Real-Time Estimation of Intake O2 Concentration in Turbocharged Common-Rail Diesel Engines

Automotive engines and control systems are more and more sophisticated due to increasingly restrictive environmental regulations. Particularly in both Diesel and SI lean-burn engines NOx emissions are the key pollutants to deal with and sophisticated Engine Management System (EMS) strategies and after-treatment devices have to be applied. In this context, the in-cylinder oxygen mass fraction plays a key-role due its direct influence on the NOx formation mechanism. Real-time estimation of the intake O2 charge enhances the NOx prediction during engine transients, suitable for both dynamic adjustments of EMS strategies and management of after-treatment devices. The paper focuses on the development and experimental validation of a real-time estimator of O2 concentration in the intake manifold of an automotive common-rail Diesel engine, equipped with turbocharger and EGR system. The paper analyzes the air intake process and the influence of the exhaust gas recirculation system based on a mean value modeling approach. All variables required are available at EMS level, thus allowing an on-board implementation without extra costs for additional sensors. The accuracy of the developed estimator is assessed by comparing simulated and experimental trajectories of O2 concentration, measured by a Universal Exhaust Gas Oxygen (UEGO) sensor located in the intake manifold. The experimental tests were carried out at the test bench, imposing severe engine transients. The results evidence that the O2 estimator presents a good accuracy vs. experiments and offers significant opportunities for improving engine control and after-treatment devices management during transient operation.