Abstract
Turbulent jet ignition with active pre-chamber (APC) could enhance the ultra-lean combustion stability thus improving the engine's thermal efficiency. Different APCs structures are analyzed in previous studies, but the lack of quantitative evaluation criteria makes it difficult to optimize the APC under various engine conditions. This paper aims to investigate the characteristic of APC hot jets and their effects on ignition capability and engine combustion performance from perspectives of jet velocity, temperature, turbulent kinetic energy (TKE), and turbulent intensity. The quantitatively evaluate method of hot jet activity based on the key intermediate species during the chemical reactions was proposed. Different APC jet flames and corresponding engine main chamber (MC) combustion performance were discussed by adjusting the APC nozzle diameter and number. The result showed that the jet velocity in a certain range of 450 to 700 m/s has a positive effect on igniting the ultra-lean mixture inside MC. The jet velocity mainly affects the ignition position of jet flame in MC, a higher jet velocity induces the ignition to occur near the cylinder wall and increases the thermal diffusion and heat losses, leading to the lower ignition ability. The jet temperature shows a relatively lower effect on igniting the ultra-lean mixture as the maximum jet flame temperature is over 2250 K. The jet TKE and velocity exhibit a strong correlation in engine performance. The jet turbulence intensity rather than jet TKE strongly influences igniting the ultra-lean mixture. The jet turbulence intensity in the range of 0.025 to 0.035 is beneficial to ignition ability and engine combustion performance. The 4-nozzle APC produces a relatively high jet activity. It’s confirmed that the jet activity higher than 0.055 is sufficient for igniting the ultra-lean mixture. The 4-nozzle APCs can achieve higher engine-indicated thermal efficiency (ITE) as compared to 6-nozzle APCs. The peak ITE of 51.6% is achieved by the 4-nozzle APC with an orifice diameter of 1.8 mm that meets all the good jet characteristics that can produce strong ignition capability.
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