Capt. Geoffrey Thorpe wrote:
wrote in message
ups.com...
Montblack wrote:
How much does the 15 minutes of air weigh - that you run through an
(average) rotax engine?
At 4 gallons per hour, the fuel rate is 6*4=24 pounds per hour. (aprox
60% power)

The air / fuel ratio of gasoline engines is about 14 / 1, so the
airflow rate would be 336 pounds of air per hour. At standard
conditions, air weighs about 0.075 pounds per cubic foot, so the air
flow rate expressed in cubic feet per minute would be 336/0.075/60=75
cfm.

tom


But of course, nearly 80 percent of that air is N2 and stuff that isn't
required for the exothermic reaction with the fuel.


Not required for the exothermic reaction, but is required to push the
pistons. The burning gas heats the excess N2, which expands to push the
piston with much lower heat than the welding torch flame that would
result otherwise. If you didn't have all that extra non-reactive mass,
you'd need some way to provide it, lest you melt your piston in very
short order.