Bert - 16-11-2022 at 08:17
There have been several iterations of small hybrid rocket engines using disposable steel nitrous oxide 8 or 16 gram cartridges:
https://aeroconsystems.com/cart/rockets-motors-supplies/scre...
A manufacturer in China is offering rather LARGER single use cartridges of nitrous oxide than those common 8 or 16 gram steel whipped cream maker
cartridges. In particular, a 640 gram cartridge made of ALUMINUM. With threaded fittings.
Well. If a 16 gram (steel) cartridge gives "E" engine range performance with loaded engine weighing 162 grams before firing, 140 after burnout?
I am interested in determining the approximate fuel grain/ combustion chamber dimensions, estimated all up weight and thrust characteristics possible
for a (possibly K or even L?!) sized reloadable hybrid rocket engine, running off of this (aluminum) 640 g cartridge.
Advantages of such a motor might be that reload "solid fuel grains" are commonly such things as cardboard or common plastic tube, not self oxidizing,
do not require an explosives license to posess or magazine for storage, while the oxidizer/tank is a relatively unregulated consumer commodity.
https://greatwhips.com/products/greatwhip-640g-aluminum-whip...
Disadvantages might be price of that single use gas cartridge, about $50 each in small lots as far as I can determine. What does a single use K motor
cost these days? Or the fuel grains + consumables reload kit for a reuseable K or L motor?
I have not even done "pencil/back of envelope" level development on this, probably need to start with researching specific impulse of the system...
Oh, another potential disadvantage- That little 16 gram cartridge engine is a (only slightly dangerous) toy. One this large might be hella dangerous
if mishandled- See the attached file re: several disasters occurring during handling of bulk nitrous oxide, especially the scaled composites disaster
which killed three engineers and injured several others. Without even igniting the motor, the in rush of nitrous during a cold flow test caused the
explosion, whomever was in charge DID NOT MAKE EVERYONE WATCH FROM THE BUNKER. Because, it's safe if it's not burning?! WRONG.
[Edited on 11-16-2022 by Bert]
Attachment: Nitrous Oxide Handling Explosions-Airgas_Investigation_Report_-_Final_-_2017-02-28.pdf (7.2MB)
This file has been downloaded 284 times
[Edited on 11-16-2022 by Bert]
Bert - 17-11-2022 at 08:36
Very rough estimate, no doubt neglecting many factors, lots of SWAGs.
If ratio of the baby engine was 16g nitrous oxide : 4g hydrocarbon fuel, 640g of nitrous oxide : 240g fuel.
Energy available if calculated for cheap cardboard (paper!) fuel, blithely discounting minor ingredients and considering it to be pure ellulose?
240g cellulose = 1.48 mols.
1 mol cellulose burned in O2 to H2O & CO2 = 2,560 kJ
640g N2O + 240g cellulose = 1,515.72 kJ
Assumption of a fairly crap efficiency at converting this energy to thrust... Let's say 40%?
About 1,500 n.
This is (barely!) in the range of "K" engines.
One (1) K engine reload kit + (1) hazmat shipping fee is around $90.00 US. Just the reload kit fuel grains + delay element, igniter & consumables
is around $40.
Even assuming you drove by Aerotech on the way to a launch & picked it up yourself, cost of a cartridge of nitrous + a slug of cardboard is a
push. Assuming igniters, Pyrodex ignition grain, grease, O rings and possible parts wear & replacements as a push, it ball parks at (not more
expensive).
It's (slightly) cheaper to fly than a single use K engine. The hybrid engine is going to weigh several times more and have about 3X the volume of the
single use, roughly similarly powerful K engine at another SWAG. Your rocket won't be quite so high performance, but frankly, that equates to a better
chance you could track and recover it?
Better fuels such as rubber + Al powder could certainly up performance...
The regulatory and storage benefits stand (Until someone with tech skills at Homeland inSecurity figures out how that engine compares to certain
motors used in ground to air man portable weaponry).
[Edited on 11-18-2022 by Bert]
[Edited on 11-18-2022 by Bert]
Bert - 17-11-2022 at 17:49
To those 10 members downloading the N2O DISASTERS PDF within the first 24 hours?
You are MY PEOPLE.
"It is essential that persons having explosive substances under their charge should
never lose sight of the conviction that, from the facts and general truths which have just
been stated, preventive measures should always be prescribed on the hypothesis of an
explosion."
-Explosives and Their Power. Translated and Condensed from the French of M.
Berthelot, London 1892
Lion850 - 17-11-2022 at 21:14
Thanks for posting the N2O pdf. Interesting read.
MineMan - 17-11-2022 at 22:47
Good thinking Burt! Have you read about the silicone AN, AP, Al motors, look cheap and easy.
For the grain, I would simply 3D print it. I have an extruder. It’s easy to load plastics with 20 percent Al and make filament.
Morgan - 18-11-2022 at 20:58
There is a distant clip of the explosion in this link. I took an interest being in my neck of the woods.
https://www.pnj.com/story/news/2017/04/20/report-poor-safety...
Bert - 19-11-2022 at 13:32
I'm doing a lot of reading on motor designs right now- One striking comment: Catastrophic motor explosions/nitrous tank explosive failures of
experimental motors are usually due to placing the nitrous tank TOO CLOSE TO MOTOR- and that any hiccup in feed pressure or combustion chamber
pressure spikes that allow hot gasses from combustion chamber to flow TOWARDS the tank is a very bad thing...
So backflow preventers + flash arresters on feed line are in order.
[Edited on 11-19-2022 by Bert]