Effect of flame holder temperature on the instability modes of laminar premixed flames

Abstract

Direct Numerical Simulations (DNS) and theoretical analysis of combustion instabilities in laminar premixed flames are performed to investigate the effect of flame holder temperature (Tc) on the self-excited instability modes. Four flames with different anchor positions and recirculation zones are triggered to be unstable by increasing acoustic losses at the boundaries. At Tc = 300 K and 773 K, intrinsic thermo-acoustic (ITA) modes dominate the oscillation frequencies both in anechoic and acoustic systems. The instability modes are mainly determined by the flame characteristics, and significantly affected by the recirculation zone and flame holder. At Tc = 400 K and 1500 K, the instability modes are mainly determined by the couplings between acoustic and ITA modes, and significantly affected by the flame characteristics and system acoustic modes. The dominant oscillation frequencies are closed to the acoustic modes at Tc = 400 K, but in low frequency ranges at Tc = 1500 K. These results indicate that the ITA modes affect the combustion instability in different ways with different flame characteristics. It may cause intrinsic instability or couple with acoustic modes to cause new instability modes. In realistic combustion systems, the ITA modes must be considered carefully in the analysis of combustion instability.