liquid-fuel engines

[Hcube]

Are amateur or homemade liquid fuel engines even possible ? i guess that you can't do much without some kind of turbopump, unless using hypergolic propellants (wich sounds like a bad idea). How did Goddard do ?

[pincushionman]

You don't need turbopumps, depending on what performance you're aiming for. You need whatever system can get the fuel to the combustion chamber fast enough and with enough pressure. It might be as simple as pressurized gas forcing the reactants out the bottom of the tank as a starting point. Performance would be pretty limited, though.

[SAI Peregrinus]

They're perfectly possible. Not particularly safe, mind, but possible. Gasoline + gaseous oxygen is an "easy" combination. It needs an ignitor, as the fuels aren't hypergolic.

http://majdalani.eng.auburn.edu/courses/09_propulsion_1/ref_roc3_How_To_Design__Build_And_Test_Small_Liquid-Fuel_Rocket_Engines.pdf

That's old, so its safety procedures are OK but out of date. For anything involving high-powered rockets these days I'd set up the launch control remotely using radio control, with a camera to watch the launch. And a mechanical "pull this string and all the fuel/oxidizer cuts off" shutoff.

[shynung]

You don't need turbopumps, depending on what performance you're aiming for. You need whatever system can get the fuel to the combustion chamber fast enough and with enough pressure. It might be as simple as pressurized gas forcing the reactants out the bottom of the tank as a starting point. Performance would be pretty limited, though.

That's what a turbopump is for - boosting pressure without using high-pressure propellant tanks, which gets heavier the higher the expected pressure goes.

BTW, stay away from hypergolics. Those stuff are highly toxic, corrosive, and expensive.

[Hcube]

thanks for the answers !

@pincushionman : well, pressurized tanks are crazy heavy so a turbopump is pretty much essential to do this pressure work...

@SAI Peregrinus : wow gasoline and gaseous oxygen ? the Isp must be terribly low !

@shynung : yeah, hypergolics are toxic, corrosive, expensive...and explosive

[Armchair Rocket Scientist]

thanks for the answers !

@pincushionman : well, pressurized tanks are crazy heavy so a turbopump is pretty much essential to do this pressure work...

Honestly, no. Pressurized tanks aren't actually that heavy compared to the alternative, which is a solid-fuel motor casing designed to withstand chamber pressures of 100 bars or higher with a very high safety margin. Plus, the vehicle will undergo very high accelerations compared to a launch vehicle, and experience very high aerodynamic loading, which means that the structure is heavy anyway. For an amateur-sized vehicle capable of supersonic flight, you'd be very lucky to get 50% of your launch mass as fuel.

@SAI Peregrinus : wow gasoline and gaseous oxygen ? the Isp must be terribly low !

I don't think the isp is that bad, although gasoline contains some compounds that would eventually mess up an engine. The main issue is that tankage for gaseous fuels is very heavy and takes up a lot of space. I doubt a GOX design would ever be used for a flyable vehicle. More likely oxidizers are nitrous oxide, which is relatively easy to work with and is used for most amateur hybrid rockets, or LOX if someone really needs the extra isp. Another potential oxidizer is hydrogen peroxide.

For fuels, I know ethanol and methanol are common. Propane should also be a good fuel; it's commercially available and very easily liquefied at room temperature. However, commercial propane contains additives to give it detectable smell for safety reasons; these could mess up an engine.

[John FX]

So a turbopump I take it is a pump that works like a turbo, meaning that like in my car, it is driven by the exhaust gases and increases the input pressure to the ignition chamber which in turn increases the exhaust gas velocity?

I assume the danger comes from a runaway situation causing an `overpressure event`

With a restriction baffle in the liquid fuel outlet would that not self regulate?

Sounds very simple to make and make safe for a one shot amateur rocket as long as it can be made strong and light enough.

I`ve obviously not thought enough about this.

[magnemoe]

So a turbopump I take it is a pump that works like a turbo, meaning that like in my car, it is driven by the exhaust gases and increases the input pressure to the ignition chamber which in turn increases the exhaust gas velocity?

I assume the danger comes from a runaway situation causing an `overpressure event`

With a restriction baffle in the liquid fuel outlet would that not self regulate?

Sounds very simple to make and make safe for a one shot amateur rocket as long as it can be made strong and light enough.

I`ve obviously not thought enough about this.

Far more complex, the turbo in the car run on the exhaust, however its already burned and not very high pressure. A turbopump is more like an jet engine/ gas turbine.

In an car its simply an bonus as it give more air, only thing you need for control is bypass valves they you run at full throttle so the exhaust over-pressure don't limit performance.

In an rocket you need to regulate the fuel and oxidizer flow, in short you need one fuel and one oxidizer pump on the axis who pump the correct amount and you can not have leaks.

In short you will need to regulate how the pump runs.

[Hcube]

So a turbopump I take it is a pump that works like a turbo, meaning that like in my car, it is driven by the exhaust gases and increases the input pressure to the ignition chamber which in turn increases the exhaust gas velocity?

I assume the danger comes from a runaway situation causing an `overpressure event`

With a restriction baffle in the liquid fuel outlet would that not self regulate?

Sounds very simple to make and make safe for a one shot amateur rocket as long as it can be made strong and light enough.

I`ve obviously not thought enough about this.

no, a turbopump is not really like a car turbo, since it pumps a reactive and not a product, like LOX and not car exhaust (as magnemoe said )

it is a very complicated machinery with many moving parts, and is very often the cause of engine failures... the biggest turbopumps even need a gas generator, a small "rocket engine" to run them ! there are some videos on NASA's YT channel where they test the gas generator that drives the F1 engine's HPOTP (high pressure ox turbopump) and it's a huge flametheower itself !

Probably not very safe to make and use, especially when pumping two fuels that like to spontaneously combust when in contact...

[Windspren]

Simple liquid-fueled rocket: Soda +baking soda/water mixture

Hey, it's a liquid!

[shynung]

Simple liquid-fueled rocket: Soda +baking soda/water mixture

Hey, it's a liquid!

More like a slurry, actually, but this'll probably work. Terrible ISP, sure, but it probably won't kill anyone.

[Hcube]

More like a slurry, actually, but this'll probably work. Terrible ISP, sure, but it probably won't kill anyone.

Unless you really like soda and use your mouth as a nozzle !

[SciMan]

There's also always the good old fashioned hydrogen peroxide steam rocket.

Basic reaction is as follows: High purity Hydrogen peroxide (liquid) =(solid catalyst bed)=> H2O(hot gas) + O2 (hot gas).

Put the reaction products thru a rocket nozzle, and you get thrust.

Might have a hard time getting high purity hydrogen peroxide, the catalyst bed is probably expensive and might need cooling, and the overall performance isn't all that great.

But it's enough to propel a person thru the air to a controlled landing at the Olympic games!

If you want better performance than that, add pretty much any liquid fuel to the exhaust of the catalyst bed.

The added fuel will burn using the excess hot oxygen gas produced by the hydrogen peroxide decomposing, and it might not even need an ignition system because the H20+O2 gas might be hot enough start the fuel burning without any help.

High purity Hydrogen peroxide can be some nasty stuff, as it has a nasty habit of easily giving up it's extra oxygen atom to anything remotely flammable. This includes human flesh, so be really careful if you decide to make a rocket engine using the stuff.