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Improving Gas Turbine Fuel Flexibility
Wajid Ali ChishtyProgram Leader at NRC Aerospace
Advanced Biofuel Symposium, Montreal, July 23-24, 2015
(Ref: Wisniewski & Handelsman 2010)
0 11.5 23.0 34.5 46.0 57.5 65.0
LHV (MJ/kg)
InquiriesNatural GasSyngas
Increasing H2
Incr
easi
ng C
2+
Traditional Variation
High reactivity fuelsChallenge:
“Flashback”
Low reactivity fuelsChallenge: Blowout
Fuel Flexibility Spread
2
Stable Gas Turbine Operational Regime
Blowout
Flashback
Mass flow rate
Equi
vale
nce
ratio
Stoichiometric
Region of stable
operation
Flashback limit Blowout limit
High reactivity fuels
Low reactivity fuels
3
Plasma Assisted Combustion (PAC)
• Types of plasma discharges Thermal Plasma
aka equilibrium plasma spark, arc
Non-thermal Plasma aka non-equilibrium, “silent” plasma DC – Corona discharge, Streamer AC - Dielectric Barrier Discharge
(DBD)
• Advantages Virtually non-intrusive when not in use Solid-state - no moving parts Simple design All electrical - fast response Robust
VDC
Corona Discharge
DBD
Electrodes Dielectric material
AnodeCathode
Zone of plasma formation
Zone of plasma formation
VDC
4
PAC - Methodologies
Other efforts to improve blowout
limit
NRC effort to improve flashback limit
Mass flow rate
Equi
vale
nce
ratio
Stoichiometric
Region of stable
operationFlashback
Blowout
• Chemical kinetic Ignition via thermal plasma Initiation of chain branching
reactions through electron excitation via non-thermal plasma
• Hydrodynamic Ionic wind/ ionic propulsion
(NRC experience)
5
Flame Flashback Mechanisms• Four types of flashback are recognized: Boundary layer Core flow Combustion instabilities Combustion Induced Vortex Breakdown (CIVB)
• Occurs if the local flow velocity is lower than the flame speed: uLocal < Su
• Criteria for flashback in the boundary layer :
(Eichler & Sattelmayer, 2011)
= ∂= ≤
∂b
f yF
b wall
S ugy
δ
δ
6
Flashback Sensitivity to Velocity Profile
(Schäfer et al., 2003)
Boundary layer flashback
Flashback through the core flow
7
NRC Experience – Dielectric Barrier Discharge (DBD)
Electrodes Insulation
Dielectric barrier
Ionic wind
Plasma region(volume)
Combustionchamber
Premixer
8
Control of Core Flow Flashback• No DBD actuation
• Application of DBD actuation
Reducing air flow rate leading to flame flashback(a): Stable→ (b): Start flashback→ (c): Flashback
(a) (b) (c)
Φ = 0.843 Φ = 0.893 Φ = 913Φ = 0.773
9
Improvement in Stability Margin
• For fixed flow rates of combustible mixture, the burner can be operated with fuels and/or blends of much higher flame speeds
• For constant flame speeds, the combustor can be operated at much lower flow rates
10
0
0.2
0.4
0.6
0.8
1
1.2
-28 -24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24 28
u (m
/s)
Radial location (mm)u without DBDu with DBD
Control of Boundary Layer Flashback
Flame front
~200 s-1 ~400 s-1
11
Improvement in Stability Margin
• DBD actuation delays flashback to higher equivalence ratios
• For given total flow rates, the DBD actuation allows to operate with mixtures of much higher flame speed
12
Conclusions• The proposed application of DBD:
Increases the velocity gradient at the wall of the premixer
Delays flashback to occurs at higher equivalence ratios and lower flow rates
The stable operation regime is extended
Allows the operation with mixtures of higher flame speedThe combustion chamber is more fuel-flexible
13
National Research Council Canada
Supporting Gas Turbine Innovation in Canada
Wajid Ali ChishtyProgram Leader at NRC Aerospace
Advanced Biofuel Symposium, Montreal, July 23-24, 2015
This document contains information that is confidential, proprietary or secret and should be treated as confidential by all recipients. If there is a confidentiality or non-disclosure agreement or protective order covering any information contained in this e-mail, such information shall be treated as confidential and subject to restriction on disclosure and use in accordance with such agreement or order, and this notice shall constitute identification, labeling or marking of such information as confidential, proprietary or secret in accordance with such agreement or order.
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• Over 3,700 employees and 575 volunteer and independent visitors
IRAP
Research facilities
National Research Council Canada
17
Help industry succeed and meet current and future societal needs
Help industry succeed through de-risking the development and deployment of technologies and innovative solutions
Mandate
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19
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