Study of Direct Injection Gasoline Combustion Using Constant-Volume Combustion Vessel

(Diagnostics of Stratification Degree in Relation to Major Design Factors)

Abstract

Stratification features in DI gasoline combustion were studied using a constant-volume combustion vessel. Indicated pressure analysis and high-speed combustion observation were carried out by changing injection-sparking interval τ_int, spray cone angle and swirl ratio. There exists a τ_int range where the mixture is ignitable and the shortest τ_int gives the highest maximum pressure rise rate (dP/dt)_max and the highest (dP/dt)_max reaches a maximum at a certain swirl ratio. The fairly large scatter found in(dP/dt)_max data plotted against τ_int is markedly reduced by plotting them against total ignition delay τ_tot(=τ_int+τ_d), where τ_d denotes ignition delay. Maximum volumetric burning velocity (S_v)_max was proposed as a measure of the stratification degree, based on the thermodynamic analysis which was carried out under the concept that a higher stratification degree increases the stoichiometric range of the mixture. It is noteworthy that as the spray cone angle is increased, (S_v)_max increases and becomes less affected by SR.