노즐 홀 출구 형상과 감압비등 현상이 직분식 다공 가솔린 인젝터의 노즐 출구 적심에 미치는 영향

Abstract

Nowadays, direct fuel injection into the engine cylinder technologies are becoming standard fuel injection regime in spark ignition engines. Unlike conventional port fuel injection (PFI) engines, Particulate matter (PM) emission from the direct injection spark ignition (DISI) engines is an important issue in the automotive industry due to stringent emission regulations. Fuel wetting on the surface of the injector nozzle tip has been pointed out as a major source of PM emission and injector tip fouling in the DISI engines. In the present study, the degree of gasoline fuel wetting on the surface of nozzle tip was evaluated, and the mechanism of injector tip wetting was explored. To measure the quantity of the wetted fuel, laser induced fluorescence (LIF) imaging technique was used. Fourth harmonic wavelength (266 nm) high intensity laser light from Nd:Yag laser was used as an excitation source. Emitted light from the wetted fuel was filtered by a bandpass filter (300-430 nm) and captured by intensified charge coupled device (ICCD) with a long distance microscope. Ambient conditions are adjusted to gasoline fuel injection timing of real engine operating conditions under different engine load, and experiment was performed in a constant volume chamber. From the result, a conventional step-hole shaped nozzle showed less fuel wetting than that of diverging shaped nozzle hole, and fuel wetting reduction potential of converging shaped concept can be expected even though it was hard to compare the results of the converging concept to the other concept. Fuel wetting under flash boiling conditions were higher than that under non-flash boiling conditions. In order to explore the mechanism of fuel wetting on the surface of the injection nozzle tip, back light illuminated spray imaging technique was utilized. The fuel wetting mechanism could be analyze through the transient fuel injection phenomenon including opening and closing events. Especially, it is thought that fuel wetting of wide near nozzle spray angle at the start of injection (SOI), transient spray angle fluctuation during the injection and low momentum liquid ligaments as well as droplets are main reasons of injector nozzle tip wetting.