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An experimental study was made to assess and to identify the role of the properties of various kinds of liquid fuels in the combustion processes and the exhaust emission of nitric oxide in a spark ignition engine. Attention was focused primarily on the chemical aspects of the fuel properties while the influence of physical parameter was kept minimized. The liquid fuels were vaporized and mixed well with fresh air prior to the spark discharge and subsequent flame propagation inside the combustion chamber. The physical state of the mixture charged inside the combustion chamber was observed by using a laser light scattering technique. The measurements were done of the cylinder pressure, the rate of heat release, the ignition delay, the combustion duration, the brake thermal efficiency and the exhaust NO emission. The influence of the fuel properties was also assessed through theoretical analysis based on the mathematical model to predict the thermal efficiency and NO formation.

Exciplex-based planar fluorescence technique was applied for two-dimensional visualization of the fuel spray including the region close to the nozzle tip. A spray doped with small amount of naphthalene and TMPD was discharged from a diesel nozzle into a pressurized gaseous nitrogen inside the test chamber installed with glass windows. The fuel spray was also allowed to evaporate in high temperature gaseous environments produced by combustion of the homogeneous mixture of methane and air in the test chamber. Photographs of the temporally frozen two dimensional image of the fuel spray were processed using an image analyzer. The image in the longitudinal cross section passing through the center axis of the spray demonstrated that the high density portion of liquid fuel appeared almost periodically downstream and that the axial distance between the neighboring high density portion increased with an increase in the downstream distance.