Experimental Investigation Of Combustion Characteristics Of Multi-Swirling Syngas Combustors

The multi-swirling lean premixed combustion technology probably is the best option of medium and low heat value syngas premixed combustion for reducing pollution. However, it is necessary to solve the key issues in hydrogen-enriched syngas premixed combustion, such as thermoacoustic oscillation, flashback and fuel flexibility etc. This paper at first briefly summarizes the combustion technologies that have been applied to fuel flexibility, combustion instability, flashback and multi-nozzle etc., and then through reviewing the theory and model research with regarding to thermoacoustic oscillation, introduces classical Rayleigh criterion, extended Rayleigh criterion and Chu criterion. Secondly, it is concluded that all these researches above supported the conclusion that the thermoacousitic oscillation in combustor is the self-excited oscillation with feedback that produced the limit cycle oscillation with stable amplitude. Accordingly, this paper introduces the theory and model analysis approach of thermoacoustic oscillation driving and damping mechanism. In later following experimental researches performed, this paper summarized the approaches applied to the time-domain and frequency-domain analysis of dynamic pressure and dynamic chemiluminescent density.With regarding to the experimental researches, this paper compares the experimental results of the multi-swirling syngas diffusive combustion research performed on a full-scale gas turbine combustor medium-pressure test rig and the single-swirling syngas diffusive combustion performed on field test rig and the medium-pressure test rig. It is found that no matter it is single-swirling or multi-swirling combustor, the combustion processes are very stable under all experimental conditions in this paper, with no intensive thermoacoustic oscillation occurred. Through comparing the temperature distribution, dynamic pressure characteristics, emission characteristics and fuel constituent changing range, it is observed that both have good fuel flexibility but the multi-swirling combustor is performing better on this regard than the single-swirling combustor.Then this paper introduced the premixed combustion experimental research performed in four single-swirling model combustors with different types of premixed gas in terms of constituents. It is observed that partial flashback and full flashback are both occurring, and the full flashback process demonstrated sub-critical bifurcation characteristics with retardation effect. When the heat value of different types of premixed gas is the same, the higher the hydrogen concentration, the lower the critical equivalence ratio, the more easily flashback is like to occur and thermoacoustic oscillation facilitates the flashback. The dynamic chemiluminescent density indicating the dynamic heat release is well relative to the dynamic pressure indicating the thermoacoustic oscillation in terms of amplitude-frequency characteristic, both are able to present the dynamic as well as flashback characteristics.At last this paper introduced the premixed combustion research performed in three multi-swirling models with different constituents of premixed gas. For seven co-swirling and counter-swirling combustors, intensive thermoacoustic oscillation is observed during the test with changing the equivalence ratio and total flow rate respectively, and the processes of oscillation start, oscillation saturation and oscillation elimination are similar. With reduced the concentration of hydrogen, the oscillation start critical equivalence ratio is higher and the maximum amplitude of thermoacoustic oscillation is larger. The oscillation start process of multi-swirling premixed combustion is a nonlinear bifurcation process. Through the phase diagram analysis of dynamic pressure phase space reconstruction, the limit cycle characteristics of thermoacoustic oscillation are observed and then it is found that the oscillation start amplitude is not only determined by the static system parameters but also by their change rates. Through wavelet transformation applied to the dynamic pressure continuous power spectral analysis, it is observed that the combustion instability inception o should be the intermittent pressure oscillation. Combining the wavelet transform and AR model on dynamic pressure for a continuous PSD analysis, high resolution in both time and frequency domain is available according to sudden change processes such as oscillation start, oscillation elimination, flashback and frequency hopping. Comparing with single-swirling combustors, multi-swirling combustors have the better flashback characteristics. Through systematically comparing flashback, distinction, thermoacoustic oscillation and pollutant emission characteristics, the safe domain in equivalence ration - total flow rate diagram is narrow, but the domain can be enlarged if N2 or water is used as dilution.In sum, this paper analyzes the experimental results with regards to the characteristics of thermoacoustic oscillation, flashback and fuel flexibility of enriched-hydrogen premixed multi-swirling combustion, provided a more solid basis for future experimental research, theory and model analysis and numerical simulation, and eventually a technology support to redesign the combustor with dry low emission technology applied for enriched-hydrogen fuels.