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Non-Premixed Turbulent Biogas Flame: Effect of The Co-Airflow Swirl Strength on the Stability Limits

This experimental study reports on the effect of swirl strength on the stability of non-premixed biogas flame. The swirl strength was varied by changing the vanes angle (25° and 50°) of the swirl generator. Zero-angle vanes swirl was also used as a reference. The results revealed that the swirl enhances significantly the biogas flame stability operating range. In addition, it was found that the biogas flame behaves differently depending on the swirl strength. The effect of low (25°-angle vanes) swirl on the flame stability was found to depend upon the co-airflow exit velocity. At low co-airflow velocity, the flame was attached and its blow-off limits are comparable to those of the zero (0°-angle vanes) swirl. However, as the co-airflow velocity increases, the low swirl attached flame lifts-off the burner and stabilizes over a wide range of co-airflow and fuel jet velocity. In contrast to low-swirl, high (50°-angle vanes) swirl generates only an attached biogas flame regardless of the co-airflow velocity. Moreover, the high swirl attached flame was found to stabilize over a wider range of flow conditions compared to that of low swirl. Particle image velocimetry (PIV) data were used to explain the stability limits and empirical correlations were proposed to describe these limits.