Numerical Simulations of turbulent non-premixed cool flames at supercritical/high pressures: dual peak structure, pressure scaling and real-gas effects*

We present adaptive mesh refinement (AMR)-based 2-D DNS-like simulations of a dimethyl ether (DME)-air temporal turbulent reacting mixing layer with detailed chemistry at 80, 120, and 150 atm. The critical pressure for the fuel mixture obtained from a Vapor-Liquid Equilibrium calculation is 147 atm–indicating mixing occurs between two supercritical gas-like fluids at 150 atm and a subcritical gas-like fuel with a supercritical gas-like oxidizer at 120 and 80 atm. The simulations are performed using both ideal gas and Soave-Redlich-Kwong (SRK) equations of state (EoS) to study real-gas effects. Contours of heat release rate (HRR), temperature, mass fractions of LTC-specific species of DME (e.g., CH3OCH2O2) and CH2O reveal the formation of cool flames that subsequently transition into spotty hot flame kernels. Mixture-fraction conditioned averages of the above quantities exhibit a dual-peak structure due to the unsteady nature of the flow and the presence of multiple temperature-dependent reaction pathways. Deviations in the order of 10-20% are observed between real and ideal gas EoS in predicting temperature and density and up to 30-40% for radical mass fractions at both high-pressure subcritical and supercritical pressures.