ASSESSMENT OF ATOMIZATION MODELS FOR DIESEL ENGINE SIMULATIONS

Abstract

Liquid fuel injection and atomization have a significant influence on the combustion and emission characteristics of diesel engines. Using x-ray radiography, it is possible to obtain quantitative and time-resolved data in the primary breakup region close to the injector nozzle. However, most previous studies on model validations have employed optical measurements that are not applicable in this dense spray region. In the present study, atomization models, based on Kelvin-Helmholtz and Rayleigh-Taylor instabilities, are extensively validated using x-ray and optical measurements for non-evaporating sprays, as well as detailed measurements for evaporating sprays. The data include spray penetration, axial velocity, liquid mass distribution, cone angle, Sauter mean diameter, and vapor penetration. Simulations are performed using a computational fluid dynamics (CFD) code "CONVERGE", which employs an innovative grid generation technique, and state-of-the-art spray models. Postprocessing tools are developed to facilitate a detailed comparison of predictions with x-ray and optical measurements. The effect of rate of injection uncertainties on spray evolution is also quantified. Although the model globally reproduced the experimentally observed trends and the effects of various parameters on atomization and spray characteristics, it underpredicted spray dispersion, especially for non-evaporating sprays, indicating the need for further model development. In addition, the model could not capture the experimental trends in terms of the effects of nozzle orifice geometry on spray development, implying that effects of cavitation and turbulence generated inside the injector need to be included in the model.