Predicting Radiative Heat Transfer in Oxy-Methane Flame Simulations: An Examination of Its Sensitivities to Chemistry and Radiative Property Models

Abstract

Measurements from confined, laminar oxy-methane flames at different O2/CO2dilution ratios in the oxidizer are first reported with measurements from methane-air flames included for comparison. Simulations of these flames employing appropriate chemistry and radiative property modeling options were performed to garner insights into the experimental trends and assess prediction sensitivities to the choice of modeling options. The chemistry was modeled employing a mixture-fraction based approach, Eddy dissipation concept (EDC), and refined global finite rate (FR) models. Radiative properties were estimated employing four weighted-sum-of-gray-gases (WSGG) models formulated from different spectroscopic/model databases. The mixture fraction and EDC models correctly predicted the trends in flame length and OH concentration variations, and the O2, CO2, and temperature measurements outside the flames. The refined FR chemistry model predictions of CO2and O2deviated from their measured values in the flame with 50% O2in the oxidizer. Flame radiant power estimates varied by less than 10% between the mixture fraction and EDC models but more than 60% between the different WSGG models. The largest variations were attributed to the postcombustion gases in the temperature range 500 K–800 K in the upper sections of the furnace which also contributed significantly to the overall radiative transfer.

Assessing uncertainties in prevailing methodologies for modeling radiative transfer in simulations of oxygen-enriched methane flames

“…Figure 2a provides the geometric details of the furnace simulated in this study. Experimental measurements and numerical simulation of methane flames in this geometry at different O 2 /CO 2 dilution ratios in the oxidizer stream have been reported in several studies [7,10,13,19]. However, results from 100% O 2 -methane flames have not yet been reported and were simulated in this study for a range of fuel inlet Reynolds numbers (2600-14,000).…”

“…In order to assess the prediction sensitivities to the uncertainties in the thermal boundary condition, the calculations in Cases 1-4 were repeated at wall temperatures of 500 and 700 K employing the SLW model. The wall temperature range 300-700 K investigated in this study is representative of those found in enclosed environments burning oxymethane flames [7,10,13,19]. The sensitivity of the centerline (0, 0, z) radiative source term (-r•q) prediction to the wall temperature is shown in Fig.…”

“…Based on our previous simulations of oxy-methane flames at different oxidizer concentrations [13,19], representative furnace environments characteristic of methane combustion at oxidizer oxygen concentrations of 30-100% were first generated employing the SLW model [18]. Four cases were investigated corresponding to oxidizer compositions of the following: (Case 1) 30% O 2 -70% N 2 ; (Case 2) 50% O 2 -50% N 2 ; (Case 3) 70% O 2 -30% N 2 and (Case 4) 100% O 2 , respectively.…”

“…T e is the exit temperature at z = 1 m. The gas compositions and T max for the different cases are summarized in Table 1. The gas compositions and peak temperatures representing different oxy-methane flames of different oxidizer compositions were estimated from previous calculations and simulations reported in the literature [4,13]. Inside the enclosure a circular region or a cylinder around the centerline can be imagined, where R = 0.2 m is the radius of the cylinder.…”

“…Parametric uncertainties: these can result from differences in the spectroscopic database and the curvefitting procedures employed to estimate the gas radiative properties from total emissivity data. While this assessment has been made in a few laminar oxygen-enriched methane flames [13], it is important to recognize that oxygen enrichment can cause the adiabatic flame temperatures to rise beyond 3000 K [4]. Many of the gas radiative property models that are currently employed in turbulent combustion simulations have only been validated to a temperature of 2500 K [14][15][16] with a few models validated up to 3000 K [17,18].…”