Background
The automotive sector's roadmap to support decarbonization includes hydrogen (H2) as one of the low/no carbon fuels. While several studies are aimed at using H2 in internal combustion engines (ICEs), this project aimed at understanding the combustion performance of high-pressure direct-injection (DI) H2 in a single-cylinder ICE for future H2 ICEs. More specifically, different combustion modes for various operating regimes spanning from spark ignition to spark-assisted compression ignition to diffusion-like combustion were explored. The rationale was that such strategies could allow higher power density and diesel engine-like efficiencies while avoiding the typical challenges associated with knock and pre-ignition without the need for advanced boosting.
Approach
The project team converted a PFI NG single-cylinder engine to operate on DI H2 fuel. A piezo gasoline injector was installed in the engine capable of injecting H2 at 170 bar injection pressure. Both lean and stoichiometric operating regimes were explored to understand the benefits of homogeneous, stratified, and multi-injection strategies.
Accomplishments
The primary emissions from an H2 ICE are NOx emissions. The engine-out emissions need to be reduced to single-digit ppm levels for such engines to meet/improve upon the proposed emissions regulations for medium and heavy-duty engines in 2027 and beyond. In this project, we demonstrated that a significant decrease in NOx emissions could be realized for cases that employed a late DI pulse near the spark timing of the engine albeit with an engine efficiency penalty. In addition, the stoichiometric operating load of the H2 ICE was also increased significantly with the usage of high-pressure DI. These results were also highlighted in the SAE publication (SAE Technical Paper, 2023-01-0287).
Due to injection hardware challenges, several questions remain unanswered at the end of this internal research project. There exists a consensus amongst consortium participant members to study this further in the upcoming CHEDE-9 consortium starting in January 2024.