Transient Spray Characteristics of Air Assisted Fuel Injection 2015-01-0920
Gasoline direct injection (GDI) technology is already in use in four wheeler applications owing to the additional benefits in terms of better combustion and fuel economy. The air-assisted in-cylinder injection is the emerging technology for gasoline engines which works with low pressure injection systems unlike gasoline direct injection (GDI) system. GDI systems use high pressure fuel injection, which provides better combustion and reduced fuel consumption. It envisages small droplet size and low penetration rate which will reduce wall wetting and hydrocarbon emissions.
This study is concerned with a CFD analysis of an air-assisted injection system to evaluate mixture spray characteristics. For the analysis, the air injector fitted onto a constant volume chamber (CVC) maintained at uniform pressure is considered. The analysis is carried out for various CVC pressures, mixture injection durations and fuel quantities so as to understand the effect on mixture spray characteristics. For the numerical solution of governing differential equation, velocity and pressure boundary conditions to the fluid domain are applied. In addition, steady state experiments were also conducted using a steady state test rig to measure the mass flow rate of mixture under atmospherics pressure of CVC. From this study, it is concluded that in air-assisted system, CVC pressure creates inertia for the spray to penetrate and it controls the penetration and spread of spray and can potentially reduce HC emissions. The penetration and spread characteristics are also affected by the fuel quantity and will be beneficial during medium and high loads on the engine. It is also seen that the overall Sauter Mean Diameter (SMD) of fuel particles is in the range of 4 to 14 micrometre.