High-Speed Optical Diagnostics of Misfire Limits in a Spark-Ignited Heavy-Duty Hydrogen Engine

This study investigates the ignitability of hydrogen in an optical heavy-duty SI engine. While the ignition energy of hydrogen is exceptionally low, the high load and lean mixtures used in heavy-duty hydrogen engines lead to a high gas density, resulting in a much higher breakthrough voltage than in light-duty SI engines. Spark plug wear is a real concern, so there is a need to minimize the spark energy while maintaining combustion stability. The first part of this study was performed on an optical engine fitted with a metal piston. In this configuration, we mapped the combustion stability and frequency of misfires with two different ignition systems: a common inductive system and an actively controlled capacitive system. The equivalence ratio and dwell time were varied for the inductive system while the capacitive system instead varied spark duration and spark current in addition to equivalence ratio. A key finding was that leaner mixtures require longer dwell time or longer spark duration but the effect from increased spark current is limited. Furthermore, several different phenomena were noted at ultra-lean conditions and low spark energies where misfires were common: successful spark but extremely delayed heat release, restrikes, and failure to form a spark. In the second phase of this study, which is ongoing, we employ an intensified high-speed camera to directly view the ignition process. The optical piston’s bowl in combination with the camera lens acts as a long-range microscope which allows us to capture highly magnified images of the early flame development. The goal of this phase is to follow the mapped misfire limits and optically observe the previously mentioned phenomena. The mechanism behind misfires is of particular interest – specifically whether a flame kernel forms and extinguishes, or fails to form altogether.