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another burner question/paul t.

updated thu 12 dec 02


Craig Martell on wed 11 dec 02

Paul asked:
>What is a hybrid compound injector?

Hello Paul:

A compound injector is a burner with more than one mixing stage. There's
the main mixer with the air shutter and orifice etc, which entrains air
with a pressure drop and generated negative pressure in the mixing
chamber. Then you have another stage with a pressure drop made by an
expansion of the tube diameter. Then the gas passes into the venturi and
finally thru whatever kind of nozzle you have attached. The term "hybrid",
refers only to the fact that I'm making this burner with spare parts from
different manufacturers plus some parts I'm making myself.

>So much in this subject seems to lack quantifiable measurement.
>there is so little firm data. Because there is no firm data any bodies
>opinion is right and what makes for more right is emotional certainty as
>opposed to reasoning.

The design and function of venturi type burners, or inspirating burners is
not discussed much by engineers who work for combustion and fuel
engineering companies. The reason for this is obvious. The best we can do
is devour what material is available and look at different types of burners
in an effort to figure out what works and how we can make stuff work better
for us. Trial and error. Live and learn!!

> Form your posts I gather that you feel that with enough thought you can
>build a venturi system that utilizes air efficiency enough to make it as
>efficient at mixing air and gas as in forced air burner - If you crack that
>I would be interested too .

I don't know if I can do any of this or not. I'm trying some prototype
burners and I'll let you know how it goes.

>As for the forced air burner I am wondering what mixes the air and gas in
>the forced air burner . just because it is forced through the same tube it
>does not necessarily mix, or is the turbulence in the length of tube enough
>to mix the gas and air.

Burners are designed to move air. Doing it without a blower requires some
sophisticated physics but the mixing part is pretty much the same with
both. With forced air, you don't have to "entrain" any air and you don't
need as much secondary air and you can cut chimney height etc. A blower
will mix air thru sheer force and the fact that a combustion reaction
(flame) is seeking oxygen to react with the fuel source. The blower gives
the fuel source all the oxygen it needs, providing things are set correctly.

regards, Craig Martell Hopewell, Oregon