| Biodiesel,as the most promising alternative fuel in the 21 st century,can be mixed with diesel oil in any proportion.It does not need to change the structure of diesel engine when it is used.Biodiesel can effectively reduce the emission of particulate matter by oxygen.It has been proved that it is a feasible method to reduce the emission of particulate matter by using biodiesel.However,when biodiesel is used to reduce particulate emissions,it will also change the particle size distribution and carbonaceous composition.In this paper,a four cylinder electronically controlled high pressure common rail diesel engine which meets the national V emission standard is used.Under the selected working conditions,the bench tests of diesel and three kinds of biodiesel(soybean oil,palm oil and gutter oil biodiesel)are carried out to collect the particulate matter.The difference of particle size distribution,average particle size,box counting dimension and carbon composition of different fuel particles are analyzed.(1)The engine exhaust particle size spectrometer was used to measure the particle size distribution of different fuels at 2400r/min and 100% load.Compared with diesel fuel,biodiesel fuel can reduce particulate matter emissions by up to 85%.The particle size corresponding to the peak concentration of biodiesel particles is smaller than that of diesel particles.Soybean oil biodiesel with higher iodine value has the highest particulate matter concentration,while gutter oil biodiesel with lower iodine value has the lowest particulate matter concentration.(2)When the rotating speed is constant,the particle concentration of biodiesel increases with the increase of load at 1800 r / min.the particle size corresponding to the peak value of biodiesel particulate matter concentration is 60.4 nm and 39.2 nm,which is35% smaller.At 2400r/min,the number and concentration of particulate matter increased with the increase of load.The amount and concentration of diesel particulate matter increase with the increase of load at 1800r/min and 2400r/min.At 25% load,the concentration of biodiesel at 1800r/min was higher than that of particulate matter at2400r/min.At 100% load,the concentration of biodiesel and diesel particulate matter increased with the increase of engine speed.(3)Transmission electron microscope was used to observe the particles collected by the self-made particulate matter collection device.The results show that there is no obvious difference in the micro morphology of different fuel particles.The average particle size of diesel is 28.6% larger than that of biodiesel.The box counting dimension of diesel particulate matter is smaller than that of biodiesel particulate matter,which indicates that the structure of diesel particulate matter is loose and the agglomeration degree is low.The box counting dimension of biodiesel particulate matter is larger,the particle size is smaller,the agglomeration degree is higher and the structure is more compact.(4)The organic carbon analyzer was used to analyze the carbon composition of particulate matter collected on quartz filter membrane with NIOSH 870 and IMPROVE-A different analysis protocols.Under the two analysis protocols,the organic carbon(OC)content of biodiesel particulate matter was higher than that of diesel particulate matter,and the OC / EC Value of biodiesel particulate matter was higher than that of diesel particulate matter.T-test showed that the results of total carbon(TC)and elemental carbon(EC)had good comparability.There was significant difference between OC and EC.The OC / EC values of the two analysis protocols were not comparable.(5)Scanning electron microscope and energy dispersive X-ray spectrometer were used to analyze the C and O elements in the particles.The average oxygen content of biodiesel particulate matter is 8% higher than that of diesel particulate matter.The higher the oxygen content in fuel,the higher the oxygen content in particulate matter. |
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