Monday, January 16, 2017

Computer software for pintle injector design data

Pintle injector designer is a beta version of a small throttleable liquid rocket engine design software. It is currently being beta tested and will be available free of cost within 3 months. Currently,this software is used for Face Shut Off type pintle injector, final product will be capable of providing design data for Slit type as well. Future versions will have results of calculation for dimensions of the injectors in CAD software recognizable format.

Calculating the mass flow rates of a rocket engine is a time consuming process.  Pintle injector design software eases the calculation process. This software reduces mass flow rate and discharge area calculation for a liquid fueld combustion chamber to just 5 minutes.

You can use the current version of pintle injector design software to calculate the mass flow rate and discharge are needed for a pintle injector to be used in liquid rocket engines.

 The resulting data is printed to a file called "myfile.txt".

How to use the pintle injector design software to calculate the mass flow rate and discharge ?
  • STEP 1-Select the thrust and propellants of the rocket engine.
  • STEP 2 -Combustion chamber pressure.
  • STEP 3- Fix the optimum mixture ratio of the rocket engine
  • STEP 4- Find out the Flame Temperature, Molar Mass, Specific heat Ratio and Characteristic velocity(C star) of the exhaust gases in the rocket combustion chamber. These values can be found out using NASA CEA application.
  • STEP 5-Download and open Pintle Injector Design Software
  • STEP 6-Enter the Specific Heat ratio.
  • STEP 7-Exit pressure(Sea level/Vacuum pressure in Pascal)
  • STEP 8-Enter the Inside pressure as the combustion chamber pressure.
  • STEP 9-Enter the thrust of the engine to be designed
  • STEP 10- Flame temperature in the Temperature of Combustion field.
  • STEP 11- Enter the optimum mixture ratio in the mixture ratio field.
  • STEP 12-In Gas Constant field enter the specific gas constant(It is universal gas constant/Molar mass) and submit.

Pintle injector Design software- entering inputs such as Thrust of  rocket engine, Mixture ratio etc
The out put will be shown on the right side of pintle injector design software. Out put includes the thrust co-efficient of the rocket, throat area of the nozzle. Mass flow rate of the fuel and oxidizer required for the selected thrust of the rocket engine. Click on Next button for calculating the discharge area needed to reach the required mass flow rates of propellants.

  • STEP 13- Enter the discharge co-efficients of fuel and oxidizer exits. They can be reasonably approximated to 0.7 or exact value can be found after the fabrication.
  • STEP 14- Enter the pressure drop of fuel and oxidizer in the next. A good approximation is 20% drop from the combustion chamber pressure as noted from SP-125 NASA rocket design book.
  • STEP 15- Enter the Density of fuel and oxidizer in kg/metre cube.

Entering propellant properties in the pintle injector design software

  • STEP 16-Next page is to find the pintle dimensions, just enter the pintle diameter. Outer and inner diamter is used to find the annular gap. This portion is yet to be developed. So enter some junk values and do manual calculation for this data for your design.
  • You can download the pintle injector design software here Download. Please make sure that you have the latest Java version installed on you PC.
    Special thanks to Albin Shaji (Computer Science Department-Karunya University) for writing the code for this software.
    The full data required for the pintle injector will be written to "myfile.txt" file created on the same folder where this software is installed.

    Sunday, January 15, 2017

    Design of a pintle injector for 5000 N liquid rocket propellant engine

    A 5000N engine with LOX anf Kerosine has been selected and a pintle injector has been designed to meet the requirements of this engine. The combustion chamber pressure was 25 bar (2500000 Pa). The specific heat ratio (K) was 1.16. Gas constant R was 704.8 J/Kg-K. Exit Pressure Pe was 1 bar. The temperature at the combustion chamber was taken as 3141.07 K. 

    Thrust co-efficient was calculated using the below mentioned equation.

    Throat area of the Nozzle can be found out using:

    Now we have to find the characteristics velocity c* to know the mass flow required for this 5000N engine.

    The characteristic velocity, also called c-star or simply c*, is a figure of thermochemical merit for a particular propellant and may be considered to be indicative of the combustion efficiency.

    Now mass flow rate can be found out from

    The stoichiometric mixture ratio was taken for the calculation of propellant flow rates. The stoichiometric oxidizer to fuel ratio for liquid kerosene and liquid oxygen is 2.5.

     Oxidizer flow rate can be found out using:

    Area required to inject the propellants at the above mentioned flow rates can be found out from

    Veleocity of fuel discharge is 19.09 m/s

    Where Cd is the discharge co-efficient, discharge coefficient (also known as coefficient of discharge) is the ratio of the actual discharge to the theoretical discharge.

    Discharge co-efficient of .7 was assumed as it was found experimentally for the pintle injector design in one of the research papers. Density of kerosene at 15° was 806 kg/m3. Density of kerosene at -182.96° is 1141 kg/m3.

     A reasonable pressure drop of 3 bar for the propellants was assumed.

    Corresponding fuel injection velocity is found out in the last equation mentioend above.

    Corresponding oxidizer injection velocity can be found out using

    1.1            PINTLE DESIGN

    As per the design procedure mentioned by Min son et all, a pintle diameter of 20 mm was chosen.

    Now, the gap between pintle’s slanted surface and annular casing has to be determined. This area is the area of the cylinder with the diameter of pintle pintle. Area of that Oxidizer discharge gap is

    Fuel discharge gap-"annular gap" between two concentric circles is 0.43 mm.

    Drawing of a pintle injector dimensions for 5000 N engine using LOX and kerosine

    Cut away view of pintle injector with two inlets marked on the right side