Investigations of the Effects of Flame Configuration on the Combustion of Laminar Diffusion Flame

Abstract

Motivation and objective to study double inverse diffusion flame is introduced, followed by the literature survey on soot formation in inverse diffusion flame (IDF), application of the unique structure of double inverse diffusion flame (DIDF), radiation effects on DIDF, factors that affect the formation of nitric oxide and effects of elevated pressure on diffusion flames. Numerical method is validated by the result of flame height for IDF, which is consistent with result from previous research. In present work, two DIDF burner configurations with different size are used to conduct the simulation. Ethylene is used as the fuel. For each of the burner, three different flow rates of fuel are applied. By comparing the simulation result from DIDF burner with that from normal diffusion flame (NDF) burner, it is found that with the same flow rate of fuel, DIDF always produces less soot and nitric oxide (NO) than NDF does. The conclusion is drawn that DIDF burner configuration leads to less pollution than NDF burner configuration does. And this result is independent on the size of the burner. Factors that affect DIDF flame are also investigated. Flame radiation, including soot radiation and gas radiation, leads to decreased flame temperature, decreased soot and NO formation. Preheating of primary air in DIDF results in more NO formation because flame temperature becomes higher. Elevated operating pressure has great effect on DIDF too. When the operation pressure is elevated, narrower flame is formed; more soot and more NO are produced. Diluted fuel by nitrogen can result in less soot and NO formation, which can help to reduce pollution. As for NO formation in DIDF, there are two mechanisms in present work: thermal mechanism and prompt mechanism. It is found that thermal NO and prompt NO forms at different positions in DIDF and thermal NO is dominated compared with prompt NO.