Spray wall interaction modelling by dimensionless data analysis

Spray wall interaction is a phenomenon commonly observed in modern direct injecting engines at stratified charge. To optimise the engine design with respect to soot, NOx and un-burnt hydrocarbon emissions, simulation techniques increasingly complement prototyping. Thus it is necessary to use a model that describes wall interaction as realistic as possible. Existing models are often valid in a restricted range of conditions only. Hence there is a demand for a more general model combining the existing knowledge from previous models with new detailed experimental data. Although first investigations on drop/wall-interaction started in the 19th century, the mechanisms of drop impact are still far from clear. A large number of studies dealing with the investigation of the impingement process have been published, examining the impingement phenomena from the theoretical or the experimental side. Especially theoretical studies trying to consider the underlying physical mechanisms that occur during the interaction process show that even if the physics is known it is still hardly possible to simulate the impingement of a single drop with accuracy in a reasonable time. As especially the influence of the thermal processes is still not fully understood and as computing power is still too low it will – at least in the near future – remain impossible to simulate the details of the impingement of millions of droplets. With this knowledge it is obvious, that one can only simulate the spray impingement process by simplifying the mechanisms by application of a suitable model, which can be derived from theoretical considerations or by deduction from experimental observations.