Linear stability analysis of a premixed flame in curved micro-combustors

A micro-combustor is an attractive concept to enable a high-energy-density power supply for microelectromechanical applications. This work concerns the combustion instability in micro-combustors with curved geometries. We calculate the base-flame solutions and present a systematic linear stability analysis of anchored premixed flames suited in curvatured-affected flow fields with the focus on the so-called intrinsic thermoacoustic (ITA) modes. By varying the ratio of channel radius of curvature to channel height, Rc/H, the global eigen spectrum shows that the first ITA mode tends to destabilize with the growth of Rc/H and then stabilize at a very strong curvature where a significant flame bending is present. A flame-transfer function based on streamwise velocity perturbations confirms that the classical −π phase-lag criterion remains valid even under strong curvature. To pinpoint the regions most responsible for mode growth or decay, we perform an adjoint-based structural sensitivity analysis. The resulting wavemaker maps reveal two key loci: one enveloping the flame front and another upstream in the inflow region, highlighting the critical role of convective velocity disturbances in ITA formation. Unlike straight channels, curved geometries support multiple ITA branches, each exhibiting dominant sensitivity to inlet perturbations. Our findings not only elucidate the physical origins of curved-channel ITA instabilities but also verify a rapid criterion-based prediction in non-planar ducts. The identified “safe” curvature intervals offer practical guidance for the geometry of micro-thermophotovoltaic combustors.