Supersonic Engine Emissions
Depletion of the Earth's natural ozone layer and
climatic changes affect everyone. These problems are both global and national
concerns. How and how much do aircraft emissions affect our environment? These
are important issues facing the aircraft industry.
There are several types
of aircraft emissions. Each type has an effect on the environment. If the
aircraft industry continues to grow as predicted, reducing these emissions is
critical. The following emissions shall be controlled for certification of
aircraft engines: Smoke, Gas emissions ( Unburned hydrocarbons (HC), Carbon
monoxide (CO), Oxides of nitrogen (NO).
An aircraft produce
up to 4 percent of the annual global CO2 emissions from fossil fuels near
the Earth's surface as well as at higher altitudes (25,000 to 50,000 feet).
A jet engine is an
internal combustion engine, just like an automobile engine is. In a jet engine,
the fuel and an oxidizer combust (or burn) and the products of that combustion
are exhausted through a narrow opening at high speed. Modern jet engine fuel is
primarily kerosene. Kerosene, a flammable hydrocarbon oil, is a fossil fuel.
Burning fossil fuels primarily produces carbon dioxide (CO2) and water vapor
(H2O). Other major emissions are nitric oxide (NO) and nitrogen oxide (NO2),
which together are called NOx, sulfur oxides (SO2), and soot.
CO Standard
The CO standard applies to newly manufactured aircraft gas turbine
engines (turbofan and turbojet engines).
CO = 118 grams/kilonewton
(g/kN)(rated output)
NOx Standards
The NOx standards apply to newly certified and newly manufactured
aircraft gas turbine engines (turbofan and turbojet engines).
• For engines of a type or
model of which that date of manufacture of the first individual production
model was on or before December 31, 1995 and for which the date of manufacture
of the individual engine was on or before December 31, 1999:
NOx = (40 + 2(rated
pressure ratio))g/kN(rated output);
• For engines of a type or model of which the date of manufacture
of the first individual production model was after December 31, 1995 or for
which the date of manufacture of the individual engine was after December 31,
1999:
NOx = (32 + 1.6(rated pressure ratio))g/kN(rated output).
The first NOx emission standard
presented above matches the ICAO standard that became effective in 1986. The
second NOx emission standard above matches the ICAO 1993 amendments which will
result in a 20 percent reduction and will become effective in the year 1996 for
newly certified engines and in the year 2000 for newly manufactured engines.
There is a four year period between when newly certified engines must meet the
standards and when all newly manufactured engines must meet the standards to
provide lead time for the production of 100 percent compliant products.
Emission
Index (grams per kilograms of fuel used) of various materials for supersonic aircraft for cruise condition.
Values in parentheses are ranges for different engines and operating
conditions.
Species (gm MW)
|
Supersonic Aircraft
|
CO₂ (44)
|
3160
|
H₂0 (18)
|
2130
|
CO (28)
|
1 .5 (1.2-3.Q)
|
HC as methane (16)
|
0.2 (0.02-0.5)
|
SO₂
(64)
|
1 .0
|
NOₓ as N0₂
(46)
|
depends on design (5-45)
|
Supersonic
Aircraft
Concorde, Tupolev TU1 44
The first generation of civil supersonic aircraft (Concorde, Tupolev TU1
44) incorporated turbojet engines of a technology level typical of the early 1
970s. The second generation, currently being considered by a number of
countries and industrial consortia, will have to incorporate technology capable
of meeting environmental requirements.
A comprehensive study of the scientific
issues associated with the Atmospheric Effects of Stratospheric Aircraft (AESA)
was initiated in 1 990 as part of NASA's High Speed Research Program (HSRP;
Prather et al., 1 992). No engines or prototypes exist and designs are only at
the concept stage. A range of cruise EI(NOx) levels (45, 15, and 5) has been
set as the basis for use in atmospheric model assessments and in developing
engine technology. An EI(NOx) of 45 is approximately what would be obtained if
HSCT engines were to be built using today 's jet engine technology without
putting any emphasis on obtaining lower EI(NOx) emissions.
Jet engine experts have great confidence
in their ability to achieve an HSCT engine design with EI(NOx) no greater than
15 and have set a goal of designing an HSCT engine with EI(NOx) no greater than
5. Laboratory-scale studies of new engine concepts, which appear to offer the
potential of at least 70-80% reduction in NOx compared with current technology,
are being pursued. Early results indicate that these systems seem able to
achieve the low target levels of EI(NOx) = 5 (Albritton et al., 1993).
NOx/H20/
Sulfur Impacts on Atmospheric Chemist
Supersonic Aircraft The impacts of HSCT emissions on chemistry are
discussed in detail in Stolarski and Wesoky (1993b ). Here we give a short
summary. Effects of emissions from HSCTs on ozone are generally predicted to be
manifested through gas phase catalytic cycles involving NOx, HOx, ClOx, and
BrOx. The amounts of these radicals are changed by two pathways. First, they
are changed by chemistry, either addition of or repartitioning within nitrogen,
hydrogen, and halogen chemical families. Predicted changes in ozone from this
pathway are initiated primarily by NOx chemistry.
Second, they are changed when HSCT emissions affect the properties of
the aerosols and the probability of polar stratospheric cloud (PSC) formation.
Changes in ozone from this pathway are determined primarily by ClOx and BrOx
chemistry, with a contribution from HOx chemistry. Heterogeneous chemistry on
sulfate aerosols also has a large impact on the potential ozone loss. Most
important is the hydrolysis of N20s: N20s + H20 ---7 2 HN03. Several
observations are consistent with this reaction occurring in the lower
stratosphere (e.g., Fahey et al., 1993; Solomon and Keys, 1992). Its most
direct effect is to reduce the amount of NOx. Indirectly, it increases the
amounts of CIO and H02 by shifting the balance of CIO and ClON02 more toward
CIO during the day and by reducing the loss of HOx into HN03.
As a result, the HOx catalytic cycle is
the largest chemical loss of ozone in the lower stratosphere, with NOx second,
and both the ClOx and BrOx catalytic cycles have increased importance compared
to gas phase conditions. The addition of the emissions from HSCTs will affect
the partitioning of radicals in the NOy , HOy , and ClOy chemical families, and
thus will affect ozone. The NOx emitted from the HSCTs will be chemically
converted to other forms, so that the NOx!NOy ratio of these emissions will be
almost the same as for the background atmosphere. As a result, the NOx
emissions will tend to decrease ozone, but less than would occur in the absence
of sulfate aerosols. The increase in H20 will lead to an increase in OH,
because the reaction between O(ID) that comes from ozone photolysis and H20 is
the major source of OH; however, increases in NOy will act to reduce HOx
through the reactions of OH with HN03 and HN04.
On the other hand, HN03, formed in the
reaction of OH with N02, can be photolyzed in some seasons and latitudes to
regenerate OH. When all of these effects are considered, the amount of HOx is
calculated to decrease-H02 by up to 30% and OH by up to 10%. Thus, the
catalytic destruction of ozone by HOx, the largest of the catalytic cycles, is
decreased. Finally, ClOx concentrations decrease with the addition of HSCT
emissions for two reasons. First and most important, with the addition of more
N02, the daytime balance between ClO and ClON02 is shifted more toward ClON02.
Second, with OH reduced, the conversion of HCl to Cl by reaction with OH is
reduced, so that more chlorine stays in the form of HCl. Thus, the catalytic
destruction of ozone by ClOx is decreased. The addition of HSCT emissions
results in increases in the catalytic destruction of ozone by the NOx cycle
that are compensated by decreases in the catalytic destruction by ClOx and HOx.
Because the magnitudes of the changes in catalytic destruction of ozone are
similar for the NOx, HOx, and ClOx cycles, compensation results in a small
increase or decrease in ozone. Model calculations indicate a small decrease.
The decreases in the catalytic destruction of 03 by CIOx and HOx involve the
effects of increased water vapor and HN03 on the rates of heterogeneous reactions on sulfate
and the probability of PSC formation. The addition of sulfur to the
stratosphere from HSCTs will increase the surface area of the sulfate aerosol
layer. This change in aerosol surface area is expected to be small compared to
changes from volcanic eruptions, with a possible exception being the immediate
vicinity of the aircraft wake.
Model calculations by Bekki and Pyle ( 1
993) predict regional increases of the mass of lower stratospheric HzS04·H20
aerosols, due to air traffic, by up to about 100%. The importance of sulfur
emissions from HSCTs in the presence of this large and variable background
needs to be assessed.
IATA’s Operational Fuel Efficiency
The
aviation industry has developed many operational measures to minimize fuel
usage. Operational improvements could provide a 6% overall fuel
saving.
Efficiency Goal
Airlines
have adopted a voluntary fuel efficiency goal. This is to reduce fuel
consumption and CO2 emissions (per revenue tonne kilometer) by at least
25% by 2020, compared to 2005 levels.
Less Fuel = Less Emissions
Aircraft
engine emissions are directly related to fuel burn. Each kilogram of fuel saved
reduces carbon dioxide (CO2) emissions by 3.16 kg. So the key for
airlines to minimize their environmental impact is to use fuel more
efficiently. IATA airlines improved their fuel efficiency by 3.1% in 2006
and 2007.
-
New aircraft are 70% more
fuel efficient than 40 years ago and 20% better than 10 years ago.
-
Modern aircraft achieve
fuel efficiencies of 3.5 litres per 100 passenger km.
-
The A380 and B787 are
aiming for 3 liters per 100 passenger km – better than a compact car!
IATA Fuel Action Campaign
IATA
has launched a fuel action campaign and is working with
industry partners to reduce fuel requirements and associated emissions.
Measures for
Improved Fuel Efficiency
IATA Green Teams work with airlines to
evaulate fuel efficiency and emissions reductions initiatives.
Technology
Through
gradually incorporating advanced technology into their fleets, airlines have
made impressive fuel efficiency improvements.
Together with a number of
industry experts, IATA has developed the IATA Technology Roadmapwhich
provides a summary and assessment of technological opportunities for future
aircraft. The publication looks at technologies that will reduce,
neutralize and eventually eliminate the carbon footprint of aviation. Some
of these technologies could also be used for retrofits to the existing fleet.
Thanks to visit my blog.
Esra Daldal
This comment has been removed by the author.
ReplyDeleteI would like to start by looking at the NOx Standards, where you stated " The NOx standards apply to newly certified and newly manufactured aircraft gas turbine engines (turbofan and turbojet engines)". and you also mentioned some rules that can be taken in to consideration:
ReplyDelete• For engines of a type or model of which that date of manufacture of the first individual production model was on or before December 31, 1995 and for which the date of manufacture of the individual engine was on or before December 31, 1999.
• For engines of a type or model of which the date of manufacture of the first individual production model was after December 31, 1995 or for which the date of manufacture of the individual engine was after December 31, 1999.
in addition of this,in Kyoto protocol there were countries who commit to reduce carbon dioxide and five other greenhouse gases,or engage in emissions trading if they maintain or increase emissions of these gases. A total of 141 countries have ratified the agreement. Notable exceptions include the United States and Australia
ReplyDeleteDear Esra;
ReplyDeleteYour topic is very attractive for me, I learned new information about engine emissions. On the other hand, I feel sad because aviation industry damages our earth day by day; but you said that ''The key for airlines to minimize their environmental impact is to use fuel more efficiently. IATA airlines improved their fuel efficiency by 3.1% in 2006 and 2007''. Such is a good news! I expect that will continue..Finally, I really like your visual stuff, especially your video. Thank you for your sharing.
Dear Esra,
ReplyDeleteFirst of all, our topic much a matter requiring information moreover very comprehensive and heavy a topic , the information you gave a very good way and it was an understandable text and you use simple language
Thank you for everything,
A nice article, it is not too long and it is not boring. I like it :)
I think my writing a bit boring :))