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This study investigated the formation of an active prechamber (APC) jet flame based on the synergy of airflow. A single-cylinder gasoline direct injection engine installed with an APC was operated under ultra-lean conditions with a lambda value of 2.5. Different APC structures with nozzle swirl angles ranging from 0° to 30° were designed to produce different flow fields and mixture formations. 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. • The formation of an active prechamber jet flame based on the synergy of airflow was investigated. • Different prechamber nozzle swirl angles were designed to produce different flow fields. • The fuel-air mixing and spray impingement inside pre-chamber were analyzed. • The synergistic interaction between swirl and tumble flows promotes jet flame ignition capability. • A larger nozzle swirl angle promotes jet flame propagation. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the mechanism of the asymmetric jets of the TJI system. We analyzed the effects of fuel injection and air flows in pre-chamber and main chamber, initial flame kernel, and evolution of turbulent hot jets. The evaluation indexes of asymmetric jet were proposed. The results show when adding fuel injection into the homogeneous PC with off-central spark plug, the average relative velocity range and average degree of velocity non-uniformity increased by 50.8% and 32.8%, which increased by 75.1% and 46.7% for the real engine condition with intake airflow and fuel injection. A similar phenomenon was observed for central spark plug settings but with a much stronger impact on the asymmetry of jets velocity as proved by the increment of 138.5% and 93.2% under real engine condition. The asymmetric jets can be divided into the asymmetry of jets size and the asymmetry moment of flame jets. The former of different jets' velocity is attributed to the tumble flow in main chamber. The latter is attributed to the irregular flame propagation caused by the off-central ignition and the uneven mixture distribution in pre-chamber. The optimization strategies to efficiency utilize the flow exchange between PC and MC were proposed. • The formation of asymmetrical jets from turbulent-jet-ignition system was investigated. • Different PC structures with spark plug centrally and off-centrally installed were designed. • Ideal homogeneous conditions via semi-ideal environment to real engine operations were discussed. • The asymmetric jets phenomenon was a spatial-temporal related to jets size and flame jets moment. • Specific strategies and PC design were carried out to improve the PC jet performance. [ABSTRACT FROM AUTHOR]

The oxygen-deficient combustion characteristics of methane in a localized stratified vortex-tube combustor (LSVC) are studied by diluting combustion air with nitrogen. The influences of oxygen mole fraction (0.13–0.21) on flame configuration, combustion stability, combustion efficiency, and NO x emission characteristics are experimental investigated at the inlet temperature of 300 K. Combined with the numerical simulation method, the NO x generation, and emission mechanisms are analyzed in this combustor. Results show that the LSVC can achieve a wide stability limit, in which the global equivalence ratio can be as low as 0.22 at the lowest oxygen mole fraction (β) of 0.13. To ensure high combustion efficiency, the β should be kept above 0.16 since the oxygen-deficient condition reduces the reaction rate and flame temperature. The combustor can achieve ultra-low NO x emission of below 10 ppm (@ 15 vol% O 2) due to low oxygen concentration and flame temperature. Furthermore, part of NO x entrained into the fuel-rich reduction zone by the swirl flow field is reduced by the reductive species (i.e., CO and H 2) to further lowering NO x emissions. The results of this paper can guide the development of the LSVC in the high-efficiency and low-emission combustion fields. • Low NO x emission with high stability can be achieved via a simple structure. • Steadily combustion results from the optimization structure of this combustor. • Low combustion temperature is the principal reason for the low NO x emission. • Generated NO x can be reduced by the stratified species distribution. • The flow field can promote the transport of the NO x to the reduction region. [ABSTRACT FROM AUTHOR]