Development of a transient spray cone angle correlation for CFD simulations at diesel engine conditions

The accurate modeling of fuel spray behavior under diesel engine conditions requires well-characterized boundary conditions. Among those conditions, the spray cone angle is important due to its impact on the spray mixing process, flame lift-off locations and subsequent soot formation. The spray cone angle is a highly dynamic variable, but existing correlations have been developed mainly for diesel fuels at quasi-steady state and relatively low injection pressures. The objective of this study was to develop spray cone angle correla-tions for both diesel and a light-end gasoline fuel over a wide range of diesel-engine operating conditions that are capable of capturing both the transient and quasi-steady state processes. Two important macroscopic characteristics of solid cone sprays, the spray cone angle and spray penetration, were measured using a single-hole heavy-duty injector using two fuels at diesel engine conditions in an optical constant volume vessel. Charge gas conditions for the experimental spray data for the two fuels included injection pressures of 100-250 MPa and charge gas densities of 10-167 kg/m3. It was observed that the spray cone angle experienced three stages, beginning with a large initial value, dropping to a quasi-steady state, and then finally rising again near the end of injection. These observations were then used to construct correlations for the transient process for inputs for spray computational fluid dynamics (CFD) simulations. The model showed good agreement with experimental measurements at different ambient conditions, leading to improved prediction accuracy in CFD studies