# Rocket Engine Design

1. Sep 22, 2004

### Mahler765

I'm a junior attending an accelerated high school who's working on this year's science project. As of right now, I'm planning on building a liquid fuel rocket that is powered by gasoline with concentrated hydrogen peroxide acting as an oxidizer. I am currently working through the equations needed to design a deLaval nozzle. So all that I know so far is what the rocket will be fueled by and that it will have a deLaval nozzle. The size of the rocket depends on the design of the engine as does the amount of fuel because i would not have an accurate idea of how much thrust i would need. I'm planning on either making the deLaval from a ceramic or copper, I'm still not sure which. My research has told me that copper will do fine for a combustion chamber. However my worry is that the copper will act as a catalyst for the hydrogen peroxide and cause decomposition when I don't want it to happen. Another question is if i really need a catalyst since the combustion of the gasoline will be generating large amounts of heat.
I'm operating on a short budget so obtaining all the pumps or mechanical parts to build a detailed engine is basically out of the question. One thing that would make the design easier is if I could pre-mix the hydrogen peroxide and the gasoline which would eliminate the need for a pump(s). Another thing that I have been toying around with is the idea of burning a gasoline ice cube. I've tried freezing gasoline in my freezer and it's freezing point is apparently lower than that of water. If all else fails, I do have access to liquid nitrogen through a local university but i'm hoping that dry ice or a better freezer will suffice. With the gasoline frozen, it could then be used as a solid fuel with an oxidizer and I could just fill the combustion chamber with gasoline, freeze it, and then keep it frozen until it's time to launch.
For the project I will be measuring things such as burn rate, etc. If any of you have any ideas for an alternate liquid fuel that I could compare the gasoline and hydrogen peroxide with your suggestions will be much appreciated. I am two years ahead in math and a year ahead in science so I actually have some idea of what I'm doing but I've already been told not to do the project by three college professors. Also, I have taken an accelerated three week course in aerospace engineering through the Duke TIP summer program so I also have a background in that. If you have any suggestions as to different variables that i could test in this project please be sure to mention them. All thoughts on the matter will be welcome.
Thanks

2. Sep 22, 2004

### enigma

Staff Emeritus
Hi Mahler,

Welcome to PF!

You probably want a thrust to weight ratio about 2.5-3. To get it that high, you'll need a pretty high chamber pressure.

Do you know the combustion temperature of the gas/H202? Metals lose strength at temperatures much lower than the melting point.

Yeah, that's commonly referred to as a 'bomb'

Without pumps you will have a big problem getting the fuel into the chamber to maintain the reaction. Once you fire it off, the pressure will rise in the combustion chamber, and unless your feed pressure is higher, the combustion gases will flow backwards into the fuel/oxidizer tanks and start a combustion there. This is commonly referred to as a 'bomb'.

VERY dangerous idea! This is commonly referred to as a 'bomb'.

If your fuel is solid how are you going to continue supplying more to the combustion chamber? The mass flows through rockets are pretty high, and unless you've got a huge (read: heavy) combustion chamber the fuel will be depleted before you get very far.

I hate to say it, but I'm going to chime in with them. Building a liquid rocket is no small task. It took the best engineers in the country years to get the first one working, and without the background knowledge given to you by people who have been in the field, you'd basically be starting from scratch in terms of experience. Even if you could get it working safely, there is practically no way you'll be able to do it in a year by yourself. What you're proposing is extremely advanced even for a multiple year, multiple person graduate level project with adequate funding. Everything needs to work correctly in rocketry or you get an explosion.

Here is what I would recommend to you:

Look into picking up some larger model rockets. Most of those use solid fuels, and all of the components are sized to prevent explosions. If the manufacture of components is a requirement for your project (and you're dead set on designing nozzles), I'd recommend building different expansion ratio nozzles and mounting them to the existing upper half of the motor. You can still test mass flow, thrust, specific impulse, etc. that way. The lower combustion temperatures of model rockets would mean you could probably get away with plastic, ceramic, or composite nozzles without melting them.

Here are a few other ideas you might try (I think these are probably more do-able, but I don't know your exact assignment):

* You might be able to bore small pressure taps into the nozzle and measure static pressure distributions along the length (this would probably need to be done in a static fire situation).

* If you've got moderate funding, you could try to get an accelerometer and a microprocessor to gather and store the acceleration profile of the rocket during a launch. Programming a microprocessor and getting valid data would really be impressive! Learning assembly language is tough! This would also test your soldering and electronics abilities and let you design a shock absorber for the electronics and a parachute deployment system to return the "black box" safely to the ground.

* You can talk to various university professors or maybe even a local distributor of FEMLAB (or similar) and model flow through various rocket nozzles. You can probably manage to borrow or beg a semester or two long student license from someone. You can see how well the results correspond to theory, and you'll be able to see firsthand how the shape of the nozzles affect flow parameters. This would include (among other things): flow separation from the walls as you make the nozzle be more and more bell-like, exit mach number variations as expansion ratio is varied, etc. Additionally, the pictures this project would give you would wow any presentation, and familiarity with FEMLAB would practically guarantee you a research position with a professor during your undergraduate years.

You're shooting for the stars right now. If I'm understanding your situation correctly, you need something that's reasonably attainable in a semester or two (and won't be the only thing you're working on, either). The main point of science projects is to learn something. The second point is to do something cool which interests you and you have fun with. Speaking from experience, for a project to be fun, it has to be do-able.

A book which you would probably find valuable is:
Space Propulsion Analysis and Design by Humble, Henry, and Larson.

It is an upper undergraduate level textbook, but you should be able to work your way through it if you're determined. It goes all the way from basic equations on rocket operation and fluid dynamics to specifics of electrical and nuclear propulsion motors.

Hope that helped some, without discouraging you too much! :tongue2:

Last edited: Sep 22, 2004
3. Sep 22, 2004

### Janitor

Not to cast a wet blanket on things, but have you considered aiming for merely a static test of your engine instead? At least as a first step? And in that case, obviously you will want to use a videocam for close observation of the firing, and probably sand bags or a bunker of some sort for protecting any humans who are in harm's way. Concentrated hydrogen peroxide is a famous killer, as German engineers discovered in the WWII years.

4. Sep 23, 2004

### Mahler765

Thanks for the Help

I'm used to discouragement by now so don't worry about it. Your suggestions for alternative variables are really great ideas. What exactly is FEMLAB? I'm in Birmingham, Alabama so I may even be able to find something like that in Huntsville with the Space and Rocket Center. I was planning on testing the engine just by itself while it was stationary to see if it would work the first place before I even tried installing it in the rocket. I'd be working closely with my math teacher who used to be a physicist for NASA and my uncle who's a chemical engineer. I think that I will try to do just a static test. That will eliminate the size limits of the engine and allow me to actually use materials that will provide me with something that works.

As to the gasoline being provided to the combustion chamber. My idea was to freeze the gasoline in the combustion chamber with a whole through the middle and just have the H2O2 flow with the whole to oxidize the gasoline.

Speaking of the Germans. I have a friend in Germany who is helping me do research and he found an engineer in Switzerland who builds hydrogen peroxide engines for small companies and we were using him as a source. And apparently, they sell the 30% concentration H2O2 over the counter in drug stores in Germany just as we sell the 3% concentration. I thought that was interesting.

So you are saying just to build the engine and get it to work. And then test it using different nozzles? I've researched a little on this and I found several different kinds of software that deal with this. As far as requirements for the project, there aren't any. I'm doing this by choice because it's what i'm interested in. Most people like doing the inferior biology projects where they just going some kind of bacteria and see what happens when the conditions are changed a bit. I'll be researching your suggestions more thoroughly this weekend when I have a little more free time.
Thanks for your help.

5. Sep 23, 2004

### enigma

Staff Emeritus
FEMLAB is a http://www.comsol.com/showroom/gallery/. A teammate used it to model fluid flow through various rocket nozzles for a design project I was working on. We were looking to find the smallest expansion ratio we could use and still have sonic flow at the throat.

What you are thinking of doing is very dangerous. That geometry provides what is called 'progressive'. As the fuel burns, the area available for burning increases, which increases the rate of the reaction, which increases the pressure in the chamber, whcih increases the burn rate, which increases the area available for burning, which increases the rate of the reaction, which increases the pressure in the chamber, which blows out your combustion chamber, which leaves you will a big smoking crater where your lab used to be and gives you a trip to the hospital, morgue, or both in turn. That's not to mention what happens when the temperature in the chamber gets hot enough to melt the frozen gas and the entire thing starts to burn at once. Solid fuels don't transmit heat very well for a good reason.

No, I'm saying go out and buy some model rockets and test them. Once you get some data, then look into replacing certain parts and seeing what happens.

You're seriously shooting too high. Even if you're Werner van Braun re-incarnated, I place heavy odds against you building something in a year. I'd even place odds against a team from Lockheed or Boeing getting a new design built in a year. If by some miracle, you do get a working prototype built, what happens if it blows up? 20-30% of professionally built rockets blow up on the first launch, and that's even with proper training, staffing, funding, production facilities, testing and much more time than you have. It took Goddard years to build his first rocket, and he had much more training and experience than any of us.

It took 8 junior and senior aerospace engineering students (myself included) an entire semester to do preliminary engineering analysis on a rocket design. Our final report was nowhere even close to the point where we could build anything with it. We had to make tons of simplifying assumptions to get any results at all, because we didn't have the capability to do the preliminary experimental research needed.

BTW: historically, it has costed about 7.125 * (mass in kg)^.55 Million in \$2002 to build a liquid fueled rocket from scratch.

Last edited by a moderator: Apr 21, 2017 at 9:03 AM
6. Sep 23, 2004

### Staff: Mentor

Solid model rockets are a good idea (and a fun hobby). Even they are a serious undertaking. The Discovery channel is currently running a show on model rockets and the centerpiece of the show is a 15' high rocket that was launched to a height of about 30,000 feet. It took a small team of hobbyists a year or so to build. I don't want to encourage you to scare your chemistry teacher too much, but the larger solid rocket motors are hand-made by hobbyists and there is some experimentation that can be done there.

A word on this type of project: I don't know your specific situation, but I did a year-long project in 9th grade where my task was to design a fighter-jet from scratch and test it in a wind tunnel (of my own construction). It took several months just to build the wind tunnel and by the end of the year, all I had was a few sketches and a concept for the plane. But I learned a lot about aerospace engineering (like, wtf is a "slug"!?) and that was still worthy of a A.

7. Sep 23, 2004

### sigma

wtf is a slug?

8. Sep 23, 2004

### Cliff_J

Find someone who's been unlucky enough to be around an exploded tire. Deaf, blind, missing a finger or more comes to mind. That's a simple rubber donut at 80-90psi and there's millions of them all designed to handle thousands of pounds of weight. But when they fail...

Even the solid rocket motors require licencing to build past a certain size and the licencing is a progression from smaller engines to larger ones.

I'd stick with the advice given above. Even a store bought rocket can have problems at launch and turn itself into a projectile. But at least its designed to not become a bomb as well.

Cliff

9. Sep 23, 2004

### Staff: Mentor

A slug is an English unit of mass apparently only used by Aersospace Engineers.

10. Sep 24, 2004

### Mahler765

As to the slug question. When I took the aerospace engineering course at Duke, we used it alot. My understanding is that something equivilent to a newton. English units are used in all the aerospace equations in the atmosphere. So the air pressure at sea level is something like 2377 x 10 raised to the -6 slugs per cubic foot. Correct me if i'm wrong.

11. Sep 24, 2004

### Janitor

And of course Goddard had a wealthy benefactor in Daniel Guggenheim, through the advocacy of Charles Lindbergh.

In my late teens I had similar thoughts of building my own single stage liquid propellant rocket, but I never got beyond the point of doing some library research and sketching some ideas for the combustion chamber and the associated plumbing. I remember jotting down a list of materials that some library book said were compatible with various propellants. Concentrated peroxide had a very brief list of compatible metals and sealing materials!

Around that same time I came across a book by some German who was part of rocket development in the war years (Dornberger?), and I think it was in that book that I read about an Me-163 pilot whose corpse was basically melted from exposure to C-stoff, or whatever it was the Germans called hydrogen peroxide.

12. Sep 24, 2004

### enigma

Staff Emeritus
Other way around. A slug is a unit of mass like the kilogram. It is 32.2 times as large as a pound-mass.

13. Oct 6, 2004

### Evil Knievel

Useful contact?

Mahler

Hi. Follow this link: http://www.aardvark.co.nz/pjet/spinning1.shtml . This guy actually builds pulse jet engines as a hobby and he seems quite handy. This particular link shows how he built a metal spinning lathe with which he turned venturi's. I am sure that you could get him interested.

Good luck!!

Knievel

Last edited by a moderator: Apr 21, 2017 at 9:18 AM
14. Oct 6, 2004

### Janitor

The lathe is surely the way to go for making parts that have an axis of symmetry. Does anybody know if underwater explosive forming is still used for giving metal a compound curve? Or is that an obsolete method?

15. Oct 13, 2004

### MaximumTaco

I've been reading through the many many project logs on the Armadillo Aerospace website, they have alot of interesting things regarding their work with H2O2 monopropellant and catalyst systems

16. Jun 9, 2005

### ZA

Not to discourage you, but it is obvious that you have NO IDEA OF WHAT YOU ARE REALLY DOING! This may sound coincidental, but I too am a junior designing a liquid fuel rocket engine. I have done research and calculations on rockets and rocket engines for over a year now. I have also finished first year college level physics (Mechanics and E&M) and first year college level inorganic chemistry with high "A"s. I am also currently doing Calculus so I know what I am talking about.
First of all, YOU NEED TO KNOW WHAT YOU'RE DOING! you need to know exactly the thrust that you're shooting for, the pressure your engine will operate at, the burn temperature of your reactants at that pressure, consider a cooling mechanism that will prevent a meltdown ESPECIALLY WITH COPPER (where you're looking at a meltdown at a measly 1083 Celcius), know the strength characteristics of your metal or alloy used at the temperatures operated at (which differ greatly with temperature for some metals), have a target mass for the engine, consider the oxidation of your engine at high temperatures and have it galvanized with an inert metal such as platinum (it's dirt cheap if you're putting on a very thin layer). work through the primitive versions of DeLaval equations to get a rough idea of your engine's characteristics, and finally, FIGURE OUT THE FEED SYSTEM YOU WILL EMPLOY.
I strongly discourage you from using hydrogen peroxide as your oxidizer, as it is not the optimal oxidizer simply because most of the oxidizer's mass will end up as water and will not be involved in the main exothermic reaction. Instead, you should really try liquid oxygen, which is MUCH more effective as an oxidizer, doesn't spontaneously decompose, and it can pressurize your feed system. I realize there are problems in making and storing liquid oxygen, but the advantages more than compensate for the inconvenience.
Also, as already mentioned, premixing your reactants for a liquid fueled rocket engine is not only stupid, it's plain suicidal! If the heat from your combustion chamber gets conducted back to your fuel tank, a huge explosion will follow immediately, and shrapnel from the engine will kill anyone nearby! Trust me, your teachers know what they're talking about!
I don't know where you got the crazy idea for using copper for your rocket engine. Copper melts at 1083 Celcius under normal conditions, and at the temperatures you are operating at, even if you somehow prevent melting with a really good cooling mechanism, copper will simply be too plastic to withstand the pressures you're supposed to be aiming at. I am designing my engine to consist of either Titanium, or a thin walled Tungsten. The greatest problem with these metals is machining, which I am trying to figure out now.
I also strongly discourage you from building a hybrid engine with frozen gasoline because of two reasons. First of all, your entire fuel supplies will have to be stored in the combustion chamber, which will mean either a short flight duration, or a huge combustion chamber to hold all of your fuel, which will mean a huge mass for your engine. The second reason is that most of your gasoline will be located in a chamber at a temperature of a few thousand Kelvin which will melt and evaporate at a rate MUCH faster than the stoichiometric ratio flow of the oxidizer, which will result in an extremely inefficient engine.
I am planning my engine to work on Liquid Hydrogen-Oxygen which gives an extremely high efficiency, and a relatively low combustion temperature. Gaseous Oxygen and Hydrogen can be obtained easily and then liquified via adiabatic compression and expansion. Using these components eliminates the need for a pump and simplifies the feed system by pressurizing the fuel tanks, which can be kept at a needed pressure with properly adjusted pressure valves.
If you have more questions, which I may or may not be able to answer, e-mail me at hyperspace12000@yahoo.com

Last edited: Jun 9, 2005
17. Jun 9, 2005

### NateTG

Alternative approaches

Something else to consider is using a $H_2O_2$ single-fuel rocket, which can be much simpler. The standard approach is to have a nitrogen tank and use that to pressurize the $H_2O_2$. Then the peroxide is fed into the 'combustion' chamber where it mixes with a catalyst (usually silver screens).

Peroxide rockets are relatively inefficient, but quite simple, and are 'cold'. (I think somewhere around 600C.) They're used in the 'rocket packs' that occasionally show up in the movies.

18. Jun 9, 2005

### FredGarvin

I can't say I agree with recommending working with LOX to anyone who does not completely understand what they are doing.