What Makes HHO Torches Different From HHO Rocket Nozzles?

Force is mass times acceleration or mass times the rate of change of velocity. A rocket engine is designed to increase the velocity of the propellant to as high as velocity as possible. The fuel is burned in the combustion chamber and the nozzle is specially shaped to convert the combustion chamber pressure into propellant exhaust velocity.

Rocket thrust is caused by pressures acting in the combustion chamber and nozzle. From Newton's third law, equal and opposite pressures act on the exhaust, and this accelerates it to high speeds.

The four expansion regimes of a de Laval nozzle:
• underexpanded
• perfectly expanded
• overexpanded
• grossly overexpanded

https://en.wikipedia.org/wiki/Rocket_engine

A torch is designed to burn the propellant at ambient pressure and to utilize the heat produced.

"On this slide, we show a schematic of a rocket engine. In a rocket engine, stored fuel and stored oxidizer are ignited in a combustion chamber. The combustion produces great amounts of exhaust gas at high temperature and pressure. The hot exhaust is passed through a nozzle which accelerates the flow. Thrust is produced according to Newton's third law of motion.

The amount of thrust produced by the rocket depends on the mass flow rate through the engine, the exit velocity of the exhaust, and the pressure at the nozzle exit. All of these variables depend on the design of the nozzle. The smallest cross-sectional area of the nozzle is called the throat of the nozzle. The hot exhaust flow is choked at the throat, which means that the Mach number is equal to 1.0 in the throat and the mass flow rate m dot is determined by the throat area. The area ratio from the throat to the exit Ae sets the exit velocity Ve and the exit pressure pe. You can explore the design and operation of a rocket nozzle with our interactive thrust simulator program which runs on your browser.

The exit pressure is only equal to free stream pressure at some design condition. We must, therefore, use the longer version of the generalized thrust equation to describe the thrust of the system. If the free stream pressure is given by p0, the thrust F equation becomes:

F = m dot * Ve + (pe - p0) * Ae

https://www.grc.nasa.gov/www/k-12/airplane/rockth.html

HHO, as an energy source that produces more energy in it's combustion than it does to separate back into H₂ and O₂, is a scam/hoax.

Better to say "stoichiometric mixture of hydrogen and oxygen that, when burned, produces water (H₂O).

In a torch, you are not containing/enclosing the reaction. In a rocket nozzle, you are allowing the combustion to take place in a chamber and restricting its pressure through a nozzle.

Thanks for the replay

But what I am looking for is for gasses which travel at a speed less that 0.3 Mach . In that case the above said equations won't work

My question is what makes a torch different from , let's say for example a converging nozzle (not convergent divergent nozzle which is used in Space rocket ) when operated with the same HHO generator ?

I suspect that this is a homework question. You may be in over your head, but:

Introduction to Compressible Flow - Mechanical Engineering ...

fluid mechanics - Why is Mach 0.3 the threshold separating ...

The rest is up to you.

The torch does generate thrust, it's just very small in comparison to the mass of the torch and hoses. The mass flow rate out of a torch nozzle is very low. Imagine turning an air hose nozzle down to 10 psi compared to normal pressure of about 125 psi. The thrust goes down accordingly. Also the torch flame velocity is down in the 3 meters per second range so that the flame propagates back to the torch orifice. More than bout 3 meters per second and the torch will blow itself out unless a flame holder is built into the torch. Realize that the torch flame is external to the torch orifice while a rocket motor or jet engine are built with a contained combustion chamber or a flame holder baffle to keep the flame lit. Flame velocity in the combustion chamber or behind the flame holder baffle is less than 3 meters per second, but increase dramatically when directed through the nozzle on a rocket or mix it with air around the edges of the flame holder baffle in a jet engine.

Controlled throttling of the combustion results, ie: the 'control' difference between combustion and explosion.

Kinda like the difference between this:

And this:

Different size.
Different geometry.
Different fuel/air flow.
Way different ΔP.

Thanks for the reply

To make things more clear , what should I do to convert an HHO torch to a HHO rocket nozzle ? or in other words what should I do to increase the thrust of my torch ?

Increase the mass flow rate, specifically a bigger torch with higher fuel flow rates and increase the velocity, specifically turn up the pressure on the system and add a flame holder arrangement to the combustion area.

Basically this means start from scratch and build a rocket engine geometry.