Nikita T. Saxena

Tufts University, Medford, Massachusetts

Anna E. Thomas

Georgia Institute of Technology, Atlanta, Georgia

Dale T. Shouse and Craig Neuroth

Air Force Research Laboratory, Wright-Patterson Air Force Base, Wright-Patterson AFB, Ohio 

Robert C. Hendricks

Glenn Research Center, Cleveland, Ohio

Amy Lynch, Charles W. Frayne, Jeffrey S. Stutrud, Edwin Corporan, and Terry Hankins

Air Force Research Laboratory, Wright-Patterson Air Force Base, Wright-Patterson AFB, Ohio

Alternate-Fueled Combustor-Sector Emissions

NASA/TP—2013-217734

September 2013
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Nikita T. Saxena

Tufts University, Medford, Massachusetts

Anna E. Thomas

Georgia Institute of Technology, Atlanta, Georgia

Dale T. Shouse and Craig Neuroth

Air Force Research Laboratory, Wright-Patterson Air Force Base, Wright-Patterson AFB, Ohio 

Robert C. Hendricks

Glenn Research Center, Cleveland, Ohio

Amy Lynch, Charles W. Frayne, Jeffrey S. Stutrud, Edwin Corporan, and Terry Hankins

Air Force Research Laboratory, Wright-Patterson Air Force Base, Wright-Patterson AFB, Ohio

Alternate-Fueled Combustor-Sector Emissions

NASA/TP—2013-217734

September 2013

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

14th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery 

(ISROMAC–14)

sponsored by the Fluid Systems Technology (FST) of Technische Universitat Darmstadt

Honolulu, HI, February 27–March 2, 2012
Acknowledgments

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This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by expert reviewer(s).
NASA/TP—2013-217734 1 

Alternate-Fueled Combustor-Sector Emissions 

Nikita T. Saxena 

Tufts University 

Medford, Massachusetts 02155 

Anna E. Thomas 

Georgia Institute of Technology 

Atlanta, Georgia 30332 

Dale T. Shouse and Craig Neuroth 

Air Force Research Laboratory 

Wright-Patterson Air Force Base 

Wright-Patterson AFB, Ohio 45433 

Robert C. Hendricks 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Amy Lynch, Charles W. Frayne, Jeffrey S. Stutrud, Edwin Corporan, and Terry Hankins 

Air Force Research Laboratory 

Wright-Patterson Air Force Base 

Wright-Patterson AFB, Ohio 45433 

Summary 

In order to meet rapidly growing demand for fuel, as well 

as address environmental concerns, the aviation industry has 

been testing alternate fuels for performance and technical 

usability in commercial and military aircraft. In order to make 

alternate fuels (and blends) a viable option for aviation, the 

fuel must be able to perform at a similar or higher level than 

traditional petroleum fuel. They also attempt to curb harmful 

emissions, and therefore a truly effective alternate fuel would 

emit at or under the level of currently used fuel. This report 

analyzes data from gaseous and particulate emissions of an 

aircraft combustor sector. The data were evaluated at various 

inlet conditions, including variation in pressure and temperature, fuel:air ratios, and percent composition of alternate fuel. 

Traditional JP–8+100 data were taken as a baseline, and 

blends of JP–8+100 with synthetic-paraffinic-kerosene (SPK) 

fuel (Fischer-Tropsch (FT)) were used for comparison. Gaseous and particulate emissions, as well as flame luminosity, 

were assessed for differences between FT composition of 0, 50, 

and 100 percent. The data show that SPK fuel (an FT-derived 

fuel) had slightly lower harmful gaseous emissions, and smoke 

number information corroborated the hypothesis that SPK–FT 

fuels are cleaner burning fuels. 

Introduction 

Currently, alternate aviation fuels must satisfy MIL–DTL–

83133F(2008) (military) or ASTM D 7566–Annex(2011) 

(commercial) standards and are termed “drop-in” fuel 

replacements. Fuel blends of up to 50 percent alternative fuel 

blended with petroleum (JP–8), which have become a practical alternative, are individually certified on the market. In 

order for a fuel alternate to be truly effective, it must have a 

sustainable supply and cause little environmental harm. Combustor emissions are of great relevance in alternate fuel 

considerations for both combustor efficiency as well as environmental and human health. The life cycle analysis (LCA) of 

fuel feedstocks carries a great effect on the usability of the fuel 

in aviation and is directly related to the combustor emissions 

data. The LCA estimates the impact of the greenhouse gas 

emissions for the entire fuel process, from production to distribution to usage, and can determine the true efficacy of using 

alternate fuel blends (Ref. 1). The testing discussed in this 

study represents only the emissions created when the fuel is in 

use. Because alternative fuels from multiple feedstocks are still 

being explored, fuel-flexible engine combustors are the primary 

targets for these tests, as they will be used for most of the fueling with alternate fuels in the near future. 

The emissions trending described in this paper proves some 

expected trends while highlighting differences for further 

observation. Data were taken from “Combustor A,” a proprietary-geometry three-cup combustor sector representative of 

current engine combustor technology (details withheld because of proprietary concerns). Both the gaseous and particulate sampling probes were placed at the nozzle exit plane. The 

probes were specially built for the cell facility at WrightPatterson Air Force Base. The facility has two identical fueling 

systems in place: one for the JP–8+100 (herein referred to as 

“JP–8”) fueling purposes and one for the Fischer-Tropsch (FT) 

fuel. The fuel is blended on line to achieve the desired blend. 

Further details regarding the facility, errors, postprocessing 
NASA/TP—2013-217734 2 

parameters, and so forth, are available in Reference 2. This 

report provides a full analysis of the data set introduced in 

that paper. 

Generally, the FT fuel is expected to be a cleaner burning 

fuel than the JP–8 fuel, and the blend falls somewhere 

between the two. The blend data appear to lean closer to the 

JP–8 emissions count rather than the FT emissions, allowing 

us to conclude that JP–8 is the dominating fuel in the blend, 

which is of potential importance when determining carbon 

credits or other emissions implications. This is corroborated 

by observations in performance data sets for these tests. 

Combustor Parameters and Collection 

of Data 

Data from Combustor A emissions were assessed for the 

following variables: 

(1) Inlet pressure (P) and temperature (T): 75 psia (0.52 MPa) 

and 500 F (533 K), 125 psia (0.86 MPa) and 625 F 

(603 K), 175 psia (1.21 MPa) and 725 F (658 K), and 

225 psia (1.55 MPa) and 790 F (694 K) 

(2) Combustor pressure drop (ΔP): 3, 4, and 5 percent 

(3) Fuel blends: 100 percent JP–8, 50:50 JP–8:FT, and 

100 percent FT (±5 percent) 

(4) Fuel:air ratio (F/A): 0.010, 0.015, 0.020, and 0.025 

Data were collected for the following emissions: NO (ppm), 

NO2 (ppm), NOx (ppm), CO (ppm), CO2 (percent), O2 (percent), and total hydrocarbon (THC) (ppm). Photodiode output 

voltage was also taken, and both still and high-speed photography were used and can be correlated with this luminosity data. 

Data such as smoke number information and particulate 

emissions are analyzed, in part, because of an incomplete data 

set. Data from collaborative testing sites are summarized in 

relevance to the paper to illustrate uniformity of the results. 

Gaseous Emissions 

Emissions such as nitrogen and carbon oxides are 

important to military and civil aviation. The emissions data 

collected in this study are listed below. 

(1) NO emissions: Nitric oxide (NO) emissions (with molecular atomic dimension 0.115 nm), measured in ppm, show 

uniform results for all pressure levels. There is a monotone 

decrease as the change in percentage combustor pressure drop 

(%ΔP) increases and a monotone increase as F/A increases. 

(2) NO2 emissions: Nitrogen dioxide (NO2) emissions, 

measured in ppm, (0.221 nm) follow a monotone increase 

with F/A. There is little change as %ΔP increases. The FT fuel 

trends show greater NO2 emissions than the JP–8 fuel. Unlike 

other emissions data, the 50:50 blend trends towards the FT 

fuel data rather than the JP–8 data. 

(3) NOx emissions: Nitrogen oxide (NOx) emissions (ppm) 

were taken as a combination of NO (ppm) and NO2 (ppm) 

data. Because NO emissions were greater, the NO trends are 

dominant in the NOx emissions data. Therefore, the emissions show a monotone decrease as %ΔP increases, and a 

monotone increase with F/A (Fig. 1), similar to the NO emissions. NOx emissions also increase with absolute pressure. 

Emissions from the 100-percent FT blend do tend to be lower 

than those of the JP–8 fuel, but the difference is too small to 

be conclusive. 

(4) CO2 emissions: The percent of carbon dioxide (CO2) 

emissions (0.116 nm) did not show a significant difference 

between fuels or %ΔP, and maintained a monotone increase 

with F/A. 

(5) CO emissions: Carbon monoxide (CO) emissions (ppm) 

(0.113 nm) showed significant increases with F/A. In the 

75-psia (0.52-MPa) pressure combustor, the only pressure for 

which the F/A data go up to 0.025, the CO concentration 

doubled from F/A of 0.020 to 0.025 (Fig. 2). 

The FT and 50:50 fuels showed a more pronounced jump 

with the increasing F/A (0.020 to 0.025) than the JP–8. CO 

emissions also showed a drastic decrease as absolute pressure 

increased. 

Figure 3 shows overall trends in CO emissions differences 

between the JP–8, the 50:50 blend, and FT fuels. A greater 

difference is apparent at higher F/A values. The 100-percent 

FT and 50:50 fuels generally emit less to similar amounts 

than JP–8 over the range of (ΔP) yet at higher F/A and lower 

inlet pressures (P), emit higher amounts with increasing (ΔP). 

The differences in CO become less significant at higher P and 

lower F/A. 
NASA/TP—2013-217734 3 
NASA/TP—2013-217734 4 

TABLE I.—COMBUSTOR EFFICIENCY DATA SUMMARY AT 75 psia (0.52 MPa) 

 Combustor pressure drop, 

ΔP

3 percent 4 percent 5 percent 

Fuel:air ratio, 

F/A

Fuel:air ratio, 

F/A

Fuel:air ratio, 

F/A

0.010 to 0.020 0.025 0.010 to 0.020 0.025 0.010 to 0.020 0.025 

Fuels 

 JP–8 99.61 99.32 99.56 99.10 99.46 99.20 

 50:50 blend 99.65 99.24 99.56 99.09 99.46 98.90 

 Fischer-Tropsch (FT) 99.66 99.20 99.58 98.96 99.48 98.87 

Average efficiency, percent 99.64 99.25 99.56 99.05 99.47 98.99 

Standard deviation 0.024 0.058 0.011 0.080 0.013 0.181 

(6) O2 emissions: The percent of oxygen (O2) emissions 

(0.116 nm) did not show a significant difference between 

fuels or %ΔP, and maintained a monotone increase with F/A. 

(7) THC emissions: Total hydrocarbon (THC) emissions 

do not show trends directly related to F/A, fuel type, or %ΔP 

for F/A <0.025. For the 75 psia (0.52 MPa) pressure data, there 

is again a significant increase in THC concentration, particularly for FT and 50:50 fuels relative to JP–8, from F/A of 0.020 to 

0.025 (Fig. 4). The smoke number data are not available for this 

F/A of 0.025. 

It is possible that a F/A of 0.025 represents the combustor 

efficiency drop-off ratio as the amount of uncombusted fuel 

rises significantly because of the fuel itself or combustor 

configuration (e.g., poor atomization, F/A, reactant-product 

mixing, or decreased heat content), contributing to higher 

emissions as shown in CO and THC data (Figs. 2 and 4). 

The data taken at the combustors show that in the 75 psia 

(0.52 MPa) data, the combustor efficiency at F/A = 0.025 is 

slightly lower than the rest (Table I). At 3 percent ΔP, the 

efficiency of all fuel blends averages to 99.64 percent with a 

standard deviation of 0.024 for F/A of 0.010, 0.015, and 0.020. 

However, at 0.025, the average efficiency is 99.25 percent with 

a standard deviation of 0.058. Similar trends are shown at 

4 percent ΔP, with averages and standard deviations of 99.56 

and 0.011 along with 99.05 and 0.080, respectively, as well as 

5 percent P with averages and standard deviations of 99.47 

and 0.013 along with 98.99 and 0.181, respectively. 

The efficiency difference between the first three F/A values 

and the fourth is much more significant than between the 

various types of fuel, as shown by the standard deviation. The 

data at 5 percent ΔP and F/A = 0.025 ratio is the one exception, as the difference between fuel blends is definite. The 

efficiency difference between fuel blends is more pronounced 

at higher %ΔP and F/A. The combustor efficiency for all 

three blends decreases as ΔP increases, but for all F/A values 

before 0.025, the efficiency differences between the blends 

are insignificant. 
NASA/TP—2013-217734 5 

Smoke and Photodiode Numbers 

The smoke number measurements were taken by filtering an 

exhaust sample and comparing the change in reflectance. The 

smoke data and the THC emissions (ppm) are expected to be 

somewhat correlated. The smoke number data from this testing 

run are partially incomplete, but the data obtained show some 

definite trends. Smoke number decreases as 100 percent FT 

fueling is approached, with more distinct decreases at higher F/A. 

Figure 5 illustrates this with the available smoke number data. 

The change in flame photodiode luminosity is related to all 

variables tested. It increases with F/A and decreases steadily 

with increasing %ΔP and %FT composition (Fig. 6). The 

decreased luminosity of the 50:50 blend and the FT fuel show 

that they are cleaner burning fuels than JP–8 (Fig. 7). The 

luminosity indicates carbon presence in the flames, and therefore the potential for carbon deposits within or coming 

through the engine to be released into the environment. The 

decrease in luminosity as the fuel blend approaches full FT 

fuel implies that the radiative heat loss is also decreasing as 

would liner temperature. This decrease occurs across increasing %ΔP and decreased F/A as well, signifying lower heat 

losses, cleaner burning, and a higher exit temperature from 

the combustor of the engine. 

 
NASA/TP—2013-217734 6 

Particulate Emissions 

The particulate emissions of any fuel are of utmost concern 

for both environmental and human health (Ref. 3). Like the 

gaseous emissions, they relate to engine temperature and 

pressure, %ΔP, F/A, and fuel composition. The data available 

from this study do demonstrate the clear reduction in particulate emissions from FT fuel at all pressures and F/A values 

(Fig. 8). Because the particulate emission size-distribution 

data available from this particular study was not enough to 

make definite conclusions, the effects of particulates will be 

left for another report. A figure of particulate sample size 

distributions has been included (Fig. 9) to illustrate again the 

significant difference between pure FT fuel and the blend and 

JP–8. The total number of particulates is visibly smaller, as is 

the peak size of the particles. This indicates the need for further studies into the size-related particle health effects. There 

are many analyses underway to characterize and compare 

particulate emissions for alternate fuels (e.g., alternative fuels 

testing on a C–17 aircraft (Ref. 4)). 
NASA/TP—2013-217734 7 

The effect of these particulate emissions on human health 

has been concluded by a number of researchers (Ref. 5), and 

the U.S. Environmental Protection Agency has launched a 

program involving multiple research centers to further investigate the hazards. The hazards include distress in respiratory 

and cardiovascular function—contributing to the development 

or worsening of common distresses such as asthma, chronic 

obstructive pulmonary disorder, angina pectoris, myocardial 

infarction (heart attack), and more. The possibility and problems associated with particles moving into the blood stream 

and being transported to other vital organs is also being considered (Ref. 6). 

Engine Emissions Testing 

Further testing that provides other insight into particulate 

emissions for both small and large engines has been done in 

collaboration with a large group of organizations, including 

government agencies, private industries, and educational 

institutions. 

Testing run by General Electric (GE) showed that for alternate fuels, the emissions level of the regulated emissions 

(NOx, CO, hydrocarbons, and smoke number) were within 

the limits set for traditional fuels. The GE study observed 

power levels starting from idle through to takeoff, capturing a 

full performance that the data in this report does not span. 

This study corroborates our results, presenting alternative fuel 

emissions and indicating that similar trends occur all through 

the flying process, offering further insight for true LCA 

(Ref. 7). 

A small-engine test with similar fuel parameters to ours 

was conducted with a Pratt & Whitney small turbine engine, 

with 100 percent FT fuel and JP–8 as well as a 50:50 blend. 

The trends observed in this test were similar: small reductions 

in NOx emissions as the SPK–FT fuel percentage increased, 

especially at higher power. The smoke number data was more 

conclusive, with the FT fuels having significantly lower 

smoke measurements than the JP–8 fuel (Ref. 8). 

Larger engine tests, such as those conducted in the Alternate Aviation Fuel Experiment (AAFEX) study (Refs. 9 and 

10), point in the same direction with regards to emissions 

trends. The C–17 test also tested both gaseous and particulate 

emissions data with similar results (Ref. 4). 

Emissions Implications 

The European Union has recently moved to implement a 

carbon emissions tax on airlines flying in and out of its airspace, an act that has enraged officials in foreign countries 

such as the United States and China. America’s aviation 

industry contributes approximately 2 percent of greenhouse 

gas emissions, and a law requiring payment per metric ton of 

carbon emission could place an overwhelming burden on an 

industry having hard times at present (Ref. 11). In order to 

maintain current flight profit and availability as well as market 

competitiveness, it is necessary for countries to move towards 

alternate fuels such as those proposed in this report. 

Concluding Remarks 

Gathering preliminary data is essential for establishing 

baseline information to compare performance and emissions 

data for alternate-fuel-flexible combustor-sector systems. 

Observing pure synthetic-paraffinic-kerosene (SPK) fuel 

(Fischer-Tropsch (FT)) and blended fuel with respect to 

JP–8+100 fuels can lead to the future development of new, 

efficient, and effective combustor systems for these up-andcoming types of fuel. Fuel-flexible systems are the near-term 

goal for the industry, and analysis of combustor performance 

is necessary for utilization of alternative fuels. The data from 

Combustor A summarized in this report provide analysis and 

comparison based on a variety of engine variables. 

Inlet temperature and pressure, fuel-to-air ratio (F/A), combustor pressure drops, and fuel blends were the parameters 

varied for this study. 

Generally, the gaseous emissions varied more based on F/A

than the fuel blend used. This report indicates that both 

100 percent FT and the 50:50 blend emit at or under currently 

acceptable rates. Although the differences were not enormous, FT fuel did have generally lower NOx emissions, one 

of the primary regulated emissions species today. However, at 

higher F/A, the combustor efficiency drops and emissions 

increase more with FT fuel blends than with JP–8. 

The smoke number differences were very distinct and point 

to the fact that, as hoped, SPK fuels are cleaner burning than 

JP–8 fuels, and the 50:50 blend is an intermediate step towards 

environmentally friendly fuel. It is important to note that a 

50:50 blend does not directly correlate to a 50 percent reduction in smoke or emissions, which has implications towards the 

effectiveness of using a blend as an economic substitute. 

Multiple studies and data sets show that SPK fuel and fuel 

blends do not have a significant negative impact on the performance of combustor sector systems, and that emissions 

produced certainly do not exceed the current limitations on 

traditional fuel. Taking into account the life cycle analysis 

and emissions reduction for alternate fueling, these SPK fuels 

are a promising near-term alternative for jet fuels. 

Glenn Research Center 

National Aeronautics and Space Administration 

Cleveland, Ohio, September 23, 2013 

References 

1. Stratton, Russell W.; Wong, Hsin Min; and Hileman, James I: 

Life Cycle Greenhouse Gas Emissions from Alternate Jet Fuels. 

Partnership for Air Transportation Noise and Emissions Reduction, PARTNER Project 28 Report, Version 1.2, 2010. 

http://web.mit.edu/aeroastro/partner/reports/proj28/partnerproj28-2010-001.pdf Accessed Sept. 23, 2012. 
NASA/TP—2013-217734 8 

2. Shouse, D.T., et al.: Alternate-Fueled Combustor-Sector Performance: Part A: Combustor Performance: Part B: Combustor 

Emissions. ISROMAC13–2010–49, 2010. 

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2010001741

3_2010018362.pdf Accessed Sept. 24, 2012. 

3. Hendricks, Robert C.; and Bushnell, Dennis: Particulate Emissions Hazards Associated with Fueling Heat Engines. Int. J. 

Rotating Mach., vol. 2011, no. 415296, 2011. 

http://www.hindawi.com/journals/ijrm/2011/415296/ Accessed 

March 28, 2013. 

4. Corporan, Edwin, et al.: Alternative Fuels Tests on a C‒17 Aircraft: Emissions Characteristics. Air Force Research Laboratory, Interim Report, 2010. 

5. Environmental Protection Agency: EPA Finds Greenhouse 

Gases Pose Threat to Public Health, Welfare/Proposed Finding 

Comes in Response to 2007 Supreme Court Ruling. News 

Release, 2009. 

http://yosemite.epa.gov/opa/admpress.nsf/0/0EF7DF675805295

D8525759B00566924 Accessed Jan. 22, 2013. 

6. Lippmann, Morton, et al.: The U.S. Environmental Protection 

Agency Particulate Matter Health Effects Research Centers 

Program: A Midcourse Report of Status, Progress, and Plans. 

Environ. Health Perspect., no. 111, no. 8, 2003. 

7. Kinder, James D.; and Rahmes, Timothy: Evaluation of BioDerived Synthetic Paraffinic Kerosenes (Bio-SPK). Sustainable 

Biofuels Research & Technology Program document, The Boeing Company, Seattle, WA, 2009. 

http://www.boeing.com/aboutus/govt_ops/reports_white_paper

s/pas_biofuel_exec_summary.pdf Accessed Sept. 24, 2012. 

8. Rahmes, T.F., et al.: Sustainable Bio-Derived Synthetic Paraffinic Kerosene (Bio-SPK) Jet Fuel Flights and Engine Tests 

Program Results. AIAA 2009–7002, 2009. 

9. Bulzan, D., et al.: Gaseous and Particulate Emissions Results of 

the NASA Alternative Aviation Fuel Experiment (AAFEX), 

GT2010‒23524, 2010. 

10. Anderson, B.E., et al.: Alternative Aviation Fuel Experiment 

(AAFEX). NASA/TM—2011-217059, 2011. 

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2011000720

2_2011007929.pdf http://ntrs.nasa.gov/search.jsp 

11. CleanBiz: Trade War Looms Over EU’s Airline Carbon Tax. 

CleanBiz Asia, 2011. 

http://www.cleanbiz.asia/story/trade-war-looms-overeu%E2%80%99s-airline-carbon-tax. 
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14. ABSTRACT

In order to meet rapidly growing demand for fuel, as well as address environmental concerns, the aviation industry has been testing alternate 

fuels for performance and technical usability in commercial and military aircraft. In order to make alternate fuels (and blends) a viable 

option for aviation, the fuel must be able to perform at a similar or higher level than traditional petroleum fuel. They also attempt to curb 

harmful emissions, and therefore a truly effective alternate fuel would emit at or under the level of currently used fuel. This report analyzes 

data from gaseous and particulate emissions of an aircraft combustor sector. The data were evaluated at various inlet conditions, including 

variation in pressure and temperature, fuel-to-air ratios, and percent composition of alternate fuel. Traditional JP-8+100 data were taken as a 

baseline, and blends of JP-8+100 with synthetic-paraffinic-kerosene (SPK) fuel (Fischer-Tropsch (FT)) were used for comparison. Gaseous 

and particulate emissions, as well as flame luminosity, were assessed for differences between FT composition of 0, 50, and 100 percent. The 

data show that SPK fuel (an FT-derived fuel) had slightly lower harmful gaseous emissions, and smoke number information corroborated 

the hypothesis that SPK-FT fuels are cleaner burning fuels.

15. SUBJECT TERMS

Green aviation; Fueling; Energy; Particulates; Pollution control; Air pollution; Combustion product; Combustor design 

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U 

19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18