Effect Of Oxygenated Fuel On Combustion And Soot Generation Of Compression Ignition Engines

Petrochemical energy consumption and environmental pollution have become two major problems in the development of automotive internal combustion engines.The development of alternative fuels is not only an important measure to alleviate the oil crisis,but also based on fuel design and fuel composition reconstruction is also important to achieve efficient combustion of internal combustion engines.In recent years,the development of oxygen-containing biomass clean alternative fuels has attracted wide attention from scholars at home and abroad.Because of its self-supporting oxygen characteristics,it can effectively reduce the soot,HC and CO emissions of engines,which creates conditions for coupling combustion boundary conditions and further improving the "trade off" relationship between the NOx and soot of the compression ignition engine.The soot emission of the engine seriously affects the environment and human health.Therefore,an in-depth understanding of the combustion process of the engine and the process of generating soot helps to find practical technical measures to reduce soot emissions from the source.In this study,the optical test method was used to test the combustion of ignited fuel in the compression ignition engine and the generation of soot.The combustion process and soot generation process of the oxyfuel with different oxygen content and different molecular structure were explored.The influence law reveals the extent and extent of the influence of coordinated control of oxygenated fuel and combustion boundary conditions on the soot generation characteristics of compression ignition engines.This study is based on a compression ignition optical engine and builds an engine combustion optical diagnostic test platform.The high-speed photography method was used to collect the image of the combustion flame in the engine cylinder.The dynamometer analysis method was used to analyze the combustion pressure and heat release law in the cylinder.The two-color method was used to obtain the in-cylinder temperature field and characterize the soot during the combustion process.Based on the KL factor of concentration,the combustion history and soot generation characteristics of the compression-ignition engine fueled with oxygenated fuel were analyzed.The main research contents include: 1)Using coal-based synthetic diesel(CTL)as the base fuel,blending 15% and 30% n-butanol respectively to prepare test fuels with different oxygen contents,and exploring different proportions of n-butanol/CTL mixed fuel Combustion and soot generation under different injection parameters and different intake oxygen concentrations.2)Using CTL as the base fuel,blending 15% n-butanol and 5% dimethyl carbonate(DMC)respectively to prepare oxygenated mixed fuel with the same oxygen content and different molecular structure,and exploring the influence of molecular structure of oxygenated fuel on combustion and soot formation.3)The experimental fuels with different oxygen contents were prepared by blending 15% and 30% n-butanol respectively with the national fifth diesel fuel as the base fuel,to explore the combustion and soot generation rules of n-butanol/diesel fuel with different proportions under the conditions of different injection parameters and different intake oxygen concentrations.Furthermore,the combustion and soot generation characteristics of n-butanol /CTL and n-butanol/diesel were compared and analyzed to explore the influence of n-butanol on the combustion and soot generation of fuels with different physical and chemical characteristics.The main findings are as follows:1)For butanol/CTL mixed fuel,as the blending ratio of butanol increases,the self-carrying oxygen in butanol inhibits the formation of soot during combustion,reduces the radiant luminescence of soot particles,and makes the bright flame disappears,the high temperature flame region and the large KL factor distribution area are greatly reduced,the combustion duration is shortened,and the burning rate is increased.Because the latent heat of butanol vaporization is larger than CTL,the low calorific value is lower than CTL,and after blending butanol,the peak value of the cylinder pressure and heat release rate is reduced.The effect of blending butanol greater than 15% has a weaker effect on combustion and soot formation.The effects of butanol on combustion and soot formation were not significantly different under different fuel injection parameters.2)The effects of fuel oxygen and ambient oxygen on CTL combustion and soot formation indicate that blending butanol and increasing the concentration of intake oxygen in CTL will inhibit the formation of soot during combustion and reduce the area of high-brightness flame.The existence time of the large-area flame is shortened,the KL factor distribution area is reduced,and the soot formation during the combustion process is in the transition region from the flame high temperature to the low temperature,which is the edge portion of the intense combustion region in the flame image.The increase of the ambient oxygen concentration shortens the retardation period.Compared with the ambient oxygen concentration,increasing the oxygen concentration of the fuel has a greater influence on the flame brightness and flame area of the combustion process,and the amount of soot generated during the combustion process is less.3)The combustion characteristics of butanol/CTL and DMC/CTL mixed fuels indicate that the molecular structure of oxygenated fuel has different effects on the combustion and soot generation process.The retardation period of DMC/CTL mixed fuel is shorter than that of butanol/CTL.The flame area and flame brightness during combustion are larger than those of butanol/CTL.Compared with DMC,butanol has better effect on reducing the temperature of the flame zone and suppressing the formation of soot during combustion.4)For the butanol/diesel blended fuel,as the blending ratio of butanol increases,the large-area high-brightness flame becomes a sporadic flame,and when the butanol blending ratio is 30%,the moment when the combustion flame appears is obviously shifted back,and at the same time The high temperature flame region and the large KL factor distribution area are significantly reduced.This is because the self-carrying oxygen atom of butanol increases the oxygen concentration in the combustion zone,inhibits the formation of soot during combustion and enhances the late oxidation of soot.,reducing the radiant luminescence of soot particles.With the increase of the blending ratio of butanol,the retardation period is prolonged and the combustion duration is shortened.The longer retardation period makes the combustion mainly premixed combustion,and the peak of the heat release rate curve increases,but the cylinder pressure is due to the ignition lag.The peak value of the curve is reduced.When the blending ratio of butanol is 15%,the effect on diesel combustion and soot formation is weak.When the blending ratio is 30%,it has a great influence on combustion and soot formation.The effects of butanol on combustion and soot formation were not significantly different under different fuel injection parameters.5)The effects of fuel oxygen and ambient oxygen on diesel combustion and soot formation show that with the increase of intake oxygen concentration,the retardation period is significantly shortened,the premixed amount of mixed gas is reduced,the premixed combustion ratio is reduced,and the combustion duration is reduced.When the temperature is extended,the peak value of the heat release rate is lowered,the peak value of the cylinder pressure curve is increased,the inhibition effect of ambient oxygen on the formation of soot in the combustion process is weakened,and the area of the bright flame area and the distribution area of the KL factor are increasing.Increasing the effect of fuel oxygen concentration on combustion and soot formation is contrary to increasing the ambient oxygen concentration,but both the ambient oxygen concentration and the fuel oxygen concentration have a greater impact on combustion and soot formation when the ratio of increase is larger.6)The combustion characteristics of butanol/diesel and butanol/CTL mixed fuels indicate that the butanol/diesel and butanol/CTL retardation periods are prolonged as the butanol blending ratio increases,but butanol/diesel The extension of the retardation period is relatively obvious,the peak of the combustion heat release rate of butanol/CTL decreases,and the peak of the combustion heat release rate of butanol/diesel increases,and the former decreases more than the latter.As the blending ratio of butanol increases,the combustion flame darkens,and the combustion flame of butanol/CTL is darker.The combustion flame of butanol/diesel appears to lag behind,appearing in the downward process of the piston,and in the stage of diffusion combustion.More pointy flames.The two-color method showed that the flame temperature and KL factor decreased with the blending ratio of butanol,and the flame temperature of butanol/CTL and the KL factor of flame region were more obvious,indicating the ratio of different fuels to butanol blending.Sensitivity is different.The effect of butanol on CTL combustion and soot formation is greater than that of diesel.Butanol/diesel only has a greater effect on the combustion and soot formation process when the butanol blending ratio is 30%,however,the butanol/CTL blending ratio of butanol is 15%,which can significantly reduce the temperature and soot concentration in the high temperature combustion zone.