Research of DPF regeneration with NOx-PM coupled chemical reaction

Diesel engine exhaust gas flows through the DOC upstream of the DPF system. In this process, NO contained in NOx is oxidized into NO2 and then enters DPF. The presence of NO2 can greatly reduce the light-off critical temperature of soot particles, so that the soot particles captured by DPF will conduct a certain amount of continuous passive regeneration at a lower temperature. However, there is the complex coupling reaction relationship between NOx and PM contained in the DPF, not only the reaction between the particulates and NOx, but also a series of reaction between CO and NOx. And except NO and NO2 of NOx in diesel engineer exhaust which are recognized and studied widely, there is a small amount of N2O generated as the intermediate product in the entire reaction process of DPF generation. The oxidation ability of NO2, NO, and N2O contained in NOx are different, and the change of diesel engine exhaust composition also affects the quantity and proportion of them. These factors have a close relationship with the removal of soot particulate, in other words, the regeneration of DPF. This paper builds the NOx-PM reaction mechanism in DPF, and studies the chemical reaction process between NOx and PM under different inlet conditions. This paper defines the coefficient α, which is used to characterize the ratio of NO2 in diesel engineer exhaust at the DPF inlet accounting for the total amount of NOx. The results show that when α is between 0.7 and 0.8, the good regeneration removal effect of soot particulates under the premise of not worsening NOx removal efficiency is achieved. The molar ratio of NOx at the DPF inlet and carbon in the PM is defined as β. When β ≈ 1, NOx removal efficiency is the maximum. When β ⩾ 8, the soot particulates can complete continuous passive regeneration totally only by relying on the mutual reaction of DPF internal reactants in this condition. Investigation results show that N2O and CO are important intermediate products during the reaction process of NOx-PM.