Biodiesel and Exhaust AfterTreatment
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Diesel Emissions and Exhaust After-Treatment for Modern Diesel TechnologyNational Biodiesel Board Technician Outreach ProgramRachel Burton & David Stehouwer 2009
Changes in diesel engine emissions regulationsBasics of diesel engine emissionsChanges in hardware required by emissions regulationsInteractions of fuels and fuel systemsMethods of exhaust aftertreatmentExhaust aftertreatment & biodieselResources
US On Highway Emissions Standards
Fuel technologyCombustion technologyAftertreatment technologyFuel system technologyBetter understanding of combustionAlternate Fuels (Biodiesel)Low sulfurDe-NOxDOCPM trapRate controlHigh pressure Multi-injection EGR technologyOthersControl technologyEmission Reduction in Diesel Engines
Injection performanceHigher injection pressure 1600-2000+ bar Multiple injectionNOx, PM controlNoise controlAftertreatment dosing, trap regenInjection Rate ControlSoft SOI Better BSFC/NOx tradeoffSharp EOI Better PM/smoke controlPrecise injection control minimum variationMinimum emission variation Tamper resistantStable over useful life (>8000 hours)
Summary of Requirements for High Pressure Common Rail Fuel SystemTime
Injection performanceHigher injection pressure 1600-2000+ bar Significant increases in fuel economyAt equivalent emissions
Summary of Requirements for High Pressure Common Rail Fuel System (contd)Time
Fuel properties effects on Common Rail FIE
Biodiesel Specifications Minimize ConcernsOxidation StabilityGumming and stickingFuel system depositsCorrosion and wear Total and Free GlycerinCorrosion & WearFilter pluggingWater ContentShortened injector life
Water in Fuel is a ProblemAll non-dissolved water can cause problems:Serves as growth medium for organisms that plug filtersConcentrates acids and ionic species that cause corrosion and depositsFreezes at cold temperatures and reduces fuel flow Reacts with some additives to form precipitates and depositsPlugs injector nozzles at extreme conditionsReduces fuel lubricity when in emulsified form
Fuel-Water Removal More Difficult in FutureULSD additive package lowers interfacial tension making removal more difficultBiodiesels have lower interfacial tension and hold more water, again adversely impacting removalFWS more challenging as biodiesel percentage in blends increaseSolvency of biodiesel blends makes coated cellulose media option less effective
Exhaust Aftertreatment for Emissions Control Diesel Particulate Filters (DPF)Non-Catalyzed TrapsCatalyzed DPFNOx Adsorber TechnologySolvent Catalyzed Reduction (SCR)
Diesel Particulate Filter (DPF) MaintenanceCarbon particulates are burned off with on-board regenerationAsh remains in the DPF and must be removed periodicallyThis requires removal from vehicle
Catalyzed Diesel Particulate Filter (CDPFs)Uses chemicals in exhaust to continuously burn carbon in Soot FilterMust still be removed to clean ash
NO2 Oxidizes Soot in Filter 2NO2 + C CO2 + 2NO
NOx Adsorber TechnologyFilter removes particlesLNA absorbs NOx on lean operationControls switch to rich operation to NOx to harmless NitrogenFilter regeneration and LNA regeneration are separateComplex; costly; & fuel economy lossReference: Volvo
Selective-Catalysts Reduction (SCR)Aqueous UreaSolution TankAmmonia Slip Catalyst Engine
Selective-Catalysts Reduction (SCR)Uses aqueous Urea instead of fuel to convert NOx to NitrogenRequires extra tank etc.Must add Urea distribution system to supply chainReduced EGR or no EGRFuel economy gains compared to NOx AdsorberProven durability for European applicationsFavored by some for large truck and stationary applications
What Will Be in the Marketplace?All of the above!Particulate Traps (or Soot Filters) were across the board in 2007NOx Adsorbers are on some pick-up truck applicationsSCR is favored for many HD truck and stationary applications
How Does Biodiesel Effect Emissions & Aftertreatment ?Fuel SystemConcern over deposits and corrosionAddressed by ASTM specificationsEngine EmissionsLower HC and ParticulateNOx emissions depend on duty cycle Aftertreatment hardware / durabilityEasier DPF regenerationStudies at NREL / ORNL show no adverse effects on hardware durability
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 filterDuty-cycle