Download - Diesel Engine Exhasut Compositions
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September 16-17, 2003Houston, Texas
Session Chair – Wayne Cole, Cole Engineering
ENVIRONMENT
The Diesel Engine and the Environment
David SteffensWartsila North America, Inc.
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Introduction
The diesel engine and the environment - rules and regulations
- emission reduction technologies
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WFI-M MarineTypical composition of diesel engine exhaust gas
Nitrogen N2 : 76%Oxygen O2: 13%Carbon dioxide CO2: 5% Low due to high efficiencyWater H2O: 5%
Sulphur oxides SOX Fuel choice relatedCarbon monoxide CO Low due to good combustionHydrocarbons CXHy Low due to good combustionParticles Low at steady state operation
Influenced by fuel ash and sulphur content
Visible smoke FSN Low load related (<25% load)Nitrogen oxides NOX To be controlled
Together> 99.5%
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Exhaust compounds and their environmental impactNOx:
– acid rain, acidification– ozone/smog formation in the lower atmosphere(potential damage on vegetation and human health)
Particulates:– some considered carcinogenic– blackening with soot
SOx:– acid rain, acidification– potential detrimental effect on human health
CO:– ozone/smog formation in the lower atmosphere
CO2:– the major greenhouse gas
Hydrocarbons: – ozone/smog formation in the lower atmosphere– some considered carcinogenic– contribute to the greenhouse effect
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Annex VI to MARPOL 73/78
Applies to: Ships of 400 GRT or above,Platforms and Drilling Rigs
Enters into force: 12 month after the date on which not less than 15 states, constituting not less than 50% of the gross tonnage of the world’s merchant fleet, have signed the protocol
It is important to note that the NOx emission regulation is linked to the date, 1st of January 2000. Ships constructed after this date will be required retroactively to comply with these requirements when Annex VI enters into force.
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IMO MEPC Proposal for Global Marine NOxLegislation
0
20
18
16
14
12
10
8500
NO
xem
issi
ons,
wei
ghte
d (g
/kW
h)
1000Rated engine speed (rpm)
ISO 8178 Test ProcedureReference Fuel: Marine Diesel Oil
1500 2000
NOx (g/kWh) = 17= 45 x rpm= 9.8 2000
130 rpm < 130
rpm >< rpm < 2000-0.2
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Diesel NOX Formation
Thermal NOX formation (65-75%)
Nitrogen source: combustion air
Formation process: extremely complex including hundreds of different reactions
Strong temperature influence (exponential)
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Thermal NOx Formation
02
4
68
1012
14
1618
20
400
200
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Local Temperature (K)
Rel
ativ
e N
Ox
-Con
cent
ratio
n
NOx Equilibrium Concentration
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Typical NOx-Emissions for Different Types of Engines
8
13
4
8
0.651.3
Typical NOx Emissions in g/kWh:
DieselLiquid Fuel
Gas Diesel
Lean BurnGas Engine
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operating on MGO
0
2
4
6
8
10
12
14
Diesel engine withSelective Catalytic
Reduction
Aeroderivative gasturbine
Diesel engine withDirect Water
Injection
Diesel engine
NO
x g/
kWh
NOx emissions of different prime movers
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Emission reduction
Technologies to reduce emissions:
• Primary Methods - During Combustion
• Secondary Methods - After Combustion
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Primary NOx control - diesel engines
Available today - Combustion ModificationEmission rating
– Adjustment of fuel injection timing/TC specification– NOx reduction potential: 10 - 20 %– Simple and cheap– Increased fuel consumption and thermal load
Low NOx combustion– Rearranged diesel cycle– NOx reduction typically: 25 - 35 %– NOx well below the IMO limit– Unchanged or improved fuel consumption
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Primary NOx control - diesel engines
Direct water injection– Humidification of the combustion process– NOx reduction typically: 50 - 60 %– Improved thermal load and engine cleanliness
Available today - Water Injection
Water-in-fuel emulsions– Humidification of the combustion process– NOx reduction potential typically: 20 %– Limitations
• emulsion stability• fuel injection system capacity• poor engine performance in “non-water” operational mode• cavitation risk in injection system
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Low NOX Combustion Engine Design
Rearranged diesel cycle– Very late fuel injection start– Higher compression ratio– Early inlet valve closing (4-stroke)– Late exhaust closing (2-stroke)– Optimized combustion chamber– Optimized fuel injection pressure
Results– Lower combustion temperatures– Shorter duration at high temperatures
Conclusions– NOX reduction typically 25-35%– Unaffected fuel consumption
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Low NOx Combustion
-90 -90-60 -60-30 -300 030 3060 6090 90120 120
Cyl
inde
r Pre
ssur
e
Cyl
inde
r Pre
ssur
e
Pressure riseinduced fromcombustion
Pressure riseinduced fromcombustion
Pressure riseinduced fromcompression
Pressure riseinduced fromcompression
Conventional DesignEngine Maximum Firing Pressure
Low NOx DesignEngine Maximum Firing Pressure
Application: All Fuel Types
TDC TDC
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Implementation of Low NOx Combustion onWärtsilä Vasa 32b
100%
80%
100% 97%
Relative NOx Emissions Relative Spec. Fuel Cons.
Σ = 12WV32
Σ = 13.8WV32LN
Σ = 12WV32
Σ = 13.8WV32LN
Compr.Ratio
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Features of fuel-water emulsionsDisadvantages
– Increased camshaft torque and cam load.– Full load of engine not possible at high water ratios due to
limitations in the fuel injection equipment.– Same nozzles not optimal for operation with and without
emulsion.– Negative impact on injection equipment reliability and
lifetime.– Increased fuel viscosity, higher preheating temperatures
needed.Advantages
– Improved low load smoke.– Lower NOx. The NOx limitation is limited to about 20%,
because unlimited water amounts cannot be kept in a stable emulsion.
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FSNMEC Test on W6L46CR, Vaasa
2-19 December 2002INFLUENCE OF WATER EMULSION ON FSN
Standard Nozzle: 12x0.64x160°, Fuel: HFO
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0 10 20 30 40 50 60 70 80 90 100 110
Engine load [%]
W/F ratio = 0, without MECW/F ratio = 0, with MECW/F ratio = 0.1W/F ratio = 0.2W/F ratio = 0.3
FSN
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NOx emissionsMEC Test on W6L46CR, Vaasa
2-19 December 2002INFLUENCE OF WATER EMULSION ON NOx EMISSIONS
Standard Nozzle: 12x0.64x160°, Fuel: HFOReference NOx: Without MEC
0.75
0.80
0.85
0.90
0.95
1.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
W/F ratio
100% load85% load75% load50% load
Rel
ativ
e N
O
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The principle of Direct Water Injection
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Direct Water Injection
Flow fuse
High pressurewater pump
Watertank
Water
Fuel
Water needle
Fuel needle
Solenoidvalve
Controlunit
T
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Direct Water Injectiontypical water/fuel timing and duration
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•CASS (Combustion Air Saturation System)
Emission Control Technologies - Tomorrow’s solutions
Future Technologies:
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CASS
CASS
The hot air after the compressor is cooledto the saturation point by injecting watermist
After heating in the “charge air cooler” the mixture is again saturated by injecting ofmore water
Heating of the air by HT-water
Compressor “Intercooler”/heater
Receiver
Heat
Water injection
Water injection
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Efficiency of humidification methods
Relative NOxformation
0.5 1.0 1.5 2.0
Direct Water Injection
Combustion Air Humidification
1.11.00.90.80.70.60.50.40.30.20.1
Water/Fuel flow ratio
W20
W32
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Predicted NOx behavior with different control methods on Wärtsilä 46
NOx
5
10
15
50 100 150 200 250Water amount as % of fuel consumption
Fuel Water Emulsion
CASS
FWE + CASS
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Secondary NOx control - diesel engines
Available today
Selective catalytic reduction (SCR)– NOx reduction typically: 85 - 95 %– Urea/water solution injected – Integrated part of the engine package– Exhaust temperature window 330 - 450 °C at HFO operation– Investment and operating costs relatively high
Compact SCR– Combined silencer and SCR unit– Minimized size
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Principle of Selective Catalytic Reduction
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SCR Reactions With Urea
Before Entering the Reactor:(NH2)2 CO + H2O 2 NH3 + CO2
In the Reactor:4 NO + 4 NH3 + O2 4 N2 + 6 H2O
6 NO2 + 8 NH3 7 N2 + 12 H2O
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Retrofit of Compact SCR
Birka Princess at Lloyd Werft
SCR plants have been retrofitted in several passenger ships in existing engine casing = no lost space!
A Compact SCR occupies a little more space than a normal silencer which it replaces.
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Particle Emissions– Particle emissions are seen as smoke– More prevalent at low loads and start-up
Smoke Reduction Methods– Common rail fuel injection
Smokeless Diesel Engine
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Targets for the Smokeless Engine• No visible smoke at start-up• No visible smoke at any load• NOx emissions to be reduced• CO2 emissions to be reduced even lower by further
improvements in efficiency
Smokeless Diesel Engine
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Conventional injectionsystem
Common Rail Injection
Fuel pressureproduced each time by the injection pump
Mechanical./hydrauliccontrol at the injectors
Constant fuelpressure
Electronic / hydrauliccontrol of injection
Conventional vs common rail fuel injection
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WÄRTSILÄ COMMON RAIL SYSTEM
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Common Rail advantages
• Smokeless operation at all loads and speeds.
• Smokeless start of the engine.
• Smokeless load pick-up ramps.
• NOx reduction down to 3…4 g/kWh with humidification possible without visible smoke.
• Improved total fuel economy.
• Flexibility for different fuels without hardware modifications (heavy fuel, diesel oil, gas turbine fuel, water-fuel emulsion).
• Improved safety and comfort because more engines can be kept running with still good fuel economy and no smoke.
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Wärtsilä 46 Common Rail
FSN status at engine laboratory and delivery test run
Engine load (%)
Filte
r sm
oke
num
ber
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0 10 20 30 40 50 60 70 80 90 100 110
**
** *
Best lab. results with modified piston shape
Conventional injection
THIS ISSMOKELESS
Production engines May 2002 and for upgrading
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