Investigation of spray characteristics in a spray-guided DISI engine using PLIF and LDV

Abstract

The spray characteristics of a prototype piezo pintle-type injector are investigated in a single-cylinder optical direct injection spark ignition (DISI) engine based on the spray-guided concept where mixture preparation is dominated by the spray dynamics. The high-pressure piezo electric injector has an annular nozzle providing a hollow cone spray. Planar Laser-induced Fluorescence (PLIF) and 2-dimensional Mie scattering were used to study the spray structure and characteristics under different in-cylinder back pressures and to obtain cycle resolved measurements of the planar fuel distribution inside the cylinder. The obtained results give information about the extent of charge stratification, spray stability and fuel/air mixture formation process under operating conditions. PLIF results revealed that there is a rich mixture at the spark plug position for all these conditions, ensuring stable combustion over the entire engine operating range. In addition, LDV measurements were carried out in order to provide information on the in-cylinder flow field near the spark plug, and to assess its influence on the mixture formation process. LDV results showed that the influence of the flow field strength during the late compression injection on the liquid fuel spray structure is low. The tumble generated in the cylinder is transformed into turbulence at the end of the compression stroke, which aids fuel evaporation and vapour dispersion just before ignition.