Search Results

The internal flow in Diesel injector nozzles significantly affects the spray formation, atomisation and air/fuel mixing rates. A multi-dimensional model has been developed to numerically predict the spray evolution patterns with particular focus on capturing the influence of the injector nozzle flow on the near-nozzle spray dispersion. The link to the internal flow is established by using as initial conditions for the injected fuel, the transiently and spatially resolved distribution of the flow field at the nozzle hole exit plane as calculated from a multi-dimensional and multi-phase nozzle flow simulation model. The local spray dispersion angle is estimated by assuming that the disintegration of the liquid jet is function of the distribution of liquid velocity, cavitation vapour volume fraction and liquid turbulence level at the exit of the injection hole.

The numerical methodology used to predict the flow inside pressure-swirl atomizers used with gasoline direct injection engines and the subsequent spray development is presented. Validation of the two-phase CFD models used takes place against film thickness measurements obtained from high resolution CCD-based images taken inside the discharge hole of a pressure swirl atomizer modified to incorporate a transparent hole extension. The transient evolution of the film thickness and its mean axial and swirl velocity components as it emerges from the nozzle hole is then used as input to a spray CFD model predicting the development of both non-evaporating and evaporating sprays under a variety of back pressure and temperature conditions. Model predictions are compared with phase Doppler anemometry measurements of the temporal and spatial variation of the droplet size and velocity as well as CCD spray images.