Question

Why does Flame expansion occur for premixed combustion ? Use Science direct to write about this matter. 150-250 words please

Answer 1

Ans:

Premixed combustion

Fuel and Oxidant gas are mixed together at ambient condition before being delivered to the flame zone. As the mixture approaches the flame front, it is heated by conduction and radiation, flame front does not depend on the diffusion of reactants. The flow entering the combustor behaves more like a free jet and forms circular vortex rings that undergo a twisting shear motion leading to their eventual breakdown, When swirl is increased beyond a critical value, the high swirling motion of the fuel-air mixture and the rapid expansion at the entrance of the combustor causes an adverse axial pressure gradient along the centerline. This pressure gradient causes rapid breakdown of the vortex rings, slows down the axial motion and forms a recirculating bubble near the centerline. The coupling between the vortex motion and flame is broken, and the flame is pushed radially outwards and also upstream finally stabilizing very close to the inlet. For a fixed incoming fuel-air mixture, increase in swirl therefore, stabilizes the combustion process. Decreasing the equivalence ratio for a fixed Swirl Number, increases the pressure oscillation amplitude. This phenomenon is precursor to combustion instability. The current effort is now on adaptive control of the instability whereby, the pressure signal is recorded and analyzed online and then used to change the incoming swirl of the fuel content to stabilize combustion when the fuel-air mixture is made leaner.