Long Haul Exhuast

[jtr]

Just wondering, when I lob off on a long haul, and burn up 150t of Jet A-1, how much CO2, CO, NO(2?) etc is produced?

[Old Aero Guy]

The CO2 is pretty easy, just multiply the Fuel Burned weight by 3.16 to get the CO2 weight.

The rest of the pollutants depend on the particular type of engine involved.

[jtr]

So 150t = 470ish t of CO2:eek:

[Notso Fantastic]

Yeah, but that night the Amazonian Rain Forest gobbles it up and spits out Oxygen again. So if the Brazilian farmers are burning up the rain forest, shoot a farmer and it's all in balance again. And as for all them cows........methane! My Word, the methane!

I've come to the personal conclusion that all this 'man-made pollution- we're poisoning the world' green philosophy is nonsense. Several volcanos or one super volcano will spit out more pollutants than mankind can. All the animals in all history happily producing all the methane they can (and I have to admit I have been known to join them on occasion) don't seem to have had us choking yet. Ice Ages come and go quite happily of their own accord, probably all to do with sunspots or the precession of the poles whatever- mankinds involvement is negligible. But it doesn't fit in with current Green philosophy ('it's all OUR fault, we must get out of our cars and ride bikes'). I shouldn't worry about it! By the way, what was the question again?

[lomapaseo]

Right on Notso Fantastic!

Hell one Gulf war will add more pollutant than 50 years of crappy flying.

The greens just don't have their priorities right. There's far bigger things that affect pollutants to go after, but I guess they feel good after making a billion dollar impact against an industry without real relavancy.

Oops, I've slipped off my soapbox and broke my crowne.

[BLK 33]

HEEELLLPPP! Can someone explain how 470t of gas can come out of 150t fuel,

and,

as I watch various 777s depart, the stuff emanating from the UA ones is so much blacker ( not necessarily less benign? ) than any other airline's 777.

[Specnut727]

Here's a rough explanation of BLK 33's question (mech engineer's idea of a chemical engineering question, so numbers aren't exact). Any chemical engineer's out there are quite welcome to correct me if I'm wrong.

For 'complete' combustion of 140 tonnes of Jet-A1 you need to stuff about 1,600 tonnes of air into the core engine (bypass air is another story). Total into the engine 1,740 tonnes.

Out of the tailpipe you'll get about 420 tonnes of CO2, 100 tonnes of water, and 1,220 tonnes of nitrogen. Total out of engine 1,740 tonnes.

The 140 tonnes of Jet-A1 contained about 80 tonnes of C, so with 340 tonnes of O2 from the air, we have 420 tonnes of CO2.

About 7 tonnes of H2 in the Jet-A1 combined with more O2 from the air gives us the 100 tonnes of water. That's where the contrail comes from.

Both CO and NOX are products of inefficient combustion, so should only be there in small amounts (measured in parts per million).

Not sure about the black exhaust of the 777. It would be soot from really poor, incomplete combustion. Haven't noticed it much since the days of early 707's and DC-8's

[411A]

.......or, the Convair 880's, now that was black.

Anyone remember 1958...it was International Geophysical Year, and nearly everyone was worried about the coming ICE age.

How perceptions change.

IF you're on the coast (low level)....move, the tide is rising:eek: :rolleyes:

[ETOPS]

When you load up in Europe you are getting Jet A1 but in the states it is Jet A. The refining process is different and Jet A is known as a "wide cut" fuel hence the different freeze points.....

[lunkenheimer]

The remarks about the rain forest etc. are correct but bear in mind that the carbon dioxide being liberated by burning fossil fuels has been 'out of circulation' for millions of years. The end effect of burning these fuels will be to place this CO2 back in circulation where it will unfortunately have the definite effect of increasing the concentration in the atmosphere. Whether or not this is serious is the important part of the debate.

Sorry to digress...

[Capt Claret]

Does the combustion in the engine actually produce nitrogen, or is the nitrogen that is naturally in the air simply sucked in and then blown out?

[Specnut727]

G'day CC, yes, air is nearly 80% nitrogen, which just gets sucked in, heated, and blown out the back. We can't do anything about it, but it costs us quite a bit of fuel just to heat it to exhaust temperature. Works just the same for piston engines.

[GlueBall]

Just the Mount St. Helen's eruption alone had spewed more CO2 into the atmosphere than that of all the World's automobile exhausts.

In any case, with World War III just around the corner, a nuclear winter would easily take care of any global warming.

[Mike Southern]

Just a small correction to Specnut...

The NOx doesn't come from inefficient combustion, it is part of the 80% or so in the atmos which, under the high temp/pressure environment inside the jet engine, reacts with the Oxygen - and it gets blown out the back end. Other than that a great explanation.

Inefficient combustion will indeed lead to CO and soot (brown/black exhaust trails), but I would have thought that there would be a vast excess of oxygen in the jet engine, so if that is happening it must be poor vaporisation of the fuel

[Dupre]

Notso Fantastic: What you say is wrong! Forests are steady state - a mature forest loses just as much carbon as it absorbs! (losing carbon mainly through decomposition). Forests only act as sponges when they are not mature. Nearly all of the worlds forests are mature, and so DO NOT chew through any more carbon than they spit out - they are reservoirs, not sinks.

How many cows would nature have had grazing? Not many! Humans have caused all that methane by creating large stocks of cattle and sheep that would not have been there otherwise! (One partial solution to that would be to affix little pilot lights to the rear of the animals at birth...)

Glueball: Look at the averages - 5x10^11 kg/year CO2 from volcanic activity. 18x10^12 kg/year from all human activities. So humans produce 36 times the amount of CO2 that volcanoes do - it's no use making an arbitrary comparison that no-one can put into context with any accuracy (playing on their emotions, rather than giving hard numbers).

As for whether it is significant? Pre industrial revolution CO2 was 210-350ppm (averaging 280ppm). Now it's more than 367ppm and rising - a definite increase. The computer models that estimate what this will do the Earth's temperature all say it will rise, between 3 and 8 degrees celcius. This will destroy some low levels of the food chain, and hence the global ecosystem (including humans) will collapse. No-one knows exactly when, nor how bad the collapse will be, but it will probably be extremely ugly - I personally think a war over food and water will kill most of the human population. War is extremely unpleasant.

So yes, it is significant, but no, it is not exact.

[Specnut727]

G'day Mike S, Thanks for the correction and comment.

Of course you are correct about NOx. That opens up a whole new can of worms on engine design to reduce the effects of temperature and pressure. As usual, we're stuck between a rock and a hard place, because generally, higher temperature and pressure inside the engine lead to increased efficiency, and also increased NOx production. Same problem with piston engines. The automotive guys have to use catalytic converters etc to reduce NOx, but so far, I don't think anything like that is practical on turbine engines.

Thanks again, you've prompted me to do some more reading.

[Groaner]

Dupre,

Not quite right about (mature) forests being steady-state and not sequestering carbon. Forest detritus builds up (some of the carbon indeed recycles into the atmosphere, but some does not), eventually (geological timing) gets buried, eventually turns into coal and/or hydrocarbons.

A mature forest does indeed suck up carbon from the atmosphere. Immature forests suck up even more (net), because the forest mass (trunks, leaves etc) increases, and has a large carbon component.

[Notso Fantastic]

Dupre-<<Look at the averages - 5x10^11 kg/year CO2 from volcanic activity. 18x10^12 kg/year from all human activities. So humans produce 36 times the amount of CO2 that volcanoes do - it's no use making an arbitrary comparison that no-one can put into context with any accuracy (playing on their emotions, rather than giving hard numbers).>>

It's all very well trotting out (hard) numbers like this, but where exactly do they come from and really, how exact do you think they are. I would say they were 'leap of faith' environmentalists projections producing the result they want. The world has a 'steady state' restoring trend (otherwise it would have gone runaway greenhouse or the other way eons ago). I would say that it can cope with the minute amount of carbons etc humans 'pollute' with- it has after all coped with monstrous meteors opening up the crust and creating continent wide super volcanos (i.e. Indian Deccan Traps). I hope humans have advanced enough to take off to another world when conditions get bad enough (if they do- the jury is still out) and go pollute elsewhere- but you can bet, Ice Ages come and go, climates change with volcanic activity. The sum total of human damage ain't so bad and will be recovered from. I used to be a strong environmentalist in Greenpeace and FOE until I realised they were mainly on a doom preaching strangely political agenda and definitely dodgy. I burn hundreds of tons of fuel a day with a clean conscience!

[Oktas8]

NOx (mixture of NO and NO2) is dirty brown in colour; it is a key ingredient in smog that most of us have seen around cities in inversion conditions.

I would suppose (never read it definitively) that NOx is the main cause of brown exhaust trails. You can see the brown tint quite clearly even on NG jets if you stand in a position to look up the exhaust trail - looking up the length of the exhaust as it were.

Regarding the CO2 numbers quoted earlier - the numbers weren't quite right Specnut. 12t of C reacts with 32t of O2 to make 44t of CO2.

So 80t of C in Jet A(1) should react with air to give 293t of CO2.

cheers,
O8

[Old Aero Guy]

Oktas8,

Can't agree with your analysis. It would be fine if kerosene were a pure carbon.
(Carbon(12)+Oxygen Molecule(32))/Carbon 12 = 44/12 = 3.66 = 293/80

However, fuel is a hydrocarbon so each carbon atom has hydrogen atoms associated with it.
As was noted earlier, the two most prominent byproducts of kerosene combustion are CO2 and H2O.
The hydrogen present throws off the ratio developed above.

Fuel density varies around the world based on the carbon/hydrogen ratio of the crude used to refine it.
On average, the ratio of CO2 to fuel is 3.155.

Therefore, 80 tonnes of fuel would produce 252 tonnes of CO2.

[Mike Southern]

Just another add-on to the Dupre/Notso debate;

If all us humung beans did was belch out CO2 it wouldn't be so bad, unfortunately we seem to have been clever enough to develop molecules which are thousands of times more potent than CO2 in terms of their greenhouse capability (and jolly stable too, so they hang around for ages'n'ages).

Furthermore, just to make everyone feel even worse, the exhaust from planes is injected into the upper atmos where things work better as greenhouse gases and are no so easily mixed up with the stuff that plants breathe down here at ground level. Ho hum, still I'm more part of the problem than part of the solution, so I don't wish to appear to be holier than anyone else....

I seem to remember reading something shortly after Sep 11th about the impact (or lack of) on the climate attributed to the empty skies over USA, anyone else remember that.... something about the insuylating properties of contrails if my booze addled memory serves...

[Oktas8]

Thanks for the clarification OAG - my post was quite misleading. It was written with the comment that inspired it in mind, reproduced here:

The 140 tonnes of Jet-A1 contained about 80 tonnes of C, so with 340 tonnes of O2 from the air, we have 420 tonnes of CO2.

In context, my working was correct I think. I take your point about the average ratio of CO2 to fuel being 3.155. Perhaps the appropriate correction to the above statement should be that there is ~120t of C in 140t of fuel, and left the CO2 product alone?

This is all getting quite hair-splitting. I'm off...
O8

[Old Aero Guy]

No problem Oktas8.

After posting, I realized part of the problem was the earlier posting saying there was only 80 tonnes of carbon in 140 tonnes of fuel.

I quite agree that the actual carbon content is 120 tonnes.

I also agree that this topic is getting a bit stale.