Dynamics and mitigation strategies of knock in hydrogen-fueled internal combustion engines

Abstract

In the context of utilizing hydrogen as a fuel for internal combustion engines, it is crucial to address its tendency to induce knock more readily under certain conditions compared to gasoline. Knock not only reduces fuel efficiency but also has the potential to inflict detrimental effects on engine components. It is generally believed that knock is primarily caused by the spontaneous combustion of the end-gas mixture. Current research focuses on the frequency, intensity, and statistical characteristics of knock signals.This study aims to introduce two prevalent and effective methods for mitigating knock: increasing the Exhaust Gas Recirculation (EGR) ratio and water injection into the engine. Experimental observations suggest that at low rotational speeds (n=900 rpm), the amplitude spectra of knock induced by hydrogen and gasoline show similarities. However, at higher speeds (n>3000 rpm), the amplitude of hydrogen-induced knock not only exhibits a greater number of peak values but also intensifies in strength. Notably, the efficacy of increasing the EGR ratio diminishes at high speeds, potentially due to the propensity of methane to also cause knock under high-temperature conditions. In contrast, water injection, while generally effective, may adversely impact the lifespan of engine components.In summary, effective suppression of knock in hydrogen-fueled internal combustion engines is vital for accelerating the adoption of hydrogen in the power sector and making significant contributions to environmental conservation. This paper aims to delve into the analysis of these methods effectiveness and proposes directions for future research.