Fuel value

[AdmiralDonSnider]

Following topics about chemical substitutions, especially such of chlorine donors in color or strobe stars, I often read about fuel value and the necessity to account for it. One recent example involved the substitution of HCB with Saran in a blue star which had some stearine as the fuel. The author - Mike Swisher - suggested to cut the stearine to account for the fuel value of Saran (assumably higher than that of HCB in a 1:1 substitution). If the amount is not adjusted based on this thoughts, the color suffers (assumably due to the higher temperature of the burn?).

 

I´m interested in:

- how people know or determine the fuel value of chemicals or chlorine donors

- principles to account for fuel value when substituting chemicals

- detrimental impacts of substitutions, which don´t balance the fuel value - and the reasons of which

 

Thank you!

Edited December 15, 2011 by AdmiralDonSnider

[dan999ification]

i saw a file recently on millitary pyrotechnics that had the oxygen content of most oxidisers i imagine there must be similar data for chlorine content of some chemicals.

as for fuel value is there a standard unit of measure like calorific content im sure ive seen it used for he fuels.

 

dan.

[Potassiumchlorate]

50AE is good at estimating fuel values.

 

It's pretty easy with charcoal, resins and such. It's harder with parlon. In that case the theoretical fuel value doesn't seem to be correct in reality.

[Mumbles]

Dan, you're probably thinking of oxygen balance with regard to the HE's. It's not quite as straight forward as calculating the oxygen content, which is pretty simple. However, there is a formula for it, and it's really not that hard.

 

It seems the standard with regard to pyro is the measure of how much oxygen (in grams) it takes to burn 1g of the material in question. In some cases it can be calculated with stoichiometry. In some other cases it can be measured empirically I believe, or are at least estimated. There are some compounds, like certain resins and organic fuels, which have a theoretical fuel value, but due to incomplete combustion and side reactions (or unknown true composition) a modified fuel value to account for real world conditions exists in some cases.

 

The two simplest cases of not correctly balancing the fuel value is an over abundance of fuel, or an over abundance of oxygen. An extreme over abundance of fuel can introduce a carbon halo or tail to some stars. Don't get me wrong, most stars work best being fuel rich, but you can certainly over do it. An over abundance of oxygen in the flame generally causes color to suffer. When you allow oxygen into the flame, it can produce other color emitters than the desired one. Things like copper, barium, or strontium oxides and hydroxides. These have different emission spectra that people tend to associate with poor colors. The strontium ones are a little on the orange side than red. The barium ones are that lime yellow that occasionally shows up in ghost flames and poor stars.

[Arthur]

And after all the calculations some formula simply don't burn as you expect and some fine tuning is needed.

[AdmiralDonSnider]

Very insightful, Mumbles.

 

So is there something like a fuel value table for common pyro chemicals?

[dan999ification]

i understand [ the concept ] of oxygen balance, what i was trying to say was how is fuel value measured? and offer what i could, by joining in i learn, surely if there was a set number or unit of measure for a fuels value balancing the oxygen or not wouldn't be too hard once you know the oxygen content of the oxidiser [and fuel?] [ i am learning ] ive seen some apparatus that burn material and measure its value/calories it must be by measuring the amount of oxygen in grams required to combust it or measuring the energy released when combusted or both i'll try to find what its called,but im sure the fuel value is returned in calorific content on this device [ maybe not usefull in pyro ] saw a demo of a det with cornflakes as fuel.

is there a table of fuel values?

 

sorry for the bump if i added nothing

 

dan.

[Mumbles]

The device you're thinking of is called a calorimeter, or a bomb calorimeter depending on how it's setup. In these devices, there is a great excess of oxygen present to ensure complete combustion, thus allowing a determination of the energy contained within the sample. Typically there is either a bath of water surrounding the device, or the internal temperature and/or pressure is measured. This is how they obtain calorimetry data. They do not normally measure amount of oxygen consumed, although that would be possible.

 

I thought Chemistry of Pyrotechnics by Conkling had some info on it, but I don't have that book with me. I believe Principles of Pyrotechnics by Shidlovskiiy would also be a good reference. I know the details of fuel values, and probably how they're measured are out there somewhere. 50AE may know.

[dagabu]

http://abundantbrain.com/wp-content/uploads/2010/05/bombcal.jpg

 

-dag

[dan999ification]

your right on the money there, the "calirometer" i saw was a much simpler device than dags pic, clear combustion chamber and was small enough to be able to handle.

 

dan.

[Mumbles]

Oh yeah, they can be extremely simple. It wont work for combustion, but you can do some crude measurements in styrofoam cups. However what Dag posted is what I would consider a standard quality real calorimeter. Anything less will introduce not insignificant error.

 

The easiest way to determine a fuel value empirically is probably to mix whatever fuel you're interested in with potassium chlorate or perchlorate in various proportions until you get a clean burning mix.

[50AE]

Dan,

 

For all fuels it's easy to estimate theoretically how much oxygen would they need. But in practice some do not burn completely (parlon for example).

 

The most simple way is to do stoichiometry. Simple maths.

 

For example, the fuel value of pure carbon

 

C + O2 -> CO2

 

C + O2 -> CO

 

As you see above, you have an option between two products and you have to decide what you want. CO is favorable for fast burning comps without color purity needed (burst charges), whereas CO2 for colored stars. AFAIK, CO affects the color.

 

So

 

2C + O2 -> CO2

 

Check the molar masses of each chemical

mC = 12 g/mol

mO2 = 16*2 g/mol

mCO2 = 12 + 16*2 = 44g/mol

 

Then you know that 32 grams of oxygen are needed to completely burn 12g of carbon, then just simplify this propotion to /grams of fuel per 1 gram oxygen/ (x)

 

12 x

32 1

 

x = 12 / 32*1 =0,375g C per gram oxygen

 

In the case of 2C + O2 -> 2CO

 

24 y

32 1

 

y= 24 / 32*1 = 0,75g C per gram oxygen.

 

 

EXERCISE: Try doing the same for C6H12O6

Edited December 21, 2011 by 50AE

[Mumbles]

I think you have your ratios inversed 50AE. The way you divided you have grams of oxygen per gram of carbon.

[50AE]

You're correct Mumbles, sorry 'bout it. I'm editing my post.

 

Some fuel values I have calculated in the past:

Shellac : 0,43g

Red gum :0,5

Iditol : 0,416

 

I have a big list of stoichiometry of this kind that I did while bored in lectures once. I just have to find the sheet and post all the values here.

I was even going to write a thread on this, but I forgot.. Here is just another example of stoichiometry:

 

2KClO₃ -> 2KCl + 3O₂ Molecular weights are below:

 

2*122,5 -> .... + 3*32

245 -> 96

= 2,552

 

That way you know that 2,552 grams of KClO₃ are needed to produce a gram of oxygen.

 

PVC

 

C₂H₃Cl + 2O₂ -> CO₂ + H₂O + HCl

= 0,78g per gram oxygen

Dextrin

 

C₆H₁₀O₅ + 6O₂ -> 6CO₂ + 5H₂O

= 0,844g per gram oxygen

Edited December 21, 2011 by 50AE