Desulfurizing at least one catalyzer downstream of IC engine where oxygen storage capacity of catalyzer is criterion for desulfurizing

摘要

The need for desulfurization is determined as a function of at least one criterion. During desulfurization, the catalyzers (18, 20) to be desulfurized are fed, at a raised temperature, with a rich exhaust gas with lambda 1. At least one criterion determining the need to desulfurize is the oxygen storage capacity of a catalyzer in the system, specifically the catalyzer to be desulfurized. An internal combustion engine (10) can operate with a poor mixture. The oxygen storage capacity of the catalyzer(s) together or individually is determined using the evolution of oxygen concentration in the exhaust gases downstream of the last catalyzer in the system. The oxygen concentration is detected and evaluated after a change in the engine lambda (lambda mot) from a predetermined poor lambda (lambda m) to a predetermined rich lambda (lambda f) and/or vice versa. A time lapse flows from the change in engine lambda until a leap in lambda downstream of the catalyzers. When a catalyzer near the engine has reached its extinction temperature and a catalyzer further from the engine has not yet reached its extinction temperature, the oxygen storage capacity of the catalyzer near the engine can be determined. The total oxygen storage capacity of the catalyzers can be determined when they have all reached their extinction temperatures, and thus the capacity of the catalyzer further from the engine can be determined as the difference between the two. The oxygen concentration downstream of the catalyzers is measured using a lambda probe or NOx detector. The catalyzer to be desulfurized is a NOx accumulator upstream of which a pre-catalyzer is mounted. The need for desulfurization is determined by measuring oxygen storage capacity, NOx storage capacity and/or the rate of conversion of NOx in the catalyzer to be desulfurized and/or the sulfur present and/or a time lapse since the previous desulfurization. An independent claim is made for a device to carry out the above process, where the exhaust catalyst system includes a device for determining the oxygen storage capacity of the catalyzers and determining the need for desulfurization is carried out as a function of the oxygen storage capacity among other criteria. The device comprises an oxygen measuring device, in particular a lambda probe or NOx detector placed downstream of the last catalyzer. A control unit (26) contains an algorithm for guiding the desulfurization.