Stability Limits of Premixed Methane-Air Microflames for Micropower Generation
Stability limits of premixed microflames were experimentally and computationally studied in order to understand the fundamental behavior of the flames when applied for micropower generation. Single microflames were generated on microtubes with inner diameters of 300-420 μm for methane-air mixtures at temperatures of 298-400 K and atmospheric pressure. For all the microflames at normal temperature, the stability limits were observed in a fuel-rich region, which is different from conventional macroflames exhibiting fuel-lean stability limits. Similar to the macroflames, however, the stability limits of the microflames show C-shaped curves in a tube exit Reynolds number (Re) – fuel equivalence ratio diagram, due to insufficient residence times and heat losses. For elevated temperature that is realistic condition for micropower generation using a heat-recirculation concept, the stability limits were extended toward the fuel-leaner conditions. Numerically predicted structure of microflames near the critical point (that is defined as the fuel-leanest condition among the C-shaped fuel-rich stability limits) showed significant fuel-dilution immediately near the tube exit due to a low Re effect, explaining why the stability limits of microflames are observed only in the fuel-rich region. Microcombustors for micropower generation should be designed to completely consume fuel for better performance.
Soon-Bok Lee and Yun-Jae Kim
O. C. Kwon et al., "Stability Limits of Premixed Methane-Air Microflames for Micropower Generation", Key Engineering Materials, Vols. 326-328, pp. 1133-1136, 2006