## CO2 Emissions from Aviation Growing Rapidly

##### 27 June 2006
 Total aviation carbon dioxide emissions resulting from six different scenarios for aircraft fuel use. Click to enlarge.

Carbon emissions from aviation could triple to 0.40 Gt carbon/year to account for 3% of the world’s anthropogenic carbon emissions by 2050 (relative to the mid-range IPCC emission scenario (IS92a)) according to the reference scenario in the latest climate change study by scientists at Manchester Metropolitan University (MMU) (UK). For the range of scenarios, the range of increase in carbon dioxide emissions from aviation to 2050 could be 1.6 to 10 times the value in 1992.

In 1992, air traffic contributed 2% of the then global anthropogenic carbon emissions, or 0.14 Gt carbon/year—about 13% of carbon dioxide emissions from all transportation sources.

Scientists at MMU’s Centre for Air Transport and the Environment calculated C02 emissions based on traffic predictions from sources including the International Civil Aviation Organization. The forecasts account for improvements in technology and air traffic management as total air traffic is predicted to increase by six to eight times 2000 levels by 2050.

Preliminary results will be presented to the Transport, Atmosphere and Climate conference jointly staged by CATE and the German Aerospace Center (DLR) at Oxford University on June 26-29.

This research confirms the message from the Aviation White Paper that the aviation sector is forecast to make up a considerable proportion of global emissions in the future. The results highlight that the rate of growth of aviation is far outstripping the rate of technological progress and improvements in efficiency.

—David Lee, Professor of Atmospheric Science at MMU

New aircraft today are about 70% more fuel efficient per passenger-km than those built 40 years ago. The majority of this gain has been achieved through engine improvements and the remainder from airframe design improvement.

A further 20% improvement in fuel efficiency is expected by 2015 and a 40 to 50% improvement by 2050 relative to aircraft produced today.

The 2050 scenarios developed for this report already incorporate these fuel efficiency gains when estimating fuel use and emissions. Engine efficiency improvements reduce the specific fuel consumption and most types of emissions; however, contrails may increase and, without advances in combuster technology, NOx emissions may also increase.

The report notes that engine research programs are in progress with the goal of reducing Landing and Take-off cycle (LTO) emissions of NOx by up to 70% from today’s regulatory standards, while also improving engine fuel consumption by 8 to 10%, over the most recently produced engines, by about 2010.

There would not appear to be any practical alternatives to kerosene-based fuels for commercial jet aircraft for the next several decades.

The report also concludes that improvements in air traffic management (ATM) and other operational procedures could reduce aviation fuel burn by between 8 and 18%.

The results are part of an EC audit of emissions called QUANTIFY which is looking at the relative effects of different modes of transport—road, rail, air and sea—on the climate. The study also indicates that shipping could have a stronger effect than aviation from its CO2.

Resources:

What is the development status of Liquid Hydrogen for planes?
Perhaps NASA should send up one fewer mission and get going on this project.

The state of aviation development seems to have stalled.
A current small private piston engine prop. plane has the SAME type engine used before WWII and they burn leaded gas. By the way, they are 4 stroke. The so called 2 stoke wieght advantage goes away when you have to carry all the extra fuel most of them burn. Some homebuilds do use them however.
There have been some great developments in diesel engines for prop planes.
The new airbus and boeing planes are not faster than the ones they replace. They do have better fuel economy and are not as noisy.
The SST's like Concord are gone.
The dreamliner from boeing was cancelled, it would have been as fast as possible without breaking the sound barrier.

I hate to be the nitpicky guy, but it was the Sonic Cruiser that was cancelled, not the Dreamliner. The Dreamliner is better known as the 787, and is kicking Airbus's ass in the marketplace.

It is not what you do not know that hurts you, it is what you know that is not so...
Thank you for the correction on the Sonic Cruiser. I think when you are under competition you have to innovate yourself out of it. I was disappointed when it was cancelled.
The new Airbus looks like a 747 designed by a committee.
They should do well when converted to air frieght.

Well the problem with the airbus is they spent far too much money developing it and it costs far to much money to buy. On the other hand boeing managed to make a stretched version of thier fuel eff plane and make it more so much cheaper.

The main market for the super airbus is links that are full and can only expand via larger planes.. most of those are in asia.

The main problem with emissions from aviation are

(a) jet fuel is not taxed, so people fly on weekend jaunts and poorly prepared business trips because it's cheap to do so. In the process, they produce more CO2 on one flight than they save all year by driving a more fuel efficient vehicle (if they own one).

(b) emissions (e.g. N20) are released high up in the stratosphere, where they can do more harm.

Wrt Boeing vs. Airbus: neither the 787 nor the 380 are BWB designs. Those would feature a lower top speed but higher fuel efficiency. Apparently, focus groups hated the idea of extremely wide rows with little or no natural light.

http://oea.larc.nasa.gov/PAIS/BWB.html
http://www.twitt.org/bldwing.htm

Passenger and freight airships are the way forward!!
That and globally negotiated incrementally increasing carbon tax.

I rest my case

( and offer no supporting evidence)

Rafael - I'm somewhat of an aviation enthusiast, and am always interested in new aircraft design. But as a passenger, I'm not sure I'd want to fly in a BWB either. The most likely application of this design will be in next-gen military airlifters.

Where in the world is Jet A not taxed? In the US it costs nearly $3/gal on average due to the taxes. The last sentence, "The study also indicates that shipping could have a stronger effect than aviation from its CO2." What's that all about? Boat transport is the most efficient. Is Wal-Mart buying so much from China that this is really outweighing ait travel? When it comes to CO2 emmisions, big ship slow speed diesel engines are great. They are 50% eff. 180g/hp-hr of fuel is normal. Of course they are the very dirty in Every other way. 17g/kW-h of NOx, 2.5% sulfur in the heavy bunker fuel, on average, making SOx. That is 25,000 parts per million versus 500 parts per million on current US diesel fuel. Max legal is now 45,000 PPM. In northern europe SECA next year it goes down to .5% or 5000ppm.In the fall, ULSD will be below 15 ppm. Particulate matter is completely unregulated at sea, and in port the use a modified Ringlemann scale to see what percentage of the sky is obscured by smoke. It is not that ships are getting worse, everyone else is getting better. THe biggest unregulated pollution source in LA right now is the ship engine pollution. Rafael, Jet fuel is more expensive nowadays. At$2+ (from $0.5 just 4 years ago), they are trimming items left and right. They are adding winglets to take advantage of wingtip vortex modification. Computerized route modification to take advantage of wind paterns are also better used. Matthew, While BWB aircraft are efficient (B-2 runs on less fuel than others), the larger ones face problems of having very thick wings. Pressurization of passenger jets could also be a problem due to large flat sections (most pressurized bodies are round/cylindrical). Here's some stuff on aircraft concepts/designs: http://www.globalsecurity.org/military/systems/aircraft/gra.htm http://www.globalsecurity.org/military/systems/aircraft/nsa.htm http://www.globalsecurity.org/military/systems/aircraft/gra-pics.htm _ also: http://www.globalsecurity.org/military/systems/aircraft/future.htm http://www.globalsecurity.org/military/systems/aircraft/hlvtol.htm http://www.globalsecurity.org/military/systems/aircraft/ultra.htm JPadula: A combined cycle (gas turbine/steam from blades-exhaust) propulsion system may yield 60%+ efficiency vs ~50% with today's large 2 cycle diesels. Ironic: Carbon tax, carbon fiber construction to save fuel and thus emmit less GHGs, ie. CO2 and NOX. Tom Deplume - you are right, jet fuel used on domestic US routes is taxed at$0.219 per gallon. Last year, the tax collection procedure was changed to address the industry's complaints regarding possible fraud by truckers - which is illegal as Jet-A contains lead. Now, they are asking for a complete tax amnesty.

http://en.wikipedia.org/wiki/Jet_fuel

"Under the legislation, the collection of aviation fuel taxes would be suspended until October 1, 2007, when all aviation taxes expire."

International flights, including those between European countries, are subject to old treaties that explicitly exempt the aviation sector from fuel taxes. The EU is trying to fix that, beginning with intra-European flights but is facing an uphill battle from airlines that are well-connected with national politicians:

http://www.euractiv.com/en/transport/meps-want-polluter-pays-principle-applied-air-traffic/article-155694

Are you guys sure that boats are as super efficient as you think? I know that if you compare an SUV to a powerboat for example, both with a 5.7 liter General Motors engine, the SUV can hold 7-8 people or so and get around 15-18 miles per gallon on the highway. A boat large enough to accomidate 7-8 people doing even 50mph will be lucky to get more than 4 miles per gallon. At low speed it isn't much better since it never gets on plane.

I know for bulky stuff like cars, ships are the cheapest way to transport to most venues, although I've seen aircraft used even for bulk automotive transport, esp of high dollar vehicles like Mercedes, so it certainly exists. I'd imagine that the main advantage of ships is that it's mainly just the weight that matters, not the size, but for aircraft you're very constrained by both weight and size together.

3% by 2050? Not something we should be focusing on.

We could always go back to using zeppelins. Maybe a nuclear powered model that wouldn't need frequent refueling?

To reduce CO2 emission on aircraft, there is no better way than to use LH2 as fuel. No matter how much more efficient aircraft is going to be there will eventually be a physical limit that one cannot go beyond. Kinda like Moore's law in integrated circuitry. Meanwhile, more affluent China and India will grow their domestic aviation industry and the aviation CO2 emission will hit the roof.

All carbon-based fuels are too heavy for aircraft use. For long-range flight, over 1/3 to 1/2 of an aircraft's gross weight is devoted to fuel, while less than 1/3 to 1/4 of the gross weight is payload. Liquid Hydrogen has 3 1/2 times the energy per unit weight than kerosene. If converted to LH2, the payload of a commercial jet can double for a given unit of fuel energy. So, even if LH2 is to cost double that of kerosene per unit BTU, it will still come out even commercially, but will be a lot better for the environment. GE and others are developing ways to make H2 cost competitive with petroleum fuel in the near future. A modified gas turbine should be able to run on hydrogen equally well. Given the high detonation potential of H2, a novel detonation jet engine of the future can even cut fuel usage by 30% or more. The LH2 takes up more volume than kerosene, but not too much more, and a cylindrical insulated cryogenic tank put up in the roof of the airliner can be use to store LH2. The wing can store an additional amount of LH2.

Blended-Wing-Body (BWB) design has drawbacks in that its stability in the pitch axis is less than desirable, and is more susceptible to rapid flipping over, stall or spin in turbulent air. BWB has poor longitudinal authority and stability, hence cannot use large front and real flaps of the wing to tripple its wing's coefficient of lift during take off or landing. The use of large flaps causes great change in pitching moment coefficient of an airfoil, requiring a long fuselage to provide long tail moment arm for adequate authority in the pitch axis. With much smaller flaps, the wing area required will need to be twice as large during the takeoff and landing regime. But, such a huge wing area during high speed cruise will cause 2 times the G force upon encountering wind gust in flight. This means that every fastener, every structural component of a BWB aircraft must be designed to be 2 times stronger to withstand gust loading in flight. The weight saving in combining the wing and the fuselage will be lost in internal structural design to withstand higher gust loading. Furthermore, doubling the wing area will negate a lot of interference drag saving from blending the wing and body together.

which is illegal as Jet-A contains lead

Why would that be? It's not as if knocking were a problem for jet engines!

I think you are confusing it with aviation gasoline (used in aircraft piston engines).

The LH2 takes up more volume than kerosene, but not too much more,

Just (!) a factor of more than three, for a given quantity of fuel energy (LHV). This is a huge problem for aircraft design, all the way back to the failed 'Suntan' hydrogen-fueled spyplane effort. The need to keep the hydrogen very cold also severely complicates the design.

Hydrogen is even losing in many rocketry applications, where the importance of high propellant density is not always appreciated (high density ==> lower tank mass, lower pump power). This is especially relevant for first stages.

Good point, Paul.
But if you can double the payload for the same aircraft maximum gross weight, then, for the same payload, you can design the airplane lighter, a lot lighter, with smaller wings, smaller engines, smaller landing gears etc..You'll save a lot on structural weight, and guess what, you will need a lot less BTU to carry the same payload. So, the fuel volume may just double.

Paul,
Thanks again for bringing up a very important issue regarding the future of commercial aviation.
I did further look up and made some calculation. Let's take the Boeing 777, the latest Boeing model in production, with an empty operative weight of ~300,000 lbs and a gross takeoff weight of ~600,000 lbs, for ~300,000 lbs of useful load. This aircraft can seat ~400-440 in economical arrangement. Allowing 230-250 lbs per seat including luggage, which is more generous than FAA allowance of 180 lbs per passenger and 30 lbs luggage. So the maximum payload weight is ~100,000 lbs for the passenger version, leaving a remaining 200,000 lbs of useful load for fuel capacity. This should be good for a range of over 4000 nautical mi. Since LH2 weights 3-1/2 times less than kerosene for the same BTU value, expect weight of LH2 of ~60,000 lbs. So, with LH2, the total useful load required, fuel and payload,is now only 160,000 lbs instead of 300,000 lbs as when kerosene is used. This means that the aircraft can be totally redesigned aiming for much lower useful load. Every components can be made lighter and smaller, wings, engines, landing gears, tail empenage, and yes, even the fuselage, because a substantial amount of fuel is carried inside the fuselage as well as inside the wings. With much lighter fuel load, then the fuselage can be made lighter. So, now, we should shoot for a maximum gross weight rating of no more than ~300,000 lbs in order to obtain an useful load of ~150,000 lbs. Of the 150,000 lbs useful load, 100,000 lbs is payload as before. But, since the airplane is now smaller (Wings and Tail empanage) and and weighing half as much, it only requires 1/2 the fuel weight to fly as far, or may be a little more, given the fuselage that still must be of the same size in order to have sufficient space to carry the passenger load. So, instead of requiring 60,000 lbs of LH2 to carry a gross wt. of ~600,000 lbs, we now only need ~35,000 lbs of LH2 to fly a new airplane with a gross wt. of ~300,000 lbs. With fuel of 35,000 lbs of LH2 and 100,000 lbs of payload, we still have ~15,000 lbs of spare useful load capacity, perhaps for carrying extra USPS mail, parcels or other loads. So, even though LH2 requires 3x the volume of kerosene for the same BTU, less LH2 will be required, thus bringing down the increase in volume to 35,000 / 60,000 x 3 = 1.75. The aircraft fuselage can be made slightly taller to accompany the extra volume of fuel. The fuselage weight and drag increase will be quite small.

With smaller engines, fuel load, and airplane weight for a given payload, the cost of flying can be reduced by ~40% if the price of LH2 can be brought down to the same level of kerosene for a given BTU amount. If GE and others can bring down the price of LH2 as promised some day in the future, we will expect airlines and aircraft builders to switch to LH2 as the primary aviation fuel.

Roger: your calculations ignore some points.

The hydrogen tanks become larger, which increases the surface area of the plane, so the drag does not decrease to nearly the extent you suggest.

Second, the hydrogen cannot be stored in the wings (in a conventional aircraft, not a BWB, which was addressed by a previous post), as much jet fuel is, due to the need to minimize the thermal load on the cryogenic tanks. Distributing the load along the wing saves structural mass over putting it all in the fuselage, since in the latter case the wing must resist a larger bending force. So more of your mass savings evaporate.

Finally, most airplane flights are not over very long distances, so the fraction of fuel at takeoff is lower. Designing an entirely new fuel infrastructure for a minor fraction of the flights would be economically challenging.

Paul,
Very important details you have raised.

When the wing area is reduced by nearly 1/2, the wing volume will be reduce probably to a 1/3 of the previous wing volume, so, you are right, it is not worth it to put LH2 in the wings, especially when thick insulation layer will be needed. But, please realize that jet airliners has relative thin wings, and must store 1/2 or more of its fuel volume in the fuselage. So, before, you have ~80,000 lbs of fuel in the wings, and ~120,000 lbs of fuel in the fuselage. This, plus a heavier fuselage structure capable of holding 220,000 lbs or more of load, aka dead weight. With the newer lighter fuselage designed to handle less load, plus only 135,000 lbs of "dead weight", meaning that your new smaller wing now only have to handle ~1/2 of the bending load of the previous twice-as-large wing. Furthermore, a wing that is only 1/2 as large will have a wing span only 70% that of the larger wing when keeping the same wing aspect ratio. This shorter-span wing will further reduce the bending moment at the wing root, leading to less actual bending load proportionally. A point to consider in structural load design is that as the scale of the structure got larger, then all load-bearing structures if made of the same material must be proportionally thicker to support the weight of the larger structure. That's why dinosaurs and elephants have proportionally much larger bones diameter than smaller animals to support their weight. A larger structure has larger bending moment in addition to mere larger mass, necessitating heavier structure.

Assuming that 1/6th of the fuselage volume of the 777 is for fuel storage, then to double this fuel tank capacity in the new fuselage, its volume only has to be increased by 7/6, and its surface area only has to be increased by 7/6 raised to the 2/3 power = 1.11, or only 11% larger. However, this not accurate, since you want to keep the fuselage's width the same, and only to enlarge its height. So, the increase in surface area may amount to about ~14%. The total wet surface area of the fuselage is well less than 1/2 of the total wet surface area of the whole aircraft, so the increase in fuselage size contributes to but less than 7% of the total skin friction drag of the aircraft. Airliners are designed to cruise at speed nearly the maximum lift/drag ratio (L/D), and at this speed, the skin friction drag made up ~ 2/5 of the total aerodynamic drag, considering that at 0.8 Mach, you are approaching compressibility, hence considerable wave drag occur that would be a lot higher than cruising at 0.6 Mach or lower, while induced drag at maximum L/D speed at 0.8 Mach would grab another 2/5 of total drag. So, 7% x 2/5 = 3%. A measly 3%. I hope you don't think that I took accounting lessons from Andrew Fastow, CFO of Enron. To reduce wave drag, keep the nose section fairly sharp and increase cross-sectional area in front and behind the wing.

"Most airplanes flight are not over long distances, so the fuel fraction of takeoff would be lower" Ah, great, I'm so glad to hear that. Quite true! So, for most of the percentage of the flights, you don't have to worry about LH2 taking up too much of fuel volume, do you? Now that you admit that not that much fuel will be used for shorter flights. But, the reduction of CO2 released will be enormous no matter short or long flights, because frequent takeoff and landing in shorter flights consume a disproportional amount of fuel in comparison to a long flight at high altitudes.

The main thing about h2 is its extrmely light. The weight savingd from going to h2 in a jumbo jet is about 55 tons even with the much larger fuel tanks. 110000 lbs is one hell of a savings.

Paul,
In my previous posting, the required increase in fuselage volume to put all the LH2 in fuselage tank (and none in the wings) was miscalculated as ~2x. It should be 2.9x, which can be rounded up to 3x. (1.75 x 120,000/200,000= 2.91) Assuming still that 1/6th of the old fuselage's volume is devoted to fuel storage. Thus, the new fuselage volume now should be 8/6 times the previous volume. I was also previously wrong about postulating to enlarge the fuselage vertical diameter while leaving the horizontal diameter the same. This is because when the fuselage is pressurized at high altitude, fuselage deformation can occur unless the entire cross-sectional area is perfectly circular. To increase the new fuselage volume, it is best to keep the length the same while enlarging the cross-sectional area only, in order to minimize increase in surface area. Thus, the mean cross-sectional area of the new fuselage will be increased proportionately with the new volume of 8/6 times previous volume. And therefore, the surface area of the new fuselage will increase proportionately to the circumference of the mean circular cross-section of the new fuselage, or the square root of 8/6 = 1.15. The new fuselage will have 1.15 times the surface area of the old fuselage, or a 15% increase. Divide this 15% by 1/2 and multiply by 2/5 as discussed in my previous posting will result in = 3%. Still only a meagerly 3% increase in cruise drag even though the new fuselage now has 3x the fuel volume as the old fuselage.

Paul,
I did look up the exact dimension of the cabin width and length of the B-777 and they are: 5.85m and 48m respectively. To calculate the cabin's volume: (5.85/2) squared x pi x48 = 1290 meter cubed, or 1,290,000 liters. The fuel volume that 200,000 lbs of kerosene would take up can be calculated as 200,000 / 1.77 lbs/liter = 113,000 liters. Multiply the 113,000 liters of kerosene by 1.75 which is the volume required for LH2 = 198,000 liter. Let's say that ~60,000 liters is the internal fuselage fuel volume of the B777. So, substracting 60,000 from 198,000 will give 138,000 liters as the additional volume required for the new fuselage, which should have 1,290,000 + 138,000 = 1,428,000 liters. 1,428,000/1,290,000= 1.11, or only a 11% increase and not a 33% increase that I had estimated before. Taking the square root of 1.11 = 1.05, which is the increase in surface area of the new fuselage when the length is kept the same and only increase fuselage width. Now, I was wrong before regarding the proportion of the fuselage surface area in comparison to the total aircraft's surface area, given the fact that the new aircraft has the wings and tails 1/2 the size of the older heavier airplane, while the fuselage is slightly larger by 5%. So, new guestimation is that the fuselage surface area is 60% of the total surface area of the new aircraft. So, the 5% increase in fuselage surface area now amount to ~3% increase in total surface area of the aircraft. Since surface area drag is ~2/5 of total drag of the aircraft,multiply 3% by 2/5 = 1.2%.

So, officially, the increase in drag as the result of a slightly larger fuselage to accompany the larger fuel volume will be only 1.2% of the total drag of the new aircraft, and not the 3% that I estimated earlier. The bottom line is that it is easy to accommodate the increase in fuel volume of LH2, while the super light-weight of H2 vs kerosene can allow nearly 50% reduction in energy cost of long-distance flight and perhaps nearly as much in total acquisition and operating costs, given the fact that a lighter aircraft is cheaper to build, to own, to service or to maintain.

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