Optimization on the combustion and performance of high-EGR engine by Air-assisted Pre-chamber Turbulent Jet Ignition (APTJI)

Abstract

With the increasing demand for carbon and pollutant emission reduction, the development of the technologies aimed at improving fuel efficiency and reducing emissions in internal combustion engines (ICEs) has become an urgent priority. Unlike conventional TJI systems, this study introduces an air-assisted pre-chamber turbulent jet ignition (APTJI) system, which integrates dual scavenging process achieving by the additional pre-chamber fuel or fuel/air mixture injection to optimize combustion stability under high EGR conditions. The proposed system can effectively reduce residual exhaust gas in the pre-chamber, enhance jet intensity, and accelerate flame propagation, thereby improving ignition reliability and combustion efficiency of the engine. In such situation, this study investigates the potential of APTJI enhancing both combustion and engine performance under conditions of high-EGR rates in gasoline engines, and also the effects of operating strategy and pre-chamber parameters of APTJI are analyzed. The results show that dual scavenging mode (Mode 2) has a positive impact on combustion stability by injecting fresh air first to effectively remove the residual exhaust gas in the pre-chamber. This results in an 8 % reduction in the misfire rate and an 11.3 % improvement in fuel efficiency. Compared to single scavenging mode (Mode 1), the scavenging timing has less influence on engine performance under Mode 2. Moreover, optimizing pre-chamber nozzle diameter is critical for maintaining combustion stability, and a nozzle with a diameter of 4 mm can achieve a maximum EGR rate of 30.7 %, while achieving optimal performance and ultra-low NOx emission of 0.544 g/kWh. Increasing the compression ratio can enhance the Heat Release Rate (HRR), contributing to improved combustion efficiency; however, it is limited by engine knock at low EGR rates.