Hybrid Rocket Engine

Hybrid rocket engine first testings

Fuel: paraffin (sometimes charcoal)

Oxidizer: gaseous oxygen @ 100psi

Injector: 1/2" hole (flow is limited to what can travel through the 1/4" fittings)

Nozzle: 1/8" mild steel, concrete with mild steel insert

Chamber: approx 3.5" diameter

Thrust: not much

The first nozzle was made with six flat pieces of 1/8" mild steel for the convergent - divergent sections of the nozzle, and with a 1" inside diameter ring for the throat. To seal the nozzle to the chamber, a metal ring that fit the inside of the chamber was used.

This is a side view of the nozzle. The piece that holds the nozzle into place is shown above the nozzle.

This is a back view of the nozzle and chamber. The white stuff on the right is the paraffin. In later tests, I reduced the size of the hole, but this did not seem to have much of an effect on the performance.

This is the nozzle after the firing. the hole is about 1" across, and 1/2" high. The hole was on the convergent section of the nozzle. It may have melted down here because of a small hole where a weld ended. The next nozzle is made of concrete, with a steel insert.

Due to inconsistent ignition, a chunk of the convergent section of the nozzle blew out. The high pressure and fast exhaust velocities took out a large amount of concrete from the divergent sections. The nozzle was fitted into the chamber by pressure, but gases still escaped. The metal insert did not show any signs of wear afterwards.

This is the new nozzle setup. It is the salvaged metal nozzle with concrete poured around it. The idea behind this is that the concrete may sync some of the heat from the nozzle, and prevent gas leaks from quickly burning large holes. To seal the nozzle to the chamber, high temperature gasket material was used. This time, the oxygen will be injected by four 1/16" divergent injectors at the oxygen bottle pressure (2000 psi).

To inject the oxygen at these pressures, high pressure fittings are used. The valve is good to 7,250 psi, and cost $27, and the hose is good to 5,000 psi, and cost around $15. The valve has been spring loaded shut, and a rope is pulled to open it. Because of how loud the 100psi tests were, and the 6 foot flame that they shot out, this will be tested in the desert, rather than my backyard. They have not yet been tested.