Theoretical studies of supercritical real-fluid oxidations of diverse fuels by using the 3rd-order virial equation of state with nonlinear effects

The 3rd-order Virial equation of state (EoS) with nonlinear effects was constructed and applied to simulate various real-fluid fuel oxidations, including hydrocarbons and oxygenated fuels under supercritical conditions. The real-fluid effects for hydrocarbon and oxygenated fuel oxidations have been discussed by using the Redlich-Kwong (RK) and the 3rd-order Virial methods. The compressibility factors calculated using the 3rd-order Virial EoS possess better agreements with experimental data for H₂, N₂, and H₂O at different temperatures and below 300 atm than the previous 2nd-order Virial EoS and the RK EoS. The calculations of thermodynamic properties by using the 3rd-order Virial EoS also showed a better agreement with experimental data for H₂O than using the RK EoS. The RK method exhibited contradictory speciation predictions against the ideal-gas 0-D and 1-D simulations in H₂O and N₂/CO₂ diluent gases, respectively, while the 3rd-order Virial method kept its consistency. Especially, the ignition delay simulation by using the 3rd Virial EoS is extended to the operation conditions relevant to the recent SpaceX Starship Raptor engines in CH₄/O₂ mixture at 600 atm. It shows the decreases in the ignition delay times by 3 times by including the real-fluid impact. The simulation results were also compared with a series of existing experimental data for ammonia, larger alkanes, and gasoline blends, which show significant real-fluid effects at low temperatures. Instead of inputting critical pressure and temperature parameters of different species manually in the typical empirical methods with high inconvenience and uncertainties, the required parameters in the 3rd-order Virial method can be directly obtained from the input transport document for real-fluid computations.