Investigation on the development law of methanol spray impinging on intake valve during port fuel injection

Spray inevitably impacts curved valve during port fuel injection. The existing simplified method of spray impacting flat plate in regular channel cannot truly describe the impingement process. Based on combination of transparent port with optical distortion correction and valve, this study investigated port methanol spray characteristics after injection and its velocity loss after impacting valve. The effects of injection pressure, valve lift, inlet flow velocity and valve temperature were discussed and various regimes of spray droplets impacting valve were proposed. Different from the spray impacting flat wall, methanol spray developed towards its both sides after impacting valve, i.e. the left impinging spray with smaller area and velocity and the right impinging spray, whose velocity losses were more than 60 % and 40 %, respectively. Higher injection pressure and inlet flow rate increased the impinging spray area and velocity, but the former deteriorated port wet wall and the latter accelerated oil film evaporation. Both of them had limited effect on reducing velocity loss of the impinging spray. The pressure and drag force of inlet flow led to slenderer impinging spray, which mainly formed mixture below valve. Higher valve lift decreased port oil film area and caused impingement position to shift to right, thus reducing velocity loss of the left impinging spray. Raising valve temperature to above Leidenfrost point caused the impinging spray to ‘slide’ along valve surface, resulting in less impingement momentum loss and lower impingement spray height. The minimum velocity loss of the left impinging spray was reduced by nearly 20 %, greatly promoting the impinging spray diffusion.