Experimental study on combustion characteristics of n-C4H10/air mixtures in a meso-scale tube partially filled with wire mesh

Abstract

Liquid fuels are good candidates for combustion-based miniature power sources due to their large specific energy. In this study, combustion characteristics of n-C4H10/air mixtures in a tube (ID = 6 mm) partially filled with wire mesh was experimentally explored over an equivalence ratio of ϕ = 0.5–1.5. In most cases, partially submerged flames and surface flames were observed on the downstream side of the porous media. An external diffusion flame was established under high inlet velocities for fuel-rich mixtures of 1.2 ≤ ϕ ≤ 1.5. The flame with a center convex started to appear at a certain inlet velocity due to the relatively higher local velocity, which was a result of the rolling up method of the wire mesh. Moreover, a lower extinction limit of 0.1 m/s was achieved over 0.9 ≤ ϕ ≤ 1.2, whereas the blow-off limit rose almost linearly up to 0.8 m/s with the equivalence ratio even on the fuel-rich side. The underlying mechanisms for this tendency were comprehensively analyzed from the preheating effect, heat loss effect, volumetric expansion effect as well as the support effect from the external diffusion flame. Furthermore, for an identical inlet velocity, the wall temperature first rose until ϕ = 1.1 and then decreased when ϕ > 1.1. Under a constant equivalence ratio, both the maximum wall temperature and the exhaust gas temperature increased with an increasing inlet velocity. However, for an identical inlet velocity, the exhaust gas temperature at low and moderate inlet velocities remained almost invariable versus the equivalence ratio. This was speculated to be the relatively small variation of heat loss ratio versus equivalence ratio. In summary, these findings enriched the knowledge of n-C4H10/air combustion in small tubes partially filled with porous media.