I'm an engineer..to bad it's on a fire engine.

Anyway. One of our old club memebers used to fly steam rockets and at one point he brought a steam powered go cart. I watched as heated up the water and remembering how he had a wet rag over the "on/off' valve. It looked to be just a normal looking 1/4 turn gas valve. He had a piece if rope tied to it that ran up front of the go-cart. Once he pulled the cord he was off. IIRC it went pretty fast but was of short duration. You might do some googling ..his name is William Inman.

Tony

Three words: "Strap on boosters". I say we weld some 98mm casings to that Bessie and really move things along.

No need to thank me - I'm glad to help 😀

Thanks John that helped immensly

Hey everyone,
I have quite the engineering question that I need some ideas on. In my Engineering Projects class, we have started our final year project. I convinced my group to try to make a steam powered rocket motor. Here is the basic outline of the design and process we are trying to re-create.

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-The upper container will hold all water, in a perfect world no air.
-The upper container will be sealed and then heated to temperatures above boiling point
-The upper container will be pressurized using a water pump to a specified PSI
-Then on demand, we will open a valve at the bottom of the tank releasing the water as fast as possible into the nozzle
-When the water that was under pressure comes in contact with atmospheric pressure, the boiling point will go back to 212 degrees (When the water is in the upper container and pressurized, the boiling point will be much higher then normal) it will "flash" into steam, and expand dramatically
-The steam will move out of the nozzle and create thrust

We have come to a couple of problems in the design. First we can’t find a valve that can do three things. Withstand extremely high temperatures and pressures, and most importantly release the water quickly enough so the system doesn’t bleed out. Second we don’t know a way to heat the water once it is sealed in the upper container and raise it to roughly three hundred degrees.

Any thoughts? I have had sessions with many professors going over equations of thermodynamics and dynamics to find equations for this system. Even if we do find equations we don’t know how to actually build it physically.

I don't know much about steam powered rockets, but this does remind me of when I was in high school, trying to sanitize a bike water bottle in the microwave. I filled it with water, heated it up nice and hot, and it was just sitting there. Then when I grabbed it, the nozzle opened and a stream of superheated water/steam came out and took the skin right off of a patch of my abdomen. If I remember correctly, it didn't generate that much thrust because the water boiled off into steam after it left the bottle. I guess that's what your 12" section is for.

Also, there was a Mythbusters on this subject, where the three younger crew had a contest to see who could make the highest-flying steam-powered rocket. Turn out it was the one who built it the lightest.

For heat, you will definitely want something you can turn on and off remotely (very remotely). That probably means electric heat. Some resistive heating elements and insulation would probably do the trick. Also make sure to have some remote temperature sensing. I don't have an answer for you on the valve. That's the hardest part of any similar device. I was working on a compressed gas deployment system once and ran into a similar problem.

I wouldn't consider myself an engineer, but I like to day dream.

for the valve: how about a round ball resting against the bottom of the boiler tank as it sits on the pad. It would have to melt/flash at the particular temperature that the pressurized water is heated?

There must be some kind of concoction of Mother Nature or Mankind that provides the right combination.

How to heat it?

as a kid, the magnifying glass offered untold hundreds of episodes of spontaneous combustion.

crazy ideas but fun

Adrian: Like most water rockets built as a kid, the "thrust" is mostly the water pushing agianst the ground pushing the bottle up. In this case the steam should expand and if the diameter is small enough actually create thrust. Thats the hope anyway.

For the valve, a couple of ideas have gone around. One is we make a break valve, where at a certain pressure or heat, it will break open. A other idea is a boiler valve, because they are used to withstand high pressures and temperatures.

The kind of valve your describing is a boiler relief valve. Problem is they are heavy, and the smallest size they usually come in is 3/4"

Another possibility would be a pneumatic solenoid valve. They would handle the pressure but I'm not sure about the heat. They tend to be smaller, maybe too small

Using a heating element from a water heater would require external power until right before lift off. Plus a way to monitor pressure and temp.

The combination of Sch80 pipe, valve, heating element, pressure and temperature monitoring is going to make it pretty heavy. I say go with the 98's

Were not actually trying to put it in a vehicle and attempt a launch. We were going to make a test stand for it so we could get data off of it. We looked at solenoid valves, some of them can get up to 200-300 psi which is still to low, and cant hold the temperatures. On top of that there 250$ plus.

Firstly, I would consider a "burst disk" instead of a valve. They are available in precisely calibrated pressure ratings and were extensively used in Apollo and in other expendables for a wide variety of purposes.

A resistive heater would probably be the best option, but the electricity source for such a high current requirement should certainly be left on the ground. Think multiple car batteries and a detachable umbilical.

This seems like a really interesting idea, but I do see a couple of problems.

1) You'll need to get the water EXTREMELY hot, since when it flashes to steam, it also cools substantially (energy is absorbed by the phase transition). Then, when a gas flows through a converging-diverging nozzle, it cools further, and if you aren't careful, the steam could condense in the nozzle. This would absolutely wreck your thrust. Of course, the issue with getting the water hot enough is that the pressure in the tank will rise the hotter the water is. I can run some numbers on this tomorrow, to get a better idea for the initial temperature needed...

2) In a rocket, the chamber will maintain a pretty high pressure, so it will remain mostly full of water until a substantial amount of the propellant has exited the rocket. In order for a rocket nozzle to work, you need a gas (not a liquid) flowing through it, so you'll effectively have to have the nozzle hooked to the top of the tank. If you have the nozzle on the bottom (or side) of the tank, it will act as a glorified water rocket spewing boiling water. It will work, but it will be drastically lower efficiency than if you had gas flowing through the nozzle.

3) Why does your nozzle design have an extremely long throat? You want to keep your nozzle length relatively short, and if you have to extend a section of the chamber, you want to extend the part prior to the nozzle. Basically, the narrow tube you've drawn (the 12 inch long one) needs to be substantially larger than the throat of the nozzle, so the flow through that region is relatively slow. The nozzle should then contract, have a fairly short throat, and then expand out into the divergent section. If you have a long region of minimum area, I suspect you will have subsonic flow in the divergent section, once again wrecking the thrust.

As I said, I can run some calculations if you want - I'm quite familiar with the relevant formulas, so it shouldn't be too hard.

Do you have any details on your current design? Chamber temp, pressure, etc? Rough numbers would be a nice starting point, but if you don't have any, I could always invent some plausible exit values and work from there. I'd also be interested to see the equations you've been over with your profs...

Chris
(Aero engineering graduate student who has taken far too many fluid dynamics courses)

Chris, you are dead-on in everything you've said. A "steam engine" emits gas not water (regardless of temp). Otherwise, it is a bottle rocket (and, not the fireworks kind), i.e., not taking advantage of the con/div nozzle, although the "bottle rocket" does... because it is a rocket. Anything coming out of a rocket engine that is not gas is not a rocket, by definition. Period. Otherwise, the escaping gas won’t be supersonic at the end of a con/div nozzle. Another… period. Pursue it, Chris.

Chris,

1. Yes the possibility is very high in the steam condensing or cooling off before its exits the system. So testing will have to be done to make sure we do get the water hot enough so it keeps above boiling until it exits the nozzle.

2. I don’t understand exactly what you mean by "top of the tank" I’m going to add another picture of our new design. I do understand though that, lets say for example, we don’t heat the water at all we just push it through the system as water. No nozzle is needed all we would need is a hole at the end for it to "squirt" out. Now that its going to be steam were messing with gases which is similar to solid propellant. With steam we can harness the power of it expansion using an actual nozzle.

3. Your right the throat is much to long, new design is attached.

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The new design is a little simpler. We will put the water in the tank before anything, then we will close the valve that’s in front of the nozzle, open the other valve then pressurize it. Once it’s pressurized we will close all valves and heat the tank. Once it is ready we will open the valve in front of the nozzle.

The problem remains on what valve to use that can release it quickly and handle the stresses were putting on it.

Chris, have at it! There are so many falsehoods in Shredders' post...

Hey be nice.....