How do water and CO2 impact the stability and emissions of the combustion in a micro gas turbine? — A Large Eddy Simulations comparison

Abstract

Micro Gas Turbines have to become more operational and fuel flexible, and carbon clean. Applying cycle humidification and Exhaust Gas Recirculation (EGR) in combination with Carbon Capture offers a solution. However, current advanced mGT cycle development is limited by the combustor. To improve the cycle performance further, stable and complete combustion has to be achieved under unconventional diluted conditions. Accurate data predicting the stability and performance of specific mGT combustors under these diluted conditions are still missing. A comparison between classic natural gas combustion in an mGT and three diluted cases with water and/or CO2 using Large Eddy Simulations (LES) is presented in this paper. Results show that complete and stable combustion was reached for all cases. Although the flow dynamics are identical, diluted operating conditions lead to a wider reaction zone. An outlet temperature reduction could be observed in the water diluted cases due to the higher specific heat of the humidified combustion air. Regarding CO emissions, the humidified case presents slightly lower concentrations (25 ppm) compared to the reference case (32 ppm), while the dry EGR case shows the highest values (50 ppm). Based on high fidelity LES results, the feasibility of mGT combustor operating under diluted conditions has been proven.