Strategies for the Control of Particulate Trap Regeneration

The reduction of particulate emissions from Diesel engines is a key issue to meet future emission standards. Particulate traps represent an attractive solution to the problem of this source of pollution. However, they have the disadvantage of requiring periodic and safe regeneration to release exhaust back pressure and to recover filtration efficiency. Natural regeneration of the particulate filter may occur. Nevertheless, with light-duty vehicles and their low level of exhaust gas temperature, it may be necessary to facilitate or force the regeneration. The objective of this work is to give an overview of the possibilities offered by the engine management system to increase significantly exhaust gas temperatures. Thus, different engine tunes, through injection timing, boost pressure or EGR rate, may be sufficient to ensure safe regeneration of the trap. Indeed, in low load conditions, increases of exhaust gas temperature of 100°C to 175°C may be easily obtained by injection timing or EGR. In high load conditions, opening the waste gate leads rapidly to an increase of 150°C. If these changes in the engine tunes are not enough, the gap between exhaust gas temperature at the output of the engine and the regeneration temperature of the particulate trap may be filled by a catalytic combustion of post injected hydrocarbons. When the oxidation catalyst is active an increase of 300°C may be reached. A sooting sensor has also been developed which can already be used for the OBD of a particulate trap.