Combustion Characteristics of Wall-Impinging Diesel Fuel Spray under Different Wall Temperatures

The flame structure and combustion characteristics of wall-impinging diesel fuel spray were investigated in a high-temperature high-pressure constant volume combustion vessel. The ambient temperature (T_a) was set to 773 K. The wall temperatures (T_w) were set to 523 K, 673 K and 773 K respectively. Three different injection pressures (P_i) of 600 bar, 1000bar and 1600bar, two ambient pressures (P_a) of 2 MPa and 4 MPa were applied. The flame development process of wall-impinging spray was measured by high-speed photography, which was utilized to quantify the flame luminosity intensity, ignition delay and flame geometrical parameters. The results reveal that, as the wall temperature increases, the flame luminosity intensity increases and the ignition delay decreases. At the condition of P_a = 2 MPa, the flame height increases as the wall temperature increases; the ignition position is always observed in the wall jet region firstly and the distance between the ignition position and the axis of the spray decreases as the wall temperature increases; the region of high luminosity intensity is observed in the head vortex region. At the condition of P_a = 4 MPa, the flame height decreases as the wall temperature increases; the ignition position is observed in the impingement region firstly and the region of high luminosity intensity appears in the location near the wall. As the injection pressure increases, the flame luminosity intensity decreases. Finally, it can be concluded that the change of the wall temperatures mainly affects the flame luminosity and the ignition delay. The change of the ambient pressures mainly affects the flame height and the ignition position. For injection pressure, its change mainly affects the flame luminosity.