International Journal of Modern Engineering Research (IJMER) www.ijmer.com Vol.2, Issue.5, Sep.-Oct. 2012 pp-3138-3142 ISSN: 2249-6645

Review of Advanced EGR and Breathing Systems for High Performance and Low Emission HSDI Diesel Engine Pundlik R Ghodke1, Dr. Jiwak G. Suryavanshi2 Research Scholar, Mechanical Engineering Department, VNIT Nagpur / Dy. General Manager, Mahindra Research Valley, Chennai, India Associate Professor, Mechanical Engineering Department, VNIT, Nagpur, India

ABSTRACT:

In The Future, Beyond 2010 Additional Measures Is Required To Be Taken In To Account For Careful Selection Of Egr And Boosting Technology In Conjunction With After-Treatment System. At The End The Cost To Benefit Ratio Of After-Treatment System And The Performance Of Egr-Boost Systems Will Determine The Future Diesel Engine System Configurations. Diesel Particulate Filter (Dpf) Became As Essential Element Herein Beyond Euro 4 Emissions. This Paper Deals With Different Engine Boosting Systems Taking Into Account The Special Needs Of Turbochargers And The Interaction Between Egr And Boosting Technology In Conjunction With Selection Of After-Treatment System. The Investigation Has Been Done With A Calibrated Simulation Model For Selection Based On Benefit Verses Cost Of The System.

Key words: DPF;HP EGR; LP EGR; NOx; PM; VGT Turbocharger

I. INTRODUCTION All modern diesel engines with passenger car or truck application, Selection of EGR, boosting system and after-treatment systems together is key for engine performance and cost benefit to meet future stringent emission norms beyond Euro4. Figure 1 shows various options of after-treatment systems in conjunction with EGR. Layout of EGR affects the engine out NOx and PM emissions and performance of turbocharger due to change in exhaust flow rate going over the turbine. Also back pressure due to after- treatment system influence the turbocharger efficiency and air flow and EGR rate. This effect the engine performance, fuel economy and engine out emissions. Hence lot of attention is required while selection of EGR layout, intake system layout and exhaust system layout. This was done with building simulation model and assessing the performance with various combinations before design stage.

II. EGR-BOOST CONCEPT High pressure EGR (HP EGR) take the exhaust before the turbine via an ECU controlled EGR-valve to the air intake as shown in figure 2. For better breathing efficiency, EGR-coolers are used. EGR cooler reduces EGR gas temperature and it helps increase in volumetric efficiency of engine. With addition of exhaust gas oxygen content reduced and it help reduction of NOx formation at part load condition. In addition, the application of gas/water charge air coolers may meet special package requirements. Niche applications today require even 2 stage cooling circuits to achieve the best thermodynamic results as shown in figure 5. Deposit formation is an issue which cannot be totally prevented. For that reason the untreated exhaust should not pass the charge air cooler which excludes its usage during part load conditions. Classical HP-EGR reduces the turbine gas flow. The energy, driving the compresses or, decreases while the necessary compressor pressure ratio to keep the engine running at the same load points. Closing the Variable turbine geometry (VGT) increases the exhaust back pressure and the energy provided to the turbocharger. Mild EGR concepts used for Euro 4 application this kind of strategy is absolutely elegant and sufficient.

Fig 2: High Pressure EGR-Boost System However, as more EGR rate is required, the turbocharger cannot be keep up and the operation point in the compressor map moves toward the surge line as shown in figure 3. For advanced EGR concepts where more stringent emission of Euro 5 , the turbocharger may not be able to deliver the necessary mixture of fresh air and exhaust to the engine. There are different matching opportunities to improve this situation, but engine power output and fuel efficiency is going to suffer.

Fig1: Diesel Engine with different EGR and after-treatment system Layout.

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International Journal of Modern Engineering Research (IJMER) www.ijmer.com Vol.2, Issue.5, Sep.-Oct. 2012 pp-3138-3142 ISSN: 2249-6645

Fig 5: Influence of VGT, EGR-split and EGR-cooling Fig 3: Influence of High Pressure EGR on compressor map.

2.1 Low Pressure Egr System Low pressure loop EGR system is a well known technology that offers an alternative to meet the requirements mentioned above. The exhaust is taken after turbine and introduced in front of the compressor as shown in figure 4. Before the market introduction of Diesel particulate filter (DPF), the entire air intake system including the compressor would have been subject to deposit formation. This was one of the main reasons that limited the application of this kind of system. The DPF can be therefore seen as enabler of LPEGR. The exhaust is cooler as compare to HP-EGR is clean. It is expected, even after recompression, that the thermal behavior is superior to HP-EGR as the charge air cooler (CAC) is used in addition. The LP-loop, like the HP-loop, is equipped with an EGR Valve. To increase the pressure difference between exhaust and air intake, especially to drive higher rates, an exhaust throttle is needed which will be closed to increase exhaust back pressure thereby increasing EGR.

The engine parameters like air/ fuel ratio, BMEP and BSFC can be analyzed in figure 6, 7 and 8. Areas of air/fuel ratio smaller than 1 have been excluded. The results are based on the relationship of turbine efficiency depending on the VTG-position, pumping losses as part of boost pressure, the efficiency chain turbine-compressor and the necessity to add energy by fuel, represented by lambda. Closed VTG and a high turbine flow (LP-EGR) increase the pumping losses in principal. The corresponding lambda is high due to availability of excess air in the combustion chamber. At the end this leads to the best BSFC at the air fuel ratio of one for the widest open possible VTG position, represented by the right bottom corner of the operation maps within the compressor mappings. The best distance from the smoke limit will be reached by the higher boost pressures created by closing VTG. This has to be paid by a slightly higher BSFC caused by higher pumping losses.

Fig 6 : Air Excess Ratio at 2500 rpm, 12 bar BMEP and 30% EGR

Fig 4: Low Pressure EGR system layout 2.2 Thermodynamic Comparison Of Lp And Hp Egr System Figure 5 shows the introduction of the LP EGRpath. The engine has been operated at 2500 RPM at a load of 12 bar BMEP and an EGR rate of 30%.The very left line in the map represents the HP-mode. The other vertical lines represent increasing amounts of LP Loop EGR. For each of the lines, VTG-position is varied from open (Bottom) to closed (TOP). The very right, nearly vertical lines expresses the same as before but under LP-mode. The lines in between are splits of HP-and LP-loop systems. The overall EGR –rate does not change. It can be clearly seen that the air mass flow is increased when replacing HP-EGR by LPEGR. The turbine flow is also influenced positively and better compressor efficiencies are expected obviously. EGR-cooling helps to decrease the necessary pressure ratio and allows opening the VTG leading to better turbine efficiencies.

Fig 7: Pumping Losses @ 2500 rpm, 12 bar BMEP and 30 % EGR rate

Fig 8: Specific Fuel consumption@ 2500 rpm, 12bar BMEP and 30 % EGR rate

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International Journal of Modern Engineering Research (IJMER) www.ijmer.com Vol.2, Issue.5, Sep.-Oct. 2012 pp-3138-3142 ISSN: 2249-6645

Fig 9: Air Excess Ration @ 2000 rpm, 2bar BMEP and 60% EGR rate

Fig 14: Specific Fuel Consumption @ 4000 rpm and 20% EGR rate

For low load conditions @ 2000 rpm and 2 bar BMEP and high EGR rate of 60 % same results are seen. Refer figure 9, 10 and 11. In addition, the benefit of higher exhaust gas flow can be easier seen even where the turbocharger does not build up a significant boost pressure.The significance between boost pressure and lambda is higher as both turbine and compressor are just starting to work.

Two operations are mentioned above are important for pass car diesel engines due to the requirements in the emission test procedure. Truck applications have to deal with EGR at high speeds and loads. As the compressor efficiencies are decreasing by higher flows and turbine conditions aren‟t improved, either the best BSFC are reached on the HP-loop mode area. An EGR-split of 25% LP and 75% HP flow seems to be the best operation point. Figure 6 to 14 shows an advantage of a split between HP and LP EGR. The split just optimizes the exhaust gas flow as a best fit to the turbine characteristics. At low engine speeds/loads LP helps to increase the energy flow to the turbine. At high speeds HP EGR may help to avoid turbine efficiency deterioration by wide VTG position.

Fig 10: Pumping Losses @2000 rpm , 2 bar BMEP and 60% EGR Rate

Fig 11: Specific Fuel Consumption @ 2000 rpm and 60% EGR rate

III. ENGINE BREATHING MATCH This understanding is even supported by different matching‟s applied to both Low pressure (LP) and high pressure (HP) EGR as shown in figure 15. The x-axis shows the principal matching trend path like smaller compressor and/or smaller turbines. The clear objective is to help the system to pump air and EGR to the engine at low speeds/loads as indicated by the operation point. The energy freedom in available energy potential in terms of air/fuel ratio and turbine power output gained by a new turbo matching is obvious but not sufficient. The peak power output is being deteriorated by that measure.After including low pressure (LP) EGR the additional energy potential is visible. Turbine power is increased by factor of 3. Air fuel ratio can be increased even at the basic turbo matching. The sensitivity of the LPEGR system in terms of turbo matching is another not surprising result.

Fig 12 : Air Excess Ratio @ 4000 rpm and 20% EGR Rate Figure 15: EGR-Split Turbo matching, @ 1500 rpm, 2 bar BMEP and 60% EGR rate

Fig 13 : Pumping Losses @ 4000 rpm, 12 bar BMEP and 20 % EGR rate

IV. TRANSIENT BEHAVIOUR Low pressure EGR (LP-EGR) systems comprise a large air intake volume than high pressure EGR (HP-EGR) systems. Especially applications with under floor DPF will show a huge difference. Most of the discussions therefore focus on this possible disadvantage of LP-EGR systems

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International Journal of Modern Engineering Research (IJMER) www.ijmer.com Vol.2, Issue.5, Sep.-Oct. 2012 pp-3138-3142 ISSN: 2249-6645 when it comes to the transient behavior of the diesel engine. The additional pipes and volumes have to be emptied of the air/exhaust of the previous operation point which might require some time. For that reason the comparison was run to fond the relationships between HP- and LP-system-acceleration times shown in figure 16. The load step goes from 2 bar BMEP to 9 bar, including a reduction in EGR. This load step represents part of the Euro 5 where especially small engines in heavy vehicles are facing the NOx-challenge. These 3-Charts in figure 16 present the BMEP, the necessary EGR-rate and the lambda. The graphs show the differences between LP and HP, including different control strategies for HP.

In addition, the interaction with VTG position is much less important than in a HP system. The result can be seen in figure 16 where the targeted EGR rate is reached and kept with high precision. When EGR rates will increases in future emissions regulation the demand of more responsive LP-systems will increase as shown in figure 18. The higher the EGR rate, the larger the difference in response time based on the dominant energy balance at the turbine.

Figure17: Load change @1500 rpm

Fig 16: Load change @ 1500 rpm (H1: Strategy to achieve highest boost pressure,H2 compromise betweenH1 and H3 and H3: strategy to achieve highest EGR) All the strategies reach the soot limit of lambda equal to 1.05 easily. The low LP –EGR system reaches the required BMEP first and shows a nearly stable EGR-rate. Strategy H1, with the focus on the fast increasing boost pressure, needs approximately one sec to catch up and does not reach the necessary EGR response but is running near the smoke limit: the operating point represents the borderline performance of a HP-system even at 9 bar BMEP. The example emphasizes the superior behavior of a LP-system at mid loads and low speeds considering future need of EGR-rates as mentioned before. The diesel engine used has a power output of less than 45 kW/litre. The basic ability to handle EGR at low loads/speeds should be reasonable. Nevertheless LP shows significant advantages. Application with more than 50 kW/litre specific power output should therefore depend even more on the LP EGR-system properties. The additional volume in the air intake of the LP EGR system can be seen as damping factor during transient during the filling process of a charged EGR-rate and boost pressure. Add on volume is created by the compressor and necessary tubes, which have been assumed to fill 5 to 6 liters. Figure 17 is extracts the BMEP curve of figure 16. The disadvantage caused by the LP-add on volume is negligible compared to the advantage in BMEP rise after 1.4 sec. The higher initial turbocharger speed, enabled by the higher exhaust mass flow through the turbine, ensures a smaller “perceivable” load step for the turbocharger. The simplified explanation for the enhanced dynamic response is a sort of replacement of EGR by fresh air. In that defined load step the compressor is just considering rather small increase in turbocharger speed. This LPAdvantage in transient response corresponds to the controllability.

Fig 18 : Load Change for different EGR Rate and EGRSplit V. CONCLUSION AND CONCEPT COMPARISON OF HP VERSES LP EGR

Fig 19: Comparison of LP and HP EGR-Boost System

Figure 20: Comparison of Future Emission Concept with constant Peak power output. Based on these results, EGR-systems will enable diesel engines to breathe even more exhaust than today. LPEGR systems will allow lower NOx-emissions without any

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International Journal of Modern Engineering Research (IJMER) www.ijmer.com Vol.2, Issue.5, Sep.-Oct. 2012 pp-3138-3142 ISSN: 2249-6645 after-treatment, which helps system costs lower, weight and complexity down refer figure 19. Adding a 2nd cooling stage will lowering NOx by similar air intake temperatures. To optimize the best configuration depending on the situation in the vehicle is the task how compromise between the parameters mentioned in figure 19. The single stage cooled LP-EGR system offers the most advantages based on the number of points and parameters. The established HP-EGR system offers advantages like compact packaging, low compressor intake temperatures even at high power outputs, and low exposure of components to water and acid. The thermodynamic disadvantages have been explained and limit the HPcapabilities significantly. The LP-EGR system, enabled by the DPF is new and seems to consume package volume, which can be smart designs like closed coupled filters and catalysts. Water and acid precipitation are subject to current development to limit or exclude their impact in the future. EGR-systems will enable diesel engines to breathe even more exhaust than today LP-EGR systems will allow lower NOx-emissions without any after-treatment, which will help to keep system costs, weight and complexity down.

References [1] [2]

[3]

HEYWOOD,J.B, Internal combustion Engines Fundamentals, Mc Graw-Hill,Inc.,1988 WATSON,N.and JANOTA,M.S, Turbo charging the internal combustion engine-wiley-interscience, 1982

JUNMIN,WANG and et.al.:2008-01-1198: Development of High Performance Diesel Engine Compliant with Euro V Norms, 2008 World Congress, Detroit ,Michigan April 2008 [4] Ramdasi SS and Etal : 2011-26-0033, SIAT2011, „Design and Development of 3 Cylinder 75 kW/Litre High Power Density Engine for Passenger Car Application to Meet EIV /E V Norms [5] Borg-Wirger Turbo & emission systems Modern turbo charging systems for pass car/Future breathing system requirements for clean diesel engines. [6] Steven D. Arnold: 2004-01-1354: Turbocharging Technologies to Meet Critical performance Demands of Ultra low Emissions Diesel Engines, 19th cliff Garret Turbomachinary Award lecture, SAE international. [7] Sylvain Saulnier and ET al :2004-01-0929: Computational study of diesel Engine down sizing using two stage Turbocharging,SP-1826,2004 SAE World Congress, Michigan. [8] Rabih Omranand Et al : 2008-01-1732 : Optimizations of the In cylinder Air Filling For Emission Reduction in Diesel Engines, June 2008 SAE International, Powertrains, Fuel and Lubricants Congress, Shanghai, CHINA. [9] Tie Li and Et al : 2008-01-0647 : Effect of Exhaust Catalysts on Regulated and Unregulated Emissions from Low Temperature Diesel Combustion with High Rates of Cooled EGR, SP 2168, Incylinder NOX and Particulate Control, 2008.

[10] G Avolio and Et al : 2007-24-0014: Effect of Highly Cooled EGR on Modern Diesel Engine Performance at low Temperature Combustion Condition, ICE 2007, Kapri Naples, Italy, SAE international. [11] Naoya Ishikawa and Et al :JSE 20077302:2007-011881: Study of effects on EGR Cooler on Performance on Combustion Properties of the Premixed Compression Ignition Combustion By multi Cylinder DI Diesel Engine, Society of Automotive Engineers of Japan. [12] Robert D Chalgren and Et al : 2002-01-0076 :Controlled EGR Cooling System for Heavy Duty Diesel Application Using Vehicle Cooling System, SAE 2002 World Congress, Detroit, Michigan. [13] Raffael Schubinger and Et al: 2001-01-3497: Influence of EGR on Combustion and Emissions of Heavy duty DI Diesel Engines Equipped with Common Rail system, International Fall Fuels and Lubricants Meetings and Expositions, San Antonio, Texas Sept 200129. [14] Carlos Castano and Et al: 2007-26-019: Advantages in the EGR Cooler Performance by Using Internal Corrugated Tubes Technology, SIAT 2007, and SAE international. [15] Yohan Chi and Et al : 2002-01-0504 :Effect of VGT and Injection Parameters on Performance on HSDI Diesel Engine with Common Rail FIE System, 2002 World Congress, Detroit, Michigan April 2002, SP 1696,Diesel Fuel Injection and Spray 2007 [16] Peter Lanzerath and Et al :2010-01-1212 :Investigations of Chemical Aging of Diesel Oxidation Catalyst and Coated Diesel Particulate Filter, SAE International [17] Alexzandar Sappok and Et al : 2010-01-0811:Ash Effect on Diesel Particulate Filter Pressure Drop Sensitivity to Soot and Implication for Regeneration Frequency and DPF Control, SAE International. [18] Keld Johaneson and et al :2010-01-0559 :NO2 Reduction, Passive and Active Soot Regeneration Performance of Pd Base Metal Coating on SiC filter, SAE International. [19] Jim Parks and Et al: 2007-01-3997; Characterisation of In Cylinder Techniques For Thermal Management of Diesel After treatment. Power Trains Fuels and Lubricants Meeting, Rosemont , lllinos Oct 2007 [20] Dr. Olaf Weber and Et al, Future Breathing System Requirements for Clean Diesel Engines, 2005 [21] Oldrich vitek and Et al , Comparison of different EGR Solutions, 2008-01-206,SAE International Definitions, Acronyms, Abbreviations LP-EGR : Low pressure exhaust gas circulation HP-EGR : High Pressure exhaust gas circulation DPF : Diesel pariculate filter BMEP : Brake Mean Effective pressure EGR : Exhaust Gas Recirculation BSFC : Brake specific fuel consumption PM: Particulate matter HC: Hydrocarbon NOx: Oxides of Nitrogen VGT : Veriable Turbine Geometry

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