Modeling of Pollutant Emissions of Jet-Stabilized Combustors for Micro Gas Turbines Using a Chemical Reactor Network

Abstract In addition to synthetic fuels from renewable energy sources, alternative combustion concepts are a promising solution for achieving climate targets and future emission standards. In this respect, a combustion system based on the jet-stabilized combustor concept represents a technology with high potential to significantly reduce pollutant emissions from micro gas turbines (MGTs), such as nitrogen oxides (NOx) and soot emissions. This is achieved by the formation of a robust inner recirculation zone in the jet-stabilized combustor, allowing for stable operation with a high degree of flexibility in terms of fuel, stoichiometry, and load conditions. For the numerical investigation of the combustion behavior of MGTs, a chemical reactor network (CRN) is utilized with a focus on pollutant emissions. The CRN is formed by a series of two idealized reactor models, consisting of a perfectly stirred reactor (PSR) and a plug flow reactor (PFR), representing the recirculation zone and the burnout area, respectively. The combustor conditions are numerically reproduced by assigning the respective residence times to each reactor. This simplified model allows for the efficient analysis and characterization of the investigated jet-stabilized combustor including detailed chemical kinetics. The CRN is a well-established approach in combustion research, but the determining the residence times is a major challenge. In this study, a jet-stabilized MGT combustor is investigated, by applying a semi-empirical method for the residence time estimation. In the first step, the CRN simulations for pollutant emissions are validated in a wide range of equivalence ratios and temperatures as well as from atmospheric to higher pressures for various MGTs with different thermal powers and combustor designs. The variations include different small hydrocarbon fuel mixtures, combustor sizes and number of nozzles. In the second step, a case study is performed with the CRN to investigate the effect of water admixture to hydrocarbon fuels with a focus on emission behavior in a jet-stabilized combustor. The study demonstrates the applicability of the developed CRN approach for versatile operating conditions. Thereby, deeper understanding is provided on the emission behavior, which can be used to optimize combustion chamber design in different requirement scenarios.