Test Stand for a 1000lbf Kerolox Rocket Engine

 

The Project

This project is what I like to call Rocket Kart 1.0. It's a test stand built entirely out of 80/20 designed for the capacity of a 1000lbf ablative kerolox rocket engine. Equipped with high flow engine purges, load cells, PTs and TCs and several safety mechanisms, this test stand will serve all kinds of projects for many months to come. 

Overview

Looking at the stand's P&ID you can see the high flow purges and pressurization system are fed by two 3kpsi GN2 tanks. These feed into the their respective propellant circuits. Given the often unpredictable nature of fluids inside of a 3D printed injector, there are two regulators for each propellant. This will allow the user to control the set pressure of each tank in the event that the pressure drop across the fuel elements is different than that of the oxidizer (which it often is). Moving further down, each tank has redundant relief mechanisms, one burst disc and one relief valve, and a fail open vent in case our stand loses power or pneumatic pressure. Past the propellant tanks are fill QDs (quick disconnect) and moving even further down are the engine's main valves. On the engine itself there are three surface mount thermocouples. These will allow us to track which parts of the chamber's ablative are being consumed the fastest. There are also additional propellant PTs (pressure transducers) and a singular chamber PT.

When designing the stand, I refused to make compromises with safety even with our low budget. This is why the high flow purge valve has a pneumatic lock out and a manual isolation valve upstream to prevent a test stand operator from blasting someone with high pressure nitrogen. Additionally, relief valves on both propellant tanks are offset by a few PSI to prevent chattering and sized for a fire scenario per API 521 standards. Furthermore, the instrumentation on the engine are tied to redlines in our autosequence. Below is a sample sequence guide. The program that runs the autosequence for the engine (controlled by a Productivity P2000 PLC) will be written to this guide for each test. 

Most of the redlines and bluelines here are still arbitrary, as the engine nears its final design these will become more clear. It should be noted that I have the LOX main valve open before the kerosene main valve. This is important because it allows liquid oxygen to flash into GOX briefly in the injector before fuel injection. This will ionize the oxygen and allow it to more readily combust with kerosene while the igniter is firing. Since the engine runs at an O/F of about 2.2 and kerolox engines run at a stoichiometric ratio around 3 or 4, it would be better to have the LOX valve close first. That way one could avoid potentially moving through their stoichiometric ratio during engine shutdown (this is actually incorrectly depicted in the autosequence above).

Next Steps

The test stand still has quite a lot of work left. Programming the LabVIEW interface to talk to the PLC API, running structural analysis on the test stand's structure, securing logistics for moving this thing to FAR for testing and even finding a place to build it are all challenges to be faced in the coming months. Even without physical hardware, this test stand design has taught me a tremendous amount. The learning benefit alone makes it worthwhile.