Theoretical rocket performance parameters can be calculated for either infinite-area (IAC) or finite-area (FAC) combustors.   Mixture thermodynamic properties and composition can also be calculated for the combustor, throat, and several selected exit points.   For the IAC option (fac = false), there is an option to assume either chemical equilibrium for all points or to freeze composition after combustion, throat, or any exit point.   For the FAC option (fac = true), only equilibrium calculations are allowed because it is difficult to define freezing points.   An option to calculate thermal transport properties is available for either case.

For equations, assumptions, and definitions, refer to Chapter 6, NASA RP-1311, Part I, 1994.   IAC examples 8, 11, 12, and 13 and FAC examples 9 and 10 were taken from NASA RP-1311, Part II, 1996.

Use the ENTER, RETURN, or TAB key, or click on the next empty cell after each table entry.

PRESSURE UNITS
A selection of several units is available for initial pressure Pin (P_inf for IAC or P_inj for FAC), namely bar (default); atm; psia; or mmHg.   The selected unit applies to all the values listed.   The estimated or assigned combustion temperature Tc may be selected as either Kelvin (default), Rankine, Celsius, or Fahrenheit.   The default estimated value is 3800 K.

INITIAL PRESSURE
Up to 16 values may be entered for the initial pressure Pin ( P_inf for IAC or P_inj for FAC).   A complete rocket performance profile will be calculated for each value as specified by the remaining input.

COMBUSTION TEMPERATURE
Assuming the same velocity (either zero or otherwise) at the combustion chamber inlet, identical thermodynamic results are obtained for the combustion inlet condition for both the IAC and FAC models.   Normally, combustion temperature is obtained from the mixture enthalpy of the reactants.   For this case a temperature estimate is required.   The default value of 3800 Kelvin will be used unless the user chooses a different value.   The combustion point is an assigned enthalpy and temperature problem that sometimes requires inserting possible condensed species with the initial composition estimates-see the Help menu for Insert dataset.

Sometimes the temperature is known and the value may be set by the user.

INFINITE-AREA COMBUSTOR
The user may choose for all calculated points to assume chemical equilibrium or he may choose to have the products frozen after a specified point.   Both of these options may be selected for any run.   Freeze points selections are combustion, throat, or exit1.   The exit1 value will be one of the Optional Exit Points described below.   CEAgui will pick the first exit value listed starting with the left column for Pin/Pe.    Example12 illustrates freezing composition at the throat.

All points are isentropic with respect to the combustion point.

FINITE-AREA COMBUSTOR
Because of the difficulty in defining the freeze point for this option, only equilibrium calculations are permitted.

The chamber in the FAC model is assumed to have a constant cross-sectional area.   In this chamber combustion is a non-isentropic, irreversible process.   During the burning process, part of the energy released is used to raise the entropy, and the pressure drops.   Expansion in the nozzle is assumed to be isentropic.

One of two input parameters is required, either the contraction ratio A_c/A_t or the mass flow rate per combustor area A_c.   Output includes values for A_c/A_t and P_inj/P_inf in addition to properties and composition for the injector, combustor, throat, and optional exit points.

OPTIONAL USER-ASSIGNED ENTHALPY
Total enthalpy for the combustor will be calculated from the enthalpies of the individual reactant values unless the user chooses to assign a value.   This value is h/R in units of (g-mol)K/(g of mixture).

OPTIONAL EXIT CONDITIONS
Three columns are available for optional exit points in the nozzle.   The left column is for assigned pressure ratios Pin/Pe where Pin is injector pressure P_inj for FAC problems and P_inf for IAC models.   Pe is the exit pressure P_e.   The middle column is for subsonic area ratios A_e/A_t and the right column is for supersonic area ratios A_e/A_t (i.e. exit area relative to the throat area).   Up to 13 values may be entered into each column.

HELP
The Help button displays the help menu for the Rocket problem.

SAVE
The Save button saves the data and returns to the Problem dataset.

RESET
The Reset button resets the data to the default settings.