The Portland State Aerospace Society (PSAS) is seeking to launch a liquid bi-propellant rocket to a height of 100 km. One of the principal challenges in this endeavor is the development and testing of the rocket engine and associated subsystems.
PSAS chose to develop a smaller scale, 2.2kN test engine prior to attempting a 100 km capable design. This is in keeping with PSAS’s technology development philosophy of iterative design where initial designs are built, tested, broken, and iterated towards fully functional and flight ready designs.
The 2.2kN engine was designed to employ a liquid oxygen (LOX) centered pintle. In this design, LOX flows through the center of the pintle and is sprayed outward in a radial pattern. The fuel enters a chamber surrounding the base of the pintle and flows into the engine through the annular gap between the outer diameter of the pintle and the engine. (See Figures 1 & 2) Inside of the combustion chamber, the two propellants impinge upon each other at right angles. This, ideally, results in a cone shaped spray of well mixed fuel and oxidizer.
Figure 1: Cross section of 2.2 kN engine. Fuel flow path shown in red, LOX flow path shown in green.
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Figure 2: cross section view of genaric pintle V1 & V2 geometry.
The choice to use this style of injector was finalized by the 2015-2016 capstone team who designed the 2.2kN engine. The use of a pintle type injector is not specifically required for this size of engine. That stated, the initial 2.2kN engine was designed specifically to work with a pintle type injector, which locked a number of the design parameters which may have otherwise been available. The most noteworthy restrictions imposed are that the injector can only be LOX centered, and has a maximum envelope for the outer diameter of the annular gap.
An instructional document was created while developing the injector for our first engine that attempts to distill the fundamental theory, design parameters, and the lessons learned from this project.
The first pintle injector design developed is the V series.