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