Study of the stabilising effect of hydrogen in lean premixed combustion

In this paper a mathematical model of lean premixed combustion is developed to perform the bifurcation analysis in order to obtain the stability maps of lean propane combustion in the presence of different amounts of hydrogen. Bifurcation diagrams were built as function of the residence time for pure propane, pure hydrogen and intermediate mixtures. It was found that even a small amount of hydrogen greatly affects both the steady and the dynamic features of lean propane combustion. The region of existence of stable steady operating points enlarges on increasing hydrogen content. The existence of stable oscillations prior to extinction found for propane-air mixture is controlled by hydrogen substitution: the presence of hydrogen in the mixture leads to narrower region of existence of stable oscillations and shifts them to values of the operating parameters far away from the typical operating conditions of pure propane-air combustion. The effect of hydrogen is not only quantitative but also qualitative: the bifurcation diagrams of hydrogen-propane mixtures, cannot be viewed as a simple homothetic morphing of the bifurcation diagrams of the pure fuels but new stability features arise. Model results were found to be in qualitative agreement with the experimental results reported in the literature.