N2 and Ar dilution on the premixed biogas jet flame under external acoustic enforcement

In this study, combustion instabilities and flue gas emission changes under different dilutions of N₂ (nitrogen) and Ar (argon) of a promising biogas mixture (70% CH₄ - 30% CO₂) in the fight against greenhouse gas emissions were investigated. In the experiments, additions were made from 0% to 50% at intervals of 10% for both gases. In order to detect the instability of the flame, external acoustic enforcements at different frequencies was applied through the speakers placed in the combustion chamber arms. The dynamic pressure fluctuation values were recorded. The results showed that low dilution ratios were effective in reducing flame instability for both inert gases. However, as the dilution ratio increased, the fuel/air mixture became leaner and blowoff occurred. In the case of comparing two different gases, it has been observed that the effect of argon gas on reducing dynamic pressure fluctuation is higher. Burner outlet temperature and brightness values of the flame decreased in both Ar and N₂ dilution. CO and NO_x emissions increased with increasing diluent volume for all dilution conditions. When the emissions of the two diluent gases are compared, the CO emission, which was 3134 ppm in the undiluted condition, increased up to 4949 ppm in 50% Ar dilution, while it increased to 4521 ppm in 50% N₂ dilution.