Study On The Formation Mechanism Of Carbon Deposits During Biodiesel Combustio

Under the influence of today’s intensified climate crisis,epidemic situation and international instability,pursuing green and low-carbon energy transformation and developing renewable green energy is an inevitable requirement to solve the climate crisis and energy crisis.Biodiesel is an ideal alternative fuel for fossil fuels,and has attracted much attention due to its advantages such as zero carbon emissions,clean environmental protection,and renewability.However,in practical applications,it has been found that biodiesel is more prone to carbon deposition and coking compared to fossil diesel,which seriously affects combustion efficiency,operational stability,and equipment safety,reducing the service life of parts.At present,the mechanism of carbon deposition in biodiesel is still unclear.Therefore,understanding the formation mechanism of carbon deposition in biodiesel and proposing effective methods to suppress carbon deposition during the combustion process of biodiesel is of great significance for the promotion and application of biodiesel.In this paper,the influence of biodiesel and its different components,different molecular structures on the tendency of carbon deposition was explored through two indicators of carbon residue value and actual resin content.The effects and mechanisms of oxidation degree and antioxidant addition on carbon deposition in biodiesel were investigated using characterization methods such as Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry.Carbon deposition experiments were conducted on Jatropha biodiesel using a premixed combustion platform.Modern instrument analysis techniques were used to analyze the physicochemical properties and changes in the deposition process and chemical structure of biodiesel deposits.The main research conclusions of this article are as follows:(1)The carbon residue value and the actual gum content of the eight kinds of biodiesel are much higher than those of petrochemical diesel,and the actual gum content is 900-1750mg/100 m L.Except for castor oil biodiesel,the carbon residue value is 0.16-0.51%.The carbon residue value and actual gum content of the four main fatty acid methyl ester of biodiesel are lower than that of biodiesel itself.The increase of degree of unsaturation of biodiesel molecule,the increase of carbon chain length and ester chain length will lead to the increase of coking tendency of biodiesel(2)During the long-term oxidation process,the carbon deposition index of biodiesel significantly increases with oxidation time.The actual gum content and residual carbon value increased from 1140mg/100 m L to 11300mg/100 m L and from 0.0272% to 0.277%,respectively.The increase in the content of ether,carboxylic acid,ketone carbonyl,and some lipophilic impurities after oxidation.The addition of antioxidants has a significant inhibitory effect on the actual gum content of the residual carbon agent.Among them,tert butyl hydroquinone reduced the actual gum content by 58.3%,and methyl gallate reduced the residual carbon value by 21.1%.The results indicate that antioxidants can effectively inhibit the self oxidation and free radical polymerization reactions of biodiesel,thereby inhibiting the formation of carbon deposits.(3)The carbon deposition of biodiesel is mainly an amorphous structure dominated by amorphous carbon,and the microscopic carbon deposition is composed of 2-20 μm massive and layered structures.With the extension of test time,the C / O of carbon deposition increased,the degree of graphitization deepened,the proportion of easy pyrolysis components decreased,and the pyrolysis residue increased from 1.25 % to15.97 %.The formation of carbon deposition in biodiesel can be roughly divided into four stages : the formation of surface oil film,the adsorption of carbon deposition precursors,the growth and aggregation of carbon deposition precursors,and the long-term carbonization of surface and bottom carbon deposition.By comparing the molecular structures of methyl enoate,aldehydes,carboxylic acids and methyl enoate after pyrolysis before and after carbon deposition test,the auto-oxidation reaction path and free radical polymerization reaction path of methyl enoate in biodiesel were verified.