Investigation On Combustion And Soot Particles Formation Characteristics Of 2,5-dimethylfuran/diesel Blends

Fossil energy crisis and ecological pollution have been the focus of attention of the current government,academia and industry,which are also difficult to be solved.The development of alternative and renewable fuels and the construction of diversified energy supply system can reduce the reliance on conventional petroleum fuels and exhaust emissions in the use of compression ignition engines.In addition,soot particle emissions from diesel engine adversely affect human health and the environment,whose formation mechanisms are highly complex and has drawn the international combustion field's concern.Recently,2,5-dimethylfuran(DMF)as the oxygen alternative or additive fuel in internal combustion engines is gaining public and scientific attention,because it can ease the energy crisis and reduce pollutant emissions.Thus,the objective of this work is to experimentally and theoretically explore the effects of DMF addition on the diesel fuel combustion and soot particle formation.Fristly,an experimental study was conducted on a diesel engine added with DMF under different engine loads,fuel injection timing and EGR ratios,the results indicated that(1)DMF addition can improve the combustion process,but it may produce high pressure rise rates and worsen combustion with the rise of DMF content,(2)DMF addition can reduce the total particulate mass concentration and particulate mean diameter,but increase the total particulate number concentration,(3)DMF addition can decrease the number of particles demonstate in the state of cluster and the degree of primary particle density,therefore the spatial structure was less compact.Meanwhile,DMF addition can weaken the primary particle internal structure of the surface of micro-crystalline and lead to the increase of amorphous nanostructure characterized.Secondly,numerical investigations were conducted to give an insight into the combustion and soot particle formation of DMF/diesel blend fuels,the main contents are listed as follows:(1)A reduced n-heptane/toluene/DMF tri-component fuels combustion mechanism composed of 99 species and 395 reactions was developedbased on the systematic multi-stage mechanism reduction strategy and decoupling methodology,and then was extensively validated against the experimental results,including measured ignition delays,species mole fraction profiles,laminar flame speeds and homogeneous charge compression ignition engine combustion.(2)The physical properties of DMF and DMF/diesel blends were obtained using physical property prediction methods and the method of fitting experimental results.(3)A soot model was built that couples the proposed kinetic mechanism,and it is assumed that pyrene molecule as soot inception species and can also be deposited directly on the particle surface in this model,meanwhile the reaction rate of soot nucleation,PAHs deposition on the soot particle surface and OH-induced soot oxidation were calibrated.(4)A three dimensional calculation platform was established using KIVA-CHEMKIN code implementing the proposed reduced mechanism,fuel physical property databases and soot model framework,then was used to simulate the combustion behavior and soot particle formation of blend fuels in constant volume chamber and diesel engine.The numerical simulation studies gave the following results:(1)The proposed n-heptane/toluene/DMF tri-component reduced mechanism is able to predict ignition delays,species mole fraction profiles,laminar flame speeds and homogeneous charge compression ignition engine combustion within extensive ranges.(2)The simulation results with the computation platform show that the predicted lift-off length,the concentration and distribution of soot volume fraction,as well as soot formation regions,agree quite well with the experimental results in constant volume diesel spray combustion cases.The predicted concentration and evolution of PAHs and soot also agree quite well with the experimental results in diesel engine cases.The combustion process and soot emission of diesel and D30(70%diesel/30%DMF,by mass)can also be well predicted.(3)The main sooting region is located in the area where the equivalent ratio is greater than 1.5 and the ambient gas temperatures varies from 1700 to 2100 K,meanwhile,it located in the upstream of the main production area of pyrene,and it is consistent with the main production area of acetylene.(4)The peak soot level in a fuel jet decreases with increasing ambient oxygen concentration,increasing injection pressure or increasing orifice diameter.(5)DMF addition can prolong the ignition delay time,increase the lift-off length,whichis helpful to improve the fuel-air mixing,menwhile it can provide oxygen atoms,this results in lower equivalence ratio and reducing the carbon remaining in the form of soot precursors and soot particle.Experimental and modeling study of the combustion and soot particles formation characteristics of DMF/diesel blends,as well as operating parameter effects,which is helpful to optimize the combustion efficiency and soot particles emission control of diesel engine,to provide theoretical and experimental basis for the application of new fuel,it has great theoretical value and practical significance for easing energy crisis and improving environmental quality.