Characterization of diesel spray combustion using two-color pyrometry and OH∗ chemiluminescence imaging- comparison between micro-hole and ultra-high injection pressure effects

Increasing the injection pressure and reducing the hole diameter are development directions for future diesel engines. In this study, the effects of increasing the injection pressure to 300 MPa and reducing the injector diameter to micro-hole (0.07 mm) on the characteristics of liquid length (LL) and combustion are investigated. The results show that the flame temperature distribution of a micro-hole injector is dispersed, whereas that of a large-hole injector is concentrated. Although the flame temperature distributions of the micro-hole injector and ultra-high injection pressure condition shift to the low-temperature region, the flame temperature of the micro-hole injector under a low injection pressure (Pinj = 100 MPa, D = 0.07 mm) encompasses a higher-temperature range and has a higher percentage in this range. Soot generation during combustion is evaluated based on the ratio of the integrated KL (IKL) to the integrated fuel mass (IFM). The IKL/IFM value of the large-hole injector under an ultra-high injection pressure (Pinj = 300 MPa, D = 0.133 mm) and the micro-hole injector (Pinj = 100 MPa, D = 0.07 mm) are smaller than other conditions, which indicates that reduce the hole diameter and increase injection pressure can inhibit soot generation more effectively. The LL/LOL has a linear relationship with stoichiometric air entrained. Increasing the injection pressure and reducing the hole diameter can reduce the value of LL/LOL, thereby reducing soot generation. Through the intersection of the liquid length and lift-off length (LOL) trend line, the functional equation is established to obtain the region where LL/LOL is less than one (low-soot region) under different conditions. The determination of this region and equation provides guidance and suggestions for the selection of the hole diameter of injectors and injection pressure for diesel engines.