Diesel Emissions and Exhaust After-Treatment for Modern Diesel Technology
National Biodiesel Board Technician Outreach Program
Rachel Burton & David Stehouwer 2009
Today’s Topics
Changes in diesel engine emissions regulations
Basics of diesel engine emissions Changes in hardware required by emissions
regulations Interactions of fuels and fuel systems
Methods of exhaust aftertreatment Exhaust aftertreatment & biodiesel Resources
US On Highway Emissions Standards
19881990
19911994
19982000
2002
20100.80
0.330.134
0
2
4
6
8
10
12
NO
x, g
/kW
-Hr
Particulate, g/kW-Hr
8.058.056.76.76.76.7
5.45.4
3.33.3
1.51.5
0.0130.013
14
1614.414.4
2007
0.270.27
Fuel technology
Combustion technology
Aftertreatment technology
Fuel system technology
Better understanding of combustion
Alternate Fuels (Biodiesel)Low sulfur De-NOx
DOC
PM trap
Rate controlHigh pressure Multi-injection
EGR technology
Others
Control technology
Emission Reduction in Diesel Engines
Injection performance
Higher injection pressure 1600-2000+
bar
Multiple injection
• NOx, PM control
• Noise control
• Aftertreatment dosing, trap regen
Injection Rate Control
Soft SOI Better BSFC/NOx tradeoff
Sharp EOI Better PM/smoke control
Precise injection control – minimum
variation
Minimum emission variation
Tamper resistant
Stable over useful life (>8000 hours)
Summary of Requirements for High Pressure Common Rail Fuel System
Time
Nee
dle
lif
tP
ress
ure
at
nee
dle
sea
t
Noise
NOX
Aftertreatment
Soot
Increased injection pressure
Injection performance Higher injection pressure
1600-2000+ bar Significant increases in fuel
economy• At equivalent emissions
Summary of Requirements for High Pressure Common Rail Fuel System (cont’d)
Increasing Injection Pressure
200 bar
2
4
6
8
Fuel Economy Improvement (%)
Increasing Injection Pressure
200 bar
2
4
6
8
Fuel Economy Improvement (%)
Time
Fuel properties effects on Common Rail FIE
• Startability• Accurate SOI• Controlled HR
• Leakage control• Pressure control• Durability/Fatigue• Filter plugging
• Gumming, sticking• Deposits • Filter plugging • Corrosion / Wear
Specified Fuel properties: chemical, contamination, physical
Cetane # Density Aromatics & Volatility
Sulfur Flash Pt
Hard Particle and ashcontamination
Watercontamination
OxidationStability
Lubricity
Viscosity
Fatty Acid Methyl Esters
• Pressure control
• Quantity control
• Elastomeric compatibility
• Cavitation damage
• Corrosion• Acid oxidation• Catalyst poisoning• Smoke & Particulates
• Fire Hazard• Spill
Hazard• Spark
Hazard
• Wear• Scuffing• Seizure
• Gumming, sticking• Deposits • Filter plugging • Corrosion & Wear
• Rough running (misfire)
• Corrosion • Wear
• Abrasive Wear • Filter plugging
OTC and Refiner Additives• Anticorrosion• Cetane improvers• Cold flow improvers• Lubricity improvers• Conductivity improvers
Refining process contaminants• Catalysts• Desulfurization agents• Cross contamination
Distribution and storage process contaminants• tank bottoms * pumps, pipes• microbial * corrosion• algae *varnish/sludge
Biodiesel Specifications Minimize Concerns
Oxidation Stability Gumming and sticking Fuel system deposits Corrosion and wear
Total and Free Glycerin Corrosion & Wear Filter plugging
Water Content Shortened injector life
Water in Fuel is a Problem
All non-dissolved water can cause problems:
Serves as growth medium for organisms that plug filters
Concentrates acids and ionic species that cause corrosion and deposits
Freezes at cold temperatures and reduces fuel flow
Reacts with some additives to form precipitates and deposits
Plugs injector nozzles at extreme conditions
Reduces fuel lubricity when in emulsified form
0
50
100
150
200
250
300
Injector Life
(%)
25 100 200 400 500 750 1000500010000
Amount of Water in Fuel (ppm)
Effect of Water on Injector Life
Fuel-Water Removal More Difficult in Future
ULSD additive package lowers interfacial tension making removal more difficult
Biodiesels have lower interfacial tension and hold more water, again adversely impacting removal FWS more challenging as
biodiesel percentage in blends increase
Solvency of biodiesel blends makes coated cellulose media option less effective
0
20
40
60
80
100
120
0 10 20 30 40
interfacial surface tension, dynes/cm
time weighted efficiency, %
original or clay treated fueladditized
more additized
ULSD
BiodieselB20 50
Exhaust Aftertreatment for Emissions Control Diesel Particulate Filters (DPF)
Non-Catalyzed Traps Catalyzed DPF
NOx Adsorber Technology Solvent Catalyzed Reduction (SCR)
Diesel Particulate Filter (DPF) Maintenance
Carbon particulates are burned off with on-board regeneration
Ash remains in the DPF and must be removed periodically This requires removal from vehicle
Catalyzed Diesel Particulate Filter (CDPFs)
Uses chemicals in exhaust to continuously burn carbon in Soot Filter
Must still be removed to clean ash
NONO2 2 Oxidizes Soot in FilterOxidizes Soot in Filter
2NO2NO22 + C + C CO CO22 + 2NO + 2NONONO2 2 Oxidizes Soot in FilterOxidizes Soot in Filter
2NO2NO22 + C + C CO CO22 + 2NO + 2NO
ConvertsConvertsNO NO 2NO 2NO22
ConvertsConvertsNO NO 2NO 2NO22
Soot FilterSoot FilterSoot FilterSoot FilterPlatinum Catalyst Platinum Catalyst
Exhaust Gas Exhaust Gas
NOx Adsorber Technology
Filter removes particles LNA absorbs NOx on lean operation Controls switch to rich operation to NOx to harmless Nitrogen Filter regeneration and LNA regeneration are separate Complex; costly; & fuel economy loss
Filter
Diesel Injector
NOx Sensor
DOCValves
DOC
Diesel Oxidation Catalyst
LNA
BypassReference: Volvo
Selective-Catalysts Reduction (SCR)Aqueous UreaSolution Tank
AmmoniaSlip
Catalyst Engine
12
34
56
T
Air Induction
Pump and Injector
Atomized Urea
Solution
Catalyzed Particulate
Filter
SCR Catalyst
Air to Air CoolerC
Reference: DDC
Turbo-Charge
NO EGR
Selective-Catalysts Reduction (SCR)
Uses aqueous Urea instead of fuel to convert NOx to Nitrogen Requires extra tank etc. Must add Urea distribution system to supply chain
Reduced EGR or no EGR Fuel economy gains compared to NOx
Adsorber Proven durability for European applications Favored by some for large truck and
stationary applications
How Does Biodiesel Effect Emissions & Aftertreatment ?
Fuel System Concern over deposits and corrosion Addressed by ASTM specifications
Engine Emissions Lower HC and Particulate NOx emissions depend on duty cycle
Aftertreatment hardware / durability Easier DPF regeneration Studies at NREL / ORNL show no adverse
effects on hardware durability
What Will Be in the Marketplace?
All of the above! Particulate Traps (or Soot Filters)
were across the board in 2007 NOx Adsorbers are on some pick-up
truck applications SCR is favored for many HD truck and
stationary applications