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High boiling point components of gasoline have been shown to have an adverse effect on engine-out hydrocarbon emissions for port fuel injected (PFI) engines. Fuel charge inhomogeneity and wall wetting contributes to the abnormally high hydrocarbon emissions associated with cold and warm engine starting. In this work, a series of aldehydes with varying molecular weight and boiling points were used as fluorescent tracers to study the effect of fuel volatility and engine operating conditions on the in-cylinder charge distribution. The tests were conducted in an optically accessible engine consisting of a production GM Quad-4 cylinder head and intake manifold, with an FEV systemmotor crankcase and “Bowditch” transparent piston. Planar laser induced fluorescence was used to study the in-cylinder fuel vapor distribution and to determine the presence of liquid droplets.