Stratification Features of Swirl Nozzle Sprays and Slit Nozzle Spray in DI Gasoline Combustion

The stratification feature of DI gasoline combustion was studied by using a constant volume combustion vessel. An index of stratification degree, defined as volumetric burning velocity, has been proposed based on the thermodynamic analysis of the indicated pressure data. The burning feature analysis using this stratification degree and the fuel vapor concentration measurement using He-Ne laser ray absorption method were carried out for the swirl nozzle spray with 90° cone angle and the slit nozzle spray with 60° fan angle. Ambient pressure and ambient temperature were changed from atmospheric condition to 0.5∼0.6 MPa and 465 K, respectively. Air Swirl with swirl ratio of 0∼1.0 were added for the 90° swirl nozzle spray. Single component fuels with different volatility and self-ignitability from each other were used besides gasoline fuel. The major findings are as follows. High ambient temperature improves stratification degree due to the enhanced fuel vaporization and vapor diffusion. But, too high volatility condition such as highly volatile and poorly self-ignitable fuel combined with high ambient temperature and high swirl ratio deteriorates the stratification degree. These feature well correlates to the fuel concentration distribution measured. The stratification feature with the 60° slit nozzle spray is more sensitively affected by the volatility in the above mentioned broad sense and the spark position than the 90° swirl nozzle spray. The optimized spark gap position with the 60° slit nozzle spray brings about much higher stratification degree than that with the 90° swirl nozzle spray, though the former does not always results in stable stratification at low ambient temperature.