Measurements of Equivalence Ratio Fluctuations in a Lean Premixed Prevaporized (LPP) Combustor and its Correlation to Combustion Instability

摘要

Experimental evidence correlating equivalence ratio fluctuations with combustion instabilities and NOx emissions in a jet-A fueled lean pre-mixed prevaporized (LPP) combustor utilizing a non-proprietary 'generic' fuel injector is presented. Real-time laser absorption measurements of equivalence ratio, together with dynamic combustor pressure, flame luminosity and fuel pressure were obtained at inlet air conditions up to 16.7 arm and 817 K. From this data, an extensive database of real-time variables was obtained for the purposes of providing validation data for future studies of LPP combustion modeling. In addition, time and frequency space analysis of the data revealed measurable levels of acoustic coupling between all variables. Equivalence ratio and dynamic pressure cross-correlations were found to predict the level of combustion instability. Furthermore, NO_x production was found to follow the root-mean-square (RMS) flame luminosity and RMS combustor dynamic pressure. However, the unmixedness of the fuel-air mixture was not found to predict NO_x production in this combustor. The generic LPP injector, although not optimized for low-emissions or combustion stability, provides some of the essential features of real injectors for the purposes of studying the relationship between fluctuations in equivalence ratios and combustion instability. In particular, the fuel premixer advection time was found to have a significant and direct impact on the level of combustion instability. The results of this work support the time-lag concept for avoiding combustion instability when designing injector/premixers in LPP combustors.