“…The use of heat-recirculation within a porous reactor allows combustion at extremely low equivalence ratios or with very-low-energy-content fuels, resulting in low NO x exhaust emissions [362,364,365,373]. Similar gains can be achieved with counter-flowing streams of reactive mixtures separated by heatconducting walls [362,366,374], such as the swiss-roll burner [362,363,368,372,374] or the counter-flow heat-exchanging burner [362,374,375]. Recent work has shown that the flames in such burners stabilize through ignition at the locally-high wall temperatures within the excess-enthalpy zone and that flame stretching can significantly increase the flame stabilization over a wider range of firing rates, allowing further fuel-flexibility or variability in the power output, as well as showing that 2-D effects can hinder the flame stabilization for very small channels [370].…”