A Study On Spray Characteristics Of High-Pressure Fuel Injection For D.I. Diesel Engine

This thesis describes an investigation of the fuel spray characteristics under high pressure fuel injection for medium duty truck diesel engines. The experiment was carried out in a wind tunnel specially designed for studying the spray characteristics in an air flow field. The spray characteristics of both free spray and spray with fuel impingement upon wall were studied by means of high- speed schlieren photography and MALVERN Laser Diffraction Particle Sizer for injection pressure between 60-100MPa Considering the situation of this country, a combustion system with high pressure injection between 80-100MPa and low swirl ratio may be applied, so several helical inlet ports of low swirl ratio were developed.The results of high-speed photograph under the condition of free spray show that under the condition of high pressure fuel injection the time of fuel drop breakup is shorter, the spray penetration and spray tip velocity decrease quickly against the injection time, and the phenomena of air entrainment appears early. A two -dimension spray model on the theory of gaseous jet was used to calculate both spray penetration and spray tip velocity. The results prove that the spray model on base of gaseous jet can calculate the developing process of spray well. The measurements of drop size show that the sauter medium diameter is smaller and the drop-size distribution is much uniform,The results of spray impingement on a wail show that the wall temperature has a strong influence on the ratio of fuel drops rebounded after spray impact ion. In the air environment, much fuel accumulate in the region near the wall after spray impact ion. At the wall temperature of 538K, the high- speed photography shows that, the air entrainment appears obviously due to heat radiation from wall. Under the condition of smaller orifice and higher pressure injection, the spray tip velocity decrease obviously before impact ion, and there is a richer fuel region over the impingement region. The wall temperature has strong effect on the fuel drops rebound and vaporization espically at the temperature of 573K. It shows that the proper wall temperature will promote...