Propellant Specification

Propellant Specification Screen

Propellant Specification screen is intended to specify used propellant component/s.

Propellant Specification screen (Lite Edition)

Propellant Specification screen (Standard Edition)

You can choose between bipropellant and monopropellant propulsion systems, selecting the corresponding item in the listbox at the top of the screen:

Note: although you have the choice between bipropellant and monopropellant propulsion systems only, there is a possibility to specify three (or more) propellant components.
See section How to... on this web site for further details.

For bipropellant systems, the lists for both Oxidizer and Fuel are enabled (see figure "Propellant Specification screen" above), as well as the fields for specifying a mixture ratio.

The mixture ratio can be specified either as an O/F ratio (ratio of "oxidizer flow rate" to "fuel flow rate"), or as an oxidizer excess coefficient, given as ratio of desired O/F to stoichiometric O/F.

You can also select an item "optimum":

In this case the mixture ratio will be optimized for getting maximum specific impulse under given conditions. The found optimum O/F ratio will be displayed on the screen Chamber Performance.

For monopropellant system, the single list of propellant components is enabled, whereas the Fuel list and fields for specifying mixture ratio are disabled.

Specifying monopropellant system

Note: for the thermodynamic calculation, the only difference between bipropellant system and monopropellant system that contains two species, is how the species mixture is defined. Actually, you can define any bipropellant system (as well as three- or more propellant systems) as a monopropellant system, specifying the proper mass fraction for each component on the list.
For instance, the following "monopropellant" configuration is equivalent to the bipropellant one with O/F=0.7245/0.2755=2.63:

Each component list (Oxidizer, Fuel, or Propellant) contains one or more species, displayed on the single row. To add species to the list, click the button Add at the bottom of the corresponding list. To remove the selected species from the list, click the button Remove.

To add new species, click the button Define new (available in RPA Standard Edition only):

In the appeared dialog window, specify at least the name, the exploded chemical formula, and the heat of formation of new species.

Once the new species was defined, it is stored in the user thermodynamic database and permanent available for using in other problems.

Component Properties

The component on the list features 4 parameters: species name, mass fraction of the species in the component (for bipropellant systems) or propellant (for monopropellant systems), initial temperature of the species, and initial pressure of the species.

Initial species temperature and pressure are optional parameters. If not specified, the follwing default values will be assigned automatically:

• p = 1 atm, T = 298.15 K  for non-cryogenic species
• T = [boiling point temperature]  for cryogenic liquids

When composing component (for bipropellant systems) or propellant (for monopropellant systems) from several species, the sum of all the mass fractions of components on the same list has to be equal to 1. To change the mass fraction for the species, double-click on the corresponding cell, enter the new value and press Enter button (or click away).

Each list features the automatic mass fraction checker, that displays the current sum in the list footer. If the sum is correct, the background color of the footer is light-green, otherwise the color is light-red:

To specify the initial temperature and/or pressure of the species, double-click on the corresponding cell, enter the new value and then press Enter button (or click away):

To change the unit, double-click on the corresponding cell, select the desired unit on the list, and tnen press Enter button (or click away):

The temperature can be entered using one of the following units: K, C, F, R.

The pressure is an absolute pressure and can be entered using one of the following units: MPa, atm, kg/sm2, bar, psi, Pa.

Note: the initial temperature and/or pressure can only be specified for the components which are supplied together with thermodynamic properties either in the polynomial form or in tabular form.
See chapter Thermodynamic Database Editor for further details.

Note: if the components change their temperature/pressure due to the work performed by components themselves, you should assign initial (T,p) which components had before the work is performed.
For instance, in staged combustion engine, a turbopump is powered by components, and the correct initial parameters correspond to components' conditions at the pump inlets, in opposite to the conditions at pump outlets or combustion chamber injector.

Components Database

After clicking on button Add, the dialog window "Components" appears. The content of the dialog window depends on the type of target list, where component will be added.

Components Database

When adding new component to the oxidizer list, the dialog window displays available oxidizers; when adding new component to the fuel list, the dialog window displays available fuels. For monopropellant systems, both oxidizers and fuels will be displayed in the dialog window.

You can filter the list in the dialog window, using a regular expression. The filter pattern is applied to both columns of the table.

Mark the checkbox "Show cmplete list of available reactants and product of reaction" if you want to see all species, including atomized and/or ionized products of reaction, or keep it unmarked if you want to see only possible propellant components.

Select one or more species on the list and click the button OK. Click the button Cancel if you want to leave without adding any species.

Last modified: February 27, 2011