Research On GDI Technology Of Small Model Two-stroke Kerosene Engine

The two-stroke piston gasoline engine is widely used in small aircraft such as UAV,but compared with gasoline,heavy fuel has higher flash point,which is safer and more reliable for the use,storage and transportation of fuel.However,due to the heavy fuel viscosity and poor evaporation performance,the octane number is low(29-46),which makes the atomization effect of the heavy oil in the cylinder poor,and the cold start of the engine is difficult,and the knock limit power is very low.On the one hand,GDI(direct injection in cylinder)can improve the atomization quality of heavy oil fuel at the ignition time(using high pressure swirl nozzle spray or air assist atomizer with better atomization quality),ensure that the engine still has the power of the prototype after the replacement of the fuel;on the other hand,the GDI can greatly reduce the scavenging losses and subsequent exhaust losses,thereby reducing the engine fuel consumption,what's more,it is helpful to use turbocharging technology to enhance the power of the engine at high altitudeThis paper takes Hirth company's 4201 engine as the prototype,using the company's ANSYS flow analysis software FLUENT and dynamic mesh technique for numerical simulation of flow field and spray field of each scheme before and after the retrofit of the combustion chamber,and the key technology and design idea of the direct injection transformation of the combustion system of the small model piston engine is pointed out.The results show that the modified combustion chamber structure can significantly improve the efficiency of the engine under high speed conditions,and improve the quality of atomization of heavy fuel.When the injector is about 5 degrees in the vertical direction,there is a certain stratification effect in the fuel mixture in the cylinder of the biasing scheme,and a thicker combustible mixture is formed near the spark plug.In order to further realize the product,the design of the high pressure swirl nozzle is designed at the end of this paper.In Marelli company's one swirl nozzle as the prototype,design parameters of nozzle needle assembly structure by using UG software,and the electromagnetic valve module is designed and matched with the AMESim software,the flow characteristics of the designed nozzle meet the oil supply demand of the small two stroke piston engine.It lays a good foundation for the further development of experimental research and development of engineering prototype.