We develop a hybrid rocket engines with mandatory adherence to the following principles:
1. the most simple design.
2. not sensitive to adverse conditions.
3. unlimited time ready to start and start with a single button.
We have developed 4 hybrid engine, three of which are for amateur rocketry.
As an oxidant, we apply N2O. As fuel....
As fuel we used the composition based on paraffin wax. As additives, we used aluminum powder and coal. Unfortunately pure paraffin is not strong, and also has an extremely high regression rate (1,7-2 mm/sec).
To increase the strength of grain, we made an alloy with polyethylene wax in different proportions. We were convinced that it will be difficult to size the wax grain. And we could not get a stable operation of the engine and specific impulse not more than 212 sec.
Interesting results were obtained from experiments with hexamine fuel. The basic method of making fuel grain is compression molding. The raw materials are granulated hexamine, but it is very fragile without plasticizer. Therefore, we used plasticizers, which also helped to reduce the pressing power.
As such binders we were tested epoxy, polyurethane, liquid rubber MPB-1, butadiene rubber, rubber & n-hexane solution, and numerous commercial composition.
During six month we got a good regression rate (up to 1.2 mm / s) and a specific impulse of up to 217 seconds from epoxy resine/hexamine composition. Unfortunately, we could not get grain with sufficient ductility. As a result, the final test of flight engine was faild. As well there was no stable operation of the engine because of burnout layers adding aluminum powder. We conclude that the composition of the epoxy resin gives the best results at the pressure in the combustion chamber not less than 50 bar. Fuel is extremely sensitive to pressure in the chamber and the O/F ratio.
The second binder, which we learned was liquid polyurethane (http://www.penta-junior.ru/pentakast.htm). We introduced up to 20% of binder in powder hexamine with a special mixing plants, similar to a large grinder.
At 12 the percentage of binder, we got a checker with a ductile fracture. Unfortunately, flexibility is still not sufficient. Be able to handle his sword in a lathe and it is well withstand the vibration, but splitting a fall from a height of 500 mm on the table. The specific impulse of 198 seconds. we did not fit. The regression rate - 1-1.2 mm / s.
November 2012 we found a suitable material - butadiene rubber. For mixing rubber with hexamine I had to build a small rolls.
With their help, we do composition with 10% rubber and 90% powder hexamine. Once received flat pieces of fuel, we put them into the extruder and extruded through a die. At the exit of the die, we get a perfectly mixed material in the form of long "spaghetti".
"Spaghetti" we are wound on the rod, and extruding piece.
This technology, we are able to mix the fuel quality and obtain ultra-flexible material. Change the size of the die, we get the spaghetti with a diameter equal to the thickness of the wall grain. This allows the material to shrink less when pressed. Shrinkage will be even less, if the die will have a square cross-section, but we have not reached before. In addition, we tried liquid rubber (HTPB) as binder and got a great flexible fuel. In January 2013 we will be studying the compositions of liquid and solid rubber and make a choice.
As an additive to fuel, we use spherical aluminum powder and ferrocene. We want to get a specific impulse of at least 210 seconds. on rubber/hexamine fuel and then our experiments with a choice of fuel will be complete.