Modelling, analysis and control of two-stage in-series turbocharged diesel engine air-path for low speed operation

Abstract

This research presents low engine-speed behaviour analysis of a two-stage inseries turbocharged air-path diesel engine. A variable geometry turbine (VGT) at the high-pressure stage and a high-pressure exhaust gas recirculation (EGR) path are included. A 1D computational fluid dynamic model of the air-path is simulated using Ricardo Wave and analysed for steady-state and transient behaviour. A mean value model of the air-path is constructed in MATLAB and validated against theWave model for model based control. First it is demonstrated that operating single-stage turbocharged diesel engines under steady load at low speeds is fuel efficient but the resulting reduction in power due to limited available air and torque will make the low-speed operation difficult during load transients. The engine's ability to track load transients is limited by emission constraints due to the rate of production values for smoke and nitrogen oxides (NOx). Then the proposed two-stage in-series air-path configuration is shown to meet performance expectations by extending the air-path operating range and reducing its response time at low engine-speeds. The configuration improves the typical part-load performance of regulated two stage in-series arrangements at low engine-speeds through closed loop adjustments to the turbine expansion ratios. Better EGR rates (NOx reduction) at low engine-speeds can be achieved while the engine transient response is maintained. The resulting interactions are complex and for optimal behaviour multivariable control with control objective switching during steady load and transient load conditions is proposed. The control proposals are validated in simulation using MATLAB and calling the Wave model.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Judith Apsley (Supervisor) & William Heath (Supervisor)