The Numerical Simulation And Experimental Research On Oxygen-enriched Combustion Chamber Of Micro Gas Turbine

With the development of the distributed energy systems and the energy utilization approaches, and the increasing environmental requirements, the micro gas turbines (MGT) technology has attracted increasing attention in China. The combustor, which is also a key component in the efficient and clean utilization of energy, plays a vital role in the MGT. Investigating the flue gas recirculation based oxygen-enriched combustor is crucial for the efficient and clean utilization of energy. Based on the National Natural Science Foundation project, in this thesis the design methods of50KW flue gas recirculation based oxygen-enriched combustor are investigated and an experimental platform is built up.Finally the performances of the combustor are experimentally and numerically evaluated.On the basis of common technical experiences, the thermal calculations and the design computations are implemented, the flue gas recirculation based oxygen-enriched combustor is preliminarily designed. According to the characteristics of the premixed combustion, the cold-state flow field and the combustion of the combustor are simulated by the RNG turbulence model, the average mixture fraction/PDF combustion model and the finite rate of the EDC model and the SIMPLEC algorithm. Based on the numerical results, the structure of the combustor is optimized, and the resulting model is determined.The performances of the combustor are investigated by experimental and numerical approaches, and the main research finding is summarized as follows.1. By the optimization design, the resulting parameters of the combustor are outlined as follows:the maximum cross-sectional area empirical coefficient of the combustor is about two times larger than the original empirical coefficient; the ratio between the cross-sectional area of the flame tube and the maximum cross-sectional area of the combustor is0.45-0.56; the height of the annular channel is about1.5times higher than that of original channel; the air surplus coefficient of the primary air is1.5-1.8; the ratio of the primary air volume and the total air volume should be higher than20%; the depth of the jet is (0.3-0.5) Df. Additionally, the turbulent mixing intensity should be enhanced by increasing the length of the mixing and the diameter of the cooling hole.2. By the numerical simulations, the following research findings are obtained:(1) the combustion temperature in the flame tube increases with the rising inlet temperatures. The concentration distributions of methane and carbon monoxide gradually decrease near the combustion area. The total pressure loss coefficient and the uneven temperature coefficient gradually decrease, and the combustion efficiency exceeds99%;(2) the combustion temperature in the flame tube increases with the increase of the inlet oxygen concentration, and the combustion temperature will remain unchanged when the oxygen concentration is higher than30%. The concentration distributions of methane and carbon monoxide near combustion zone gradually decrease, and the total pressure loss coefficient increases. The uneven temperature distribution coefficient in the outlet is the smallest when the designed concentration of oxygen is30%, which will increase with the rising deviations of the designed values. When the concentration of oxygen is21%, the combustion efficiency is97%. When the concentration of oxygen is higher than24%, the combustion efficiency is higher than99%;(3) the combustion temperature increases with the increase of loads. The concentration distributions of methane and carbon monoxide near combustion zone gradually decrease, and the total pressure loss coefficient decreases. The uneven temperature distribution coefficient will gradually increase when the load is lower than50%; however, when the load is higher than50%, and the uneven temperature distribution coefficient will decrease; the combustion efficiency is higher than99%.3. By the numerical simulation approach, the following pollutant emission characteristics are obtained:the concentration of NOx in the exit is about0.00005mol/mol in the designed combustor. With the increase of temperature, the potential surface of the NOx generation ratio in the flame tube gradually expands to the combustion zone from the mixing zone. With the rising oxygen concentration, the generation ratio of NOx will increase, which will remain unchanged when the oxygen concentration exceeds35%. The inlet moisture will restrain the formation of NOx, and the NOx emission concentration does not decrease when the moisture content is higher than10%.4. Experimental results indicate that:(1) the relationship of the pressure and the gas flow rate and the on working flame is weak, and the working torch can remain stable combustion in a large range of the gas flow rate;(2) there is close correlation between the working torch and the oxygen concentration, the color of the flame will become orange from the incandescent state with the increase of the oxygen concentration. When the oxygen concentration is22%, the color of the flame is blue, and the flame is instable when the oxygen concentration is18%, and the working flame will extinguish when the oxygen concentration is14%;(3) the fuel/air ratio of the working torch descends with the decrease of the inlet air volume, and the working flame can ensure the stable combustion when the fuel air ratio decreases to0.02-0.03.These research findings pave a way for the development of the structure design of the flue gas circulating based oxygen-rich combustor, the optimization of the flow field and experimental studies.