An exhaust gas purification device for an engine

TLDR: In this paper, the flow distribution ratio of the first and second branch exhaust passages is determined in such a manner that the amount of the NOX produced by the oxidizing catalyst and the NH generated by the NH passing through the second-branch exhaust passage (4b) are stoichiometric to produce N₂ and H‚O.

Abstract: In the present invention, the exhaust gas from the engine (1) is divided into a first (4a) and a second branch (4b) exhaust passages after it passes through a three-way reducing and oxidizing catalyst (11), and the two branch exhaust passages merge into an exhaust gas outlet passage (5). In the first branch exhaust passage (4a), an oxidizing catalyst (13) is disposed, and in the exhaust gas outlet passage (5), a denitrating and oxidizing catalyst (15) is disposed. NOX in the exhaust gas from the engine is all converted to N₂ and NH₃ by the three-way reducing and oxidizing catalyst (11) and a part of the NH₃ generated by the three-way catalyst flows into the first branch exhaust passage (4a) and is converted to NOX again by the oxidizing catalyst (13). The amount of NOX produced by the oxidizing catalyst (13) and the amount of NOX flowing through the second branch exhaust passage (4b) is determined by the flow distribution ratio of the first and the second branch exhaust passages. In this invention, the flow ratio is determined in such a manner that the amount of the NOX produced by the oxidizing catalyst (13) and the amount of the NH₃ passing through the second branch exhaust passage (4b) are stoichiometric to produce N₂ and H₂O. Therefore, when these exhaust gases flow into the denitrating and oxidizing catalyst (15) after they mix with each other in the exhaust gas outlet passage (5), all the NOX and the NH₃ are converted to N₂ and H₂O by the denitrating and oxidizing catalyst (15) without producing any surplus NOX or NH₃.