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6 State of the Industry Report on Air Quality Emissions from Sustainable Alternative Jet Fuels Copyright National Academy of Sciences. All rights reserved. 2. BACKGROUND This State of the Industry report is a âreference documentâ that captures the current status of knowledge regarding emissions from the use of sustainable alternative jet fuels (SAJF). The research team conducted a review of available research, literature, and measurement campaigns to enhance our current understanding of the local air quality emissions benefits and impacts of SAJF as well as SAJF blends relative to conventional jet fuel. We drilled down into the data and extracted and analyzed the essential emissions testing data to quantify typical emissions impacts of SAJF use. The review results are focused specifically on air quality emissions of criteria pollutants from SAJF. The report also includes an analysis of gaps in our current understanding of the production of pollutants from SAJF. 2.1. TEST CAMPAIGNS Department of Defense (DoD) and National Aeronautics and Space Administration (NASA) have been primarily responsible for most of the SAJF testing to date. DoD conducted tests on many of the different aircraft they operate to qualify their use of SAJF. NASA has been conducting research on aircraft engine emissions to evaluate their environmental impact for several years. Many of these research programs included DoD research labs, Federal Aviation Administration (FAA) experts, aircraft and engine manufacturers, universities, and scientific experts. Some of the more significant test programs were: â¢ APEX, September 2006 â¢ AAFEX-I, January 2009 â¢ AAFEX-II, March 2011 â¢ ACCESS-I, February-April, 2013 â¢ ACCESS-II, May, 2014 Much of the literature reviewed in this report comes from reports on these projects or analyses of the data produced during these projects. 2.2. AIRCRAFT ENGINES Todayâs commercial and military aircraft rely on modern, high-efficiency, sophisticated turbine engines to deliver the safety, operability, and efficiency demanded from the sector. Additionally, auxiliary power units (APU) are smaller turbine engines utilizing similar design principles which also perform consistently and reliably. Aircraft main engines and APUs were the primary test beds for SAJF emissions testing. The various testing campaigns showed that emissions testing on a given engine could produce repeatable and consistent results for any given fuel. However, engine to engine differences are significant. The age/pedigree of the engine, time since last overhaul, and cleanliness of fuel components, such as nozzles, can affect combustion and consequently emissions. For a series of tests performed on a given engine, the changes in emissions will be a reflection of the thrust setting (i.e., fuel flow) and fuel composition. In general, fuel chemistry has a much greater impact on emissions than the difference among engines. The relationship between fuel composition and emissions is discussed below. The emissions tests conducted in the reports included in this literature review were performed at various engine thrust settings intended to reflect an aircraftâs main engine performance. The basis for selecting specific thrust settings correlates with the landing-and-takeoff (LTO) cycle as defined by the International Civil Aviation Organization (ICAO) and used for engine certification testing. As a general representation, taxiing aircraft use low thrust (4%). Full thrust (100%) is used to represent takeoff as the aircraft comes up to speed quickly to get off the ground. Once in the air, the thrust is reduced somewhat (85%) as the aircraft climbs to cruise altitude. A thrust setting of 30% is representative of the thrust an aircraft uses on approach to landing. These thrust settings are commonly used for emissions testing although in actual operation, thrust settings vary and typically are lower than these values. In a similar way, tests conducted on APUs use three power settings â âno loadâ or âready-to-load,â environmental control system, and âmaximum loadâ or âmain engine start,â which reflect in-use APU thrust settings. The no load setting is equivalent to idle on aircraft main engines. The environmental control system setting is an intermediate power setting used when the APU is providing secondary electric power and ventilation to an aircraft parked at the gate. The main engine start setting is a high-power setting used when starting the aircraft main engines. Aircraft main engines are designed to operate most efficiently at cruise power since the majority of fuel use is during cruise. Lower power operation, such as for idling and taxiing, is less efficient from a fuel combustion standpoint. As a result, emission species that reflect engine efficiency, notably CO and UHC, are higher per unit of fuel consumed at low power operation and lower at high power operation. Conversely, NOx emissions, which State of the Industry Report on Air Quality Emissions from Sustainable Alternative Jet Fuels opyright ational cade y of ciences. ll rights reserved.
5 State of the Industry Report on Air Quality Emissions from Sustainable Alternative Jet Fuels Copyright National Academy of Sciences. All rights reserved. While the primary purpose for airlines to use SAJF is to reduce CO2 emissions, emissions of other pollutants may also be reduced, which could be significantly beneficial to airports. However, these reductions are not yet well defined, leaving airports unable to realize what may be substantial benefits. The research team team analyzed the published technical literature to validate that SAJF use does reduce air pollutant emissions (i.e., PM2.5, SOx, CO, UHC, NOx) and does not cause any of them to increase. Table ES-2 summarizes the body of literature that was screened to identify essential reports that include quantitative data on results from emissions testing of SAJF. The data in these reports was analyzed in detail to define the impact of using SAJF on air pollutants of interest to airports. The summarization of these reports and their emissions data shows that SAJF, when blended with conventional jet fuel as defined in D7566, significantly reduces SOx and PM, generally reduces CO and UHC emissions, and minimally reduces or has no effect on NOx emissions. Figure ES-2 summarizes the impact of SAJF on aircraft emissions. This report describes why these findings are expected based on an understanding of the mechanisms of pollutant production when burning jet fuel in aircraft engines and how this is repeatedly confirmed by the data collected from numerous tests and measurement campaigns. Following this Executive Summary, Section 2 provides a discussion of the scope of this report including emission testing campaigns, SAJF production and approved fuels, and pollutant species. Section 3 provides information on the source of the different pollutant species that result from fuel combustion. Section 4 describes the knowledge gaps in the current literature and testing to date. Section 5 is an annotated bibliography that highlights key findings from several reports, which influenced the findings of this literature survey. Section 6 includes a complete reference list, and Section 7 is an appendix, which summarizes the impacts of alternative fuels on the emissions of SOx, PM2.5, CO, UHC, NOx, and HAP from individual reports. Figure ES-1: Fuel Production Pathways Currently Undergoing Review Document Hits Search Criteria 35,136 Alternative jet fuel emissions 9,369 Alternative jet fuel emissions + criteria pollutants 73 Alternative jet fuel emissions + criteria pollutants + emission measurements 51 Reports with quantitative emissions analysis (used in this literature review) Table ES-2: Identifying Reports for Literature Review SOx PM2.5 CO UHC NOx HAP 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Neat 50% Blend R ed uc ti o ns (% ) Figure ES-2: Representative Air Pollutant Emission Reductions from the Use of SAJF FUEL PRODUCTION PATHWAY ATJ-SPK; Expansion of Annex A5 (ATJ-SPK) to include the use of ethanol as a feedstock HDO-SAK; Synthesized Aromatic Kerosene via the catalytic conversion of sugars CHJ; Catalytic Hydrothermolysis Jet via Isoconversion of lipids, fats, oils or greases HFP-HEFA; High Freeze Point HEFA, using HDRD (aka Green Diesel) as a blending agent State of the Industry Report on Air Quality Emissions from Sustainable Alternative Jet Fuels opyright ational cade y of ciences. ll rights reserved.
4 State of the Industry Report on Air Quality Emissions from Sustainable Alternative Jet Fuels Copyright National Academy of Sciences. All rights reserved. 1. EXECUTIVE SUMMARY Aviation has a long and successful record of improving operational performance and fuel efficiency over time and is now seeking to reduce its greenhouse gas (GHG) emissions and offset emissions that may result from growing demand for air travel. U.S. and international airlines have committed to reducing lifecycle CO2 emissions from aircraft operations. The primary means for reducing these emissions is using alternative jet fuels produced from non-petroleum sources, referred to as sustainable alternative jet fuels (SAJF). The aviation industry uses an ASTM International specification standard (ASTM D7566) to define alternative fuels that have been approved by the industry as being safe for use in commercial aircraft. To date, five different fuel production pathways have been defined. Table ES-1 summarizes those fuels as well as the number of reports in the literature that evaluated emissions from testing of those synthesized fuels. The industry is presently reviewing additional alternative jet fuel production pathways, which may add new qualified fuels to this list in the future. Figure ES-1 summarizes those fuels and Section 2 of the report defines them in more detail. Annex # Fuel Production Pathway Number of Emissions Tests Reported in Literature A1 Fischer-Tropsch Hydroprocessed Synthetic Paraffinic Kerosene (FT-SPK) 15 A2 Synthesized Paraffinic Kerosene from Hydroprocessed Esters and Fatty Acids (HEFA-SPK) 13 A3 Synthesized Iso-Paraffins Produced from Hydroprocessed Fermented Sugars (HFS-SIP) 3 A4 Synthesized Kerosene with Aromatics Derived by Alkylation of Light Aromatics from Non-Petroleum Sources (FT-SPK/A) 0 A5 Alcohol-to-Jet Synthetic Paraffinic Kerosene (ATJ-SPK) limited initially to the use of ethanol and isobutanol, but eventually intended to allow the use of any C2-C5 alcohol 4 Table ES-1: Industry Approved Alternative Jet Fuels included in ASTM D7566 State of the Industry Report on Air Quality Emissions from Sustainable Alternative Jet Fuels opyright ational cade y of ciences. ll rights reserved.
3 State of the Industry Report on Air Quality Emissions from Sustainable Alternative Jet Fuels Copyright National Academy of Sciences. All rights reserved. CONTENTS 1. EXECUTIVE SUMMARY ________________________________________________________________________________________ 4 2. BACKGROUND _______________________________________________________________________________________________ 6 2.1. Test Campaigns ___________________________________________________________________________________________ 6 2.2. Aircraft Engines ___________________________________________________________________________________________ 6 2.3. Conventional Jet Fuel ______________________________________________________________________________________ 7 2.4. Synthetic Fuels ___________________________________________________________________________________________ 7 2.5. Sustainable Alternative Jet Fuel Production ___________________________________________________________________ 8 2.6. Pollutant Species __________________________________________________________________________________________ 9 2.7. Report Identification _______________________________________________________________________________________ 9 3. POLLUTANT EMISSIONS _____________________________________________________________________________________ 10 3.1. CO2 and H2O ____________________________________________________________________________________________ 10 3.2. SOx _____________________________________________________________________________________________________ 10 3.3. PM2.5 ____________________________________________________________________________________________________ 10 3.4. CO _____________________________________________________________________________________________________ 11 3.5. UHC ____________________________________________________________________________________________________ 11 3.6. NOx _____________________________________________________________________________________________________ 12 3.7. HAP ____________________________________________________________________________________________________ 12 4. KNOWLEDGE GAPS _________________________________________________________________________________________ 12 4.1. Scope of Testing _________________________________________________________________________________________ 12 4.2. SOx _____________________________________________________________________________________________________ 14 4.3. PM _____________________________________________________________________________________________________ 14 4.4. CO _____________________________________________________________________________________________________ 14 4.5. UHC ____________________________________________________________________________________________________ 14 4.6. NOx _____________________________________________________________________________________________________ 14 4.7. HAP ____________________________________________________________________________________________________ 15 4.8. Future Testing ____________________________________________________________________________________________ 15 5. ANNOTATED BIBLIOGRAPHY _________________________________________________________________________________ 15 6. REFERENCES _______________________________________________________________________________________________ 29 7. APPENDIX __________________________________________________________________________________________________ 32 State of the Industry Report on Air Quality Emissions from Sustainable Alternative Jet Fuels opyright ational cade y of ciences. ll rights reserved.