CFD Modeling of Impinging Sprays under Large Two-Stroke Marine Engine-Like Conditions

To improve the combustion and emission characteristics of the large-bore marine engines, the spray is usually designed as an inter-spray impingement to promote the fuel-air mixing process, which implies frequent droplet collisions. Properly describing the collision dynamics of liquid droplets has been of interest in the field of spray modeling for marine engine applications. In this context, this work attempts to develop an accurate and efficient methodology for modeling impinging sprays under engine-like conditions. Experimental validations in terms of spray penetration and morphology are initially carried out at different operating conditions considering the parametric variations of ambient temperature and pressure, where the measurements are performed on a large-scale constant volume chamber with two symmetrical injectors. The existing models, including O'Rourke and Nordin's collision models, are also applied and the obtained results are compared to further assess the accuracy and efficiency of the present model. The collision regimes are analyzed to explore the outcomes of the spray-spray impingement and to guide the future work of injection optimization for large two-stroke marine engine applications. The results suggested that the O'Rourke model overestimates the collision probability, while the Nordin and Nordin-MR approaches show similar accuracy since the outcomes of reflective separation and shattering are negligible in current impinging spray configuration and the lack of bouncing does not make significant difference in modeling the fuel evaporation and mixing processes at 800-K ambient. The similar computational cost were achieved by the Nordin and Nordin-MR models, suggesting that both of them are applicable to practical marine engine simulations. Besides, the spray impingement could strongly stimulate the droplet breakup at the impinging location, which leads to a subsequent enhanced mixing with the potential to mitigate the soot emission in engine applications.