NUMERICAL PREDICTIONS FOR A SIMULATED METHANE FIRE

A buoyant, turbulent methane flame with a base diameter of 0.25 m and a heat release rate of 28 kW was numerically modeled. Soot formation was included in the model by a phenomenological soot formation scheme. Gas radiation was treated by a weighted-sum gray-gas model. A non-isothermal, non-homogeneous field approach was utilized and the thermal radiation was included by incorporating a four flux radiation model into a finite-difference scheme. The methane fire did not show appreciable soot concentrations to the extent that the radiation was significantly affected. The radiation present was predominantly due to gaseous species. The centerline flame properties such as the axial velocity, mean temperature, and entrainment behaviors are generally well reproduced by the theory. However, the radial expansion of the flame is underestimated near the flame base because of the neglect of the elliptic behavior in the present approach. An analysis of the thermal radiation behavior revealed a approach. An analysis of the thermal radiation behavior revealed a non-uniform heat feedback flux distribution. Unlike in sooting flames, where the flux maximizes usually midway between the centerline and flame edge, we observe the maximum flux at the pool center in the methane fire. In sooting flames, this behavior arises because of radiative energy blockage by the cold fuel vapor and soot in the core. A reduced radiation blockage in the methane flame is a distinguishing feature of the methane fire compared with sooting pool fires.