How do hydrogen peroxide rockets work?


Monopropellant rockets

Monopropellant rocket

The simplest rocket is the monopropellant rocket. It works in the following way:

* The liquid hydrogen peroxide is fed with high pressure from a tank to a chamber filled with a decomposition catalyst.
* The decomposition catalyst causes the hydrogen peroxide to decompose into water steam and oxygen. Heat is released by the reaction. The temperature of the formed gas mixture is about 650 oC.
* After passing through the catalyst chamber the hot, high pressure gas mixture is released through a rocket nozzle.
* The velocity of the gas flow after the nozzle becomes well over 1000 m/s and gives the rocket a considerable reaction force thrust.

Bipropellant rocket
The gas mixture after the decomposition of the hydrogen peroxide contains oxygen. The thrust force is increased if this oxygen is used to burn an organic fuel, before it is released through the nozzle.

The fuel can be in liquid form - e.g. ethanol that is sprayed in after the catalyst chamber. Such a rocket is called a bipropellant liquid fuel rocket.

The fuel can also be solid - e.g. a rod of polyethylene placed after the catalyst chamber. Such a rocket is called a hybrid rocket.

Calculations
If you click here you will be able to make calculations for monopropellant hydrogen peroxide rockets in an excel program. (Updated in March 05)

Input figures (red colour):

H2O2 %: The standard qualities that we produce are 80, 85 and 90% conc. If you put in a conc. lower than about 75%, the calculation results will be unreliable because there may be a cold and wet gas flow out from the rocket and the decomposition reaction may be incomplete.
Run time: Put in how long time you want the tank to last before it is emptied (at fully opened throttle valve). NB:In the rotor tip rocket case, two rockets are connected to the same tank so the run time for a certain tank volume will only be half.
Pressure drop over the distribution tray: The distribution tray needs to work as a shower head with a good flow in each hole. In order to get such an even distribution there need to be a pressure drop of 0.1 to 0.3 bar over the distribution tray. .
Hole Diameter: The holes on the distribution tray needs to be as small as you can drill them, so there will be as many holes as possible and a good distribution. 2 to 3 mm is a typical hole diameter.
Catalyst activity:
My pre-activated pure silver screens can decompose up to around 100 kg H2O2/liter catalyst package and minute, when the screens are new and stacked in a pile of circles or rolled to a cylinder (1 liter is 1 dm3).
If you put in a higher number than 100, you are running a risk of getting a so called wet start with cold and wet gas and incomplete decomposition. When the screens have matured, after a minute of operation or so, they can decompose over 200 kg/minute and liter of catalyst. You can put in a number lower than 200 and you will than have more silver screens than needed and a bigger margin before having any problems with wet starts.
Liquid feed load: If you put in a low feed load, the catalyst package will be short with a big diameter. This will give you a low resistance and a low pressure drop. A typical load is 0,010 kg/mm2,minute
Pressure, inlet: This is the pressure before the nozzle but after the catalyst package. The pressure after the pump - or in the tank, if you have a pressurized tank - is calculated by the program. (The rotor is working as a pump in the case of rotor tip rockets, so pressure calculations becomes a little more complicated)
The pressure drop over the flow control valve and in the feed lines has not been taken into account in this calculation.
Pressure,exit:If you put in the atmospheric pressure, 1 bar (absolute), the program calculate the nozzle exit diameter so the gas will expand to the ambient atmospheric pressure. If you put in a higher pressure, the gas will be "under expanded" at the exit and will continue to expand after the nozzle. If you put in a lower pressure than ambient, the gas flow will leave the walls of the nozzle, before comming to the exit or there will be a slight under pressure at the exit. I recommend putting in the ambient pressure, 1 bar.
Thrust Put in the thrust that you want your rocket to have. For a rotor tip rocket on a small helicopter you need about 7 kgf. per rocket. For a personal rocket belt you need the thrust to be big enough to lift your own weight plus the weight of the rocket system, including the fuel.
The rocket thrust needed for racing vehicles, like drag racing, can be estimated using this program. Please note there are 2 pages in the xls file! Page 1: Calc. of acceleration, speed and travelled distance. Page 2: Calc. of aerodynamic drag.

This article was updated on September 27th, 2009