Influence of Equation-of-States on Supercritical CO2 Combustion Mixtures

Fossil fuel based direct-fired supercritical CO2 (sCO2) cycles are gaining the attention of industry, academia, and government due to their remarkable efficiency and carbon capture at high-source temperatures. Modeling plays an important role in the development of sCO2 combustors because experiments are very expensive at the designed operating conditions of these direct-fired cycles. Inaccurate density estimates are detrimental to the simulation output. Hence, this work focuses on comprehensive evaluation of the influence and applicability of various equation-of-states (EOS) which are being used in the supercritical combustion modeling literature. A state-of-the-art supercritical combustion modeling methodology is used to simulate counter-flow supercritical CO2 flames by using various equation-of-states. The results show that using the corresponding state principle to evaluate compressibility factor is not accurate. Also, van der Waal type EOSs predictions can be as accurate as complex Benedict–Webb–Rubin EOSs; hence van der Waal EOSs are more suitable to simulate sCO2 combustor simulations. Non-ideal effects are significant under the operating conditions considered in this work. The choice of EOS significantly influences the flame structure and heat release rate. Also, assuming the binary interaction parameter as zero is reasonable in sCO2 combustion simulations.

Influence of Equation-of-States on Supercritical CO2 Combustion

Fossil fuel based direct-fired supercritical CO2 (sCO2) cycles are gaining the attention of industry, academia and government due to their remarkable efficiency and carbon capture at high-source temperatures. Modeling plays an important role in the development of sCO2 combustors because experiments are very expensive at the designed operating conditions of these direct-fired cycles. Inaccurate density estimates are detrimental to the simulation output. Hence, this work focuses on comprehensive evaluation of the influence and applicability various equation-of-states (EOS) which are being used in the supercritical combustion modeling literature. A state-of-the-art supercritical combustion modeling methodology is used to simulate counter-flow supercritical CO2 flames by using various equation-of-states. The results show that, using the corresponding state principle to evaluate compressibility factor is not accurate. Also, van der Waal type EOSs predictions can be as accurate as complex Benedict-Webb-Rubin EOSs; hence van der Waal EOSs are more suitable to simulate sCO2 combustor simulations. Non-ideal effects are significant under the operating conditions considered in this work. The choice of EOS significantly influences the flame structure and heat release rate. Also, assuming the binary interaction parameter as zero is reasonable in sCO2 combustion simulations.

Application of a Nonadiabatic Flamelet/Progress-Variable Approach to Large-Eddy Simulation of H2/O2 Combustion Under a Pressurized Condition

A new nonadiabatic procedure of the flamelet/progress-variable approach (NA-FPV approach) is proposed, and the validity is assessed by performing a large eddy simulation (LES) employing the NA-FPV approach for an H2/O2 combustion field in a single element coaxial combustor under a pressurized condition. The results show that the LES employing the NA-FPV approach can successfully predict the heat flux and capture the effects of heat loss through the cooled walls on the combustion characteristics. This procedure is quite useful especially for the numerical simulations of combustion fields with high temperatures, where there remain reactive radicals (e.g., OH, CH) with high concentrations, such as pressurized combustion, supercritical combustion, and oxygen combustion.