Study On The Effect Of Pyrolysis On Ethanol/Diesel Particulate Matter In Diesel Engine

Clean alternative fuel is an important way to realize energy saving and emission reduction of internal combustion engine.Alcohol ester fuel belongs to clean alternative energy,which is sulfur-free.It can effectively reduce the emission of particulate matter by mixing with diesel.The research object focused on the diesel engine fueled with ethanol/diesel particles,using the way of test and simulation,the 186FA diesel engine test bench and the ethanol/diesel tubular flow pyrolysis reactor test platform were built,and the pyrolysis and oxidation kinetics mechanism of n-heptane-ethanol-pahs was constructed.The high-temperature pyrolysis products,the aromatics forming process and the morphology and oxidation characteristics of particles were analyzed.The influence of pyrolysis on combustion particles was discussed.In order to analyze the product distribution of ethanol/diesel under different pyrolysis conditions,an experimental platform of ethanol/diesel tubular flow reactor was built to measure the molar concentration of gas-phase and liquid-phase products and the quality of solid products produced by the pyrolysis of ethanol/diesel at different pyrolysis temperature,ethanol blend ratio and equivalence ratio.The influence of different pyrolysis conditions on the pyrolysis products of ethanol/diesel was analyzed.The results showed that the main pyrolysis products of the mixed fuel were hydrocarbons,including alkanes,olefins,aromatics,etc.The total concentration of alkenes was higher than that of alkanes and aromatics,and the highest concentration components of alkanes,alkenes and aromatics were methane,ethylene and benzene respectively.When the pyrolysis temperature was fixed and the ethanol blending ratio was 5%,10%and 15%,the soot yields generated by the pyrolysis of mixed fuels were reduced by 6.57%,11.27%and 17.84%;when the ethanol blending ratio was fixed,with the pyrolysis temperature increasing,the concentrations of alkane,olefin and aromatic hydrocarbon were increased,and the soot yields were increased;when the ethanol blend ratio and the pyrolysis temperature were fixed,with the increase of equivalence ratio,the soot yields were increased,the concentration of alkane,olefin and aromatic hydrocarbon was rised.The kinetic mechanism of n-heptane-ethanol-pahs pyrolysis and oxidation reaction was established by PFR model in the CHEMKIN-PRO.The variation of main pyrolysis products and product generation rate with pyrolysis temperature,ethanol blend ratio and equivalence ratio was analyzed.The main generation path of benzene and the chemical reaction process of aromatic hydrocarbon were simulated,and the influence on the generation and elimination of aromatic hydrocarbon was analyzed by the main chemical reaction rate and sensitivity.The results showed that when the pyrolysis temperature was fixed,the pyrolysis products of olefins,alkanes and aromatic hydrocarbons decrease by less than 5%with the increase of ethanol blend ratio of 5%;when the pyrolysis temperature was fixed,the formation rates of methane,ethylene and benzene increased rapidly in a short residence time,and generally increased first and then decreased;When the pyrolysis temperature or the ethanol mixing ratio was fixed,C₅+C₅ and C₂+C₄ were the main paths of benzene formation without oxygen,C₅H₅+CH₃?C₅H₅CH₃ had promotion on the formation of toluene,styrene and naphthalene but C₂H₄+CH₃?C₂H₃+CH₄ had obvious inhibition.When the pyrolysis temperature and the ethanol mixing ratio was fixed,peak value of methane,ethylene and benzene formation rate increased with the increase of equivalence ratio,C₃+C₃ and C₂+C₄ were the main paths of benzene formation with oxygen,CH₃+HO₂?CH₃O+OH and C₂H₄+OH?C₂H₃+H₂O promoted the formation of aromatic hydrocarbons.H and HO₂ radicals played an important role in inhibiting the formation of aromatic hydrocarbons.186FA diesel engine bench test was set up to collect the emission particles of different ethanol blending ratios?0,5%,10%,15%?under the maximum torque condition.By means of SEM and TEM,the changes of the microstructure,average particle size,box dimension and other structural characteristics of the combustion particles of the diesel engine fueled with ethanol/diesel fuel mixture and the particles produced by the cracking of the mixture under different pyrolysis temperature,blending ratio and equivalence ratio were compared and analyzed.The results showed that the carbon deposits formed by the pyrolysis of diesel at low temperature were irregular plate structure,and the morphology of the particles formed by the pyrolysis of ethanol/diesel was similar to the morphology of the particles emitted by diesel engine,which were mainly chain and cluster structure.Under the maximum torque condition,the particles exhausted by the diesel engine fuled with the mixed fuel with different ethanol blending ratio,with the increase of ethanol blend ratio,the average particle size decreased,the box counting dimension increased,the overlapping degree of particles increased,and the structure was tight.The particles formed from the mixed fuel with different ethanol blend ratio by high temperature pyrolysis in the tubular pyrolysis reactor,the structural characteristics of particles had the same change trend.Through the thermogravimetry test,the variation rules of the oxidation characteristic parameters of the particles formed in the pyrolysis of ethanol/diesel and the maximum torque condition of diesel engine were compared.The results showed that under the maximum torque condition,when the particles were formed from the diesel engine fueled with mixed fuel with different mixing ratio?5%,10%,15%?,with the increase of ethanol blend ratio,the T_soot,T_maxax and T_end were gradually increased,the activation energy was reduced;the oxidation characteristic parameters of the particles formed by the high-temperature pyrolysis of the mixed fuels with different ethanol blend ratios?5%,10%,15%?in the tubular pyrolysis reactor were determined,with the increase of mixing ratio,the T_soot and T_max of the particles decreased,the T_end increased and the activation energy decreased.The research work provided a reference for discussing the formation and control of particles in the process of diesel engine burning ethanol/diesel,and promoting the application of ethanol/diesel blend fuel.