Model-Based Diesel Engine Management System Optimization - A Strategy for Transient Engine Operation

Doctoral thesis, 2013

To meet increasingly strict emission legislation and stronger demands on fuel consumption, typical passenger car diesel engines become increasingly complex with more and more controllable systems added. These added systems open up for the possibility to operate the engine at more efficient conditions, but it also becomes more challenging to optimize the settings in the engine management system. Methods to optimize settings in an engine management system based on steady-state engine operation are well developed and described in the literature, and also used in practice. Methods to handle transient engine operation are not as well developed, and typically various compensations are added in an engine management system to account for effects during transient engine operation. Calibration of these compensations is currently a manual process and is largely performed to meet regulations rather than to optimize the system. This thesis consists of papers that describe the introduction of a novel method to optimize settings in a diesel engine management system with an aim to minimize fuel consumption for a given dynamic vehicle driving cycle while keeping accumulated engine-out emissions below given limits. The strategy is based on existing methods for steady-state engine operation, but extended to account for transient effects in the engine caused by dynamics in the gas exchange system in a systematic manner. The strategy has been evaluated using a simulation model of a complete diesel engine vehicle system. The optimization strategy has been shown to decrease fuel consumption for a diesel engine vehicle compared to existing methods based only on steady-state engine operation. Using the simulation model, the strategy has been shown to decrease fuel consumption for a vehicle driving according to the New European Driving Cycle with 0.56%, compared to a strategy based only on steady-state engine operation. This thesis also consists of papers that describe the complete diesel engine vehicle system simulation model. The model can perform a simulation of a vehicle driving according to a predefined dynamic driving cycle, and it estimates fuel consumption together with NOx and soot emissions throughout the simulation depending on settings in the engine management system. The model accounts for transient effects on fuel consumption and emissions caused by dynamics in the engine gas exchange system. The simulation model is implemented in the \textsc{Matlab} Simulink environment, and the simulation time is in the range of 10 to 20 times faster than real-time.