Analysis of ignition in a diesel particulate filter

Abstract

We derive explicit criteria predicting the inlet gas temperature and time needed to ignite the particulate matter (PM) deposit in an initially cold diesel particulate filter (DPF) using a limiting two-phase two-channel model. The criteria predict that the ignition temperature can be lowered without affecting the ignition time by increasing the PM thickness and/or oxygen concentration. The ignition time can be decreased without affecting the ignition temperature by decreasing the filter wall thickness and/or solid volumetric heat capacitance. Increasing the channel aspect ratio (L/D) under constant volumetric inlet flow rate and DPF volume has a minor impact on the ignition temperature and time when the effective heat Peclet number is under transverse heat Peclet number control. The ignition temperature (time) decreases (increases) with increasing channel hydraulic diameter and cell density. The explicit predictions are in good agreement with simulations of the full model.Depending on the system design and operating conditions ignition may occur either at the upstream, middle or downstream. When the magnitude of the peak temperature is not a constraint, upstream ignition is the best option as it leads to a more efficient and complete combustion of the deposited PM. The peak temperature and thermal stress generated by a middle or downstream ignition are lower than those following an upstream one, but it may lead to only partial regeneration. The peak regeneration temperature can be reduced with complete PM combustion by use of a two-step ignition (starting with downstream/middle ignition followed by upstream ignition).