Exhaust gas recirculation control through extremum seeking in a Low Temperature Combustion diesel engine

Low Temperature Combustion (LTC) modes in diesel engines are characterized by enhanced homogeneity of the combustion mixture resulting from a longer ignition delay when compared to conventional diesel combustion. This is enabled by charge density and dilution control, coupled with modulation of fuel injection parameters. Charge dilution is achieved by exhaust gas recirculation (EGR), while turbocharging enables in-cylinder charge density increase. The coupling between the EGR and turbocharging systems exhibits highly non-linear interactions in the engine air-path. In this work, a two part control strategy is investigated for the regulation of EGR and turbocharging in a diesel engine to direct the combustion to approach LTC without largely compromising the combustion efficiency. Firstly, a simplified engine air-path model is presented that emphasizes the correlation between the intake oxygen concentration ([O_2-int]) set-point and the individual EGR and turbocharging actuator set-points at different engine operating points. Thereafter, experimental data is presented that highlights the sensitivity of engine-out NOx emissions and combustion efficiency against the [O_2-int]. Secondly, an extremum seeking (ES) algorithm is used to determine the [O_2-int] set-point using a cost function that results in a desirable emission and combustion performance. Finally, the coordinated execution of the ES algorithm and the air-path model to generate the air-path actuator set-points is discussed.