Experimental Study On Oxidation Characteristics Of Diesel Soot

Diesel Particulate Filter?DPF?is the most effective means of reducing soot emissions from diesel engines.Excessive deposition of soot in DPF can result in blockage of the exhaust pipe of the diesel engine and reduce economic efficiency.So DPF needs to be regenerated regularly to oxidize the deposit soot.Studies have shown that soot oxidation activity is related to its own physical and chemical properties and oxidation atmosphere.This paper studied the oxidation characteristics of diesel soot by experiments to provide theoretical guidance for efficient oxidation of soot in DPF.The soot functional groups are closely related to its oxidative activity,while the existing functional groups testing methods are only qualitative analysis.This paper attempted to apply the Boehm titration method to functional groups quantitative analysis of soot,determined the applicative titration process for soot samples.Based on the established quantitative analysis method,it was found that the surface functional groups contained in original soot were very little: the contents of Ar OH,-COOR,and-COOH were 5.24 mmol/g,0.54 mmol/g,and 0.29 mmol/g,respectively.Low concentrations of nitric acid slightly increase the content of Ar OH.Then,based on the quantitative measurement of the soot functional group,based on the thermogravimetric analysis method,the effect of surface functional groups on the soot oxidation activity was further investigated.The contents of Ar OH and-COOH on the soot surface were modified by chemical modification methods such as nitric acid/alkali liquor,and the functional groups and oxidation characteristics of the samples before and after modification were analyzed.The results showed that nitric acid can loaded a large amount of Ar OH,-COOH to the surface of the samples,and Ar OH can significantly increase the oxidation activity of the sample.Oxygen-containing functional groups can form Na-containing compounds on the sample surface with Na+,significantly improving the oxidation activity of the sample.NO₂ can oxidize soot at relatively low temperatures.This paper explored the oxidation process of soot under NO₂ atmosphere by setting up a temperature programmed oxidation bench.The results showed that the proportion of CO₂ generated under the oxidation process with NO₂ was higher than O₂.NO₂ interacted with the soot to form oxygen-containing functional groups such as C=O to enhance the oxidation activity of soot samples.When H₂ O was present,H₂ O and NO₂ could form both nitric acid and nitrous acid on the soot surface,led to the increasing of Ar OH on soot samples,soot oxidation activity further improved.