Numerical analysis of relight in an annular spray-flame combustor with preheated walls

Abstract

Successful relight of aero-engine combustors is subjected to certification specifications and must be ensured under various scenarios which can involve substantially different combustor wall temperatures. Unlike restart from windmilling, quick relight is likely to be performed with hot combustor walls, affecting the resulting ignition time. Few published studies exist which address wall temperature effects on ignition: for example, experiments in the annular spray-flame combustor MICCA with preheated walls have revealed that the ignition time—also referred to as light-round duration—decreases compared to cold combustor walls for otherwise same operating conditions. Numerical simulations of ignition have been carried out as well, but usually rely on approximations for the imposed wall temperature boundary condition (mostly adiabatic, iso-thermal at best) due to the lack of detailed experimental data. Therefore, the present work aims at studying the effect of preheated walls on light-round in more detail. Conjugate Heat Transfer simulations are first carried out to compute more realistic wall temperature profiles under steady reacting operating conditions in MICCA-Spray. These temperature profiles are then used in non-reacting Large-Eddy Simulations (LES) to establish preheated initial conditions. Finally, LES of light-round ignition with preheated walls are carried out. The predicted light-round duration is compared to experimental measurements, and effects on the governing flame propagation mechanisms as well as the liquid phase are examined. Differences with regard to light-round with ambient temperature walls are pointed out and the importance of an appropriate choice of boundary conditions is briefly discussed.