Determining untreated NOx concentration upstream of NOx catalyst, briefly enriches fuel mixture and measures ammonia concentration downstream of catalyst

摘要

The engine is operated momentarily with the fuel mixture enriched. The NH3 concentration is measured downstream of the catalyst (3). From this, the actual value of untreated NOx emission is calculated. For the calculation, the NH3 concentration is multiplied by a factor (K) which is a function of operational parameter(s). It is a function of the NOx/NH3 conversion rate of the catalyst (3). The NH3 concentration is measured using a strongly NH3-sensitive, NOx sensor (7). During calculation this strong cross-sensitivity is taken into account. The actual value of NOx concentration is employed in a model to determine the untreated concentration of NOx emitted by the engine. The NH3 concentration is first used, when a sub-stoichiometric (rich) lambda value is detected downstream of the catalyst.