Minimizing Fuel Use During Power Transients for Naturally Aspirated and Turbo Charged Diesel Engines

Recent development has renewed the interest in drivetrain concepts which gives a higher degree of freedom by disconnecting the engine and vehicle speeds. This freedom raises the demand for active control, which especially during transients is not trivial, but of which the quality is crucial for the success of the drivetrain concept. In this work the fuel optimal engine operating point trajectories for a naturally aspirated and a turbocharged diesel engine, connected to a load which does not restrict the engine speed, is derived, analysed and utilized for finding a suboptimal operating point trajectory. The analysis and optimization is made with dynamic programming, Pontryagin’s maximum principle and a suboptimal strategy based on the static optimal operating points. Methods are derived for using Pontryagin’s maximum principle for finding the optimal operating point trajectories, for simple load cases. The time needed for computation is reduced a factor 1000−100, depending on engine layout, compared to dynamic programming. These methods are only applicable to very simple load cases though. Finally, a suboptimal calculation method which reduce the time needed for computation a factor > 1000 compared to dynamic programming, while showing a < 5% increase in fuel consumption compared to the optimal, is presented.