Effect of biogas addition on combustion instability of propane flame at different external acoustic enforcement frequencies

Abstract

In this study, the effect of biogas addition to propane flame on combustion instability and luminous intensity was investigated. A premixed and swirl assisted burner was used in the experiments. After the combustion of pure propane, biogas mixture was added from 30% to 100% in 10% increments. A mixture of 60% CH4 − 40% CO2 was used as biogas. In all experiments, the burning power was kept constant as 5 kW, the swirl number as 1 and the equivalence ratio as 0.8. The resonance frequencies of the combustion chamber were determined as 95 Hz, 180 Hz and 300 Hz. As a result, it was determined that the addition of biogas suppressed the combustion instabilities of the propane flame. While the pure propane flame under external acoustic enforcement experienced blowoff at all resonance frequencies, it did not blowoff primarily at 300 Hz as the biogas addition rate increased. When the propane ratio approached 0%, the flame showed stable combustion under all forcing frequencies. In addition, while the length of the pure propane flame was high, the flame length decreased with the addition of biogas, but its brightness increased.