Hi Jeff.

Thanks. Comments below.

Jeff Liebermann wrote in message . ..
On 17 Mar 2004 12:02:15 -0800, (John Michael
Williams) wrote:

However, the first radios transmitted
sparks, so in principle it should be possible to
transmit near a long wire separated by a small gap from
ground or another wire and get a small spark.

There were few spark transmitters mounted in automobiles. They were
just too inefficient, big, and clumsy to be functional. Transmitters
in vehicles really didn't start until tube type transmitters became
popular. The problem was that the typical mobile radio used a
dynamotor (motor-generator) combination to generate the necessary high
voltages. With the radio and dynamotor mounted in the trunk of the
vehicle, there was a good chance that gasoline fumes would accumulate
in the trunk of the vehicle and be ignited by the spark from the
dynamotor commutator. See the photo of the 80D at:
http://www.telmore.com/ka1nvz/old_tw...ola/49-59.html
The dynamotor is the black cylinder near the handle. The 140D was
twice as big and heavy.

Ships around the turn of the 20th century transmitted morse code by
spark, I think.


Back in the 1960's, my 1960 Ford Falcon had an assortment of Motorola
80D and 140D radios in the trunk. I experienced a small explosion in
the trunk ignited by the dynamotor. I had filled up the gas tank at
the local gas stop (for 19 cents per gallon). Warm weather caused it
to expand and leak vapour into the trunk. Key the transmitter, the
dynamotor starts, sparks, and boom.

I then attached a 1.2 m monopole antenna to an oscilloscope.
This antenna has a Schottky hot carrier diode and impedance
matching resistors builtin.

Lovely. A harmonic generator. Any reason you want lots of harmonics?
Shottky diodes or any other non-linear device, do not belong in
antenna matching circuits.

It's home made, but it's probably
as good as any other wire about that long.

Wrong. Optimum for CB is either a 1/4 wave monopole (102 inches) or
two of them to form a half wave dipole.

So, first conclusion: To get even a 1 V spark would take a
wire at least 9 m long, all somehow kept within 1 m of the
transmitter. Thus, it appears it is not feasible to create a
hazardous spark with a CB at a gas station.

Find a 4 watt flourescent light. Attach a 1/4 wave antenna to your 5
watt CB radio. Transmit. Hold lamp in hand and touch the end of the
102" antenna. It will light when you talk. (Note: With AM
modulation, you only get 5 watts when you yell into the microphone.
Without modulation, you only get about 2.5 watts of RF).

Interesting idea. I would have thought that a tube would require
more V than a neon lamp to get started. I'll try it if I can
find a lamp.

What you seem to be suggesting is that I simply connect the
lamp to the 1/4 wave receiving antenna, right? Why introduce
my hand? For ground on the other lamp contact?

I don't see the point of attaching a long
wire to the CB, because they don't come with long bare wires.
Clearly, I could get a good spark by attaching a wire to the
CB batteries, and avoid all the RF stuff!

Now, ask
yourself what voltage is required to light the flourescent lamp.

In order to get a spark, you need to generate enough voltage to ionize
the air between the contacts. That's about 20KV/inch. If we
eliminate the antenna, 5 watts of RF into 50 ohms will generate:
P = E^2 / R
E = 16v rms
E(peak) = 1.4 * 16 = 22 volts
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches
Kinda small, but given a microscope, a 1 mil spark gap will arc. Of
course the VSWR protection circuity in the transmitter will instantly
shut down the transmitter when it arcs, but that takes a few millisec.

22 V is a lot more than I could get with a 1 m monopole: I only
got 100 mV peak to peak. It appears my 1 m wires
were too short; but, if I use a long wire, the distance from the
transmitter will lower the power transfer to some
of the wire, won't it? Or, I'll have to move away, into the
far field--but that will also lower the power.

There's no question 5 W is enough to make a spark of arbitrary
size, given an inductor somewhere around, but I don't see where
the 50 ohms comes from, if I'm looking for a spark caused by the RF?


Notice that this is a voltage phenomenon, and is not dependent upon
the power level. Therefore, an antenna that offers a voltage step-up
will generate a higher voltage. However as the antenna is in the air
and nowhere near a close enough ground to arc, it doesn't matter. If
there's gonna be any arcing, it will be between the xmitter output and
the base of the antenna.

The transmitter antenna is coated with about 3 mm of rubber; I think
cell phones are the same way. A spark has to come from the RF,
I think. There is a BNC connector, but that implies complete
shielding (even flame suppression!) at the antenna base.

I have a telescoping antenna intended for a receiver that is bare
metal, though. I could substitute it.


The typical mobile FM transmitter of the day (1960's) cranked out
between 15 and 150 watts. Most were around 75 watts. Run the calcs
again for 75 watts and see if the gap is more reasonable (I'm lazy).

The next question is how much heat is necessary from the arc to ignite
the gasoline vapour. I'll leave that as an exercise for when I have
more time to burn. Gotta get back to lying and cheating on my taxes.

I think if I can see the spark, it can ignite gas vapor,
provided the flame had a path out of the gap.

John

John Michael Williams

On 20 Mar 2004 23:28:38 -0800, (John Michael
Williams) wrote:

Ships around the turn of the 20th century transmitted morse code by
spark, I think.

The Lusitania, Mauritania, Titanic, and Olypic all ran on coal. No
gasoline in sight. Later vessels ran on bunker C fuel oil, which is
more like tar than gasoline. I don't think one has to worry about
sparks on such a vessel unless it's finely devided coal dust, which
finished off the Lusitania in a secondary explosion after the torpedo.

Interesting idea. I would have thought that a tube would require
more V than a neon lamp to get started. I'll try it if I can
find a lamp.

Neon lamp needs about 60 volts to light and 40 volts to stay lit. The
4 watt flourescent tube wants at least 90 volts to start, and I think
(i.e. guess) about 50 volts to stay lit.

What you seem to be suggesting is that I simply connect the
lamp to the 1/4 wave receiving antenna, right? Why introduce
my hand? For ground on the other lamp contact?

Yep. You're the ground. You should be fine with a 5 watt CB and a 1/4
wave whip. The high voltage point is near the tip. However, don't
try it with an illegal CB linear. You'll get an RF burn for your
troubles.

Incidentally, there are cell phone antennas with lights in them.
http://cellphones-accessories.com/12stobligcel.html
They're LED's which require much less power to light than a 4 watt
flourescent bulb. Still, it's kinda interesting.

I don't see the point of attaching a long
wire to the CB, because they don't come with long bare wires.
Clearly, I could get a good spark by attaching a wire to the
CB batteries, and avoid all the RF stuff!

Exactly. Same with an open relay contact or toggle switch. However,
don't foget that you need containment to create an explosion.
Sparking the DC inside the trunk is the mostly likely location.

22 V is a lot more than I could get with a 1 m monopole: I only
got 100 mV peak to peak.

The 22 volts peak is at the RF connector. I'm assuming that if there
is a spark gap, it will be in the coax cable or associated antenna
connectors.

It appears my 1 m wires
were too short; but, if I use a long wire, the distance from the
transmitter will lower the power transfer to some
of the wire, won't it? Or, I'll have to move away, into the
far field--but that will also lower the power.

Inverse square law. Double the distance, and you get 1/4 the power.
For a fix load resistance, 1/4 the power is 1/2 the voltage. However,
you'll get vary bad coupling efficiency with such an arrangement. I
could grind the near field equations but you'll never get ALL the
power (5 watts) delived to your random wire pickup. Think resonance
and close coupling if you want to do better.

There's no question 5 W is enough to make a spark of arbitrary
size, given an inductor somewhere around, but I don't see where
the 50 ohms comes from, if I'm looking for a spark caused by the RF?

That's the approximate impedance of the antenna as found on a typical
mobile installation. Again, I'm assuming that if there is a spark to
be found, it will be at the coax ends or connectors. They're all 50
ohms.

The transmitter antenna is coated with about 3 mm of rubber; I think
cell phones are the same way. A spark has to come from the RF,
I think. There is a BNC connector, but that implies complete
shielding (even flame suppression!) at the antenna base.

A BNC connector is quite open but is good for maybe 150 volts of RF.
However, all it takes is a sloppy coax connection, with some of the
braid wires slopped around near the center pin of the BNC, and you
have a potential spark gap.

I have a telescoping antenna intended for a receiver that is bare
metal, though. I could substitute it.

Won't make much differnce. At 0.001" gap necessary for a spark with 5
watts can only happen with a defective installation.

I think if I can see the spark, it can ignite gas vapor,
provided the flame had a path out of the gap.

I beg to differ. The ignition of a gasoline oxygen mixture requires a
specific amount of energy to ignite. Anything less will not produce
the requiste chemical reaction. Think spark plug heat ranges and glow
plugs in model airplanes. I'll grind the numbers if you want, but
it's now midnight, I'm tired of waiting for Windoze update, and I'm
going home.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
#
# 831.421.6491 digital_pager AE6KS

Jeff Liebermann wrote in message . ..
On 20 Mar 2004 23:28:38 -0800, (John Michael
Williams) wrote:

snipped lots of good stuff

I think if I can see the spark, it can ignite gas vapor,
provided the flame had a path out of the gap.

I beg to differ. The ignition of a gasoline oxygen mixture requires a
specific amount of energy to ignite. Anything less will not produce
the requiste chemical reaction. Think spark plug heat ranges and glow
plugs in model airplanes. I'll grind the numbers if you want, but
it's now midnight, I'm tired of waiting for Windoze update, and I'm
going home.

The ignition of a gaseous oxygen-gasoline mixture, or a (potentially
more sensitive) hydrogen-oxygen mixture does require a specific
minimum amount of energy, which depends on the partial pressures of
the oxygen and the fuel, and - IIRR - the partial pressures of any
inert diluent gases around.

Lesser amounts of energy can induce the requisite chemical reaction,
but the reaction will fizzle out, rather than providing enough energy
to ingnite the surrounding shell of a gas mixture and produce a
self-propagating flame front.

The controlling relationship is between the volume of the sphere in
which the reaction is first initiated, and the surface area of that
sphere - if the intial volume is too small, not enough energy is
released to heat the surrounding shell of gas to the ignition
temperature.

Once you've got the basic idea,the thermodynamics is pretty
straightforward.

I had to work through the equations many years ago for an experiment
intended to monitor the process in which one of the "Dewar benzenes"
converted itself to normal - Kekule's - benzene, which is an
enormously energetic process, involving about an order of magnitude
more energy per molecule than you get out of TNT and PETN. I really
didn't want to blast my experimental apparatus to smithereens.

When I went through the calculations with my supervisor, he pulled a
very long face - the motivation for the experiment had been some
unexpected flashes of light seen when a dumb organic chemist had
released small drops of liquid "Dewar benzene" into a hot cell, and my
calculations made it clear that the flashes of light were just thermal
radiation from a hot plasma, rather than fluorsecence from from an
electronically excited state of Kekule benezene, which is what my
supervisor had been hoping for ...

For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/...enzenering.htm

-------
Bill Sloman, Nijmegen

I read in sci.electronics.design that Bill Sloman
wrote (in ) about 'CB
Radios, Cellphones and Gasoline Vapor Ignition', on Sun, 21 Mar 2004:
For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/...enzenering.htm

Dewar benzene can actually be made? Do you know when it was discovered?
What about the prismatic form? I would have thought that was a lot
easier to make, if I didn't have a suspicion that that is where simple
bonding ideas break down.

--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

John Woodgate wrote in message ...
I read in sci.electronics.design that Bill Sloman
wrote (in ) about 'CB
Radios, Cellphones and Gasoline Vapor Ignition', on Sun, 21 Mar 2004:
For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/...enzenering.htm

Dewar benzene can actually be made? Do you know when it was discovered?
What about the prismatic form? I would have thought that was a lot
easier to make, if I didn't have a suspicion that that is where simple
bonding ideas break down.

IIRR all three Dewar benzenes can be made - with difficulty.

They've been available since before 1971 at least - which is when my
project fell apart - but they were newish then.

The three-carbon rings at either end of the prismatic version do have
a lot of steric strain, but they can be made - I think pyrethroid
insecticides include just such a cyclopropane ring.

----------
Bill Sloman, Nijmegen

(Bill Sloman) wrote in message . com...
...

The controlling relationship is between the volume of the sphere in
which the reaction is first initiated, and the surface area of that
sphere - if the intial volume is too small, not enough energy is
released to heat the surrounding shell of gas to the ignition
temperature.

...
-------
Bill Sloman, Nijmegen

This makes sense. I think I can see a spark 0.1 mm in
radius, at say 4000 K. That's about 4 cubic picometers
in volume and about 0.1 square micron in surface area (assuming
sparks have smooth surfaces). But, I'm not sure how to relate
that to the threshold of flame propagation.

If energy is a factor, rather than power, the duration of
the spark would seem to be relevant, too.

John

John Michael Williams

(John Michael Williams) wrote in message om...
(Bill Sloman) wrote in message . com...
...

The controlling relationship is between the volume of the sphere in
which the reaction is first initiated, and the surface area of that
sphere - if the intial volume is too small, not enough energy is
released to heat the surrounding shell of gas to the ignition
temperature.

...
-------
Bill Sloman, Nijmegen

This makes sense. I think I can see a spark 0.1 mm in
radius, at say 4000 K. That's about 4 cubic picometers
in volume and about 0.1 square micron in surface area (assuming
sparks have smooth surfaces). But, I'm not sure how to relate
that to the threshold of flame propagation.

If energy is a factor, rather than power, the duration of
the spark would seem to be relevant, too.

Sparks are much faster than flame fronts - when I was involved in
instrinsic safety nobody paid any attention to spark duration, and for
all practical purposes the energy stored in the capacitance of a spark
gap is dumped into the gas much faster than it can be dissipated.

------
Bill Sloman, Nijmegen

In , Bill Sloman wrote
in part:

I had to work through the equations many years ago for an experiment
intended to monitor the process in which one of the "Dewar benzenes"
converted itself to normal - Kekule's - benzene, which is an
enormously energetic process, involving about an order of magnitude
more energy per molecule than you get out of TNT and PETN. I really
didn't want to blast my experimental apparatus to smithereens.

When I went through the calculations with my supervisor, he pulled a
very long face - the motivation for the experiment had been some
unexpected flashes of light seen when a dumb organic chemist had
released small drops of liquid "Dewar benzene" into a hot cell, and my
calculations made it clear that the flashes of light were just thermal
radiation from a hot plasma, rather than fluorsecence from from an
electronically excited state of Kekule benezene, which is what my
supervisor had been hoping for ...

For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/...enzenering.htm

If this produces anything near 10x the energy per weight of TNT or PETN,
then a version with controlled reaction rate would make one heck of a
rocket propellant.

I thought the ultimate energy per mass was magnesium and oxygen (or was
it beryllium and oxygen?), just a few times as much energy per mass as TNT
and not good like usual rocket propellants for producing gas to use as
rocket exhaust.

I am surely skeptical of changing one isomer of a molecule to another
producing even comparable energy to, let alone more energy than
decomposition of a similar or somewhat greater mass molecule of high
explosive.

- Don Klipstein )

(Don Klipstein) wrote in message ...
In , Bill Sloman wrote
in part:

I had to work through the equations many years ago for an experiment
intended to monitor the process in which one of the "Dewar benzenes"
converted itself to normal - Kekule's - benzene, which is an
enormously energetic process, involving about an order of magnitude
more energy per molecule than you get out of TNT and PETN. I really
didn't want to blast my experimental apparatus to smithereens.

When I went through the calculations with my supervisor, he pulled a
very long face - the motivation for the experiment had been some
unexpected flashes of light seen when a dumb organic chemist had
released small drops of liquid "Dewar benzene" into a hot cell, and my
calculations made it clear that the flashes of light were just thermal
radiation from a hot plasma, rather than fluorsecence from from an
electronically excited state of Kekule benezene, which is what my
supervisor had been hoping for ...

For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/...enzenering.htm

If this produces anything near 10x the energy per weight of TNT or PETN,
then a version with controlled reaction rate would make one heck of a
rocket propellant.

I thought the ultimate energy per mass was magnesium and oxygen (or was
it beryllium and oxygen?), just a few times as much energy per mass as TNT
and not good like usual rocket propellants for producing gas to use as
rocket exhaust.

It depends on the electrochemical gradient, I think.
Hydrogen burning in fluorine probably produces more combustion
energy than anything else, per unit mass.


I am surely skeptical of changing one isomer of a molecule to another
producing even comparable energy to, let alone more energy than
decomposition of a similar or somewhat greater mass molecule of high
explosive.

I share this skepticism. Burning TNT probably would produce 10x more
free energy than detonating it.



John

John Michael Williams

(John Michael Williams) wrote in message . com...
(Don Klipstein) wrote in message ...
In , Bill Sloman wrote
in part:

I had to work through the equations many years ago for an experiment
intended to monitor the process in which one of the "Dewar benzenes"
converted itself to normal - Kekule's - benzene, which is an
enormously energetic process, involving about an order of magnitude
more energy per molecule than you get out of TNT and PETN. I really
didn't want to blast my experimental apparatus to smithereens.

When I went through the calculations with my supervisor, he pulled a
very long face - the motivation for the experiment had been some
unexpected flashes of light seen when a dumb organic chemist had
released small drops of liquid "Dewar benzene" into a hot cell, and my
calculations made it clear that the flashes of light were just thermal
radiation from a hot plasma, rather than fluorsecence from from an
electronically excited state of Kekule benezene, which is what my
supervisor had been hoping for ...

For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/...enzenering.htm

If this produces anything near 10x the energy per weight of TNT or PETN,
then a version with controlled reaction rate would make one heck of a
rocket propellant.

Not really. The crucial feature of chemical explosives is that they
produce their energy fast, which is to say by intra-molecular
rearrangement. Burning a hydrocarbon in oxygen produces a lot more
energy per unit mass of fuel and oxidiser than does letting off TNT or
PETN where the oxygen comes from the nitro groups attached to the
hydrocarbon core, whence the popularity of fuel-air bombs, but you
don't get the same brissance.

I thought the ultimate energy per mass was magnesium and oxygen (or was
it beryllium and oxygen?), just a few times as much energy per mass as TNT
and not good like usual rocket propellants for producing gas to use as
rocket exhaust.

It depends on the electrochemical gradient, I think.
Hydrogen burning in fluorine probably produces more combustion
energy than anything else, per unit mass.

Atomic hydrogen recombining into molecular hydrogen would be better
(as a rocket fuel) but has never been reduced to practice. What I
remember from what I read on the subject - many years ago - was that
hydrogen-fluorine was the best possible fuel-oxidiser combination.
Nasty exhaust fumes ...

I am surely skeptical of changing one isomer of a molecule to another
producing even comparable energy to, let alone more energy than
decomposition of a similar or somewhat greater mass molecule of high
explosive.

Check out the published literature - that is all that I was doing at
the time.
Chemical explosives are relatively wimpy as far as energy per unit
mass goes - the rate of energy release is the crucial feature.

I share this skepticism. Burning TNT probably would produce 10x more
free energy than detonating it.

Trinitrotoluene is C7H5N3O6 and would burn to 7 CO2 molecules, 2.5 H2O
molecules and 1.5 N2 molecules - for which you'd need 10.5 extra
oxygen atoms, over and above the six oxygen atoms available in the
original TNT molecule.

Being simple-minded about it, 16.5/6 is 2.75, not ten, and that
exaggerates the advantage, because burning carbon to carbon monoxide
release quite a lot more energy than burning carbon monoxide to carbon
dioxide, which is where you use up seven of your extra 10.5 oxygen
atoms.

The exact amounts of energy involved are all available in the open
literature - that is where I found them, some thirty years ago, and
I'm sure that they are still available now.

-------
Bill Sloman, Nijmegen