Catalytic conversion of nitrogen oxides in exhaust gases using urea reductant is controlled by time differentiation of engine operational parameter, adjusting reductant excess more swiftly as a function of the result

摘要

An operational parameter (T) influencing dosing accuracy is measured. On falling below or exceeding a limiting value (Tmin), dosing is either no longer possible or must be limited. In this case, reductant (R) is dosed in excess of the stoichiometric value indicated by the nitrogen oxides concentration, before addition of reductant is either ended or continued at the below-stoichiometric level. Preferred Features: The operation parameter is : exhaust temperature, exhaust mass flow rate, engine loading or rpm. The magnitude is derived from the operating parameter (T) by its differentiation with respect to time, or by forming differences between values measured at intervals. Excess is adjusted from the result. Excess reductant quantity dosed (Rmax) is adjusted in this way, until the limiting value (Tmin) of the operational parameter (T) or that of the derived magnitude is exceeded or undershot. Excess reductant dosing is a function of the temperature- (especially) dependent storage capacity of the denitration catalyst. The value of excess is stored.