Investigations On The Thermo-Acoustic Instability Of Premixed Flame

Lean premixed combustion can reduce NOx effectively. Because the operating conditionsdeviates the chemical equivalent ratio, it leads to the thermoacoustic instability of flame, whichmakes unstable flame, lifted flame and even destroys combustor seriously. The thermoacousticcombustion instability of methane/air lean premixed combustion was simulated andexperimented in this thesis.Firstly, the flame extinct limits of fuel-lean and fuel-rich of methane / air flame weremeasured,and the flame structures were analyzed by using high speed camera. The stabilizeflame mechanism of swirl and porous is theoretically discussed.Secondly, the acoustic oscillations of premixed chamber and combustion chamber weremeasured by using SQlabâ…¡Noise and Vibration Analyzer. The results show that the inlet ofcombustion chambe(r swirl and porous media), the altitude of combustion chamber and length ofgas pipe have significant influences on frequency and amplitude of thermal-acoustic combustioninstability. Accounted for the very strong oscillation of precessing vortex core(PVC), the flameheat release and air pressure oscillations are all oscillate with mutual effect strongly. However,the mixed gas, which flowing through the porous, has rectifier and hackle. Along with the heatload decreasing, frequences of thermal acoustic oscillations gradually decrease in different sizesof combustion. However, the corresponding amplitude is improved, and the dynamic instabilitiesof flame occurred. When gas pipe is the longer, initial oscillation in the combustion chamber isthe less obvious.Besides, the process of methane/air premixed combustion and part-premixed combustionwere simulated by using FLUENT 6.3 software in the paper. The changes of temperature andpressure oscillations of the premixed flame are analysised compare with the partial premixedflame, and have further analysis on the cause of the thermoacoustic instability of flame. Thetemperature, pulsation of pressure and NOx of that of premixed combustion are lower than part-premixed combustion. Lean Oxygen Partially Premixed/ Rich Oxygen SupplementalCombustion(LOPP/ROSC)which was simulated by using FLUENT 6.3 software is introducedelementarily.The results of this thesis provide fundmental experimental data for the strategy ofcontrolling thermal-acoustic combustion instability in lean premixed combustion.