Part 4. DNS Relevant to Compression Ignition Engines and ...
Laser Ignition of Engines: Development of an Ignition...
Transcript of Laser Ignition of Engines: Development of an Ignition...
GE Jenbacher 1
CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Laser Ignition of Engines: Development of an Ignition Laser
MembersHeinrich Kofler
Kurt IskraGeorg Tartar
Filip OrbanJohannes Tauer
Prof. Ernst Wintner
Photonics InstituteLaser Ignition GroupTechnische Universität WienGußhausstraße 25-291040 Wien, Österreich
GE Jenbacher 2
CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Contents
1. Why laser ignition?
2. Why do we need a new ignition system?
3. Some facts about laser ignition
4. Concept 1: Ignition laser direct on the cylinder head
5. Concept 2: External laser source and fiber transportation of the pulse
6. Summary and outlook
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
What is the aim of laser igntion?
Replacement of theconventional spark plug bya laser!
A focused pulsed laserbeam creates a plasmaigniting the air/fuel mixture.
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Why do we need a new ignition system? Problems of conventional ignition systems:
-Reduced lifetime due to electrode erosion
-Engine efficiency is limited by the spark plugs
-Quenching effects due to the electrodes and walls
GE Jenbacher gas engine producingelectrical and thermal energy (CHP plant) with an electrical power 0,25 – 3 MWel .
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Laser ignition IHow laser ignition works:
λ [−]
1,2 1,6 2,0 2,4 2,8 3,2
MP
E [m
J]
0
4
8
12
16
20
150°C275°C400°C
20 bar
Air/fuel equivalence ratioand the temperaturedetermine the pulse energyfor ignition
Experiments in a stationary bomb lead to the requirement pulse energy of 8-12 mJ@1-2 ns
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Laser ignition IIAdvantages of laser ignition:
- Higher pressures possible higher efficiency- Combustion of very lean mixtures higher engine efficiency
lower NOX emissions- No quenching effects- Longer lifetime due the absence of any electrodes- Focal point can be arbitrarily choosen
Application of laser ignition:
- Stationary gas engines for CHP (Maybe 2012??)- Automotive engines (Maybe 2020?)
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Laser ignition IIITwo possible concepts of realisation:
-Solid state laser mounted on the cylinder head
-Ignition pulse is generated external and propagates along an optical fiber
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Where we are now?
1. Why laser ignition?
2. Why do we need a new ignition system?
3. Some facts about laser ignition
4. Concept 1: Ignition laser direct on the cylinder head
5. Concept 2: External laser source and fiber transportation of the pulse
6. Summary
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Concept of an ignition laser I
A diode pumped passivelyQ-switched solid-state laseris directly mounted on thecylinder head.
Requirements:Pulse energy 8-12 mJPulse duration ≈ 1 ns
- easy realisation- robust- cheap
Crystal: Nd3+ :YAG 0,8-1,4 at. % doped, @ 1064 nm, ø 2mmQ-Switch: Cr4+:YAGPump fiber: Standard fiber 300-600µmPump source: GaAs laser diode @ 808 nmLens: aspheric lensMirror: dielectric mirrors
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Concept of an ignition laser IISome experimental results:
Efficiency (Pump duration ≈ 180 µs): 10%Efficiency (Pump duration ≈ 300 µs): 6.4%Output energy varies 10% whereas the
Input energy varies in the order of 40%!Pump
PPump
1 exp -ττη
τ τ⎡ ⎤⎛ ⎞
= −⎢ ⎥⎜ ⎟⎝ ⎠⎣ ⎦
Pump efficiency
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Concept of an ignition laser III
Pulse durations in the order of a few ns were achieved!
Nd:YAG crystals with diameter 5-10 mm
Pulse energy ≈ 12 mJwith a non-Gaussian Beam
Profile
20 25 30 35 40 45 50 55 60 650,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
2,4
2,6
2,8
R=50% Linear Fit R=50% R=35% Linear Fit R=35%
Puls
e du
ratio
n t
P [n
s]
Initial transmission absorber T0 [%]
GE Jenbacher 12
CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
1. Why laser ignition?
2. Why do we need a new ignition system?
3. Some facts about laser ignition
4. Concept 1: Ignition laser direct on the cylinder head
5. Concept 2: External laser source and fiber transportation of thepulse
6. Summary
Where we are now?
GE Jenbacher 13
CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Pulse transport via optical fibers I
The ignition pulse propagates along an optical fiber.
Pulse energy ≈ 10 mJPulse duration ≈ 1 ns
Peak power ≈ 10 x 106 W/cm²
Consider a SIF with a=50 µmIntensity ≈ 1.2 x 1011 W/cm²Optical damage!!
Since the damage threshold for ns – pulses is around 5 GW/cm²!
Hollow core fibers!
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Pulse transport via optical fibers II
One way out of this problem hollow core PCF
2 dimensional -periodic structure in the cladding
Hollow core for guided pulse propagation
Incoupling lens: f=7.5 mm
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Pulse transport via optical fibers III
Some Experimental facts:
Maximum in-coupled pulse energy 1.1 mJ!!
Coupling efficiencies of up to 83 %were achieved!!!
Fiber damage @ in-coupling energies > 1.2 mJ!
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Summary and outlook
Fiber transportation using conventional fibers seems to be unrealistic due to the damage threshold of the material!
The use of PCF in laser ignition will be still a topic research even though there are big problems in high-power pulse propagation (pulse energy, damage of the periodic cladding…).
The ignition laser is the most promising concept – the required pulse energy and therefore the intensity in the focal point were already achieved…..
…but there are still some problems to solve (temperature, vibration,…).
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CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines
Where we are now?
At the end ;-)
Thank you!