Influence Of Post-injection Strategy On The Surface Functional Groups And Oxidation Reactivity Of Diesel Engine Particulate Matters

To date, Diesel exhaust particles have become one of the main contributors to the fine particulate matter(PM2.5)in the atmosphere, and their formation mechanism and control technology have received more attention in the relevant research field. As an effective approach, post-injection strategy has widely been employed in diesel engines. Therefore, this paper addresses the effects of post-injection strategy on the surface function groups and oxidation reactivity of soot particles emitted from diesel engines.In the study of aliphatic C-H function groups on the exhaust soot particles, it is found that when diesel engine adopts small post-injection quantity, the concentration of aliphatic C-H function groups on the exhaust soot particles is lower than that when signal injection is used, while big post-injection quantity will produce higher concentration of aliphatic C-H function groups than signal injection does. With the delay of post injection timing, the concentration of aliphatic C-H function groups shows an increase after a slight decrease. By contrast, the concentration of aliphatic C-H function groups gradually increases with an increase of post injection quantity.When the post injection timing is too early or post injection quantity is too large, the O/C ratios in oxygenated surface functional groups are higher than those for the signal injection. With the delay of post injection timing, the O/C ratios are almost unchanged after a gradual drop. The O/C ratios hardly change at the beginning and then increase as the post injection quantity increases. Besides small amount of carbonyl groups, the main component of oxygenated surface functional on soot particles is hydroxyl ones. Only in the situations when post injection timing is too early or post injection quantity is too large, the concentrations of oxygenated surface functional groups are higher than those for signal injection. Other post-injection strategies lead to a decrease in the concentration of hydroxyl(C-OH) and carbonyl(C=O) groups. With the increase of post injection quantity or the delay of the post injection timing, the variations in the concentrations of oxygenated surface functional groups are similar to those in the O/C ratios.The light-off and burn-out temperatures of soot particles for signal injection are505.3oC and 597.5oC respectively, and the apparent activation energy is175.5 k J/mol. By contrast, the light-off and burn-out temperatures of soot for post-injection strategy re in the ranges of 470.4~521.5 oC and 580.2~611.7 oC respectively, and the apparent activation energies are ranged from 146.6 to 201.3 k J/mol. The oxidation reactivity of soot particles for small post-injection quantity is lower than that for signal injection, while the opposite results are obtained for large post-injection quantity. With the delay of post injection timing, the oxidation reactivity shows an increase after a decrease, while the increase of post injection quantity results in an increase in the oxidation reactivity of soot particles. shows an upward trend. The concentration of surface function groups directly affects the oxidation reactivity of soot. Aliphatic C–H groups act as a more important role in governing soot oxidation reactivity than hydroxyl and carbonyl groups.