Study On The Internal Burning Of Soot Particles During The Combustion Process Of Diesel Engines

The particulate matter(PM)emission of diesel engines is closely related to the in-cylinder soot oxidation.The internal burning plays a curicul role in the oxidation of in-cylinder soot particles.Therefore,it is of great importance to study the oxidation process and the internal burning of in-cylinder soot particles.A developed total cylinder sampling system was employed to obtain the in-cylinder soot samples at different engine intake pressures.The internal burning possibility of in-cylinder soot was investigated using the soot physicochemical parameters,such as the distribution of primary particle diameter,nanostructure and oxidation reactivity.In addition,the factors affecting the internal burning were also studied based on the soot physicochemical parameters and the results of numerical simulations to evaluate the possibility of internal burning.The major work and achievements of this dissertation are listed as follows:At the same injection strategy,the in-cylinder mean pressure increases with the increase in the intake pressure from 1 to 2 bar,resulting in soot particles with larger fringe length,higher separation distance and tortuosity.Thus,the soot possesses less-ordered nanostructure,lower degree of graphitization and lower apparent activity energy,which in turn favor soot oxidation.However,the decrease in the in-cylinder mean temperature by the elevated quantity of fresh charge weakens the soot surface burning.As a result,the possibility of soot internal burning is increased in the late diffusion combustion phase at the intake pressure of 2 bar.The internal burning increases the surface area for soot oxidation,which further promotes the soot oxidation reaction.In addition,the effectiveness factors of evaluating the possibility of internal burning show an increase after an initial decrease during the combustion process.Increasing the intake pressure will lead to an increase in the effective factor.At the intake pressure of 2 bar,the internal burning of soot particles occurs after the diffusive combustion phase finishes.When the internal burning occurs,the oxygen diffuses into the interior of soot,burns the lower fringe layer of soot and develops a central hollow structure.Such a behavor increases soot oxidation rate.Besides,the internal burning increases the fringe length and decreases the separation distance and tortuosity of soot particles,resulting in soot with more ordered structure.