Investigation of the thermal and emission characteristics of an impinging inverse diffusion flame

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Investigation of the thermal and emission characteristics of an impinging inverse diffusion flame


Author: Ng, Tsz-kwan
Title: Investigation of the thermal and emission characteristics of an impinging inverse diffusion flame
Degree: M.Phil.
Year: 2007
Subject: Hong Kong Polytechnic University -- Dissertations.
Jets -- Fluid dynamics.
Heat -- Transmission.
Fluid dynamic measurements.
Department: Dept. of Mechanical Engineering
Pages: xx, 204 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record:
Abstract: The main objective of this study is to determine the thermal and emission characteristics of an inverse diffusion LPG/air flame as a single jet impinged vertically upward on a horizontal flat copper plate under different conditions. Experiments were carried out on finding their characteristics and inter relationships under different air-Reynolds number (Reair), overall equivalence ratio (o) and the nozzle-to-plate distance (H/dIDF). Similar experiments were also carried out using a premixed flame jet for comparison. Five major tasks were performed successfully by using two main experimental setups to achieve the main objectives of this study. In the first task, the physical appearance of the IDF as a free jet and also an impinging jet was qualitatively noted. The effects of the Reair, o and H/dIDF on the flame shape and length were recorded using a digital camera. Such images were useful in explaining the results obtained in the experiments. In the second task, the temperature distribution and the pollutant exhaust emissions of the free jet IDF were investigated experimentally. The effect of Reair at o=1 on the axial and radial temperature distributions were examined and the IDF was shown to have low pollutant exhaust emissions. In the third task, the stagnation and radial profiles for the flame temperature and heat flux were measured under impinging experiments, while the radial combustion species concentrations were also measured. The effects of Reair, o and H/dIDF on the flame temperature, heat flux and also the combustion species were fully studied. The cool core zone significantly affected heat transfer for the impinging IDF when H/dIDF is low. High temperature and high heat flux, together with high CO2, CO and NO concentrations and low O2 concentration were found near the stagnation point. Such effects became more obvious when Reair or o was increased. Also, the concentrations of HC and CO showed that there was more incomplete combustion in the IDF in higher values of o or when Reair was increased. In the fourth task, the area-averaged heat flux and the heat transfer efficiency of the impinging IDF were calculated by considering the radial heat flux distribution in the integration area with 50 mm in radius. H/dIDF had slightly effect on the two parameters at 4<=H/dIDF<=10. The area-averaged heat flux increased with Reair and o, while higher heat transfer efficiency was obtained at Reair=1500 when o=0.8 and Reair= 2000 when o=1.2. In the fifth task, similar experimental investigations were performed to study the thermal and emissions characteristics of the round premixed impinging flame jet. Comparison between the results obtained from the impinging IDF and the premixed impinging flame jet provided the evidence that the IDF seems to have the advantage of having higher heat transfer efficiency than the premixed flame over a rather large range of nozzle-to-plate distances with lower pollutant species emissions. This study provided a fully investigation on the heat performance and also the pollutant emissions of the IDF. The IDF could achieve quite high heat transfer efficiency over a rather large range of nozzle-to-plate distances. Also, less pollutant emissions were produced by the IDF when compare to a premixed flame.

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