More stringent regulations on emissions in the automotive industry increase the need of improving all areas of the engine operation. An area where the emission formation is problematic, but has not before been prioritized regarding computer simulations, is the engine start-up at cold conditions. A simulation model is an effective tool in order to study the cold start behaviour and emission formation dependent on engine characteristic parameters, without extensive assets used.
This report aims at analysing engine cold start behaviour, the critical areas and the requirements needed to implement a simulation model in GT-Power, for both gasoline and diesel engines. Two models were created, one for a gasoline engine with manual transmission and one for a diesel engine with automatic transmission, which aimed to simulate engine start-up at 20°C and -30°C. Test-rig data was used to validate the results. Simplifications for different systems were however needed in order to create the start-up models.
It was found that it was not possible to simulate the start-up at -30°C with the simplifications made, due to the extensive amount of friction at this temperature. The results show however that it was possible to create simulation models for 20°C, which correlate with test-rig data. The models can be used to get a general understanding of the start-up, but the use of the models is limited due to the necessary simplifications.
The start-up process is complex and even though the results show good correlation between the models and test runs, the subsystem needs to be considered in detail in order to create valid simulation models. The accuracy of the models are strongly dependent on how the starter motor, friction and inertia is modelled, and small deviations can give consequences leading to an invalid model. If the models are further developed and adjusted with proposed changes, they could be used to predict the behavior of different start-up events and to improve the cold start and reduce emissions.
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