Aluminum in Hybrid fuel

[lyuv]

I usualy see pure polymers as fuel for hybrids. Woudn't it be a good idea to add some aluminum powder in order to get more heat (hence gas volume)?

 

[bobkrech]

No. Hybrids are more like liquids than solids. It would lower performance.

 

[New Ocean]

How about adding large mesh titanium... ?

 

[cjl]

No. Hybrids are more like liquids than solids. It would lower performance.

Not true. Aluminized fuel performs significantly better than non-aluminized fuel in hybrids, for the same reason that it helps solids. In small (hobby sized) motors, it wouldn't make a huge difference, but in larger motors, it can be a significant benefit.

Aluminum works by significantly increasing the chamber temperature during combustion, and this is just as beneficial for a hybrid as for any other rocket. Too much aluminum would be a problem, since the aluminum also reduced the gas volume generated (aluminum oxide is not a gas in the chamber/exhaust of rocket motors), but for small amounts of aluminum, the increase in combustion temperature causes a greater benefit than the loss of gas products in the exhaust. Aluminized HTPB is one of the best hybrid fuels available at the moment, and is used extensively in large commercial hybrids.

 

[karlbaum]

How about adding large mesh titanium... ?

I believe Contrail uses titanium in their sparky motors

 

[bobkrech]

Not true. Aluminized fuel performs significantly better than non-aluminized fuel in hybrids, for the same reason that it helps solids. In small (hobby sized) motors, it wouldn't make a huge difference, but in larger motors, it can be a significant benefit.

Aluminum works by significantly increasing the chamber temperature during combustion, and this is just as beneficial for a hybrid as for any other rocket. Too much aluminum would be a problem, since the aluminum also reduced the gas volume generated (aluminum oxide is not a gas in the chamber/exhaust of rocket motors), but for small amounts of aluminum, the increase in combustion temperature causes a greater benefit than the loss of gas products in the exhaust. Aluminized HTPB is one of the best hybrid fuels available at the moment, and is used extensively in large commercial hybrids.

It depends on the propellant and the loading.

If you have a poor propellant, that's one with oxygen, nitrogen, chlorine, or other heavy atoms, you may get some improvement by adding aluminum to make the heavy oxides move faster. If you use polyethylene, poly propylene or wax as the fuel which make light molecular weight products and therefore higher Isp, I doubt adding aluminum will significantly improve the Isp as Al2O3 itself does not contribute to the thrust.

I ran propep for 89% polypropylene or wax and 11% nitrous and obtained and Isp of 266 second under standard conditions. Reducing the HC by 1% and adding 1% aluminum increase the Isp by less the 1 second. Making it 2% reduced the Isp versus the baseline.

My conclusion not worth the effort.

Bob