Emission characteristics and combustion instabilities in an oxy-fuel swirl-stabilized combustor

This paper presents an experimental study on the emission characteristics and combustion instabilities of oxy-fuel combustions in a swirl-stabilized combustor.Different oxygen concentrations(Xoxy=25%-45%,where Xoxy is oxygen concentra-tion by volume),equivalence ratios(=0.75～1.15)and combustion powers(CP=1.08～2.02kW)were investigated in the oxy-fuel (CH4/CO2/O2)combustions,and reference cases(Xoxy=25%～35%,Cha/N2/O2 flames)were covered.The results show that the oxygen concentration in the oxidant stream significantly affects the combustion delay in the oxy-fuel flames,and the equivalence ratio has a slight effect,whereas the combustion power shows no impact.The temperature levels of the oxy-fuel flames inside the combustion chamber are much higher(up to 38.7%)than those of the reference cases.Carbon monoxide was vastly producedwhen Xoxy>35% or >0.95 in the oxy-fuel flames,while no nitric oxide was found in the exhaust gases because no N2 participates in the combustion process.The combustion instability of the oxy-fuel combustion is very different from those of the reference cases with similar oxygen content.Oxy-fuel combustions excite strong oscillations in all cases studied Xoxy=25%～45%.However,no pressure fluctuations were detected in the reference cases when Xoxy>28.6% accomplished by heavily sooting flames which were not found in the oxy-fuel combustions.Spectrum analysis shows that the frequency of dynamic pressure oscillations exhibits randomness in the range of 50～250 Hz,therefore resulting in a very small resultant amplitude.Temporal oscillations are very strong with amplitudes larger than 200 Pa,even short time fast Fourier transform(FFT)analysis(0.08 s)shows that the pressure amplitude can be larger than 40 Pa.