National Academies Press: OpenBook
« Previous: Chapter 2 - Key Project Findings
Page 13
Suggested Citation:"Chapter 3 - Key Environmental Factors." National Academies of Sciences, Engineering, and Medicine. 2011. Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14531.
×
Page 13
Page 14
Suggested Citation:"Chapter 3 - Key Environmental Factors." National Academies of Sciences, Engineering, and Medicine. 2011. Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14531.
×
Page 14
Page 15
Suggested Citation:"Chapter 3 - Key Environmental Factors." National Academies of Sciences, Engineering, and Medicine. 2011. Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14531.
×
Page 15
Page 16
Suggested Citation:"Chapter 3 - Key Environmental Factors." National Academies of Sciences, Engineering, and Medicine. 2011. Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14531.
×
Page 16
Page 17
Suggested Citation:"Chapter 3 - Key Environmental Factors." National Academies of Sciences, Engineering, and Medicine. 2011. Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14531.
×
Page 17
Page 18
Suggested Citation:"Chapter 3 - Key Environmental Factors." National Academies of Sciences, Engineering, and Medicine. 2011. Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14531.
×
Page 18
Page 19
Suggested Citation:"Chapter 3 - Key Environmental Factors." National Academies of Sciences, Engineering, and Medicine. 2011. Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14531.
×
Page 19
Page 20
Suggested Citation:"Chapter 3 - Key Environmental Factors." National Academies of Sciences, Engineering, and Medicine. 2011. Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports. Washington, DC: The National Academies Press. doi: 10.17226/14531.
×
Page 20

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

13 In order to present a complete cost–benefit analysis for the transition to an alternative fuel, it is necessary to examine changes in fuel consumption as well as emissions that affect air quality and global climate change. For some airports, the moti- vating factor for transitioning to an alternative fuel may be the emissions benefits. This section summarizes how changes in emissions, both those affecting air quality and life-cycle green- house gas emissions, and fuel consumption for the alternative fuels can be estimated. This information was used to develop the emissions components of the AFIT computational tool. 3.1 Fuel Consumption The different fuel properties of SPK or ULS Jet (ULSJ) could produce a change in fuel use in both diesel engines within GSE and the gas turbine engines that power aircraft. As dis- cussed below, the change in fuel burn for diesel engines that use alternative jet fuels varies based on the specific engine and testing cycle, whereas the fuel burn changes in aircraft depend on the fuel-specific energy. 3.1.1 Changes in Jet Fuel Use in Jet Engines Aircraft engine combustion of either SPK or ULSJ should also result in a change in fuel use because energy content is the driver of fuel consumption. For this study, the change in fuel use is estimated based on the ratio of fuel energy content. As discussed previously, the energy content of a fuel can be deter- mined on a gravimetric or volumetric basis. If the energy den- sity (volume) is not sufficient, there may not be enough room in the aircraft’s fuel tanks. If the specific energy (gravimetric) is not sufficient, the aircraft will have to carry more fuel, mak- ing the aircraft heavier and again requiring extra fuel. Because most commercial aircraft do not fly with full tanks, specific energy is more salient for calculating a change in fuel use. The specific energy densities of Jet A, ULSJ, and SPK have been summarized by Hileman et al. (forthcoming), and are shown in Table 3. The baseline value of Jet A is based on the average value from the Petroleum Quality Information System (PQIS) database of military JP-8 jet fuel. The specific energy for ULSJ is based on the decrease in energy density and related increase in hydrogen content due to the hydrodesul- furization process. SPK specific energy values are based on a literature review of actual fuel testing. A 50-50 blend would have the average specific energies of the fuels comprising the mixture. Because of their increased specific energy, using a 50-50 SPK fuel blend in aircraft would to lead to a 1% decrease in fuel consumption, as measured on a mass basis. 3.1.2 Changes in Fuel Use in Diesel Engines Studies comparing the use of a synthetic paraffinic diesel fuel to conventional diesel fuel in diesel engines show con- flicting results. Schaberg et al. (1997) found a 1% to 2.9% decrease in fuel use using a transient engine test with a heavy-duty DDC 60 series engine. However, in full-vehicle dynamometer testing completed with a diesel bus and semi- truck tractor, Clark et al. (1999) found a 4.4% average fuel use increase. Using up to an 85% blend of hydroprocessed renew- able diesel (HRD), Rantanen et al. (2005) found no change in fuel use. Military studies examining jet fuel use in diesel engines also show conflicting results. Initial predictions ranged from a 1% to 5% increase in fuel usage based on the change in energy density (BTU/gallon) of the fuels, while engine testing indi- cated a 2% increase in fuel use (U.S. Army ACOM-TARDEC, 2001). Additional testing by Fernandes et al. (2007) initially found an increased fuel consumption of 1% with JP-8 when testing engines at low load but then found a decreased fuel consumption of approximately 1% with modified injection timing (Fernandes et al., 2007). Yost et al. (1996) found vary- ing levels of fuel consumption based on loading, which ranged from –5.4% to 3.9%. Overall, military field testing of diesel vehicles burning jet fuel indicates that “there has been no C H A P T E R 3 Key Environmental Factors

indication of a significant increase in fuel consumption being evidenced” (U.S. Army ACOM-TARDEC, 2001). Due to the variation in fuel use change across studies, both positive and negative, it is assumed herein that there is no change in either SPK or ULSJ fuel use within diesel engines. 3.2 Aircraft Emissions Affecting Air Quality The focus of the air quality aspect of this work was on ambi- ent concentrations of PM2.5. Aircraft emissions of nitrogen oxides, sulfur oxides, and primary particulate matter all con- tribute to ambient concentrations of PM2.5; as such, these are the focus of this section. Emission factors, also called emis- sions indices, are the key ingredient for an emissions inven- tory. This section provides scaling factors for aircraft and GSE emissions. Further details on their derivation can be found in Donohoo (2010). A review of the existing literature was used to estimate the changes to NOx, SOx, and primary PM emissions from the use of both SPK and ULS Jet A in aircraft. It must be noted that the Alternative Aviation Fuels Experiment (AAFEX) team acquired considerable data after the analysis presented here was completed. These data were presented in a public forum in January 2010. As such, the scaling relationships presented herein do not reflect all of the latest scientific knowledge. 3.2.1 Nitrogen Oxides Aircraft NOx emissions are created by oxidation of atmo- spheric nitrogen, and their rate of production is determined by combustion temperature. For a ULS jet fuel, there should be negligible change in the combustion temperature; there- fore, the amount of NOx produced per mass of fuel consumed should be unchanged. There is preliminary data indicating SPK use could reduce NOx emissions by roughly 5% to 10%; however, these results were within experimental uncertainty (Miake-Lye and Timko, 2008). Since this is preliminary data based on one study, a conservative assumption was made that NOx emissions are unchanged with SPK fuel use. As more data, such as the AAFEX results, are published, these scaling relationships should be updated. 3.2.2 Sulfur Dioxide SOx emissions from an aircraft engine scale directly with the sulfur content of the fuel. The Emissions and Dispersion Modeling System (EDMS), used for emissions analysis on this project, assumes a fuel sulfur content of 680 ppm. Thus, the SOx emissions from a fuel with a different fuel sulfur con- tent would simply be the ratio of the alternative fuel’s sulfur content to 680 ppm. ULS jet fuel is intentionally processed to an ultralow sulfur level. A typical ULS diesel leaves the refinery gate at 7 ppm such that it contains less than 15 ppm when it reaches the fuel tank. For this study, a sulfur level of 15 ppm was assumed for jet fuel when it reaches the aircraft fuel tank, although this may not be the most cost-beneficial level; instead, it matches the level in use by diesel fuel. Due to the nature of the fuel processing techniques used, SPK fuels have essentially zero sulfur level. However, their transport in pipelines could result in some trail-back of sulfur from other flows such as from conventional jet fuel. As such, a value of 15 ppm sulfur was also chosen for SPK fuels. 3.2.3 Primary Particulate Matter Primary particulate matter emissions were calculated accord- ing to the first order approximation (FOA) methodology. FOA was developed by the FAA’s Office of the Environment in response to a need for a scientifically based methodology to estimate primary PM; prior to FOA, emissions were based on a small number of aircraft tests or diesel particulate matter emissions estimates. EDMS uses a conservatively modified form of the third version of FOA (FOA3a). A complete dis- cussion of the evolution and methodology behind the FOA methodology can be found in Ratliff (2007) Ratliff et al. (2009). The FOA methodology speciates PM into volatile and non- volatile components. The nonvolatile component (PMNV) refers to the solid particulate component. PMNV is a result of incomplete combustion and is also referred to as soot, hard particles, black carbon, or elemental carbon. The volatile com- ponent of aircraft PM comes from the condensation of volatile compounds in the exhaust plume. Volatile PM is broken down into three categories: PM from sulfur (PMS), PM from unburned fuel organics (PMFO), and PM from lube oil (PMLO). The sum of each of these components yields the full primary PM emissions. In this report, it is assumed that the PMLO emissions index (EI) and PMFO EI values do not change with fuel composi- tion. Recent testing from the AAFEX team indicates that there could be a reduction in PMFO with the use of SPK fuels. As such, this assumption is overly conservative and should be cor- rected in future work. The PMS component was assumed to 14 Table 3. Fuel scaling factors and energy content for aircraft fuels. Fuel Specific Energy (MJ/kg) Fuel Scaling Factor Jet A 43.2 1 ULSJ 43.4 0.995 100% SPK 44.1 0.979

scale in a similar manner as the SOx emissions. The conversion rate of fuel sulfur to sulfuric acid, the precursor to PMS emis- sions, was assumed to be unchanged with fuel composition. Recent measurements in a wide range of gas turbine engines have shown that the use of F-T fuels reduces PMNV emissions. This trend has been observed in four different types of gas tur- bine engines with varied combustor technologies: a turboshaft helicopter gas turbine (T63), a low bypass ratio engine with older combustor technologies from the B52 (TF33), the Pratt and Whitney 308 engine (PW308), and a higher bypass ratio engine with a modern combustor design used in the Boeing 737 (CFM56). Given the wide range of engine vintages and tech- nologies that have this reduction in emissions, it is most likely that the reduction is due to the lack of aromatic compounds in the fuel. For ULSJ, it is conceivable that there could be reductions of PMNV as a result of reduced aromatic content due to the hydrodesulfurization process; however, data used by the EPA for the ULSD rulemaking indicate that aromatic content is not significantly affected (<10% reductions) by the hydrodesulfu- rization process. For this study, it is assumed that ULSJ has the same aromatic content as conventional jet fuel and that it will have the same emissions of PMNV per unit of fuel consumed. For SPK fuels, F-T emission measurements have been used to provide an approximation to the PMNV reductions that may be experienced with the use of an SPK fuel blend with conventional jet fuel. As shown in Figures 1 and 2, PMNV emission reductions are generally greater at reduced thrust settings as compared to higher thrust settings. An approximation of the PMNV reduction was created with a least-squares fit of data from the CFM56 and PW308. This curve fit was used to calculate PMNV reductions at each of the thrust settings in the landing takeoff (LTO) cycle. The final scaling factor was calculated using these reductions 15 Figure 1. Reduction in PMNV mass for gas turbine combustion of a 50-50 blend of SPK with conventional jet fuel as a function of thrust setting [from Donohoo (2010) with permission]. -100% -80% -60% -40% -20% 0% 0% 20% 40% 60% 80% 100% Percent Thrust Pe rc en t R e du ct io n in P M N V CFM56 50% FT PW 308 AFRL 50% FT PW 308 NASA 50% FT T63 50% FT TF33 50% FT Figure 2. Reduction in PMNV mass for gas turbine combustion of 100% SPK as a function of thrust setting [from Donohoo (2010) with permission]. -100% -80% -60% -40% -20% 0% 0% 20% 40% 60% 80% 100% Percent Thrust Pe rc en t R e du ct io n in P M N V CFM56 100% FT PW 308 AFRL 100% FT PW 308 NASA 100% FT T63 100% FT

weighted by the total fuel burn in each stage (taxi/idle, climb- out, takeoff, approach). The fuel burn was calculated using the average time in mode and thrust from ICAO Annex 17 and the fuel burn at each corresponding thrust point from the ICAO engine databank (International Civil Aviation Organization, 1993). The engine specific reductions in PMNV for the LTO cycle are shown in Figure 3. The 100% F-T PMNV reductions range from 76% to 86%, while the 50-50 blend shows a broader range of reductions, from 42% to 69%. An average value for the Air Force Research Laboratory (AFRL) PW308 50-50 blend is not included because the highest reduc- tions occur at the low power settings and AFRL data does not include measurements at thrusts lower than 65%. The rel- atively tight range of values for 100% SPK within Figure 3 should not be interpreted as meaning the fleet-wide reduc- tion in PMNV is well known because different engine types may produce varied reductions in PMNV and the measure- ments still contain uncertainty. The scaling used in this study is based on the PW308 data provided by NASA as recommended by experts in the field, Dr. Miake-Lye and Dr. Timko from Aerodyne Research, Inc., because the PW308 NASA data has smaller uncertainty bands and it used an improved testing methodology (Miake-Lye and Timko, 2008). The PMNV reduction for blends having SPK concentration between 0% and 50% was assumed to be linear between zero and the reduction value for the 50-50 blend. This is likely an erroneous assumption since the measured PMNV reduction for a 100% SPK fuel is not twice that observed for a 50-50 blend; future work should therefore refine this estimate. Once they are published, PMNV measurements from more recent tests, such as the AAFEX campaign, should be used to augment these data. 3.2.4 Carbon Monoxide For both ULSJ and SPK fuels, it is assumed that the emissions of carbon monoxide (CO) are unchanged on a per-kilogram- of-fuel basis. For ULSJ, this was based on the similarity of fuel composition to conventional Jet A. For SPK, this was based on a lack of experimental data, although preliminary results may indicate changes and are discussed below. Therefore, the emis- sions of CO were scaled only with fuel use for both ULSJ and SPK fuels, as was done for NOx emissions. 3.3 Diesel GSE Emissions Affecting Air Quality The emissions from diesel GSE were scaled based on exper- imental measurements with surrogate fuels that have similar fuel properties to those being considered. This is an imperfect solution to deal with a lack of emissions data from the com- bustion of ULSJ and SPK fuels in diesel engines. The change in emissions depends on a variety of factors, including age of engine, type of testing cycle, installed pollution control, and fuel properties such as cetane number, fuel density, and aro- matic content (Lee, Pedley, and Hobbs, 1998). These are dis- cussed with each pollutant alongside a scaling factor that could be used with the NONROAD model formulae as described in more detail in Donohoo (2010). 3.3.1 Unburned Hydrocarbons, Nitrogen Oxide, and Carbon Monoxide Scaling factors for hydrocarbons (HC), NOx, and CO were derived from the literature for ULSJ and SPK fuels using JP-8 and synthetic diesel fuels as surrogates. The JP-8 tests were conducted in support of military needs relating to the Single Battlefield Fuel initiative, and as a result, the testing focused exclusively on heavy-duty engines (Fernandes et al., 2007; Yost, 1993; Yost, Montalvo, and Frame, 1996). F-T diesel fuels are not substitutes for SPK fuel; however, there is only one pub- lished diesel engine test of an SPK fuel that the project team identified, but there have been many tests of synthetic paraf- finic diesel fuels (e.g., F-T diesel and HRD). One possible dif- ference in the fuel properties between F-T fuels for jet engines and F-T fuels for diesel engines is the cetane number, which reflects the ignition properties of the fuel. Using synthetic paraffinic diesel as a substitute for SPK fuel use, scaling val- ues were derived from F-T diesel fuel tests that compared a certification diesel with an F-T diesel in the same engine using identical test schemes (Alleman and McCormick, 2003; E. A. Frame, 2004; Fanick, Schubert, Russell, and Freerks, 2001; Nord and Haupt, 2002; Rantanen et al., 2005; Schaberg et al., 2000; Schaberg et al., 1997). A variety of testing cycles with varied engine cycles were examined. Also included was testing of a synthetic jet fuel (S5) that was formulated to meet require- ments for the U.S. Navy. The results from this literature sur- vey are summarized in Table 4. SPK, ULSJ, and S5 fuels all produced NOx reductions within 2% of each other. The reduction was expected due to changes in cetane number, aromatic content, and density, which all indicate a decrease in NOx emissions (Lee, Pedley, and Hobbs, 16 Figure 3. Engine-specific PMNV reductions for LTO cycle [from Donohoo (2010) with permission]. -76 -77 -87 -42 -69 -100 -80 -60 -40 -20 0 PW 308 NASA PW 308 AFRL CFM56 Pe rc en t R e du ct io n in PM N V 100% FT 50% FT

1998). The reductions for SPK (F-T diesel proxy) and S5 were within 1%, indicating that F-T diesel is an appropriate substi- tute for F-T jet fuel for NOx scaling. The trends for HC emissions matched expectations, although the gross reductions did not. Due to the decreased density of jet fuel compared to diesel and the similar cetane number of jet fuel to diesel fuel, it was expected that unburned hydrocarbon emissions would increase. The testing, however, reflects a 10% decrease in emissions. The expected change for the SPK (F-T diesel proxy) HC emissions was neutral since the decrease in emissions due to cetane number was expected to be offset by an increase in emissions due to a decrease in density. The experimental results, however, reflected a 45% to 67% decrease. This may be because cetane has the domi- nant influence on emissions; it could be due to the fact that Lee, Pedley, and Hobbs only explored increasing rather than decreasing density values; it may also be due to other uncap- tured variables, such as a reduction due to polyaromatic com- pounds or changes resulting from engine geometry. Some percentage of emissions may also be due to decreased fuel use. Additionally, for HC emissions, F-T diesel may be a conserva- tive proxy for SPK jet fuel since the S5 results were 22% lower than the F-T diesel results. CO emissions were also reduced more than expected. Again, based on Lee, Pedley, and Hobbs (1998), it was expected that CO emissions would increase with the use of a jet fuel and decrease or remain stable for a synthetic fuel; however, all three fuels showed significant (34% to 53%) reductions in emissions. As with HC emission changes, this indicates that some element of fuel composition or effect of engine geome- try is not being captured. The emission changes also indicate that F-T diesel may be a conservative surrogate for SPK CO emissions since S5 emissions were 14% lower than F-T diesel. 3.3.2 Sulfur Dioxide For calculations in the NONROAD model, which EDMS uses to estimate diesel engine GSE emissions, the sulfur diox- ide emission factor is a function of the sulfur content of the fuel, the unburned hydrocarbon emissions, and the quantity of fuel burned. As such, this model was used for both ULSJ and SPK fuels to estimate sulfur dioxide emissions with assumed fuel sulfur content of 15 ppm (0.15 weight percent). As such, the specific blend of SPK, ULSJ, or ULSD is irrelevant because of the 15-ppm sulfur assumption. The ULSJ fuel sulfur content of 15 ppm was chosen to mirror the maximum allowed in the U.S. ULSD standard, and SPK was also assumed to have a sul- fur content of 15 ppm due to contamination in pipelines. The actual sulfur content of these fuels will be less than 15 ppm. For example, the EPA published estimates of sulfur content for NONROAD diesel fuels, as seen in Figure 4. 3.3.3 Particulate Matter The NONROAD model calculates two sizes of particulate matter, PM2.5 and PM10, where the subscript indicates the 17 Table 4. GSE SPK (F-T diesel proxy) HC, NOx, and CO scaling factors [from Donohoo (2010) with permission]. Fuel Term HC NOx CO ULSJ (Jet A or JP-8 proxy) Number of tests 6 9 6 Scaling factor 0.90 0.84 0.66 Standard deviation 0.18 0.17 0.11 SPK (F-T diesel proxy) Number of tests 14 14 13 Scaling factor 0.55 0.87 0.61 Standard deviation 0.17 0.11 0.15 S5 (from 2 tests) 0.33 0.86 0.47 Figure 4. EPA Estimated sulfur content of NONROAD diesel fuel in continental United States (U.S. EPA, 2004).

maximum diameter in micrometers of the particulate matter. The NONROAD model calculates PM10 and assumes that 90% of PM10 by unit mass is PM2.5. For this document, PM refers only to PM2.5, and the 90% scaling is implicitly assumed in the calculations. Table 5 presents a comparison of the primary PM emissions from diesel engine combustion of various fuels. The JP-8 data were based on the studies of Yost, Montalvo, and Frame (1996) and Fernandes et al. (2007), who examined a ∼300-ppm sul- fur diesel fuel and compared that to 1100-ppm and 40-ppm sulfur JP-8 fuel, respectively. The study of Yost, Montalvo, and Frame (1996) was also examined, but the sulfur content of the diesel fuel that was used as a baseline (9500 ppm fuel sulfur content) was deemed excessively high to yield a useful com- parison. Reducing sulfur also has the effect of reducing PM emissions, but this is only the case when sulfur levels drop sig- nificantly, from 3,000 ppm to 500 ppm. At sulfur levels below 500 ppm, the driving factor behind PM emission becomes PM filters and emission traps (Lee, Pedley, and Hobbs, 1998). Sixteen different engine tests were compiled for the F-T diesel data point in Table 5 (Alleman and McCormick, 2003; Cheng and Dibble, 1999; Clark et al., 1999; Frame et al, 2004; Fanick et al., 2001; Nord and Haupt, 2002; Rantanen et al., 2005; Schaberg et al., 2000; Schaberg et al., 1997; Sirman et al., 2000; Tao Wu et al., 2007). These studies included six light-duty engine tests and 10 heavy-duty engine tests and included transient test cycles, both hot and cold, and steady-state test studies. These studies also used a 300-ppm sulfur diesel fuel baseline. The average scaling factors for JP-8 and S5 (scaling factors of ∼0.48) are both about 0.19 lower than the scaling factor for synthetic diesel (0.67). Further, the scaling factors for JP-8 and S5 do not fall within two standard deviations of the F-T diesel scaling factor. This reduction in particulate matter is in agreement with observations from Lee, Pedley, and Hobbs (1998), which indicate that PM should decrease because of the reduced density of jet fuel relative to that of diesel. Lee et al. indicated that reducing aromatic content and increasing cetane have relatively little impact in comparison to the change in density. Because of this, the JP-8 value was used as a proxy for the reduction that could be anticipated with the use of either ULSJ or SPK in diesel GSE engines. As with both CO and HC, PM emission reductions matched the expected trend from Lee et al., but with greater reductions than expected. Reduction for both ULSJ and SPK were expected due to decreases in fuel density; however, F-T diesel showed lesser reductions than either S5 or JP8. This again indicates that Lee et al. do not capture some necessary element of fuel composition or engine geometry. 3.4 Life-Cycle Greenhouse Gas Emissions To accurately assess the impact of fuel combustion on global climate change, it is essential to consider the full fuel life cycle, from feedstock extraction through fuel combus- tion. If one only considers combustion, then for the fuels considered here (conventional jet fuel, SPK, and ULSJ fuel) the emissions of an alternative fuel will vary by less than 4%, and this is true regardless of the feedstock used to create the fuel (petroleum, natural gas, coal, or biomass) or how the fuel is processed. It is only from a life-cycle standpoint that one can see that biofuels offer the potential to reduce avia- tion’s impact on global climate change. Biofuels can lessen aviation’s production of greenhouse gases because the bio- fuel feedstock was created by photosynthetic reaction of water with carbon dioxide; thus, if atmospheric carbon diox- ide was used to grow the biomass, then the combustion of the biofuel results in the carbon dioxide being returned to the atmosphere from which it came and there is zero net emission of carbon dioxide into the atmosphere from fuel combustion. This is not true for fossil fuel combustion, where the fuel feedstock contains carbon that has been sequestered from the atmosphere for millions of years. Further back- ground information and guidance on creating a life-cycle GHG inventory can be found within the Framework and Guidance for Estimating Greenhouse Gas Footprints of Aviation Fuels (AFLCAWG, 2009). The life-cycle GHG emissions from a variety of potential alternative jet fuels are plotted in Figure 5; these data are from the analysis of Stratton et al. (2010). The results of Figure 5 include an assessment of the anticipated impact of variations in feedstock properties and process efficiencies on life-cycle GHG emissions as well as an analysis of the impacts of land- use changes. Five life-cycle steps were considered: feedstock recovery (e.g., mining, farming, pumping), feedstock trans- portation, feedstock processing (e.g., gasification, F-T synthe- sis, refining), transportation (of finished fuel), and fuel combustion. Because of the increased energy intensity of feed- stock extraction, unconventional petroleum fuels (oil sands and oil shale) have increased life-cycle carbon dioxide emis- sions relative to fuels created from crude oil. A ULS fuel has a slight increase in life-cycle carbon dioxide emissions because of the additional processing (i.e., refining) that is necessary to 18 Table 5. PM scaling results for JP-8, F-T diesel, and S5 relative to diesel [from Donohoo (2010) with permission]. Fuel JP- 8 F-T Diesel S5 PM scaling factor 0.48 n=7 =0.15 0.67 n=16 =0.067 0.47 n=2

19 Figure 5. Life-cycle GHG emissions from a variety of potential alternative fuel pathways that could result in SPK, ULS, or conventional fuels [from Stratton et al. (2010) with permission].

20 desulfurize the fuel. To achieve emissions comparable to con- ventional fuels, F-T fuels must either use carbon capture and sequestration (CCS) or incorporate biomass. Without CCS, F-T fuels from coal will have roughly twice the life-cycle carbon dioxide emissions. HRJ fuels have emissions that are highly dependent on the feedstock that is being used, with emissions from either direct or indirect land-use change dom- inating. The biomass to F-T fuel analysis assumes that the fuel was created from waste products or products from marginal land; thus there would be negligible net CO2 emissions from land-use changes. The production of biofuels from food crops can lead to emissions that are either an indirect or a direct result of land- use changes. Direct land-use change emissions result from the conversion of non-cropland (e.g., grasslands, rainforests, peatland) to cropland, while indirect land-use change emis- sions occur because food crops are diverted to biofuel produc- tion and this results in non-cropland elsewhere being diverted to create food crops—the latter is subject to much debate within the scientific community because of the complexity of the problem. The magnitude of the emissions depends on the type of land being converted to cropland, and in certain cases (e.g., conversion of rainforest or peatland), the emissions from land-use change can lead to a dramatic increase in life-cycle GHG emissions. The land-use change emission estimates within Figure 5, which are described in Table 6, are meant to provide a range of GHG emissions that may result from con- verting food crops to biofuel use. Table 6. Land-use change scenarios explored [from Stratton et al. (2010) with permission]. Land-Use Change Scenario 0 Scenario 1 Scenario 2 Scenario 3 Switchgrass None Carbon depleted soils converted to switchgrass cultivation n/a n/a Soy oil None Grassland conversion to soybean field Tropical rainforest conversion to soybean field n/a Palm oil None Logged over forest conversion to palm plantation field Tropical rainforest conversion to palm plantation field Peatland rainforest conversion to palm plantation field Rapeseed oil None Set-aside land converted to rapeseed cultivation n/a n/a Salicornia None Desert land converted to Salicornia cultivation field n/a n/a

Next: Chapter 4 - Air Quality Assessment for a Selected Airport »
Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB’s Airport Cooperative Research Program (ACRP) Report 46: Handbook for Analyzing the Costs and Benefits of Alternative Aviation Turbine Engine Fuels at Airports consists of the Alternative Fuel Investigation Tool (AFIT), a handbook on the use of AFIT, and a report on its development. AFIT is an analytical model designed to help airport operators and fuel suppliers evaluate the costs associated with introducing “drop-in” alternative turbine engine fuel at airports and the benefits as measured by reduced emissions.

AFIT, which is included in CD-ROM format with the print version of the report, takes into account options for using alternative fuel for other airside equipment, including diesel-powered ground support equipment.

The report also addresses characteristics of current fuel usage and distribution, and describes what is required to switch to alternatives.

The CD-ROM is also available for download from TRB’s website as an ISO image. Links to the ISO image and instructions for burning a CD-ROM from an ISO image are provided below.

Help on Burning a .ISO CD-ROM Image

Download the .ISO CD-ROM Image

Warning: This is a large file and may take some time to download using a high-speed connection.

CD-ROM Disclaimer - This software is offered as is, without warranty or promise of support of any kind either expressed or implied. Under no circumstance will the National Academy of Sciences or the Transportation Research Board (collectively “TRB’) be liable for any loss or damage caused by the installation or operations of this product. TRB makes no representation or warranty of any kind, expressed or implied, in fact or in law, including without limitation, the warranty of merchantability or the warranty of fitness for a particular purpose, and shall not in any case be liable for any consequential or special damages.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!