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Trend Spotting: Hydrogen Combustion Engines

There is another hydrogen-related transport trend that some engine manufacturers, car companies and other original equipment manufacturers (OEMs) are exploring: hydrogen internal combustion engines (H2-ICEs). Tightening vehicle emission and fuel economy standards in North America, Europe, China and Japan are in part driving the interest in the trend. Zero emission vehicle (ZEV) policies that will eliminate the traditional ICE has OEMs and others searching for alternatives to electric vehicles (EVs) — both battery electric (BEV) and plug-in hybrids (PHEVs) (for the light-duty vehicle fleet).

But it’s more than that. What if neither BEVs or PHEVs take off in the market? What if some governments are ready to move away from the ICE, but their citizens are not? Moreover, what happens to the existing legacy fleet? How can it be decarbonized? Another issue of concern, particularly for heavy-duty engine manufacturers, is that BEV and fuel cell electric vehicles (FCEVs) are simply not ready to meet high-power requirements needed for the various types of conditions heavy-duty vehicles (HDVs) experience.

These are the foundational questions I believe are propelling interest in the H2-ICE. Jim Nebergall, General Manager of Hydrogen Engines at Cummins noted as much recently:

“We need decarbonisation solutions for the mobility industry, and hydrogen internal combustion engines are a practical option. Hydrogen engines are a breakthrough technology essential to reaching Destination Zero. They are low cost, highly efficient, perform like diesel in aggressive duty cycles, are robust to hydrogen fuel impurities, are durable in extreme operating environments, and are versatile.


Hydrogen engines also have lower installation complexity because the technology integrates well into existing chassis using existing vehicles accessories and driveline components. The low initial cost also provides a significant TCO advantage amongst zero-carbon fuelled powertrains…


There won’t be one winner in this race. The industry needs multiple solutions to meet the needs of all customers and all applications considering the variation in duty cycles and operating environments, both on- and off-highway. Both hydrogen ICE and fuel cell electric powertrains will play a role in decarbonisation, and we need them both.”

To that end, several of these companies are reconsidering hydrogen combustion as an additional component of their future powertrain portfolios, alongside batteries and fuel cells. H2-ICE’s advantages include lower payload penalties and space requirements, faster refueling times compared to BEV trucks, lower costs, and higher tolerances for heat and vibrations. The thinking is that various vehicle segments could benefit from these advantages, especially certain heavy-duty vehicles (HDVs), as well as mining, construction and agricultural vehicles.

Existing engines in the light-, medium- and HDV fleets could be adapted to run on H2by swapping out certain components, such as the spark plugs and fuel delivery system. This would reduce the number of changes required for switching cars to H2 instead of gasoline or diesel, and would allow automakers to maintain existing powertrain platforms without the need for massive changes and investments into other powertrains.

There are some impediments. Depending on the source of the hydrogen, GHG emissions would be very low to zero, but there would still be some degree of NOx emissions. That may pose a problem for the vehicles in parts of the world (particularly Europe) that are increasingly developing low and no emission zones in major metropolitan areas. NOx could be controlled, however, with SCR aftertreatment. H2-ICEs have low ignition energy and wide limits of flammability, which make these engines particularly prone to pre-ignition. The situation is further aggravated by hydrogen’s high flame speed.

Hydrogen’s exceptionally low ignition energy requires that the average temperature prevailing within the combustion space during induction be sufficiently low so that the formation of hot spots is avoided. This requires appropriate cooling of the cylinder head, piston, valves, combustion chamber wall, and the use of cold spark plugs (non-platinum tipped spark plugs). Then, there are the impediments that already exist for FCEVs such as the need to expand fueling infrastructure.

Who’s working on H2-ICE’s?

  • Isuzu Motors, Denso, Toyota Motor, Hino Motors and Commercial Japan Partnership Technologies (CJPT) announced a collaboration earlier this month to research and develop H2-ICEs.
  • Westport Fuel Systems unveiled its Hydrogen HPDI Fuel System, which it says will enable HDVs to operate on hydrogen with improved power, torque, efficiency, and performance as diesel engines while meeting global emissions regulations.
  • Subaru, Mazda, Toyota, Kawasaki, and Yamaha announced in 2021 a joint effort to expand the use of alternative fuel technologies—including H2-ICEs.
  • Toyota has commissioned Yamaha Motor to develop a H2-ICE, a 5.0-liter V8 engine for passenger cars.
  • Kawasaki and Yamaha are conducting joint R&D on H2-ICEs for both two-wheeled and four-wheeled vehicles.
  • Chinese automaker GAC is conducting R&D on an H2-ICE.
  • Cummins in 2021 demonstrated a proof-of-concept test for H2-ICE in the HDV sector.
  • Renault, which has developed a hydrogen-ICE passenger car.
  • Ford was granted a U.S. patent for a H2-ICE design.
  • In the current HIMET project (Hydrogen in an Integrated Maritime Energy Transition), Ricardo is designing, developing and testing the combustion system and the engine hardware to convert an existing natural gas engine to 100% hydrogen operation in order to decarbonize maritime transport emissions in Scotland.
  • Rolls-Royce (the aerospace company) and easyJet are testing hydrogen combustion in its aircraft.

How do H2-ICEs stack up against other alternatives, including bio- and synfuels? I like the chart below from McKinsey, which looks at emissions, total cost of ownership (TCO) and other factors.

The four zero-emissions technologies have advantages and disadvantages.

For both FCEVs and H2-ICEs , the availability of hydrogen refueling stations and the cost of hydrogen at the pump are the key factors that will determine success and are of greatest concern today. What about competition with the FCEV?  The thought is that the H2-ICE could help bring down the cost of FCEVs. According to McKinsey, allowing OEMs and tank suppliers to amortize R&D and capex over a larger number of vehicles will help bring down the cost curve for all hydrogen vehicles and support the competitiveness of both solutions.

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