Discussion:
Simple gas combustion
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Phil
2004-12-09 04:47:55 UTC
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Hi!
This is my first time posting here (5 newsgroups).
I sure would appreciate some advice on a couple of things.

First, what volumetric ratio is the optimal mixture for combustion of butane
with air at STP?
What temperature is required to initiate the combustion reaction?
At what rate would a combustion front propagate through this mixture?
If volume is held constant before and after combustion, by what amount will
the temperature of the mixture have increased after the reaction?
Finally, if the mixture is made leaner, will the temperature increase be
reduced roughly proportionally to the amount of fuel present?

Thanks.
Phil.
a***@gmail.com
2004-12-09 08:25:01 UTC
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Post by Phil
Hi!
This is my first time posting here (5 newsgroups).
I sure would appreciate some advice on a couple of things.
First, what volumetric ratio is the optimal mixture for combustion of butane
with air at STP?
What temperature is required to initiate the combustion reaction?
At what rate would a combustion front propagate through this mixture?
If volume is held constant before and after combustion, by what amount will
the temperature of the mixture have increased after the reaction?
Finally, if the mixture is made leaner, will the temperature increase be
reduced roughly proportionally to the amount of fuel present?
Thanks.
Phil.
Uncle Al
2004-12-09 19:21:17 UTC
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Post by Phil
Hi!
This is my first time posting here (5 newsgroups).
I sure would appreciate some advice on a couple of things.
First, what volumetric ratio is the optimal mixture for combustion of butane
with air at STP?
Depends what you want out. For raw temperature, a stoichiometric mix
in pure oxygen. If you wnat to get work out of it in a real world
engine, other considerations intrude.
Post by Phil
What temperature is required to initiate the combustion reaction?
Not temp necessarily, energy input. Look up sparks and explosions. A
little Pt catalyst may set it off spontaneously. It is a free radical
chain - exponentiation chugs along.
Post by Phil
At what rate would a combustion front propagate through this mixture?
Depends. Confined or unconfined? Shape? Surface/volume ratio?
Deflagration, explosion, or detonation?
Post by Phil
If volume is held constant before and after combustion, by what amount will
the temperature of the mixture have increased after the reaction?
Finally, if the mixture is made leaner, will the temperature increase be
reduced roughly proportionally to the amount of fuel present?
Doesn't that sound like a poorly stated p-chem homework problem,
folks?
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
Phil
2004-12-10 04:15:21 UTC
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Thanks a lot for responding, Uncle Al!

I'm a complete newbie at usenet. I've never needed it much in my line of
work.
Phil wrote:> > Hi!
Post by Phil
This is my first time posting here (5 newsgroups).
I sure would appreciate some advice on a couple of things.
First, what volumetric ratio is the optimal mixture for combustion of butane
with air at STP?
Depends what you want out. For raw temperature, a stoichiometric mix
in pure oxygen. If you wnat to get work out of it in a real world
engine, other considerations intrude.
I want a rapid increase in pressure within a vessel whose volume won't
change

much at first. But it's not a bomb, though it sounds a lot like one. The hot
gas is

to escape through a small opening a fraction of a second later.
Post by Phil
What temperature is required to initiate the combustion reaction?
Not temp necessarily, energy input. Look up sparks and explosions. A
little Pt catalyst may set it off spontaneously. It is a free radical
chain - exponentiation chugs along.
I had been under the impression that some small bit of the unstable mixture
had

to absorb enough energy to effectively achieve a threshold temp in order to

trigger combustion in the neighboring bits and so on, regardless of what
source

that energy comes from: electrical arc, localized catalytic reaction,
adiabatic

heating, etc.

If one were to insert into the mixture an electrical filament and slowly
increase

it's temp, at what point would it trigger the reaction? Or within about 10 C
anyway.
Post by Phil
At what rate would a combustion front propagate through this mixture?
Depends. Confined or unconfined? Shape? Surface/volume ratio?
Deflagration, explosion, or detonation?
Locally. What I mean is, neglecting any movement caused by the pressure

wave emitted by earlier parts of the reaction, ignoring any overall pressure
and

temperature changes caused by it, and assuming that the reaction front is
not

dramatically curved or distorted.

Well, actually a general rough average with a precision of about 2 sig dig
would

be fine for my purposes.



Butane burning in air starting at standard temp and pressure would be

deflagration, wouldn't it? Could it produce a strong enough shock wave to
act

as a true explosive?
Post by Phil
If volume is held constant before and after combustion, by what amount will
the temperature of the mixture have increased after the reaction?
Finally, if the mixture is made leaner, will the temperature increase be
reduced roughly proportionally to the amount of fuel present?
Doesn't that sound like a poorly stated p-chem homework problem,
folks?
Uh, ya. I suppose it kind of does...

I'm not a chemist, just a guy that builds cars.

I meant something like: Half the fuel, therefore half the energy distributed

through the same amount of air would have half the effect, wouldn't it? I'm

guessing...
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
Thank you again for taking the time to reply to me.



Phil.
Uncle Al
2004-12-10 16:11:56 UTC
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Raw Message
Post by Phil
Thanks a lot for responding, Uncle Al!
I'm a complete newbie at usenet. I've never needed it much in my line of
work.
Phil wrote:> > Hi!
Post by Phil
This is my first time posting here (5 newsgroups).
I sure would appreciate some advice on a couple of things.
First, what volumetric ratio is the optimal mixture for combustion of
butane
Post by Phil
with air at STP?
Depends what you want out. For raw temperature, a stoichiometric mix
in pure oxygen. If you wnat to get work out of it in a real world
engine, other considerations intrude.
I want a rapid increase in pressure within a vessel whose volume won't
change
much at first. But it's not a bomb, though it sounds a lot like one. The hot
gas is
to escape through a small opening a fraction of a second later.
hand gun, rifle; pressure vessel with frangible disk. "escape through
a small opening a fraction of a second later" may be very optimistic.
Post by Phil
Post by Phil
What temperature is required to initiate the combustion reaction?
Not temp necessarily, energy input. Look up sparks and explosions. A
little Pt catalyst may set it off spontaneously. It is a free radical
chain - exponentiation chugs along.
I had been under the impression that some small bit of the unstable mixture
had
to absorb enough energy to effectively achieve a threshold temp in order to
trigger combustion in the neighboring bits and so on, regardless of what
source
that energy comes from: electrical arc, localized catalytic reaction,
adiabatic
heating, etc.
Spark plug. This stuff has been exhaustively addressed in gasoline
and diesel engines, including dwell angle. The hardware and its
dynamic tuning have been refined to a fare-thee-well.
Post by Phil
If one were to insert into the mixture an electrical filament and slowly
increase
it's temp, at what point would it trigger the reaction? Or within about 10 C
anyway.
[snip]
Post by Phil
Butane burning in air starting at standard temp and pressure would be
deflagration, wouldn't it? Could it produce a strong enough shock wave to
act
as a true explosive?
Gas-air bomb. Yeah.
Post by Phil
Post by Phil
If volume is held constant before and after combustion, by what amount
will
Post by Phil
the temperature of the mixture have increased after the reaction?
/_\H reaction and specific heat (Cv !!) of the mix is a good start.
Post by Phil
Post by Phil
Finally, if the mixture is made leaner, will the temperature increase be
reduced roughly proportionally to the amount of fuel present?
Doesn't that sound like a poorly stated p-chem homework problem,
folks?
Uh, ya. I suppose it kind of does...
I'm not a chemist, just a guy that builds cars.
I meant something like: Half the fuel, therefore half the energy distributed
through the same amount of air would have half the effect, wouldn't it? I'm
guessing...
If Detroit can design an engine anybody can do it with the same
$billion. Wouldn't it be best to go into the literature and see what
has been documented, theory and practice? The thermodynamics and
hydrodynamics of an engine are immensely complex. There are guys who
make a fat living minutely sculpting the interiors of race car intake
and exhaust manifolds to balance pressure along length and lessen
turbulence, respectively. The watershed improvement in high
performance engines was to locate valve lifters at nodes so vibration
didn't eat them and their operation.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
Phil
2004-12-12 17:10:56 UTC
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Thanks for the help!
I think I have some redesigning to do...

Phil.
Post by Uncle Al
Post by Phil
Thanks a lot for responding, Uncle Al!
I'm a complete newbie at usenet. I've never needed it much in my line of
work.
Phil wrote:> > Hi!
Post by Phil
This is my first time posting here (5 newsgroups).
[snip]
Post by Uncle Al
The watershed improvement in high
performance engines was to locate valve lifters at nodes so vibration
didn't eat them and their operation.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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