High-fidelity numerical analysis of non-premixed hydrothermal flames: Flame structure and stabilization mechanism

Abstract

Hydrothermal flame is a fast oxidation process that occurs in supercritical aqueous environment. Flame structure and stabilization mechanism of laminar non-premixed hydrothermal flames (under a pressure of 25.0 MPa) are studied via homogeneous auto-ignition calculations and two-dimensional high-fidelity numerical simulations, and the effects of oxidizer temperature are investigated. The simulations are conducted with a low-Mach number reacting flow solver where the numerical framework for real-fluid properties are implemented. The bi-branchial edge flame structures are investigated in detail via the distribution of key intermediate species. An isolated reactive region, characterized by the existence of moderate radical H, is observed at the upstream of the stabilization point in the fuel-rich side. Transport budget analysis is conducted on the simulation results. With a high oxidizer temperature, the hydrothermal flame is mainly stabilized by auto-ignition. And with the decreasing of oxidizer temperature, the contribution of flame propagation to flame stabilization increases. The isolated reactive region is further identified as a propagation-dominated reaction zone, which is facilitated by radical H2O2.