Abstract
Keywords - soot sensor, on-board diagnostics, soot load, engine control, particle filter
The definitions for particle mass and particle count in the automotive exhaust gas will be application specific and correlated to the measuring principles, because they are no well defined physical properties.
Three different automotive on-board sensor applications will be highlighted:
The first particle sensor application was intended for the engine out emissions, to provide a feedback for engine control. The trade off between particle- and NOx-concentration could have been controlled in a closed loop.
Since legislation substantiated the OBD requirements concerning particle filter systems, a sensor downstream of the particle filter is requested for a reliable detection of system mal-functions.
Since the implementation of particle filters in diesel vehicles, methods for measuring the particle load, especially the mass of the stored carbon were requested. Sensor systems for direct soot load measurement could make an essential contribution to the reliability of the filter systems.
The sensor systems can be divided in two groups, the fast sensors and sensors which detect the agglomeration of particles on a sensor surface.
In the first group are the electrostatic systems, which measure the flow of electric charge, caused by particles. These sensor systems could provide a real time signal as feedback for engine control as well as for on-board diagnostics.
The second group of sensors will be usable only for failure detection in particle filter systems, because of the poor time resolution. A sensor downstream of the particle filter will not be able to provide information for use in engine control, because the filter will attenuate each impact of engine control parameters on soot below the limit of detection.
A basically different sensor system is intended for measuring the soot load in particle filters. The task is a reliable measurement of the stored carbon mass to optimize regeneration cycles and to notify if ash cleaning is required.
Problems and approaches concerning the above mentioned groups of sensors will be presented.