Visualization Study On Spray Impingement On The Wall And Combustion Processes In A Gasoline Engine

Direct injection（DI）and air dilution can improve the thermal efficiency of gasoline engines and reduce fuel consumption.In order to understand the dependence between the spray characteristics of direct injection and the combustion of gasoline engines,the development characteristics of spray-wall interaction in a constant volume bomb were studied by using schlieren methods.Then the heat release process and flame development process under the conditions of direct injection and port fuel injection at1000 r/min in an optical engine were studied.The main conclusions are as follows:After direct-injection gasoline impinge the wall,the pattern of the spray on the left and right sides of the collision point changes greatly.The spray moving to the right side entrains the surrounding gas,forming a counterclockwise swirling area in the late stage of the fuel injection,reducing the spray development to the outside.Increasing the fuel injection pressure,reducing the ambient pressure and the collision distance can help reduce the area of dense spray area near the wall and increase the spray area.The fuel injection parameters have little effect on the characteristics near the left side of the wall.When the excess air ratio is 1.4,the spark time（ST₁）is-20°CA after top dead center（ATDC）,the spark time（ST₂）is-17.6°CA ATDC,the first direct injection time（SOI₁）is fixed at-160°CA ATDC.When the second injection time（SOI₂）is delayed from-40°CA ATDC to-30°CA ATDC,the combustion process happened earlier and the combustion duration is shortened,indicated mean effective pressure（IMEP）increased by 12%,and under the same ignition strategy,when the port fuel injection is adopted,the combustion duration of the gasoline engine is longer than that under the direct injection condition,and the peak heat release rate and IMEP are also lower than that under the direct injection condition.After the SOI₂,the flame appears earlier in the direct injection condition than the port fuel injection,and the initial flame development speed and light intensity are greater.When ST₁ is fixed at-20°CA ATDC and ST₂ is postponed from-17.6°CA ATDC to-15.2°CA ATDC,the flames under both direct injection and port fuel injection conditions appear after ST₂.At the same moment,the area and brightness of the combustion flame under direct injection conditions are greater than that of port fuel injection,but under direct injection conditions,yellow flames are more likely to be produced.Under port fuel injection,keep ST₁ at-20°CA ATDC,ST₂ at-17.6°CA ATDC,and increase the total discharge energy from 103.4m J to 162.1 m J,the ignition of the gasoline engine is advanced,the combustion duration is shortened,and at the same crankshaft angle,the flame area and relative light intensity are greater,and the IMEP and indicated thermal efficiency are increased by 24.5%and26.7%.