Study On In-Cylinder Wall Impingement From A GDI Engine On Steady Flow Test Bench

As having obvious advantages and great potential on dynamic property and fueleconomy, Gasoline direct injection (GDI) engines become a hot tendency in thegasoline engine field. Fuel direct injection make in-cylinder wall wetting, which leadsto increased Particulate matter and HC emissions. In order to meet the limit of futureproposed emission standards such like EuroⅥ standard, GDI engine need to avoidwall wetting. There are theoretical significance and engineering value in finding theinteraction relationship of intake airflow and fuel spray.To study the spray process in different intake airflows, a visualization systemwhich includes injector drive circuits, high-pressure fuel pumps and visualizationhigh-speed camera, was set up on a steady flow test bench. A special spray imageprocessing program was also developed by MATLAB codes to analyze the shadowimages of gasoline spray.The influence of injection pressure, some key factors of GDI engine controlparameters, like injection pulse width, intake port pressure drop and valve lift werestudied. The result shows that:1) As the injection pressure increases, the penetrationincreases, the influence of intake airflow reduces, so the probability of fuelimpingement on cylinder increases.2) The injection pulse width has no markedimpact on fuel impingement.3) The intake airflow has pattern offset, extrusion anddiffusion effect on spray inject process. This effect is increased with higher portpressure drop when fixed valve lift, and it first increases then decreases with valve liftrises.4) The intake airflow also affects the regional distribution of the wall wettingarea. When fixed the valve lift, wall wetting region falls down and the sprayimpingement becomes not very obvious when the port pressure drop increases. Whenfixed the port pressure drop, wall wetting region falls down a little more in mediumvalve lifts.5) Combined with the position of spray tip and the piston can predict thesituation of spray impingement on the top of piston. It is evident that later injectiontimings could avoid spray impingement. A lower injection pressure and a fasterengine speed, make the critical injection timing smaller. This Paper also has do simulation about the spray process under different intakeairflows. The result shows that, it is the airflow which flows near the wall make thespray offset and reduce the impingement fuel mass. The spray injection at the centerof the cylinder promotes air movement, which improve the turbulent kinetic energy,and promote the formation of mixture gas.