Control of the air system of a diesel engine using the intake oxygen concentration and the manifold absolute pressure with nitrogen oxide feedback

Abstract

In production-type engine control systems for passenger car diesel engines, the mass air flow is commonly used as a feedback variable for control of the exhaust gas recirculation system. However, the mass air flow is not appropriate as a feedback variable for control of the exhaust gas recirculation system because the mass air flow has a weak correlation with the formation of the nitrogen oxide emissions. Another defect of production-type engine control systems is that the emissions-relevant systems are controlled without emissions feedback. In order to address these problems, this study proposes air system control using the intake oxygen concentration as it has a strong correlation with the formation of the nitrogen oxide emissions with nitrogen oxide feedback. The intake oxygen concentration is estimated using a closed-loop observer, and the estimated intake oxygen concentration is used as a feedback variable for control of the exhaust gas recirculation system. The measured nitrogen oxide concentration is used as emissions feedback control. When the measured nitrogen oxide concentration exceeds the reference nitrogen oxide value, emissions feedback control is activated and causes the set value of the intake oxygen concentration to decrease in order to reduce the nitrogen oxide emissions when the measured nitrogen oxide concentration exceeds the typical value. The proposed air system control method is validated with engine experiments, and the nitrogen oxide emissions are reduced by 11.5–39.8% using nitrogen oxide feedback control in various test cases which cause the drift of the nitrogen oxide emissions.