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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