Patent ID: 7472545
Filing Date: 2009-01-06
Classification: F01N,Y02T

Abstract:
1. An engine exhaust emission control system providing on-board ammonia generation, said system comprising: a NOx sensor for detecting NOx in exhaust gas from an engine; a lean NOx trap (LNT) for removing and retaining NOx from said engine exhaust gas; an on-board reformer for providing reformate fuel to said system; a first conduit for conveying reformate fuel from said on-board reformer to said LNT, said reformate fuel reacting with NOx retained in said LNT, reducing said NOx and thereby forming NH a selective catalytic reduction (SCR) catalyst disposed downstream of said LNT for catalytically reducing NOx; a second conduit by-passing said LNT for conveying said engine exhaust gas to said SCR catalyst; a valve disposed upstream of said LNT and said SCR catalyst, said valve operating between a first position and a second position to selectively control the flow of said engine exhaust gas, said first position directs said engine exhaust gas through said LNT and said SCR catalyst, said second position directs said engine exhaust gas through said second conduit to by-pass said LNT; and a controller comprising an algorithm that monitors engine operating conditions and exhaust gas conditions, estimates the cumulative amount of exhaust gas created by said engine and the amount of NOx stored in said LNT, and calculates the amount of NOx required to be converted to NH wherein, while reformate fuel is being conveyed from said reformer to said LNT, said valve is in said second position to cause said exhaust gas to bypass said LNT and flow directly to said SCR catalyst.