From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: low temp flames?
Date: 14 Jan 1996 05:00:34 GMT

In article <30F99009.4318@cybergate.org>, James Miller
<jim@cybergate.org> says:

>Michael Freiert wrote:
>> 
>> hi ya folks
>> 
>> i know some liquids burn at low temperatures (ie 70-110 F of
>> around 30 C for you metric people) 
>
>I am currious, what is the temperature of the flame... I know it sounds
>stupid, but .. well, I'm currious if it can be used as an ignitor for a
>higher temp. combustable ?

It may depend on what you mean by "flame." There are compounds that
can oxidize spontaneously in air with resultant light emission.
Such a reaction is not necessarily combustion in the normal sense 
where the heat of reaction warms the unreacted material and thereby 
propagates a "flame."

There is extensive literature on "cool flames," but the latter 
rarely arise from burning a liquid in kerosene lamp fashion. If
any of the longer aliphatic hydrocarbons or certain other 
compounds including ethers  are premixed with oxygen in the 
vapor phase, preferrably in non-stoichiometric ratios, careful 
heating to 200-300 degrees can produce a "cool flame."
Such a flame is characterized by intermediate reaction products
which may be capable of supporting a much hotter secondary
flame or explosion.

Usually, a cool flame has a hot ignition source which provides
radicals to keep the low energy reaction going. For instance
one might have a steady state double flame (hot and cool)
going in a gas flowing in a tube of conically varying diameter.
Under extraordinary circumstances it is possible to rig up
a flowing gas self-sustaining cool flame, but it is very
unlikely that one will find a liquid that will furnish anything
but a hot flame under normal conditions.

There are flames, such as those of the lower alcohols which
give the illusion of coolness, but they are merely carbon
free and hot but not very luminous.  The tricks one sees
involving burning hands, etc. rely on thermal insulation
or the cooling effect of low-boiling liquids (evaporative
cooling). Such tricks are very dangerous and best left to
the pros.   

Jerry (Ico)

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: alt.engr.explosives
Subject: Re: petrol bomb instructions
Date: 14 Dec 1996 00:59:00 GMT

In article <01bbe93a$99d26ca0$8ba72499@mage>, "mage"
<mage2@earthlink.net> says:

>if you use rubbing ach... as athe fuel it is safer than gasoline 
>i made a spray bottle into a bug stopper theose flying bugs won't live
>throught the first shot most of the time
> 
>the ach is not as volitale

Bad advice.  Assuming "ach" is cute talk for one of the alcohols, you
should be warned that the flames are a lot hotter than most teenybombers
think. People tend to underestimate the heat of alcohol flames because
they are nearly invisible compared with the sooty flames of hydrocarbons.  
What you see is not always what what you get in energetic chemistry.

Jerry (Ico)

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Alcohol flames, how hot are they?
Date: 10 Mar 1997 20:28:57 GMT

Having noted the most prolific thread these days seems to  
consist of jingoist idiots of various nationalities engaged
in a pointless argument about whose inventors can lick whose
inventors, it appears the assemblage could use a cathartic dose 
of thermochemistry.

Some have suggested that alcohol flames are relatively "cool"
as compared with, say, those of hydrocarbons.  This stubborn
minority has persisted in their beliefs despite numerous you're-
full-of-boloney (bologna) retorts by resident gurus.

The combustion of alcohol in air proceeds via the following
somewhat rounded-off equation (assumes air is 4:1 N2:O2):

2C2H6O + 6O2 + 24N2 -> 4CO2 + 6H2O(g) + 24N2  Delta H = -611 Kcal

and ethane, a second cousin of ethyl alcohol burns like this:

2C2H6  + 7O2 + 28N2 -> 4CO2 + 6H2O(g) + 28N2  Delta H = -683 Kcal

It thus appears that the relative amount of heat produced by 
ethanol as compared to ethane on a molar basis is 611/683, which
amounts to a tad under 90 percent.

If we look a little closer at the two equations we note that there
are 34 moles of reaction products from the alcohol and 38 from
the ethane.  This means that the heat from the alcohol reaction 
per mole of products is 38/34 times as great as that of the ethane
reaction.

Given that the distribution of product species from the two reactions
is quite similar, we can sort of gloss over the modest difference
in the average molar heat capacity of the two product mixes and 
estimate the relative temperature of alcohol and ethane flames as
approximately (611/683)X(38/34) = 1.0. Those last numbers take
into account the lesser heat of reaction of alcohol compensated by
that heat being concentrated in fewer moles of products -- a wash.

The wiggly bottom line appears to be that alcohol can be expected
to burn just about as hot as a typical hydrocarbon in air.

It is, of course, just possible that I cheated in making these 
calculations.  It will make a fine exercise for budding pyrotechnic
chemists to peruse my methods with a critical and suspicious eye.
One might start by noting that the heat capacities of water and
CO2 are higher than that of nitrogen, especially at higher 
temperatures.  This difference will result in a lower estimate of 
the alcohol temperature.  Just how much lower is left as an 
exercise for the patient student or impatient chemist. Hint: Don't
expect to be able to stick your finger in the flame based on the
adjustments for heat capacity.

Jerry (Ico)

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: Carbide
Date: 12 Mar 1997 09:52:17 GMT

In article <332613CE.336EDE04@netcom.com>, Jose <jbatista@netcom.com> says:

>Given what I knew about alcohol before, I believed that it burned at
>least a few dozen degrees cooler than most other liquid fuels.

[Snip]

>At any rate, I was just stating that Gerald's argument was invalid, 
>regardless of whether he's right or wrong about the alcohol.

You are undoubtedly correct in your assertion that I am wrong even if
I am right.  It happens to me all the time as a married man.  I would,
however, appreciate your letting me know the nature of my invalid 
argument. I cannot find a clue in the text of your message.  I need 
to know where I erred so that I can be properly contrite.

BTW,  your previous belief that alcohol might burn "a few dozen degrees
cooler than most other liquid fuels" might well be true depending on
what you mean by "most other."  Given, however, that typical 
hydrocarbon flames reach temperatures of the order of 3300 deg F in
air, I am a bit puzzled at what significance you attach to a
mere hundred degrees or so in the context of your post re the use of 
a "cooler" alcohol fuel for the burning hand trick.  A few dozen
degrees hardly sounds like a margin worth mentioning in the sense
of enabling the burning hand trick.

Lest we forget, here is a snippet from your earlier post regarding
those cooler alcohols:

   >> Yea, right ! and this is from the same guy [referring to Tom
   >> Perigrin] who posted about gargling chemicals and setting his 
   >> alcohol soaked hands on fire for fun.

   >Um, certain alcohols burn at such a low temperature that this is 
   >safe to do under certain conditions. 

There really are phenomena known as "cool flames" in the literature.
Such flames may exist at temperatures as low as a few hundred degrees,
but you're not likely to ever witness these elusive will-o'-the-wisps 
while lighting your hand for a parlor trick.

Jerry (Ico)