in Wiley InterScience (www.interscience.wiley.com).Non-premixed methane-oxygen flame dynamics and structures confined within an alumina combustor are described. Non-stabilized, transient flame dynamics and phenomena leading to the formation of a stable edge-like flame and distinct cellular structures that take place within combustor channels of dimensions 35 mm long, 5 mm wide, and 0.75 mm high (combustor volume $ 130 mm 3 ) are discussed. These confined flames are surveyed by measuring the external wall temperatures, high-speed and stillframe visual flame imaging, recordings of emitted acoustics from the combustor, and capturing visible, CH*, and OH* chemiluminescence through a sapphire window. The observed dynamic flame structure is an oscillating edge-like flame accompanied by ignition-extinction events that precede the formation of a stable edge-like flame and flame cells in the reaction channel. The cellular flame structures in all cases exhibit a confined tribrachial structure with a folded or extinguished rich branch while the lean branch survives.
Growing interest in small-scale, portable energy systems such as fuel cells has necessitated the development of small-scale fuel processing or reforming systems. Many fuel reforming systems require reliable heat sources as in some cases temperatures in excess of 600°C maybe required. Sub-millimeter combustors can provide such a heat source; however, a broader set of design rules are needed for constructing systematically engineered heat sources. In this article, experimental observations and computational fluid dynamics modeling results are presented for stable and steady confined flame structures within an alumina sub-millimeter combustor. Influence of inlet flow and thermal boundary conditions are evaluated through a parametric study. The inlet flow rates and relative gas composition, the thermal boundary conditions that include thermal conductivity of the walls, convection of heat to and from the walls, and radiation of heat energy through the walls all determine the position, structure, and temperature of the reacting fluid and combustor walls. The model shows the importance of radiative heat transfer in the formation of the steady-state flame structures within the microcombustor.
Unsteady flames within alumina combustors with one submillimeter dimension are evaluated and discussed in this extended abstract. The flame dynamics within the combustors are characterized by non-stabilized and transient flame structures accompanied by acoustic emissions. These flames are studied experimentally and are discussed here. The experimental observations are carried out via two imaging techniques, high-speed and still-frame imaging. The acoustic emission and external wall temperature measurements are also recorded.
This paper describes experimental observations of flame dynamics within an alumina non-premixed combustor with a sub-millimetre (0.75 mm) minimum size. These flame dynamics occur within a total combustor volume of 130 mm 3 and are imaged through a sapphire window. The confined flames are surveyed using visual still-frames, high-speed flame imaging, measurement of external wall temperatures, and recordings of acoustic emissions from the combustor. The observed flame dynamics are characterised by an oscillating edge-flame that is anchored at the combustor inlet and is accompanied by ignition/extinction events leading to the eventual formation of a stable edgeflame and distinct cellular structures along the reaction channel. This paper investigates the unstable and unsteady flame dynamics within the nonpremixed sub-millimetre combustors from ignition to the formation of stable flame structures.
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