RE: Stove efficiency

["Prasad, K." <K.Prasad@tue.nl>]

Dear Piet, Tom, Rogerio and other Stovers

Stove efficiency - the subject never dies. Piet mentioned about the
Eindhoven professor. Yes I was also at the meeting. Like Piet said that
statement was not published. Maybe it was quoted in some other context in
one of our many publications - alas I have not had the patience to plough
through all the material. To be fair to the gentleman, I will repeat his
remarks - of course out of memory. He was stating you can have something
like 75% combustion efficiency, but you can still get a 50% stove efficiency
since there is lot of heat generated by inefficient combustion. He also
added that you may have 90% combustion efficiency, but that 10% unburnt or
incompletely burnt biomass can cause a hell of lot of damage by way of
pollution - indoor/outdoor.

A fairly detailed account of the thoughts of Eindhoven Group on efficiency
is available now at the following website:
<www.cookstove.net>

And I would like to emphasize a remark by Piet Verhaart. Nobody will accept
Italian, French, and British cooking are the same. All of them happily use
the standard gas stove or one of the new fangled electric stoves/ovens to
prepare the food they prefer to eat. One can make too much of the
social/cultural aspects. At least the Eindhoven group felt strongly enough
not to be overly concerned with this aspect.

I was also a party to the VITA meeting that drafted the testing procedures.
What our group thought of the agreed test procedure recommended by VITA is
also available on the website.

Two more remarks: the quantity of air to be used. Too much or too little air
can hurt the efficiency as well as quality of combustion. That window is
rather small. We have data on this. Hopefully it will get on the website one
of these days.
The second point concerns an inaccurate remark: it is quite often stated
that higher efficiency is obtained at the expense of quality of combustion.
This is simply not true. Of course there are careless designs that can
produce such a result.

Prasad

What Eindhoven group thought about efficiency has been on record in many
publications.

-----Original Message-----
From: Peter Verhaart [mailto:pverhaart@optusnet.com.au]
Sent: Saturday, May 04, 2002 8:20 AM
To: Tom Reed
Cc: stoves@crest.org
Subject: Re: Stove efficiency


Dear Tom,

         First of all, your posting contained an attachment that was marked 
as containing a virus by my PC-Cillin.
Since I value what you wrote, I will, much against my habit, leave it whole 
in my reply. The file has the extension .jpg but with a lot of zeros after 
it. I will delete your original message and wait for my reply to arrive.

I too, tried the approach you mentioned. I studied a book on kerosene 
burners in which mention was made of the mode of operation of multi-wick 
burners. In a normal flame a fuel rich gas burns in air where the 
air/oxygen has to diffuse into the flame. If the flame is too thick, the 
oxygen can't reach the inner flow of fuel and this being exposed to high 
temperature, decomposes into muck, hydrocarbons and soot.
In the multiwich burner, the fuel is gradually exposed and mixed with 
oxygen causing aldehydes to be formed and later burnt, according to the
author.

I built a stove with perforated concentric cages which could be supplied 
with air through natural draft. I called it "The Aldestove" and tried it 
out during a holiday in Portugal in 1984. I made the mistake of not 
lighting it from the top. It could at times burn with flames that could be 
called blue with some goodwill. I have slides of it.

Before venturing on the design I burned xylene in a multiwick burner to see 
if a fuel with a comparable boiling point and a lot less hydrogen in the 
molecule could be made to burn without sooting. It could.

Yes, I know the Alladin lamp. The Woodburning Stove Group bought one, since 
we were asked by the World Bank to look into kerosene burners for possible 
use in third world countries. We tested a large number of them, made in 
India Sri-Langka and Indonesia. One of the best burners came from 
Indonesia. Later some 50 were sent to Niger or some other African country 
for an extended test.

"Sort of" is indeed the measure of success in the quest for blue flames. 
The difficulty is insuring a constant supply of gas of constant composition.

Thank you for your comment.

Peter Verhaart


At 06:08 3/05/02 -0600, you wrote:
>Dear Peter:
>
>I have also been looking for a method to burn wood with blue flames - and
>have found it  - sort of...
>
>Kerosene is hard to burn with a blue flame too, but in mantle lamps and
>stoves it is done by having "micro air" access to the kerosene vapors.
>There is typically a tubular wick with air coming up through the middle and
>around the outside and passing through perforated plates to form a few
>hundred small jets of air, drawn in by the chimney.
>
>We achieved the same thing with our natural draft inverted downdraft stove
>(below) by putting a 6 mm gap between the gasifier and chimney.  We had an
>internal flame holder (gas wick, an unfortunate name)10 mm away that
>constrained both the gas and the air to mix in a column of burning gas 10
mm
>thick.  This gave a blue flame.
>
>Without the flame holder the amount of combustion products was not enough
to
>fill the chimney, resulting in poor draft and "spherical" combustion and
>some yellow in the flame.
>
>I hope to see Paul Anderson in a week or two and explore this futher with
>him.  I hope that both of you will buy yourselves or visit in a store an
>Alladin mantle lamp and study it.
>
>Comments?  Keep in touch...
>
>TOM REED
>
>
>
>
>
>
>
>


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