RoΔdrunner
Member
- Joined
- Apr 3, 2019
- Messages
- 6
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For a background, I've been constructing solid rocket motors for the past year or so. Although success has been marginal, I am reasonably confident that a simple, 50 psi (3.5bar) chamber pressure monoprop engine is within the realm of possibility. I've already crunched the numbers for everything (at 1am), sorted out the materials, Guesstimating a chamber diameter of about 5/8ths an inch (1.5cm), by 3 inches (7.62cm) in length tested the pyro igniter, and should be just about set to test out the fuel mixture.
Now the fuel mixture is the fun part, a reasonably unstable mixture if i'm honest, potassium nitrate dissolved into ethanol (or gasoline if i'm feeling frisky) to create a liquid monopropellant (should be just about as unstable as a solid), abiet being fuel-rich. This will be pressurized with compressed air, saying that its a monopropellant so it shouldn't change the blow-back problems (probably a loop in the propellant line, as the combustion gasses cannot propagate past 90 degrees) . The primary reason for the fuel rich of the mixture is cooling, as I do not have the ability for welding or brazing, its going to be mostly screw-on fittings, o rings, and solder (guessing a flame temp from 3000f-4000f, or 1600c-2200c-ish). I am aware that solder will not withstand the flame temperature, hence threaded fittings. Furthermore, copper will not handle the temperature of construction, so a cooling jacket running water through at a good click (so it doesnt boil) should keep the combustion chamber from melting. The brass injector plate, under thermal loads should have a higher thermal expansion rate than the copper cooling jacket/combustion chamber, so it should create a better seal on the copper. My only problem as of late is securing the bottom of the cooling jacket onto the nozzle exit, the solder (melts at like 300f) wouldn't be able to withstand the temperatures, melting away, and eventually causing a burn-through.
Pictures will be added once I get the opportunity
Now the fuel mixture is the fun part, a reasonably unstable mixture if i'm honest, potassium nitrate dissolved into ethanol (or gasoline if i'm feeling frisky) to create a liquid monopropellant (should be just about as unstable as a solid), abiet being fuel-rich. This will be pressurized with compressed air, saying that its a monopropellant so it shouldn't change the blow-back problems (probably a loop in the propellant line, as the combustion gasses cannot propagate past 90 degrees) . The primary reason for the fuel rich of the mixture is cooling, as I do not have the ability for welding or brazing, its going to be mostly screw-on fittings, o rings, and solder (guessing a flame temp from 3000f-4000f, or 1600c-2200c-ish). I am aware that solder will not withstand the flame temperature, hence threaded fittings. Furthermore, copper will not handle the temperature of construction, so a cooling jacket running water through at a good click (so it doesnt boil) should keep the combustion chamber from melting. The brass injector plate, under thermal loads should have a higher thermal expansion rate than the copper cooling jacket/combustion chamber, so it should create a better seal on the copper. My only problem as of late is securing the bottom of the cooling jacket onto the nozzle exit, the solder (melts at like 300f) wouldn't be able to withstand the temperatures, melting away, and eventually causing a burn-through.
Pictures will be added once I get the opportunity
.
