The main objectives of FIRST were to deliver a fuel spray atomisation prediction capability, which can represent the unsteadiness of the atomisation process, for gas turbine injectors and to deliver an improved soot / particulate modelling methodology for combustion Computational fluid dynamics (CFD).
Before the FIRST project there was very little information available to describe the properties of atomisation from Rolls-Royce aero engine rich and lean burn fuel injectors. Lefebvre correlations were typically used to estimate the fuel spray boundary conditions for CFD modelling of these injectors in combustor flows. This coarse method used for numerical modelling made accurate prediction of combustor flow fields, and consequently emissions, difficult. Actual measurements of the fuel particle sizes and velocities were required before further progress could be made in improving modelling techniques.
A new test facility was built in the combustion laboratories in Rolls-Royce Derby that was specifically designed to enable PDA measurements of fuel sprays from engine injectors. All of the PDA and flow visualisation measurements for this study were performed by SCITEK. Test geometries were designed and made that represented a single sector of an engine combustor so that the spray conditions were more closely representative of reality. Lean and rich burn fuel injectors were tested at a range of conditions relevant to their respective engine cycles and detailed measurements of droplet sizes and velocities were made at numerous locations. The work was extended to include sprays from alternative fuels as a comparison to a standard kerosene spray.
The measurements of the spray from the fuel injectors have now provided the boundary conditions required for CFD modelling of Rolls-Royce engine combustors and has described the progression of the atomisation process as the flow moves downstream away from the fuel injectors. This is vital information for the improvement of numerical models to predict engine reacting flows. The CFD models can now be validated against the spray measurements for a wide range of geometries and conditions and a step change in modelling accuracy will be the result. Future designs of aero engine combustors and fuel injectors will benefit from the improved modelling accuracy.