Laser Spark Ignition for Advanced Reciprocating Engines

Presenter: Mike McMillian

December 3, 2003

2003 Distributed Energy Peer Review

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ARES Overview: Program Benefits

*Efficiency

*EmissionsNOx

EconomicBenefits

38% 50%

Will provide domestic engine manufacturers the leverageto compete against foreign manufacturers in this theexpanding U.S. Distributed Generation and World

1 g/bp-hp0.05 g/bp-hp

- Savings of $320M/yr in fuel cost- Reduction of 8-12M tons/yr CO2

* Assumes 25% market penetration in 300-3000kW rangein current NG receprocating Engine Market

From To

- Reduction of 40,000 - 60,000tons/yr NOx

OutcomeImprovement

M99000346 C7

NETL

The ARES Programprovides greater energy

efficiency, cleaner air andeconomic advantage.

Benefits

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ARES Overview: Technology Requirements

Air

HighTurbocharger

Efficiency

HeatRecovery

ExhaustAftertreatment

Ignition

AdvancedMaterials Friction

Reduction

Combustion

M99000345 C7

Ignition targets the issues with spark plug wear and lean-burn combustion limits in natural gas engines.

Advanced Combustion methods are needed to achieve the target low NOx emission and high efficiency levels and especially a widened knock margin. Focused efforts are needed on computer modeling and simulation of advanced concepts.

Advanced Materials are projected to be an important element of the ARES program for applications in demanding high-temperature designs and components.

Advanced Sensors and Controls will be needed as part of a next-generation system for engine controls to meet the aggressive emissions and efficiency targets. New exhaust emission sensors for NOx, in-cylinder pressure measurement, dynamic torque sensors, advanced engine diagnostic strategies are examples of key components.

Exhaust Aftertreatment is a key element of achieving the low emission targets. Development of specific catalysts for these engines will be one of the most significant challenges. Spin off technologies will benefit other stationary and mobile applications.

Heat Recovery and Friction Reduction have shown to be two very important issues from recent engine modeling by Southwest Research Institute and the ARES Engine Consortium. Novel coatings that reduce ring pack friction and reduce heat transfer to engine liner and piston will be investigated.

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Goal and Objective

• Develop scientific and engineering foundation for commercial laser spark ignition in reciprocating engines−Why do we need a new ignition technique?

• A durable high performance spark ignition system is a barrier technology for development of engines with low emissions and simple-cycle efficiency exceeding approximately 45%.

• The DOE’s goal is 50% simple cycle electrical efficiency with less than 0.1 g/bhp-hr NOx emissions for stationary natural gas fueled engines.

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Introduction: Why Laser Ignition?• Potential for Improved Durability

− Regulations on NOx Emissions Have continue to force Operation of Natural Gas Engines to Leaner Air/Fuel Ratios

− Lean Air/Fuel Ratios Are More Difficult to Ignite, Conventional Systems Require High Ignition Energies

− In Ultra-lean, high BMEP natural gas engines, Spark PlugService Life Is Very Low due to Increased Ignition Coil Energy Requirement

− Rugged, low cost lasers are available for numerous industrial processes, which used as an ignition source, offer the potential for extended service life

• Potential for Improved Engine Performance− Robust spark breakdown has shown greater ignitability,

potential for misfire limit extension and low emissions− Further performance improvements (multipoint ignition,

decreased real estate, bigger valves, this technology may enable other “tricks”)

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TECHNOLOGY STATUS• Previous engine work was focused on laser ignition of gasoline

(Dale, et al., 1979) , or propane (Smith, 1979).− Recent lab scale work has demonstrated increased

flame speed and combustion pressure over conventional spark systems (Tran and others).

− Current work at NETL, ANL, SWRI, CSU.− Big investment in Europe by Jenbacher.

• Mass production of lasers at significantly reduced size and cost is imminent

• However, delivery of high peak power laser energy is problematic− 50 mJ, 5 ns Nd:YAG pulse in a 1mm dia. Optical fiber

produces 1.27 GW/cm2

− Current damage threshold is somewhere around 0.5 to 3gw/cm2 for short duration. Divergence effects further limits fiber size to approx. 0.1mm (127 GW/cm2)!!!

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Work Summary

• Fundamental Studies• Laser ignition tests using a constant volume cell and turbulent jet

diffusion flames have been carried out

• Investigated effects of optical properties and fuel properties on the ignition probability and the minimum ignition energy

• Developed theoretical ignition model for laser ignition

• Considered benefits of laser ignition and its potential applications for gas engines

• Identified many technical difficulties and potential solutions

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Fundamental Laser Ignition Lab

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Fundamental Laser Ignition Lab (cont.)

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Engine Testbed Schematic

Press.

Temp.

-80 -60 -40 -20 0 20 40 60 80Crank Angle, Degree

CylinderPressure

Fuel LinePressure

Needle Lift

PressurizedAir Intake

ViscousFlow Meter

SecondarySurge Tank& Air Heater(Insulated)

PrimarySurge Tank

Dynamometer

SingleCylinderEngine

Analyzer Bay

High-SpeedData Aquisition

Mini Dilution Tunnel

Pump

70 mmSample Filter

Press.

Press.

Temp.

Temp.

BackPressure

Valve OpacityMonitor

To Stack

P

Test FuelSupply

GravimetericFuel Flow

Measurement

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INSULATION

SampleConditioner

II

INSULATION

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PISTON

NETL ENGINE

LASERPLUG

10% TRANSMISSIVEMIRROR

LASER BEAM

Nd YAGLASER

70oOPTICALWINDOW

PLANO-CONVEXLENS

BEAM SHIFT

POWER METER

Laser Arrangement (Temporary)

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A Few Details

Ignition Coil

Voltage Probe

Spark Gap

+ -

+ -

Current Probe

Ignition Control Cable

Ignition Coil

Voltage Probe

Spark Gap

+ -

+ -

Current Probe

Ignition Control Cable -2.50

-1.50

-0.50

0.50

1.50

2.50

3.50

-0.0

005

0.00

15

0.00

35

0.00

55

0.00

75

0.00

95

0.01

15

Time (seconds)

Spar

k Pl

ug V

olta

ge (k

V)

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Spar

k Pl

ug C

urre

nt (A

)

VoltageCurrent

Coil Energy Storage

Sustained Breakdown

Ringing In Coil

Decreasing Current Flow

PCX PCCHR

HR

HR

HR/BS

PCX

2.1% BS EM

ADJ. BE

HeNe Align. Laser

Nd:YAGHigh Energy Laser

BELaser Spark

Optical Bench System Setup (Off Engine)

Laser Spark Plug (On Engine)

PMT

PCX

Fiber Coupler

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Knock and Misfire Boundaries (32obtdc constant timing, 10% IMEP COV)

0.50

0.52

0.54

0.56

0.58

0.60

0.62

0.64

0.66

0.68

0.70

7.00 8.00 9.00 10.00 11.00 12.00 13.00

BMEP (bar)

Eq

uiv

alen

ce R

atio

LaserSpark Plug

Knock Boundaries

Misfire Boundaries

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Knock Boundary Affected by Ignition Delay

SOCav (oCA)

No

of o

bser

vatio

nsB

ME

P 8

0

2

4

6

8

BM

EP

10

0

2

4

6

8

Ignition Type: Plug

BM

EP

12

-16.5-16.0

-15.5-15.0

-14.5-14.0

-13.5-13.0

-12.5-12.0

-11.5-11.0

-10.5-10.0

-9.50

2

4

6

8

Ignition Type: Laser

-16.5-16.0

-15.5-15.0

-14.5-14.0

-13.5-13.0

-12.5-12.0

-11.5-11.0

-10.5-10.0

-9.50.59

0.60

0.61

0.62

0.63

0.64

0.65

0.66

0.67

0.68

9.5 10.0 10.5 11.0 11.5 12.0 12.5BMEP (bar)

Eq

uiv

ale

nce R

ati

o

Laser 32 deg btdc

Plug 32 deg btdc

Plug 34 deg btdc

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Conventional Spark: Lines of Constant NOx and Thermal Efficiency

18

22

26

30

34

38

0.50 0.55 0.60 0.65 0.70 0.75

Equivalence Ratio

Tim

ing

(deg

rees

BTD

C)

Predicted Phi for5% COV IMEPSPredicted Phi for50 ppm S

Predicted Phi for100 ppm S

Predicted Phi for200 ppm S

Predicted Phi at1 bar S

40 % ThermalEff.

40.7% ThermalEff.

38.1% ThermalEff.

Max Thermal Eff.

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Laser Spark: Lines of Constant NOx and Thermal Efficiency

18

22

26

30

34

38

0.50 0.55 0.60 0.65 0.70 0.75

Equivalence Ratio

Tim

ing

(deg

rees

BTD

C)

Predicted Phi for5% COV IMEP L

Predicted Phi for25 ppm L

Predicted Phi for50 ppm L

Predicted Phi for100 ppm L

Predicted Phi for200 ppm L

Predicted Phi at1 bar L

40 % ThermalEff.

40.7% ThermalEff.

38.1% ThermalEff.

Max. ThermalEff.

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THC Emissions

2400 2000 1600 1200 800 Run Descrip: Spark Plug Run Descrip: Laser

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Conclusions

• Optical and spectroscopic data have revealed and/or validated that:

−The ignition process seems to be dominated by the hot ball of gas remaining after the laser spark has dissipated.

−Multipoint ignition via laser delivery offers potential for engine applications to further extend misfire and knock limits.

− Ignition energies well less than 50mJ/pulse are may be sufficient for laser spark (50mJ/pulse represents a level in which energy effects “flatten”)

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Conclusions (cont.)

Engine Testing to date has indicated:

− Window fouling was not apparent although longer duration testing is required to verify this observation

− The misfire limit is shown to be significantly extended for laser ignition. (approximately 0.535 to 0.513 with laser ignition assuming misfire limit at an IMEP COV of 10%)

− Ignition delay was approximately 7% shorter for laser ignition resulting in a 2oCA advance in SOC

− Burn duration was slightly longer for laser spark combustion.

− Significant extension of the operating windowthus providing lower NOx emissions at equivalent levels of hydrocarbon emissions and thermal efficiency.

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Future Direction• Basic combustion/ignition studies

− Burn rate limited or ignition limited?− What are performance limits?

• Multipoint laser ignition studies− Higher apparent flame speed may provide additional knock margin

as well as improved ignitability. Higher apparent burn rate.• Prototype Laser Ignition System Development (CP)

− Multi-pulse Ignition• May provide improved ignition, leaner combustion and lower

emissions• May provide a way to circumvent beam delivery issue

− Distributed ignition• May provide a way to circumvent beam delivery (energy density)

issue− In progress (will be reported on next time including engine testing

of key prototypes)• Multi-cylinder Engine testing (CP)

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Work Plan Summary• Engine Performance Testing for Laser Ignition Systems

− Single Point Testing− Optical Engine Testing− Multipoint Testing

• Laser System Development− Optical Fiber Coupling− Optical and Electrical Distributors− Optical Access− Design and Packaging− Prototype Evaluation

• Multi-cylinder Engine Demonstration Testing• Advanced Concepts

− Fiber Optic Delivery of High Peak Power− Misfire limit extension− Reducing Breakdown Intensity− Laser ignition applications to HCCI− Spectroscopic A/F Diagnostic Development− Flame Kernel/Spark Interaction Spectroscopy− Engine Testing of Advanced Concepts

LensesLaser Rod AmplifiersFiber Optics

Pump Laser

Seed Laser

Engine Controls Beam Combiner/

Distributor