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

[Paul Medwell]

Unless there is a specific question that would benefit this mailing 
list, without seeing and knowing the intricacies of particular 
commercial burners I can't, won't and don't see the point of making any 
comment on those, however, I'd like to respond to a couple of the more 
general issues...

> <snip> If a natural gas flame is not pre-mixed it needs more time and 
> space to burn well.  For a given number of Joules it needs more 
> volume.  This can be demonstrated (be careful!) by closing the 
> premixing hole in a gas stove burner and watching what happens. <snip>

Comparing the premixed flame length to a nonpremixed flame length is 
like comparing chalk-and-cheese. The laminar flame thickness is 
surprisingly similar, but not the total flame length. However, the 
initial discussion came from the comparison of methane and propane, so 
in terms of flame length, I'll steal an example from the second edition 
of Steve Turns' wonderful textbook...
Examples 13.1 and 13.2 do the exact task of comparing flame length for 
the same burner geometry and heat input. Paraphrasing the question: 
"Estimate the flame length of a propane jet flame in air at ambient 
conditions, with a fuel mass flow-rate of 3.66 g/s and a jet exit 
diameter of 6.17mm. Compare the flame length of a methane flame for the 
same heat release and jet exit diameter."
The answer:  Propane flame length = 1.94m, Methane flame length = 1.71m
This is only one example, but demonstrates that the volumetric heating 
capacity of the fuel does not proportionally affect the flame length.

> <snip> Is there a common device burning natural gas that does not use 
> a premixed flame? <snip>
>

Basically any furnace firing natural gas (e.g. cement plant, glass 
plant, steel plant,....)

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