Study of Direct Injection Gasoline Combustion Using Constant-Volume Combustion Vessel. Diagnostics of Stratification Degree in Relation to Major Design Factors.

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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 τint, spray cone angle and swirl ratio. There exists a τint range where the mixture is ignitable and the shortest τint 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 τint is markedly reduced by plotting them against total ignition delay τtot(=τint+τd), where τd denotes ignition delay. Maximum volumetric burning velocity (Sv)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, (Sv)max increases and becomes less affected by SR.