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This paper describes the development of an engine performance simulation programme using both the method of characteristics (MOC) and the filling and emptying method (F&E) to optimise the use of computer time and achieve accurate simulation results, with the emphasis being given to the modelling of turbocharger compressors and turbines for different matching conditions. The possible turbocharger matching options are discussed, and the associated models are developed for multiple compressors and turbines. In these models, each inlet and outlet of the devices is modelled firstly, by using either the MOC or F&E method, or both, and then coupled to each other according to the matching option. The performance characteristics of both devices inputted in the form of performance maps, are converted into different forms with different matching options.

An eleven litre four stroke medium speed marine diesel engine has been studied with different wastegate turbocharging systems to improve low speed/part load engine performance. A previous Glasgow College model was adapted to simulate the engine operation under steady conditions. A variation to the Single Zone Fuel Model developed by Watson, Pilley and Marzouk was proposed and a Schwitzer-type wastegate turbocharger model was developed. A series of exhaust wastegate turbochargers have been simulated and tested to identify matching of the various turbomachinery configurations and the effects of these on engine performance. Both simulation and experimental results show that the wastegate bypass system can be modified to advantage by proper selection of the wastegate discharge flow mixing point along the engine exhaust system. The best low speed engine performance was obtained with the wastegate discharge flow exhausting directly to the atmosphere.