Diesel emissions and exhaust after treatment
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  • Most of you have seen this slide, which discloses the various technologies that are being applied to achieve Tier 2-4 emissions levels. I will only discuss the fuel system where the migration to common rail systems are a key leverage for achieving low emissions.
  • Injection pressure requirements for large engines have evolved from the stringent emissions requirements and a desire to achieve as low an in-cylinder NOx, smoke and particulate solution as possible. This is to reduced the burden on future aftertreatment systems. For Tier 2 and 3 we were able to avoid use of aftertreatment, but for Tier 4 it seems clear some aftertreatment will be required. HPCR is a necessary building block in the total system for emissions solutions. It offers improvements in NOx, fuel economy, smoke, noise, UHC, CO and particulate control that would not be available through conventional mechanical or electronic unit injection systems. The multiple injection events, injection rate control, and precision injection timing control over the life of the engine are critical to achieving and maintaining emissions without deterioration.
  • Injection pressure requirements for large engines have evolved from the stringent emissions requirements and a desire to achieve as low an in-cylinder NOx, smoke and particulate solution as possible. This is to reduced the burden on future aftertreatment systems. For Tier 2 and 3 we were able to avoid use of aftertreatment, but for Tier 4 it seems clear some aftertreatment will be required. HPCR is a necessary building block in the total system for emissions solutions. It offers improvements in NOx, fuel economy, smoke, noise, UHC, CO and particulate control that would not be available through conventional mechanical or electronic unit injection systems. The multiple injection events, injection rate control, and precision injection timing control over the life of the engine are critical to achieving and maintaining emissions without deterioration.
  • This 6-sigma critical parameter flowdown is meant to illustrate how we try to tie the controlled properties of commodity diesel fuels to those properties that fuel system manufacturers required. The Red boxes are the ones most critical to us, and unfortunately are generally the least controlled by the refiners and fuel delivery infrastructure. And only through disciplined and expensive sampling can the fuel properties even be ascertained to be acceptable. These only are snapshots of the fuel quality and not representative of the total time history of fuel consumed by the engine. So for the most part, end customers get a wide range of fuel qualities, most within the broad specification of ASTMD975 or EN590 and outside North America and Europe the control of fuel quality is even less disciplined There are some notable exceptions -- certain areas like western Canada where the refiners of synthetic crude derived from tar sands seem to have excellent control over fuel quality.
  • Water in fuel can also aggravate HPCR wear through corrosion products that are as hard as hard particles. And they can serve as growth mediums for microorganisms that plug filters and create acids and ions that promote corrosion and deposits. Freezing of water in fuel is problematic during cold weather operation. Reaction of water concentrates of acids and bases to form organic soaps that plug filters is less well understood. Under extreme conditions these can plug injector orifices and nozzles. And lubricity can be drastically reduced with only 1000 ppm of water in fuel.
  • Highly refined S15 UltraLow Sulfur (ULSD) diesel fuel may have additive packs to improve lubricity and corrosion resistance, but these may lower interfacial surface tension on filter medias that make water removal more difficult. Fuel Water Separation is more challenging as biodiesel percentages increase, and solvency of biodiesel blends makes coated cellulose media less effective.
  • Factors influencing frequency of maintenance; Size of filter Duty-cycle

Transcript

  • 1. Diesel Emissions and Exhaust After-Treatment for Modern Diesel Technology National Biodiesel Board Technician Outreach Program Rachel Burton & David Stehouwer 2009
  • 2. 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
  • 3. US On Highway Emissions Standards 1988 1990 1991 1994 1998 2000 2002 2010 0.80 0.33 0.134 0 2 4 6 8 10 12 NO x , g/kW-Hr Particulate, g/kW-Hr 8.05 6.7 6.7 5.4 3.3 1.5 0.013 14 16 14.4 2007 0.27
  • 4. Fuel technology Combustion technology Aftertreatment technology Fuel system technology Better understanding of combustion Alternate Fuels (Biodiesel) Low sulfur De-NOx DOC PM trap Rate control High pressure Multi-injection EGR technology Others Control technology Emission Reduction in Diesel Engines
  • 5.
    • 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 Needle lift Pressure at needle seat Noise NO X Aftertreatment Soot Increased injection pressure
  • 6.
    • 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) Time
  • 7. 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 ash contamination Water contamination Oxidation Stability 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
  • 8. 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
  • 9. 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
  • 10. 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
  • 11. Exhaust Aftertreatment for Emissions Control
    • Diesel Particulate Filters (DPF)
      • Non-Catalyzed Traps
      • Catalyzed DPF
    • NOx Adsorber Technology
    • Solvent Catalyzed Reduction (SCR)
  • 12. 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
  • 13. Catalyzed Diesel Particulate Filter (CDPFs)
    • Uses chemicals in exhaust to continuously burn carbon in Soot Filter
    • Must still be removed to clean ash
    NO 2 Oxidizes Soot in Filter 2NO 2 + C  CO 2 + 2NO Converts NO  2NO 2 Soot Filter Platinum Catalyst Exhaust Gas
  • 14. NO x 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
    Reference: Volvo Filter Diesel Injector NO x Sensor DOC Valves DOC Diesel Oxidation Catalyst LNA Bypass
  • 15. Selective-Catalysts Reduction (SCR) Aqueous Urea Solution Tank Ammonia Slip Catalyst Engine 1 2 3 4 5 6 T Air Induction Pump and Injector Atomized Urea Solution Catalyzed Particulate Filter SCR Catalyst Air to Air Cooler C Reference: DDC Turbo-Charge NO EGR
  • 16. 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
  • 17. 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
  • 18. 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