Hi Tom, Actually the exhaust gas does not dilute the gas going to the motor under standard operating procedures. The CO2 in the engine exhaust reacts with the hot carbon to make more CO. If there is any moisture in the air, it too will be a component of the exhaust which the hot carbon will convert to CO and H2.
Now your statement is correct if you put too much exhaust gas back into the charcoal gas generator. This is easily seen as you add more and more exhaust while watching the colors of the oxidation zone. The yellow hot oxidation zone turns to dark red, resulting in too much cooling which will not convet the CO2 into CO. This is not a standard operating procedure because it will eventually shut your engine down.
Regarding multiple nozzles. I have not experimented with it but my feeling is each one will be just as hot. The lobe of hot charcoal may be smaller, but the temp will not change. I suppose there is a point you could get too many nozzles. In this case the fire is cooler but you run the danger of not getting the oxidation zone hot enough to convert CO2 to CO. It will probably be very dependent on the pull of the engine too. Just my 2 cents for what it is worth
Gary in PA