US Patent 7472545 Engine exhaust emission control system providing on-board ammonia generation

An exhaust emission control system that provides on-board ammonia generation includes a valve disposed upstream of the LNT and SCR catalyst that operates to selectively control the flow of engine exhaust gas to an LNT and/or an SCR catalyst; while reformate fuel is being conveyed from a reformer to the LNT, the valve operates to cause the exhaust gas to bypass the LNT and flow directly to the SCR catalyst. The exhaust emission control system further includes a controller provided with an algorithm that monitors engine operating conditions and exhaust gas conditions, estimates the cumulative amount of exhaust gas created by the engine and the amount of NOx stored in the LNT, and calculates the amount of NOx required to be converted to NH3.