Emission Control for Hydrogen Internal Combustion Engines

Licentiatavhandling, 2025

Hydrogen internal combustion engines have the potential to reduce greenhouse gas emissions from the transportation sectors, especially for heavy-duty road transport, such as long-haul trucks.

There are however still local emissions from hydrogen internal combustion engines that need to be minimized. These include nitrous oxides and particle emissions. Any high temperature combustion process that occurs in an excess of air has the potential to generate significant number of nitrogen oxides.

The particle emission on the other hand stems from the combustion of engine lubricating oil. This occurs in engine running on fossil fuel as well, but the effect on the emissions may be less significant when compared to those of incomplete burning of fossil fuels. The particle emission can also be significantly higher, as the short quenching distance of hydrogen flames allow combustion to take place closer to cylinder walls, as well as transferring more heat into the walls.

Another issue is that the exhaust after-treatment system can cause emission nitrous oxide, N2O, or laughing gas, which is a very potent greenhouse gas with close to 300 times the greenhouse warming potential of carbon dioxide.  

Experiments were conducted to measure the engine out emission, both regulated and unregulated of a direct injection, spark ignition hydrogen internal combustion engine. The results showed that air to fuel ratio is the most important factor for determining NOX emissions. At the same time, the particle emissions increased dramatically when the engine was throttled, and cylinder and intake pressure reduced to below crankcase pressure.

A heavy-duty, direct injection, spark ignition, engine fitted with ah exhaust after-treatment system has been used for measurement of the impact of engine operating parameters on the engine out emissions, as well as the effect of these engine parameters on the performance of the different components in the exhaust after-treatment system. The results indicates that low tailpipe emission is possible, although the experimental setup does not provide enough precision in operating conditions for the catalyst to quantify the effects of water content and catalyst efficiency, due to unsteady emission levels and confounding between variables.