Observer-Based Estimation of Air-Fractions for a Diesel Engine Coupled With Aftertreatment Systems

This paper presents a control-oriented air-fraction dynamic model for a complete diesel engine and aftertreatment system, as well as an observer to estimate the air-fractions in the integrated diesel engine and aftertreatment system. To reduce engine-out emissions and further improve engine efficiency, advanced combustion modes including low temperature combustion, premixed charge compression ignition, and homogenous charge compression ignition, are under intensive investigations. With the popular configuration of dual-loop exhaust gas recirculation (EGR) systems including a high-pressure loop exhaust gas recirculation and a low-pressure loop EGR (LP-EGR), alternative combustion modes can be potentially accomplished. In addition, aftertreatment systems including diesel oxidation catalysts (DOCs), diesel particulate filters (DPFs), and selective catalytic reduction (SCR) systems, are becoming necessary to satisfy stringent emission standards. With the increasing complexity of modern diesel engines and aftertreatment systems, air-path loop control for the diesel engine systems becomes further challenging partially because LP-EGR couples the aftertreatment systems with the diesel engine air-path system. Most of the current air-fraction dynamic models and observers only consider the air-fractions through the diesel engines and air-fraction dynamics through aftertreatment systems are ignored, which, however, will introduce significant modeling errors in the situations when active DPF regenerations and post-fuel injections are implemented. The purpose of this paper is to develop a control-oriented air-fraction dynamic model for a complete diesel engine and aftertreatment system. Based on the developed model, a Luenberger-like observer is proposed and analyzed using a Lyapunov method as well as the physical meaning of system parameters. Experimental results show that the developed air-fraction model is highly accurate and the designed observer is able to make the estimated air fractions converge to the corresponding true values quickly in both steady-state and transient operations.