Optical Test Research On The Effects Of Fuel Characteristics On Spray And Combustion Process In CI Engine

CI engine has excellent dynamic and economy performance as well as poor NOx and soot emission performance.By using oxygenated fuels,optimizing fuel injection parameters,using EGR stratification,and utilizing advanced optical testing techniques,the research on the key issues that affect the process of engine combustion and emissions is significant for achieving high efficiency cleaning combustion in CI engine.In this paper,a constant volume bomb test platform and an optical engine test platform were built.Comprehensive study was carried on the effect of fuel characteristics,injection parameters and EGR stratification on the spray,combustion and soot emission in CI engine by high-speed imaging method.The research can be divided into three parts:1)F-T synthesis diesel(F-T)and its blended with 5%DMC(D05),10%DMC(D10)and 15%n-butanol(B15)were used in the study on fuel spray characteristics in constant volume bomb test platform,analyzed the penetration,spray angle and spray area.2)Did Research on the effect of injection parameters and fuel spray characteristics on combustion flame propagation process in optical CI engine.And then conducted experimental research on the effect of fuel characteristics on combustion process in CI engine,analyzed the effect of fuel characteristics on combustion process from four aspects by specific combustion position,different crank angle,flame area and Red channel flame image.The influence of fuel oxygen content and oxygen-containing functional groups on combustion characteristics was studied.3)Studied the effect of fuel characteristics,EGR rate and EGR stratification method on the temperature and KL factor of combustion process.The main conclusions are as below:1)Spray characteristics test result showed that spray penetration,near field spray angle,far field spray angle and spray area were increased with the injection pressure increases,the reasonable increase of injection pressure could optimize the spray atomization.F-T diesel blended with DMC can also optimize the spray atomization.But F-T diesel spray atomization was worsened after blending with 15%butanol.2)Experimental results of the influence of fuel injection parameters on the development of macroscopic flames showed that with injection pressure increased,bright spot-like flame decreased,flake flame increased,ignition delay was almost unchanged while burning duration increased obviously.Injection angle was advanced gradually resulted in the rising of ignition delay,the decrease of ignition points,dark flame and the invariant flame area in the late combustion.And the increase of injection duration resulted in the increase of combustion duration but had almost no effect on ignition delay,the flame area and flame brightness increased at the same time.3)Study on the effect of fuel characteristics on combustion characteristics indicated that with the increase of DMC blending ratio,ignition delay increased and combustion pressure decreased,ignition points increased and distributed in the cylinder evenly,R channel value decreased so that bright flame changed into even low temperature flame.The difference between the combustion processes of D05 and B15 with the different oxygen-containing functional groups was that the combustion process of B15 was more gradual in the late combustion,and the flame area was larger in B15 and the flame brightness was darker.The blending of oxygenated fuel with F-T diesel can reduce soot production during combustion.4)With the increase of DMC blending ratio,both the combustion temperature and the combustion temperature gradient in the cylinder gradually decreased.The amount of soot produced during combustion decreased with increasing DMC blending.With the increase of EGR rate,the combustion temperature decreased gradually.EGR could reduce the combustion temperature,reduced NO_x emission and had little effect on soot emission.There were obvious differences in the combustion flame temperature,which sorted from largest to smallest was homogeneous>spiral catheter>spiral>tangential catheter>tangential.The sort of soot emission amount in five stratified forms was consistent with the sort of temperature field.5)The cooperation of oxygenated fuel and EGR stratification could reduce NO_x and soot emissions simultaneously.The use of oxygenated fuel could reduce the amount of soot generation during the combustion process.The spiral EGR stratification which form the radial stratification of thick in the middle and diluted around help to reduce the amount of NO_x generation,and had little effect on soot generation at the same time.