Study On The Effect Of Biodiesel Molecular Structure On The Particulate Matter Of Diesel Engine

Facing the increasingly severe energy crisis and the increasing environmental pollution problems,finding efficient and clean alternative fuels has become one of the important ways to ease the pressure of nergy and reduce the emissions.As a clean and renewable alternative fuel,biodiesel can be blended with fossil diesel in any proportion and directly applied on diesel engine,and it can significantly reduce diesel particulate emissions.It has been widely concerned by scholars at home and abroad.Therefore,based on the particulate matter sampling and analysis system developed by the research group,this paper studies the influence of the differences in the molecular structure of biodiesel on the combustion process,the number concentration of particulate matter,the micro morphology,and the microstructure of primary particles.The specific conclusions are as follows:1.As the length of the carbon chain increases,the ignition delay shortens,the combustion start time advances,the combustion duration increases,and the proportion of premixed combustion decreases.The increase of the double bond will cause the ignition delay increase,the combustion start time is delayed,the combustion duration is shortened,the premixed combustion ratio and the maximum cylinder pressure increase.Compared with methyl oleate,the ethyl oleate has a longer combustion duration and a lower maximum in-cylinder pressure.In addition,as the load increases,the premixed combustion ratios of the six fuels are gradually reduced,and the diffusion combustion ratios are gradually increased.2.As the length of the carbon chain increases,the nucleation mode particle and total particle number concentration decrease at low and medium loads,and show a trend of first increasing and then decreasing at high loads;accumulation mode particle number concentration showed a trend of increasing first and then decreasing.With the increase of double bonds,the the nucleation mode particle and total particle number concentration increase,and the accumulation mode particle number concentration decreases.Compared with methyl oleate,the nucleation mode particle and total particle number concentration was lower,while the accumulation mode particle number concentration increased significantly.3.The particulate matter from diesel engine are,fractal-like agglomerates consisting of quasi-sphere primary particles.As the length of the carbon chain increases,the fractal dimension decreases first and then increases;the increase in double bonds reduces the fractal dimension of the particulate matter;compared with methyl oleate,the fractal dimension of the particulate matter is larger.In addition,as the load increases,the fractal dimension of the particulate matter from the six fuels shows a trend of decreasing first and then increasing.4.Most of the primary particles produced by burning biodiesel are onion-shell crystallitic carbon structure.The double bonds in the fuel molecules will change the core structure of the primary particles.As the length of the carbon chain increases,the average particle size of the primary particles gradually increases;the increase in double bonds will reduce the average particle size of the primary particles;compared with methyl oleate,the average particle size of the primary particles is larger.In addition,as the length of the carbon chain increases,the separation distance and tortuosity of the primary particles decrease first and then increase,and the change trend of the fringe length of primary particles is opposite.The increase of double bonds will lead to the increase of the separation distance and tortuosity of the primary particles,and the fringe length decreases.Compared with methyl oleate,the separation distance and tortuosity of the primary particles of ethyl oleate are smaller,and the fringe length is larger.