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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.

For the final goal of developing the natural gas fueled spark ignition engine with high thermal efficiency and low pollutant emission, the effects of the fluid flow inside a combustion chamber on the combustion process of a homogeneous lean mixture of natural gas and air were examined using a rapid compression combustor. The rapid compression combustor was designed to simulate the combustion process in a spark ignition engine involving the rapid compression of a mixture and the heal release during flame propagation. The main advantage of using this combustor is that experiments can be made under the idealized and well-controlled conditions. The time history of pressure in the combustion cylinder was measured with a pressure transducer. The fluid flow in the combustion cylinder was varied using two kinds of experimental technique. First, compression ratio, piston speed and the configuration of the piston head were changed.

An experimental study was made of the fundamental aspect of the mixture formation in the combustion chamber of automotive spark ignition engine with the multipoint fuel injection. The mixture formation during intake stroke of an engine was simulated by the timed or continuous injection of Freon-113 or Freon-12 into the steady flow of dust-free dry air through an intake port. The vapor concentration in the transparent combustion cylinder was determined with the application of the laser Rayleigh scattering. The results showed that the present optical system was useful for the time and space resolved measurements of vapor concentration in the combustion chamber in the case of liquid and gaseous fuel injections. The spatial distributions of the time averaged vapor concentration were highly heterogeneous. It was also found that the vapor concentration profile was largely affected by the place for fuel injection and the intake valve lift.

An experimental study was made to investigate in-cylinder flow field in a natural gas fueled spark ignition engine and the effects of engine specifications on in-cylinder flow field. The instantaneous two-dimentional flow fields in a single-cylinder visualization engine, which has 75mm bore and 62mm stroke, were measured in various cross sections perpendicular to the cylinder axis by using the laser light sheet PTV method at various crank angles during intake, compression, and expansion strokes over the wide range of piston combustion chamber configuration, top clearance, and nominal swirl ratio. Flow fields during compression and expansion strokes were also calculated using KIVA2 simulation code for better understanding of the measured results. The results showed that induction-generated swirl is getting concentric to the cylinder center in compression stroke, and is shifted in the radial direction in expansion stroke.

An experimental study was made to investigate the effect of combustion chamber configuration, top clearance, nominal swirl ratio, and spark plug position on in-cylinder combustion in a spark-ignited natural gas engine, which is converted from a direct injection diesel engine. Flame propagation in a single-cylinder visualization engine was measured from the cylinder axis direction by the high speed schlieren method, over the wide range of combustion chamber configuration, top clearance, nominal swirl ratio, and spark plug position. The results showed that flame does not propagate concentrically to the spark plug, but is shifted by swirl, which is the main flow in this engine. Smaller piston cavity diameter led to more rapid flame propagation, resulting in larger heat release rate and larger cylinder pressure. Piston cavity diameter does not affect the initial combustion until TDC.