Advanced Plasma-based Ignition Strategy for Future Spark Ignition Engines

Internal combustion engines will continue to play an important role in transportation for decades to come because of the high onboard energy density. For present passenger vehicles, efforts have been made to reduce the cold start emissions and improve engine efficiency. To reach such goals, lean and diluted mixtures are needed to reduce the chemical reactivity of the mixture, so a higher engine compression ratio can be used to improve thermal efficiency. The decreased flame temperature of the lean/diluted mixtures are also beneficial for NOx reduction. Strong in-cylinder flow is needed to increase flame propagation speed for efficient and complete combustion process. Strong ignition sources are needed to provide robust ignition to support the combustion process. In this paper, the application of advanced plasma-based ignition strategies are reviewed, with special attention to the on-demand plasma energy profiling, which has flexible control over discharge duration and current amplitudes. The ignition performance of multi-site ignition is compared with on-demand energy profiling under cold start and engine idling conditions. For heavy-duty applications burning low and zero carbon renewable fuels with less chemical reactivity, such as ammonia and natural gas, a novel ignition source with remote chamber and detonation tube is also demonstrated for the first time. The air-fuel mixture in the remote ignition chamber can be ignited, and the flame front can propagate and accelerate along the detonation tube to detonation stage, known as the deflagration-to-detonation transition. The high-speed detonation wave has much stronger ignition capability to improve combustion efficiency of mixture with low chemical reactivities.