Hybrid Rocket Injector Plate Design Research

[Wasure]

TL;DR

Looking for insight related to the research of how to improve the injector plate design for hybrid rockets.

Hello,

First of all, I hope this post is in the right section (aerospace engineering).

I am doing research on the injector plate design for a hybrid rocket and I'm no where at the moment. I was thinking that I could improve the geometry of the injector plate in order to help improve some issues with the hybrid rocket - such as the burn regression rate.

Another option could be to figure out a way to project the injector plate since the heat from the ignited fuel can damage the injector plate quite easily.

I don't mind admitting that I'm obviously terrible at engineering since I just sort of stare at research papers and don't know how I wold go about my own research. Any advice would be appreciated.

 

[anorlunda]

Your question is a bit puzzling. You are doing research but you have trouble understanding other research papers. That makes it hard for us to give a reply because we can't know at what level to aim it.

Can you give more information on your background and on the nature of your research?

Also, the terms hybrid rocket and injector plate are not specific enough to identify exactly what you are asking about. Please elaborate on those.

 

[Wasure]

Well, I majored in aerospace engineering for undergraduate and I'm pursuing a masters now.

I want to model the geometry of the injector plate in such a way that it will improve the regression rate. Then I need to find how what design I need to test in order to attempt this. That's going to be the goal of my research. Whether I succeed or not is probably not an issue. I just need to figure out what kind of design to test and how I'll experiment with it. Sounds simple when I write it, but I feel a bit lost.

 

[hutchphd]

A little general advice. If you can, plan on building two versions of your device. The first should be as simple as it can be...get your hands dirty and have a device that works albeit not in an optimal way. And do this as quickly as you can. Having completed this, you will know lots of things not to do.

Now proceed to design the real deal, testing ideas and subassemblies as you can on the existing prototype. Thus will save you lots of agita

Sounds like fun...hope it works well

 

[ChemAir]

Interesting project.

In the US, some of these specific design considerations are regulated by ITAR (International Traffic in Arms Regulation), since they can be used for ICBM's/etc... Many other designs are protected by patent, or otherwise kept 'in house' at the various motor designers where manufacturers want to protect their intellectual property. I don't believe you will find many current designs published for distribution.

I would look to see if there are unclassified designs from Russia or the US from a few decades ago. These may be out of date, but will be a decent starting point, if this is just an academic exercise.

This may give you some ideas for what it takes to make a basic apparatus for a test liquid motor. If you are doing a simulation, a smaller sim might be easier to model.

If you plan to actually fire one of these, there is an extraordinary amount of care that needs to go into the design to limit risk, and mitigate fire/explosion damage if the design isn't right. I would not attempt this without consultation with someone that has done it before.

EDIT: after re-reading you are asking about hybrids, here are a couple of sites that sell these systems at a little more than a basic hobby level.
https://www.rattworks.net/
http://www.aeroconsystems.com/motors/skyripper/skyripper_home.htm

You may have to get certification by one of the two bodies in the US, either NAR (National Association of Rocketry), or Tripoli Rocketry Association to be able to purchase any of these parts.

 

[Wasure]

This is a great start. I didn't consider that I would need two injector plate designs. I guess it does make sense from a scientific perspective so that I can compare my design with a general design. I intend on employing both experimental and simulation methods to test whether my design is better or worse.

Some other helpful background info:

I'm not in the US, so whatever designs I create on CAD and send to the manufacturer should be fine. I can't say that I understand what kind of general standards that I must consider for my test design. Maybe there's a book or resource for that somewhere? I haven't found one after searching. I could try asking my professor and he may know.

Also, where would I find out more info on whether a design is patented or not? I would like to avoid stealing other people's designs if possible. My goal is to sort of make my own afterall.

I'm also not too sure how I would go about my experiment. I've seen several different methods, so I'm not sure what I should use.

 

[etudiant]

The big challenge with hybrids is that the fuel usually gets burned unevenly, so that eventually chunks get ejected without getting burned. This makes the mass fraction unacceptably bad. If you can develop a fuel shape or retainer that eliminates that problem, you will have made a serious contribution.

 

[etudiant]

Just to add to this, the fuel configuration is usually created to ensure that the vehicle acceleration is relatively constant, no easy task when the weight of the vehicle is rapidly changing as the fuel is consumed. So ideally the burn should be highest early and fade as the fuel is depleted.
In theory, it might be possible to manage this by controlling the oxidizer flow, but that raises combustion management challenges which are at least equally intractable.

 

[Wasure]

I'm at the point now where I'm wondering which parameters I should focus on when looking at the oxidizer flow. I guess I should look at designing an injector plate that is capable of regulating the oxidizer flow?

 

[etudiant]

Modulating the oxidizer flow has its own challenges, particularly if the aim is to keep the acceleration more or less constant.
That is not essential however, there is lots of precedent for rockets that accelerate at increasing rates, including all the manned space vehicles. The main challenge with hybrids is to maintain fuel integrity and to get all the fuel burned, not perforated and ejected.
That suggests the long pole in the tent is configuring the fuel to provide stable access to the oxidizer even as the lump of fuel is consumed entirely. Modulating the oxidizer flow will probably be needed as well, as the available fuel surface will change as the fuel is consumed.