Effect of Equivalence Ratio on NO Distribution inside a Spark Ignition Engine by Using Laser-Induced-Fluorescence Method

Planar Laser-Induced-Fluorescence technique was applied to measure the NO fluorescence distribution in a spark ignition engine. The fluorescence intensity had high value near the flame front, and gradually decreased from the flame front to the postflame gas. The fluorescence was distributed in the broad flame zone as compared with the case of the constant-volume combustion chamber. The effect of equivalence ratio on the NO fluorescence intensity were investigated. At the flame-development duration, the total NO fluorescence intensity was high as the equivalence ratio became rich. However, at the rapid-burning duration, the total NO fluorescence intensity of a slightly lean condition had a maximum value. As the equivalence ratio became lean, the peak intensity of the radial NO fluorescence distribution increased and the width of the high intensity zone in radial distance broadened. The peak intensity and the width of the radial distribution reached the maximum value at a slightly lean condition.