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On-line fuel-efficiency optimization of Diesel engines using constrained multivariable extremum-seeking

Advanced control concepts are required to maximize the fuel-efficiency of Diesel engines and to comply with emission legislation. The aim of this paper is to develop a controller that fully utilizes the fuel-path and air-path hardware, and is adaptive for real-world disturbances. The control design comprises a feedback control system, which uses air-path actuators and fuel injection settings to robustly track engineout NOx emission and engine power demands, as well as two parameters that are known to influence the NOx emission versus fuel consumption trade-off; combustion phasing and pumping losses. Furthermore, an on-line implementable convex cost criterion is proposed that evaluates the injector opening time to obtain a cost output which is equivalent to fuel efficiency. A multivariable constrained extremum-seeking method is applied to minimize the cost output, as a function of combustion phasing and pumping losses, subject to constraints on the tracking performance of the low-level control system. The control design is implemented on a Euro-VI Diesel engine equipped with exhaust gas recirculation and a variable geometry turbine, as well as in-cylinder pressure sensors. The experiments demonstrate the effectiveness of the applied extremum-seeking approach in finding the (constrained) optimum, for a constant engine speed and torque.