Experimental Study Of Subcritical/supercritical Spray Characteristics Of A Gasoline Direct Injection Multi-hole Injector

Through continuous exploration and research,the supercharging and gasoline direct injection(GDI)technology is increasingly becoming one of the main development directions of gasoline engine.However,GDI technology will produce a large number of atmospheric pollutants such as nucleation mode and accumulation mode particles.For the current turbocharged direct injection gasoline engine,the gasoline fuel in the form of a supercritical fluid is injected into the cylinders have the potential to break through the thermal efficiency limits of the gasoline engine and reduce particulate emissions to achieve high-efficient and clean combustion.Thus,this article mainly studies the subcritical/supercritical spray characteristics of a multi-hole GDI injector.Spray experiment with gasoline,ethanol,normal octane,and ethanol-normal octane mixed fuel is conducted on supercritical spray platform.The main conclusions are as follows.The spray characteristics of gasoline are different greatly in low-subcritical region,subcritical region and supercritical region.With the temperature rising,the penetration distance increases slowly in low-subcritical region,decreases rapidly when the temperature rises to subcritical region,and gradually rebound in supercritical region.With the increase of temperature,the spray area rises up first,and appears a peak value in subcritical region and then declines rapidly;the spray perimeter declines first,and then rises up rapidly;the ratio perimeter Lr decreases dramatically first,and rises up rapidly.In addition in low-subcritical region,the ratio perimeter Lr is in an increasing tendency with the rise of pressure,while leading to the opposite tendency in supercritical region.Supercritical spray is not instantaneous gasification,and it is divided into the thick-core region and the thin-diffusion region by a highly folded surface;Mach disk structure appears at the exit of the spray,indicating the great similarity of highly under-expanded jet between supercritical spray;With the increase of spray temperature,the thick-core region is in a declining tendency,while the thin-diffusion region is in an increasing tendency,indicating that high temperature can promote the gasification of supercritical spray;By comparing the spray characteristics of single-hole and six-hole in subcritical/supercritical region,the existing six-hole GDI injector is not suitable for the spray development of supercritical gasoline,and it is necessary to design and optimize a new injector for supercritical gasoline.The spray characteristics of ethanol are different greatly in low-subcritical region,subcritical region and supercritical region.Ethanol spray characteristics(spray penetration distance,area and perimeter)will increase slowly in low-subcritical region and decline sharply after crossing the subcritical region,and keep declining when arriving at the supercritical region;the ethanol spray characteristics will be further develop with the increase of fuel pressure.By comparing the subcritical/supercritical spray characteristics of ethanol,normal octane and E50 under different working conditions,it shows that inertia force and cohesive force are the main factors affecting spray development in low-subcritical region.In subcritical region,the degree of superheat of fuel has become the main factor affecting spray development.In supercritical region,the spray penetration distance and area of ethanol,normal octane and E50 present a declining tendency with the increase of temperature.In addition,it is also shown that in low-subcritical region,the spray characteristics of E50 and normal octane remain the same.While in the subcritical region,the spray characteristics of E50 and ethanol are highly similar.