Will the high pressure that develops at the intersection

of the exhaust

and inner tube drive the exhaust gases backwards and
out thru the cooling tube?

Scott Gettings

Scott, A adjustment might be needed in where the inside tube stops. 
There are many uses of annular exit mufflers. The pulses directed 
down the tailpipe DO create LOW pressure at the exit of the inside 
tube. In a tractor configuration a forward facing opening in the 
cowl will also allow the air to be pushed through the center tube 
as well. The key is to be sure the exhaust flow is turned to flow 
into the tailpipe. The continuing exhaust pulses causes the continued 
flow. There is momentum in the exhaust gas that prevents it from 
turning around. When you shut off the engine the exhaust gas
 WILL backflow out the front. Bill Jepson

 
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