Nitrous/Ethane Pintle Injector

Project

The Variable Engine Gaseous (VEGAS) test stand aims to deliver rapid, low-cost testing of small-scale engine concepts. This injector for a 600 lbf ethane/nitrous engine aims to mount onto VEGAS and interface with the chamber team. The role of the injector is to mix and atomize the fuel and oxidizer to optimize combustion inside the engine chamber.

Purpose

BURPG has collected abundant data and proved the functionality of its triplet-impinging injectors from cold flows and static fires. Nevertheless, triplets were hard and expensive to manufacture due to high tolerances on hole size and orientation. This project aimed to explore the pintle for its reliability, high efficiency, and simplicity.

product

After passing a critical design review, the injector was planned to be outsourced due to machining complexity of the pintle and film cooling holes. However, the team had to change the scope of the VEGAS program to accommodate member training and reduced budget. The project is currently undergoing redesign.

Table 1: Given/Target Values

Table 2: Calculated Injector Specifications

Injector design

I utilized flow equations (mass flow continuity, pressure drop across orifice) and the Moody friction diagram to size the pintle. Starting designs with first principles ensured system reliability and compliance with fluid requirements.
I cross-referenced research papers to gain intuitions on design parameters. For verification, I compared my injector characteristics such as the total momentum ratio and spray angle to typical values.
With rapid iterations in mind, I selected optimal experimental values for a few chosen variables including film cooling fuel percentage and skip distance.
I designed the injector following manufacturing processes. Features including stock size, standard drill size, and machine setup were considered.

Plenum Design

Due to the lack of public research on plenum sizing, I dimensioned the plenum to be reasonably small according to engineering judgment.
Plenum sizing required spacial planning. Each plenum and its holes needed to remain separate and accommodate the O-rings to prevent leaks. The plenum also interfaced with many instrumentations such as pressure transducer, load cell, and fluid fittings. The plenum could also not interfere with the threaded connections.

Assembly

Since the pintle was known for its vulnerability to heat damage, I designed it to be replaceable. The pintle body was sandwiched between plenum plates by bolts.
The entire assembly had an overall size of 5.1'' X 5.1'' X 2.6''. It consisted of 4 main plenum plates and 1 face plate that absorbed combustion heating.
To facilitate ox cleaning and repair, all plates remained separate and connected via 8x M3-70 mm bolts and lock nuts. The injector assembly would mount to the engine via 8 tapped holes on the chamber wall.