SAE TECHNICAL PAPER SERIES 2005-01-0471 Metal Supported Particulate Matter-Cat, A Low Impact and Cost Effective Solution for a 1.3 Euro IV Diesel Engine Lorenzo Pace, Roman Konieczny, Manuel Presti EMITEC GmbH The Engineering Society For Advancing Mobility Land Sea Air and Space INTERNATIONAL SAE World Congress Detroit, Michigan April 11-14, 2005 400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel.: (724) 776-4841 Fax: (724) 776-5760
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2005-01-0471 Metal Supported Particulate Matter-Cat, A Low Impact and Cost Effective Solution for a 1.3 Euro IV Diesel Engine Lorenzo Pace, Roman Konieczny, Manuel Presti EMITEC GmbH ABSTRACT Modern Diesel Engines equipped with Common-Rail Direct Injection, EGR and optimized combustion technology have been proven to reduce dramatically engine raw emissions both in terms of Nox and Particulate Matter. As a matter of fact the recently introduced FIAT 1.3 JTD 4 Cylinder Engine achieves Euro 4 limits with aid of conventional 2-way oxidation catalyst. Nevertheless some special applications, such as platforms with relatively higher gross vehicle weight possibly yield to PM-related issues. The present paper deals with the development program carried out to design a cost effective aftertreatment solution in order to address particulate matter tailpipe emissions. The major constraint of this development program was the extremely challenging packaging conditions and the absolute demand to avoid any major impact on the system design. The flow-through metal supported PM Filter Catalyst has been extensively tested on the specific vehicle application with aid of roller bench setup. Partial engine load soot loading, continuous regeneration and long term soot trapping efficiency have been addressed during the present work. INTRODUCTION The Diesel Emission Legislation is a highly discussed topic nowadays. Especially the suspected health issues related to particulate emissions derived by the massively increased market success of diesel powered vehicles are currently one of the most important topics. In the recent years the introduction of wall flow Particulate Traps has been considered to be the only acceptable way to comply with legislation and political discussion. Consequently several car manufacturers introduced wall flow particulate filters as original equipment in different applications, with special attention to heavier vehicles such as segment D/E cars, which otherwise might not achieve Euro 4 limits. Meanwhile it has become more and more apparent that such aftretreatment systems might come along with major design and engineering challenges, hence conflicting with the increasingly stringent cost reduction targets, especially in lower segments passenger cars. Consequently several car manufacturers are investigating alternative avenues, such as flow through filters. In the present paper the application engineering of a Metal supported PM-Filter Catalyst on a production 1.3 L 4-Cylinder Diesel Engine is discussed with aid of experimental data, in order to present a cost effective and low-impact aftertreatment solution, which can be easily fitted in an already designed exhaust system as original equipment. PM FILTER CATALYST BASIC PRINCIPLES The PM-Filter Catalyst is a metal supported substrate, consisting of flat and corrugated foils similar to well known metal, even though there are some major differences. The corrugated foils are structured with blades or shovels to deviate the flow towards the flat layers. These consist of a porous metal fleece, which actually trap the Particulate Matter present in the exhaust gas. The temporarily trapped particles are subsequently oxidized by means of NO (Fig. 1, Fig. 2, Fig. 3,). 2
Detailed description of operating principles of the PM Filter Catalyst have been already presented [1, 2, 3]. Due to its design, the PM-Filter Catalyst is a partially open structure, which cannot clog due to excessive soot accumulation. Therefore it can be installed in relatively cold applications, which would have major regeneration problems in case of traditional wall flow Particulate Traps. Furthermore flow through devices, such as the PM Filter Catalyst, are not sensitive to ash accumulation issues. C Fig. 3 Operating principle of the PM Filter Catalyst EXPERIMENTAL SETUP Fig. 1 Corrugated layer of the PM Filter Catalyst Fig. 2 Flat layer (porous fleece) of the PM Filter Catalyst The PM-Filter Catalyst has been already tested and successfully proved on several engine applications, from medium size passenger cars up to heavy duty commercial trucks [4, 5]. In the recent years one evident market trend in Europe is the increasingly successful introduction of very small diesel engines (less than 1.5 L displacement) on a relatively broad range of passenger cars. These modern engines, equipped with EGR and high pressure fuel injection, easily comply with Euro4 emission limits both with respect of HC/CO as well as NO x /PM. On the other hand, due to the high specific power and torque of such powertrains, they often equip relatively heavy vehicles such as microvans, hence leading to potential issues with respect of overall PM emissions. In order to investigate this kind of application, a FIAT Doblo vehicle, equipped with a 1.3 L JTD Diesel Engine has been tested on a roller bench rig. Both CVS bag and modal data have been measured during the ECE Test Cycle with particular focus on NO 2 /C Ratio, PM Trapping efficiency and soot loading stability. The tested engine is equipped with a Euro3 Stage calibration. The baseline exhaust system consists of a close coupled catalyst (4.66 x5 /350/5.5) loaded with 70gr/ft 3 Pt. TEST PROCEDURE Each catalyst system before being tested with respect to HC/CO conversion efficiency and PM Trapping efficiency, has undergone a preconditioning cycle consisting of three EUDC modules repeated in row. This procedure is finalized to eliminate any soot residuals in the PM Filter Catalyst.
Subsequently the systems have been tested during the complete ECE + EUDC Test Cycle. To ensure statistical significance, the test has been repeated three times. Results from these tests represent the PM Trapping efficiency in fresh conditions. Subsequently a soot loading procedure was performed consisting of 12 hours of ECE modules. During this low load phase the exhaust gas temperature is very low (< 170 C), hence almost no regeneration due to NO 2 is expected, leading to soot accumulation in the porous fleece of the PM Filter Catalyst. Before testing the system again with respect to PM trapping efficiency, the preconditioning cycle (3 times EUDC module repeated in row) is carried out again. TESTED CATALYST SYSTEMS Uncoated PM Filter Catalyst in underfloor position The baseline system has been retrofitted with a PM-Filter Catalyst 98.4x150/200cpsi in underfloor position (Fig. 4). ~600 mm PM [g/km] 0.045 0.040 0.035 0.025 0.020 0.015 0.010 0.005 0.041 Serie Serie + PMFC unloaded Serie + PMFC loaded 0.028-31% 0.034 Fig. 6 - Soot tailpipe emission of the baseline system and the PM Filter Catalyst equipped system. Differently the Soot Tailpipe emissions are significantly decreased by means of the PMFC. The results can be considered quite stable as the error bands are in the range of 5%. The fresh preconditioned PMFC allows a Soot reduction of about ~ 31%, whereas the same device after the 12 hrs soot loading procedure has a long-term trapping efficiency of ~ 17%. Considering the extremely low exhaust gas temperatures during the test (Fig. 7) these results are promising. Nevertheless further optimization can be easily achieved. PM - 17% Oxicat 4 66 x5 /350/5 5 PMFC Fig. 4 - PM-Filter Catalyst retrofitted to the baseline system With reference Fig. 5, it can be noticed that the introduction of the PMFC in underfloor position does not affect the tailpipe emissions of HC, CO and NOx. This is considered a major advantage in this case, as the PMFC is conceived here as a retrofit device, which optimally should not require any engine management modification. Temp. [ C] 350.00 300.00 250.00 200.00 150.00 100.00 50.00 T pre PMFC unloaded T post PMFC unloaded HC, CO, NOx [g/km] 0.350 0.300 0.250 0.200 0.150 0.100 Serie Serie + PMFC unloaded Serie + PMFC loaded HC CO NOx 0.00 0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 Time [s] Fig. 7 Exhaust gas temperature profile during the MVEG Cycle. Coated PM Filter Catalyst in underfloor position In order to investigate the influence of catalytic coating on the PMFC, the same substrate has been coated with 30 gr/ft 3 Pt (Fig. 8) Fig. 5 - HC, CO and NOx Tailpipe Bag Emissions of the baseline system compared with the same system equipped with PM Filter
Fig. 8 Baseline system retrofitted with a coated PM Filter Catalyst While no major influence is given to HC tailpipe emissions, an advantage of about ~ 20% in CO can be achieved by the additional catalytic activity in the underfloor PMFC. HC, CO, NOx [g/km] 0.350 0.300 0.250 0.200 0.150 0.100 Serie ~600 mm Oxicat 4 66 x5 /350/5 5 Serie + coated PMFC unloaded Serie + coated PMFC loaded PMFC Referring to Fig. 10 it can be seen that the coated PMFC in underfloor position does not boost the maximum potential trapping efficiency as initially expected, since the oxidation properties should increase the overall NO2 content and therefore the steady-state PM trapping efficiency. The reason for this phenomenon is related to two different mechanisms. On one side there is a much higher affinity between CO and Pt rather than between NO and Pt. This leads to limited oxidation of NO NO2, which is requested for stable PM Trapping efficiency. On the other hand, any CO residual interacts with NO2 creating CO2 and NO, according to NO2 + CO CO2 + NO. Consequently the overall NO2 related PM long term trapping efficiency might be limited, even though the system has a higher PGM loading. Therefore further optimization of the PMFC system can be achieved by drastically reducing CO present in the exhaust gas in order to avoid any interference between CO and NO2 oxidation, by means of a highly efficient oxidation catalyst located immediately upstream the PMFC. In order to obtain this target the flow properties of this dedicated oxidation catalyst are enhanced by means of structured foils such as LS-technology. Optimized underfloor system: coated UFC oxycat (LS technology) + uncoated PM Filter Catalyst Fig. 9 HC, CO and NOx tailpipe emissions of the baseline system compared with a system retrofitted with a coated PMFC. PM [g/km] 0.045 0.040 0.035 0.025 0.020 0.015 0.010 0.005 HC CO NOx Serie Serie + coated PMFC unloaded Serie + coated PMFC loaded 0.041-27% 0.034 Fig. 10 PM tailpipe emissions of the baseline system compared with a system retrofitted with a coated PMFC. PM - 17% ~600 mm Oxicat 4.66 x5 /350/5.5 98.4x50.8/300-600LS Oxycat Fig. 11 PM-Filter Catalyst system consisting of an LS oxycat and an uncoated PMFC retrofitted to the baseline system It is apparent from Fig. 12 that the overall CO conversion efficiency is significantly improved (by approximately 47%) with aid of the LS oxidation catalyst upstream the PMFC. This is considered a very good result being the Pt content in this oxidation catalyst even lower than the Pt amount loaded on the PMFC discussed in the previous section (1.09 g in the LS Catalyst rather 1.20 g in the coated PMFC) and given the cold underfloor location. Therefore the boosted CO conversion efficiency is related to the highly enhanced mass transfer properties of the LS substrate (Fig. 13).
HC, CO, NOx [g/km] 0.350 0.300 0.250 0.200 0.150 0.100 Serie Serie + coated Oxy + PMFC unloaded Serie + coated Oxy + PMFC loaded HC CO NOx Fig. 12 - HC, CO and NOx tailpipe emissions of the baseline system compared with a system retrofitted with a coated LS oxicat and an uncoated PMFC. PM [g/km] 0.045 0.040 0.035 0.025 0.020 0.015 0.010 0.005 0.041 0.025-40% Fig. 14 PM tailpipe emissions of the baseline system compared with a system retrofitted with a coated PMFC. PM Serie Serie + coated Oxy + PMFC unloaded Serie + coated Oxy + PMFC loaded - 27% As a result the PM Trapping efficiency is improved to a level of ~40% in fresh condition and ~27% in loaded conditions. 1 0.9 NO2 [g] 0.8 Fig. 13 Operating principle of the LS substrate. Turbulent-like flow is created along the channel axis, improving mass transfer properties This reason is twofold: on one side the LS blade creates a secondary cell increasing the effective overall cell density of the substrate; on the other hand the fully developed laminar flow is repeatedly interrupted. This means that the flow, which would otherwise be fully laminar and therefore with diffusion governed mass transfer, can now be considered turbulent-like with consequent convection governed mass transfer. Once the CO amount has been significantly reduced, is of utmost importance to increase NO2 content in the exhaust gas to ensure long-term PM trapping efficiency. It is apparent from Fig. 15 that the 300LS oxidation catalyst improves the NO2 concentration by 16% in addition to the highly increased CO conversion. 0.7 NO2 upstream LS oxycat NO2 downstream LS oxycat Fig. 15 NO2 improvement by implementation of 300LS oxycat upstream the PMFC. Close-coupled DOC-PM Filter Catalyst System In the present work a close-coupled hybrid system, consisting of a 300LS oxicat and a PMFC have been installed replacing the production CC oxicat. The baseline close-coupled 350cpsi DOC has a volume of 1.4L and is loaded with 70 gr/ft 3 Pt while the DOC 300LS-PMFC system has been loaded with 100 gr/ft 3 Pt and 30 gr/ft 3 Pt respectively. The DOC 300LS is a 127x50.8mm and the PMFC is a 127x74.5mm substrate, therefore the total Pt loading on the new system is lower compared to the baseline system. Even with that reduction of PGM loading the conversion efficiency of the system is unchanged. Considering that the baseline DOC has a cell density of 350 cpsi and the PMFC of 200cpsi, it can be concluded that a coated
PMFC acts as a highly efficient DOC (Fig. 16) by keeping quite a PM filtering performance (Fig. 17). HC, CO, NOx [g/km] Fig. 16 Conversion efficiency of the LS-DOC/PMFC System compared to the baseline system. PM [g/km] 0.400 0.350 0.300 0.250 0.200 0.150 0.100 0.045 0.040 0.035 0.025 0.020 0.015 Baseline DOC + coated PMFC aged HC CO NOx 0.039 Baseline DOC + coated PMFC aged 0.033-15% PM [g/km] 0.045 0.040 0.035 0.025 0.020 0.015 0.010 0.005 0.039 Fig. 18 PM Trapping efficiency of the uncoated LS- DOC/PMFC System compared to the baseline system. The interesting results is given by the remarkably high CO conversion efficiency of the DOC LS itself. As a matter of fact, the DOC has 54% lower volume than the conventional 350cpsi baseline DOC and 34% lower Pt content. Even so the CO conversion efficiency in fresh condition is significantly lower than the conditioned baseline system (Fig. 19). This result can be explained by the flow properties in a conventional converter compared to a LS substrate. While in the former laminar flow leads to strictly diffusion governed mass transfer mechanism, in the latter a turbulent-like flow enhances mass transfer to the catalytic wall (Fig. 13). PM Baseline DOC + uncoated PMFC - 25% 0.010 0.005 Fig. 17 PM Trapping efficiency of the coated LS- DOC/PMFC System compared to the baseline system. The relatively low PM trapping efficiency of the Closecoupled PMFC compared to the UFC PMFC system can be easily explained considering that the CC PMFC has 15% less volume and a different diameter/length ratio compared to the UFC PMFC. It has been observed that smaller diameters tend to lead to higher trapping efficiencies. Furthermore the washcoat might negatively affect the filtering porosity of the device itself. Moreover a close-coupled DOC-PMFC system consisting of a 300 LS DOC and an uncoated PMFC has been investigated. An overall PM filtering performance of ~ 25% can be achieved (Fig. 18) with this system, proving that the coating process of the PMFC needs some optimization steps. PM HC, CO, NOx [g/km] 0.400 0.350 0.300 0.250 0.200 0.150 0.100 Baseline Fig. 19 Conversion efficiency of the fresh LS-DOC compared to the baseline system. CONCLUSION DOC LS + uncoated PMFC HC CO NOx A production 1.3 L 4 Cylinder engine equipped with Euro 3 Stage application has been investigated on a roller bench. In particular the baseline exhaust aftertreatment system consisting of a close-coupled oxidation catalyst has been integrated with an underfloor PM Filter catalyst with the main purpose to prove the feasibility of a retrofit solution towards PM reduction incentives in Europe.
The PMFC has been tested both in uncoated and coated version, after being preconditioned. Afterwards each system has been tested in fresh conditions to define the baseline values. Being the on-road compliance of utmost importance for a PM reducing device, a soot loading procedure, consisting of 12 hrs of ECE modules (low load and low exhaust gas temperature) has been performed. Afterwards the preconditioning has been repeated and subsequently the systems have been tested on the EC Driving Cycle to determine long term PM trapping efficiency at loaded conditions. The results show that the introduction of the uncoated PMFC does not negatively affect the HC/CO and Nox emissions, while the PM tailpipe emissions have been reduced by ~ 31% in fresh condition and ~ 17% in loaded conditions. These relatively low values lead to the conclusion that further optimization of the retrofit system is needed. A first step of modification consisted in coating the PMFC, therefore improving CO emissions by ~20%. On the other side PM Tailpipe emissions are reduced similarly to the uncoated PMFC version. Being the PM trapping efficiency strongly dependant on NO 2 available at the PMFC inlet, an additional optimization step has been developed consisting of an UFC Oxicat with LS technology upstream the uncoated PMFC. CO Emissions are significantly improved by 47% while PM Emissions are reduced by 40% in fresh and 27% in loaded conditions. These results show that the PMFC represents a low impact solution, which can be easily installed on an existing exhaust aftertreatment system. In particular, considering the Euro3 Stage engine calibration, it can be stated that the PMFC represent an optimal system to achieve Euro4 emission limits, provided that minor calibration tuning is performed on the engine. This is considered to be a significant result as tax incentives policies are increasingly popular in the EC countries for EU4 compliant Diesel powered vehicles. In this case, an aftertreatment system, which is not causing major vehicle cost increases, might represent the optimal solution. Furthermore, being the system cost challenges more demanding in the future, packaging considerations have been made. In particular, a close-coupled system consisting of a LS DOC and a PMFC have been investigated, in order to eliminate any UFC canning. Even though the PM trapping efficiency has not been improved due to different flow properties in the PMFC itself (bigger diameter compared to the previous UFC system) a remarkable improvement in CO conversion efficiency has been observed. This is considered a very important result, as the trubulent-like flow induced by LS structured foils in the DOC has positively influenced overall efficiency, hence allowing for catalyst volume reduction of 54% and a Pt loading reduction of 34% compared to the baseline system.
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