Effects Of Injection Pressure On Number Concentration,Fractal Dimension And Oxidative Reactivity Of Diesel In-cylinder Particles

As an important factor that effects the particle emission of diesel engine,the numerical change of fuel injection pressure plays an important role in the overall combustion process.Therefore the introduction of fractal dimension in high fuel injection pressure and combining with the correlation analysis contributes to the comprehension of effects of fuel injection pressure on soot oxidative reactivity.In-cylinder particle samples are obtained from a total cylinder sampling system under different fuel injection pressure with post-injection strategies.The evolutions of particle size distribution,fractal dimension and the oxidative reactivity of in-cylinder soot are analyzed applying engine exhaust particle sizer,transmission electron microscope and thermogravimetric analysis.The relevance among apparent activation energy,fractal dimension and relative concentration of small-size particles?<30 nm?is also discussed in this paper.The main results are concluded as follows:Diesel engine particle number concentration decreases after rising with the increase of crank angle.The increase in fuel injection pressure will reduce the total number of particles effectively during combustion process.In addition,there is an obvious bi-modal distribution of in-cylinder particles which would disappear when the fuel injection pressure is 120 MPa,and the number of small-size particles?<30nm?reaches the minimum.In-cylinder soot oxidative reactivity parameters including Temperature of initiation?T_i?,Temperature of maximum oxidation(T_max),Temperature of buring-out?T_h?and Apparent activation energy?E_a?generally increase with the increasing of crank angle.With the increase of fuel injection pressure and the introduction of post-injection,all the parameters of in-cylinder soot oxidative reactivity increase rapidly after a period of decrease and the apparent activation energies of diesel soot varies in the range of 126.348¹79.132 kJ/mol.Fractal dimension for the in-cylinder soot particles varies in the range of 1.31¹.89 and shows the tendency of growth after the reduction.Increasing fuel injection pressure would decrease fractal dimension for in-cylinder soot.Nevertheless,overlarge fuel injection pressure has opposite effects.During diesel engine combustion process,the apparent activation energy has a positive correlation with fractal dimension but shows little correlation between relative concentration of small size particles?<30 nm?.