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6:29 am
December 13, 2010
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rpulkrabek
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BigMike said:
Have we been able to calculate the temperature that we'd be experiencing at the injector plate?
No, we haven't done any such calculations. Thus far, all I know is that it will be quite hot :D I understand this isn't good enough. I think we could be able to use what others have experiences as a baseline. If it's 1000C, then we might be able to get away with some sort of brass. If it's more than that, we would probably want some sort of titanium. The only other thing I think we would need to overcome is the little bit of stress that is applied. I don't see that as a problem, as you can see how thin the aluminium walls of the combustion chamber are. For the heat applied to the combustion chamber, I am thinking we would use some sort of phenolic protection.
brmj said:
In regards to the material, I doubt Titanium will be necessary if we don't have to use it elsewhere. With recently expanded pressurised gas flowing over it quickly, it ought to be the best cooled portion of the engine if my intuition is corect.
I am not sure about this at all. This could very well be the case, though.
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1:51 pm
December 13, 2010
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BigMike
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rpulkrabek said:
No, we haven't done any such calculations. Thus far, all I know is that it will be quite hot :D I understand this isn't good enough. I think we could be able to use what others have experiences as a baseline. If it's 1000C, then we might be able to get away with some sort of brass. If it's more than that, we would probably want some sort of titanium. The only other thing I think we would need to overcome is the little bit of stress that is applied. I don't see that as a problem, as you can see how thin the aluminium walls of the combustion chamber are. For the heat applied to the combustion chamber, I am thinking we would use some sort of phenolic protection.
One other thing to keep in mind about the material choice is corrosion. You have an oxidizer moving at a very high rate, which tends to increase the rate of corrosion. This could degrade the performance of the injector plate significantly as your directional holes grow in size and eventually become one giant hole. But that is still a secondary thought compared to ascertaining the temperature experienced as well as what stresses it will see. If I had any notion at all of what the chemical reaction would be doing I'd look at it, but that's way out of my knowledge zone. But we really can't say whether or not a material will be suitable until that is known.
As far as the injector plate design, I see that all of the holes are either straight (or perpendicular to the flat plane of the plate), or angled in the direction of the circular path. Have you tried angling the holes radially inward towards the centerline of the plate? That might help the issue with flow in the center of the chamber.
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4:38 am
January 11, 2011
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rpulkrabek
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BigMike said:
As far as the injector plate design, I see that all of the holes are either straight (or perpendicular to the flat plane of the plate), or angled in the direction of the circular path. Have you tried angling the holes radially inward towards the centerline of the plate? That might help the issue with flow in the center of the chamber.
Good idea. I will try this with a few models to see what happens.
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6:47 am
January 17, 2011
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rpulkrabek
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Post edited 6:51 am – January 17, 2011 by rpulkrabek
I have done some more simulations. This time I was trying to do a radical design. I know that with in CSTART we want to keep things as simple as possible. I tried this design any way. Sometimes creative designs can lead to something good.
My idea was to design an injector plate that rotated, so that the fluid would cover the cross sectional area evenly. It would use the fluid flow to push the plate around.
Here is a picture of the assembly
Here is a picture of the plate itself.
That then led me to this result. I wasn't happy with it, since all of the fluid was pushed to the outter edges of the chamber.
I then thought that it would be better to have the fluid applied at a more central region of each "slit". This would be accomplished with a manifold. I then created a manifold with hoses to connecting to the injector assembly. The CFD analysis looked like this:
This is where I realized my flaw. All of the simulations I have shown have used stream lines. These stream lines simulate the flow of a massless particle. If the particle hits a wall, it basically becomes annihilated. This then means that my previous simulations were misleading. There were done correctly, but I should have used something other than a stream line.
I am capable of creating what is called an iso surface. This creates a surface for varying fluid velocities. It's difficult to show with a picture, but I can see it better if I rotate the model around.
I am also now under the impression that if the mass flow rate coming into the injector plate is greater than the mass flow rate coming out, that I can perform the simulation of a set pressure at each hole in the injector plate. This is how I plan on moving forward. I will retest some of the old designs under the assumption that the fluid pressure is even before it gets to the injector plate.
Also, just to be clear, I don't want to use a rotating injector plate. It goes against our design philosophy. It would be too difficult to account for the bearings in different pressures and temperatures. I prefer the static injector plate concept for this rocket. Any other ideas from anyone?
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11:37 am
January 17, 2011
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Rocket-To-The-Moon
| | Altus, Oklahoma, USA | |
| Member | posts 685 | |
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I am very impressed with the design work that you have been doing. I can't wait to see this coming together and being test fired (and eventually flown!). Do you have any dimensions of the current design? What is the diameter of the injector plate?
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Main Workgroups: Propulsion & Spacecraft Engineering
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5:45 am
January 18, 2011
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rpulkrabek
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| Member | posts 348 | |
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Rocket-To-The-Moon said:
I am very impressed with the design work that you have been doing. I can't wait to see this coming together and being test fired (and eventually flown!). Do you have any dimensions of the current design? What is the diameter of the injector plate?
The diameter of the injector plate above was 23.6 cm. We really haven't yet decided on final dimensions. We do know that the diamter of the rocket should be between 25cm-30cm. We haven't yet done investigations to determine was is the optimum. At this point, however, I am inclined to choose either 25cm, which is about 10 inches, or 30cm which is about 12 inches. We prefer to use the metric system, but if a 10 inch diameter could also work, it would be easier for people in the US to find material. This would purely be for simplicity.
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7:52 am
March 14, 2011
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rpulkrabek
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It has been a while since I have shown any progress towards OHKLA. For a few months, I have been struggling with the design on the injector plate. I have since compiled screenshots of 29 different configurations. The assembly uses a simple manifold type plate to spread out the fluid before it gets to the injector plate. A simplified version looks like this:
 
I was trying to find the design that would produce the most swirl and cover the most space inside the combustion chamber. Here is a PDF file that shows the screenshots of the different configurations. I am most pleased with the concept on page 25. This will require that we drill holes at an angle. This concept provided more flow compared to the concept where there is only holes drilled straight through on page 28.
For now, I will continue the design of OHKLA with the concept on page 25, but if this proves too difficult to manufacture, we can then use the concept on page 28. I will post screenshots at a later time of OHKLA with the new injector assembly.
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5:13 am
March 24, 2011
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rpulkrabek
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| Member | posts 348 | |
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Post edited 5:13 am – March 24, 2011 by rpulkrabek
I have updated the wiki with the lastest images of the CAD work from OHKLA. This now includes the injector plate design that is shown in the previous post.
Here is a sample picture of the hybrid rocket for Program Chimera. Hopefully the file size is not too large.
Please note, there hasn't been any work done towards the nose or the parachute. The valve is only shown as a solid cylinder, because this hasn't been decided on yet. Also, the dimensions and materials are not yet fully decided. Basically what I am saying is, we need to do a lot more work.
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10:08 am
March 27, 2011
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Rocket-To-The-Moon
| | Altus, Oklahoma, USA | |
| Member | posts 685 | |
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Very, very impressive work!
Do you have any mechanical drawings so that interested people could start making their own rocket? Even better would be if we could have a couple people making parts for one rocket (collaborative!).
You are an inspiration to the whole team.
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Main Workgroups: Propulsion & Spacecraft Engineering
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4:11 am
April 6, 2011
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rpulkrabek
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| Member | posts 348 | |
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Rocket-To-The-Moon said:
Do you have any mechanical drawings so that interested people could start making their own rocket?
No, I don't. The reason is because I don't want to spend time putting together 2D drawings, when the designs are going to change. I would rather finish the design first. If there is a demand for 2D manufacturing drawings, I would be willing to do this, though.
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