Effect of inhomogeneous methane-air mixtures on combustion characteristics in a constant volume combustion chamber

Abstract

The inhomogeneous mixture can improve the combustion performance under certain conditions. In this study, an experimental study of turbulent stratified combustion under different background equivalent ratio conditions (0.6, 0.8, 1.0) was carried out based on a constant volume combustion chamber. Injection of pure methane to achieve stratification of gas mixture concentration, and the ignition timing was adjusted to control the mixture stratification degree. Optical diagnosis of the flame using a high-speed camera and the optical schlieren system to understand the morphological changes in flame development. Based on the combustion pressure and ion current signals to explore the effect law of stratification degree on the turbulent stratified combustion characteristics. The results of the study show that the concentration stratification of the mixture can accelerate the flame propagation speed. The leaner the background mixture concentration, the stronger the promotion effect of the mixture concentration stratification on the propagation speed. The appropriate degree of stratification is conducive to improving the stability of the flame. Turbulent stratified combustion can increase the maximum combustion pressure, shorten the combustion duration. The degree of stratification has a large effect on the ion current signal curve during the background equivalent ratio of 0.6 mixture combustion, and almost no effect when the background equivalent ratio is 1.0. The peak moment of the combustion pressure rises rate and the peak moment of the ion current signal occur almost simultaneously under different combustion conditions. The correlation between the maximum of the combustion pressure and the maximum of the ion current is approximately linear and the correlation is greater than 95%.