Ivana Stanković from Ghent University, Belgium visited SCL and gave a seminar on "Numerical Simulations of Hydrogen Auto-Ignition in Turbulent Flows"

Abstract:

The development of new combustion technologies, featuring high efficiency while minimizing pollutant emissions, is an important task. Further development of combustion systems is limited by our ability to understand the nature of turbulent combustion and specifically auto-ignition in turbulent flows. Auto-ignition processes are particularly complex, owing to their strong dependence on chemical kinetics, as well as fluid dynamics. Any method for accurately predicting auto-ignition phenomena must incorporate unsteady chemistry, detailed chemical mechanisms and of course turbulence. Large Eddy Simulation (LES) has a considerable potential to represent time-dependent turbulent combustion and to combine cost effectiveness with accuracy. However, combustion is a sub-grid phenomenon and therefore modeling is required. The approach used here is the Conditional Moment Closure (CMC), an advanced turbulent reacting flow method, where the fluctuations of the reactive scalars are considered to be correlated with those of the mixture fraction.

We present an application of Conditional Moment Closure (CMC) in Large Eddy Simulations (LES) of hydrogen auto-ignition in turbulent flows. Two well documented experiments are investigated: the Cambridge and the Berkeley experiments. In both experiments, the fuel is hydrogen, diluted with nitrogen, igniting after mixing with pre-heated co-flow stream. The levels of dilution are strongly different. In the Cambridge experiment, different operating regimes were observed, ranging from random spots regime, flashback regime to lifted flame regime. These regimes were obtained by changing the co-flow temperature and/or the inflow velocities. In the Berkeley experiment, on the other hand, a higher ratio between fuel jet and co-flow velocity leads to a change in the flame behavior and a lifted flame was observed for the entire range of examined co-flow temperatures.