Numerical Simulation on H2 Rich Blowout Limit in Bluff-Body Burner

Abstract

In order to investigate the hydrogen rich blowout limit (RBL) at different bluff-body diameters and flow velocities, the computational fluid dynamics software Fluent was used to simulate H2 combustion in the present study. The composition probability density function (C-PDF) model was adopted to simulate H2 burning in a turbulent flame by solving two-dimensional Navier–Stokes equations. To verify the accuracy of the C-PDF combustion model, a piloted methane–air jet flame was simulated at first, and a good agreement between the numerical results and the published measurements was obtained. The H2 RBL formula about bluff-body diameters and flow velocities was summarized according to the numerical results. The results show that the C-PDF model is a reasonable method to capture flame ignition, flame extinction, and the H2 RBL. There should be an optimal bluff-body diameter in the burner which stabilizes the flame best. The flame will take an “M” shape with reaction fronts inside the central recirculation zone (CRZ) near the blow-off condition. When the bluff-body diameter remains unchanged, the relationship between the H2 RBL and the flow velocity is a logarithmic function. When the flow velocity remains unchanged, the relationship between the H2 RBL and the bluff-body diameter is a quadratic function. A successful ignition sequence requires typical three phases: the startup of ignition in the recirculation zone, the energy accumulation in the recirculation zone, and the flame propagation from the recirculation zone to the main stream. A complete extinction also requires three phases: the sudden decline of the temperature in the main stream, the energy dissipation from the recirculation zone to the main stream, and the complete extinction of the flame.