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This paper presents an original approach to modelling and simulating complex systems. The overall application used to illustrate this approach consists in modelling and simulating the transient behaviour of a diesel engine. Conventional modelling and simulation stages for small projects are presented. As a larger project needs additional tools, we have developed an original approach using two other models. We first introduced a new compound model which is a modelling approach where many white and/or black boxes are linked together. In the second stages of a project - implementation of the simulator - we introduced another Object-Oriented model. Variable granularity modelling and simulation are also presented in this project. Such a concept is a suitable for a project starting from scratch. At first the subsystems are not well understood; but as we start to understand them better, different kinds of models can be introduced.

According to the modelling principle which consists in an iterative comparison between a knowledge model and a representation model, we are building a software which simulates the dynamics of a Diesel engine. Modelling a Diesel engine requires a good accuracy in combustion simulation; therefore Vibe's two-peak model was chosen. But determining the seven necessary parameters is quite difficult due to this non-linear representation. The “downhill gradient search method” solves this identification problem if weighting factors and initial filtering are chosen carefully. After presenting our principle, we shall apply this method to two different engine speeds. Lastly, we shall compare the data measured in the test-bed with the new computed ones using our model.

This paper will describe an approach method for the complete modelling of an engine; our approach provide software for very detailed description (Knowledge model) as well as simple models (Representation model) which can be implemented in a governor to improve consistently the system behaviour. The software for very detailed description require performing workstation (SUN: Californian Computer Manufacterer; etc., …) and the simple models can be used in real time on the latest microprocessors. We will describe here essentially the knowledge model part of this research. As they offer a similar approach to all types of systems, Bond graphs are a tool of great interest for knowledge modelling. This tool has a limited expansion in Europe and even more so in the industrial area. We have used this technique to modelise and simulate the behaviour of a turbocharged six cylinder (mid-range) Diesel engine.