Study On Spray、Combustion And Soot Generation Characteristics Of Kerosene/Diesel Blends

In order to simplify the fuel supply system in the modern battlefield and improve the efficiency of logistical support,the application and research of a single fuel has been widely focused on by many researchers in recent research.Aviation kerosene,whose physical and chemical properties is between gasoline and diesel,have become the most promising option of single fuel.It’s found that the direct use of pure aviation kerosene in diesel engines results in some problems from Current studies,such as severe fuel injection system wear and poor combustion stability;The blends that aviation kerosene with diesel or biodiesel fuels possess the potential to improve diesel engine performance and reduce emissions.Therefore,the spray,combustion and emission research of jet fuel/diesel blended fuels with a wide blending ratio in a wide range of diesel engine operating conditions is noteworthily meaningful for the development of a single fuel on the battlefield.Based on the constant volume combustion chamber heated by electricity,which simulates the high temperature and high pressure thermodynamic environment in the cylinder at the compression top dead center of the diesel engine through the electric heating and high-pressure gas charging,the experiments were conducted by utilizeing schlieren method,backlight method,high-frequency backlight extinction method,wide-area low-pass filtering method and other optical diagnostic methods.Then the effects of kerosene blending ratio,ambient temperature and ambient oxygen concentration on the nonevaporating spray,evaporating spray,ignition and combustion,soot generation and distribution of kerosene/diesel blended fuels were analyzed through experimental datas obtained through self-written image processing technologyThe results show that the increase in the blending ratio of aviation kerosene RP-3 in the fuel has little effect on the breakup and atomization characteristics of nonevaporating spray.As the mixing ratio of RP-3 increases,the spray volume of the evaporating spray increases slightly,while the liquid phase penetration distance is significantly reduced,which indicates that the fuel spray with high RP-3 content is easier to evaporate,and obtain better oil and gas blending quality.Ambient temperature has little effect on the vapor phase penetration distance,spray cone angle and spray volume of the evaporating spray,but as the ambient temperature increases,the liquid phase penetration distance is significantly reduced,and the proportion of fuel gas in the evaporating spray increases.Comparing different fuels,the ambient temperature has a greater impact on the liquid phase penetration of low RP-3blending ratio fuels.The ignition delay of fuel is mainly dominated by the cetane number,and the cetane number of aviation kerosene RP-3 is low,resulting in the increase of ignition delay of fuels with the increase of RP-3 content in fuel.When the ambient temperature is high(950 K),the increase of RP-3 content makes the ignition position gradually longer;The quasi-steady flame lift length of the blended fuels is similar to that of diesel,but significantly lower than that of aviation kerosene,indicating that the combustion properties similar to pure diesel can be obtained by adding a certain amount of diesel into aviation kerosene at high ambient temperature.The mixing ratio of RP-3 has little effect on the peak of integrated flame illumination and the time to peak.When the ambient temperature is low(830K),the fuel spray characteristics are quite different.The ignition position is determined by the ignition delay and the spray characteristics.With the increase of RP-3 blending ratio,although the ignition delay period is gradually increasing,the ignition position is not obvious.With the increase of RP-3 blending ratio,the peak value of integrated flame illumination shrinks obviously,and the time to reach the peak value is obviously delayed,which indicates that RP-3 blending can significantly reduce soot emission in low temperature combustion.The higher RP-3 content in fuel,the more obvious the influence of ambient temperature and oxygen concentration on ignition and combustion process.With the increase of ambient temperature and oxygen concentration,the ignition delay,ignition position and quasi-steady flame lift length decrease,and the peak flame area and integrated flame illumination increase.Subsequently,the generation of soot from blended fuel oil was quantitatively studied by the high-frequency backlight extinction method.With the increase of RP-3 content,the amount of soot production shrinks,and the blending of RP-3 at low ambient temperature has a more obvious inhibitory effect on the generation of soot.When the ambient temperature and ambient oxygen concentration increase,the peak of soot mass increases and the time of the peak arises delays.In the later stage of combustion,soot emissions are higher under low ambient oxygen concentration conditions,because the EGR environment inhibits the generation and oxidation of soot at the same time,but it has a stronger inhibitory effect on soot generation.In general,the combustion performance of R50 is similar to that of diesel under various test conditions,and the soot emission is reduced,which is very suitable for diesel engines and can reduce soot emission.In addition,the physical properties of R50 are close to those of aviation kerosene,so it has the potential to become a single fuel.