Structure of Hydrogen-Air Partially Premixed Flames at Supercritical Conditions

In this study, the structure of hydrogen/air counterflow partially premixed flames (PPFs) at supercritical conditions has been investigated numerically. At first, initial evaluation of reaction mechanisms by comparing computed laminar burning velocity and experimental results is performed to recognize suitable mechanisms. It is found that GRI3.0 mechanism fails to predict hydrogen/air combustion at elevated pressures and therefore removed from following simulations. Afterwards, pressure has been raised to reach to supercritical conditions of reactants. In this step, results indicated that the structure of PPFs bears important changes through pressure rise. By elevating pressure in intermediate ranges, flames thickness and the distance between flames decreased while different reaction mechanisms show noticeable deviations especially at higher pressures. But at higher pressures, especially at supercritical conditions, the flame structure became relatively independent of pressure. At supercriticalconditions, change in global strain rate has a negligible effect on location of rich premixed branch of flame while at lower pressures location of this flame is very sensitive to pressure variations. Furthermore, it is shown that thermal diffusion and radiation has negligible effects on structure of partially premixed flames at supercritical conditions.

Keywords:

partial premixing , supercritical combustion , counterflow flame , hydrogen kinetics