Search

This study proposes a feedforward control method for exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT) systems based on cylinder pressure information and air path model. The proposed method calculates EGR rate and exhaust manifold pressure using cylinder pressure information which provides accurate combustion state information. The accuracy of the air system model was improved according to the precise information of the EGR rate and exhaust pressure; subsequently, the performance of the proposed model based feedforward controller was enhanced. The proposed feedforward controller was implemented in an in-house developed engine management system and validated through the engine experiments under steady and transient conditions.

This paper proposes three different methods to estimate the low-pressure cooled exhaust gas recirculation (LP-EGR) mass flow rate based on in-cylinder pressure measurements. The proposed LP-EGR models are designed with various combustion parameters (CP), which are derived from (1) heat release analysis, (2) central moment calculation, and (3) principal component analysis (PCA). The heat release provides valuable insights into the combustion process, such as flame speed and energy release. The central moment calculation enables quantitative representations of the shape characteristics in the cylinder pressure. The PCA also allows the extraction of the influential features through simple mathematical calculations. In this paper, these approaches focus on extracting the CP that are highly correlated to the diluent effects of the LP-EGR, and the parameters are used as the input states of the polynomial regression models. Moreover, in order to resolve the effects of cycle-to-cycle variations on the estimation results, a static model-based Kalman filter is applied to the CP for the practically usable estimation. The fast and precise performance of the proposed models was validated in real-time engine experiments under steady and transient conditions. The proposed LP-EGR mass flow model was demonstrated under a wide range of steady-states with an R2 value over 0.98. The instantaneous response of the cycle-basis LP-EGR estimation was validated under transient operations.

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.

Current diesel engines commonly employ a variable geometry turbocharger (VGT) to improve drivability and fuel efficiency, and this paper addresses model-based feedforward control of the VGT based on empirical models of compressor and turbine efficiencies to improve transient response. Though compressor and turbine efficiencies affect compressor air flow and turbine power, respectively, it is challenging to understand exactly the compressor and turbine efficiencies in real engines. In order to cope with this problem, we propose empirical models of compressor and turbine efficiencies. The input states are proposed based on maps of the compressor and turbine efficiencies, which are provided by turbocharger manufacturers. Parameters of the efficiency models are identified with 225 data of steady-state engine experiments to reflect engine operating conditions. The proposed compressor and turbine efficiency models were applied to the model-based VGT feedforward control algorithm to verify the effectiveness of the efficiency models. The proposed modelbased VGT feedforward control algorithm based on the compressor and turbine efficiency models was experimentally verified with 2.2 L common-rail-direct-injection diesel engines.