Automation strategies for a particle filter system for diesel engines

In particle filter systems for diesel engines in urban traffic, the regeneration of the filter by burning off the soot is a problem. Changes in the engine operating mode during the regeneration make a controlled combustion of the soot in the filter difficult. This paper presents first a simple nonlinear feedforward controller for a filter system with burner-assisted full-flow regeneration during engine operation. The goal of the control is to keep the mixed gas temperature in front of the filter at the desired value by manipulating the amount of fuel injected into the burner. It is shown that the control behaviour depends on the kind of changes in the engine operation. A satisfactory control of the mixed gas temperature during all engine operations can only be obtained with a feedback controller. The new control concept includes a process supervision which ensures that the flame in the burner does not go out, as otherwise unburned fuel will combust in the filter and/or emit as blue smoke; this has to be avoided. For the design of the process supervision, the detection of an extinguishing flame is investigated with different experiments. Measurements of the new controller performance made on a test engine show a good behaviour of the closed loop, even during large and rapid variations of engine load