10. Combustion and Reacting Flows

We measure surface temperatures and emissions of a low NOx porous radiant burner using lean methane/air mixtures blending with various percentages of hydrogen (XH2 = 10%, 30%, 50% in vol.%) at an equivalence ratio f= 0.65. The Ni-Al porous burner was manufactured by applying the high-temperature self-propagating synthesis method having a hollow top-dome cylindrical geometry of 150 mm-height, 66 mm-outer diameter, and 9 mm-porous shell thickness with a total surface of S = 0.03106 m2. The burner with a porosity of about 0.6 is operated at an internal combustion mode using three different volume flow rates (Q = 250, 303, 379 SLPM) corresponding to three different power levels (P = 10, 12, 15 kW). As such, the firing rates FR = P/S are varied from 322 kW/m2 and 386 kW/m2 to 483 kW/m2. The porous surface temperature distributions are recorded by an infrared (IR) camera with 640 x 480 IR pixels at 25 frames/s. Their corresponding radiant heat powers (Pm) are measured by a power meter positioned at a distance of d = 500 mm from the middle of the cylindrical porous burner for the estimation of radiant heat efficiency (n= PR/FR), where PR = (d/r)2Pm/S and r is the inner radius of the cylindrical burner. Results show that the surface temperatures increase with XH2 and P; n increases with increasing XH2 at the same FR, but it decreases with increasing P. We find that both [NOx] and [CO] emissions can be simultaneously low, showing a clean combustion of the present porous radiant burner. Specifically, [NOx] = 13-21 ppm and [CO] = 15.5-23 ppm at XH2 = 0; [NOx] = 23-31 ppm and [CO] = 13.5-18.5 ppm at XH2 = 0.5, where FR = 322-483 kW/m2 and emissions are corrected at 3% O2 concentration. Finally, for application, a novel hot water heater or boiler using three equilaterally-positioned porous radiant burners inside thermal-radiation-collector and fin-tube heat exchangers is proposed and discussed.