Bob,
There are other amateurs out there but they may not be as recently
active. Ones that come to mind are Paul Breed (Unreasonable Rocket),
Rocket Moonlighting, Graham Sortino, etc. There are others that email
me on occasion but for whatever reason, they decide not to post here.
To get my 100 and 250 lbf regen thermal designs to work using aluminum,
I reduced the mixture ratio down to 1.8 which lowered the chamber
temperature by 1000 degR at the expense of some performance. It wasn't
just that though, it required adjusting the chamber geometry, number of
cooling holes, and spacing to get it to converge. Finally it had to be
producible on my non-CNC shop equipment. I also took credit for some
thermal resistance from carbon layer that kerosene leaves on the chamber
walls. Every time I think of switching to LOX/alcohol to use a less
messy fuel, I remind myself of the benefit of that thermal resistance.
I haven't looked at lowering the temperature further since I have a
design that works good enough for my purposes. Even at a mixture ratio
of 1.8, the chamber temp is still around 5500 degR. However, it's not
just the melting point of the material which is 1100 degF for aluminum.
The max allowable for 6061-T6 in my design on the inside hot wall is 700
degF where it has 10% of its strength left. I'm not well versed in the
high temperature steel alloys but I took a quick peek at MIL-HDBK-5 and
the highest temperature they show in any of the tensile strength tables
is 2000 degF. ProPEP says to get LOX/kerosene to burn under 2000 degF,
it requires a mixture ratio of 0.18 which results in an Isp of 125 s.
The longest I've run my engine is 20-25 sec at a time but that is enough
for the wall temperatures to level off and reach steady state. I'm sure
if I ran it for continuously for several minutes, I would run into other
issues. There are engines out there that have demonstrated longer burn
times so it seems like giving up almost half the Isp would make a hard
problem (vehicle mass fraction) even harder.
-Bob
On 03/13/2018 03:19 AM, Robert Clark wrote:
Thanks for the update. I don’t know of another true amateur effort for a bipropellant liquid-fueled rocket intended for launch. By true amateur I meant not connected to a university which has many more resources, funding, and expert advice available.
Quite impressed you were able to get regenerative cooling to work, which is quite complicated for an amateur experimenter.
BTW, I’m investigating low temperature liquid-fueled rockets engines. Suppose you ran your engine fuel rich so the combustion temperature was lower than the metal’s melting point. How long do you think your engine could run?
Bob Clark
On Monday, March 12, 2018, Robert Watzlavick <rocket@xxxxxxxxxxxxxx <mailto:rocket@xxxxxxxxxxxxxx>> wrote:
I ran a vertical static test of my flight vehicle this weekend
using my 250 lbf LOX/kerosene engine.
Notes: http://www.watzlavick.com/robert/rocket/
<http://www.watzlavick.com/robert/rocket/>
Pictures:
http://www.watzlavick.com/robert/rocket/rocket1/tests/index.html
<http://www.watzlavick.com/robert/rocket/rocket1/tests/index.html>
I'll post videos later but it was a 12 second run. Everything
generally worked but I ran into some annoying test setup issues.
-Bob
