Yolanda R. Hicks and Kathleen M. Tacina

Glenn Research Center, Cleveland, Ohio

Comparing a Fischer-Tropsch Alternate Fuel to

JP–8 and Their 50-50 Blend: Flow and Flame

Visualization Results

NASA/TM—2013-217884

July 2013
NASA STI Program . . . in Profi le

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientifi c and Technical Information (STI) 

program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Offi cer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI program provides access 

to the NASA Aeronautics and Space Database and 

its public interface, the NASA Technical Reports 

Server, thus providing one of the largest collections 

of aeronautical and space science STI in the world. 

Results are published in both non-NASA channels 

and by NASA in the NASA STI Report Series, which 

includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major signifi cant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of signifi cant 

scientifi c and technical data and information 

deemed to be of continuing reference value. 

NASA counterpart of peer-reviewed formal 

professional papers but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientifi c 

and technical fi ndings that are preliminary or 

of specialized interest, e.g., quick release 

reports, working papers, and bibliographies that 

contain minimal annotation. Does not contain 

extensive analysis.

• CONTRACTOR REPORT. Scientifi c and 

technical fi ndings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientifi c and technical 

conferences, symposia, seminars, or other 

meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientifi c, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientifi c and 

technical material pertinent to NASA’s mission.

Specialized services also include creating custom 

thesauri, building customized databases, organizing 

and publishing research results.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question to help@sti.nasa.gov

• Fax your question to the NASA STI 

Information Desk at 443–757–5803

• Phone the NASA STI Information Desk at

 443–757–5802

• Write to:

 STI Information Desk

 NASA Center for AeroSpace Information

 7115 Standard Drive

 Hanover, MD 21076–1320
Yolanda R. Hicks and Kathleen M. Tacina

Glenn Research Center, Cleveland, Ohio

Comparing a Fischer-Tropsch Alternate Fuel to

JP–8 and Their 50-50 Blend: Flow and Flame

Visualization Results

NASA/TM—2013-217884

July 2013

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Central States Section Spring Technical Meeting

sponsored by the Combustion Institute 

Dayton, Ohio, April 22–24, 2012
Acknowledgments

This work was supported by the Subsonic Fixed Wing Project in NASA’s Aeronautics Research Mission Directorate.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

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 technical management. 

This report is a formal draft or working 

paper, intended to solicit comments and 

ideas from a technical peer group.

This report contains preliminary fi ndings, 

subject to revision as analysis proceeds.
NASA/TM—2013-217884 1 

Comparing a Fischer-Tropsch Alternate Fuel to JP–8 and Their 

50-50 Blend: Flow and Flame Visualization Results 

Yolanda R. Hicks and Kathleen M. Tacina 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

Combustion performance of a Fischer-Tropsch (FT) jet fuel manufactured by Sasol was compared to 

JP–8 and a 50-50 blend of the two fuels, using the NASA/Woodward 9 point Lean Direct Injector (LDI) 

in its baseline configuration. The baseline LDI configuration uses 60° axial air-swirlers, whose vanes 

generate clockwise swirl, in the streamwise sense. For all cases, the fuel-air equivalence ratio was 0.455, 

and the combustor inlet pressure and pressure drop were 10-bar and 4 percent. The three inlet temperatures used were 828, 728, and 617 K. The objectives of this experiment were to visually compare JP–8 

flames with FT flames for gross features. Specifically, we sought to ascertain in a simple way visible 

luminosity, sooting, and primary flame length of the FT compared to a standard JP grade fuel. We used 

color video imaging and high-speed imaging to achieve these goals. The flame color provided a way to 

qualitatively compare soot formation. The length of the luminous signal measured using the high speed 

camera allowed an assessment of primary flame length. It was determined that the shortest flames resulted 

from the FT fuel. 

1.0 Introduction 

Due to the rising cost of oil and the need to supplement the domestic petroleum supply (Refs. 1 and 

2), interest in non-petroleum-based jet fuels is increasing. Domestic supplies of coal and natural gas can 

be converted to jet fuel using the Fischer-Tropsch process (Ref. 3). Fischer-Tropsch fuels have two other 

advantages when compared to conventional jet fuel: a higher breakpoint (Ref. 4) and lower emissions of 

particulates (Refs. 1 and 5). Because of these advantages, NASA’s Fundamental Aeronautics/Subsonic 

Fixed Wing (SFW) Project has been sponsoring experiments using Fischer-Tropsch fuels. 

For example, the NASA-led Alternative Aviation Fuels Experiment (AAFEX) measured particulate 

emissions from a DC-8 aircraft with CFM-56-2 engines. The DC-8 was parked on the runway of the 

NASA aircraft facility in Palmdale, California, and emissions were measured at multiple downstream 

locations. Emissions were measured with the following fuels: JP–8, a Fischer-Tropsch fuel made from 

natural gas, a Fischer-Tropsch fuel made from coal, and 50-50 blends of the JP–8 and Fischer-Tropsch 

fuels. Results showed that the burning the Fischer-Tropsch fuel reduced both volatile and nonvolatile 

(i.e., soot) emissions, especially at low power and idle conditions (Ref. 1). 

The study described here complements the AAFEX campaign. The AAFEX campaign studied 

emissions downstream of the engine. In contrast, this study uses a flame tube to study conditions in the 

combustor itself. The AAFEX campaign used a late-1970’s technology CFM-56-2 engine with a 

conventional combustor; this study uses a low-emissions combustor concept similar to what may be used 

in future aircraft engines. 

The low-emissions combustor concept used in this study is the 9-point lean direct injection (LDI) 

concept (Ref. 6). As the name implies, in LDI the combustor operates fuel-lean without a rich front end: 

all of the combustor air except that used for liner cooling enters through the combustor dome. Like other 

lean burn combustor concepts, LDI reduces nitrogen oxides (NOx) emissions by minimizing flame 

temperature; in fuel lean combustion, NOx is an exponential function of temperature. To eliminate local 

“hot spots” that produce high levels of NOx, lean burn combustion concepts rely on the fuel and air being 

well-mixed before burning occurs. Thus, LDI requires rapid fuel vaporization and fuel-air mixing. LDI 
NASA/TM—2013-217884 2 

achieves this by using a multielement concept in which several small fuel/air mixers replace a single 

conventional fuel/air mixer. Several LDI geometries have been studied (Refs. 6 to 8); the 9-point LDI 

geometry used in this study is the baseline geometry described in Reference 6. 

Combustion performance of a Fischer-Tropsch jet fuel manufactured by Sasol (designated herein as 

FT–2) was compared to JP-8 and a 50-50 blend of the two fuels. The objectives of this experiment were 

to visually compare JP–8 flames with FT–2 flames for gross features. Specifically, we wanted to ascertain 

in a simple way visible luminosity, sooting, and primary flame length of the FT–2 compared to a standard 

JP grade fuel. We used video imaging and high-speed imaging to achieve these goals. 

2.0 Fuel Composition 

JP–8 is a standard, refined aircraft engine fuel. Table 1 shows a typical JP–8 composition. Its 

constituents fall within the standards for that JP-fuel class, and JP–8 contains up to 20 percent aromatics 

by volume, many being polycyclic aromatic hydrocarbons (PAH) such as naphthalene (C10). Thus, JP–8 

inherently contains soot precursors such as benzene and toluene, and polymerized soot constituents such 

as the PAH. Table 2 shows a comparison between the specific FT–2 fuel used for testing and a JP-8 

sample. The total aromatic content of the FT–2 fuel is only 0.6 volume percent compared to 18.6 for 

JP–8. The FT–2 fuel also has zero naphthalene and presumably no PAH content. Because the FT–2 

aromatic content is low, we expect very little soot formation and lower flame luminosity compared to the 

JP fuel. The FT–2 is slightly more volatile and has a higher H/C ratio. The higher cetane index for the 

FT–2 indicates that it has a shorter ignition delay time than does JP–8. 

TABLE 2.—COMPARISON OF THE FT–2 FUEL 

WITH A JP–8 SAMPLE 

Fuel JP-8 FT2 

Sulfur (ppm) 1148 22 

Olefins (%vol) 0.9 3.8 

Aromatics (%vol) 18.6 0.6 

Naphthalenes (%vol) 1.6 0 

Distillation 

IBP 158 160 

10% 176 167 

20% 184 170 

50% 207 180 

90% 248 208 

EP 273 231 

Residue (%vol) 0.8 1 

Loss (%vol) 0.8 0.9 

Flash point C 46 42 

API gravity 41.9 54 

Specific gravity 0.816 0.763 

Freezing point C -50 <-80 

Viscosity 4.7 3.6 

Cetane index 41 51 

Hydrogen content (%mass) 13.6 15.1 

Heat of combustion (MJ/kg) 43.3 44.1 

Fuel H/C ratio 1.88 2.12 

 

TABLE 1.—TYPICAL FUEL COMPOSITION OF 

JET-A OR JP–8 (REF. 9) 

Components Volume, 

percent 

Molecular, 

weight 

Boiling pt, 

°C 

Density, 

g/ml 

C8 paraffins 0.3 114.2 118 0.70 

C8 cycloparaffins 0.2 112.2 124 0.78 

C8 aromatics 0.1 106.2 139 0.87 

C9 paraffins 2.4 128.3 142 0.72 

C9 cycloparaffins 1.5 126.2 154 0.80 

C9 aromatics 1.0 120.2 165 0.88 

C10 paraffins 5.6 142.3 160 0.72 

C10 cycloparaffins 3.5 140.3 171 0.80 

C10 aromatics 2.3 134.2 177 0.86 

C11 paraffins 8.7 156.3 196 0.74 

C11 cycloparaffins 3.3 154.3 196 0.80 

Dicycloparaffins 3.1 152.3 201 0.89 

C11 aromatics 3.6 148.2 205 0.86 

C12 paraffins 10.8 170.3 216 0.75 

C12 cycloparaffins 8.0 166.3 221 0.88 

C12 aromatics 4.6 162.3 216 0.86 

C13 paraffins 11.5 184.4 235 0.76 

C13 cycloparaffins 8.5 182.4 225 0.80 

C13 aromatics 4.9 176.6 234 0.87 

C14 paraffins 5.9 198.4 254 0.76 

C14 cycloparaffins 4.4 192.4 290 0.94 

C14 aromatics 2.5 186.3 295 1.03 

C15 paraffins 1.4 212.4 271 0.77 

C15 cycloparaffins 1.0 206.4 300 0.90 

C15 aromatics 0.6 200.4 305 0.95 

C16 hydrocarbons 0.2 226.4 287 0.77 

Residual 

hydrocarbons 

0.1 202.3 393 1.27 

mixture density, 0.81 g/ml; average carbon number, C12; total aromatics, 19.6% 
NASA/TM—2013-217884 3 

3.0 Experimental Setup 

The fuel comparison testing was conducted using the lean direct injection (LDI) concept developed 

by NASA and described in Reference 6. As illustrated in Figure 1, this baseline configuration consists of 

an air passage that contains a 60° axial swirler, whose vanes generate clockwise (streamwise) swirl. 

Shortly after the swirler is a converging-diverging venturi section. At the throat of the venturi, the fuel is 

injected via a simplex atomizer. At the end of the diffusing venturi is the injector dump plane. Figure 2 

shows the 33, 9-pt LDI hardware used. The LDI elements are spaced on 25.4-mm centers. The hardware 

was installed in the optically-accessible flame tube illustrated in Figure 3, with the dump plane at the 

leading edge of the window which spans 38-mm in the axial direction and is 50-mm high. 

For all cases, the fuel-air equivalence ratio, , was 0.455, the combustor inlet pressure and pressure 

drop was 150-psia and 4 percent. The three inlet temperatures used were 828, 728, and 617 K. These 

produced nine combinations, as shown in Table 3. 

Figure 1.—Schematic drawing that shows the relative 

spatial positioning of the air swirler, fuel nozzle, and 

venturi for each LDI injector element. 

Figure 2.—End view of the 9-point 

LDI test hardware, with an overlay 

of the vertical center plane. 

Figure 3.—Schematic drawing of the flame tube 

combustor used for the LDI alternative fuel test. 

The injector exit coincides with the upstream edge 

of the windows. 

TABLE 3.—CONDITION MATRIX USED FOR ALTERNATIVE FUEL FLAME IMAGING TEST 

JP-8, 828 K JP-8, 728 K JP-8, 617 K 

50-50 blend, 828 K 50-50 blend, 728 K 50-50 blend, 617 K 

FT-2, 828 K FT-2, 728 K FT-2, 617 K 
NASA/TM—2013-217884 4 

The visible flame was recorded in two ways. The first used a standard, 30-Hz, color video camera, 

having a 1/3-in. format CCD array, focused near the center of the flow. The camera perspective was 

angled so that multiple injector elements could be seen. For the second imaging technique, we used a 

12-bit, grayscale, high-speed camera that has a CMOS array with 10241024 pixel resolution. Unlike the 

video camera, the high-speed camera was set up square to the rig and focused on the imaginary vertical 

plane that contains the centerline of the middle injector, (overlay in Fig. 2). The high-speed camera frame 

rate and resolution are variable. The camera can frame as fast as 5400-frames/s (5.4-kps) at full resolution 

(which provides the maximum field-of view image size), and faster at lower resolutions. For example, to 

frame at 30-kps requires a reduction in the total number of pixels (and viewable area) read out per 

image—we used a resolution of 448384 pixels. For these fuel comparison tests, we collected images 

with frame rates from 5.4 to 72-kps, with 30-kps typical. The flame chemiluminescence was collected 

using an f = 150-mm, f/1.2 lens. We used three light filtering options, as described in Table 4. These 

filters were used to reduce the amount of light collected to help optimize image exposure. The filter 

options were: (1) none, in which all visible light that the camera array is sensitive to was collected; (2) a 

filter with optical density 2 (OD2), which transmitted one percent of the light; or (3) a combination of an 

OD1 filter (10 percent transmission) combined with a 473-nm long pass filter. The long pass filter 

blocked primarily CH* chemiluminescence and allowed most of the C2* Swann band emissions to pass. 

Regardless of the imaging scheme used, all images are volume-based, line-of-sight images, meaning 

that the total intensity recorded comes from the entire combustor volume that is within the field of view. 

TABLE 4.—OPTICAL CHARACTERISTICS OF THE FILTERS USED FOR HIGH SPEED FLAME IMAGING 

Filter option Wavelength band Transmission, 

percent 

1. None Visible light 100 

2. Neutral density with OD2 Visible light 1 

3. Neutral density OD1and long pass Visible light longer than 473-nm 10 

4.0 Results 

4.1 Standard Video Results 

We used color video to get a sense of which major constituents were emitting (Ref. 10). In the visible 

region, emissions in the violet come mainly from CH*, near 432-nm. The other primary chemical species 

that emits is C2*, with Swan bands in the blue (473-nm), green (516-nm), and yellow (573-nm). The CH* 

and C2* emissions are what we typically consider as the “clean” hydrocarbon flame colors, while orange 

generally indicates a sooty flame. Soot can be a problem because it detrimentally affects heat transfer to 

engine subcomponents. Also, particles that are not burnt off before leaving the combustor will carry on 

through the engine and be exhausted into the atmosphere. 

Whether soot is the predominant visible light emitter, we can discern qualitatively by observing the 

flame color via standard video. Video image results are displayed in Figure 4. The camera was angled so 

that parts of five LDI elements can be seen. Flow passes from left to right. JP–8 images are in the top row 

of Figure 4, FT–2 in the bottom row and the blend is shown in the center. The inlet temperature decreases 

from left column to right. One expected trend for JP–8 is that as the inlet temperature drops, the flame 

goes from primarily blue-green to primarily yellowish, and there is more soot formation at lower T3. Light 

emitted by the soot at the lower temperatures is bright enough to saturate, preventing any real detail from 

being seen. We also note that even at the highest inlet temperature there is some indication of soot, though 

the dominant emissions are from the C2 and CH bond breakage. In comparison, the FT–2 flame is much 

bluer, with very little soot luminescence. The inlet temperature trend for FT–2 follows that for JP–8, but 

with much less luminosity from soot. These results are reasonable given the fuel constituent comparison 

in Table 2, in which we see that the FT–2 contains only 0.6 percent aromatics. 
NASA/TM—2013-217884 5 

Fuel 

Type 



Tinlet



828 K 728 K 617 K

JP8 

50-50 

Blend 

FT–2 

Figure 4.—Standard video images, with flow from left to right. The flow field is partially blocked in the lower left 

corner by other test rig instrumentation. 

In general, we can see distinct flames from each injector element that appear to begin burning before 

exiting the diffuser. We cannot discern any sort of angle, or flare, to the flame, nor can we determine the 

length of the primary zone. For that information, we turn to the high speed digital camera. 
NASA/TM—2013-217884 6 

4.2 High Speed Image Results 

Figures 5 and 6 each show ten consecutive frames from the high speed camera for the 828 and 728 K 

inlet temperature cases. The frame rates are 12 and 30-kps, respectively. Exposure time per image is 

1/(frame rate). Flow passes from left to right. These snapshots suggest a rapidly varying, turbulent flow. 

For each case, it appears that the downstream extent of the visible light emitted is slightly greater for the 

JP–8 case than for the alternative fuel. 

JP–8 

Blend 

FT–2 

Figure 5.—Ten successive images at T3 = 828 K framed at 12 kps that show flames burning JP–8 (top), the 50-50 

blend (center) and FT–2. The top and center images are filtered using an optical density of 1 so as to avoid 

image saturation. The bottom images are unfiltered because the exposure is inadequate (too dim) with OD1. 

Image resolution and framing is such that the center row is fully captured, plus a bit from the rows above and 

below. The downstream window edge is visible on the right as a vertical line. Flow passes from left to right. 
NASA/TM—2013-217884 7 

JP–8 

Blend 

FT–2 

Figure 6.—Ten successive frames at T3 = 728 K framed at 30 kps that show flames burning JP–8 (top), the 50-50 

blend (center) and FT–2. All images are unfiltered. The framing captures the flame from the center row of 

injectors and extends approximately 26-mm downstream. Flow passes from left to right. 

The frame rate of 12-kps provides a pixel resolution (748640) such that one can observe fully the 

center row plus parts of the adjacent top and bottom rows. The downstream window edge can also be seen 

in these images as a relatively bright (compared to its surroundings), vertical line. This frame rate is also 

slow enough that some individual images appear to have “wisps” or streaks of flame visible. This 

streakiness suggests that the fluid is moving faster than the 83-μs exposure time of the frames, and we are 

able to track to some extent “flamelets.” The exposure time is also long enough that the filter set with 

optical density 1 (which transmitted 10 percent of the incident light longer than 473-nm) was required for 

the pure JP–8 and the 50-50 blend so as to avoid excessive image saturation. The FT–2 case did not emit 
NASA/TM—2013-217884 8 

as much light, and no filter was used. Filter usage was therefore consistent with our observations of flame 

luminosity from the video camera. Also using this resolution and the FT–2 image set, one can get some 

sense of the overall spray/flame shape or boundary. 

There are fewer streaks in the 30-kps image sequences, so this exposure time does a better job of 

stopping fluid motion within each frame. The resolution for these images, at 448384 pixels, was just 

enough to capture the center row of injectors. Because the 30-kps images shown were obtained without 

filters, we can again qualitatively say that the FT–2 fuel emits less visible light than does the JP-8 when 

burning. 

Using the visible luminescence, we examine these flames for structure, length and interaction 

between adjacent rows. Figure 7 shows the average luminous intensity and flame shape for the images 

framed at 12-kps (the images in Figure 5 are subsets of the images used to determine the averages). Each 

image is scaled independently. Flow passes from left to right. The y-axis scale shows vertical distance 

from the centerline of the 9-point injector array; the x-axis scale is the distance from the injector dump 

plane (diffuser exit). There is also an overlay on each image of a dashed, white, line that represents the 

approximate vertical center of the injector array. For all cases, we note that the center row is relatively 

self-contained, with little interaction between adjacent rows, as evidenced by the relatively low signal 

between the rows. The signal about the “centerline” is slightly asymmetric, with the higher signal in the 

upper half. This asymmetry might be related to interactions induced by the air swirl (all co-rotating) of 

adjacent injectors (and is a topic outside the scope of this paper). The key differences between fuel types 

highlighted by the Figure 7 images are the shape of the luminous structure and its distance from the 

injector exit. For JP–8, the central structure has a slight flare above and below from which one might infer 

a short, conical shape. For the blend and the FT–2, the structure is more rectangular. We also observe that 

the primary heat release shifts closer to the dome for the FT–2. The average shape is such that one might 

speculate that the structure we see for the JP–8 has shifted upstream into the diffuser when burning the 

alternative fuel. That is, if we take the observed JP–8 signal and simply shift it upstream, is there a point 

where we would likely see a field similar to that for FT–2? 

 JP–8 Blend FT–2 Vertical distance from centerline, mm 

 Axial distance from dome, mm Axial distance from dome, mm Axial distance from dome, mm

high

low

Figure 7.—Average flame structure and luminous intensity obtained by averaging over 6000 frames for the T3 = 

828 K cases. Flow is from left to right. The frame rate was 12000 fps. As illustrated by the rectangular overlay in 

the above cartoon, framing fully incorporates the center row, plus part of the top and bottom rows. The axial span 

shown is approximately 0 to 30 mm downstream from the injector exit. 
NASA/TM—2013-217884 9 

Figure 8.—Comparison showing average flame length and 

luminous intensity for T3 = 828 K, for a 0.6-mm horizontal 

strip around the vertical center of the images shown in 

Figure 7. The frame rate was 12 kps. 

Figure 8 presents the signal for the 0.6-mm high horizontal strip through the center row of the 

Figure 7 images along the dashed line. The drop lines show the location of peak signal. Although the 

vertical scale has arbitrary units, the values reflect the relative maximum intensities, as they have been 

corrected based on the filter used. Assuming the intensity reflects the core flame length, we determine 

from this plot that the FT–2 fuel burns closer to the injector exit, with a peak location about 2-mm away, 

compared to 4-mm for JP–8. This result makes sense because the FT fuel vaporizes more easily, has a 

higher cetane index (which is an indicator of shorter ignition delay time) and also has a greater hydrogen 

and olefin content compared to the JP fuel, both of which are indicators of a more easily reactive fuel. 

Because aromatics tend to have longer ignition delay times, the aromatic components of the fuels will 

tend to burn farther downstream than will the saturated hydrocarbons. The aromatics will also produce the 

most soot, and the areas of the flame with the most soot will produce the highest signal levels. Both these 

characteristics are reflected in Figure 8. Another way to consider this is by computing histograms of the 

signal in the images. 

Figure 9 shows histograms for jet fuel and for FT–2 for the middle inlet temperature case (728 K), 

and all were made from 30,000 fps images. Each histogram is for one pixel; this pixel is located vertically 

on the image centerline and horizontally at the axial distance stated on the histogram (2.5, 5.0, 7.5, 10.0, 

or 15.0 mm). The x-axis of these histograms represents a bin for each possible signal value (0 to 4095), 

and the y-axis gives the percentage of images where the pixel of interest is at that level. The solid vertical 

line marks the mean at that pixel, and the dashed vertical line marks the median. The left column shows 

histograms for JP–8 fuel. These histograms result from the images taken with the third filter listed in 

Table 4: OD1 with a 473-nm long-pass filter. The right column shows histograms for Fischer-Tropsch 

fuel obtained without a filter. It was not possible to perform a good comparison using the same filtering 

for both fuels because the unfiltered images for JP–8 saturated too much (20 percent of the time); whereas 

the images obtained using filter set 3 for the FT–2 were quite dim and did not make full use of the 

dynamic range available (the mean value was always less than 200 counts, with a maximum less than 

500 counts). All images in an image set were used to construct the histograms: 5,388 images for the JP–8 

histograms and 5,073 images for the unfiltered alternative fuel histograms. 
NASA/TM—2013-217884 10 

JP–8 FT–2 

Figure 9.—Histograms derived from 30,000 fps high speed 

movies for JP–8 with filter 3 (left column) and unfiltered 

FT–2 (right). The histograms show the percent of 

occurrences of light signal level for a single pixel that lies 

along the vertical midpoint of the middle injector row (the 

relative “centerline”) at the downstream distances 

indicated. The inlet temperature was 728 K. 

The JP–8 and FT–2 histograms show some similarities. All distributions are unsymmetrical, with 

longer tails at higher signal levels than at lower signal levels. For this reason, the mean is always higher 

than the median. For both the JP–8 and the unfiltered FT–2 case, the distribution becomes more skewed 

towards higher signal levels as the downstream distance increases. In particular, the peak in the number of 

saturated (4095) values is downstream of the location where the mean peaks. For this reason, the ratio of 

the mean to the median tends to increase with downstream distance. The increased skew towards higher 

signal levels at farther downstream distances is consistent with the aromatic components of the fuel 

burning farther downstream. 

Despite these similarities, the JP-8 histograms can easily be distinguished from the FT–2 histograms. 

First, note that the JP–8 histograms show a wider distribution of signal levels than do the unfiltered 

alternative fuel histograms despite the fact that the mean value of the alternative fuel histogram is always 

wider. Second, note that skew towards higher signal levels noted above is more pronounced for the JP–8 

histograms. In particular, despite lower means, the peak percentage of saturated values is higher for the 

JP–8 case (0.33 percent at 10.0-mm) than for the unfiltered FT–2 case (0.30 percent at 7.5 mm). Again, 

the wider signal distribution, coupled with the more pronounced skew toward higher signal is consistent 

with the greater aromatic content in JP–8. 

 
NASA/TM—2013-217884 11 

As seen in the individual images (Figs. 5 and 6), there is a considerable amount of variation from one 

image to the next. Figure 10 shows the mean, standard deviation, and span per pixel for the JP–8 (top 

row) and FT–2 (bottom row) cases. As one might expect, most of the signal variation occurs immediately 

downstream from the fuel injection region, as shown by the standard deviation, with very little change at 

all in the areas at the dome face that are between the injection sites. The standard deviation plots also 

indicate that there is some communication between injectors just a short way downstream. The plots that 

show the local pixel span also serve to highlight variation from the mean. In this case, they also show a 

dead zone upstream. They also show that although the flames are short on average, there are occasional 

excursions to high signal downstream of the primary flame zone. 

Figure 11 shows the 30-kps average results for all cases except the JP–8 high T3 condition. The frame 

rate allows us to visualize only the center row. As we saw earlier in Figure 7, the high inlet case has 

higher signal in the upper half of the flame (left column), but the structure and distribution of signal 

changes as the inlet temperature decreases. In all cases the flame length increases. For FT–2, the structure 

shifts from a slightly top-heavy asymmetry at 828 K to symmetric at 728 K to bottom-heavy asymmetry 

at 617 K. In fact, at the lowest temperature the chemiluminescent structure is the same regardless of the 

fuel used, though the FT–2 peaks closer to the dome. This similarity in structure at 617 K may be because 

fuel vaporization or reaction rates are closer among the three fuel mixtures than they are at higher 

temperatures. 

 Luminous mean Standard deviation local (max – min)

Vertical dist from centerline, mm

high

low

Vertical dist from centerline, mm

high

low

 Axial distance from dome, mm 

Figure 10.—Statistics derived from processing the signal intensities of over 10000 consecutive flame images 

on a pixel-per-pixel basis. The camera frame rate was 12,000/s. Inlet conditions: T = 828 K, P = 1034-kPa, 

 = 0.45, flow left to right. Top row: JP–8; Bottom row: FT–2. 

 
NASA/TM—2013-217884 12 

 

T3

Fuel 

Type 

828 K 728 K 617 K

JP–8 

high 

low

50-50 

Blend

FT–2 

Figure 11.—Average flame structure and luminous intensity obtained by averaging individual movie frames. Each 

image is independently scaled. The frame rate was 30000/s. The image set for JP–8 at the highest inlet temperature was not adequate for comparison. The end view cartoon shows that framing is about the center row of 

injectors. The axial distance extends from the dump plane to approximately 25-mm downstream from the injector 

exit. The height is approximately 23-mm. 

 
NASA/TM—2013-217884 13 

Figure 12 shows the resultant fields when the same raw images used to produce the Figure 11 images 

are processed in a manner similar to particle image velocimetry, so as to track the relative bulk motion of 

this fluid system. The sets chosen for processing are those that had subjectively good exposures: that is, 

the images did not saturate too much, and were not too dim. Since the process attempts to correlate the 

motion from frame to frame, exposure is important and will play a role in the results generated using this 

procedure; thus these vector results are purely qualitative. Another factor to consider when looking at 

these plots is that the raw images collected the light transmitted through the bulk of the fluid of a threedimensional field integrated onto a two-dimensional array. The vectors show the bulk direction of travel; 

the contours reflect the rate of change for that region of the space. 

 828 K 728 K 617 K JP–8 50-50 Blend FT–2 

Axial distance from dome, mm Axial distance from dome, mm Axial distance from dome, mm

Figure 12.—Average flame zone structure obtained by processing the 5001 consecutive movie frames. The frame 

rate was 30,000 fps. Framing is about the center row of injectors. The contour denotes the relative magnitude of 

change within the primary flame zone and the arrows can be interpreted as showing the average direction of 

motion within the flame zone. 
NASA/TM—2013-217884 14 

Figure 13.—Average flame zone structure obtained by processing movie frames for JP–8 (left) 

and FT–2 (right) at inlet temperature 617 K. The frame rate was 16,000 fps. Framing is about 

the center row of injectors. The contour denotes the relative magnitude of change within the 

primary flame zone and the arrows can be interpreted as showing the average direction of 

motion within the flame zone. 

The vectors show that the fluid flows radially outward from the injector exit, providing the best 

evidence that the flow from the injector is conical, regardless of fuel type. The slowest relative motion is 

immediately downstream, along the injector centerline. These averages show that the greatest change per 

unit time occurs in the lower half in all cases. This is unlike the case of the chemiluminescence-based 

averages, which had a shift in intensity from the upper half to the lower half as the inlet temperature 

decreased. The second greatest area of change is on the mirror opposite side. These areas are where the 

flow from adjacent injectors downstream is most likely to interact. This can be seen more clearly in the 

images shown in Figure 13, which compares the two pure fuel cases at the lowest inlet temperature, 

617 K, for high speed movies captured at 16,000 fps and the larger field of view that enables one to 

observe the region between injector rows. 

5.0 Concluding Remarks 

Using the NASA-developed LDI injector and an optically-accessible flame tube, we visually 

compared combustion of JP–8, FT–2 and a 50-50 blend of the fuels using standard color video and high 

speed imaging to examine flame structure. We determined that these simple imaging tools allow one to 

quickly assess luminosity, soot and flame length. We used the video primarily to assess the “cleanliness” 

of the flames by considering the flame color. We saw that the JP–8 flames are more likely to soot and that 

both fuels show more incandescence from soot at the lowest inlet temperature. The high speed camera 

allowed us to examine the flame structure. We determined that the more reactive FT–2 fuel produces a 

shorter flame, consistent with the physical properties of that fuel; and that for both fuels the core flame 

length increased with a lower inlet temperature. In the cases with FT–2, it also seemed that the onset of 

burning may have moved upstream, into the diffuser area of the injector. 

For lower inlet temperature applications, there may not be much improvement in combustion 

performance when burning the alternative fuel, based on the images. Gas emissions would be needed to 

make a more complete assessment. 

 
NASA/TM—2013-217884 15 

References 

1. B.E. Anderson et al, NASA/TM—2001-217059, 2001. 

2. P.A. Muzzell, E.R. Sattler, A. Terry, B.J. McKay, R.L. Freerks, L.L. Stavinoho, SAE 2006-01-0702, 

2006. 

3. M.E. Dry, H.B. de W. Erasmus, Annual Review of Energy, 1987. 

4. J.S. Klettlinger, A. Surgenor, and C. Yen, NASA/TM—2010-216370, 2010. 

5. M.T. Timko et al., Energy and Fuels, 24 (2010) 5883-5896. 

6. R. Tacina, P. Lee, C. Wey, ISABE-2005-1106. 

7. R. Tacina, C.-P.Mao, C. Wey, AIAA-2004-0135, Reno, NV, 2004. 

8. R. Tacina, C. Wey, P. Laing, A.A. Mansour, NASA/TM—2002-211347. 

9. H.J. Clewell III, J. Aircraft, 20 (1983), 382–384. 

10. A.G. Gaydon, The Spectroscopy of Flames, 2nd Edition, John Wiley and Sons, New York, NY, 1974. 
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this 

burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB 

control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-07-2013 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Comparing a Fischer-Tropsch Alternate Fuel to JP-8 and Their 50-50 Blend: Flow and Flame 

Visualization Results 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Hicks, Yolanda, R.; Tacina, Kathleen, M. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 561581.02.08.03.44.01 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-18695 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2013-217884 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 07 

Available electronically at http://www.sti.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

Combustion performance of a Fischer-Tropsch (FT) jet fuel manufactured by Sasol was compared to JP-8 and a 50-50 blend of the two 

fuels, using the NASA/Woodward 9 point Lean Direct Injector (LDI) in its baseline configuration. The baseline LDI configuration uses 60° 

axial air-swirlers, whose vanes generate clockwise swirl, in the streamwise sense. For all cases, the fuel-air equivalence ratio was 0.455, and 

the combustor inlet pressure and pressure drop were 10-bar and 4 percent. The three inlet temperatures used were 828, 728, and 617 K. The 

objectives of this experiment were to visually compare JP-8 flames with FT flames for gross features. Specifically, we sought to ascertain in 

a simple way visible luminosity, sooting, and primary flame length of the FT compared to a standard JP grade fuel. We used color video 

imaging and high-speed imaging to achieve these goals. The flame color provided a way to qualitatively compare soot formation. The length 

of the luminous signal measured using the high speed camera allowed an assessment of primary flame length. It was determined that the 

shortest flames resulted from the FT fuel. 

15. SUBJECT TERMS

Optical diagnostics; Combustion; Fuel-air mixing; Alternative fuels; Aircraft gas turbine 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

22 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

U 

19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18