Experimental and numerical investigation on flame pattern formations of non-premixed CH4 and air in a planar micro-combustor

Abstract

Non-premixed CH4/air flames in a rectangular micro-combustor of 2.0 mm (width) × 10 mm (height) × 31 mm (length) were experimentally investigated. The results demonstrated that flame cannot occur within the micro-combustor if nominal equivalence ratio ϕ ≤ 1.0 for any average velocity (V). Five flame patterns appeared and were termed as “single internal C-shaped flame”, “dual internal C-shaped flames”, “single ε-shaped flame”, “dual internal and external flames” and “single external flame”. Cold-state numerical simulations unraveled that fuel stratification occurred in the height direction due to the buoyancy effect, which is especially pronounced at ϕ = 1.3–1.5. Consequently, “dual internal C-shaped flames” is formed, consisting of an upper flame cell and a lower flame cell. At ϕ = 1.1–1.3, fuel stratification phenomenon grew weakened, which led to “single ε-shaped flame” at ϕ = 1.2–1.3 and “single internal C-shaped flame” at ϕ = 1.1–1.2. At sufficient high average velocities, one or both flame cells will be pushed out of the combustor. In conclusion, the present work verified the possibilities of formation of stable flames inside the micro-combustor with a width less than the quenching distance of stoichiometric mixture. Moreover, this study revealed the important role of buoyancy effect in flame pattern formations within micro-combustors with a large enough channel height.