Reigniting Combustion: How Today’s Combustion Engines Are Already Compatible With The Clean Fuel Transition
There’s a common misconception that combustion engines will need major redesigns to run on hydrogen. While this might be partially true for some compression ignition (diesel) engines, it’s largely not the case for most spark-ignition engines.
There’s a common misconception that combustion engines will need major redesigns to run on hydrogen. While this might be partially true for some compression ignition (diesel) engines, it’s largely not the case for most spark-ignition engines.
Manufacturers like Horse and Acteco are already producing engines that are “hydrogen compatible” by design, but beyond these new platforms, many existing engine architectures are inherently suited to hydrogen combustion with only minor adaptations.
A lot of focus has been placed on hydrogen embrittlement (the process where hydrogen atoms diffuse into metals, causing brittleness and potential cracking). However, many of the materials already used in mass-produced combustion engines are either resistant to this effect or operate in conditions where embrittlement isn’t a critical issue within the engine's design life. Connecting rods are often mentioned as a component which can embrittle due to hydrogen present in the crank case from piston ring pack blowby and although they’re typically steel and may be exposed to trace hydrogen in the crankcase, the concentrations and pressures are far too low to cause rapid degradation over the engine’s operating life. Add to that the oil film formed on them in normal operation from the lubrication system, which acts as a barrier to hydrogen ingress, and the embrittlement rate becomes even smaller.
In practice, adapting existing combustion engines to run on hydrogen can require only modest changes, mainly to the fuel system (to fit hydrogen injectors and a compatible fuel rail), ignition components (especially spark plug materials), and crankcase ventilation (to manage hydrogen and water vapour byproducts safely).
The result is a zero-carbon engine, because hydrogen isn’t a hydrocarbon fuel, with no fine particulate emissions, and the only major byproduct of its combustion is water, with a small amount of NOx. Even this NOx can be effectively managed, either through exhaust after-treatment or combustion management. Hydrogen’s wide flammability range and high flame speed make it especially suited to lean burn strategies that reduce combustion temperatures and thus NOx formation.
What’s perhaps even more compelling is the opportunity to pair hydrogen combustion engines with electric machines to create compact, on-demand power units ideal for range extenders or off-grid applications. Viritech are already developing this technology, enabling scalable powertrain solutions for everything from passenger vehicles to heavy goods vehicles and off-highway equipment. These systems combine the strengths of both combustion and electrification while avoiding or reducing many of their respective limitations.
One thing is clear: combustion still has a lot to offer as an emissions reduction technology. As the APC noted in its 2024 report:
“Given the level of reduction in both GHG and regulated emissions available, it is also recommended that H₂ICE should be considered a net-zero emissions technology for other sectors, including on-road applications.”
Hydrogen combustion engines aren’t a relic of the past; they’re a vital part of a pragmatic, low-carbon future.
Matt Faulks
CIO, Co-Founder
With a background in motorsport and low-volume sports car production, Matt founded TDF in 2009, which specialised in development projects for motorsports and automotive customers, including Formula One Management and BAC. His wide range of engineering skills includes leading expertise in the development of vehicle control systems and mechatronics integration.
