Patent ID: 6171565
Filing Date: 2001-01-09
Classification: B01D,F01N,F02D,Y02A,Y02T

Abstract:
A process of operating a nitrogen oxides storage catalyst of an exhaust gas treatment system, the process comprising:(a) determining an amount M of nitrogen oxides which is theoretically adsorbed on the nitrogen oxides storage catalyst during a sorption phase when a .lambda.-value of the exhaust gas treated is greater than 1, wherein the determining of the amount M of nitrogen oxides theoretically adsorbed is based on:(i) predetermined temperature-dependent nitrogen oxides storage capacity data corresponding to a plurality of engine operating conditions which may vary with respect to torque, engine speed, exhaust gas mass flow, exhaust gas temperature, and nitrogen oxides concentration in the exhaust gas, and(ii) predetermined nitrogen oxides exhaust gas emission data corresponding to a plurality of engine operating conditions which may vary with respect to torque, engine speed, and .lambda.-value of the exhaust gas exiting the engine;(b) determining a target value M.sub.T for an amount of nitrogen oxides stored during the sorption phase, the determining of the target value M.sub.T being based on the theoretically adsorbed amount M determined in step (a) adjusted by a correction factor C;(c) determining an expected duration T.sub.D of a desorption and conversion phase, the determining of the expected duration T.sub.D being based on a plurality of factors including:(i) the target value amount M.sub.T of the stored nitrogen oxides,(ii) an amount of oxygen determined to be stored in the system during the sorption phase,(iii) reaction stoichiometry data,(iv) exhaust gas mass flow data,(v) exhaust gas temperature data, and(vi) a content of reductive compounds in the exhaust gas, including carbon monoxide, hydrocarbons and hydrogen;(d) attaining during the sorption phase the target value M.sub.T for the stored amount of nitrogen oxides;(e) providing an amount of fuel to the engine, upon attaining the target value M.sub.T, so as to enter the desorption and conversion phase wherein the .lambda.-value of the exhaust gas is less than 1;(f) monitoring the .lambda.-value of the exhaust gas downstream from the storage catalyst during the desorption and conversion phase and determining a time duration T at which the .lambda.-value falls below a predetermined threshold value;(g) calculating the correction factor C for use in a next cycle of process steps, the correction factor C being a ratio of the expected desorption duration T.sub.D with respect to the measured desorption duration T, corresponding to the formula C=T.sub.D /T;(h) providing an amount of fuel to the engine, when the .lambda.-value downstream from the storage catalyst falls below the predetermined threshold value, so as to again enter the sorption phase according to step (a), wherein the .lambda.-value of the exhaust gas is greater than 1; and(i) optionally repeating the preceding process steps in cyclical fashion.