Modeling uncontrolled regeneration of diesel particulate filters, taking into account hydrocarbon slip

Abstract

The effect of hydrocarbon slip from a diesel oxidation catalyst on active regeneration of a diesel particulate filter is investigated by developing a generalized zero-dimensional diesel particulate filter model to predict the wall temperature of the diesel particulate filter and the trapped mass of particulate matter. Exhaust fuel injection methodology is applied to provide a high temperature for regeneration by oxidation in the diesel oxidation catalyst. However, the diesel oxidation catalyst reactions may be incomplete and hydrocarbon slip can occur. It is confirmed that two exothermic reactions, namely soot oxidation and hydrocarbon oxidation, which proceed simultaneously may result in the synergistic effect of a rise in the temperature. This is primarily because the temperature is the common factor that affects both reaction rates, i.e. a rise in the temperature caused by one reaction can affect the increase in the reaction rate of another reaction through the exotherms created. Accurate prediction of the temperature rise during active regeneration of the diesel particulate filter is dependent on several crucial factors: the initial wall temperature of the diesel particulate filter, the inlet temperature of the diesel particulate filter, the initial loading level of particulate matter, the exhaust mass flow rate, the oxygen concentration, and hydrocarbon slip. Several simulations revealed that hydrocarbon slip can be one of the reasons for uncontrolled regeneration of the diesel particulate filter. It is concluded that, if there is a considerable amount of hydrocarbon slip, then uncontrolled regeneration of the diesel particulate filter easily occurs when the exhaust mass flow rate is rapidly reduced to the idle condition during regeneration. Flow transient simulations also confirmed that the temperature ramp-up rate and the point of time when the exhaust mass flow rate is reduced determine the overall trend of the temperature rise and the characteristics of the thermal behavior of the diesel particulate filter.