Study of turbulent jet ignition based on synergy of airflow to achieve 53% indicated thermal efficiency for hybrid ultra-lean burning engines

This paper aims to study the active pre-chamber (APC) jet flame formation based on the synergy of airflow. A single-cylinder gasoline direct injection engine installed with an APC operated under the ultra-lean (λ = 2.5) conditions. Different APC structures with nozzle swirl angles ranging from 0° to 30° were designed to generate different flow fields and mixture formation inside APC. The results showed that APCs with larger nozzle swirl angles generated smaller wall films and faster fuel–air mixing, forming a more evenly mixed distribution in the APC's top region, which improved the uniformity of the flame jets from different APC nozzles with a smaller variance in jet turbulence kinetic energy and jet velocity. Tumble flow played a dominant role in APCs with a small nozzle swirl angle, and the relatively weak swirl flow field inside the APC resulted in more locally rich mixture regions, reducing the ignition capability of the APC jet flame. APCs with a large nozzle swirl angle can accelerate the evaporation and mixing process of the fuel near the top region of the APC with a stronger swirl, and the wall film diffuses to the central area of the duct through the airflow. APC with nozzle swirl angle of 25° shows a potential to achieve 53% ITE after the optimization of synergistic airflow between APC and MC.