Temperature Excursions in Diesel Particulate Filters: Response to Shift to Idle

Abstract

Diesel particulate filter (DPF) is the most efficient method for particulate matter (PM) emissions removal. The accumulated PM is removed by periodic controlled combustion. In some cases, the regeneration leads to excessive local temperature excursions that may melt and destruct the ceramic filter. The cause of this DPF melting is still an open question. The temperature rise under stationary (constant) operation is not sufficiently high to explain these destructive events. Numerical simulations were conducted for cases in which the regeneration occurred by a moving temperature front. A shift to idle increases the oxygen concentration and decreases the exhaust gases flow rate and temperature. The simulations revealed that the transient temperature response to a rapid change from normal driving to idle is higher than those attained under stationary operation under either the initial or the final operating conditions. The magnitude of the transient temperature rise depends on when the change in the driving mode occurred relative to the time at which a moving temperature front formed. An early change may reverse the direction of the moving temperature front from that following a later change. The response to the rapid increase in the feed oxygen concentration and decreased flow rate is faster than that to the decrease in the feed temperature. However, a rapid feed temperature decrease may eventually decrease the temperature of the moving front and cause in some cases incomplete local PM regeneration. The temperature rise following a step-change of the feed conditions is higher than that when the same change occurs by a ramp. The shorter is the period of the ramp change, the higher is the transient temperature rise.