Liquid Fuel Transport Mechanisms into the Cylinder of a Firing Port-Injected SI Engine During Start Up 970865
The occurrence of liquid fuel in the cylinder of automotive internal combustion engines is believed to be an important source of exhaust hydrocarbon (HC) emissions, especially during the warm-up process following an engine start up. In this study a Phase Doppler Particle Analyzer (PDPA) has been used in a transparent flow visualization combustion engine in order to investigate the phenomena which govern the transport of liquid fuel into the cylinder during a simulated engine start up process. Using indolene fuel, the engine was started up from room temperature and run for 90 sec on each start up simulation. The size and velocity of the liquid fuel droplets entering the cylinder were measured as a function of time and crank angle position during these start up processes. The square-piston transparent engine used gave full optical access to the cylinder head region, so that these droplet characteristics could be measured in the immediate vicinity of the intake valve. Three major phases of fuel droplet flow past the intake valve were identified: first forward flow atomization from the port wall and the valve head into the cylinder as the intake valve opens and forward gas flow commences; spray contribution as the injector injects towards the open intake valve; and fuel film squeezing as the closing intake valve rapidly compresses any fuel film accumulated on the intake valve seat. The influence of injection timing relative to intake valve opening and closing on the flow of liquid fuel into the cylinder during cold start was studied also. By comparing liquid fuel behavior using iso-octane with that observed with indolene, the influence of fuel volatility was also examined. The spatial variation of the liquid fuel droplets entering the cylinder was assessed by carrying out size and velocity measurements at various positions around the circumference of the intake valve.