Study On The Characteristics Of Ultra-High Injection Pressure Spray And Emissions From A Dual-Injection System Engine Fueled With Gasoline And Ethanol

Nowadays,with the increasingly prominent problems of energy and environment,the requirements for improving fuel consumption and reducing the emission of internal combustion engines have become a much bigger concern.Especially,the particulate matter emission of GDI engine has become a research hotspot in the field of internal combustion engines.This research work based on the support of by the national natural science foundation of China“fundamental study on fuel spray impingement phenomena and interaction mechanism with oil film in gasoline direct injection engines”and the national key technology R&D program of China“development and application of supercharged gasoline direct injection engine with high efficiency and low emissions”.This research mainly focuses on particulate matter emissions of GDI engine,conducted a study of a dual-injection system engine fueled with gasoline and ethanol,to explore the potential of further reducing the particulate emissions of GDI engine,with the technology of oxygenated fuel(ethanol),ultra-high injection pressure spray and dual-injection system.Firstly,the effects of ultra-high injection pressure on macroscopic and microscopic characteristics were studied for free spray and wall spray of GDI injector with the schlieren method and PDPA test systems.Then,under the typical small load and high load working conditions,the emission characteristics of the dual-injection system engine were studied under three different injection modes of G-E,E-G and G-G,and the exploration of reducing particulate matter emissions using parameters of injection control was conducted.The conclusions of the research can be summarized as below.The results for the effect of the ultra-high injection pressure on macroscopic spray characteristics are as follows.For free spray,the occurrence time of branch-like structure became earlier and the amount increased,and the spray is more likely to break.There was an increasing trend for cone angle,penetration,area and irregular ratio as the injection pressure increased.However,under the ultra-high injection pressure,the effect of increasing injection pressure became weak for penetration and area,and the area ratio of core spray decreased obviously.The spray angle,penetration,area and irregular ratio of gasoline spray are slightly larger than that of ethanol.The penetration and the possibility of spray-wall impingement would not increase a lot.For impingement spray,under ultra-high injection pressure,the time of spray-wall impingement became much earlier.The rebound height,diffusion distance and area of impingement spray also increased significantly.The rebound height of gasoline spray is larger than that of ethanol,but the diffusion distance and area are close to that of ethanol spray.Under ultra-high injection pressure,the air-fuel mixture was enhanced,which helps reduce the rich fuel area,thus inhibiting the formation of particulate matter.The results for the effect of the ultra-high injection pressure on microscopic spray characteristics are as follows.For free spray,compared with the 10 MPa ordinary injection spray,the normal velocity and tangential velocity of droplet increased significantly.The probability of droplet diameter became more concentrated in smaller size,and the proportion of stripping region and explosive fragmentation region increased a lot.Thus,the atomization of spray enhanced which helped to reduce the generation of particulate matter during combustion.Compared with the ethanol spray,droplets of gasoline spray had higher speed,smaller size and better atomization effect.According to the prediction of the droplet about to hit the wall with the Bai-Gosman model,the adhesion and spreading ratio of the spray particles decreased and the splash ratio increased under the ultra-high pressure injection.According to the prediction of Bai-Gosman impingement spray model,for the spray particles that were approaching the wall under ultra-high injection pressure,the proportion of adhesion and spread decreased,the splash ratio increased,and the splash ratio of droplets for gasoline spray was higher than that of ethanol spray.The microscopic characteristics of the impingement spray presented that under ultra-high injection pressure,the crushing degree of impingement spray was promoted and some droplets had higher rebound velocity,however,the average normal velocity and tangential velocity slightly decreased due to the stronger irregularity of the droplets'movement direction.Furthermore,under ultra-high injection pressure,the SMD of droplets for impingement spray reduced obviously,leading more homogeneous air-fuel mixture.For impingement spray,the SMD of gasoline's droplets is smaller than that of ethanol,but the gap between them significantly narrowed with ultra-high injection pressure.The simulation results showed that under the ultra-high pressure injection,the distribution area of the impingement spray became more dispersed and its edge folds increased,which was useful to promote the vaporization of the impingement spray,leading a reduction for the formation of particulate matter during combustion.The results for the emission characteristics of the dual-injection system engine fueled with gasoline and ethanol are as follows.With the increase of ethanol mass ratio(),the combustion phase was optimized and fuel economy improved obviously.The G-E mode presented the best fuel economy with a higher.The emissions of CO,NO_X,HC and particulate matter were obviously affected by the injection mode and injection ratio.With the increase of,the emission of CO showed an obvious decrease trend,especially under the 1 MPa condition.The reduction of NO_X emission for G-E mode is larger than that E-G mode.HC emissions decreased significantly for both two injection modes.The G-G injection mode presented the worst particulate matter emission level.With the increase of,compared with gasoline,ethanol was more helpful to inhibit the generation of particles and improve the oxidation activity of particles,leading a significant reduction for the emission of particulate matter.For the dual-injection system engine fuelled with gasoline and ethanol,particulate matter emission level reduced effectively by optimizing injection control parameters.An appropriate direct injection timing or increasing injection pressure could decrease particulate matter emissions,and it was more effective under the E-G mode.For port fuel injection,the injection timing during a closed intake valve was very effective for reducing particles under G-E mode.Double injection strategy within a certain time frame could inhibit the emission of particulate matter,and the effect would be more obvious when a relatively high proportion of the second injection.