excess air (lambda) question

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Borrowed a combustion analyzer today. Great fun (but then maybe I'm weird).

I got CO and CO2 within the specified range for the Munchkin (OK, actually they were there anyway, but I tuned it up a bit just for the hell of it). However, O2 is always 4-6% and lambda (excess air) is 25-40. Now the ideal lambda ia 1.0 so this seems really high.

Am I right that all this excess air is needed to push the combustion products out the door? Or is something wrong?

Rudy

Yep, a little weird!!!

But it is great fun, isn't it!?!
Don't know what you mean by 'lambda' but it's not 'excess air'.
The excess air reading is a calculated reading based on the O2 reading and would only get to 1 if the O2 reading was at about a 0.3, which would in all likelihood would be a problem (CO wise).

The excess air reading is just another way of looking at the amount of unburned oxyger in the flue gas sample.

Also, just out of curiosity, what did you do to 'tune' it up a bit?? Do be careful!

Chuckles_3

OK,I have to check when I get home. I may have made a newbie mistake. The unburnt oxygen was about 4% to 6%, is this OK? (Munchkin wants you to measure at the highest and the lowest settings, hence two numbers.)

As for "tuning up", I just changed the throttle a bit both ways and saw where CO2 hits a maximum and where the CO starts to rise sharply and so forth, and ended up somewhere within the range specified in the manual, but with a little less CO than originally, i.e. a little more O2. Then I started to worry about whether this was too much air and whether this would hurt efficiency. But no, I haven't ended up anywhere weird; I know how the CO and CO2 curves should look like when changing the air in the mixture.

Rudy

Interesting

If Munchkin wants a 4 - 6%O2 depending on the firing rate, those are impressive O2 readings.

My understanding from discussing this issue a while back was that they wanted it 'tuned' to the CO air free reading - can't remember exactly the acceptable range but it was somewhere around 80 - 100 ppm.

Was curious what CO air free readings you had.

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Don't know the air-free reading, didn't record it because manual didn't say what it should be. If you have the target range, I'll fire it up again and check it.

By the way, my excess air report was completely wrong because when the display shows 25, it means 25%. Sorry about that.

Munchkin doesn't "want" any particular O2 reading It wants CO 0-20ppm on low and 80-135ppm on high, and CO2 of 8.5-9.5% on both low and high. I got those and then O2 was 4% at low and 6% at high. Why is that impressive? Is it bad? If I lower O2 further the CO goes through the roof.

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