Erythritol? Better than sorbitol?

[JMan]

Hi, its been a long break for me but you guys seems to know whats good with rockets. So, if you dont know, Ive been intrested with the easiest sugar rocket fuel to say the least. Sucrose was both too brittle and soo quick to harden. Sorbitol never really hardened and when it cooled it stuck to many of my mandrels to the point I have twisted steel into two pieces removing it from a grain (Not kidding I wasnt happy when I realized I didnt pull my tool out, I only pulled half of it out).

 

My next quest? Erythritol! Now that sugar alcohols are CHEEP compared to 5 years ago (thanks amazon) we all have many more fuel options in the sugar rocket world. So has anyone tried useing erythritol?

 

Its non hygroscopic!!!!!

Its got a low melting point!!!!

Its got a low viscousity!!!

Its not sticky!!

It does not decompose at high temps!

 

These are not my personal findings, this is from my research. So has anyone used it and is it the fuel of the future I think it is?

[stix]

From my notes regarding Erythritol around 5yrs ago:

 

Very crumbly - dreadful fuel - don't bother again.

 

I think I had similar results using Xylitol as well.

 

BUT, and this is very very crucial, I was using finely milled KNO3 (think flour).

 

My standard as supplied KNO3 is something like very fine table sugar. When it's used like that, then it will flow (be pourable) but doesn't burn very well. My usual test motors are 3/4" diameter. It may well perform better in a large motor, but I never tested it that way.

 

My most recent fuel is KNSU/SB. Which ends up being a nice soft pliable putty that sets up over time. The sugar is fine confectioners which isn't melted, it is suspended in the melted Sorbitol. The problem with melted sugar fuel is that it's not easy to pour unless you have a large amount, and the KNO3 is not too fine. That's why I ended up using the "putty" method.

 

In any case, we all have our methods. So by all means go for testing with Erythritol. You may well come up with a good method, and we'll all learn something.

 

Cheers.

 

[EDIT]

The cost of Erythritol and Xylitol was also an issue, but maybe not so anymore.

Edited December 20, 2018 by stix

[davidh]

It's not that expensive.

https://www.amazon.com/Erythritol-Granules-Anthonys-Non-GMO-Sweetener/dp/B00OQX5V2Y/ref=sr_1_6_a_it?ie=UTF8&qid=1545315620&sr=8-6&keywords=Erythritol

https://www.amazon.com/NOW-Foods-6986-Xylitol-2-5-Pound/dp/B0013P3KC6/ref=sr_1_3_a_it?ie=UTF8&qid=1545315802&sr=8-3&keywords=Xylitol&th=1

Edited December 20, 2018 by davidh

[stix]

David, you missed the point.

 

Regardless of the expense, there are issues.

 

Consider melted sugar/erythritol/sorbitol etc. Once melted then throw in a few ball bearing sized pieces of KNO3. Hardly any difference would be noted in the viscosity. Do the same test/s and keep reducing the size of the KNO3 particles. The smaller you go in the fine-ness of KNO3, the thicker the slurry becomes to the point it will not flow easily.

 

That, my friend, is a FACT.

[JMan]

I know you say its dry and crumbly, but sucrose can get that way too. Regardless, I think Ill try it out here soon but how do you get your sorbitol not to adhere to everything stix? Ive tried wax, silicon, wd-40 I just cant make a motor without turning it inside out while making the core. Im hoping erythritol just cracks loose kind of like sucrose does when its just been cooled and not left out. Plus non hygroscopic seems really appealing. Edited December 20, 2018 by JMan

[NeighborJ]

Coating spindles with teflon tape has recently been a large topic on other forums. It sounds like a perfect solution to your problem.

[Mumbles]

Do you load your motors hot or with cooked mix?

[JMan]

Hot, and I didnt know they made a tape, Ill look it up thanks for the suggestion. Edited December 21, 2018 by JMan

[stix]

. . . how do you get your sorbitol not to adhere to everything stix? . . .

 

Before casting, I make sure to lightly clean the mandrel with warm water, soap and super fine steel wool, then spray with silicon and wipe it off.

 

Once cast, I put into a ziplock bag and evacuate all the air then put it in the fridge for about an hour. Theoretically, when the steel mandrel is cold it shrinks slightly. The mandrel is also very slightly tapered and has squared off corners at the ends. I put it in a vise, grab the motor body and snap twist & pull. It comes off easily.

 

I also use carbon black in the mix, so maybe that helps as well.

[JMan]

Scott Fintel

 

Thefintels.com

 

Sadly this guys website isnt up anymore but the way back machine can bring it back to life. His main propellant was KNER (which I like the abbreviation of) and he has quite the resources on it. He confirms its hard, almost brittle, like sucrose (although its not because its glass transformation begins at -42 C where su is like 50 C). Hes got tons of links and videos of the propellant in use and the only downside is it does not burn very well when not under pressure. It needs a good pyrogen to get the pressure up and it preforms quite like su would.

 

All my research is confirmed with this but I am a little afraid because so few people use it. On the other hand the people who do are very professional launching massive motors. Im excited to see what my tests will yield. It arrives soon and I plan on using burst disks to get the pressure spike. Sadly I dont have a true test stand (although expecting one for Christmas maybe) but if this truly is as good as it seems Ill let you all know.

[stix]

Don't be afraid. Just be careful and do things in a methodical manner and take notes (for all of us).

 

Who cares what anyone says? Research is so much fun

[WSM]

Has anyone tried potassium nitrate, erythritol and added Iron oxide as a catalyst? I'm curious as to whether it's a viable propellant.

 

Adding carbon black would help in two ways, perhaps add to the spindle release (or maybe we could consider a small bit of graphite, though that might interfere with the burn even further?), and also help prevent radiant energy transfer through the white fuel grain (which could lead to a CATO?).

 

I have sorbitol, xylitol and erythritol, but haven't made any propellants using them,...yet.

 

WSM

[JMan]

@WSN, black carbon is not needed to release the coreing rod, it releases like a hot knife through butter (look at pic) and I dont know how the radiation works too well but Id say it wouldnt help cus this stuff burns slow (wont even sustain with open air tests but works fine under pressure) but Id imagine the grain works better when pre heated before the flame reaches is. Again I dont know too well how radiation works educate me please.

 

Ok my response to the fuel now.

 

It is great. Chronologaccly what I figured out:

Is endothermic so it takes a while to liquify and a long time to solidify.

Crystalises even with KNO3 in it which is great for strength.

Is slightly brittle but no where near su but more than sb.

Sticks to absolutely nothing (no special coreing tools needed halajaula)

Does not burn in open air.

Burns very well under even slight pressure (I made a small nozzless but forgot to record)

Is not hygroscopic (second halajula)

 

So here are my pictures, I havnt made a real motor with this yet, seeing if i get a test stand for Christmas hopefully.

 

You can see where it starts to crystallize, its fun to watch cool.

 

Pulled it out before the center solidified.

 

Open air burn test, didnt do well but I forgot to record the nozzless test it worked very nice.

 

Ahh yes look how nice the tool removed.

[dagabu]

GAHHHH! PVC!!!

 

Sorry, visions of shrapnel dance in my head! Taking out a 2" sliver of the stuff out of my left arm a couple decades ago, taught me to use paper.

 

Question: Since this is natively crumbly, how does this press onto tooling? Nothing like that huge white plume for a day launch!

[JMan]

Sorry dagabu, I never saw that post but by press onto tooling Im assuming you mean how it sticks to it? (Im probably wrong). I wont answer your question till Im sure I know what it means but I will say this. ER is not crumbly. Where SU would normally crack or fracture, a small chunck will fall off of ER. So you can handle it very roughly and it will not deform or fracture, just chip very minorly.

 

But onto why I brought this thread back up, Im back from university for summer and its time to make rockets, less than 2 days into summer break and I couldnt help but making one. Ive done tons of research on ER and designed a proper rocket for it. Starting with a KN of about 390 and increasing to around a max of 450 this stuff burns very well (you can see in the video, a kn of less than 400 is not very nice as it starts out) this stuff will bond to aluminum (unlike SU) and just works like Id image any rocket fuel to work (other than not burning at atmospheric pressure).

 

I dont have a thrust stand but the fact that the nozzle is bent out makes me think this thing defiantly would have taken off.

 

Also for anyone who thinks they need real tooling, this is my set up, made with a drill and an angle grinder to cut off the metal coreing tools. Its not perfect and real tooling helps but you can get f and g rated motors with this type of stuff.

 

Ps this is a face down burn test, and surrounded by bricks for blast protection. However, my case is made of aluminum. Is this ok or would you all still roccemmend paper because I know for nozzled rockets I will never use pvc, and for high pressure things like ER I just dont think paper would hold near the end. Is aluminum case ok or should I do paper? How does one put a nozzle on paper cases?

Edited May 4, 2019 by JMan

[Arthur]

Watching youtube vids about NASA shuttle booster rocket motors, the granule size mix of the oxidiser is critical (and they don't give the details). Maybe their mix ratio of mesh sizes is important for pourability as well as burn rate. It's very common that particle mesh size is not quoted in formulae but very important to products (we all know the mix ratio for BP but it says nothing about the mesh cut or method).

 

A motor grain is usually cast/poured into paper tube so that the structural case is insulated from the heat of the burn. The paper tube has to be chosen carefully to fit the metal motor body perfectly. Hot or big motors may have layers of card and nomex paper in the paper tube for insulation over time.

[Redrocketman]

Nakka Rocketry website. Richard is the guru of all things related to amateur rocketry, one of the most accomplished worldwide. Hes put together what I believe to be the most comprehensive site available, covering every aspect of amateur rocketry, most importantly all safety measures must be absolutely and strictly no 1 priority, tho that should go without saying!!!!

Whats this "AHHHHHHH" about PVC cased motors????!!!! Meticulous grain casting, using a quality simulator ( I use Burnsim ) have a secure test cage - no problem at all and I cant understand the concern, unless the person building the motor is incompetent of taking on that paticular design????? U must use a burn simulator without question as they do have a smaller margin for over pressure, or worse a too long a burn time. But I assure you PVC cased motors, when built to spec and after thorough testing are safe and attain spectacular results. I run my KNDX J800 pvc motor at over 900psi MEOP for 1.3 seconds and out of 7 not one has CATOed. Have completed all designs, casting moulds and simulations for the next, an M3000 using yes - PVC case!!!! Good luck and be safe to all, and dont be scared to have a crack!!!!!!!

[JMan]

I gotta agree with you red rocket man. Ive never seen the problem AS LONG as you know the dangers and prepare. A proper barrier or distance away from the motor being tested is all you need (of course being tested face down and preferably burried in sand).

[Arthur]

The trouble is that some people do not prepare for a risky project and try to invent something new at close range, then someone has to pick up six figure medical costs -or funeral costs. When NASA do a ground test they use half a county as safety zone, with instruments providing remote data, just to further reduce a set of risks and hazards

[91Wreck]

What is the best temp to cook the erythritol/KNO3 mixture? I made a crumbly mess that wouldn't burn at all.

[stix]

What is the best temp to cook the erythritol/KNO3 mixture? I made a crumbly mess that wouldn't burn at all.

 

According to wiki the melting point of Erythritol is around 121°C (250 °F). Which from memory, is pretty much correct. You can go higher without the risk of caramelisation.

 

btw. I assume you are using the "melted" method? If you are using the dissolved/re-crystallized it behaves very differently.

 

Like I pointed out above, the finer the KNO3, the thicker the mixture becomes. From my experience it was very hard to light. Nevertheless, in a larger motor, under more pressure, with a prime, I'm reckon it would work well.

 

Cheers.

[dagabu]

Meh...

 

 

...Whats this "AHHHHHHH" about PVC cased motors????!!!! Meticulous grain casting, using a quality simulator ( I use Burnsim ) have a secure test cage - no problem at all and I cant understand the concern, unless the person building the motor is incompetent of taking on that paticular design????? ...

Edited October 30, 2019 by dagabu

[FlipperFuego]

Interesting question, thanks for posting http://freeimagehost.info/i/me65gg8kLU.png