Dr. vora ppt chapter 5 diesel aftertreatment


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This is a part of Lecture Series on Automotive Fuels & Emissions for M. Tech Students at ARAI ACADEMY.

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  • Increasingly, governments beyond the US, Europe and Japan, are recognizing the importance of cleaner air. For example, Brazil, India, China and South Korea all have plans to further tighten emissions regulations through 2012. Many other countries are evaluating making these moves as well.
  • As I mentioned, diesel emissions offer new challenges, particulate matter, or PM, and oxides of nitrogen, or NOx. (CLICK) Both can be dealt with independently but the unique chemistry of diesel exhaust make it a particularly difficult challenge to provide clean diesels. So let ’ s talk about what technology is available to allow us to address this global issue and meet the regulations. The most effective and feasible technology for reducing PM emissions is the diesel particulate filter.
  • Diesel particulate filters clean by having the gas pass through the ceramic wall. Every other channel is plugged at the entrance to the filter. At the exit end, the open channels are unplugged. This product design yields the characteristic “ checkerboard ” pattern shown on the slide ’ s left side. How does the filter actually work? As particulate matter, more commonly called soot, enters the filter, it gets trapped in the channel. Soot accumulates and burns off with normal driving conditions or when conditions require assistance. The diesel systems will automatically burn off the balance. Optimization of product design becomes more critical with a catalyst that does not impact the overall performance of the filter. The challenge for filters is significant, made even more so by the expectation of delivering this performance for the expected life of light-duty vehicles and up to 435,000 miles for heavy-duty vehicles. (You may need to click twice to advance. The first click will stop the video. The second will advance.)
  • 当社は、ベータ型炭化珪素結晶体の生成に成功して以来、炭化珪素に関する固有技術の蓄積と、緻密体、多孔体のアプリケーション開発に注力してまいりました。 1988 年以降、炭化珪素素材での DPF 開発に着手し、レトロフィット市場、建機市場でのご評価をいただきながら、 DPF 固有技術の蓄積、耐久性の向上など 開発を進めて参りました。クリーンディーゼルエンジンの開発を行っていた欧州自動車会社の目に留まり、ディーゼル乗用車へ当社の DPF が世界で初めて搭載されました。 遠くでは、メキシコのコカコーラの配達のトラックに使用されている。らしい。 お客さまのご要望に沿う、 DPF の開発を行い、世界のすべての自動車グループさまにご採用頂いております。お客さまの需要にお答えすべく、 日本始め、フランス、ハンガリーに生産ラインを立上げ、現在、17ラインの生産ラインを保有いたしております。 2004 年からは 2 ヶ月に一本のペースでラインを立ち上げて参りました。 始めに量産化したお客が燃料添加材システム方式であったために、まずはその方向で進み、現在は触媒化システムの方向でも生産が可能
  • 当社は、 SiC - DPF の最大の特徴である、堅牢性を生かしたセル、気孔構造の SD991 を添加剤システムへ、 SD021 を触媒化システム向けの DPF として設計いたしました。 更に高性能エンジンの出力維持を実現できる、低圧損フィルター SD031 を設計致しました。 現在では、 Euro5 世代以降の小型化、高性能化を図った、薄壁、 OS セル構造を持つ製品の開発を行っております。
  • SiC-DPF の特徴を簡単にご紹介申し上げます。当社の SiC-DPF は、ユニットと呼ばれる、 34mm 角の柱体を複数本組上げてフィルターを作成いたしております。 SiC-DPF は、その素材の高い性能から、 DPF として必要な、耐熱性や、耐化学薬品性、均一気孔による低圧損、高捕集効率を備えております。一方他の素材と比較して熱膨張係数は大きいですが、分割構造をとる事で、解決いたしております。 自身の発する熱で自分が壊れるのを防ぐために、低ヤング率の接着剤を使用して、それを防いでいる。
  • こちらの図は、ススの捕集量と気体流速に対するフィルターの破損状況を示しております。従来の触媒担体保持材のコージェライトに対して、 3 倍のスス量をためることができます。又過捕集状態で燃焼した場合でも、 SiCDPF はクラックが発生するだけで、溶損することはありません。この事から、再生回数の低減など、 C02 低減に寄与できる物と考えております。 溶損は発生せず、
  • SiC は耐化学薬品性に優れております。排ガスに含まれるそれぞれの材料に対して高い安定性を有していることが判ります。
  • In stoichiometric gasoline applications NOx is treated to 98+% efficiency in modern automobiles. This is possible because one pollutant can be reacted against another in an oxygen-deprived atmosphere, as in: CO + NOx = N2 + CO2 In lean applications like diesel, the NOx reduction is much more difficult, because the reducing pollutant, CO or HC, prefers to react with oxygen, leaving none left for NOx reduction. The industry has been searching for decades for a selective catalyst that will selectively reduce NOx with carbon-based reductants in an oxygen-rich gas. Success has been limited. The leading selective catalyst works well using ammonia as the reductant. NH3 + NOx = N2 + H2O However, ammonia has to be provided from an external source, the most common of which is urea. As such, Europe, Japan, the US, and now India are establishing urea infrastructures to facilitate the SCR systems on trucks, allowing removal of NOx from lean exhaust up to 90%.
  • Dr. vora ppt chapter 5 diesel aftertreatment

    3. 3. Diesel Emissions Regulations Drive the Technology China: Heavy duty vehicles NOx + PM 2010 Euro IV India: 2012 Euro V Heavy duty vehicles NOx + PM 2010 Euro IV S. Korea:Brazil: Heavy duty vehiclesHeavy duty vehicles NOx + PM NOx + PM 2007 – Euro IV 2009 Euro IV 2010 – Euro V ENGINE DEVELOPMENT LABORATORY 3
    5. 5. European Fuel Sulphur Levels (PPM) Fuel Quality (Sulphur Level) is critical for controlling Emissions Euro 2 Euro 3 Euro 4 Euro 5 500 India 2010 Widely Available 400 In 2005; 100% Sulphur: 50 PPM In 2009 300 200 100 0 Gasoline Diesel Source: CAI-Asia ENGINERef: M. Walsh, Clean Fuels in China (June, 2003) DEVELOPMENT LABORATORY 5
    6. 6. DIESEL EMISSIONS PM – particulate matter or soot HC & COHC – Hydrocarbons PMCO – Carbon monoxide Diesel challenges NOx NOx – Oxides of nitrogen ENGINE DEVELOPMENT LABORATORY 6
    8. 8. DIESEL EMISSION CONTROL DIESEL OXIDATION CATALYST ( DOC )REQUIREMENTS OF DOC:e SOF portion of not oxidize SO2 to SO3 For CO & HC reduction. It does not alter NOx Reduce SOF portion of PM It should not oxidize SO2 to SO3 The catalysts such as the precious metals (Pt, Pd), which are active to oxidize the SOF are also active towards the oxidation of SO 2 to SO3. Adding base metal Oxides (Vanadia) to high Pt loaded catalyst to suppress the sulphate making reactions. At low temperature SOF is adsorbed in pores & at high temperature H2SO4 is released. This is avoided with washcoat additives such as silica, zirconia, titania. ENGINE DEVELOPMENT LABORATORY 8
    10. 10. NOx vs PM Parameter Effect Effect on PM change on NOxCycletemperature Better Combustionincreases conditions prevailsThere is excessair in bowl Towards complete combustionLonger premixed Improved initialcombustion mixing, chances ofphase better combustion ENGINE DEVELOPMENT LABORATORY 10
    11. 11. NOx – PM emission controlstrategy PM A 2-V config100% B 4-V config A C Increased inj. rate B D Inj. Timing retard C E Electronics in injection 50% D F Variable swirl E G Oxicat, EGR F H DPF, DeNOx Cat G H 50% 100% NO LABORATORY ENGINE DEVELOPMENT 11 x
    12. 12. Exhaust Gas Recirculation ENGINE DEVELOPMENT LABORATORY 12
    13. 13. Influence of EGR 200% hot EGR (20% ↓ NOx 150% 70% ↑ PM) PM cooled EGR 100% without EGR (≈ NOx 60% PM ↓) 50% 50% 75% 100% 125% NOx ENGINE DEVELOPMENT LABORATORY 13
    14. 14. HIGHLIGHTS OF THE LITERATURE STUDY AND ANALYSIS WORKEGR Methods - • High Pressure • Low Pressure • Combination Low pressure is FIRST choice for Euro-V High pressure can be used upto Euro-IV ENGINE DEVELOPMENT LABORATORY 14 14
    15. 15. Diesel Engine Euro III Technology Options ENGINE DEVELOPMENT LABORATORY 15
    16. 16. Emission control technology 4-V technologyfor Diesel Passenger Cars Electronic diesel control – Rotary pump PM EGR ?? Oxicat 0.080 EURO- 2 4-V technology Common Rail DI EGR – cooled ?? Variable swirl control - ?? Double oxicat 0.050 EURO-3 + DPF NOx Cat 0.025 Cooled EGR Variable Swirl control g/km EURO-4 0.030 0.056 0.070 HC+NO ENGINE DEVELOPMENT LABORATORY 16 x
    18. 18. Particulate MatterReduction ENGINE DEVELOPMENT LABORATORY 18
    19. 19. TREND IN DIESEL EMISSION CONTROL CRDI turbo- charged diesel engine fitted with Diesel Oxidation Catalyst (DOC) has low emissions, but still needs trade-off between Particulate Matter (PM) and Oxides of Nitrogen (NOx). High percentage of EGR upto 30% can be used to reduce NOx considerable, but this leads to increase in PM. Need for independent technology to reduce NOx & PM For PM control, we require the use of Catalysed Diesel Particulate Filter (CDPF) For NOx control, we require Lean NOx Trap (LNT) or Selective Catalytic Reduction (SCR). Use of CDPF and LNT or SCR together will produce simultaneous reduction of PM and NOx. ENGINE DEVELOPMENT LABORATORY 19
    20. 20. INTRODUCTION TO DPF The first utilization of diesel filters on car was made in California by Mercedes-Benz in 1985 Starting from 2000, the interest in diesel filter systems by automotive manufacturers was reestablished Since 2001, PSA Peugeot was the first company to utilize DPF on passenger cars with Fuel Additives for Passive Regeneration. Since 2003, Damlier Chrysler utilized Catalyzed DPF (CDPF) on Passenger cars for Passive Regeneration. Recently, other car producers started to introduce diesel filters in certain models. As regards particulate emissions, the wall-flow diesel particulate filter (DPF) is today the most efficient after-treatment device, attaining filtration efficiencies over 90% (for dry particulate) under normal operating conditions. ENGINE DEVELOPMENT LABORATORY 20
    21. 21. DIESEL PARTICULATE FILTER (DPF)OR CATALYZED SOOT FILTER (SCF) FOR PM REDUCTION  Plugged channel honeycomb  Particulates trapped on wall  Regenerated to burn particles  Catalyzed or uncatalyzed ENGINE DEVELOPMENT LABORATORY 21
    23. 23. PERFORMANCE REQUIREMENTS FOR DPFThe four basic requirements which the filter must meet are: adequate filtration efficiency to satisfy particulate emissions legislation; low pressure drop to minimize fuel penalty and conserve engine power (10 g/l loading allowed) high thermal shock resistance to ensure filter integrity during soot regeneration; high surface area per unit volume for compact packaging. ENGINE DEVELOPMENT LABORATORY 23
    24. 24. 1. Development History 1988 1998 1999 2000 2001 2002 2003 2004 2005 2006 Fine Ceramics Euro3 regulation Euro4 regulation(β-type SiC Powder) 1 st Mass-Production 1 st Mass-Production Mass-Production Lines Line in Japan Line in France in HungaryUnique features of SiC1988 - Start of DPF development - Basic Evaluation Co-Development with EU customers - Durability Test 1 st series equipment in the world SOP in June 2000 DPF for additive system FBC(Fuel Borne Catalyst) System SOP in January 2004 DPF for catalytic coating system City Bus & Construction machines ENGINE DEVELOPMENT LABORATORY 24
    25. 25. 2. Technology Roadmap 2005 Euro4 2010 Euro5 2015 Euro6 maintenance Interval 100Kkm 160Kkm 250Kkm? From Euro5 almost all cars require DPFDevelop and supply DPF C/C C-DPF 2brickhat would comply with System (20-40g/L) RD053he requirements for all (40-60g/L) RD061 ngines and generations. Thin DOC+C-DPF C/C C-DPF 2brick System (20-40g/L) Newly designed OS thin wall type: RD053 OS+Medium porosity design: SD061 U/F C-DPF System Thin DOC+C-DPF Maintenance free/Downsizing High Robustness -High Coat ability -High Coat ability Low Pressure loss -Low Pressure Loss -Low Pressure Loss DOC+C-DPF Thin wall / Low porosity type -Low Heat Capacity -Low Heat Capacity SD031 -High Ash Capacity High Robustness -High Ash Capacity Low porosity type SD991/SD021 Optimized Asymmetrical cell structure Outlet “Unique Octo-Square Cell Structure” ENGINE DEVELOPMENT LABORATORY Inlet 25
    26. 26. 6. Advantages of SiC-DPF SiC grain Characteristics of SiC-DPF + High Thermal Resistance + High Chemical Resistance + Low Pressure Loss Pore + High Filtration Efficiency Uniform pore structure ENGINE DEVELOPMENT LABORATORY 26
    27. 27. 6. Advantages of SiC-DPFHigh Thermal Resistance セLength: 150.5mm グメントの長さ :10” L 35 Accumulated soot mass [ g/ L] SiC-DPF 問題なし SiC Non crackNo problem SiC: Cracked 30 SiC-DPF クラック発生 SiC Cracked Cracked コージェライト 問題なし Cordierite crack problem Cord. Non No 25 Cordierite クラック/溶損 コージェライト Cracked/Melted Cord. Cracked or Melted 20 15 Cordierite: SiC-DPF SiC-DPF SiC-DPF  Melt 10 Melted 安全領域 Safety Safety Area area Crack 5 コージェライト Cord.-DPF Cordierite Safety Area 安全領域 Safety 0 area 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 Gas velocity [ m/ sec] -Thanks to high thermal resistance, SiC-DPF has higher SML compared to Cordierite. ENGINE DEVELOPMENT LABORATORY 27 -Failure mode of SiC-DPF is only “crack” in case of soot
    28. 28. 6. Advantages of SiC-DPF High Filtration Efficiency SiC-DPF Pore dia. distribution 3.0 2.5dV/ dlo gD Po re Vo lum e 2.0 1.5 Cordierite 1.0 0.5 0.0 1 10 100 Po re dia m e t e r (um ) Thanks to the sharp pore dia. distribution, SiC-DPF has uniform pore structure, which enables to reach high filtration efficiency. ENGINE DEVELOPMENT LABORATORY 28
    29. 29. 6. Advantages of SiC-DPFLow Pressure loss Flow velocity = 5m/sec SiC-17/100 Cordierite-17/100 SiC-14/200 High duration type 45 SiC-12/300 low pressure typePressure loss [Kpa] 40 35 30 25 20 15 10 5 0 0 2 4 6 8 10 12 14 16 18 Soot [g/L] ENGINE DEVELOPMENT LABORATORY To compare cordierite ,SiC-DPF has a low pressure 29 loss
    30. 30. 6. Advantages of SiC-DPF High Chemical Resistance Additive AshCSiei r e d o C CuO Fe 2 O 3 CeO 2 Ash CeO 2 Fe 2 (SO 4 ) 3 CuSO 4 Na 2 SO 4 K 2 SO 4 t i r -nH 2 O -5H 2 O (Condition/Temp=1350deg.C, Time = 50hrs) (Condition/Temp=1350deg.C, Time = 1hr) No reaction Discoloration Melted Cracked SiC is stable material against chemicals. ENGINE DEVELOPMENT LABORATORY 30
    32. 32. Passive Regeneration ENGINE DEVELOPMENT LABORATORY 32
    33. 33. Diesel Particulate Filter System Source: CAI-Asia ENGINE DEVELOPMENT LABORATORY 33
    34. 34. Post Injection Regeneration for an Uncoated DPF ENGINE DEVELOPMENT LABORATORY 34 (Umicore)
    36. 36. THE MAIN GOALS IN THE DEVELOPMENT OF A CATALYTIC FILTER COATING Reduction of the activation energy for soot oxidation Improvement of the passive regeneration behavior, lowering of the balance point (This is defined as the temperature at which the same amount of soot in the particulate filter is oxidized as is emitted by the engine in the same unit of time) Suppression of secondary emissions during filter regeneration Good HC/CO light-off for supporting the function of an upstream oxidation catalyst High thermal stability Preferably no negative impact on backpressure ENGINE DEVELOPMENT LABORATORY 36
    37. 37. CATALYTIC COATING OF SiC DIESEL PARTICULATE FILTERS The advantage of these new filter substrates is a higher tolerance with respect to the backpressure behavior compared to a catalytic activation. However, lower mechanical stability and reduced maximum soot loading represent disadvantages. In contrast to standard applications such as three-way or oxidation catalyst, in which the substrate serves exclusively as the carrier for the catalyst, the diesel particulate filter has its own functionality which is changed by a catalyst coating . In this way, for example the coating can increase the filtration efficiency of the filter and influence its maximum soot loading. Decisive, however, is the effect of the coating on the backpressure behavior of the filter. This interaction between filter substrate and coating must be taken into consideration in the development of a suitable catalyst. Taking these factors into account, two coating processes for particulate filters have been developed . These processes are referred to as “Microcoating” and “Macrocoating”. ENGINE DEVELOPMENT LABORATORY 37
    38. 38. Continuous Regenerative Trap (CRT)• Oxidises CO and HC to CO2 and H2O• NO is oxidised to NO2• Collects Soot in wall-flow particle filter• NO2 reacts with trapped soot to form CO2 & NO• Requirements: Fuel S < 50 ppm & NOx/PM > 20• Passive system - no external heating necessary provided Temperature is high enough (>260°C for 40% of the time)• CO, HC, PM reduction > 90% ENGINE DEVELOPMENT LABORATORY 38
    39. 39. CRT Particulate Filter Outlet Section Filter Section Catalyst SectionInletSection Honeycomb Wall-flow Catalyst Filter
    40. 40. NO2 Reaction in a CRT NO+CO2 NO NO2 ½O2 NO2 CO CO2 ½O2 NO+CO2 HC H2O+CO2O2 Flow Through Catalyst Wall Flow Filter ENGINE DEVELOPMENT LABORATORY 40
    41. 41. US 2007 Emission Control is Focused on PM ENGINE DEVELOPMENT LABORATORY 41
    42. 42. HC De-NOx (Diesel Lean NOx Catalyst DLNC)Zeolite absorbs HC during Cold Start and when the temp ishigh enough for light-off, the HC is released for reduction ofNOx. Fuel is injected downstream of catalyst which acts as aNOx redundant. Operating Temp. window 200 to 300 deg C.NOx Adsorber (Lean NOx Trap LNT)Base metal Barium Alumina absorbs and stores NOx in leanburn operation. Regeneration reqd to avoid deposition oncatalyst material. Occasionally rich mixture is fed whichconverts adsorbed Nitrate into N2 .Urea SCR (Selective Catalytic Reduction)Urea in solid or aqueous form is used. In the presence ofcatalyst urea decomposes to produce NH3, which reacts withNOx selectively. NH3 reacts with NO and NO2 converting toN2 molecules and H2O. ENGINE DEVELOPMENT LABORATORY 42
    43. 43. HC DeNOx CATALYST OR DIESEL LEAN NOx CATALYST (DLNC)  Reducing NOx by HC under the excess of oxygen is currently the most advanced diesel DeNOx concept  Zeolite absorbs HC during Cold Start and when the temp is high enough for light-off, the HC is released for reduction of NOx.  HC emissions are used to reduce NOx at around 300°C  The catalyst for the HC DeNOx is Pt on support oxide (Al2O3, SiO2,TiO2, ZrO2..)  This method requires reasonable amounts of HC in the exhaust gas, which can be achieved, either by post injection using CRDi or by secondary fuel injection.  NOx reduction up to 30% possible.  However, there is fuel penalty (3-6%) and expensive system cost. ENGINE DEVELOPMENT LABORATORY 43
    44. 44. HC DeNOx MECHANISMNO + O2= NO2[NO activation, requires reducible site]CxHy + NO2= CO2 + N2 + H2O (Preferred) [Competition for HC, on oxidizable sites]CxHy + O2 =CO2 + H2O (Not preferred)[HC oxidation, very fast] ENGINE DEVELOPMENT LABORATORY 44
    45. 45. EMISSION CONTROL USING HC DeNOx & CDPFUS2010/ EU VI De NO x Oxidation Catalyst Catalyzed Soot Filter ENGINE DEVELOPMENT LABORATORY 45
    46. 46. NOx Adsorber Catalysts• Lean conditions (lambda > 1) – Oxidises CO and HC to CO2 and H2O – Oxidises NO to NO2 – NO2 is stored as Nitrate• Rich conditions (lambda < 1) – Nitrates are reduced to NO2 – NO2 is released and reduced to N2• NOx reduction > 70% possible.• Requirements: S < 10 ppm ENGINE DEVELOPMENT LABORATORY 46
    47. 47. NOx Adsorber Catalyst Functions LEAN: NO2 generation NO2 storage (CO, HC, SOF oxidation) RICH: NOx release NOx conversion (Desulfation) ENGINE DEVELOPMENT LABORATORY 47
    48. 48. NOX ADSORBER OR LEAN NOx TRAP Since NO is known to show slower reactivity with metal oxides than NO2 and engine-out NOx primarily consist of NO (90%), NO must first be oxidized to NO2 over an oxidation catalyst (e.g. Pt based ). The adsorption of a NOx adsorber catalyst entails reaction of an acidic gas (NO2) with a basic adsorbent (oxides or carbonates of alkali and alkaline earth elements, e.g. BaO and BaCO3) to form nitrate or nitroso-species, both on the catalyst surface. The operational temperature range of the NOx adsorber catalyst is governed by the low and high limits. The low limit is controlled by the light-off temperature required for the catalyst to oxidize NO into NO2 and the upper limit is determined by the temperature of thermodynamic stability of the trapped nitrogen oxide species e.g. Ba(NO3)2 When the effective storage capacity of the adsorber is below the desirable level, reductant (e.g. diesel fuel) is injected to establish a rich environment. Under this condition, the trapped NOx is reduced to N2 following a conventional three-way catalytic conversion principle. However , the adsorbent function (e.g. BaO around Pt sites) is extremely susceptible to deactivation from sulphur oxides in the exhaust by the formation of sulfated species that hinder adsorption sites intended for NO2 storage. ENGINE DEVELOPMENT LABORATORY 48
    49. 49. EMISSION CONTROL USING CDPF & LNTUS2010/ EU VI Ox i Ca dati tal on ys t Catalyzed NOx Trap Soot Filter ENGINE DEVELOPMENT LABORATORY 49
    50. 50. EMISSION CONTROL USING LNT & CDPFUS2010/ EU VI NO xT ra p Oxidation Catalyst Catalyzed Soot Filter ENGINE DEVELOPMENT LABORATORY 50
    51. 51. SELECTIVE CATALYTIC REDUCTION (SCR) Within Europe, the principal NOx control strategy starting in 2005, is Selective Catalytic Reduction (SCR) using ammonia, derived from urea as the reductant. Here ammonia reacts with NOx selectively on a catalyst, such as V2O5TiO2, under oxygen rich exhaust gas• Urea/water solution reacts at > 200 °C to form NH3 and CO2.• NH3 reduces NO and NO2 to N2.• NOx reduction > 80 % possible.• Fuel with S up to 500 ppm can be used. ENGINE DEVELOPMENT LABORATORY 51
    52. 52. Urea SCR System Urea Injector FLOWOxidation 2 x SCR 1 x Pt Clean-upCatalyst Catalysts Catalyst ENGINE DEVELOPMENT LABORATORY 52
    55. 55. CRDPF + SCR Combined Continuously Regenerative Diesel Particulate Filter (CRDPF) with urea-based Selective Catalytic Reduction(SCR) for simultaneous PM & NOx Control. Two methods are used to achieve accurate dosing of urea:a) Detailed urea injection map based on engine information. b) Urea injection based on real time NOx input (NOx sensor based) and calculation logic. ENGINE DEVELOPMENT LABORATORY 55
    56. 56. ONE APPROACH TO SCR SCR Catalyst (S) 4NH3 + 4NO + O2 → 4N2 + 6H2O Oxidation Catalyst (V) Urea 2NH3 + NO + NO2 → 2N2 + 3H2O 2NO + O2 → 2NO2 (NH2)2CO 8NH3 + 6NO2 → 7N2 + 12H2O4HC + 3O2 → 2CO2 + 2H2O 2CO + O2 → 2CO2 Exhaust Gas V H S O Hydrolysis Catalyst (H) Oxidation Catalyst (O) (NH2)2CO + H2O → 2NH3 + CO2 4NH3 + 3O2 → 2N2 + 6H2O ENGINE DEVELOPMENT LABORATORY 56
    57. 57. SCR TECHNOLOGY : TWO TYPES OF DESIGN An NH3 slip control catalyst is also used  Within the Compact design, the gas first at the end of the SCR catalyst system to passes through the CR-DPF system, and oxidize any NH3 that is not used during is then turned through 1800 and flows the reaction. through the SCR catalysts, which are coated onto metallic, annular substrates, Many of the SCR-DPF systems are fitted around the CR-DPF system. configured in the linear design, where  This presents a wider but much shorter an SCR + Slip catalyst system follows a CRDF system packaging envelope for the combined system. It is necessary that it should meet space constraints of the vehicle The SCR catalyst is followed by an ammonia slip catalyst also coated on ceramic substrates. The size of the SCR catalyst is based on the engine exhaust flow rates. Typically the volume of catalyst is 1.5 to 2 times the engine displacement ENGINE DEVELOPMENT LABORATORY 57
    58. 58. UREA DOSING AND INJECTION SYSTEM Urea dosing and injection system  The amount of urea to be injected are different but contain similar is calculated from input signals functions. received from the following: A metered amount of urea is  Engine Out NOx (Conc.) Sensor delivered into a pressurized air  Engine Parameters via installed stream. sensors or CAN J-1939 data bus The air and urea mixture is then  Exhaust gas temperatures at transported to a nozzle that CRDPF inlet, SCR inlet and SCR atomizes and distributes the urea in outlet the exhaust flow.  Urea Temperature The mechanical functions of the  Urea and Air system pressures system consist of air pressure regulation, pumping urea from the tank to the dosing system and metering the urea into the airflow. ENGINE DEVELOPMENT LABORATORY 58
    59. 59. THE COMPONENTS IN THE UREA DOSING SYSTEM This information is used along with • The components of the urea injection application specific data entered into the system consist of a urea pump, an air ECU to calculate the amount of urea regulator and a dosing manifold. Urea needed to get the maximum possible is pumped from the tank to the urea NOx reduction, under that operating dosing manifold via a 24 volt condition. accumulator pump capable of A NOx sensor is installed in the exhaust delivering up to 157ml/min of urea. pipe at the outlet of the turbocharger. • An air regulator is used to deliver The retrofit system ECU uses an dosing manifold. algorithm that calculates the amount of • Either the test cell or the vehicle air is urea needed based on the engine outlet used to supply this air to the regulator. NOx reading and the exhaust flow of the • The air regulator is specific to the engine. system. The ECU then sends a signal to the Urea dosing manifold to deliver the required amount of urea to the SCR catalyst. ENGINE DEVELOPMENT LABORATORY 59
    62. 62. DESIGN VALIDATION TECHNIQUES USING CFD The Diesel particulate filter (DPF) is  The porous silicon carbide honeycomb, used composed of a ceramic square channel for the experiments from which data will be honeycomb with alternate channels used, has the following geometric features: plugged. The material considered for the test case is porous silicon carbide with  Cell density 200 channels/in.2 the following properties:  Wall thickness 4 mil inch Intrinsic porosity 45%  Plug length 0.07 inch Intrinsic density 3100 kg/m3  Monolith diameter 5.66 inch Permeability 5.4 × 10-13 m2  Monolith length (L) 5.66 inch Effective heat capacity 690 J/kg/K (25°C) Effective thermal conductivity 70 W/kg/K (25°C) ENGINE DEVELOPMENT LABORATORY 62
    63. 63. DESCRIPTION OF RELEVANT PARAMETERS TO BE OBSERVED• The Diesel oxidation catalyst DOC also consists of • The aim is for the above parameters to be a monolithic square channel honeycomb made of used as realistic boundary conditions for the silicon carbide, which has the coating with a application-specific models of the after- platinum catalyst. treatment devices. Specifically, within the• The DOC ( 2 Nos) has the following geometric DPF, coupling with the 3-D flow solver is characteristics: channel density 400 channels/in.2 wall thicknesses 6.5 mil inches, monolith length (L) expected to improve the predictive capability 2.5 inch, monolith diameter 5.66 inch. of the DPF regeneration model, which will in• The above properties and characteristics can be turn be assessed by observation of: translated into bulk properties (e.g. flow resistance) • a) Time response of the DPF pressure drop by analytic expressions, or are otherwise used in (flow resistance) modeling the bulk behavior of the honeycomb material regions. • b) Time response of the DPF (internal) temperatures and outflow temperature,• Hence, the focus in the current context is in the additional information, which a 3-D flow • c) Distribution of soot mass loading within solver can provide: the filter during and after the regeneration sequence.• a) Exhaust gas velocity and temperature profiles entering the DPF and DOC devices,• b) Temperature distribution within the devices due to 3-D internal heat transfer and non-axisymmetric heat losses to the exterior. ENGINE DEVELOPMENT LABORATORY 63
    64. 64. SOFTWARE & BOUNDARY CONDITIONS MODEL SETUP WITH THIRD-  OUTFLOW: PARTY SOFTWARE :  Pressure outlet: 0 gauge pressure. Exhaust The third-party software used for the flow after the devices is vented to the automotive test case was Gambit2.0 and environment. Fluent 6.0.1  WALLS: TURBULENCE MODEL  No-slip condition for momentum.  Heat loss at the walls of an exhaust system is The standard k-ε model is used. The normally treated as a function of temperature regions occupied by the DPF and DOC with a heat transfer coefficient for natural monoliths are considered laminar zones and/or forced convection. (no production or dissipation of  However, the surfaces of the experimental turbulence; momentum transfer based exhaust system are wrapped with a layer of on laminar viscosity). fibrous insulation and a covering of INFLOW: (SPECIFIED INLET aluminium foil. VELOCITY)  Therefore, a very small heat loss rate proportional to the exhaust-to-environment 25 - 35 m/s during normal (loading) and temperature contrast can be assumed. regeneration mode operation  GAS PROPERTIES: Turbulence intensity: 10%  (Assume properties of air, variable with Turbulence length scale: 0.005 m temperature) Temperature: 250 – 350 °C  Exhaust gas density: equation of state for ideal gas with molecular weight 29 gr/mol. ENGINE DEVELOPMENT LABORATORY 64
    65. 65. CONCLUSIONS For meeting BS IV Norms, optimised shallow combustion chamber with optimized CRDi, Cooled 30% EGR and DOC may be the good beginning. The next step may be addition of CDPF for PM control and engine optimization for NOx reduction. For Euro V Norms, addition of HC DeNOx, LNT or SCR may be tried for NOx reduction. In the case of new developments for Euro 4 compliance, the new design is recommended to be protected for high peak firing pressure capability. Transient behaviour of engines will become decisive and most challenging with very low engine-out emissions as mandatory for Euro V/VI. ENGINE DEVELOPMENT LABORATORY 65 65
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