1997-02-24

Evaluation on Two Stroke Engines Scavenging Models 970358

The potential of the two-stroke engine has become more and more subject to increasing research work trying to optimise the power-weight ratio as well as the pollutant emissions, especially with the development of high efficient direct injection systems. Doubtless is the scavenging process of the two-stroke engine a most complex and troublesome problem with the numerical simulation or design of new developments. Since the proposal of the perfect mixing model of HOPKINS in 1914 lots of different models have been offered to draw conclusions about the quality of the scavenging process. These may be classified into 3 main categories, the single zone, the multi zone and the fluid mechanical models, while precision and expenditure are increasing dramatically in this order.
Every category serves a special purpose. By using single zone models, a simple and handsome way is offered to collect information about the trend behaviour of an engine. In order to optimise for example the intake port design it is essential to use a model which includes detailed geometrical information. Thus leads to the complex and difficult to handle group of the fluid mechanical or comprehensive computing models. However, it is very often necessary to gather information about the scavenging process to optimise operating parameters. Therefore a model with a good ability to reproduce the real process as well as low mathematical expenditure is needed.
The multi zone models are an attempt to accomplish these demands. A lot of single and multi zone models are offered by different authors. The present paper introduces and compares the models for scavenging simulation considering the aspects of precision and expenditure to offer the operator the possibility to choose the model for his individual suiting purpose. The fluid mechanical models are expelled because off their complex nature.
It was found that the multi zone model group contains a semi-empirical model which is very capable of describing the scavenging process while positively combining high precision and acceptable numerical requirements, the CREST model. To analyse the trend behaviour of an engine, three models have to be considered qualified. These are the DANG/WALLACE, the BENSON/BRADHAM and the MAEKAWA model.

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