Inlet temperature driven supercritical bifurcation of combustion instabilities in a lean premixed prevaporized combustor

摘要

The present article reports experimental observation and analyses of a supercritical bifurcation of combustion instabilities triggered by the air inlet temperature (T-a). The studies are performed with a pressurised kerosene fuelled Lean Premixed Prevaporized (LPP) combustor operated under elevated temperature. Unlike some previous studies, starting from an unstable condition of the system, the amplitude of combustion instabilities suddenly decrease when T-a exceeds a critical value of T-a = 570 K. When the temperature is lowered back the system returns to being unstable without featuring any hysteresis behaviour, as expected in case of a supercritical bifurcation. The unstable flames feature a periodic axial motion of lift-off and re-ignition, characterized as Helmholtz mode. The phase difference between chemiluminescence and pressure signals is found to increase with T-a,T- exceeding 90 degrees (out of phase) for temperatures higher than 570 K. A low order network framework is conducted, illustrating that when T-a is increased a stability shift of this mode is predicted at T-a near 570 K, in good agreement with the experimental observations. The impact of T-a on the spray characteristics is also examined, finding that higher T-a promotes fuel evaporation and reduces equivalence ratio fluctuation at the exit of the swirler.