Predicting the temperature of a premixed flame in a microcombustor

Abstract

We apply the scale analysis and the simulation to relate the flame temperature in a microcombustor to the external wall surface temperature. In deriving the equation for predicting the flame temperature, we account for the detailed reaction mechanisms in the combustion process and we assume that the flow in the combustor tube is laminar. Experimental investigations have been conducted to validate the equation. We employ hydrogen as a fuel and obtain a stable flame in microcombustors with internal radii of 3, 4 and 6mm. Good agreement between the measured and the predicted flame temperature has been achieved. In predicting the flame temperature, we use a Nusselt number Nu=3.650 and 4.363 for the tube diameters of 6mm and above and 4mm and below, respectively.

Effects of major parameters on micro-combustion for thermophotovoltaic energy conversion

“…This explains qualitatively why the average temperature increases for the thin wall combustor. For a typical micro-combustor with a flame temperature of 1500 K [8], a 10% net reduction of axial heat loss predicts an increase of wall temperature for about 150 K, which is consistent with our experimental result. However, the thin wall structure is restricted by manufacturing and strength of material limits.…”

“…For TPV application, a micro-combustor with a backward facing step was developed by Yang et al [7], who showed that the backward facing step is capable of enhancing mixing process and prolonging residence time. Li et al [8] analyzed the combustion at micro-scale using scale analysis and numerical simulation to relate flame temperature explicitly to external wall temperature of the combustor. An excellent review on recent developments on the design of combustor for TPV system can be found in Colangelo et al [9].…”

Development of 1D model for the analysis of heat transport in cylindrical micro combustors

“…Firstly, the 1D flame model is a simplification as the scale analysis [10] noted that the reacting flow in the micro combustor is 2D in nature. However, the 1D assumption is well established and has been widely applied in studying laminar flame propagation [19][20][21]24,25]. Furthermore, Kaisare and Vlachos [37] compared the 1D and 2D (averaged in the radial direction) simulation results and noted that they were in reasonable quantitatively agreement.…”

“…Aside from these numerical studies, Leach et al [19] extended Mallard and Le Chatelier's (1D) thermal flame model to investigate the H 2 -air combustion in micro channels and noted that the heat exchange through the structure of the micro combustor leads to broadening of the reaction zone. Besides, Li et al applied the 1D flame model coupled with the heat conduction in the combustor wall and used it to correlate the flame temperature to the wall temperature [20] and analyze the entropy generation in the micro combustion process [21]. It should be noted that although Leach [20,21] to quantify two important ratios, namely, the heat loss ratio Q l /Q in (defined as the ratio of the heat loss from the flame to the heat generation in the reaction zone) and the heat recirculation ratio Q recir /Q l (defined as the ratio of the heat recirculation through the solid structure to the upstream to the heat loss from the flame).…”

“…Besides, Li et al applied the 1D flame model coupled with the heat conduction in the combustor wall and used it to correlate the flame temperature to the wall temperature [20] and analyze the entropy generation in the micro combustion process [21]. It should be noted that although Leach [20,21] to quantify two important ratios, namely, the heat loss ratio Q l /Q in (defined as the ratio of the heat loss from the flame to the heat generation in the reaction zone) and the heat recirculation ratio Q recir /Q l (defined as the ratio of the heat recirculation through the solid structure to the upstream to the heat loss from the flame). Q l /Q in determines the relative intensity of heat loss in the flame zone, while Q recir /Q l reflects the significance of heat recirculation.…”