Effects of heat transfer on flame stability limits in a planar micro-combustor partially filled with porous medium

2019 ◽  
Vol 37 (4) ◽  
pp. 5645-5654 ◽  
Author(s):  
Qingqing Li ◽  
Jun Li ◽  
Junrui Shi ◽  
Zhaoli Guo
Author(s):  
A. A. Mohamad

Convectional free flame combustion causes the temperature rise in the vicinity of the flame to be very steep, resulting in high temperatures, consequently NOx formation enhances. The fact is that the thermal conductivity of gases are very low, i.e., poor thermal conductors. Combustion in porous media elevates this problem by enhancing heat conduction and thermal radiation from the flame zone, which reduces the flame temperature and NOx formation. Also, heat transfer from the free flame to a load is mainly by convection, while heat transfer is by convection and radiation from combustion zone in porous medium to a load. Moreover, it is easy to stabilize the flame in a porous medium, where the thermophysical properties of the porous medium can engineered for specific application. Most of the work is done on flat type porous burner, where the axial flow of gaseous fuel air mixture forces through a layer of porous medium. In this report a concept of cylindrical porous burner is introduced, where the fuel air mixture is forced to flow radially. Mathematical models and simulation results are introduced for both burners, axial and radial flow burners. Preliminary results of the comparison between the thermal performances between the mentioned burners are discussed. The results revealed that the cylindrical burner has superiority over the convectional flat burner. The cylindrical burner has a wide range stability limits and may produce less NOx than the flat type burners.


Author(s):  
Seyed Mohammad Hashemi ◽  
Seyed Abdolmehdi Hashemi

Combustion process of the premixed methane–air in a novel combined porous-free flame burner was investigated numerically. Two-dimensional model considering nonequilibrium thermal condition between the gas and solid phases was used and the combustion was simulated using reduced GRI 3.0 multistep chemical kinetics mechanism. To examine the validity of the implemented numerical model, the burner was manufactured and tested. Good agreement between the numerical results and experimental data were observed. Thermal flame thickness, flame stability limit, and thermal efficiency were discussed. Multimode heat transfer in the porous medium including convection, radiation, and conduction were quantified and perused. Results showed that the thermal thickness of laminar free flame established in the perforated portion of the burner was considerably less than thickness of submerged flame stabilized in the porous medium. Predicted results suggested that the flame stability limit was augmented in the combined burner compared to the burner with full porous foam. Analyses of the heat balance showed that the thermal efficiency of the combined porous-free flame burner was less than thermal efficiency of the full porous burner. Comparison of the full porous burner with the novel combined porous-free flame burner demonstrated that the combined burner caused higher stability limits and lower thermal efficiencies.


2019 ◽  
Vol 13 (3) ◽  
pp. 5278-5293
Author(s):  
Vipul Patel ◽  
Rupesh Shah

The present research aims to analyse diffusion flame in a tube type burner with Liquefied petroleum gas (LPG) as a fuel. An experimental investigation is performed to study flame appearance, flame stability, Soot free length fraction (SFLF) and CO emission of LPG diffusion flame. Effects of varying air and fuel velocities are analysed to understand the physical process involved in combustion. SFLF is measured to estimate the reduction of soot. Stability limits of the diffusion flame are characterized by the blowoff velocity. Emission characteristic in terms of CO level is measured at different equivalence ratios. Experimental results show that the air and fuel velocity strongly influences the appearance of LPG diffusion flame. At a constant fuel velocity, blue zone increases and the luminous zone decreases with the increase in air velocity. It is observed that the SFLF increases with increasing air velocity at a constant fuel velocity. It is observed that the blowoff velocity of the diffusion flame increases as fuel velocity increases. Comparison of emission for flame with and without swirl indicates that swirl results in low emission of CO and higher flame stability. Swirler with 45° vanes achieved the lowest CO emission of 30 ppm at Φ = 1.3.


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