Visualization Study On Spray And Combustion Characteristics Of Gasoline/Hydrogenated Catalytic Biodiesel Blends Under The Double-Injection Strategy

With the increasingly serious energy and environmental problems,efficient and clean combustion of diesel engine has become a hot research topic.As a new combustion method,GCI utilizes the high octane number and high volatility of gasoline to ensure a large proportion of premixed low temperature combustion,thereby reducing nitrogen oxides and soot emissions.But there are also problems such as easy to misfire under low load and rough work under high load.Optimizing fuel properties and adjusting injection strategies are effective solutions.Based on the previous research group’s research on Hydrogenated Catalytic Biodiesel,this paper proposes to blend gasoline with Hydrogenated Catalytic Biodiesel of high cetane number to improve the ignition performance of the fuel,thus providing a way to achieve GCI combustion.In this paper,the blended fuels of G80H20 and G60H40 were prepared by blending gasoline and biodiesel at a mass ratio of 4: 1 and 3: 2.Single-injection and double-injection methods were used to carry out spray combustion visualization tests of different proportions of blended fuels and pure diesel(D100)in a constant volume combustion chamber.The effects of pilot injection pulse width and dwell time on the main injection process were analyzed.The spray characteristics of non-fire conditions(filled with nitrogen in the CVCC)were studied by the Schlieren and the Shadowgraph.The results showed that the spray vapor penetration of the main injection of the blended fuels and pure diesel continues to increase with the injection time,and the liquid penetration of the main injection increases to the maximum value and stabilizes.The spray vapor cone angle and the liquid cone angle of the main injection will also reach a stable state after a period of injection.Compared with pure diesel,the vapor penetration of the blended fuels distance of the main injection is similar,and the vapor cone angle is larger,while the liquid penetration and the liquid cone angle are both smaller,especially the blended fuel with high proportion of gasoline.Compared with the single-injection,the main injection of the double-injection has a larger vapor penetration,a smaller vapor cone angle,a smaller liquid penetration,and a larger liquid cone angle.Increasing thedwell time,the main injection vapor penetration decreases,the vapor cone angle increases,the liquid penetration increases,and the liquid cone angle decreases.The combustion characteristics under fire conditions(filled with air in the CVCC)were studied by the Schlieren and the Chemiluminescence.The results showed that:In the single-injection,the blended fuels and the pure diesel both form the ignition point at the head area of the spray first,and then the flame develops upstream.The flame distribution is relatively concentrated.The ignition delay of the blended fuels were longer than that of pure diesel,and the flame lift-off length was longer than that of pure diesel,the liquid length is shorter than that of pure diesel,and the difference between the flame lift-off length and the liquid length is bigegr than that of pure diesel.As the proportion of gasoline increases,the ignition delay of the blended fuels increases,the flame lift-off length increases,the liquid length decreases,and the difference between the flame lift-off length and the liquid length increases.In the double-injection,the main injection starts burning directly in the middle of the oil beam.The flame distribution is relatively dispersed and uniform,flame area is larger.The ignition delay of the main injection of the blended fuels is shorter than that of pure diesel,the flame lift-off length is shorter than of pure diesel,the liquid length is shorter than that of pure diesel,and the difference between the flame lift-off length and the liquid length is bigger than that of pure diesel.As the proportion of gasoline increases,the ignition delay of the main injection decreases,the flame lift-off length decreases,the liquid length decreases,the difference between the flame lift-off length and the liquid length increases.When increases the pulse width of the pilot injection,the ignition delay of the blended fuels and pure diesel main injection decreases,the flame lift-off length decreases,the liquid length decreases,the difference between the flame lift-off length and the liquid length decreases.When increases the dwell time,The ignition delay of the blended fuels and pure diesel main injection increases,the flame lift-off length increases,the liquid length increases,and the difference between the flame lift-off length and the liquid length increases,which is beneficial to reduce the generation of soot.In this paper,the spray and combustion performance of three differentproportions of blended fuels were studied,especially the double-injection method is used to obtain the spray and combustion characteristics of the main injection under different pilot injection and different dwell time,as well as the influence mechanism between the pilot injection and the main injection is obtained,which can provide some valuable conclusions for guiding the combustion process of GCI.