Keeping Combustion in the Conversation
The world needs internal-combustion engines to stick around – here’s how.
The signals are everywhere that the days are numbered for internal-combustion engines (ICE) for passenger vehicles. Volkswagen CEO Ralph Brandsteatter told a German magazine in early 2021 that VW would follow its closely linked Audi brand in ceasing development of any new IC powerplants. A report from South Korea in late 2021 said the massive Hyundai Group had eliminated its engine-development unit. Mercedes-Benz, perhaps as historically linked to ICE as any automaker, stated in July 2021 that all newly launched vehicle architectures would be electric-only starting in 2025.
Although those pronouncements seem to have a Draconian finality, nearly all reasonable industry experts note the end of the ICE for light vehicles will be a protracted sunsetting involving multiple market-dependent, regulation-dependent and regional variables. The ICE will be powering vehicles long after these ostensible deadlines – but it’s going to need new technology and new thinking to carry it through the industry’s propulsion transition.
Dean Tomazic, COO at vehicle and propulsion development R&D firm FEV North America, sees global emissions, fuel economy regulations and regional market preferences as the chief shaping agents for the ICE in the next decade or more. “In Europe, we are talking about Euro 7 [emissions regulations] now – which is still not 100-percent defined – and we’re talking about [in California] LEV IV. We're looking at new fuel economy legislation. We are looking at environmental groups. We look at the politicians and, of course, city mandates in some parts of the world that say, ‘We don't want diesel engines anymore,’ or ‘Starting in year X, we don't want any combustion engines anymore.’
“With that in mind, the different powertrain types we will be looking at in the future – and I think it’s true for the entire world – start at micro-hybrids, up to mild hybrids, full hybrids and PHEVs,” Tomazic said, citing the four main categories where combustion engines will continue. He sees ICEs playing a major role for years to come, in two configurations: conventional high-tech engines, including micro-hybrid and mild hybrids, and what he defines as ‘dedicated’ hybrid engines, which are more applicable to full-hybrid applications, as well as PHEVs.
Tomazic and others note ICE isn’t destined for the graveyard nearly as soon as the end-of-development announcements may suggest. But with the onrush of electrification and the seemingly certain prioritization of EVs in the propulsion-investment landscape, R&D for the ICE seems destined to follow a dual-path blueprint: one of emissions improvements to keep pace with tightening global regulations and a parallel course of evolution imparted by mostly known and proven technologies to conventional engine architectures.
The auto industry’s maturation has winnowed the variety of production-vehicle ICE propulsion options to gasoline or diesel, inline or vee four-stroke reciprocating engines. “Exotic” architectures that even recently have been in production or were being considered – the rotary (Wankel) and opposed-piston layouts, for example – have lost momentum. Most propulsion experts expect that tightening R&D resources will virtually guarantee the status quo.
“I think by 2030, everybody's talking about maybe 50 percent market share for EV but that clearly leaves 50 percent of the vehicle population still with some kind of engine in it – that's a very significant portion,” said Mick Winship, CTO at AVL North America. “We won't see a significant ‘stack’ change in technology, I believe. You’ll see technologies iterate from where they are today.”
Added Thomas Howell, AVL’s Conventional Powertrains Segment Lead, “I think the fundamental base modern engines are probably capable of achieving what needs to be done for the future. There will be development required to achieve the legislative targets.” He added that some of the older platforms, which are steadily being retired, will have to be retired because they will not achieve the targets.”
That’s not to say alternative ideas are no longer percolating. There have been on-again, off-again reports that Mazda, the dogged proponent of the Wankel, would use the rotary as a range extender for its new but battery-capacity-challenged MX-30 EV. As this story was written, a U.S.-based Mazda official could not confirm that the company would be taking the leap to once again fit the rotary engine in a series-production vehicle (at least for the U.S. market). A similar scenario played out with Mazda’s innovative Skyactiv-X gasoline compression-ignition I-4, which was released in Europe but has yet to appear in any U.S.-specification Mazda.
The same is true of various opposed-piston engine designs, such as that of Achates Power which hold promise, but have not made the final cut for production. Meanwhile automakers are assiduously cutting back engine families in favor of electrification investment. BMW announced the elimination of its gasoline V12; light-duty diesels of all kinds are on a fast decline (in 2021, Ford quietly dropped its 3.0L Powerstroke diesel for the F-150 pickup).
And in the truck- and SUV-obsessed U.S., many manufacturers have started to reduce availability of V8s. Strong rumors indicated Stellantis even is preparing a turbocharged I-6 to effectively replace the vaunted “Hemi” V8. In summer 2021, the Wall Street Journal reported IHS Markit forecast data indicating new-engine launches for the year to be less than 10, and dropping “essentially to zero,” compared with 20 to 70 new engines launching in prior years.
Hybrid, long-stroke hope
There no longer is absolute consensus among powertrain developers that hybridization will be ubiquitous in most light-vehicle segments. Not long ago, hybridized ICEs had driven the case for continuing ICE development and was its reason for being. Without hybridization, many experts note, a conventional ICE powertrain will not be fuel-economy or emissions compliant in many world regions.
The AVL engineers see ICEs for hybrids that adopt and enhance a variety of existing technologies to narrow the engine’s operating range even more than in today’s “full” hybrids. Such specialized designs’ operating characteristics make the engine more of a type of “generator” than a full-range powerplant. Their enabling technologies include some combination of cooled EGR, high compression ratio and longer-stroke dimensions.
“One area which I think still has not been fully exploited – and is under exploration at the moment – is low-pressure EGR in gasoline,” said AVL’s Howell. “This can be a pretty impressive enabler; AVL's been developing dedicated hybrid engines for quite a while. We've achieved 45 percent [brake thermal efficiency] out of a 11:1 [compression-ratio] engine. That uses a plethora of technologies, which are all known, but it's a matter of optimizing in order to achieve that.”
The key enabler for that type of application, Howell explained, is a “very high” stroke-to-bore ratio. But the challenge that comes with that type of application is it requires a ‘new’ engine. “So, it seems unlikely to be a mainstream in EU and U.S. because of the sunsetting of the IC engine,” he said. “But there is a lot of interest in China. We've done several engine platforms in the Chinese market.”
FEV’s Tomazic sees a developmental difference between ICEs designated for micro-hybrid and mild-hybrid duty, versus “dedicated” hybrid engines that would include those designed for HEV and PHEV applications. OEM strategies will range from, “You would only add as much technology as you need to meet the regulatory requirements, up to putting in everything you can right now,” he noted. “There's a wide array of different technologies – efficiency optimization obviously plays a very big role – otherwise from a CO2 and fuel-economy perspective, you won't meet the targets.”
He also mentioned the menu of existing technologies that can be improved in the quest for the “better” ICE, particularly “higher stroke-to-bore ratios combined with cooled EGR to deliver higher efficiencies at stoichiometric combustion.” Tomazic added that “[fuel]-injection pressures going up beyond 350 bar and pre-chamber applications could also become very important technologies which potentially also would allow us to go very lean to a point where we would see very low NOx emissions – from an aftertreatment perspective, that could mean some relief.”
Another look at alt fuels
Those seeking to extend the viability of ICE also have recharged the industry’s sporadic interest in alternative fuels – particularly for on- and offroad commercial-vehicle applications. But there is alt-fuel potential for certain specific light-duty vehicle segments, too. Hydrogen, thanks to its potential to be derived from CO2-neutral processes and the comparative ease with which ICEs can be adapted to use it, is experiencing renewed development focus as a zero-emissions alternative fuel.
Toyota (which has proceeded cautiously in the EV race) and Yamaha made news in February 2022 when they announced Toyota had commissioned Yamaha to adapt the automaker’s production-vehicle 5.0L V8 (top) to run on hydrogen. Modifications were made to the V8’s injectors, cylinder heads, intake manifold and other components, resulting in output of “up to 450 hp at 6,800 rpm and a maximum 540 Nm (398 lb-ft) at 3,600 rpm.”
Several commercial-vehicle engine and vehicle OEMs also have active programs for hydrogen fueling of diesel engines. One of the most recent developments was announced by Mahle Powertrain and offroad machinery manufacturer Liebherr Machines Bulle SA. The collaboration involves the use of Mahle’s prechamber jet ignition system (MJI), originally developed for gasoline applications. “The challenge has been to get it to run with stable combustion without resorting to reductions in compression ratios to avoid engine knock and pre-ignition. Our common work with Liebherr suggests we have the answer,” Mike Bunce, head of research for Mahle Powertrain U.S., told SAE Media earlier this year.
Another option to keep light-duty diesel in the conversation came in early 2022, when Audi (which pledged to end ICE engine production in 2033) announced production vehicles with V6 diesels would be capable of using new hydrotreated vegetable oil (HVO), a biomass-to-liquid (BTL) fuel. In addition to a 70-90% reduction in CO2 emissions, Audi said HVO has a 30% higher cetane rating than fossil-based diesel.
For commercial vehicles, “The combustion engine is still the best solution right now,” said FEV’s Tomazic. “The infrastructure is there. The energy density is there. Now, if we want to decarbonize fuel and go to hydrogen, this can be done,” he maintained. “Yes, there will be changes to the engine system, to the engine hardware, to controls, to the aftertreatment system, etc. But we know what needs to be done. What has to happen, of course, is that we have a hydrogen infrastructure.”