[Stoves] venturi system -ratios of air and gas?

[ajheggie at gmail.com]

[Default] On Fri, 8 Jan 2016 16:40:14 -0500,Crispin Pemberton-Pigott
<crispinpigott at outlook.com> wrote:

>Dear Paul
>
>If you examine a propane cooker, the gas comes from a tiny hole in the jet
>and is fed through a lot of small holes into the air. There are a myriad
>flames each small in diameter and the length varies from short to long
>depending on the gas flow rate. The gas burns on the 'outside' only with a
>hollow core, the core being unburned propane (or more likely, a blend of
>propane and butane). 

I don't have a propane flame to hand but  I don't quite see that
difference with the methane flame. Yes flame speed is what stops the
flame popping back below the venturi.

The thing I understood about the 2 stage blue flames of a methane
flame, and I cannot remember  how this was with a town gas flame, is
that the inner cone (the hottest part) is the oxidation of all the
hydrogen and the partial oxidation of the carbon to CO. Then as you
say the outer blue cone is  produced by the diffusion  of air into the
flame. The town gas flame, which was available in the science room at
my school prior to 1967, was CO and H2 with up to 10% N2 and I think
it also had the two cones but memory is vague, I just remember
lighting the Busen burner with the air slide close to give a yellow
diffuse flame and then opening the slide to premix air and get the
blue flame. So in this case was the H2 burned with premixed air and
then the CO in the diffuse flame?

Has anyone noticed this two cone flame effect with woodgas when it is
premixed. I only recall a single flame, often tinged purple which I
put down to the primary combustion volatilising potassium ions??

Andrew