Pre-chamber ignition system development for lean-burn Gasoline Direct Injection engine

Recent regulation changes to restricted fuel usage in motor-sport events resulted in motor-sport engine manufacturers focusing on improving thermal efficiency and often claim thermal efficiency figures well above equivalent road car engines. With limited fuel usage, motor-sport engines are operated with a lean mixture to benefit from higher cycle efficiency, requiring an ignition system that is suitable for the lean mixture. Pre-chamber ignition is identified as a promising method to improve lean limit and has the potential to reduce end gas auto-ignition. A pre-chamber ignition system is developed for a lean-burn gasoline direct injection engine with the objective of reducing BSFC. Initial part of the project focused on developing a multi-dimensional engine model, representing single cylinder version of a lean-burn turbo-charged Gasoline Direct Injection engine, achieving correlation to the available test data. The same CFD model is later updated to include a prechamber and studied the influence of various design features on the performance of pre-chamber ignited combustion. Pre-chamber fuel enrichment was observed to be influential in achieving combustion stability and was key factor in deciding final prechamber design along with burn duration. Two pre-chamber designs proposed for the testing based on this study, both produced compromised results for combustion duration and pre-chamber equivalence ratio. For experimental validation of the pre-chamber design, a single cylinder engine was developed along with a two-stage supercharger rig. Engine performance with base spark ignition and two pre-chamber designs were compared and one prechamber design was proposed for final implementation. Heat transfer from the pre-chamber observed to be a critical factor in avoiding pre-ignition and achieving performance. Also, conventional transducer based knock detection strategy found not working with pre-chamber combustion and a novel knock detection strategy based on cylinder pressure trace is proposed for pre-chamber based combustion. This research work delivered a pre-chamber design for higher BMEP (>25 Bar) gasoline engines and identified a novel knock detection strategy for pre-chamber ignited combustion