In recent years, significant effort has been put into studying the oxidation of diesel oxidation catalyst (DOC) and regeneration of diesel particulate filters (DPF) continuously, either through experiments or simulations. However, less attention has been paid to understanding the effect of hydrocarbon (HC) slip on the active DPF regeneration process, which is believed to generate a high temperature spike inside the DPF. It may cause uncontrolled (runaway) regeneration and, as a result, device failure through thermal stress.
In this thesis, for the first time, the influence of HC slip from DOC is investigated by developing a generalized zero-dimensional DPF model to predict DPF wall temperature and trapped mass of soot during active regeneration operation. The in-exhaust fuel injection is used to provide high temperature for DPF regeneration by oxidization in the DOC. However, the DOC reactions may be incomplete and HC slip can occur.
It is confirmed that two exothermic reactions – soot oxidation and HC oxidation – processing simultaneously may result in the synergistic effect of temperature rising. This is due primarily to the fact that temperature is the common factor that affects both reaction rates. That is, a rising temperature caused by one reaction can affect the reaction rate increase of another reaction through the exotherms created. Absolute increment of the temperature rise during active DPF regeneration is defendant on several crucial factors: initial DPF wall temperature, DPF inlet temperature, initial PM loading level inside the DPF, exhaust mass flow rate, O2 concentration, and HC slip. Several simulations and sensitivity analyses revealed that HC slip can be a reason of the uncontrolled regeneration. Especially, it is concluded that if there is a considerable amount of HC slip then the uncontrolled regeneration easily occurs when the exhaust mass flow rate rapidly reduced during regeneration.
As a possible solution for the problem, the concept of multiple injections is applied to the exhaust fuel injection profile to suggest optimal injection strategies avoiding uncontrolled regeneration.