Reaserch On The Formation And Characteristics Of Particulate Matter From Methanol/F-T Diesel Combustion Based On Chemical Reaction Kinectics

F-T diesel and methanol can be produced through coal liquefaction technology.F-T diesel,as an alternative fuel,can reduce the consumption of diesel and lower the emissions of particulate matter in diesel engines.The combustion of methanol with F-T diesel is an effective way to apply methanol and F-T diesel in diesel engines.The study on the formation process of particulate matter in the combustion of methanol with F-T diesel is of great significance for promoting the application of coal-based fuels and reducing diesel engine particulate matter emissions.The paper focuses on the particulate matter generated from the combustion of methanol with F-T diesel.The oxidation intermediates of the characterized fuel of F-T diesel were measured by using synchrotron photoionization mass spectrometry detection technology.A test bench for particulate matter collection in a diesel engine and atmospheric environment was built to measure the characteristic parameters of particulate matter generated from the combustion of F-T diesel under different methanol atmospheres.The chemical reaction kinetics mechanism of methanol/F-T diesel-PAHs was established,and the chemical formation process of particulate matter was analyzed.The impact of methanol atmosphere on the morphology and chemical formation process of particulate matter was also investigated.Measurement and analysis of the physicochemical properties of F-T diesel were conducted to establish its fuel characterization.The composition of F-T diesel was measured using gas chromatography-mass spectrometry.The results showed that F-T diesel is composed of 93.82 mol%of n-alkanes and 6.18 mol% of iso-alkanes,with n-dodecane being the main component,accounting for 26.09 mol%.The physical and chemical properties of F-T diesel were estimated based on its composition,cetane number,and lower heating value.It was determined that ndodecane(94 mol%)and iso-octane(6 mol%)were used as the characterized fuel for F-T diesel.The physicochemical properties such as cetane number,lower heating value,carbon-to-hydrogen ratio,and density,which are used to characterize the fuel,are found to be in good agreement with F-T diesel,with a maximum deviation of less than 5.9%.A study was conducted on the oxidation characteristics of the characterized fuel representing F-T diesel in the temperature range of 500 K to 890 K.A jet-stirred reactor experimental platform was constructed,and synchrotron radiation photoionization mass spectrometry detection technology and molecular beam sampling technology were applied to measure and analyze the combustion oxidation products of F-T diesel characterization fuel,and to explore the changes in concentration of various oxidation products such as alkanes,olefins,and alkynes generated during the oxidation of F-T diesel with temperature.The results showed that various carbon oxides,alkanes,olefins,alkynes,and other 52 kinds of oxidation products were detected during the oxidation process of F-T diesel characterization fuel.N-dodecane and iso-octane exhibited a significant negative temperature coefficient phenomenon in the temperature range of 500 K to 700 K,and the reactant concentration first decreased and then increased with the increase of reaction temperature,and the high-temperature reaction was initiated at 800 K,and the concentration decreased sharply.Benzene and toluene began to be generated at a temperature of 850 K.A chemical reaction mechanism was developed for F-T diesel,and the formation pathways of carbonaceous precursors were analyzed.Using a hierarchical construction approach,the mechanism of methanol/F-T diesel-PAHs(polycyclic aromatic hydrocarbons)was established by combining n-dodecane,iso-octane,and methanol reaction mechanisms,resulting in a mechanism containing 1713 species and 8492 reaction steps.Based on the experimental data from the jetstirred reactor,the mechanism was optimized through sensitivity analysis.The mechanism was verified by comparing the predicted results with the experimental data for the concentration of oxidation products,ignition delay time,and laminar flame speed.The analysis of chemical reaction pathways showed that the oxidation of n-dodecane and iso-octane is mainly carried out through dehydrogenation,oxygen addition,and cracking reactions.With increasing temperature,the role of the cracking reaction gradually strengthens.Methanol is mainly oxidized to form hydroxymethyl through the oxidation pathway at low temperatures,and methoxy is formed through the dehydrogenation pathway at high temperatures.The generation of benzene mainly occurs through the C3+C3 and C2+C4 pathways.Benzene is produced by the dehydrogenation of acetylene and the addition reaction of propyne radicals to form polycyclic aromatic hydrocarbons.The impact of different methanol atmospheres on the formation of F-T diesel particles was analyzed using the constructed mechanism.At an equivalence ratio of 1.0,an increase in environmental temperature,pressure,and methanol blending ratio all help to reduce the formation of soot precursors,while an increase in equivalence ratio leads to a significant increase in the production of soot precursors.Methanol blending enhances the concentration of radicals such as HO2 and OH in the reaction system.The O in methanol is released in the form of radicals such as HO2,which reduces the reaction rate of elemental reactions related to soot precursors and helps to reduce particulate matter emissions.The addition of methanol has a significant impact on the microstructure of particles.The intake system of a 186 FA diesel engine was modified by installing a methanol injection system,and the particulate matter generated by the combustion of diesel at a speed of 2700 r/min and a load of 75 % was collected.A atmospheric environment particle collection experimental platform was constructed to collect F-T diesel combustion particles in a methanol atmosphere.The structural characteristic parameters such as particle size and interlayer spacing of particles were analyzed.The results show that with the increase of methanol blending ratio,the interlayer spacing and particle size of combustion particles in the atmospheric environment gradually decrease,while the particle size of diesel engine combustion particles gradually decreases and the interlayer spacing gradually increases.Methanol blending inhibits the production of polycyclic aromatic hydrocarbons and promotes particle oxidation.The research work shows that the combustion of F-T diesel fuel in a methanol atmosphere can help reduce particulate matter emissions,and changes in the methanol atmosphere can have a significant impact on the formation process and morphology of particulate matter.The research has important implications for promoting the diversified and clean utilization of coal-based fuels in diesel engines.