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 concentration by volume), equivalence ratios (Φ=0.75~1.15) and combustion powers (CP=1.08~2.02 kW) were investigated in the oxy-fuel (CH4/CO2/O2) combustions, and reference cases (Xoxy=25%~35%, CH4/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 produced when Xoxy>35% or Φ>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.
展开▼
