Diesel spray and combustion of multi-hole injectors with micro-hole under ultra-high injection pressure-Combustion characteristics

Downsizing the hole diameter and increasing the injection pressure can effectively increase the fuel-gas mixture formation and thermal efficiency of the diesel engine. In this study, the characteristics of the liquid length and combustion processes were studied using diffuse back-illumination and OH* chemiluminescence imaging. The results show that the time for the liquid length to reach a stable stage reduces with the increase in injection pressure and decrease in hole diameter. Although the injection pressure has a slight effect on the liquid length, the liquid length of the micro-hole injector under ultra-high injection pressure conditions is slightly reduced. Increasing the injection pressure and reducing the hole diameter can reduce soot generation per unit fuel mass. Compared with the use of the micro-hole diameter (D = 0.07 mm, Pinj = 100 MPa), increasing the injection pressure to 300 MPa (D = 0.133 mm, Pinj = 300 MPa) can suppress soot generation per unit fuel mass more effectively. The strong oxidation reaction was distributed both in the upstream and downstream areas of the flame only when the micro-hole injector was used under ultra-high injection pressure. When the liquid length is longer than the flame lift-off length, a large amount of soot is generated during combustion. Through the intersection of the liquid length and flame lift-off length trend line, it is estimated that the region of the liquid length is less than the lift-off length under different conditions. The determination of this region provides guidance and suggestions for the selection of the hole diameter of injectors and injection pressure for diesel engines.