Increasing the injection pressure and splitting the injection stage are the major approaches for diesel engines to promote the fuel-air mixture formation process, which determines the subsequent combustion and emission formation. In this study, the free spray was injected through a single-hole nozzle with a hole diameter of 0.111 mm. The impinging spray flame formed from a two-dimensional (2D) piston cavity with the same shape as a small-bore diesel engine was also investigated. The main injection was carried out either as a single main injection with injection pressure of 100 MPa (Pre + S100) or a split main injection with 160 MPa defined by the mass fraction ratio of 75:25 (Pre + D160_75-25). The tracer laser absorption scattering technique was used to observe the spray mixture formation process. The characteristics of the combustion process of diesel spray were investigated by using a color camera that can directly perceive the flame natural luminosity and two-color pyrometry techniques. Two ambient gas strategies, 21% and 15% O-2, were adopted to investigate the effect of O-2 concentration on the combustion process. The experimental results reveal that split injection promotes the fuel evaporation process; split injection also has a positive effect on improving the combustion process. For split injection, low oxygen (15% O-2) has a significant negative effect on improving combustion and produces more soot. The mean flame propagation velocity of the free spray flame was studied, and it was found that the split injection can shorten the flame propagation duration. The spray-wall interaction has a significant effect on the fuel evaporation and combustion process.