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Colorless distributed combustion (CDC) has shown to provide ultra-low emissions of NO, CO, unburned hydrocarbons, and soot, with stable combustion without using any flame stabilizer. The benefits of CDC also include uniform thermal field in the entire combustion space and low combustion noise. One of the critical aspects in distributed combustion is fuel mixture preparation prior to mixture ignition. In an effort to improve fuel mixing and distribution, several schemes have been explored that includes premixed, nonpremixed, and partially premixed. In this paper, the effect of dual-location fuel injection is examined as opposed to single fuel injection into the combustor. Fuel distribution between different injection points was varied with the focus on reaction distribution and pollutants emission. The investigations were performed at different equivalence ratios (0.6-0.8), and the fuel distribution in each case was varied while maintaining constant overall thermal load. The results obtained with multi-injection of fuel using a model combustor showed lower emissions as compared to single injection of fuel using methane as the fuel under favorable fuel distribution condition. The NO emission from double injection as compared to single injection showed a reduction of 28%, 24%, and 13% at equivalence ratio of 0.6, 0.7, and 0.8, respectively. This is attributed to enhanced mixture preparation prior to the mixture ignition. OH* chemiluminescence intensity distribution within the combustor showed that under favorable fuel injection condition, the reaction zone shifted downstream, allowing for longer fuel mixing time prior to ignition. This longer mixing time resulted in better mixture preparation and lower emissions. The OH* chemiluminescence signals also revealed enhanced OH* distribution with fuel introduced through two injectors. [ABSTRACT FROM AUTHOR]

Distributed combustion has been shown to provide significantly improved performance with near zero emissions for stationary gas turbine applications. Characteristics of distributed combustion include uniform thermal field in the entire combustion chamber (improved pattern factor), ultra-low emissions of NOx and CO, low noise, enhanced stability, and higher efficiency. Distributed combustion with swirl have been investigated to determine the beneficial aspects of such flows on clean and efficient combustion under simulated gas turbine combustion conditions with ultra-low NOx emissions. Results are presented here on the impact of employing dual injection of air and fuel in contrast to single injection. Dual and multi-injection is of great importance for combustor design scale up as to maintain flow similarities. Results showed that careful implementation of dual injection can result in emissions as low as single air/fuel injection method. With adequate fuel injection strategy, further reduction in emissions has been demonstrated. Results obtained on pollutants emission with dual injection and different fuel injection strategies at various equivalence ratios showed ultra-low emission (<5 PPM NO and <15 PPM CO) and high performance. OH* chemiluminescence revealed relative position of the flame within the combustor under various conditions for further improvements in distributed combustion conditions and to further reduce NOx emission. [ABSTRACT FROM AUTHOR]