Control of a NOx reductant delivery system

摘要

A method is disclosed for controlling the delivery of compressed air and a reductant for oxides of nitrogen to a mixer (108) from which the air/reductant mixture flows through a nozzle (110) and into an exhaust gas created by a combustion engine (92). A control signal provided to an air compressor (112) is varied as the exhaust gas pressure changes to maintain a predetermined differential pressure across the nozzle. The desired flow rate of reductant into the exhaust gas is calculated based upon the engine speed, engine load, catalyst temperature, and gas space velocity flowing through the catalyst. A reductant control signal, based upon the calculated reductant flow rate, is provided to a metering pump (104) that delivers the reductant into the mixer. Calculations of the reductant control signal take into account the air pressure that the reductant pump sees inside the mixer.