry in doing this,” Foster noted, “because the more we can make the synthetic fuels compatible with today’s engines, the faster we can start bringing down the total CO2 emission. The legacy fleet worldwide is huge,” he said, and is vital for millions of vehicle users.

Foster explained that a drop-in fuel solution would be where the fuel feedstock is introduced at the refinery or is sufficiently compatible where it is added as a mixing agent after the refinery. “You’d bring down the carbon intensity of the fuel, and that fuel would be backward-compatible with legacy fleets. Those fleets are going to be around for a long, long time,” he said. eFuels can be used in existing infrastructure, he added.

There is much activity in ‘green’ fuels in Europe and the first production plant was launched by Porsche, Siemens Energy and partners in December 2022 in Chile. Interest is growing in North America, particularly in the commercial vehicle, power generation and marine sectors, and from those seeking a way to progressively mitigate the legacy fleet’s fuel and emission needs. The technology’s potential, Foster said, is “to progressively lower the carbon intensity of fuel. “The goal would be to make a net-zero carbon fuel, one which is a hydrocarbon – like methanol for example, but where you’re getting the carbon out of the atmosphere [the Porsche e-fuel process does this]. If you were to capture that carbon and turn it around and put it into a fuel, there would be no net increase in carbon because of that fuel.”

A hot topic
“E-fuels are a hot topic, offering a way for an industry undergoing enormous change to get some politically useful concessions from regulators,” Al Bedwell, director of global powertrain forecasting at LMC Automotive, commented in a recent blog post. “But the evidence today points to e-fuels in Europe’s light-vehicle sector being backed into a very small corner, or not getting off the ground at all.”

Cost is a major hurdle. Making e-fuels requires renewable electricity to split hydrogen molecules from H2O and combine it with carbon. The process at present scale is expensive and relatively inefficient; according to BloombergNEF, the current wholesale price of synthetic diesel in Europe is up to seven times that of conventional diesel fuel. Bedwell at LMC Automotive estimates retail e-fuel for light-vehicle use will remain roughly four times more expensive than traditional gasoline even as production scale increases. Meanwhile, battery technologies continue to improve, bringing down EV cost.

Multi-solutions advocate Foster remains pragmatic as he views the transition to BEVs. As the challenges of global electrification, economics, human behavior and geopolitical realities become apparent, hundreds of millions of legacy vehicles should be part of the decarbonization discussion and its quest for equitable solutions.

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