Fuel metering effects on hydrocarbon emissions and engine stability during cranking and start-up in a port fuel injected spark ignition engine

To gain a better understanding of engine behavior in starting, cranking tests were performed on a 2.OL 4-cylinder Ford Zetec engine. The tests consisted of varying the initial engine position, starting temperature, and fueling strategy during the first two cycles in order to elucidate the effects of these variables on IiMEPg and HC emissions. The engine stopping position is a function of the gas load balance on the piston after the engine has been shut off. The most important effect of that position is on the instantaneous engine speed during cranking, which varies according to the sequence of firing events in the engine during a given cycle. Increased speed increases engine output through improved combustion phasing and heat release schedule. For a given starting position, IIMEPg is fairly insensitive to in-cylinder X within the range of 0.65 to 1.1; this is due to the combination of decreased combustion efficiency and improved heat release phasing. For all temperatures and starting positions, the firing threshold is X 1.1; tests run under colder temperature conditions require more fuel to reach this limit. Hydrocarbon emissions are sensitive to in-cylinder X outside the range of 0.65 to 1.1; lean and rich mixtures result in high HC levels due to misfires and partial burns, respectively. In addition, for a given in-cylinder X, lower temperatures result in higher HC levels. Open valve injection causes non-uniform in-cylinder mixtures, liquid fuel deposits in-cylinder, and spark plug wetting, and is therefore detrimental to engine stability and HC emissions. Thesis Supervisor: Wai K. Cheng Title: Professor of Mechanical Engineering

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