An excess enthalpy flame combustor for extended flow ranges

An experimental study was conducted on the stability and combustion characteristics of the combustor system, based on the excess enthalpy flame, for extended flow rate ranges using a city gas (natural gas) and air mixture, and an entirely new combustor. The combustor was designed in light of previous studies, and the inner tube for combustion was surrounded by a heat exchanger to facilitate external heat recirculation, while a bundle of narrow ceramic tubes was used to produce internal heat recirculation. The stability limits in flow rate and equivalence ratio of the three flames stabilized ahead of, in, and behind the tubes were extended remarkably as compared to those of the previous studies. It became possible to burn stably mixtures as lean as equivalence ratio of 0.151 for large flow rate of 10.0 L/s. The measured temperature distributions showed that the combustion proceeded through the one-dimensional laminar flame, and that the combined external and internal heat recirculation produced very high flame temperature of more than twice the adiabatic flame temperature. The emission characteristics of the combustor were found excellent, while the pumping loss to force the flow through the narrow pores remained in the tolerable range.