Performance of two-region porous inert medium burners operating at low thermal powers

Performance of two-region, square-shaped porous inert medium (PIM) burners operating at low thermal powers (densities) of 0.7-2.5 kW (48.61-173.6 kW/m2) was investigated. The smaller-pore region was made of perforated Cordierite plate. Performance was examined for two larger-pore combustion region materials. They had similar dimensions and were made of Nickel-chromium-steel alloy wire mesh (>95% porosity) and SiC foam (10 ppi & ∼87% porosity). The temperature distribution histories were recorded along the burner system for extensive excess air ratios including the unsteady flashback, stable and unsteady blow-off operations. They were lately utilized to determine the stability limits diagram. They were shifted toward the ultra-lean range in agreement with the published data of similar power densities and deviated from that experienced at moderate and high powers. Alternatively, they had a slight dependency on the combustion region characteristics, particularly, the blow-off limit. The flashback and blow-off stability limits had peak excess air ratios of 2.2 and 2.8, respectively, at a thermal power (density) of 1.5 kW (104.2 kW/m2). The confined stable range between the two limits diminishes with power. For the investigated power range, a common operating excess air ratio range of 2.2-2.4 is recommended. Outstanding ultra-low NOx-emissions (<2 ppm) were obtained. CO-emission becomes visible at powers ≤1.5 kW.