In the past few months the hybrid propulsion group has been working along with other fellow students in a minor at the TU Delft. A minor is a semester during which students can choose to specialize in a field or discover new areas non-related to their field of study. The minor not only allowed more students to discover rocketry but to get closer to a flight ready design.

One significant improvement was the design of a vertical test bench with reduced friction and restrains movement in the vertical direction thus allowing for more accurate data gathering and analysis. Further integration resemble to a ready design was made by designing an in house developed tank to hold the oxidizer. To ensure the safety one tank was tested up till its burst pressure at 147.9 bars and the second tank was tested to be leak tight to at least a pressure of 95 bars. These test were performed at the company Advanced Lightweight Engineering

A heating system was added to be able to heat the tank to an operating pressure of 60 bars and obtain comparable data. To perform this a coil of heating wire was wrapped around the tank and epoxy was applied to the outside of the tank and the tank was insulated. The coils were equally spaced to prevent spot heating. Once all design and production was completed hot fire test were performed as shown in the picture below.

Three successful hot fire tests were performed with HDPE and sorbitol both fuels using nitrous oxide as oxidizer. Problems were encountered with the ignition of the engine, as it did not behave in the same way as in horizontal test setup. In the following weeks this problem should be resolved. The hybrid propulsion group will now work further to integrate this propulsion system into a rocket.

 

Last Friday, the 20th of May, the hybrid propulsion group had three successful system tests of the hybrid propulsion system under development for Stratos II.

The test engine had been redesigned to overcome leakage problems experienced with the previous generation of test motors.

The first test using a conventional axial oxidizer injector system ignited successfully and burned for 8 seconds creating remarkable 275 Newton of thrust. The nozzle unfortunately was damaged irreparably, but the rest of the motor stayed intact.

The second test featured a swirl injector that was tested earlier. The engine ignited properly but then blew out for yet unknown reasons.

Finally the first pyrovalve prototype was tested for leakage using nitrogen. At a pressure of 60 bar the only leakage found occurred at the threaded connection to the feed system proving the leak-tightness of the valve mechanism itself.

History was made on of Friday the 25th of March and a new era begun for DARE as the DAWN hybrid propulsion team made the first successful ignition of a hybrid engine within the student society. It also marks a great step forward in the development of the hybrid motor for Project Stratos II, DARE’s flagship project.
Previous tests from DAWN have been focused on testing particular subsystems such as the injector, feed system, pyro charge igniter and electric igniter. This test was unique because it was the first attempt to demonstrate that all the subsystems could be integrated and function as an engine.
The DAWN team had planned to conduct this test much earlier, but due delays in receiving the required permits to handle dangerous substances, all tests were put on hold. This was the case until the idea was hatched to use a new type of igniter, one which requires no restricted chemicals such as black powder or conventional solid rocket fuels. The idea was to use a resistance wire to heat magnesium ribbon to its auto ignition temperature, causing it to catch alight and in turn ignite the engine. Once this concept was proven viable in tests, the motor test could go ahead.

The DAWN team put in an intense week of late nights and early mornings to get the test ready, but come that Friday morning, everything was organized and ran like clockwork. The motor was ready, and so was the team. The countdown started. 3..2..1..ignition sequence started..3..2..1..valve open and ignition! The motor spewed smoke in every direction, enveloping the small crowd that had gathered in smoke. It was clear that not quite everything had gone exactly as planned. But  after about 7 seconds, the nitrous was turned off and the bystanders applauded. Despite the obvious problems they knew it was still a success for the DAWN team.
On closer inspection of the video, it’s quite clear to see that the motor couldn’t handle the heat and pressure of combustion, causing it to fail after 6 seconds or so of burning. After only a few seconds of burning, the rubber O-rings can be seen to creep out of place, causing the leaks to worsen. This leaking resulted in hot gases flowing past the sides of the tube and the endcaps, which eventually caused a piece of the combustion chamber to be torn out.  Unfortunately, this makes the test motor unusable. This doesn’t worry the DAWN team as this motor has served its purpose and will be redesigned to ensure that the next test will feature more than just successful ignition.

There were two sensors connected to the test bench. One was a load cell that measured the weight of the oxidizer tank. By looking at the change in weight of the tank the team hoped to retrieve information on the nitrous flow. However, the sensor did not produce any useful readings as the changes in the weight of the tank seem to be lost in the noise due to the settings of the data logger.
The second sensor on the test bench was a pressure sensor that was connected to the combustion chamber, next to the injector. The pressure sensor can also be seen in the video. Some nice readings were obtained from this sensor. The pressure graph clearly shows a nice increase in pressure as soon as the engine ignites. The pressure in the combustion chamber then holds fairly constant until after approximately three seconds when the O-ring near the injector fails. Then the pressure drops significantly. After this, the pressure is again fairly constant until the end of the burn, approximately another four seconds later. A full analysis will be posted when all the data has been gathered and analyzed.

To conclude, this test has laid the foundation of a successful motor concept, which can eventually be made into a flight motor for Project Stratos II. Although there is certainly a lot of work still to be done, this recent success will drive the DAWN team to push on to the next goal. The coming weeks are sure to be an exciting time. Watch this space!

Last Tuesday Project DAWN, the hybrid motor group of project Stratos II, had a successful test motor injector test on the former architecture field.

The test was conducted to prove the injector concept for the test motor, the feed system setup in general and to observe the nitrous oxide flow behavior.

During the test the feed system was purged with nitrogen first, followed by a couple of bursts with nitrous oxide. Eventually the effect of flowing nitrous oxide on a PVC tube was tested. Video footage can be found on below:

Early on in project DAWN, we decided that many tests would have to be conducted to ensure that we can prove that a hybrid motor is a viable concept for Stratos II. To do this, we needed a test bed with a fast turnaround time. While we already had a test motor, it had to be resealed with silicone and left to dry before each test.

This left a lot to be desired and so the last few weeks we have been redesigning the injector and nozzle and devised a way of sealing the combustion chamber without messy silicone. We have done this by crushing the two o rings in between the edge of the combustion chamber walls and the injector or nozzle. Once the bolts are done up, the o rings are crushed between the two parts, creating a tight seal as in the following picture.

During February we have been busy with the production of the new injector and nozzle and currently we are waiting for the ¼ gas fitting to be put onto the injector (second picture, bottom) after the midterm break. Once that is done, a dry pressure test using compressed air will be conducted to ensure the motor is sealed properly. Then the nozzle can be drilled out (second picture, top left), completing the motor. The new design should allow us to do at least one test per hour, and hence many tests in one day. Coming spring the architecture field we use for testing is going to be filled with Hybrid smoke!

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Dawn flight engine ready to go

On Thursday the 3th of May 2012, the hybrid propulsion team of the Stratos II project (named Dawn) successfully tested their flight engine. This hybrid rocket engine has been developed based on the research they have done during the whole span of the project. Now finally they are ready to go for the first attempt in the history of DARE to launch a hybrid rocket engine. The team has kept to their original design of an engine with a sorbitol fuel grain and a nitrous oxide oxidizer. To store the oxidizer the tank concept developed during the Spacecraft Engineering Minor [...]