Combustion instability characteristics with different equivalence ratios in a premixed arrayed micro-tube hydrogen combustor

This research experimentally investigates combustion instability characteristics in a full-scale premixed arrayed micro-tube combustor operating at ambient temperature and pressure. Experiments focus on three distinct air flow rates and a range of global equivalence ratios. The combustor employs a diffusion combustion pilot stage with a swirl cup and a main stage featuring premixed arrayed micro-tubes. Results reveal three distinct flame morphologies as the global equivalence ratio increases at fixed flow rates: (1) a detached V-shaped flame at low equivalence ratios, (2) a stable conical arrayed flame at intermediate equivalence ratios, and (3) an unstable flame exhibiting combustion instabilities at high equivalence ratios. As the global equivalence ratio approaches the instability threshold, the combustion oscillation intensity becomes highly sensitive to small changes in equivalence ratio. Specifically, a 0.01 increase in global equivalence ratio can amplify the oscillation amplitude by more than threefold. Beyond this critical threshold, the equivalence ratio forms a relatively stable plateau region for sustained combustion instabilities. Pronounced beating oscillations were observed, characterized by dual high-amplitude pressure fluctuation peaks near 500 Hz. For instance, at an air flow rate of 220 g/s and a global equivalence ratio of 0.365, distinct peaks occur at f₁ = 494 Hz and f₂ = 529 Hz, with amplitudes of 699 Pa and 1195 Pa, respectively (the larger amplitude being approximately 1.71 times the smaller). This study examines combustion oscillations in full-scale pure-hydrogen gas turbine combustion chambers, offering significant risk reduction for combustion instability in the design of industrial pure-hydrogen gas turbines.