Advanced engine design and alternative fuels bring the possibility of fuel injection at purely supercritical conditions in diesel engines, gas turbines, and rockets. The complex interactions that govern this phenomenon still need significant research for reliable modeling efforts. Boundary conditions for fuel injection are critical to accurate simulation. However, the flow inside the injector itself is often omitted to reduce the computational efforts, and thus, velocity or total pressure are specified at the injector exit, often with an assumed top hat profile and assumed turbulence levels. Past studies have shown that such simplified inlet boundary treatment has minimal effects on the results. However, these studies apply mainly to fuel injection in the compressed liquid phase, and the simplified approach breaks down at supercritical fuel conditions.

The supercritical fuel injection case has significantly more sensitivity to changes in boundary conditions due primarily to compressibility effects in the injector. In a supercritical fuel injection case, the state of the fuel at the injector outlet is difficult to know without a simulation of the injector geometry. Rapid expansion of the fluid in the injector nozzle where static pressure decreases dramatically as the velocity increases results in significant density gradients that are not present in compressed liquid cases.

In this work, relative differences between respective simulations performed in ANSYS Fluent of steady, axisymmetric, supercritical propane injection into a co-flow of nitrogen are presented. Five different boundary treatments are compared, along with two different real gas EOS formulations and the ideal gas formulation. Validation for the methodology is provided via simulations of an experimental result from published literature.


Role of Inlet Boundary Conditions on Fuel-Air Mixing at Supercritical Conditions

Division / Sponsors: 
Internal Combustion Engine Division (ICED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2020/volume/84034

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