  The present article reports experimental observation and analyses of a
supercritical bifurcation of combustion instabilities triggered by the air
inlet temperature (Ta). 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
Ta exceeds a critical value of Ta =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 Ta, exceeding 90 degrees (out of
phase) for temperatures higher than 570 K. A low order network framework is
conducted, illustrating that when Ta is increased a stability shift of this
mode is predicted at Ta near 570 K, in good agreement with the experimental
observations. The impact of Ta on the spray characteristics is also examined,
finding that higher Ta promotes fuel evaporation and reduces equivalence ratio
fluctuation at the exit of the swirler.
