Air fraction estimation for multiple combustion mode diesel engines with dual-loop EGR systems

This paper describes an innovative air fraction estimation method for diesel engines with dual-loop exhaust gas recirculation (EGR) systems to conduct multiple and alternative combustion modes for engine-out emission reduction. An observer is designed to estimate the air fractions in all the engine intake/exhaust sections using standard sensors equipped on the engine. The observer can provide indispensable information for the engine controller to exercise closed-loop control on in-cylinder conditions as well as control the in-cylinder high-pressure EGR gas and low-pressure EGR gas amounts, respectively, which are crucial for engines running alternative combustion modes with dual-loop EGR systems. The convergence stability of the observer is proved based on a Lyapunov analysis assisted by physical insights into the engine/combustion systems. The observer is also experimentally validated on a modern light-duty diesel engine with a dual-loop EGR system.