摘要:
An emission control system for the cleaning of the exhaust gases of a lean burn engine with two or more cylinders comprises a first exhaust leg for the exhaust gases of a first group of cylinders and a second exhaust leg for the exhaust gases of a second group of cylinders. A nitrogen oxide storage catalyst is arranged in each exhaust leg. The two exhaust legs are combined downstream of the storage catalysts at a confluence to form a common exhaust leg. The common exhaust leg contains an SCR catalyst. The first and second groups of cylinders are each supplied alternately in periodic intervals with lean and rich air/fuel mixtures. Lean or rich exhaust gases are thus obtained in the combustion in the cylinders and released into the corresponding exhaust legs. Lean and rich exhaust gases are adjusted with respect to one another so as to result in a lean exhaust gas after the combination of the exhaust gases in the common exhaust leg. The regeneration of the storage catalysts may result in the formation of ammonia, which is stored by the SCR catalyst and reacted with nitrogen oxides which pass through the storage catalysts in an unwanted manner during the storage phases.
摘要:
Lean burn engines require an exhaust gas system comprising nitrogen oxide storage catalysts for removal of nitrogen oxides from their exhaust gases. When the lean burn engine is operated with a sulphur-containing exhaust gas, the storage catalysts have to be desulphurized from time to time. During the desulphurization, there is the risk of high pollutant emissions. These emissions can be reduced when the cylinders of the lean burn engine are combined in two groups which release their exhaust gas to two assigned exhaust legs, in each of which is arranged at least one nitrogen oxide storage catalyst. The two exhaust legs are combined beyond the storage catalysts to form a common exhaust leg which contains a catalyst which possesses a three-way function under stoichiometric conditions. The two nitrogen oxide storage catalysts are desulphurized offset in time with respect to one another. While rich exhaust gas at a high temperature flows through one storage catalyst for desulphurization, lean exhaust gas flows through the second storage catalyst, in such a way that the combined exhaust gas is of stoichiometric composition over the entire desulphurization period. Under the stoichiometric conditions, the catalyst with three-way function is capable of converting hydrocarbons, carbon monoxide and nitrogen oxides to harmless components.
摘要:
The present invention relates to a method for the treatment of an exhaust gas comprising NOx, wherein the method comprises the step of subjecting the exhaust gas to an exhaust gas treatment system comprising, in order of the exhaust stream: (a) a first NOx storage catalytic converter (2, 2′); (b) a catalytic converter (3) for selective catalytic reduction (SCR) downstream of the first NOx storage catalytic converter; and (C) a catalytic converter (4) having oxygen storage capacity downstream of the SCR catalytic converter; wherein the exhaust gas treatment system is operated in alternating rich and lean phases, wherein the rich phase is terminated when the amount of reducing components leaving the first NOx storage catalytic converter is at least 0.05 times the N amount of reducing components consumed by the first NOx storage catalytic converter during the time interval beginning when the air/fuel ratio upstream of the first NOx storage catalytic converter turns from lean to rich conditions and ending when the air/fuel ratio downstream of the first NOx storage catalytic converter turns from lean to rich conditions. Optionally there can be provided a close coupled three-way or diesel oxidation or NOx storage catalytic converter (1, 1′).