Influence of Mixture Stratification Patter non Combustion Characteristics in a Constant-Volume Combustion Chamber

A pancake-type constant-volume combustion chamber was used to investigate the combustion and NO_x 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. The results show that the stratified mixture with center-rich or center-lean pattern was concentrically formed in the central region of the chamber by a jet flow from a tangentially-oriented port. Under the rich side of overall excess air ratio, the combustion speed of the homogeneous mixture was slightly faster than that of the stratified mixture. When the rich mixture was located near the spark ignition point, the combustion speed was fastest under the lean side of overall excess air ratio. When the mixture concentration near the spark ignition point increased, NO_x emissions increased under the lean side of overall excess air ratio but decreased under the rich side.