Reductant flow control for NOx removal from lean exhaust gases

This review article describes and discusses the literature on reducing agen t control systems for NOx emission reduction in the exhaust gas of full lea n-burn engines. The literature can be classified as feedback, feedforward, feedforward-feedback, feediorward/feedforward-feedback and periodical dosin g control systems, which can be further classified as classical, override, co-ordinated, constrained and split systems or a combination of those. As long as reproducible, fast and cheap NOx sensors are not commercially av ailable, the control system should be an inferential feedforward or feedfor ward-feedback system supplied with constraints for environmental and econom ical reasons. For future applications an oxidation catalyst downstream of t he deNO(x) catalyst should be applied to convert any inevitable reductant s lip, due to modelling errors, to harmless compounds.