Real-time control of a two-stage serial VGT Diesel engine using MPC

Real-time model predictive control (MPC) is used to experimentally assess the transient air-path performance of a two-stage serial variable geometry turbocharger (VGT) fitted to a light duty Diesel engine. The control model is based on a mean value engine model (MVEM) that is developed using data from the engine with a single stage turbocharger and modified to simulate the two-stage arrangement. A tip-in transient manoeuvre is used to assess system performance, in particular the boost-control where MPC is used to achieve close to optimal performance. This paper explores the improvement in transient performance when using two VGT turbochargers in series and considers where the differences between experiment and simulation occur.In general it is shown that there is good agreement between the experimental and simulated system performance. It is observed that the VGT actuator position must be well matched to the modelled position to achieve good on-engine performance. Other factors which affect the experimental performance are related to the actuator dynamics, cyclic-behaviour of the realtime pressure states, time-constants effecting the temperature measurement and the difficulty in accurately modelling the heat transfer in the exhaust, turbines and housings.