Lefebvre A.H., Ballal D.R. Gas Turbine Combustion: Alternative Fuels and Emissions

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490 Gas Turbine Combustion: Alternative Fuels and Emissions, Third Edition

physical properties, such as viscosity, bulk modulus, specic heat, and ther-

mal conductivity, were typical of conventional jet fuels.

Harrison and Zabarnick [60] performed the thermal stability analysis

and Figure 10.21 shows the results using a quartz crystal microbalance. The

dynamic viscosity of conventional and synthetic fuels at low temperature is

shown in Figure 10.22. Finally, the volume elastomer swell for nitrile rubber

o-rings (Parker N-602-214) was also measured and plotted in Figure 10.23.

Table 10.7 shows the properties of bio-based synthetic parafnic kerosine.

Essentially, the properties of HRJ biofuels are indistinguishable from FT

synthetic parafnic kerosine. Therefore, the blending issues for HRJ (50/50)

biofuels are also similar, namely, density, aromatic content, and GHG footprint.

At present, not much information is available on the t-for- purpose proper-

ties (lubricity, dielectric strength, cetane number), combustion operability

and emissions, material compatibility, and blending issues.

Goodger [1] has plotted composite plots of the fuel properties of conven-

tional fuels, biofuels, and alcohols. Figure 10.24 shows fuel density and

Figure 10.25 shows kinematic viscosity as a function of fuel temperature.

Finally, Figure 10.26 shows the variation of net specic energy with fuel

density.

10.9.4 Combustion and emissions Performance

10.9.4.1 Fischer–Tropsch Fuels

Moses and Roets [59] report engine and combustor performance tests as

follows:

Engine endurance•

Low-temperature atomization•

TABLe 10.6

Properties of Conventional JP-8, Synthetic FT, and JP-8/FT (50/50) Blend Fuels

Property JP-8 Min JP-8 Max FT

(100%) FT

/JP-8 (50/50)

Aromatics (vol %) -- 25.0 0.0 6.8

Total sulfur (wt%) -- 0.30 0.0 0.046

Flash point (°C) 38.0 -- 45.0 55.0

Freeze point (°C) --- –47.0 –51.0 –50.0

Viscosity at –20°C (cSt) -- 8.0 4.9 4.8

Heat of comb (Btu/lb) 18,400 -- 18,978 18,686

Hydrogen content (wt%) 13.4 -- 15.4 14.6

Density (kg/L at 15C) 0.775 0.840 0.756 0.781

JP-8 specication update

Note: Denition to include coal, biomass, and natural gas via Fischer–Tropsch; -- blend

instructions for petroleum and nonpetroleum; -- reference MIL-handbook for “t-

for-purpose” properties. Effect of these property nonconformities under evaluation.

Syntroleum synthetic JP-8 (S-8).

Alternative Fuels 491

Cold-day ignition and altitude relight•

Lean blowout•

Exhaust emissions•

The engine endurance, atomization and ignition tests showed no signicant

differences between the performance limits of fully synthetic jet fuels (FSJF)

and Jet A-1 fuels.

As shown in Figure 10.27, the Sasol FSJF had no adverse effect on lean

blowout limit. At higher altitudes, some limited fuel effects were noted, with

FSJF between the Jet A and JP-5 results. Since the lean blowout is considered

to be evaporation-limited, this result may be due to differences in boiling

point distribution of the two fuels and not due to fuel chemistry.

When an engine is certied, it must meet emissions standards recom-

mended by ICAO/CAEP (www.icao.org). Figures 10.28 through 10.30 show

the results of NO

, CO, and smoke number (SN), respectively. In the LTO

cycle, the Sasol synthetic fuel produced 4% less NO

and 19% less CO. These

emissions levels for both fuels were lower than the limits for CAEP/6. At all

other test conditions, the NO

emissions were unchanged and the CO emis-

sions were lower than that for the conventional fuel, presumably due to the

lower viscosity and ner spray produced by the Sasol fuel. The differences in

and combustion efciency were found to be negligible.

02468101214

Mass accumulation (µg/cm

)

Headspace oxygen (%)

Time (hours)

Figure 10.21

Quartz crystal microbalance (QCM) deposition at 140°C (open markers) and oxygen proles

(lled markers) for a JP-8 fuel () and synthetic syntroleum S-8 fuel (•). (From Harrison, W.E.

and Zabarnick, S., Presented at DoE Clean Coal Conference, Clearwater, FL, 2007.)

492 Gas Turbine Combustion: Alternative Fuels and Emissions, Third Edition

100

–70 –60 –50 –40 –30 –20

JP-8 (POSF-3773)

S-8 (POSF-4734)

S-8 (POSF-4820)

Dynamic viscosity (cP)

Temperature (C)

Figure 10.22

Dynamic viscosities of two synthetic (S-8) fuels compared with JP-8 fuel. (From Harrison, W.E.

and Zabarnick, S., Presented at DoE Clean Coal Conference, Clearwater, FL, 2007.)

04080120 160

JP-8 S-8

Volume swell (%)

Exposure time (hrs)

Figure 10.23

Volume swell vs. time for nitrile rubber o-ring samples. (From Harrison, W.E. and Zabarnick, S.,

Presented at DoE Clean Coal Conference, Clearwater, FL, 2007.)

Alternative Fuels 493

TABLe 10.7

Properties of Bio-Based Synthetic Parafnic Kerosine Fuels

Property SPK

ASTM Test

Method

Composition

Jatropha Coconut

Soybean/

Canola Soybean Palm

Parafn (vol%) Min 99.8 D2425

Cycloparafn (vol%) Max 5 D2425

Parafn (vol%)

Difference from

D 1319

99.3 99.5 99.5 100 98.4

1. Aromatics (vol%) Max 0.05 D 1319 0 0 0 0 0.8

2. Aromatics (vol%) Max 0.053 D 6379 0 0 0 0 0.8

Sulfur (total max %) Max 0.015 D 1266, D 2622,

D 4294, or D5453

0.00009 0.0003 0.001 0.0008

< 0.0001

1. Physical distillation D86

Distillation temp (°C)

10% recovered (temp (T10)) Max 205 172 188 189 186 197

50% recovered (temp (T50)) Report 192 200 214 226 236

90% recovered (temp (T90)) Report 223 231 248 280 254

Final boiling point (temp) Max 300 243 263 261 286 259

T90–T10 (°C) Min 25 51 43 59 94 57

Distillation residue (%) Max 1.5 1.2 1.3 1.2 1.4 1.2

Distillation loss (%) Max 1.5 0.4 0.5 0.8 1.0 0.7

2. Simulated distillation D 2887

Distillation temp (°C)

10% recovered (temp) Max 185 151.6 162 168 166.8 169

50% recovered (temp) Report 195 190.8 218.6 226.6 249

(Continued)

494 Gas Turbine Combustion: Alternative Fuels and Emissions, Third Edition

TABLe 10.7

Properties of Bio-Based Synthetic Parafnic Kerosine Fuels (Continued)

Property SPK

ASTM Test

Method

Composition

Jatropha Coconut

Soybean/

Canola Soybean Palm

90% recovered (temp) Report 237.6 238 267.2 297 269

Final boiling point (temp) Max 340 273.8 299 284.4 310.6 280

Flash point (°C) Min 38 D 56 or D 3828 50 64 62 60 64

Density at 15°C (kg/m

) 751–840 D 1298 or D 4052 751 755 763 766 769

Fluidity

Freezing point (°C) Max –47 Jet A-1 D 5872, D 7153,

D 7154, or D 2386

–63 –56 –52 –36 –44

Viscosity –20°C (mm

/s) Max 8.0 D 445

Combustion

Net heat of combustion (MJ/

kg)

Min 42.8 D 4529, D 3338, or

D 4809

44.4 44.2 43.5 43.8 44.2

Metal content D 7111

Copper (ppb) Max 100

< 0.01 ppm < 0.01 ppm < 0.01 ppm < 0.03 ppm < 0.02 ppm

Iron (ppb) Max 100

< 0.01 ppm < 0.01 ppm

0.04 ppm

< 0.03 ppm

0.02 ppm

Zinc (ppb) Max 100

< 0.01 ppm < 0.01 ppm < 0.01 ppm < 0.03 ppm < 0.02 ppm

Vanadium (ppb) Max 100

< 0.01 ppm < 0.01 ppm < 0.01 ppm < 0.03 ppm < 0.02 ppm

Thermal stability

JFTOT (2.5 h at control temp

of 280°C min)

Filter pressure drop (mmHg) Max 25 D 3241

< 0.1

25 0 0.0

Tube deposits less than 3

< 1 < 1

< 1

Source: From J. Holmgren, Private Communication, reproduced with permission, November 2008.

Balance of composition is olens.

Alternative Fuels 495

Figure 10.30 shows that the Sasol synthetic fuel produced lower smoke than

the Jet A fuel as expected because of its lower aromatic content. Harrison and

Zabarnick [60] have reported emissions from FT fuels using the T63-A-700

turboshaft engine. Figure 10.31 shows the percent change in particulate num-

ber density (PND) with percent volume of synthetic FT jet fuel in JP-8 for

cruise and idle conditions. These results demonstrate reduced (smoke) par-

ticulate emissions on addition of the synthetic fuel. Clearly, this reduction

is attributed largely to the reduced aromatic concentration in the resultant

fuel blend. Reduction of the aromatics decreases the concentration of “seed”

–40 0

Temperature °F

40 80 120

1.1

1.0

0.9

0.8

Density kg/L

0.7

0.6

–50 –30 –10 10 30 50 °C

225 250 275

Temperature

300325

Key

Freezing point

Nitromethane

Hydrazine

RFO (G)

RFO (F)

Sunflower oil

Diesel fuel

Gas oil

Avcat

Methanol

MTBE

Mogas

Avgas

Ammonia

Comml. butane (l)

Comml. propane (l)

Avtag

Ethanol

Avtur

Boiling point

Figure 10.24

Fuel density vs. fuel temperature for conventional, bio, and alcohol fuels. (From Goodger, E.M.,

Transport Fuels Technology, Landfall Press, Norwich, UK, 2000. With permission.)

496 Gas Turbine Combustion: Alternative Fuels and Emissions, Third Edition

molecules that contribute to the formation of soot nuclei, thereby decreasing

the production of ne soot particulate. Thus, blending with FT fuel signi-

cantly reduces the mean diameter of the particulate exhaust.

Lieuwen et al. [61] reviewed the impact of fuel composition on the oper-

ability of lean premixed gas turbine combustors. These workers investigated

fuel blends of CH

(LNG), CH

/CO

(landll gas), and CO/H

(syn-

gas). They concluded that the behavior of fuel mixtures can be markedly

different than that of individual constituents. Moreover, properties such as

turbulent burning velocity and ignition delay time may behave in a highly

nonlinear fashion as fuel mixture changes.

–80

–40 0

120

150

200

ULP

ULA

3000

1000

500

200

100

0.8

2.6

0.4

–60

–40

–20

100

°C

250 300

350

Temperature

Propane

Ammonia

Butane

Hydrazine

Kerosene

Gas oil

Diesel fuel

Sunflower oil

Methanol

Ethanol

Gasoline

Kinematic viscosity, cSt

Temperature °F

Residual

fuel oil

(G)

Nitromethane

Figure 10.25

Kinematic viscosity vs. fuel temperature for conventional, bio, and alcohol fuels. (From

Goodger, E.M., Transport Fuels Technology, Landfall Press, Norwich, UK, 2000. With

permission.)

Alternative Fuels 497

100

Specific energy MJ/kg net

120

0.4 0.8 1.2

kg/m

kg/L

Fuel density at 15 °C

Hydrazine

Nitromethane

Peat

Lignite

Sunflower

oil

Petroleum

fuels

Decaborane

CTF

Wood

Methanol

Ethanol

MTBE

Butane

Propane

Ethane

Ammonia

Methane

Diborane

Pentaborance

Liquics and solicsGases

Hydrogen

Anthracite

Coals

Coke

Graphite

1.6 2.0 2.4 0.8 1.0 1.2 1.4 1.6 0.8 2.0 2.2

Figure 10.26

Specic energy vs. fuel density for conventional, bio, and alcohol fuels. (From Goodger, E.M.,

Transport Fuels Technology, Landfall Press, Norwich, UK, 2000. With permission.)

1.2

JP-5

Sasol FSJF

1.1

1.0

0.9

0.8

Increasing airflow

Relative F/A at lean blowout

Figure 10.27

Lean blowout limits for JP-8 and Sasol fully synthetic jet fuel (FSJF). (From Moses, C. and

Roets, P., ASME Journal of Engineering for Gas Turbines Power, 131, 4, 2009. With permission.)

498 Gas Turbine Combustion: Alternative Fuels and Emissions, Third Edition

10.9.4.2 Biodiesel Fuels

Recently, researchers [62,63] have analyzed the inuence of biodiesel fuel on

combustor blowout, ashback, auto-ignition, and combustion stability.

Panchasara et al. [62] studied the combustion performance of biodiesel and

diesel–VO blends in a simulated gas turbine combustor. These experiments

were performed at atmospheric pressure with air-assist injector and swirling

100

% of NOx EPAP for petroleum-derived jet A

LTO SLTO Climb

Engine operating mode

Jet A

FSJF

Approach Idle

Figure 10.28

Comparison of NO

production for Jet A and fully synthetic jet fuel. (From Moses, C. and

Roets, P., ASME Journal of Engineering for Gas Turbines Power, 131, 4, 2009. With permission.)

100

% of CO EPAP for petroleum-derived jet A

LTO SLTO Climb

Engine operating mode

Jet A

FSJF

Approach Idle

Figure 10.29

Comparison of CO production for Jet A and fully synthetic jet fuel. (From Moses, C. and

Roets, P., ASME Journal of Engineering for Gas Turbines Power, 131, 4, 2009. With permission.)

Alternative Fuels 499

1.8

1.6

1.4

1.2

SN Sasol / SN jet A

0.8

0.6

0.4

0.2

0 0.005 0.01 0.015 0.02

Overall fuel-air ratio

0.025 0.03 0.035 0.04

SLTO

Cruise

Approach

Figure 10.30

Comparison of smoke number for Jet A and fully synthetic jet fuel. (From Moses, C. and

Roets, P., ASME Journal of Engineering for Gas Turbines Power, 131, 4, 2009. With permission.)

–12%

–13%

–33%

–41%

–57%

–68%

–78%

–25%

–30%

–50%

–61%

–75%

–86%

–92%

–51%

–96%

–100%

–75%

–50%

–25%

12.5% 25.0% 37.5% 50.0% 62.5% 75.0% 87.5% 100.0%

% volume of synjet fuel in JP-8

% change in particle number density

Cruise Idle

Figure 10.31

Reductions in particle number density emissions in T63 turbine engine as a function of the

concentration of the FT fuel in JP-8 blends. (From Harrison, W.E. and Zabarnick, S., Presented

at DoE Clean Coal Conference, Clearwater, FL, 2007.)