[Stoves] Magh Utham Woodgas Burner

[Crispin Pemberton-Pigott]

Dear Andrew

>You can download a copy of Damon Ogle's study on controlling draft in
Rocket Stoves here:  
<http://www.repp.org/discussiongroups/resources/stoves/Ogle/stovedraft.pdf>

That study is interesting to all stove designers for two important reasons:

1) the amount of smoke was not related to the temperature measured in the
chimney. The thesis being tested was that high temperatures were needed to
get a clean burn. The coolest burn produced the cleanest gases.

2) the quantity of heat passing through the system cannot be determined by
measuring the temperature of the gases in the flue. The fact that the
measured temperature was, say, 1500 F, does not mean that the heat generated
was 1500, but that the quantity of excess air diluting and cooling the gases
resulted in a temperature of 1500 F. Lower EA increased the temperature, but
the dry fuel was not able to deal with the extra heat, gassing continuously.

It is noteworthy that the fuel was oven dried for at least 8 hours before
the test. It is very difficult, not to say impossible, to burn ultra-dry
fuel in an air-restricted chamber that is not a true gasifier. As noted in
the paper, restricting the air rapidly turns it into a gasifier roasting
volatiles out of the wood as the correct air/fuel ratio is approached.

It shows that in order to burn ultra-dry conifer wood, you need a large
amount of excess air and a relatively long burn chamber. While that is not
typical of ordinary cooking it is still true for that case.

It would be interesting to know what the excess air level was alongside the
burn observations, and also what the result of a similar test would be using
normal moisture wood (15-30% WWB) which can burn moderately in a high
temperature, low EA environment.

Regards
Crispin