Research On Two-component Droplet Impacting On Heated Surface And Droplet Evaporation Model

As the developing trend of engine downsizing and higher injection pressure,the fuel spray impacting is unavoidable.The morphological changes of spray droplets during the impacting process directly affect the engine performance and the combustion efficiency.So experimental studies of droplet behaviors impacting on a heated surface have been performed to learn the morphological changes of droplets during the impacting process and its affecting factors.A multi-component droplet evaporation model was developed to investigate the droplets evaporation process and its affecting factors.The droplet impacting on the heated surface was observed by a high speed camera,and the morphological changes of droplets were analyzed.As the surface temperature rising four impact regimes were identified and classified for droplets.The Leidenfrost effect was observed when the surface temperature higher than the critical temperature.As the initial droplets sizes and impacting velocity increases the Leidenfrost critical temperature raises and the max contact diameter increases.The spreading velocity increases as the impacting velocity increases but the initial droplet sizes have no effect on it.The droplets breakup phenomenon was observed if the impacting velocity is too high.The critical temperature differs with droplets components and it is related to the saturation temperature.The droplet component has less effect on the spreading velocity but the max contact diameter increases as the droplet surface tension coefficient increased.And the central jet breakup phenomenon was observed because of the air dissolvability different of ethanol and water.A multicomponent droplet evaporation model was developed based on the effective diffusivity model,and its accuracy was verified.Results shows that the evaporation processes have two stages: unsteady evaporation and steady evaporation.The droplet diameter increases first and the decrease during the unsteady evaporation,but the droplet temperature increase continuously.The droplet temperature rises slowly and the droplet diameter decreased until the end of the droplet evaporation.Because of the higher saturation vapor pressure and gas diffusion coefficient the ethanol component evaporated faster than the butanol component.The increase of ambient temperature,ambient pressure,the relative velocity of the droplet and air,droplet initial temperature and the decrease of droplet initial diameter all promote droplet evaporating.And as the initial mass fraction of ethanol increases the evaporation time increases slightly.