Effect of a split-injection strategy on the atomisation rate using a high pressure gasoline DI injector 2020-01-0322
The Gasoline direct-injection (G-DI) engine can emit high levels of particulate matter and unburned Hydrocarbons when operating under stratified charge combustion mode. Injecting late in the compression stroke means the fuel has insufficient time to atomise and evaporate. This could cause fuel film accumulation on the piston surface and combustion liner. Locally fuel rich diffusion combustion could also result in the formation of soot particles.
Employing a split-injection strategy can help tackle these issues. The first injection is initiated early in the intake stroke and helps form a global homogeneous charge in the cylinder. The second injection during the compression stroke ensures a fuel-rich charge in the vicinity of the spark plug.
Many studies have established the crucial role that a split-injection strategy plays in the stratified charge operation of G-DI engines. The current study examines how a split-injection strategy affects the flow field and spray characteristics under a range of injection pressures. This is done by analysing the global spray structures and the atomisation rates. In particular, the effects of changing split ratios and the dwell times between injections on the spray characteristics of the second injection are evaluated.
The experiments are conducted in a constant volume spray chamber. A multi-hole solenoid DI injector, with maximum injection pressure capability of 35MPa, was used to carry out the investigations. The spray characteristics are analysed using high-speed imaging. The atomisation rates, breakup processes and droplet sizes are studied using Phase Doppler Particle Anemometry. Short and large pulse widths, in the range of 0.3ms to 0.8ms, have been tested. Pressures have been tested in the range of 5MPa to 35MPa.