柴油喷雾撞壁形态和油束发展特征

Shape and Development Characteristics of a Wall-Impinging Diesel Spray

在一台高温、高压定容燃烧弹上研究了不同撞壁距离、喷射压力和环境温度与压力条件下,柴油油束撞壁后近壁面区域的喷雾特性.利用高速摄像测量了自由喷雾和撞壁喷雾的油束发展历程,并结合仿真对燃油气相浓度和流场特性进行分析.结果表明:在环境温度为500~900,K、环境压力为1~4,MPa时,喷射压力对喷雾锥角影响较小;环境温度达到700,K及以上时,喷射压力对喷雾贯穿距的影响较小,特别当撞壁距离减小到30,mm和20,mm时,出现喷雾贯穿距随喷射压力增大而略微减小的趋势;相对于撞壁喷雾,环境温度对自由喷雾贯穿距的影响更大;随着撞壁距离减小,喷雾贯穿距逐渐减小,喷雾锥角逐渐增大,而喷雾高度则呈现先增大后减小的趋势.在上述4种边界参数中,撞壁距离对撞壁油束发展特征影响最大.

The near-wall spray characteristics of a diesel jet after impingement under the conditions of different im- pinging distance, injection pressure, ambient pressure and temperature in a high-temperature high-pressure constant volume combustion vessel were investigated. The development process of the free spray and impinging spray was measured by using high-speed photography. And also, the vapor concentration and flow field during the fuel injection development were analyzed with the CFD simulation. The results show that, the injection pressure has a little influ- ence on the spray cone angle at the ambient temperature of 500---900 K and the ambient pressure of l---4 MPa. It also has a little effect on the spray penetration when the ambient temperature is up to 700 K or more. in particular, the spray penetration has a trend of slight reduction with the increase of the injection pressure when the impinging distance reduces to 30 mm and 20 mm. The ambient temperature is found to have a greater influence on the free spray penetration in comparison with the impinging spray. In addition, as the impinging distance reduces, the spray penetration decreases and the spray cone angle increases as well, but the height of impinging spray firstly increases and then de- creases. Among the four kinds of boundary parameters mentioned above, the impinging distance has the most influ- ences on the development characteristics of wall-impinging diesel spray.