Effects of nozzle hole configuration of a multi-hole type gasoline direct injector on spray development under flash boiling conditions

Abstract

The flash boiling phenomenon is critically affected by not only injection conditions such as fuel temperature, ambient pressure and physical properties of fuel but also the nozzle hole configurations of the injector. In this research, two kinds of injectors, having different nozzle hole configurations (a closed type and a opened type) were used to analyze the influence of flash boiling. Near-field and far-field spray visualization was performed using a high-speed camera based on the Mie-scattering imaging technique. Test parameters were injection pressure, ambient pressure, and fuel temperature. The spray length, spray width, length-to-width ratio, and axial velocity of spray development depending on time were measured using the MATLAB program for quantitative and objective analysis. Finally, the prediction equation for the spray length was derived using the least-squares method based on the experimental results. In the case of the closed type injector, the spray center contained a wide overlapped region because of the strong links between plumes. On the other hand, with the opened type injector, there was a relatively narrow overlapped region between plumes due to weak interaction between plumes. As a result, the closed type injector had a narrow and long spray structure and the opened type injector had a partially long and wide spray structure. According to the prediction equation, the spray develops depending on time more linearly under flash boiling conditions than under non-flash boiling conditions. The influence of flash boiling was smaller in the closed type injector because the closed type injector has less variation of the spray structure with varying injection conditions, ranging from non-flash boiling conditions to non-flash boiling conditions.