Structure of High-Pressure Fuel Sprays

A multi-dimensional model was used to calculate interactions between spray drops and gas motions close to the nozzle in dense high-pressure sprays. The model also accounts for the phenomena of drop breakup, drop collision and coalescence, and the effect of drops, on the gas turbulence. The calculations used a new method to describe atomization (a boundary condition in current spray codes). The method assumes that atomization and drop breakup are indistinguishable processes within the dense spray near the nozzle exit. Accordingly, atomization is prescribed by injecting drops (‘blobs’) that have a size equal to the nozzle exit diameter. The injected ‘blobs’ breakup due to interaction with the gas as they penetrate, yielding a core region which contains relatively large drops. The computed core length agrees well with available measurements of core length in high-pressure sprays. This core length depends on the operating conditions and it can be comparable to piston-bowl dimensions in internal combustion engine applications. Since the large drops in the core vaporize slowly, these spray structure details are important to the overall spray process. Downstream of the core, drop size in the spray is determined by a competition between drop breakup and drop coalescence, and the computational results agree well with available experimental drop size, drop velocity and spray penetration data.