NOx from Gaseous and Prevaporized Fuels Burned Lean-Premixed at Atmospheric Pressure in Single-Jet Stirred Reactors

摘要

NOx measured for lean-premixed combustion of several gaseous fuels (methane, ethylene, propane, blends of C_1-C_4 alkanes, hydrogen, and blends of H_2-CO) and prevaporized liquid fuels (light naphtha and #2 diesel) is reported. Many of the experiments are conducted for a combustion temperature of 1790K, measured for the recirculation zone of the jet-stirred reactor. Pressure is 1 atm and inlet temperature is 425 to 825K. Reactor mean residence time is 1.3-4.5 milliseconds, though some experiments on hydrogen are conducted at longer times. Two jet stirred reactor sizes are used: 16 and 64 cm~3. Both use a single jet to feed the fuel-air mixture into the reactor. Jet diameters are 4, 5.6, and 9 mm. Combustion is stabilized by stagnation of the jet at the closed end of the reactor and by the interaction of the reactants of the feed jet with the recirculating and exiting gases. Several fuel-air injectors are used: a staged prevaporizer-premixer for the liquid fuels, as well as for several of the gaseous fuels, and tube and spoke premixers that connect directly to the reactor. Laser Rayleigh scattering measurements have been used to examine the degree of vaporization and mixedness of the liquid fuel-air feed jets. The NOx for methane (1790K, 4 ms) is 4-5 ppmv (15% O_2 dry), and serves as a baseline. As the C/H ratio of the fuel increases, with temperature held constant, and residence time held approximately constant, NOx increases. These results have application to low (single-digit) NOx combustion in industrial equipment. Since lean-premixed NOx can be a weak function of pressure, the results have application to power generation and pipeline gas turbines. Initial experimental results on hydrogen flashback are also reported, showing conditions of fuel-air equivalence ratio and injector velocity that induce burning in the one of the tube and spoke injectors.