Vapour trails

"Capt.Doug" wrote

Jet fuel averages 6.7 pounds per gallon with more BTUs, so the
stoichiometric ratio is slightly different.

More air, to take advantage of the BTU's, right? Plus jets are more
efficient at altitude, so more air again, right?.

Much of the air ingested by a
jet engine is used for cooling, not for burning. Do we include this air as
being ingested?

For what we were talking about, which is how much air is being used to make
con trails, (my take on it) it would seem to me we are talking about the air
that is being used to burn fuel.

Do we include the fan's cold stream as being ingested?

I wouldn't. It's just a big fancy prop, and props are not making any con
trails.

Another thing that is being overlooked, is the HP rating of the engine. In
talking about the air being injested, we have to remember that piston
engines are at most making a couple thousand HP (most lots less than that)
and the turbine engines on large jetliners are making multiples more power,
burning more fuel, using more air, and making more water vapor, and making
bigger contrails.

I'm no expert on this stuff, but I think my thinking (and guestimates) are
about right. After all, the original question was not a highly defined,
quanitative question, and neither is the answer. g
--
Jim in NC