Modeling Complex Engines as Dynamic Powertrain Members

Doctoral thesis, 1999

Engine modeling and simulation have been necessary tools for efficient product development in the automotive industry for some time. The scope of this work is novel engine models, tools, and methods for powertrain research and development. These are packaged in an equation oriented software environment: a toolbox for numerical simulation of complex engines. This toolbox consists of models of the basic physical components in turbocharged diesel engines. Mean value diesel engine models can be built from the modules in the toolbox. In these models the exhaust gas pulsating flow is considered, in order to predict the turbocharging properties in a good way. Engine models can also be built that consider torque irregularities from the individual combustion events. The toolbox provides support for studies of new diesel engine charging systems. The main contribution of this work is the methods developed. They represent a new set up of simulation tools and techniques. The methods developed use an appropriate combination of software, control theory, mechanics, and thermodynamics modeling, vehicle powertrain know- how, and support for the work to be performed to reach a certain goal. The goal is to make design recommendations for improved transient performance of future powertrains. The aim of this work is to provide a platform for engine and powertrain simulation with unique properties that will enable researchers and engineers make these design recommendations. The work includes a discussion about the differential equations and the number of states suitable for modeling thermodynamic modules, such as inlet volumes with and without heat exchange. The exhaust gas energy treatment in mean value engine modeling is discussed, and a novel suggestion for treating the exhaust manifold volume as a physical parameter is provided.It is shown that it might be possible to model some effects concerning the exhaust manifold volume, while maintaining a simple engine model that will run in real time on a regular PC. The potential of highly simplified approaches is explored in order to find good trade off between calculation efficiency and model predictability. There are four complete engine models included in the toolbox, one simple for regular turbo- charged diesel engines, one more advanced for regular turbocharged diesel engines, one for Variable Geometry Turbine (VGT) engines, and one for two-stage charging. The first three of these have been compared with measurements and show good agreement between measured and predicted data.