Visualization of liquid fuel behavior in a spark ignition engine during starting and warm-up

Abstract

The liquid fuel behavior in the intake port and the cylinder during starting and warm-up was visualized through visualization windows using a high speed CCD camera. The videos were taken with the engine firing under cold conditions in the simulated start up process, at 1.000 and 1.200 RPM and intake manifold pressure of 0.5 bar. The variables examined were the injector geometry and injector type (normal and air-assisted). The visualization results show several features of the liquid fuel behavior: 1) backward strip-atomization of the fuel film along the periphery of the intake valves by the valve overlap backflow: 2) forward strip-atomization of the fuel film on the surfaces of the intake system into droplet streams by the intake air flow: 3) film flow which forms significant liquid puddles at the valve surface and at the vicinity of the intake value: and 4) squeezing of the liquid film at the valve lip and seat into large droplets in the valve closing process. Some of the liquid fuel survives combustion into the next cycle. The time evolution of the in-cylinder liquid film is influenced by the injection geometry and port surface temperature. Photographs showing the liquid fuel features and an explanation of the observed phenomena are given in the paper.