Effect of flat-wall impingement on diesel spray combustion

The effect of spray-flat-wall interaction on the diesel combustion characteristics in a constant-volume vessel was investigated. A flat wall was fixed perpendicular to the nozzle hole axis. Three injection pressures of 100 MPa, 150 MPa and 200 MPa and a single nozzle hole with a diameter of 0.133 mm were employed. Mie scattering was adopted to detect the spray formation process; OH∗ chemiluminescence and natural colour luminosity were conducted to analyse the combustion process. The two-colour method was applied to calculate the soot emissions and the temperature distribution. The results reveal that, in comparison with a free spray flame, flat-wall impingement causes diesel combustion to deteriorate when the liquid phase-wall interaction occurs; however, when an appropriate impinging distance (longer than liquid-phase penetration) is selected, combustion is observed to be enhanced. As for the impinging spray flame, when the injection pressure is increased, soot formation decreases; however, combustion is not linearly enhanced by increasing the injection pressure, and the OH∗ chemiluminescence intensity achieves the highest value with an injection pressure of 150 MPa.