A study on the spray structure and evaporation characteristic of common rail type high pressure injector in homogeneous charge compression ignition engine

摘要

The purpose of this study was to investigate the spray structure and evaporation characteristics of common rail high pressure injector for use in a direct injection type HCCI (Homogeneous Charge Compression Ignition) engine. In this study, we measured the injection rate and visualized the spray structure of a HCCI injector according to injection conditions. The CFD simulation of the spray and the air fuel mixture formation in real engine conditions was also conducted using the VECTIS commercial code. In addition, we compared simulation results to experimental results. From the spray experiment and simulation results, we found the spray penetration to be proportional to back pressure by an exponent of 1/4. This is similar to Hiroyasu's experimental result. The fuel evaporation and air fuel mixture result indicate that the influence of the spray impingement with the ambient density was bigger than that of the intake pressure and temperature conditions in evaporation rate when the fuel was injected at the early stage of the compression stroke. The results also reveal that the fuel was uniformly distributed in the combustion chamber at this early injection time and that the air fuel mixture enhanced in this relatively rich region. However, when ambient density was kept constant, the fuel evaporation was sensitive to the influence of the intake temperature and pressure. As the fuel was injected at the later stage of the compression stroke the fuel tended to concentrate in the bowl zone and the air fuel mixture enhanced in the lean region. From these results it was confirmed that the air fuel mixture characteristics are sensitive to the impingement position of the injected fuel.