Experimental evaluation of the performance of a flameless combustor

The aim of this study was to investigate experimentally the flameless oxidation phenomena. Experiments have been performed in a small-scale combustor fired with methane, and include detailed measurements of local mean temperatures and concentrations of major gas species for four representative combustor operating conditions, and flue-gas measurements for 27 operating conditions to quantify the combustor performance as a function of the excess air coefficient, inlet air velocity, fuel thermal input and preheat temperature of the combustion air. It was demonstrated that for the present combustor it is possible to establish flameless conditions over a wide range of operating conditions. The detailed in-combustor data show that the temperature and the O2 mole fraction fields are relatively uniform, and that the maximum mean temperatures reached throughout the combustion chamber are relatively moderate, below 1500 °C, even under conditions in which the level of preheating of the combustion air is relatively high. The flue-gas data reveal that NOx emissions are always very low regardless of the combustor operating conditions. However, the CO and HC emissions, and thus the combustion efficiency, are strongly affected by the levels of excess air and preheating of the combustion air. It was found that the combustion efficiency correlates reasonably well with the parameter (Tair/Tfuel)×(m˙fuel/m˙air), varying linearly with it if its value is below ≈0.1 and remaining equal to approximately 100% otherwise.

► In the present combustor is possible to establish flameless conditions over a wide range of operating conditions.
► Temperature and O2 mole fraction fields are relatively uniform.
► NOx emissions are always very low regardless of the combustor operating conditions