Hydrogen Effects on ICE Components

Internal combustion engines (ICEs) offer an efficient, clean, cost-effective option for converting the chemical energy of hydrogen into mechanical energy. The basics of this technology exist today and could greatly accelerate the utilization of hydrogen for transportation.

It is conceivable that ICE could be used in the long term as well as a transition to fuel cells. However, little is known about the durability of an ICE burning hydrogen. The primary components that will be exposed to hydrogen and that could be affected by this exposure in an ICE are (1) fuel injectors, (2) valves and valve seats, (3) pistons, (4) rings, and (5) cylinder walls. A primary combustion product will be water vapor, and that could be an issue for aluminum pistons, but is not expected to be an issue for the exhaust system except for corrosion.

There is clear evidence that the components of an engine burning hydrogen could experience durability issues because of their exposure to hydrogen or its primary combustion product, water vapor. High-efficiency conversion of hydrogen to mechanical energy will require the use of direct injection of hydrogen. This requires the injectors to be exposed to hydrogen gas, where the tool steel or carbon steel components could experience hydrogen-induced cracking or embrittlement. This is especially a concern for the injector needle and seat, which will also experience impact and cyclic loading.

Piezoelectric actuators are one method for providing the fuel injector needle its lift, and there is some evidence that hydrogen could affect the performance of these components. Hydrogen could affect the dielectric properties of the piezoelectric material, the epoxy in which it is encased, or the electrical contacts. Testing is in progress on these components that should provide the data needed on their performance and methods for improving their durability should that be necessary.

Valves and valve seats will be exposed to hydrogen at elevated temperatures and could experience decarburization; however, it is difficult to predict their behavior based on current information. The operating temperatures of exhaust valves and valve seats for gasoline ICEs are at or below that at which decarburization occurs in carbon steels, but they are generally made from alloy steels that have higher decarburization temperatures.

Also, the operating temperature of a hydrogen ICE may differ from a gasoline ICE. Gasoline ICEs utilize aluminum pistons, and it is known that aluminum and aluminum alloys experience hydrogen embrittlement when exposed to water vapor at 70°C and above. This operating temperature is certainly within the range of engine operation, so that it is important that this issue be evaluated.