Mixing conditions with spray-jet interaction for effective soot reduction in diesel combustion

The authors have reported significant reductions in particulate emissions of diesel engines by generating strong turbulence during the combustion process. This study aims to identify optimum conditions of turbulent mixing for effective soot reduction during combustion. The experiments were conducted with a constant volume combustion vessel equipped with a jet-generating cell, from where a small amount of fuel is injected during the combustion of the main spray. The jet from the cell impinges the main flame, causing changes in the mixing of fuel and air. Observation was made for a variety of combustions distances between spray nozzle and jet orifice and different directions of impingement. It is shown that compared with the case without jet flame soot decreases when the jet impinges. When the jet is very close to the flame it penetrates the soot cloud and causes little mixing. There were no apparent differences in the combustion duration when the direction of impingement was varied, although the mechanisms of soot reduction seemed different. An analysis of local turbulent flows with PIV (Particle Image Velocimetry) showed the relationship between the scale of the turbulence and the size of the soot cloud.