Uncle Al
Jun3-06, 04:00 AM
foulbr3@yahoo.com wrote:
[snip analysis]
> My questions are:
> 1. How can I find the ideal mixture ratio of oxygen to aluminum? Why
> don't LH2-LOX rockets just have twice as much H_2 as O_2??? Why 4 times
> the O_2 as H_2 instead? It seems to me this reduces the combustion
> temperature, thus increasing the mass ratio at the expense of the
> exaust velocity (specific impulse). Will an molten Aluminum-fueled
> rocket need excess LOX too?? How can I find the ideal ratio? I want to
> compute the volume of tanks but to do this I need to know the
> Oxygen-Aluminum ratio.
[snip]
LH2-LOX engine feeds have lots of excess LH2 to reduce exhaust average
molecular weight and thereby improve Isp. You desperately want to
cool the exhaust bell inner surface, too, and have it in a reducing
environment.
A molten aluminum feed tank around 700 C minimum snugged next to the
LOX tank is crazy even for NASA. Trimethylaluminum is a volatile
liquid produced in tank car amounts for industry. It burns so hot on
contact with air that concrete melts and bystanders get UV burns.
There's your liquid fuel. However, you will suffer a much larger
exhaust average MW with Al2O3 exiting compared to H2O + H2.
AlMe3
MW = 72.086
d = 0.725 g/cm^3
mp = 15 C
bp = 127 C
/_\H(vap) = 580.43 J/g
/_\H(combust) = 9800 cal/g
http://www.albemarle.com/acrofiles/sc2012f_TMA_datasheet.pdf
Aluminum as fuel has four downsides. First, it won't be gaseous
exahust - Al2O3 has a 3000 C boiling point. Second, Al2O3 melts at
2015 C. It will coat the engine. Third, with an 8.8 Mohs hardness,
Al2O3 particulates will erode away the engine. Fourth, fuel spills
will be the stuff of legend.
Liquid fluorine as oxidant isn't clever.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf
[snip analysis]
> My questions are:
> 1. How can I find the ideal mixture ratio of oxygen to aluminum? Why
> don't LH2-LOX rockets just have twice as much H_2 as O_2??? Why 4 times
> the O_2 as H_2 instead? It seems to me this reduces the combustion
> temperature, thus increasing the mass ratio at the expense of the
> exaust velocity (specific impulse). Will an molten Aluminum-fueled
> rocket need excess LOX too?? How can I find the ideal ratio? I want to
> compute the volume of tanks but to do this I need to know the
> Oxygen-Aluminum ratio.
[snip]
LH2-LOX engine feeds have lots of excess LH2 to reduce exhaust average
molecular weight and thereby improve Isp. You desperately want to
cool the exhaust bell inner surface, too, and have it in a reducing
environment.
A molten aluminum feed tank around 700 C minimum snugged next to the
LOX tank is crazy even for NASA. Trimethylaluminum is a volatile
liquid produced in tank car amounts for industry. It burns so hot on
contact with air that concrete melts and bystanders get UV burns.
There's your liquid fuel. However, you will suffer a much larger
exhaust average MW with Al2O3 exiting compared to H2O + H2.
AlMe3
MW = 72.086
d = 0.725 g/cm^3
mp = 15 C
bp = 127 C
/_\H(vap) = 580.43 J/g
/_\H(combust) = 9800 cal/g
http://www.albemarle.com/acrofiles/sc2012f_TMA_datasheet.pdf
Aluminum as fuel has four downsides. First, it won't be gaseous
exahust - Al2O3 has a 3000 C boiling point. Second, Al2O3 melts at
2015 C. It will coat the engine. Third, with an 8.8 Mohs hardness,
Al2O3 particulates will erode away the engine. Fourth, fuel spills
will be the stuff of legend.
Liquid fluorine as oxidant isn't clever.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf