atomization vs. vaporization of fuel in micro gas turbines · atomizers wider stable operational...
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Atomization vs. Vaporization
of Fuel in Micro Gas Turbines
Daniel Kutikov and Prof. Yeshayahou Levy
Faculty of Aerospace Eng.
Technion, Haifa
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2/20
Difficulties in small-scale jet engine:
Low ignition energy
Small combustor volume
Simplicity of the atomizer/vaporizer
Atomization
Fuel distribution
Evaporation
Mixing
Ignition
Flame stability
Combustion efficiency
Impact of fuel delivery system
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3/20
Existing models for combustion of
liquid fuel
• Semi-empirical droplet sizing models for a single
atomizer
• Evaporation models for droplets
Need for integration of processes and models
• CFD involving two-phase flow and evaporation,
combustion chemistry, heat transfer
Heavy numerical calculations
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4/20
Objectives
Comparison: Atomizers vs. Vaporizers for Micro
Gas Turbines
• Ignition system
• Stable operational envelope
• Combustion Efficiencies
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5/20
Research method
• Small-scale combustor
• Comparison of fuel
supply only, not a
combustor upgrade
Fuel
Air
96mm
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6/20
Measurements:
• Air & fuel flows
• Combustor outlet temperature at 4 points
• Combustion gas concentrations at 4 points
Evaluations:
• Stable operational envelope
• Combustion Efficiency
• Chemical efficiency
Research method (cont.)
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7/20
Research method (cont.)
UHC CH4
Combustion efficiencies – definitions:
Enthalpy rise through combustor
Chemical energy of liquid fuel
Chemical energy of fuel remain in exhaust gases
Chemical energy of vaporized liquid fuel
Combustion Efficiency, η(T) =
Chemical efficiency, η(Ch) = 1 -
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8/20
Experiment setup
Air compressor
Gas analyzerCO2, CO, UHC,
O2, NOX
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9/20
Experiment setup (cont.)
Gas analyzer:
CO2, CO, UHC, NOX, O2
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10/20
Experiment setup (cont.)
Combustor setup:
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11/20
Experiment setup (cont.)
Blocked combustor
Open combustor
Nozzle ring
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12/20
Experiment setup (cont.)
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13/20
ResultsExit temperature for different air and fuel mass flow rates
°CQRf + CPinT03
T04 =CPg(1 + f)
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14/20
Results (cont.):combustion efficiencies η(T) for different configurations
ηT
Current
compressor limit
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15/20
Results (cont.)
η = F(tR)
Low efficiency:
• low inlet temperature
• low air pressure
Incomplete vaporization
Insufficient residence time
Insufficient mixing
Too low CO2
Too high O2
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16/20
Results (cont.)ηb
Differences mainly due to
unvaporized liquid fuel
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17/20
Low equivalence ratio:
almost complete
combustion
High equivalence ratio:
incomplete combustion
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18/20
Conclusions
Atomizers
Wider stable operational range
(wider fuel supply ranges: 3 – 6g/sec vs. 0.5 – 2g/sec)
Higher fuel flow rates & temperatures at the max efficiency points
(4g/sec vs. 1g/sec & 1300K vs. 800K)
Simple ignition (electric plug)
Faster transient response
X Larger combustor volume required (for evaporation & mixing)
X Higher fuel pressure requirement
Vaporizers
Higher efficiency due to longer vaporized fuel flow path
(η=0.9 vs. 0.75) (higher combustion pressure would give higher efficiencies)
X Complicated ignition (additional gas ignition system required)
X Slower transient response (thermal inertia & fuel evaporation time)
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19/20
Conclusions (Cont.)General
• Combustion efficiency increases with pressure
• Unvaporized fuel affect efficiency values, hence
should be accounted for (η(Ch) vs. η(T))
• Direct retrofitting of atomizers instead of vaporizes
widen operational envelope but reduces
combustion efficiencies
• New designs that can account for the larger volume
required by atomizer may benefit from its
advantages
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20/20
Questions?
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21/20
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22/20
Experiment setup (cont.)
Compensation of the radiative heat losses from TC:
The model was validated by comparison
of shielded and unshielded thermocouples
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23/20
Results (cont.)
f
Low efficiency: high UHC values