Optical and simulation investigation of effect of jet-wall interaction on combustion performance of methanol pre-chamber turbulent jet ignition system

The pre-chamber engine wall's structure has a significant effect on the ignition and combustion performance of pre-chamber turbulent jets. This study identified an abnormal combustion phenomenon in the case of secondary jets, which was characterized by the pre-chamber pressure rise rate exceeding 30 times the normal rate owing to pre-chamber jet impingement on the wall. To investigate this phenomenon, we examined the causes of ignition events resulting from the interaction between pre-chamber jets and the wall by using a visualized constant-volume combustion chamber experimental platform and by conducting CFD simulations. The results indicated that for a certain range of the wall-nozzle distance, pre-chamber jet impingement on the wall is advantageous for reducing the ignition delay and increasing the combustion speed. Under lean burn conditions, pre-chamber jets impinging on the wall led to both direct and delayed wall-impinging ignition owing to the wall structure. Pre-chamber jet impingement on concave or flat wall surfaces generated more intense impinging turbulence than that on convex wall surfaces, resulting in the improvement of both ignition and flame propagation speeds. Thus, the wall surface at the impingement point of pre-chamber jets should not be convex as this would reduce the jet ignition performance and increase the probability of secondary jet occurrence, leading to irreversible damage to the pre-chamber structure.