Hello! My name is Luka Peradze and i am a rocketry enthusiast. I have some experience in creating rockets in that i have created 4 solid fueled rockets. I am attempting to make a liquid fueled sounding rocket, which will be pressure fed. I have thought of using Kerosene and the fuel, and liquid oxygen as the oxidizer, however i can change these. I have run into some trouble while designing the Rocket. I will have two tanks inside the rocket one for the fuel and the other of oxidizer. In order to force these into the combustion chamber i was thinking of using compressed gas to force them into the combustion chamber. My issue is that i don't know how exactly to do this. I would greatly appreciate if you could help me.
Sincerely,
Luka Peradze
Well I am currently working with pressure fed liquids at the moment, I'll give you a bit of insight into what you are getting yourself into.
First I'll give you an idea of what this system will cost. I wouldn't expect much less than ~$50,000 in cash or materials to get to at least performing static firings.
First off you have your cryogenic service equipment, hoses are $100 a foot, throttle valves are $2000 each, prevalves are $1000. Everything must be absolutely clean. Your tanks are a very considerable investment. No one really makes tanks that are really suitable for pressure fed rockets. DOT tanks have far too large of safety factors, and most are too small. So generally you have to custom make your tanks. You also need to make more than 2, around 6 at least would be reasonable, since you have to do failure testing on them since your safety factors are much smaller than normal pressure vessels. Pressure transducers run about $200+, you need at least 3, I suppose you could get away with 1 but you will regret not having the additional information on the feed side. You will also break transducers on your chamber, everyone does. So expect to have to buy several of them during your testing. Now you get to your high pressure system, seamless tubing is pretty cheap overall, fittings aren't all that expensive either. High pressure regulators are pretty dear in cost, $700+ for large ones, $300+ for small ones.
Unless you have a CNC machine in your home, chambers will cost several thousands each to get machined. You will also be making many of them. Destroying 20-30 chambers in a development effort isn't all that unreasonable. Most places who make liquids tends to have cabinets of broken hardware.
You pretty much have to use helium as a pressurant, nitrogen wont work because it is soluble in liquid oxygen. Having nitrogen present with oxygen in a high temperature environment (the combustion chamber) will make unhappy compounds that can damage your engine among other things. Helium currently is about $1000 for a T bottle, you will probably need 1 or 2 for each test at least, and I'd recommend some sort of high pressure scavenging system so you can consolidate the half filled bottles you would make.
Liquid oxygen isn't a joke to handle. Once you have your workflow in place it isn't too bad since you have everything ready, but before then you have to take a great care in what you do. For one you cant do any sort of transfer operations around any kind of petroleum product. Including asphalt, it forms a shock sensitive explosive with asphalt, and most other petroleum products. It is entirely possible to handle safely, but you just need to know the bad things it will do, and what situations to avoid.
Switching to other oxidizers wont really do all that much to reduce the cost of components in the long run. Every oxidizer has it's gotchas. After all you want them to support very vigorous combustion in your rocket, so it makes sense that they tend to support vigorous combustion outside your rocket as well.
So if you have $50-100,000 sitting in your bank waiting to get spent on something, and are willing to slow down a bit, and get your base research done it could be reasonable to start the development effort.
After all its not the things that you know in this business that is important. It is have some idea of what you do not know that tends to be the most useful. Knowing how to pressurize the tanks is a fairly basic element, and on a difficulty scale for this endeavor would rate a 1 or a 2 out of 10 (10 being the most difficult step). I'd really recommend taking a step or two back, and gain some more experience with rockets. Start making fairly detailed checklists for your normal rocket launches, get much more detail oriented in your operations. That will start to set the groundwork for what you want to do. Going to school for propulsion would really help as well, as being able to make informed design decisions with calculations backing it will save you a lot of money and possibly even more than that.
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