Electrical conductivity of flames (OT?)

You can't understand the stuff I post, and Thompson can't see it. Of course you don't expect much. Sad old hens.

Hey, I can make 3 volts or so blasting a pair of snipped resistor leads:

Either polarity, depending on flame position. The blue part seems to work best.

Keep on cluckin!

Word salad.

This thread will soon hit 100 posts, all wild speculation, talktalktalk, and only ONE experiment so far.

Larkin, narcissistically kissing his own ass, is becoming senile. I have been quite active on technical subjects in spite of Larkin's ass-kissing sycophants being wrong and resorting to name-calling to cover their ignorance. ...Jim Thompson

Why would that create rectification? Can't electrons flow in both directions?

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I don't recall using a DC voltage, but maybe. I did make a high voltage supply from old TV parts. That might have been part of it since I don't recall what else I would have used it for. I ran the output of a tube amp through another transformer to step it up. My science teacher brought the class up to listen to it. Earlier I had moved the wire to a different tap to try to up the voltage to make it louder. But that loaded down the output transformer and it didn't work at all. I didn't figure it out until after they left so I missed my moment of glory.

Well, there *has* to be *some* difference between the electrodes for it to rectify. My bet is on the temperature difference. Since the metals are not in contact you will get a large temperature difference and this can even generate a current by the same effect as in thermocouples.

Most likely, the difference is in electron affinity of various radicals in the flame, and the work function (and temperature) of the electrodes.

Chemically, a flame is made of three things: gasses, radicals and ions.

In air, the gasses are mostly N2, plus whatever combination of O2, fuel, CHx, CO, CO2 and H2O is produced during combustion.

Radicals are fuel molecules in varying states of destruction and oxidation. If you start with methane, CH4, and ignite it in air, collisions start knocking off hydrogen atoms (which quickly form OH radicals and H2O), resulting in CH3, CH2, CH and C2 radicals. All these release characteristic photons when excited (not necessarily ionized), which can be identified:

There aren't many ions in a flame, since even a very hot flame is much cooler than a cool plasma. (Plasma itself is not usually very ionized -- most plasmas are predominantly unionized* gas. It just happens that the ions are the most exciting part, so once it's past some level, we call the whole thing plasma.)

You can also introduce a wide variety of things into a flame. Sodium is an absolutely pervasive contaminant, and is responsible for the orangish color of a flame in contact with anything hot. The sodium glow is so intense that a hot surface needn't have any apparent sodium residue on it -- your gas stove's metal grate will pick up enough dust (which is mostly composed of dead skin, which includes dried sweat, therefore containing a trace of sodium) to do this. Sodium in a flame is monatomic (something like NaCl is broken without too much energy, forming Na. + Cl. radicals, both of which are not very high energy, as radicals go). Sodium, of course, is well renouned for its ability to give up an electron with little energy expense, forming Na+, so a sodium-doped flame would be reasonably conductive.

I don't know any data offhand regarding the electron affinity (or ionization energy) of these molecules. It's likely that both kinds of ions will form. For example, the OH. radical may gain a companion for its unpaired electron, forming the hydroxyl ion, OH-, while the CH3. radical might lose an electron, forming the methyl carbocation**, CH3+.

Tim

to Alternating Potentials

THey have been using that type of sensor system in electronic gas ignites for years. There is a reason for this, over using a conventional temperature probe or photo cell.

This type of sensor will offset the AC being injected through the plasma. However, after some short time if it does not get detect it'll shut down, also, if the sensor is shorted to ground, it will generate non offset sine wave, indicating a probe short and thus not operate the gas valve.

Jamie

Here's a simplified overview of the operation. The keyword is plasma resona nce flame detection, a thoroughly failsafe method used for years, and it do es confirm what we found in the research literature about the rectification occurring at the plasma resonance frequency ( which is quite low according to these people):

I did try a simple rectification experiment, function generator and oscilloscope and a couple of electrode geometries, but no sign of rectification. The impedance of the Keithley electrometer is many orders higher than a scope.

Any results from your experiments?

If you reverse tha polarity of the applied voltage, the field map changes sign. The field intensity at any point is the same, just reversed in direction. Which is not what you said.

Did you ever take a course in electromagnetics? JT did, but you can't ask him for help because but he's forgot it all.

Hypothesis? Is that what you call that babbling?

"Real science" !! Now that's funny.

Radioisotope thermal generators do just that.

I found a Honewell manual on "flame safeguard controls" that I forgot I had. It says "the ground electrode is always designed to be much larger than the flame electrode (flame rod). For effective operation, the area of the ground electrode must be at least 4 times that of the flame rod. ... Because of the difference in electrode sizes, more current flows in one direction than in the other. When the flame rod is positive, more current will flow." The ground electrode includes the burner tubes and other surfaces the flame contacts.

This is not how I pictured flame rods working, and does not explain the exact mechanism. Maybe large ground electrodes means it can be good for both electron and ion flow, but more of the mobile electrons can get to the rod than ions.

"With most Honeywell controls, the flame signal should be at least 2 microamps and steady." This is the current in the flame rod lead, which is a sum of positive and negative currents.

My boiler uses a flame rod to prove ignition. At one point I was so pissed off at problems I worked out the circuit for the control. If it is of interest, the rod connects to 120VAC (hot) through a 12M resistor shunted by a capacitor (unknown value) in series with a 1M resistor.

Any flame safety system, other than a standing pilot, should require a flame is not detected before starting. If flame conduction (obsolete) was used and there was a shunt path the ignition process should not start.

Some other methods

IR. Since this can false-trigger on hot parts it responds only to flickering produced by the flame.

UV detection.

flame detection, a thoroughly failsafe method used for years, and it does confirm what we found in the research literature about the rectification occurring at the plasma resonance frequency ( which is quite low according to these people):

Not enough info on resonance for me to understand - others might.

It is basically fraudulent in describing flame rod false-flame detection in that it describes flame detection by "conduction", which far as I know is long obsolete. Detection by "rectification" should not fail as described. "Rectification" may have more problems with false negatives than "resonance" (or maybe less).

The PbN degree that Larkin bought at Tulane ?>:-} ...Jim Thompson