Abstract
This article employs the CoFlame Code to investigate the effects of hydrogen addition to fuel on soot formation characteristics in laminar coflow methane/air diffusion flames at atmospheric pressure. Numerical calculations were carried out using a detailed C1-C2 gas phase reaction mechanism and a soot model consisting of two pyrene molecules colliding into a dimer as soot nucleation, hydrogen abstraction acetylene addition (HACA) and pyrene condensation as surface growth, and soot oxidation by O2, O and OH radicals. Calculations were conducted for five levels of hydrogen addition on volume basis. To quantify the chemical effect of hydrogen, additional calculations are performed for addition of inert pseudo-hydrogen (FH2). The addition of H2 or FH2 does not have a strong influence on flame temperature. The results confirm that hydrogen addition can inhibit soot formation in the methane/air diffusion flame by reducing both the nucleation and surface growth steps of soot formation process. The effect of FH2 addition on soot formation suppression is more remarkable than H2, indicating that the chemical effect of hydrogen added to methane prompts soot formation. The dilution effect of hydrogen addition on soot formation suppression is stronger than its chemical effect on soot formation enhancement the present findings are consistent with those of previous numerical studies.
Highlights
IntroductionThe emission of pollutants from combustion devices has attracted the public attention
For a long time, the emission of pollutants from combustion devices has attracted the public attention
Hydrogen accelerates the formation of benzene above the main pyrolysis zone due to the increased rate of reversible reaction of hydrogen abstraction based on the hydrogen abstraction acetylene addition (HACA) mechanism, and leads to a remarkable delay in the formation of larger polycyclic aromatic hydrocarbons that reduces the soot nucleation rate and inhibits soot formation
Summary
The emission of pollutants from combustion devices has attracted the public attention. Carbon nanoparticles (soot) produced by incomplete combustion of hydrocarbon fuels are one of the main sources of PM2.5 in the atmosphere that causes severe harm to human health and the environment [1,2]. These challenges have spurred researchers to look for alternative fuels that can reduce soot emissions. Guo et al [5] carried out a numerical study on the effect of hydrogen on the growing process of soot in an ethylene/air diffusion flame They discovered that the suppression effect by hydrogen on the growth of soot was caused by the changes in the concentration ratio of [H]/ [H2] in the reaction zone. The above results show that hydrogen can inhibit soot formation to a certain extent, whereas the inhibitory mechanism of hydrogen on soot formation in hydrocarbon flames is still not fully understood
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