Dynamics and flammability limit of stretched premixed flames stabilized by a hot wall

Dynamics and flammability limit of stretched, ultralean methane/air premixed flames stabilized by a hot wall were investigated theoretically and numerically using the large activation energy asymptotic approach and the detailed chemistry approach, respectively. An analytical expression describing the flame temperature and location was obtained. Several new findings on the flame regimes, bifurcation, and flammability limit are demonstrated. The analytical results showed that the appearance of hot wall results in new flame bifurcations. Except for the high-temperature flame, there exists a hot-wall-stabilized low-temperature flame which dramatically extends the flammable region of stretched flame to low stretch. Sublimit flame can be stabilized by a hot wall and has a non-zero flame speed even with a wall temperature less than its adiabatic flame temperature. Furthermore, the results also showed that the effects of radiation heat loss and the Lewis number effect are suppressed by the hot wall, and that stretched flames at a Lewis number below unity can extinguish at a finite distance from the wall. Numerical calculations with detailed chemistry well reproduced the predictions of the analytical results. In addition, numerical results showed that except for the low-temperature flame on the low-stretch-rate side, there exists another low-temperature flame regime on the high-stretch-rate side, which dramatically extends the flammable region to the high stretch rate and yields multiple flame extinctions. Theoretical analysis qualitatively agreed well with the numerical calculations, but failed in the prediction of the low-temperature flame at a high stretch rate. The present results provided useful guidance for the application of ultralean combustion in new combustion technology.