Supersonic Engine Emissions

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.

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                                            Esra Daldal