Development of a behavioral model of a CI engine for HiL implementation - Characterization of the Core Engine

Models have a wide area of application in the automotive industry. They are used to test innovative control strategies in the development phase or to design more advanced engine management systems to reduce pollution and fuel consumption. A model can also be a useful tool for diagnosis, making possible the simulation of faults without affecting costs. Different kinds of models exist, describing engine performances at a very high level of detail. However with a limited set of experimental data, behavioral models are preferable for automotive companies, which benefits from their simplicity, their relatively accurate results and not being computationally demanding. This thesis aims to elaborate a model of an internal combustion engine for Hardware-In-The-Loop simulations. It should describe the behaviour of a four cylinders turbocharged compression ignited engine with sufficient accuracy and be real time executable. The model structure emphasizes parameterization so that it results adaptable to different engine variants. The work has been developed at Kineton, in collaboration with another student of Mechatronic Engineering, Stefano Ferini Strambi. The first part of this project deals with the study of the main components and operations of a diesel engines at the state of the art. This constituted a reference for the development of the model. Furthermore the Hardware-in-The-Loop technique is illustrated together with a brief overview on electronic control units. It is also described the simulator for HiL on which runs the real-time application specifying the engine behaviour. This is modelled in Matlab/Simulink ambient which allows to set up subsystems. The different subsystems have been realized in parallel with my team co-worker. In this thesis focus is given to models for the description of in-cylinder phenomena, such as the pressure trace and the heat released by combustion, and how they affect engine performance. Submodels for the the exhaust gas recirculation and diesel anti-particulate filter are also presented, as well as a submodel for the estimation of chemical species for an analysis of the emissions. The development was followed by an open loop testing phase where the model has been fed with input signals recorded from the simulation of typical manouvres with a GT-Power physical model of the same engine, used as test bench. The corresponding outputs were evaluated and compared with the GT-Power results. Manouvres have been set from the graphical user interface ControlDesk. The model has been successively implemented on the HiL platform. Parallelized calculations, strategic usage of 'memory' blocks and 1D / 2D look-up tables with optimized resolution and interpolation algorithm removed algebraic loops and allowed the model run-time to achieve target time of one millisecond. Hardware in the loop simulations were made to observe the performances of the same manoeuvres made in the open loop control, highlighting the compliance and differences with respect to the expected behaviour. The overall behaviour is satisfying, proving that the engine model is good on the behavioral aspect. The most fulfilling result is the low run time achieved, that is lower then the target one of at least one order of magnitude. The real-time model will allow the development of control strategies before the engine hardware is available, meaning more time can be spent ensuring the engine can meet performance and emissions requirements.