Experimental Investigation of Stability and Structure of Vertical LPG Inverse Diffusion Flames Issuing from an Elliptic Burner | ||||
| Engineering Research Journal | ||||
| Article 8, Volume 171, Issue 0, September 2021, Page 119-137 PDF (1.52 MB) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/erj.2021.193812 | ||||
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| Authors | ||||
| A. A. Mahgoub* ; A. M. Hussien; K. A. Emara | ||||
| Department of Mechanical Power Engineering, Faculty of Engineering at El-Mataria, Helwan University, Massaken El-Helmia, P.O. 11718, Cairo, Egypt. | ||||
| Abstract | ||||
| The present paper experimentally examines the influence of the progressive variations of the central air jet velocity in a concentric circular-elliptical inverse diffusion flame (IDF) on the visual and thermal structure and stability of the developed flames. All experiments are conducted at a fixed fuel flow rate (liquefied petroleum gas) throughput that emerges from the annular elliptic passage having an aspect ratio of 2:1. The visual images are aided via a digital camera and shadowgraphs, while the thermal structure (axial and radial temperature profiles) is acquired using a bare fine wire (125 μm) thermocouple; rendering radiation loss insignificant. The visual images and shadowgraphs clearly indicate the existence of four regimes: (i) an annular partially premixed region at the burner rim, (ii) an inner central premixed blue flame, (iii) an outer luminous yellowish post combustion zone and (iv) the flame tip buoyant zone. The progressive increases of the central average air velocity (ðĖ ð = 7.4 m/s up to 31.3 m/s) result in shortening the visible flame length and narrowing the flame width. These are coupled with changing the flame appearance from a yellowish diffusion flame with a sooty core regime to an intense central premixed flame surrounded by a soot ring to blue flames exhibiting intense central radiation regime associated with soot oxidation. At extremely high air velocity > 21 m/s, locals flame extinction and re-ignition occurs at the boundaries of the ellipse minor axis and further increase of ðĖ ð causes complete extinction of the main flame. These findings are very much supported by the mean gas temperature measurements that indicate steep temperature rise associated with the formation of a central premixed combustion within the flame core which is followed by the diffusion mode of combustion. A plateau of the axial temperature profiles is observed in the transition zone between the two regions whereby the rise in temperature due to soot oxidation is balanced by the radiation loss. | ||||
| Keywords | ||||
| Inverse diffusion flame; Elliptic burner; Liquefied petroleum gas; Flame structure; Flame stability | ||||
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