Study Of Effects On Spray Characteristics And Formation Factors Of Injector Deposition In GDI Engine

With the growth of the world's motor vehicle ownership,global energy and environmental issues are also increasingly prominent,more and more importance has been attached to GDI engine due to its fuel economy,dynamic performance and exhaust emission.Compared with the traditional PFI engine,the injector of GDI engine is directly exposed to the combustion environment in the cylinder,it is more easy to form carbon deposition in the injector head by the higher combustion temperature of the cylinder and the influence of the fuel combustion products.The deposition may affect the quality of the mixture,resulting in a decrease in the performance of the engine.This study combines the research status at home and abroad,carrying out the research of the effect of carbon deposition on the spray characteristics and the key factors influencing the formation of carbon deposition.Spray characteristics were studied to investigate the influence of the GDI engine's performance and the theoretical basis for the calibration and optimization of injector in the engine development process is also provided.This paper carried out a research on spray placement,far-field spray angle and penetration with the methods of Mie scattering,White LED scattering and backlighting.The research shows that when the injector is blocked,the area and the brightness of the placement are reduced,and the oil distribution is uneven,the droppoint barycenter of coking injector spreads outward compared to the clean injector,the offset of barycenter may lead to the spray-wall impingement resulting in deterioration of engine combustion and emissions.The placement stability and reproducibility of the spray become worse because of the fuel cavitation and the disturbance of the injector tip' s deposition.The overall spray cone angle of the deposited injector shows great difference in different directions,it may lead to change of the integral spray form from the normal cone to the ellipse cone.Different from the whole spray cone angle,the single hole spray cone angle of the injector nozzle becomes smaller.In the actual injection process,the injector may appear the post injection phenomenon due to the needle valve seating force.At normal atmospheric temperature there will be a significant fuel fracture zone between the main injection and post injection during the whole process of spray development.The fuel of post injection is in the shape of the ligament during the process of development.In the process of crushing,the ligament breaks into oil droplets with large diameter,which may influence the quality of atomization.High injection pressure and high fuel temperature are in favor of the evaporation and breakup of post injection,the combustion quality of the mixed gas is good,and the carbon smoke is less,which can relieve the formation of carbon deposition in the head of the injector.But for injector that already has deposition,the low velocity fuel injected by the second post injection in the high injection pressure and the severe atomization of the fuel near the nozzle under the high temperature will increase the adsorption capacity of the deposition on the tip of the injector,and high temperature fuel will increase the temperature of the injector head,these factors will accelerate the accumulation of the deposition on the tip of the injection.The deposition was obtained in different conditions on the engine bench.It shows that the average temperature in the cylinder and the carbon smoke in the cylinder have an important influence on deposition in the tip of the injector.The deposition are more in the same time under high carbon smoke environment.High cylinder temperature will promote the evaporation of fuel and oil,so as to make the deposition on the tip of the injector more dense.