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Combusting Jets Issued from Rectangular Nozzles of High and Low Aspect Ratios with Co-Flowing Air

[+] Author and Article Information
Rong Fung Huang

Department of Mechanical Engineering, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Road, Taipei, Taiwan 10672, Republic of China
rfhuang@mail.ntust.edu.tw

Reuben Mwanza Kivindu

Department of Mechanical Engineering, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Road, Taipei, Taiwan 10672, Republic of China
rkivindu@uonbi.ac.ke

Ching Min Hsu

Department of Mechanical Design Engineering, National Formosa University, Huwei Township, Yunlin County, Taiwan 63246, Republic of China
cmhsu@nfu.edu.tw

1Corresponding author.

ASME doi:10.1115/1.4039055 History: Received October 26, 2017; Revised November 29, 2017

Abstract

The flame behavior and thermal structure of gaseous fuel jets issued from rectangular nozzles of high and low aspect ratios with co-flowing air were experimentally studied. Two rectangular nozzles with aspect ratios AR = 36 and 3.27 and with side channels for co-flowing air were examined. Flame behaviors were studied by photography techniques. Flame temperatures were measured using a fine-wire thermocouple. The AR = 36 burner exhibited three characteristic flame modes: attached flame, transitional flame, and lifted flame. The AR = 3.27 burner presented three characteristic flame modes: diffusion flame, transitional flame, and triple-layered flame. High AR jets promoted entrainment and mixing in the region around the flame base, whereas low AR jets enhanced mixing in the regions along the flame edges. At low co-flows, at Rec < 1200, the low AR burner flames were shorter, but at Rec > 1200, the high AR burner flames became shorter and wider. At Rec > 950, the high AR burner recorded higher flame temperatures, compared to the low AR burner by over 100 ºC. At high fuel jet Reynolds numbers and moderate co-flow, high AR burner flames presented better combustion performances when compared to low AR jet flames. The good combustion performance of the high AR jet flames was due to enhanced entrainment and mixing, which were induced by flame lifting. However, at low Rec and high co-flow, the low AR jet flames exhibited desirable flame characteristics due to improved entrainment and turbulence at the jet interfaces.

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