Simulation of Ethylene Wall Fires Using the Spatially-Evolving One-Dimensional Turbulence Model

Abstract

The mechanism of flame propagation in fuel beds of wildland fires is important to understand in order to quantify fire spread rates. Fires spread by radiative and convective heating and in some cases require direct flame contact to achieve ignition. The flame in an advancing fire is unsteady and turbulent, making study of intermittent flames in complex fuels difficult. A 1.83 m tall, 0.61 m wide vertical wall fire, in which ethylene fuel is slowly fed through a porous ceramic, is modeled to investigate unsteady turbulent flames in a controlled environment. Three fuel flow rates of 235, 390, and 470 L/min are considered. Simulations of this configuration are performed using a spatial formulation of the one-dimensional turbulence (ODT) model which is able to resolve individual flames (a key property of this model) and has been shown to provide turbulent statistics that compare well with experimental data for a number of flow configurations including wall fires. In the ODT model diffusion–reaction equations are solved along a notional line of sight perpendicular to the wall that is advanced vertically. Turbulent advection is modeled through stochastic domain mapping processes. A new Darrieus–Landau combustion instability model is incorporated in the ODT eddy selection process. The ODT model is shown to capture the evolution of the flame and describe the intermittent properties at the flame/air interface. Simulations include radiation and soot effects and are compared to experimental temperature measurements. Simulated mean temperatures differ from the experiments by an average of 63 K over all measurement points for the three fuel flow rates. Predicted root mean square temperature fluctuations capture the trends in the experimental data, but overestimate the raw experimental values by a factor of two. This difference is discussed using thermocouple response and heat transfer correction models. Simulated velocity, soot, and radiation properties are also reported.