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

GE Jenbacher 3

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.

GE Jenbacher 4

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 .

GE Jenbacher 5

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

GE Jenbacher 6

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?)

GE Jenbacher 7

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

GE Jenbacher 8

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

GE Jenbacher 9

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

GE Jenbacher 10

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

GE Jenbacher 11

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!

GE Jenbacher 14

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

GE Jenbacher 15

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!

GE Jenbacher 16

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,…).

GE Jenbacher 17

CLEO 2007, 18.-22.7.2007 MunichLaser Ignition of Engines

Where we are now?

At the end ;-)

Thank you!