Extinction Prediction and Emission Analysis of a Bluff-Body Stabilized Ammonia-Hydrogen-Nitrogen Premixed Flame With Conjugate Heat Transfer

Abstract

Ammonia/hydrogen blends represent a promising carbon-free fuel for gas turbine combustors. To minimize the NOx emission, premixed ammonia/hydrogen/nitrogen flames under ultra lean equivalence ratios are investigated. This paper simulates the extinction process of a bluff-body stabilized flame. Large eddy simulation with Dynamic Smagorinsky model is employed to resolve the turbulent flame, while the thermal state of the bluff body is modelled by conjugate heat transfer (CHT). The flow field and flame from the experiments are compared with the simulations to validate the result. After keeping the flame stable with constant inflow condition, the inlet velocity is gradually changed to cause extinction. The wall heat flux along the bluff body is monitored and compared with the total heat release rate from the flame. Furthermore, an adiabatic boundary condition is implemented for the bluff body to analyze the heat transfer effect on the flame. The extinction velocity is accurately predicted by the simulation within the experimental error. The heat flux analysis shows that the heat loss at the upper surface of the bluff body does not contribute much to the flame heat loss. However, without taking conjugate heat transfer into consideration, the simulation predicts earlier extinction than the case with conjugate heat transfer. The NOx emission difference between the CHT case and adiabatic case is also analyzed.