Novel mixing for ultra-high thermal intensity distributed combustion

Abstract

Ultra-high thermal intensity colorless distributed combustion has been examined for our quest to achieve near zero pollutants emission and enhanced performance. Reverse-cross flow configuration has been investigated at thermal intensities in the range of 270–420MW/m3-atm with specific focus on the exhaust emissions, distribution of intermediate radical species and flow field within the combustor. Novel simplified geometry is used for easy transition to practical ultra-high thermal intensity gas turbine engine applications. The combustion intensities demonstrated here are significantly higher than that used in current gas turbine engines. Numerical simulations under non-reacting conditions are used to understand the effects of fuel injection in reverse-cross flow configuration. Ultra-low NO emissions were achieved for both the premixed (2ppm) and non-premixed (5ppm) mode at thermal intensity of 317MW/m3-atm. The CO emission of about 100ppm and UHC emission of less than 10ppm, revealed very high combustion efficiency at high heat release intensities. Novel mixing technique is also investigated to further decrease the emissions and enhance reaction distribution. In this case the fuel jet is diluted with a portion of the required air while a portion of the fuel is introduced with the air jet. The equivalence ratio of each of the air jet and fuel jet were kept well outside of the methane air flammability limits, for mitigating the possibility of flame flashback. This approach has demonstrated near zero NO emission, equivalent to that encountered in premixed combustion mode. Numerical simulation and OH* chemiluminescence showed that the mixing and combustion behavior is dictated by the high momentum of the diluted fuel jet suggesting favorably mixed oxidizer prior to ignition that results in lower NO emissions. Results obtained with different air jet and fuel jet equivalence ratios on the emissions of NO and CO, and OH* chemiluminescence are presented with view to further develop ultra-high thermal intensity zero emission combustors.