Research On Spray Combustion Of Multi-component Fuel Based On Swirl Injector

The spray combustion of multi-component fuel based on swirl injector is proposed aiming at the efficient stable combustion of a gas generator,which is applied in the ground test of the scramjet engine.The atomization,droplet evaporation and combustions subprocess during the spray combustion of hydrous ethanol are researched respectively using experiment as well as theoretical analysis.The thesis aims to improve the combustion efficiency and stability by investigating the basic issues including the interflow and spray characteristics of swirl injector,the multi-component droplet evaporation and the response to the oscillation of background pressure as well as analyzing the characteristics and principles of the spray combustion of hydrous ethanol in gas generator.The spray experiment of transparent swirl injector was conducted firstly,observing and validating the stationary surface wave structure of the interflow.The influence of inlet Reynolds number and the layout of tangential channels on the interflow pattern were analyzed,and the phenomenon of air core oscillation in the swirl chamber was discovered.For a quantified analysis,an optical calibration of the spray image was conducted,and the liquid film thickness and the air core diameter were extracted.The liquid film thickness at outlet is focused on and a experimental correlation of the liquid film thickness applicable to the swirl injector used in this thesis is put forward,and the effect of outlet expansion angle on the liquid film thickness is considered.The comparative analysis is used in the research of the influence of the layout of single/double rows of tangential channels,the number of channels as well as the row distance on the flow and atomization characteristics in the spray experiment,finding that the primary atomization is worsened when the row of the tangential channels increased from 1 to 2.The design of “more channels with smaller diameter” is better in primary atomization than “less channels with bigger diameter”.The perception of dimensionless row distance is proposed and optimized for a better atomization performance.A method to obtain the liquid film thickness downstream the outlet based on the spray image is proposed and validated.A multi-component droplet evaporation is established,and an application analysis of the vapor-liquid phase transition model is conducted,gaining a vapor-liquid phase transition model which is applicable to the ethanol-water system.Using this evaporation model,the evaporation characteristics of ethanol-water droplet bi-component under stable pressure and relative velocity are investigated,respectively.The pressure and temperature effect as well as the species concentration influence are analyzed,especially the response of ethanol-water evaporation to the background pressure oscillation,obtaining the response principles of droplet temperature,evaporation speed,separation factor and droplet lifetime to pressure oscillation.The results can contribute to analyzing the relationship between the evaporation subprocess and combustion instability.Finally,the spray combustion characteristics and principles of hydrous ethanol are researched,discovering that the combustion efficiency decreased with increasing excess oxygen coefficient.The analysis indicates that because of the lower total temperature of hydrous ethanol combustion and the long characteristics time of ethanol-water droplet evaporation,either increasing the oxidant mass flow rate or decreasing the fuel mass flow rate will lead to more spray droplets out the combustor lower combustion efficiency.The combustion stability of hydrous ethanol-oxygen full-scale gas generator is analyzed,discovering that the unstable combustion indicates as two patterns,that is,disordered oscillation(rough combustion)and ordered oscillation(low-frequency unstable combustion).