Science: Spacecraft: Propulsion
Venturi Rocket Injection   (0)  [vote for, against]
Use venturis to inject air/fuel at low pressure into high pressure combustion chamber

Large liquid fueled rockets use expensive centrifugal pumps to raise fuel and oxidizer pressures up to the point where they can be injected into the rocket motor. The higher the pressure of the pumps the higher the pressures you can run the motor and the more efficient the system is.

The general solution for small rockets is to eliminate the pumps by using pressurized tanks. The down side of this is the weight. The more pressure the tanks can take the more they weigh.

So what if instead of using pumps to force fuel and oxidizer into the chamber, we start with one small high pressure fed rocket which feeds into a fuel and oxidizer cooled venturi which then sucks in the large amounts of fuel and oxidizer into a second combustion chamber where it should combust efficiently because of all the mixing done by the venturi action.

The small rocket will also act as a pilot light for reignition.

-- MisterQED, Sep 15 2009

...idea blew up on the launch pad?
-- phoenix, Sep 15 2009

[+] for the design possibility but "huh?" for "The more pressure...": if you want <x> amount of fuel then you need to pressurize it or build bigger tanks for lower pressure.

it's called an "afterburner".
-- FlyingToaster, Sep 15 2009

OK, let me explain this a little better. Let me start by stating the obvious. Big tanks that take high pressure are heavy and expensive. Small tanks that take high pressure are cheaper and lighter.

So start with a pair of small tanks pressurized with helium to a high pressure. Let's say 2000psi. These two tanks are only large enough to fire a very small rocket for two minutes. The rocket we are firing also is high pressure, let's say 1500psi. This is all normal stuff and "reasonably" easy to do.

Now instead of using this rocket for thrust, we run it's exhaust into a venturi and use the low pressure point in the venturi to inject more fuel/oxidizer from large low pressure tanks. The exhaust from the first rocket will mix and ignite the injected mixture in a second chamber which is pressurized to a high but lower pressure, say 1000 psi before being blown out for thrust.

The questions to be answered is whether the pressure drop from the venturi will be enough to make the exercise worth while considering that the exhaust then has to pass into a second pressurized chamber and/or whether the pressure in the first chamber has to be ridiculously higher than the pressure in the second chamber for the pressure drop to occur.
-- MisterQED, Sep 15 2009

//OK let me explain a little better//...
-- FlyingToaster, Sep 15 2009

//OK let me explain a little better//... So I missed a "this" and a comma. Revision: "OK, let me explain this a little better." Is that better?
-- MisterQED, Sep 15 2009

not yer grammar and I assume you didn't really mean "helium": the idea. I don't get what you're going on about tankwise. If you need 1,000 litres of H2 and 2,000 litres of O2, the most cost-effective way is small, high-pressure tanks AFAIK.

Anyways, it's a venturi afterburner, right ? but for a rocket.
-- FlyingToaster, Sep 15 2009

Yes, I meant helium, it is the preferred gas used to pressurize fuel and oxidizer as it is very light and completely inert and doesn't mix with either fuel or oxidizers. //If you need 1,000 litres of H2 and 2,000 litres of O2, the most cost-effective way is small, high-pressure tanks AFAIK.// Well at those numbers, it would pay to switch to pumps, but I'll follow your lead. If you want to create a 1000psi rocket, you will need to have tanks that will hold the H2 and O2 at ~1500psi. If this idea works I'm wondering if you could maybe use a 500 liter 2000psi H2 tank, a 500 liter 100psi tank, a 1000 liter 2000psi O2 tank and a 1000 liter 100psi tank.
-- MisterQED, Sep 16 2009

random, halfbakery