The system Operating Pressure is used to calculate density using the ideal gas law. When the Compressibility Effects option is enabled, the name Operating Pressure is changed to Equilibrium Operating Pressure since the Non-Premixed combustion model operating pressure can differ from the flow operating pressure. Section 15.7.2 provides more information about this value.
You can use the steady or unsteady laminar flamelet model for reactions in liquid systems. To do so, enable Liquid Micro-Mixing under PDF Options. The Liquid Micro-Mixing option is discussed in detail in Section 15.5.1.