Background
The hydrogen internal combustion engine, or H2-ICE, has been a topic of interest in decarbonized on-road heavy duty transportation solutions. The technology works very similarly to today’s commercially available spark ignition engines but without the consumption of a hydrocarbon-based fuel like natural gas. Instead, the engine utilizes hydrogen fuel, which reduces carbon emissions by 99.9% relative to a diesel or natural gas engine. Although H2-ICE largely mitigates carbon emissions, other pollutants, like smog forming nitrogen oxides, are still generated in the combustion process. Today’s heavy-duty engines have catalyst technologies that chemically process gaseous criteria pollutants before engine exhaust is introduced into the ambient air. These are relied upon to ensure emissions compliance during product certification testing and more importantly, during field operation. Since H2-ICE has been the subject of commercialization viability, there remain many unknowns regarding engine and catalyst operation. This includes the aftertreatment durability potential for future heavy duty emissions compliance standards. The efforts considered attempt to identify dominating aging conditions on H2-ICE aftertreatment systems.
Approach
The initial work considered an H2-ICE exhaust emission speciation from SwRI’s demonstration engine platform. The primary objective was to identify and quantify the gaseous species present in the exhaust, which would subsequently guide small-scale bench-top reactor catalyst testing. Once the conditions at the catalyst inlet were established, catalyst aging experiments could be initiated using various aging protocols. These protocols included exposure to different water vapor concentrations and high-temperature operation to assess any inhibitory effects of water on catalyst performance. Results from the small-scale reactor testing aim to identify the most significant exhaust conditions contributing to catalyst degradation. The remaining portion of the efforts focused on transposing accelerated aftertreatment aging protocols onto H2-ICE catalyst applications.
Accomplishments
To date, the H2-ICE engine emission speciation work was successfully completed. This included characterizing exhaust species for the cold start heavy-duty federal test procedure (HD-FTP), hot start HD-FTP, low load cycle (LLC), and the ramped modal cycle (RMC). Analysis of the H2-ICE emissions revealed a higher concentration of water vapor compared to a conventional diesel internal combustion engine (diesel-ICE) platform. This implies that nitrogen oxide (NOX) reduction technologies adapted from diesel engines will face challenges with low-temperature performance in H2-ICE applications. Additionally, the demonstration engine exhibited elevated H2 emissions throughout the testing sequence. For oxidation aftertreatment technologies, this could pose issues at elevated temperatures, such as 400°C, due to the highly reactive nature of H2. These findings, in conjunction with insights gained from the CHEDE-9 consortium and other internal research efforts, indicate multiple pathways for the development of H2-ICE aftertreatment solutions. However, each will have its own challenges to consider.