Effect of N2 dilution on combustion instabilities and emissions in biogas flame

Biogas compositions are known as carbon free fuels for energy productions. In this study, biogas mixtures which consist of %60 CH4 - %40 CO2 are tested with %0-%60 N2 dilution ratios. All experiments, equivalence ratios and swirls number keep constant as 0.7 and 1, respectively. External acoustic enforcement was applied on the flame at different frequencies including 110 Hz and 190 Hz by loudspeakers located in side arms of the combustor. The effect of N2 addition on flame stability under acoustic stress conditions has been investigated. The results showed that the combustion stability of biogas mixture increase with the nitrogen ratio up to %30 N2 ratio. However, when the 30% N2 dilution was exceeded, there was a decrease in stability. In the absence of nitrogen dilution, the flame could not resist against the 110 Hz acoustic frequency. However, the flame continued to burn steadily under same acoustic frequency after nitrogen dilution. In addition, dilution of the biogas composition with nitrogen causes the increasing of the CO emissions. However, NOx pollutant emissions decreased up to 20% N2. After 20% N2 dilution, NOx emission has increased