Table of Contents
A prototype engine was built to carry out small scale tests and to optimize sub-systems before integrating them onto our full-scale engine. This smaller chamber allows us to test repeatedly and safely at a lower cost then if we were to test them on the full scale engine. We aim to test the following using this test fixture:
- Engine Controller
- recording pressure/temperature data
- controlling solenoid
- igniting pyro-charge
- Ignition System
- Fuel Regression Rate
- Firing Procedures and Protocols
- Molding Paraffin
Test Set UpOur test set-up consists of a 2" steel chamber, test stand, feed system with gaseous nitrous oxide, test sensors, and an enclosed yet ventilated room.
- Set up pipe system as in schematic
- Test solenoid operation with whatever method we're using to control it
- Test sensor operation
- Pressure test up to solenoid (IE open nitrous, and make sure there are no leaks with the solenoid closed)
- Ignite engine (either light a sparkler and insert it, or use the internal igniter)
- Open solenoid
- Nitrous regulator can be set either high or low. Generally we set it low, and ramp up during the test.
- Observe test
- When engine starts coughing ludicrous amounts of smoke, close solenoid
- Wait for room to clear before entering
1/15/18These series of tests were the initial tests for lighting the engine. There was not an end-cap on the chamber since there was no intention to build chamber pressure. Different ways of igniting the engine were tried. We were able to produce a good amount of flame with the low pressure flow, but observed that most of the paraffin had melted and not burned.
Test successful: paraffin and nitrous combined will burn (or melt at least)
1/18/18In this test, we added a chamber end-cap with a large hole in an attempt to build up minimal chamber pressure. We were not able to build any pressure, and again, most of the paraffin melted. The paper used to ignite the engine was shot out of the end cap as it burned and temporarily blocked the end cap causing it to "cough". We will attempt to reduce the end cap exit area and build pressure in the chamber in the next test.
In this test we learned that the paraffin really needs to be ignited from the top of the chamber. The theory going in was that the paper inserted into the engine would burn up to the top of the chamber, but then of course only the paper has burned up there and the paraffin has been burning/melting out the backend.
1/23/18This test was used to determine if utilizing a sparkler as an igniter for preliminary testing purposes would work. We first burned some sparklers outside of the chamber to determine how long they burned for so that we could time the ignition sequence. This test showed that this would be an acceptable way of igniting for preliminary testing purposes.
A sparkler was used because we couldn't burn most things in the low oxygen environment inside of the combustion chamber. A sparkler comes with a built in oxidizer, so it allowed us to light it, shove it in to the top, and then flow nitrous before it went out.
2/01/18For this test, we used end cap with a smaller exit area (1/4" diameter). We were able to get good combustion from the fuel grain, but it was not very stable. Moving forward, we believe we need to increase the flow rate of nitrous oxide.
The working theory for this "combustion looks unstable" phenomenon is that most of the paraffin vapor does not burn inside the combustion chamber due to a low O/F ratio, and is instead vented as "smoke". As soon as the vapor mixes with oxygen outside of the chamber, it is combustible, and will flash fire, creating a visual effect of "unstable combustion". To fix this issue, a higher nitrous flow rate will need to be achieved.
2/13/18This test fire aimed to collect pressure and temperature data throughout the burn, while using a sparkler as the ignitor. We also had a thermal imaging camera in-place to record temperature data along the length of the chamber as well as read the temperature of the exhaust gasses. The first attempted fire seemed to self-extinguish in a way producing a very small flame and a cloud of smoke. The second attempt resulted in a more robust burn, possibly due to a more primed chamber, but still showed some combustion instability.
These smaller "throat" tests are showing some pressure increase during the burn, but not a lot and it isn't super quantifiable. We need to re-calibrate our pressure transducer to accurately measure them. In addition, it's hard to differentiate the pressure increase from random noise, but possible using a rolling average.