Characteristics of Impinging Spray and Corresponding Fuel Film under Different Injection and Ambient Pressure 2019-01-0277

It has been found that the spray impingement on piston for SIDI engines significantly influences engine emission and combustion efficiency. Fuel film sticking on the wall will dramatically cause deterioration of engine friction performance, incomplete combustion, and substantial cycle-to-cycle variations. When increasing the injection pressure, these effects are more pronounce. Besides, the ambient pressure also plays an important role on the spray structure and influences the footprint of impinging spray on the plate. However, the dynamic behavior of impinging spray and corresponding film was not investigated thoroughly in previous literature. In this study, simultaneous measurements of macroscopic structure (side view) and its corresponding footprint (bottom view) of impinging spray was conducted using a single-hole, prototype injector in a constant volume chamber. A high pressure supply system was employed to change the injection pressure, and the ambient pressure was controlled by a vacuum pump. The macroscopic spray structure was captured by high-speed Mie-scattering imaging, while for the film measurement, laser induced fluorescence (LIF) technique was used to measure the spatial distribution and temporal development of the thickness of droplet film deposited on the plate. Rhodamine 6G was resolved by ethanol as the tracer, which can be excited by 527 nm laser and the fluorescence signal is at the range of 560-590 nm. A high speed imaging system was employed to capture the film characteristics. The LIF signal was converted to film thickness following a calibration procedure where LIF signals from a series of known-thickness film were captured. It was found that, with the increase of injection pressure, more fuel was detached after impinging the plate and the average film was thinner. Besides, the change of ambient pressure had a relationship with air entrainment and influenced the spray structure remarkably.