Numerical And Experimental Investigation On A Low NOx Emission Combustor For Micro Gas Turbine

In recent years, with the quickly development of the distributed energy systems, microgas turbine has been received great attentions in China. The combustion chamber is one ofthe core components of the micro gas turbine. It is a manifestation of an advanced enginewith the combustion chamber of high efficient and low emissions. The thesis supported bythe national 863 project studied the design methods for a low NOx emissions combustionchamber of a 100kW grade microturbine. Its flow, combustion characteristics and NOxemissions were investigated numerically and experimentally. The main contents of thedissertation are as follows:1. The design methods of the low NOx emissions combustor were developed. Theoutlet of the methods is that the combustor is a two-stage premixed combustor designedfor use with natural gas fuel. The piloting flame severiced as the duty torch to stable thelean premixed flame. The primary premixed passageway is concentric about the pilotpremixed passageway, which operatered at lean premixed mode. The features of thedesign are the increase of the dome air volume fraction and the decrease of the flame zonepeak temperature while maintaining stable operation of the combustion chamber. As aresult, the NOx emissions were greatly reduced.2. Effects of structural and operating parameters on combustion performances andNOx emissions were investigated by using the 3-D CFD methods. The variation trendsdescribed the influences of the inlet temperature, the primary flow swirling intensity, thepilot flow swirling intensity, as well as the fuel ratio of the main passageway to the pilotpassageway on the combustor's flow, combustion and NOx emissions. The results showthat, with the increase of the inlet temperature, the total pressure recovery coefficientdeceased linearly. For example, when the inlet air temperature increased from 300K to873K, the total pressure recovery coefficient decreased from 97.5% to 93.3%. With the increase of the primary inlet swirling intensity, the peak flame temperature decreased. TheNOx emission is also decreased significantly. That is to say, the increase of the primaryinlet swirling intensiy was benefited to decrease the NOx emission of the combustor. Thevariations of the pilot inlet swirling intensities were unimportance for the temperatureprofiles and NOx emissions. But when the pilot inlet swirling intensity increased a certaindegree, the flashback maybe observed, which could cause safety threat of the combustor.The fuel allocating experiments showed that NOx emissions sharply increased with theincrease of the pilot fuel fraction.3. Numerical simulations were completed for the designed combustor with 3-Dfull-scale model. According to the results, the performances of this combustor wereevaluated. It is shown that the total pressure recovery coefficient was 93.3%, and the NOxemission of the combustor was 15ppmv.4. An experimental setup for the micro gas turbine combustion chamber wasestablished. Experimental investigations were completed to study the performances of thereference the 100kW combustor. The experimental results indicated that 100kW designedcombustor was ignition flexible, high combustion efficiency of 99.8%, medial totalpressure recovery factor of 92.2%, low NOx emission of 9ppmv and low CO emission of16ppmv. By comparison of the experimental results with the numerical results, they havethe identical variation trends, although the data are different. This is because of thecomplex of the combustion simulations. However, the results showed that the numericalmethods used in this thesis are feasible from the perspective of engineering application.