# How Much Water is there in Jet Engine Exhaust? [About 1.3 Gallons per Gallon of Fuel Used]

Discussion in 'Contrails and Chemtrails' started by NikTesla, Jul 25, 2014.

1. ### JazzyClosed Account

Yes, a simple sword through the heart normally works.

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2. ### Sierra EchoNew Member

"Lead in jet fuel" why when where? Citation?

I suspect they were confusing jet fuel with avgas, which still generally contains lead.

4. ### penkNew Member

I'll note the OP has vanished (hopefully with their tail firmly between their legs) and is no longer participating, so I think this thread is dead.

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5. ### TrailblazerModeratorStaff Member

Just a slight correction to the title of this thread. It's correct to say that you get on average about 1.37 units of water per unit of kerosene by mass, but not by volume. You also have to take into account the fact that kerosene is less dense than water, by a factor of about 0.82.

So a gallon of kerosene contains less mass units than a gallon of water, meaning that the VOLUME of water produced from a gallon of kerosene will be more like 1.37 x 0.82 = 1.12 gallons.

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6. ### rhymerezNew Member

In a mile a jetliner uses at most 50 of fuel, most quite a bit less, per mile. That would make around 8 gallons of water. Will someone please show me, using the equations that describe the actions of water vapor in the atmosphere how that little amount of water can spread out to be 5 degrees wide at 36k feet(that would be an area .6 miles by one mile) and persist for 30 minutes in a clear sky? It must solved in the dynamic atmosphere.
You say that it is just water vapor, there are equations that describe the actions of water vapor in the atmosphere. Use science to show the amount of water vapor put out by a jetliner can act in the manner observed.
If you think my numbers are too large an area or long of a time, show how much area and how long a cloud could persist.

7. ### TrailblazerModeratorStaff Member

The water from the exhaust is only a tiny part (1 in 10,000 or less) of the mass of a persistent contrail. The rest of it comes from the surrounding atmosphere (which is why contrails only persist and spread when there is sufficient water in the surrounding air).

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Even with short contrails the majority of the water in the trail you see comes from the atmosphere. Contrails form when the relative humidity (with respect to water) is briefly raised above 100% which triggers condensation.

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9. ### TWCobraSenior Member

The other question to ask is how can the substances ascribed by chemtrail believers; aluminium, barium and strontium etc, exhibit the trait of expansion without the dissipation that happens with every other substance (smoke oil, pesticides, fire suppressants, cloud seeding materials etc etc) that gets sprayed into the atmosphere.

Contrails grow because exhaust water is released into an atmospheric region already saturated with water.

No such supply of supposed chemtrail chemicals exist in that same atmosphere, so how do chemtrails expand and thicken?

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10. ### Hama NeggsSenior Member

Asked a hundred times. Answered zero times, except for some vague references to the idea that "chemtrails" are a combination of normal contrails + added chemicals or some very reaching references to the idea of moisture-absorbing substances (I forget what that is called, technically).

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Hygroscopic.

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12. ### Clouds GivemethewilliesActive Member

How did you reach this conclusion?

Via lack of coffee. I was thinking of the case when the humidity is JUST too low for contrails to persist, but even then the atmospheric water will only be the majority at certain temperatures.

So in a non-persistent contrail, the majority of the water still might be atmospheric, but probably not.

Last edited: Apr 3, 2017
14. ### Clouds GivemethewilliesActive Member

I think it is somewhat moot if a particular water molecule in an ice contrail came from the engine or the surrounding air. There is no net mass increase in the mass of a short contrail (RHi <100%) due to water from the surrounding air, above that from the engine exhaust alone. .IMO

I agree it's somewhat moot, I was originally just trying to convey the point that not everything you see in a contrail is from the jet exhaust. A contrail particle is going to go through a variety of stages during mixing of the exhaust with the ambient air
1. condensation from gas to liquid water, RHw > 100%
2. freezing to ice
3. deposition of ice, RHi > 100%
4. sublimation to gas, RHi < 100% (maybe after fully mixed)
If there's any local humidity then some of the molecules are going to be from the ambient air (both intake, and the mixed ambient air).

16. ### SvartbjørnSenior Member

Just for the layman's sake (like me).. how can you have more than 100% humidity? Is that referring to greater than 100% in that specific localized streak where the aircraft is flying the RHI is temporarily raised over 100% behind the engine; or is that more in reference to overall humidity at altitude?

*Edit - I apologize for that nasty run-on.. just couldnt think of a better way to be specific enough for definition.

Relative Humidity is not the percentage of air that is water.

Relative Humidity is the amount of water in the air expressed as a percentage of the amount of water that air can hold before it starts to condense out (RHw) or build up (deposit) on an ice surface (RHi).

So if a cubic meter of air was capable of holding 100 grams of water before mist forms and it had 30, then that's 30% RHw

So if RH is above 100% that means that it will condense out (RHw) or deposit (RHi) - providing there's something that it can do that on to.

Condensing is easier, so if we are above 100% RHw (w=water) then we are generally in a mist or cloud. Deposition is harder for water, as it likes an ice nuclei (or similar molecule, like silver iodide) to deposit on. So if there's no ice around (or no ice nuclei) then we can easily have RHi (i=ice) above 100%. The aire is all ready to deposit ice, but there's nothing to deposit it on.

When a plane comes along it actually (mostly) does the condensing stage first, and that freezes, and provides something for the ice to deposit on.

Last edited: Apr 5, 2017
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And in my post above, normally I'm referring to RHI>100% in the ambient air - so the air is persistent contrail friendly. But here I'm talking about short contrails, and the brief time while the air and exhaust are still mixing. The ambient air is <100% RHi, but the mixture is >100% RHi for a few seconds, allowing the ice crystals to increase in size.

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19. ### SvartbjørnSenior Member

Gotcha.. ok that makes sense.. I just wanted to make sure I was on the same page you were on, which I wasnt obviously lol. Thanks Mick

20. ### TrailblazerModeratorStaff Member

Related to this, I have seen the claim from chemtrail believers that because the air at high altitude is thinner and can hold less water, that makes contrails less likely. See bottom left here:

In fact, that's almost totally backwards. If the air can hold less water, then it takes less additional water to push the relative humidity over 100% and initiate condensation.

As this graph shows, at -40C the air can hold only a tiny amount of water, far less than a gram per cubic metre, compared to about 16 grams at room temperature.

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21. ### skephuSenior Member

Note that the air itself has nothing to do with it. It's not the air that somehow "holds" water. It's the volume. If you remove all the air from the given volume, nothing changes. So phrases like "x amount of air can hold y amount of water vapor" are inaccurate.

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22. ### Clouds GivemethewilliesActive Member

" you remove all the air from the given volume, nothing changes" Not quite "nothing", the relative humidity changes, as does the mass mixing ratio.

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23. ### skephuSenior Member

No, the relative humidity would not change.

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24. ### TrailblazerModeratorStaff Member

You are correct: relative humidity is defined as the ratio of the partial pressure of water vapour to the equilibrium vapour pressure over water (or ice, as appropriate), and by the ideal gas law, partial pressures are independent of the presence of any other gases (eg the air). So the air doesn't play any part in "holding the water", but I'm not sure how useful it is to make that distinction, considering that in the real world the air is there.

It's easier to understand aerodynamic contrails if you consider the air expanding in the low pressure zone above an aircraft wing: the temperature of the parcel of air drops, and therefore the relative humidity will increase. Planes fly in air, they don't fly in water vapour.

That is correct. If you removed just the air from the atmosphere, you wouldn't be left with a vacuum, and the oceans wouldn't boil away. You'd have a water vapour atmosphere containing exactly the same amount of water vapour there is currently in the atmosphere, and the equilibrium wouldn't change.

I think

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25. ### Clouds GivemethewilliesActive Member

Skitt’s Law . :-(

26. ### Cq ZhangNew Member

Dear Mick, is there any reference for these figures? I saw them before, but couldn't find the source.