NUMERICAL PREDICTION OF A LEAN BLOW-OUT EVENT OF A LAB-SCALE, SWIRL-STABILIZED SPRAY FLAME

Alternative jet fuels have a high potential to reduce emissions in aviation and to increase the independence from mineral oil. However, as a safe operation must be guaranteed, new fuels have to pass elaborate and expensive tests to be finally certified. To reduce the costs and time of the certification process, numerical simulations can be used to assess the impact of a new fuel on combustion. Further, the detailed simulations provide an insight into the fuel sensitive sub-processes. The lean blowout (LBO), i.e. the lower stability limit of a gas turbine combustor, is of primary concern for safe operation and the approval of alternative jet fuels. The paper at hand focuses on the formulation of a calculation protocol for the numerical representation of a lab-scale LBO experiment. The test case is a swirl-stabilized spray flame, which mimics several key features of aero-engine combustors. The LBO-limits are determined by a stepwise reduction of the fuel mass flow starting from a stable operation point above the measured blowout limit. Towards extinction, the heat release rate in the combustor drops. Furthermore, fuel is still evaporating, but less fuel is burned, leading to an accumulation of fuel in the combustion chamber. The blow-out is defined by a steep drop in heat release combined with a large increase of the gaseous fuel mass fraction in the computational domain. The semi-automated calculation protocol is able to successfully capture a blowout event at an equivalence ratio of phi = 0.32 and can thus be applied to evaluate alternative jet fuels in the future. In addition, a reignition event is observed for equivalence ratios slightly above phi(LBO).