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

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

primary air around it. Figures 10.32a and 10.32b show the axial proles of CO

and NO

for 15% atomizing airow and Figures 10.32c and 10.32d for 25% atom-

izing airow, respectively. The results showed that fuel composition or chem-

istry effects were minimal; since one could minimize combustion emissions

for a given fuel by controlling fuel atomization. Moreover, the 70–30 diesel–VO

blend was equivalent to biodiesel fuels in terms of drop size and emissions.

Liu et al. [63] examined biodiesels as an alternative fuel in Siemens DLE

combustor (SGT-100) at atmospheric and high pressure. At atmospheric pres-

sure, reliable ignition could be achieved across a range of air mass ow rates

and air fuel ratios.

At high pressure, Figure 10.33 shows the lean ignition limit for biodiesel

fuel at a pressure of 2.72 atm. It shows that at high airow rates, the biodiesel

is easier to ignite than diesel, with ignition being possible at signicantly

50403020100

504030

Diesel

70-30 diesel-V0

80-20 diesel-V0

90-10 diesel-V0

Diesel

70-30 diesel-V0

80-20 diesel-V0

90-10 diesel-V0

Diesel

70-30 diesel-V0

80-20 diesel-V0

90-10 diesel-V0

Diesel

70-30 diesel-V0

80-20 diesel-V0

90-10 diesel-V0

Axial distance (cm)

100

NOx (ppm)

200

50403020100(c)

(a)

(b)

(d)

50403020100

50403020

Axial distance (cm)

100

50403020

Axial distance (cm)

100

50403020

Axial distance (cm)

100

150

100

200

100

150

100

NOx (ppm) CO (ppm)

CO (ppm)

Figure 10.32

Axial proles of CO and NO

emissions at the combustor exit plane for diesel and diesel-

vegetable oil blends for (a-b) 15% atomizing airow and (c-d) 25% atomizing airow. (From

Panchasara, H., Simmons, B., Agrawal, A., Spear, S., and Doly, D., ASME Journal of Engineering

for Gas Turbines Power, 131, 031503, 2009. With permission.)

Alternative Fuels 501

higher air fuel ratios. At the lower ow rates, the opposite is true, i.e., diesel

ignites at higher values of AFR. Also, it was found that reliable ignition can

be achieved for the SGT-100 combustor operating with biodiesel.

Figure 10.34 shows the lean extinction limit burning biodiesel in air at 2.72

atm. This result shows that lean extinction occurred for both air tempera-

tures at the same conditions, which were similar to those observed for the

lean ignition.

1.2

1.0

0.8

Biodiesel, T

air

= 0°C

Biodiesel, T

air

= 15°C

Biodiesel, T

air

= 30°C

Diesel 4.0 bar

Diesel 2.0 bar

Predicted light

up window

0.6

0.4

0.2

0.3 0.4 0.5 0.6 0.7

Normalised air mass flow rate

Normalised air fuel ratio

0.8 0.9 1.0

Figure 10.33

Lean ignition limit for dry low-emissions (SGT-100) combustor burning diesel and biodiesel fuels

at air-assist injector pressure of 2.72 atm. (From Liu, K., Wood, J.P., Buchanan, E.R., Martin, P.,

and Sanderson, V., ASME Journal of Engineering for Gas Turbines Power, 2010. With permission.)

1.0

0.8

0.6

0.4

0.2

0.3 0.4 0.5 0.6 0.7

air

= 30°C

air

= 0°C

0.8 0.9 1.0

Normalised air mass flow rate

Normalised air fuel ratio

1.2

Figure 10.34

Effect of ambient air temperature on dry low emissions (SGT-100) combustor lean extinction

limit burning biodiesel fuel at air-assist injector pressure of 2.72 atm. (From Liu, K., Wood, J.P.,

Buchanan, E.R., Martin, P., and Sanderson, V., ASME Journal of Engineering for Gas Turbines

Power, 2010. With permission.)

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

Figures 10.35 (a–d) show the effect of ame temperature and combustor

pressure drop on NO

emissions at 14 and 9 bars. In these gures, ame

temperature is normalized such that the value of 1:0 represents full load con-

dition. At high pressure, diesel fuel has higher NO

emissions than biodiesel

fuel. Also, higher combustor pressure drop causes a strong reduction in NO

emissions due to: (1) a decrease in residence time, (2) better mixing due to

high turbulence, and (3) improved mixing due to downstream displacement

of the ame. However, once perfect mixing is achieved, a further increase in

combustor pressure drop will only reduce residence time and limit a further

decrease in NO

emissions.

(b)

(a)

P=9 bar

P=14 bar

Biodiesel, ∆P/P=3.7%

Biodiesel, ∆P/P=4.7%

Biodiesel, ∆P/P=5.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

Biodiesel, ∆P/P=3.7%

Biodiesel, ∆P/P=4.7%

Biodiesel, ∆P/P=5.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

Normalised flame temperature

0.94

0.96 0.98

1.00

1.02

1.04

1.06

1.08

1.10

0.94

0.96 0.98

1.00

1.02

NOx (ppmv @ 15% O

) NOx (ppmv @ 15% O

)

1.04

1.06

1.08

1.10

Figure 10.35

Effect of ame temperature and combustor pressure drop on NO

emissions from diesel and

biodiesel fuels for two different combustor pressures. (a–b) measured NOx, (c–d) measured NOx

corrected for fuel-bound nitrogen (FBN). (From Liu, K., Wood, J.P., Buchanan, E.R., Martin, P.,

and Sanderson, V., ASME Journal of Engineering for Gas Turbines Power, 2010. With permission.)

Alternative Fuels 503

Campbell et al. [64] have demonstrated that biodiesel fuels have compa-

rable NO

emissions to diesel fuels. However, this could be because their

biodiesel and diesel fuels had comparable nitrogen content. Figures 10.35c

and d show NO

emissions after correcting for fuel-bound nitrogen. It is

observed that biodiesel fuels produce slightly higher NO

emissions than

diesel fuels.

Figure 10.36a through d show comparisons of CO and unburned hydro-

carbon emissions, respectively, and reveal that biodiesels have higher CO

emissions, especially low load conditions due to low ame temperature.

Also, it is observed that biodiesels have lower unburned hydrocarbon (UHC)

emissions than diesel fuel.

The frequency and amplitude of combustion dynamic pressure were mea-

sured by a pressure transducer mounted at the pilot burner face. Figure 10.37

Biodiesel, ∆P/P=3.7%

P=14 bar

Biodiesel, ∆P/P=5.7%

Biodiesel, ∆P/P=4.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

Biodiesel, ∆P/P=3.7%

P=9 bar

Biodiesel, ∆P/P=5.7%

Biodiesel, ∆P/P=4.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

0.94

0.96

0.98

1.00

1.02

1.04

Normalised ﬂame temperature

NOx after FBN correction (ppmv)

1.06

1.08

1.10

0.94

(d)

(c)

0.96

0.98

1.00

1.02

1.04

1.06

1.08

1.10

Figure 10.35 (Continued)

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

shows these results. It is seen that biodiesels have generally lower dynamic

pressures than diesel fuel and both fuels have comparable dynamic

frequencies.

10.9.4.3 Highly Aromatic (Broad Speciﬁcation) Alternative Fuels

A measure now being studied is to widen the distillation range of jet fuels

to increase the available fuel supplies for industrial gas turbines. An effect

of such widening would be to increase the aromatic content of fuels to as

high as 35% by weight. Of course, the immediate effect of an increase in

1000

100

0.94

1000

100

0.94

0.96

0.98

1.00

1.02 1.04

1.06

1.08

1.10

Normalised flame temperature

CO (ppmv @ 15% O

)

CO (ppmv @ 15% O

)

0.96 0.98 1.00 1.02 1.04 1.06 1.08 1.10

Biodiesel, ∆P/P=3.7%

P=14 bar

P=9 bar

Biodiesel, ∆P/P=4.7%

Biodiesel, ∆P/P=5.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

Biodiesel, ∆P/P=3.7%

Biodiesel, ∆P/P=4.7%

Biodiesel, ∆P/P=5.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

(a)

(b)

Figure 10.36

Effect of ame temperature and combustor pressure drop on emissions from diesel and

biodiesel fuels for two different combustor pressures: (a–b) CO emission, (c–d) unburned

hydrocarbon (UHC) emissions. (From Liu, K., Wood, J.P., Buchanan, E.R., Martin, P., and

Sanderson, V., ASME Journal of Engineering for Gas Turbines Power, 2010. With permission.)

Alternative Fuels 505

aromatic content on burning quality is to enhance the propensity toward

soot formation in the ame. This is demonstrated in Figure 10.38, which

shows, for a variety of fuels, how the smoke point varies with aromatic

content. In practice, an increase in aromatic content is synonymous with a

decrease in hydrogen content. A typical correlation between hydrogen con-

tent and liner wall temperature is shown in Figure 10.39. Figure 10.40 shows

a similar correlation for hydrogen content and SN. Both sets of data were

obtained with a single-can JT8D combustor at simulated takeoff and cruise

conditions [65,66]. Based on measured values of the liner wall temperature,

the relative liner life was estimated to fall by 53% for the F101 combustor

and 65% for the J79 combustor when the fuel hydrogen content was reduced

from 14.5 to 12%.

2.0

(c)

(d)

1.5

1.0

0.5

0.94

8.0

6.0

4.0

2.0

0.0

0.94

0.96

0.98 1.00

UHC (ppmv @ 15% O

)

Normalised flame temperature

P=14 bar

Biodiesel, ∆P/P=3.7%

Biodiesel, ∆P/P=4.7%

Biodiesel, ∆P/P=5.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

P=9 bar

Biodiesel, ∆P/P=3.7%

Biodiesel, ∆P/P=4.7%

Biodiesel, ∆P/P=5.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

UHC (ppmv @ 15% O

)

1.02 1.04 1.06 1.08 1.10

0.98 1.00 1.02 1.04 1.06 1.08 1.10

Figure 10.36 (Continued)

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

Moliere and Geiger [67] performed a study of the combustion of highly

aromatic fuels in industrial gas turbines. They examined a 77% aromatic

content Benzene Heart Cuts (BHC) fuel, which results from the removal of

mono-aromatics from gasoline and a poly-aromatic fuel (PArF with 58% aro-

matic content) rich in di- and tri-aromatics, such as light cycle oil (LCO). A

GE frame 6B gas turbine was used. These eld tests used diesel oil #2 as

reference fuel.

Table 10.8 shows the results of these tests. For dry combustion, the NO

emissions for BHC (at 290 ppm) and LCO (at 230 ppm) showed an increase

of 30% and 22%, respectively, over diesel oil #2. With water injection, NO

2.0

1.6

1.2

0.8

0.4

0.0

1.2

1.1

1.0

0.9

0.8

0.94 0.96 0.98 1.00 1.02 1.04 1.06 1.08 1.100.94

Biodiesel, ∆P/P=3.7%

Biodiesel, ∆P/P=4.7%

Biodiesel, ∆P/P=5.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

Biodiesel, ∆P/P=3.7%

Biodiesel, ∆P/P=4.7%

Biodiesel, ∆P/P=5.7%

Diesel, ∆P/P=3.7%

Diesel, ∆P/P=4.7%

Diesel, ∆P/P=5.7%

Normalised flame temperature

(b)

(a)

Normalised rms dynamic pressure

Normalised frequency

Figure 10.37

Comparison of combustion dynamics produced due to the burning of diesel and biodiesel

fuel at an inlet air pressure of 14 atm. (a) Frequency, (b) RMS dynamic pressure. (From Liu, K.,

Wood, J.P., Buchanan, E.R., Martin, P., and Sanderson, V., ASME Journal of Engineering for Gas

Turbines Power, 2010. With permission.)

Alternative Fuels 507

emissions dropped to around 200 ppm VD at 15% O

. These fuels also dis-

played higher CO and smoke emissions. In summary, the authors concluded

that heavy-duty industrial gas turbines have the ability to clearly burn BHC-

and LCO-type fuels. Such fuels can emerge as cheap alternatives to conven-

tional fuels with aromatic content below 30%.

Smoke point, mm

Aromatics content, mass percent

020406080

Figure 10.38

Relationship between smoke point vs. fuel aromatic content. (From Singh, P.P., Bazarian, E.R.,

Malik, P.R., Bauserman, G.W., Cohn, A., and Stein, T.R., ASME Paper 80-GT-64, Gas Turbine

Conference, New Orleans, LA, 1980.)

1300

1200

1100

1000

900

800

10 11 12

Maximum liner temperature, K

Hydrogen content, mass percent

13 14 15 16 17

Figure 10.39

Effect of fuel hydrogen content on maximum combustor liner wall temperature. (From

Gleason, C.C. and Bahr, D.W., ASME Paper 80-GT-55, Gas Turbine Conference, New Orleans,

LA, 1980.)

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

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TABLe 10.8

Emissions of NO

and CO from burning highly aromatic alternative fuels

Base load power output = 34 MW

100% DO 100% BHC 100% LCO

VOC (mg/Nm

wet) 13 12 –

CO (mg/Nm

D at 15% O

) 1 4

< 2

(ppm VD at 15% O

) 222 290 230

(ppm VD at 15% O

with DeNO

water) 114 136 121

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permission.

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Alternative Fuels 509

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