Comparative study on the local hybrid combustion characteristics of the CH4-NH3 laminar premixed flames with/without the wall effects.

The CH 4 -NH 3 (50%:50%) premixed flame with/without the wall effects are simulated and compared at the stoichiometric condition in this study. The effects of cold wall and local flame dynamics on the flame temperature, heat release rate (HRR), CH 4 /NH 3 oxidations and local CO/NO formations are analyzed quantitatively. Results show that the flame temperature and HRR are decreased and increased respectively along the flame front towards the axis of free flame, but they are both declined significantly towards the wall owing to suppressed chemical kinetics by the heat loss. The negative flame stretch and differential diffusion at the flame tip suppress the CH 4 oxidation and the fast path (NH 3 →NH 2 →NH→N 2) of NH 3 oxidation effectively, but affect the slow path (NH 3 →NH 2 →HNO→NO→N 2) of NH 3 oxidation moderately. This contributes to suppressed CH 4 /NH 3 oxidations and improved NO production at the flame tip of free flame. Based on NRR variations and ROP analysis, compared with CH 4 oxidation, wall heat loss exerts stronger suppressions on the fast path of NH 3 oxidation, while it decelerates the slow path of NH 3 oxidation less evidently. Since the fast path is the primary pathway of the NH 3 oxidation, the NH 3 oxidation suffers more effective suppression of the wall heat loss than the CH 4 oxidation. Furthermore, considering the significance of the slow path to the NO formation, the relatively enhanced importance of the slow path to the NH 3 oxidation in the near-wall region predominates the comparatively effective NO formation in the CH 4 -NH 3 flame compared with the pure CH 4 flame under the influence of wall heat loss. For the CO/NO formations, the local CO production/oxidation in the wall-impinging CH 4 -NH 3 flame are decelerated simultaneously due to the strong heat loss, while the local NO production/destruction are inhibited/improved by the wall heat loss. • The CH 4 /NH 3 oxidizations in the near-wall region are compared and investigated. • The individual/coupling effects of flame dynamics and cold wall are studied. • Different oxidization pathways of NH 3 suffer different influence near the wall. • Major oxidization pathway of NH 3 is weakened more effectively by the cold wall. • CO/NO formations are affected by flame dynamics, wall heat loss and burned gases flow. [ABSTRACT FROM AUTHOR]