Re: using excess air

[AJH <andrew.heggie@dtn.ntl.com>]

On Fri, 28 Jun 2002 04:56:34 -0700, "Dean Still" <dstill@epud.net>
wrote:

>
>But, there is perhaps a third best option. Larry Winiarski, Damon Ogle and Jim Wilmes were not sure how exactly to do it but they'd like to leave the increased airflow alone until it is slowed down by creating turbulence in the fire. Creating a frenzied, jumpy fire like we see when using jets of air from a fan, that used up the excess air at speed, would be a nice trick.


I concur with your analysis that given the same inlet conditions a
higher chimney will develop a higher depression at the inlet and thus
increase air supply.

Now, as excess air increases mass flow and decreases heat transfer,
you need to retune the inlet air to get back nearer to stoichiometric
conditions BUT as you now have higher draught you can convert some of
the power in the airflow to produce sufficient turbulence to both
increase residence time and reduce induction of excess air. The
classic way is to cause the incoming air to run counter current to the
flame, this provides mixing (turbulence) and consumes power to do so.

I wish I had met up with you when you were in London I could probably
have done a quick demo of this.

Now you are running with chimneys there is much more scope for better
combustion without recourse to fans.

I had meant to post on my steam aspirator, I have had it successfully
running but I feel like a poor version of Howard Hughes struggling to
get his spruce goose off the sea before an end to hostilities was
called (I believe his contract specified that), anyway whilst it
sustains combustion in a device that self extinguishes in the absence
of a fan, it needs much more fettling. In fact the steam content very
much modifies the flame, such that I do not think my monotube boiler
and nozzle are at all matched to the task. I have some jpegs I could
send.

I now think it would probably better suit when used to provide only
primary air or as an eductor. In essence I must be achieving very very
poor mass and power ratios on the aspirator, such that Ken Boak's
mechanical propeller could well have better conversion of the steam to
air motion.

BTW I have been following the thread on whether our little devices are
allowed to be termed gasifiers and (whilst interested in gasifiers) am
quite happy to let the purveyors of vapourware keep the term whilst
actual stoves that can be deployed in the field get designed and made.

AJH

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