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To investigate NO formation in a combustion flame, PLIF (Planar Laser-Induced-Fluorescence) technique was applied to measure the NO fluorescence distribution in a constant-volume combustion chamber and in a sparkignition engine. The NO fluorescence distribution was taken by an image intensified CCD camera. In the constant-volume combustion chamber, the high NO fluorescence intensity was concentrically observed in the thin flame zone along the flame front. In postflame gas behind the flame zone, the NO fluorescence was widely distributed with weak intensity. In the case of the engine, the fluorescence was distributed in the broad flame zone. The fluorescence intensity had high value near the flame front, and decreased from the flame front to the postflame gas. As the equivalence ratio was changed, the fluorescence intensity reached maximum value at slightly lean condition.

In-cylinder flow and fuel behaviors in the piston cavity of a direct injection SI engine were measured by using PIV and LIF. The effect of the cavity wall on the mixing process was the focus in this study. The optical prism was installed inside piston to observe air flow and fuel behavior on a horizontal plane of the cavity combustion chamber in the piston. The fuel spray mainly impinged on the cavity bottom surface and rolled up along the cavity wall near the spark plug by it's own momentum. Then it was evaporated and diffused by swirl flow. The effect of fuel injection timing on the mixing process was also investigated. Earlier injection timing made fuel momentum small up to the time of impingement. Therefore, the fuel vapor was considerably diffused by swirl flow in the piston cavity and fuel vapor concentration near the spark plug was low.

A pancake-type constant-volume combustion chamber was used to investigate the combustion and NOx emission characteristics of propane-air and hydrogen-air mixtures under various charge stratification patterns, which were obtained by variations of the initial charge and injected mixture concentrations and the ignition spark timing. A planar laser-induced fluorescence from nitrogen dioxide as gas fuel tracer was applied to measure the mixture distribution in the test chamber. The second harmonic output of pulsed Nd; YAG laser was used as a light source for fluorescence excitation. The fluorescence images were corrected by a gated image-intensified CCD camera. The quantitative analysis of fuel concentration was made possible by the application of linearity between fluorescence intensity and NO2 concentration at low trace level.