I was just looking at a small but impressive compressed air/water rocket that launches off of a metal rod that runs through the nozzle and spans 3/4 of the length of the rocket. As the team increased pressure for subsequent launches, I wondered about a great or terrible idea to really make something like it move.
Suppose the rod was an anode, and the water tank was a cathode. Could an extremely high voltage be discharged through the water to quickly split it into hydrogen and oxygen, which would then ignite from compressive heating?
I would image that the simplest design, a full tank of water with a large durable anode rod would simply explode, but there are some things we could do to increase the odds of survival for the rocket:
- Use a long, narrow body so that there is lots of surface area on the electrodes, compared to the volume of water
- Ensure that the anode immediately flashes to a plasma, so that it does not obstruct the escaping fuel. For a very short time period, that column of plasma might still function as a conductive anode as the last of the water splits
- Wrap the tank in the highest ultimate tensile strength material known to Wikipedia, monolayer graphene (130 GPa!), and expect it to deform during launch
- Don't fill the tank completely full of water, include a compressible gas like helium to dampen the forces from explosion to a sort-of controlled burn
- Try to prevent the oxygen and hydrogen from mixing too quickly, so that it burns instead of detonating
This all hinges on the ability to electrolyse many litres of water in milliseconds. Has this been investigated? Is there any fundamental reason why it couldn't work?