Influence of two-stage air supply on behavior of kerosene combustion and NOx emission in porous ceramic burner

A porous ceramic burner has already been proposed for high turn down ratio in kerosene combustion. However, at higher loads, considerable amounts of NOx are found to be emitted. This present paper proposes a two-stage air supply system for reducing NOx emitted from kerosene combustion on a porous ceramic burner, and other combustion characteristic of this burner are experimentally studied. It has been confirmed from experimental works that by introducing two-stage air supply the fuel lean limit is lowered to as low as 0.2 equivalence ratio and that the stable combustion area ranges from 2.0 to 11.5 kW. Then the corresponding turn down ratio achieves 5.8. Since the ratio of primary air to total air greatly influences not only the temperature distribution in the burner but also the soot formation, the CO concentration and the NOx emission at the exit of the burner, this value is regarded as an important operating factor in this burner. By using the optimum ratio of primary air to total air, the NOx emission is found to be approximately one-quarter to that of the emission with single-stage air supply.