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Hybrid fuels?

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rocket999

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I just got a micro hybrid motor and it looks really cool. Now, what could I use to increase isp in these small motors? I was thinking something along the lines of wax with 10-15% aluminum powder. Any suggestions on additives and/or different fuels?

Sam

P.S. Does anyone else get the "Sorry, forums are closed" message on the rocketry planet forums?
 

rocket999

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Thank you for the responses. I am a member of the micro hybrid group and I just joined the hybrid forum. I will post the question there too.

I am open to answers here too. :)

Sam
 

troj

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All sorts of fuels have been used in hybrid motors, with plastics being the most common, because they're so easy to work with.

There's a school (I forget which one) which has had tremendous success with wax hybrids. In addition, Alpha Hybrids is a motor company which was working on bringing wax hybrids to market; I'm not sure of the status of their products.

One of the challenges of wax is finding something that won't soften excessively on warmer days. There are ways around this; the hybrid group may have some ideas, otherwise you'll have to experiment.

Yes, I do know one way around it, but it was provided to me by the guy behind Alpha Hybrids, so unless he tells me otherwise, I'll treat it as proprietary information.

-Kevin
 

WiK

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There's a school (I forget which one) which has had tremendous success with wax hybrids.
Was it Stanford? I remember reading a paper on aluminzed (if that;s the word) wax hybrid grains from there, or somewhere similar, a while ago.

I've also read about people putting hot-glue in with their wax to help it hold together a bit more, but not tried it myself.

Phil
 

bobkrech

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Wax is a class of substances with physical properties similar to beeswax, enumerated below:
Waxes may be natural secretions of plants or animals, artificially produced by purification from natural petroleum or completely synthetic. In addition to beeswax, carnauba (a plant epicuticular wax) and paraffin (a petroleum wax) are commonly encountered waxes which occur naturally. Earwax is an oily substance found in the human ear. Some artificial materials such as silicone wax that exhibit similar properties are also described as wax or waxy.

Chemically, a natural biological wax is a type of lipid that may contain a wide variety of long-chain alkanes, esters, polyesters and hydroxy esters of long-chain primary alcohols and fatty acids. They are usually distinguished from fats by the lack of triglyceride esters of glycerin (propan-1,2,3-triol) and three fatty acids. In addition to the esters that contribute to the high melting point and hardness of carnauba wax, the epicuticular waxes of plants are mixtures of substituted long-chain aliphatic hydrocarbons, containing alkanes, fatty acids, primary and secondary alcohols, diols, ketones, aldehydes.[1] Paraffin waxes, refined waxes obtained from crude oils or coals, are hydrocarbons, mixtures of alkanes usually in a homologous series of chain lengths.

Natural waxes do not have as much chemical energy as refined waxes because they are partially oxidized. Dependig on the origin, the energy content is similar to sugars to alcohols. Refined paraffin waxes are simply long chain hydrocarbons so they have the same energy content as kerosene, and make a more efficient hybrid propellant as evidenced by a higher Isp.

Waxes used in hybrid fuel grains should have a relatively high melting point so that the grain shape doesn't change on a hot day, but should be relatively soft, like rubber and not brittle, so that the wax will not crack due to the pyroshock when the motor is ignited.

Reference: First three paragraphs abstracted from http://en.wikipedia.org/wiki/Wax and corrected for technical errors.

Bob
 

AlphaHybrids

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Alpha Hybrids does in fact have a hybrid motor that uses wax as a fuel on the market - check the website at www.alphahybrids.com.

As far as formulas we wrote a short PDF on two of our formulas. The PDF can be found at: http://tinyurl.com/ch6atr

In the size that you are talking about the most I could see gaining is in the tenths of newtons. If you want to experiment more invest in a Skyripper Systems 29mm or 38mm case - you will have a lot more options there.

Legs

Alpha Hybrids Spokesfrog
 

bobkrech

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Alpha Hybrids does in fact have a hybrid motor that uses wax as a fuel on the market - check the website at www.alphahybrids.com.

As far as formulas we wrote a short PDF on two of our formulas. The PDF can be found at: http://tinyurl.com/ch6atr

In the size that you are talking about the most I could see gaining is in the tenths of newtons. If you want to experiment more invest in a Skyripper Systems 29mm or 38mm case - you will have a lot more options there.

Legs

Alpha Hybrids Spokesfrog
Since you published it, I'll add that paraffin wax is simply a (CH2)n refined hydrocarbon wax, hot glue is simply a (C2H4)n polyethylene polymer somewhat similar to a hydrocarbon wax, and carbon black is an opacifier to prevent in-depth radiative heating of the wax.

This combination makes the propellant potentially similar to "solid" kerosene in performance in full scale motors. In hobby rocket size motors, you won't get this level of performance due to less than ideal vaporization rates of wax in a small bore, but it's a good perfromer and certainly relatively simple to make.

Smells great too.

Bob
 

dedleytedley

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I know very little about hybrids but I am interested. Does a wax fuel grain liquify during combustion or does it burn like a plastic, maintaining it's shape and eroding as it burns? Ted
 

MarkII

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An earwax propellant grain - now there's a thought. Do you have any friends who are Ferengi?

I wonder if you could use a hard ski wax; some of them are VERY hard and have relatively high melting points. A fuel grain made from a sub-zero ski wax would probably be obscenely expensive, though.

MarkII
 

AlphaHybrids

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Even plastics liquefy, just at a much slower rate than wax. The geometry will erode, but at an improved rate than other lower regression materials.

Legs
 

dedleytedley

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If I understand correctly the fuel grain is consumed faster than it will substantially melt?
I seem to recall reading about restarting a wax fueled hybrid(spaceship2?). That would suggest that the fuel grain maintains it's shape during combustion.
Ted
 

mhacker

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We made a few tests on Paraffin + Hot melt StickGlue + Graphite Poweder compared with Polyester resin + Polypropylene powder grains on our EX hybrid motor.

Our tests showed us that the increase in performance did not justify the complication in the process of grains elaboration.

This process involves a continuous centrifuge to prevent contraction of the paraffin inside the isolator tube.

Static tests (50% charge of N2O):
[YOUTUBE]h-zKb7JgKC8[/YOUTUBE]
[YOUTUBE]XrGl763qbng[/YOUTUBE]

Centrifuge process:
[YOUTUBE]nBIVSffRFk8[/YOUTUBE]
 

rocket999

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We made a few tests on Paraffin + Hot melt StickGlue + Graphite Poweder compared with Polyester resin + Polypropylene powder grains on our EX hybrid motor.

Our tests showed us that the increase in performance did not justify the complication in the process of grains elaboration.

This process involves a continuous centrifuge to prevent contraction of the paraffin inside the isolator tube.

Static tests (50% charge of N2O):
[YOUTUBE]h-zKb7JgKC8[/YOUTUBE]
[YOUTUBE]XrGl763qbng[/YOUTUBE]

Centrifuge process:
[YOUTUBE]nBIVSffRFk8[/YOUTUBE]
Very cool. Which video is the wax and which is the polyester resin? I couldn't read the description for it (what language?).

How much more thrust was achieved with the wax?

Thank you for testing this.

Sam
 

mhacker

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Very cool. Which video is the wax and which is the polyester resin? I couldn't read the description for it (what language?).

How much more thrust was achieved with the wax?

Thank you for testing this.

Sam
Both videos are with wax. One with half tank and the 2nd with full charge.

The language is spanish (Argentina) :madnote:

Thrust measurements:

1st test: GRAIN N# 4 (polyester resin + polyethylene) - Full tank - combustion chamber broke - Class I560
[youtube]useN8ZULoOs[/youtube]

2nd test: GRAIN N# 1 (paraffin + hot-glue-stick) - Half tank - test ok - Class I520
[youtube]h-zKb7JgKC8[/youtube]

3rd test: GRAIN N# 2 (paraffin + hot-glue-stick) - Half tank - test ok - Class I530
[youtube]XrGl763qbng[/youtube]

4th test: GRAIN N# 3 (polyester resin + polyethylene) - Half tank - test ok - Class I580
(short video - run out of memory)
[youtube]A4s8NzZw-FA[/youtube]

Thrust comparation on 4 tests:
 
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