Experimental Study And Numerical Simulation Of Gas Flameless Combustion Induced By The Inner Structure

Flameless combustion was promoted to suppress thermal NOx formation and increase thermal efficiency。It can be achieved by the flue gas recirculation with the combination of the burner and inner combustor structure. Numerical simulation and experimental study was used to investigate the thermal, fluid dynamics and chemical kinemics effect of the flameless combustion induced by the inner structure, which benefit the study of the formation, stabilization and the pollutant production for flameless combustion.Firstly, a test platform for the reactive fluid such as methane, hydrogen, oxygen and the air was built to control the mass flow of gas fuel and oxidizer. The system containing the gas supply ststem, the burner and the test system, and supply the reactive gas for the futher designed combustor and burner for flamless combustion.Secondly, the thermal model is used to study the flameless combustion induced by the inner structure. Thermaldynamical data from the chemkin software is used to analysis the critical process for the methane/air working in the flameless combustion mode. Enthalpy variation in the mixing process of the fresh gas and the burned gas was studied the effect of the temperature and recirculation ratio. Mixture temperature is examined to analysis the effect of the recirculation ratio in the combustion and the inner heat transfer process. Outer heat transfer is estimated for the flameless combustion of the methane and air under different recirculation ratio. And the enthalphy efficiency is caculated in different flue gas temperature and recirculation ratio.Thirdly, instantaneous acetone-PLIF is performed to investigate the 2D radical and axial density flowfield of the jet exit for the low-swirl partially premixed burner. Acetone-PLIF images of the burner exit jet and the profile of normalized density along the radial and axial axes are obtained under two driving pressures. The images show that the axial jet expansion angle is relatively small and the radial jet expands to 1/3 radius region in low driving pressure of 0.2MPa. In high driving pressure of 0.4MPa, axial jet expansion angle increases and the density distribution are more uniform. The radical jet expands to the whole radius region. Furthermore, the outer-downstream edge of vortical structure issued from the low swirl burner is similar to that observed in other research work. An experiment platform including gas supply, calibration and test system was built to investigate the flow characteristics of the flameless oxidation burner for preheating. Constant temperature anemometer was used to examine the flow field near the burner outlet. The results indicate that the distribution of the axial velocity shows saddle-shape along the center section of the burner outlet. The axial velocity gradient near the burner outlet is similar under different fuel/air ratio, and the axial velocity jet boundary of cold flow is close to that of hot flow in different tests. The velocity measurement provides the data for further study of the numerical simulation and experimental study in the flameless oxidation furnace.Furthermore, numerical simulation was carried out to research the flameless combustion induced by the inner structure based on the CFD Fluent software. Different turbulent combustion model is discussed to simulate the flameless combustion. And the thermal quality is examined under different reactor, jet condition and combustion model. Oxygen concentration and the axial temperature in the axis is also discussed.Finally, PSRN model was used to model the flameless combustion in the air for four fuels:H2/CH460/40%(by volume), H2/CH440/60%, H2/CH420/80%and pure hydrogen. The results show that the NOx emissions below 30ppmv while CO emissions are under 50ppmv, which are coincident with the experimental data in the "clean flameless combustion" regime for all the four fuels. The simulation also reveals that CO decreases from 48ppmv to nearly zero when the hydrogen composition varies from 40%to 100%, but the NOx emission is not sensitive to the hydrogen composition. In the highly diluted case, the NOx and CO emissions do not depend on the entrainment ratio.