Numerical Study Of Suppression Evaluation In Laminar Diffusion Flame Based On Damkohler Number

Reality fire scenarios often involve co-combustion of multiple fuels. The diversification of the fuels led to the complication of the combustion process, the combustion process includes thermodynamics, hydrodynamics, chemical kinetics and transport phenomena. There are multiple scales in combustion problems, the differences exist in the time scales of different chemical reactions in the premixed combustion are enormous; at the same time there are chemical reaction time scales and mixing time scales in diffusion combustion, chemical reaction and diffusion coupled to each other. It is difficult to measure the microscopic changes in combustion through experiments, while numerical simulation has a unique advantage to this problem. Therefore, numerical simulation was used to study premixed flame structure of the mixed fuel and chemistry coupling with mixing in diffusion flame, which has a very important significance for a comprehensive understanding of the combustion process.In this paper, the numerical simulation of chemical kinetics was used to study premixed flame structure and combustion characteristics of mixed fuels to analyze the influence of the mixing ratio on the ignition delay time, the flame thickness, laminar burning velocity, reaction residence time and distribution of the species. The study on ethanol/hydrogen/air premixed flame shows that when more hydrogen was added to the fuel, the ignition delay time was shortened to some extent, and the effects of hydrogen addition on ignition delay time got weak with increasing temperature. The laminar burning velocity increased with the increase of the mixing ratio, particularly when the mixing ratio is greater than 0.4. Flame thickness and characteristic residence time gradually decreases with the increase of hydrogen fraction. In addition, further analysis of the distribution of different species shows that hydrogen addition gives rise to higher H, O, OH peak concentrations, and there is a linear correlation between the peak concentration of H+O+OH and the laminar burning velocity.To study the coupling of chemical and mixing process in diffusion flame, this paper presents the evaluation of inhibitory effect based on Damk(?)hler number. The simpler hydrogen detailed reaction mechanism was used to conduct the simulation of the planar symmetrical co-flow diffusion flames. The study aims to analyze the influence of the diffusion and chemical reaction on the suppression effect of the flame inhibitor by analyzing the changes of the Damk(?)hler number. A numerical study on hydrogen-air co-flow nonpremixed flames with and without flame inhibitor was carried out to investigate the effects of Br2 on the flame temperature, the main radicals, characteristic chemical time as well as characteristic diffusion time. We calculated the Damk(?)hler number and the inhibitor-based scalar dissipation rate to study the physical and chemical effects on hydrogen-air co-flow nonpremixed flames. The result shows that the flame inhibition cycle enhanced the chemical process of the flame, while the inhibitor-based scalar dissipation rate had a significant impact on the overall scalar dissipation rate. In most radial zone of the flame Damk(?)hler number were lower than the case of undoped flame, the inhibitor reduced the flame region and decreased the intensity of the combustion reaction zone. The inhibition effect gradually decreased with the increase of the flame height.