The Effect of NOx /Soot Ratio on the Regeneration Behaviour
`of Catalysed Diesel Particulate Filters for Heavy Duty
`Applications
`
`2005-26-347
`
`K V R Babu and Basu Sudipto
`Umicore Marketing Services, India
`
`B S Kang, Nicola Seeger, Lothar Mussmann and Ralf Sesselmann
`Umicore AG & Co. KG, Germany
`
`Owen Bailey and Masao Hori
`ICT Inc.
`
`Copyright© 2005 Society of Automotive Engineers, Inc.
`
`ABSTRACT
`
`is becoming
`The control over particulate em1ss1ons
`increasingly important in modern diesel engines for
`Heavy Duty applications, that will comply to more and
`more stringent emissions norms. Use of particulate traps
`is an effective means of achieving this with the need to
`regenerate the particulate trap being imperative.
`
`PM
`(g/
`kW
`h)
`
`Passive regeneration using N02 by conversion of NO, as
`well as
`regeneration at
`lower
`temperatures with
`catalyzed DPF and the influence of NOx to soot ratio on
`this, is the subject of the paper.
`
`Both coated and uncoated filters in fresh and aged state
`are evaluated at temperatures typical of passive N02 and
`Oxygen-based soot
`regenerations and
`the
`results
`discussed.
`
`INTRODUCTION
`
`the 1980s, exhaust em1ss1on
`the middle of
`Since
`regulations for commercial vehicles have been updated
`and tightened. In Europe Euro 4 is
`introduced in 2005
`and the further step will be introduced 2008 (EURO 5)
`using both transient and steady state certification tests,
`(European Stationary Cycle) and ETC
`the ESC
`(European Transient Cycle). Significant the legal limits
`for 2005 and 2008 include important reductions in NOx
`and Particulate Mass (PM).
`
`Similarly, regulations in Japan and the United States
`have been established which enforce even more severe
`reductions in NOx and PM. India is also having Euro 3
`equivalent norms in 2005 and Euro 4 is proposed by
`2008 or 2010 (Fig. 1 ).
`
`0.0
`
`1.0
`
`2.0
`
`3.0
`
`4.0
`
`5.0
`
`NOx(glkWh)
`Fig.1 Future Emission Regulation Limits for
`Commercial Vehicles
`
`As a result, heavy-duty (HD) engine manufacturers may
`be required to use advanced exhaust aftertreatment
`systems to meet these limits in the future.
`
`While the control over CO and HC conversions by use of
`Diesel Oxidation Catalysts is well known, the trade off
`between particulate matter and NOx emissions may be
`addressed by:
`
`•
`
`•
`
`Particle reduction by optimizing engine control
`parameters combined with NOx
`reduction by
`appropriate aftertreatment devices (e. g. Selective
`Catalyst Reduction or Lean NOx Traps)
`
`NOx reduction via cooled EGR combined with
`particle reduction using Diesel Particle Filters (DPF)
`
`BASF-2013.001
`
`

`
`A variety of filter materials is available that provide
`filtration efficiencies of 95 %. This level of particle
`reduction appears to be sufficient to meet the strictest
`regulations, however, the accumulation of soot on the
`filter leads to higher back pressure and corresponding
`increases in fuel consumption. Today's development
`therefore concentrates on the reliable regeneration of
`filters by soot combustion.
`Ideally, this regeneration
`should take place with a minimal input of energy or
`additives, yet be quick and reliable. This demand can be
`achieved by using catalysed filters [1-6].
`
`By converting NO to N02 , catalytic coatings significantly
`decrease filter regeneration temperatures. N02 is known
`to support soot combustion at temperatures of 300 oc.
`For the complete combustion of a given amount of soot,
`is required.
`In future
`a stoichiometric mass of N02
`applications,
`the amount of N02 available for soot
`combustion may be
`limited due
`to
`two significant
`restrictions:
`
`•
`
`•
`
`Decrease of NOx emissions by engine measures
`such as EGA or other advanced combustion
`methods
`
`Diminishing activity of the catalytic coating due to
`aging mechanisms [5]
`
`Hence, a major task of catalyst development is to help
`ensure an adequate supply of N02 necessary for
`regeneration of the soot-loaded filter. This goal is even
`more challenging because of the expected lowering in
`NOx raw emissions by future engine concepts [4].
`
`In this paper a study will be presented showing the
`influence of NOx concentration and exhaust flow rate on
`the regeneration rate of soot-loaded filters.
`
`EXPERIMENTAL SETUP
`
`The experiments described below were performed on a
`turbocharged,
`heavy-duty bench equipped with a
`engine with
`intercooled
`in-line 6-cylinder diesel
`with a sulfur
`specifications shown in Table 1. Fuel
`concentration of 30 ppm was used.
`
`Displacement
`
`Rated power
`
`Peak torque
`
`Table 1 Engine Data
`
`6.37 liter
`
`205 kW @ 2300 rpm
`
`1100 Nm @ 1200-1600 rpm
`
`Fuel Injection System
`
`Pump - Line - Nozzle
`
`Certification
`
`EUR03
`
`The test cell's dynamometer allowed the engine to
`operate across its entire speed-load map, including fully
`transient test cycles like the ETC and HD FTP. Data
`were recorded at a frequency of 1 Hz.
`
`(SCR) system was placed in front of the Catalysed
`Diesel Particulate Filter (CDPF) to lower the level of
`engine out NOx emissions to simulate expected future
`limits and
`their
`impact on CDPF soot
`emission
`regeneration. The urea injection strategy was controlled
`by a NOx emission map stored in the ECU of the dosing
`unit.
`
`6.4101 TCI
`Fig.2 Schematic Representation of the Test Bench
`
`A valve in front of the filter allowed exhaust flow to be
`bypassed around this device on demand. While being
`operated in this mode, a flow of inert gas was passed
`across the CDPF to flush the system. This configuration
`was designed to produce defined and reproducible soot
`burning by avoiding any uncontrolled chemical reactions
`which might otherwise occur within the CDPF during this
`·
`operation.
`
`The test bench was equipped with standard exhaust gas
`.measuring systems. The focus of these tests was
`measuring the concentrations of NO and N02 at the
`following locations within the exhaust line:
`
`• Upstream of the SCR catalyst (raw emission)
`• Downstream of the SCR catalyst
`• Downstream of the CDPF
`Additionally, NH3
`concentrations were measured
`downstream of the SCR catalyst and CDPF by a Laser
`based SIEMENS LDS 3000 unit and an ABB LIMAS 11-
`respectively. Thermocouples were
`UV
`instrument,
`installed upstream and downstream of the SCR system
`the CDPF. Additionally, a differential pressure
`and
`sensor was employed to measure the pressure drop
`across the CDPF during soot loading and regeneration.
`
`The test procedure to analyze soot burning rate as a
`function of NOx concentration required referencing of the
`soot loading within the CDPF before each stationary and
`transient test. To do this, filters were first conditioned at
`130°C in an oven and immediately weighed. They were
`then loaded with 50 grams of soot by operating the
`engine at constant speed (1400 rpm) and a load
`generating a filter inlet temperature of 240 oc [51.
`Subsequently, the filter was conditioned and reweighed.
`CDPFs were regenerated for 10 minutes, and again
`conditioned and weighed. This procedure helped ensure
`the reproducibility of filter state before each test.
`
`Figure 2 shows the configuration of the test equipment
`used for these studies. A selective catalytic reduction
`
`The geometric dimensions (diameter x length) of all
`evaluated filters were 10.5 x 12 inch giving a filter volume
`
`BASF-2013.002
`
`

`
`of 17 liters. Catalysed filters with 200 cells per in2 (cpsi)
`were utilized throughout these studies. The catalysed
`filter
`is with 35 g/cft precious metal
`loading on a
`cordierite NGK DHC 611 substrate.
`
`INVESTIGATION OF THE IMPACT OF NOx/SOOT
`RATIO ON SOOT OXIDATION RATE
`
`In order to study the soot-burning rate as a function of
`different NOx/soot ratios, engine speed, and CDPF aging
`state, the setup shown in Fig. 2 was employed. The
`strategy was to utilize an SCR catalyst unit upstream of
`the CDPF to reduce NOx concentrations within the
`exhaust. By doing this,
`it was possible to simulate
`different engine-out N.Ox levels at selected load points
`and engine speeds without changing the corresponding
`soot production rate, or other raw emission levels. The
`level of NOx reduction for a given load point was
`controlled by adjusting the rate of urea solution injection.
`Conversion levels were limited such that no ammonia
`slip was detected downstream of the SCR catalyst.
`
`To study the soot oxidation rate of the catalytic soot
`filters on
`this engine bench setup, a specific test
`procedure shown in Fig. 3 was established.
`
`For the evaluation of the soot burning rate as a function
`of average CDPF temperature in the range of 300 -
`450 oc, torque was adjusted at engine speeds of 1000,
`1400 and 1800 rpm. The nominal temperatures ~nd
`engine-out NOx emissions
`for
`the selected engine
`operating points are shown in Fig. 4.
`
`Temperature COPF ['C]
`
`S!'ftd[rpm]
`
`Nitrogen Oxides - t40.x [ppm]
`
`~J~
`
`~JJ
`
`5JJ
`
`~
`
`1'J:)
`
`D:!
`
`i"
`2:.
`~
`~ ,..
`
`F=~~~----~--~--_,----T----T----T
`11.
`onoln• oo.~J<I dawn I
`~·xt---rt====~==db===rt----1----t--~
`~
`'!'trQii!'ner~n
`:·:.o ,......._....
`
`:ecc
`
`'tlme-[c]
`
`:ace
`
`Fig. 3 Overview of Soot Regeneration Test Conditions
`
`The general procedure starts with a conditioning phase
`of low torque for 5 minutes. The regeneration of the soot
`is initiated by a load jump at constant engine speed
`which is maintained for 10 minutes before the cool down
`phase begins. During the cool down phase, engine
`exhaust is bypassed around the CDPF. At the same
`time, the filter is cooled in a nitrogen atmosphere to
`the 1 0 minutes soot
`quench soot burning after
`regeneration period. To determine soot burning rate,
`filter was weighed before and after the
`test
`each
`sequence.
`
`To generate reproducible results, this procedure required
`a well-defined initial state of loading within the CDPF
`before and after testing. The test filters were loaded with
`3 g/L soot at an engine speed of 1400 rpm using a
`specially designed soot loading procedure [1]. The soot(cid:173)
`loaded filter was conditioned in an oven at 130 oc and
`weighed. Afterwards the CDPF was installed in the test
`equipment shown in Fig. 2 and regenerated according to
`the procedure outlined in Fig. 3. The filter was then
`removed, conditioned in an oven and reweighed to
`determine the mass of burned soot.
`
`Fig. 4 Average Temperatures in CDPF and Engine-Out
`NOx Emissions for Selected Evaluation Points
`Used in the Soot Regeneration Test
`
`For the experiments with modified NOx/soot ratio, the
`same engine operating points as shown above were
`selected, however, NOx reductions of 50 and 70% were
`targeted by operating the SCR unit upstream of the filter
`during the corresponding soot regeneration test. The
`specific NOx output (i. e. NOx input to the CDPF) ranged
`from < 1.5 g/kWh for the 70 % NOx reduction case to 2.0
`- 2.4 g/kWh for the 50 % NOx reduction case, based on
`an engine-out NOx level of 4.2- 5.5 g/kWh.
`
`Impact of NOx/Soot Ratio at Constant Engine Speed
`
`At a constant engine speed of 1400 rpm the average
`soot burning rate (SBR) was determined at several
`temperatures, as well as at varying NOx emission level?
`at the inlet to the CDPF. The results are summarized in
`Fig. 5.
`
`At a constant NOx mass flow (flux), the soot burning rate
`(SBR) rises with increasing exhaust gas temperature.
`Similarly, with increasing NOx mass flow the soot burning
`rate increases as well.
`
`BASF-2013.003
`
`

`
`Evaluation of the Influence of Engine Speed on Soot
`Burning Rate
`
`To investigate the impact of different mass flow rates on
`filter regeneration behavior, experiments have been
`performed at engine speeds of 1 000, 1400, 1800 rpm.
`For this set of experiments engine out NOx levels were
`not reduced by the use of the SCR unit upstream of the
`CDPF. These tests .also utilized the conditioned CDPF.
`In Fig. 7, the average soot-burning rate is plotted versus
`temperature and the NOx flux at the inlet to the CDPF.
`
`1CII
`
`UG
`
`211
`
`Fig.? Average Soot Burning Rate as a Function of NOx
`Flow Rate and Temperature at 1000, 1400 and 1800 rpm
`
`In general, the impact of different NOx and temperature
`levels as found at a constant engine speed (see Fig. 5)
`seems
`to be confirmed. Upon closer
`inspection,
`however, an interesting difference is revealed. At lower
`temperatures, an increasing NOx mass flow does not
`necessarily result in a higher soot burning rate.
`
`To understand this phenomenon a detailed consideration
`of the chemical processes associated with soot filter
`regeneration is necessary. The main chemical reactions
`that are involved in soot combustion are summarized in
`equation (1) and (2):
`
`c + N02 ~co+ NO T > 2oooc
`
`(1)
`
`(2)
`
`While diesel exhaust gas generally contains an excess of
`oxygen needed for the reaction described in equation
`(2), it contains only low levels of N02 which is required
`for reaction according to equation (1 ). An oxidation
`catalyst is needed to facilitate the conversion of NO to
`N02 according to equation (3), thereby enabling low
`temperature soot burning as described in equation (1 ).
`
`(3)
`
`The NO oxidation given in equation (3) is subject to
`thermodynamic restrictions. At higher temperatures the
`equilibrium is shifted to the left side of reaction (3)
`resulting in a limited NOiNO ratio. Fig. 8 provides a
`
`Fig. 5: Average Soot Burning Rate (SBR) as a Function
`of Temperature and NOx Mass Flow at 1400 rpm for
`CDPF (Conditioned).
`
`The change in soot burning rate with change in NOx flux
`(A SBR) also strongly depends on temperature. For the
`same increase in NOx mass flow (150 ·- 750 g/h) the
`change in soot burning rate at 440 oc is twice that
`observed at 320 oc.
`·
`
`This effect is also observed when the amount of soot
`emitted by the engine is taken into consideration. In
`Fig.6, ~he average soot-burning rate is presented as a
`function of NOx/soot ratio.
`
`---.c----
`
`-~======~~~--------~-----------,
`-- ..owc-...---1-------TIC<mont!<!!!!!!!!.:-!l:!!l!!!!!i-i!l!!L-----l
`IIIli
`m ---...---1---------1---,.-------l
`~
`: /.#"""'
`i>OII "'----..-
`l·~r-------------~~---------l
`jmr-------~--#~~~~,~~~1------~
`i llliT------------~-~.~~~------~--------~
`t ~r-----------~~-------l
`.... ..
`~r-------,-~~~-~-~-·~·-··-·-·~··-------~
`20+-----=~~~~:j
`a-1-
`'•
`~ ~ n
`a ~ ~ ~ ~ ~ ~ m ~
`a
`Noataol-[~
`Fig. 6 Average Soot Burning Rate as a Function of
`NOx/Soot Ratio at Constant Speed and Different
`Temperatures
`
`.• -
`
`The balance point of the investigated CDPF was earlier
`determined to be about 300 oc. Accordingly, the soot(cid:173)
`burning rate is low even at a high NOx/soot ratio such as
`that indicated by the solid black circle in Fig. 6. Fig. 6
`suggests
`that CDPF can be
`regenerated at all
`investigated temperatures, even at NOx/soot ratios as
`low as projected for future heavy duty engines.
`
`At temperatures up to 350 oc, passive filter regeneration
`is already
`limited at today's NOx/soot
`levels. Yet,
`lowering the NOxfsoot ratio only results in a slight
`decrease in soot burning rate. The lower the temperature
`of the investigated engine operating point, the less the
`impact a decrease in NOx/soot ratio has on soot burning
`rate.
`
`BASF-2013.004
`
`

`
`comparison between the theoretical N02/NO limited ratio
`and the experimentally observed values, both as a
`function of exhaust gas temperature.
`
`-~~=----=~----------~~----------~
`11111
`..
`~V+-----~~--~~~~~--~~=-----~
`Hvt-~--------------~~~~~~~~~
`
`1111
`
`1-
`
`0
`
`Ill
`
`•
`
`•
`
`IIIII
`
`, ........ t
`...,_
`1·1--
`
`••
`...
`
`·•
`
`•"
`--pq
`..
`
`-
`300
`-
`-
`-
`lllll
`Fig.9 N02 Concentration as a Function of Temperature
`and Engine Speed
`
`II
`
`Ill
`
`Ill
`
`"
`• •
`
`•
`
`5()0 ,--
`
`...
`
`300
`
`200
`
`, ..
`100 ..
`
`•+---~~--~--~--~----~--~--~~
`•
`m
`•
`~ •
`•
`~ •
`~ •
`•
`'-fCI
`Fig.8 N02/NO Ratio as a Function of Temperature:
`Thermodynamic Equilibrium Compared to Experimentally
`Obtained Values in the Exhaust Gas
`
`the experiment decreases with
`in
`N02 formation
`increasing temperature due to thermodynamic restriction
`as
`indicated by
`the dashed
`line. The
`lower
`the
`temperature the more the experimental values differ from
`the equilibrium. This means that in the lower temperature
`range the oxidation of NO to N02 is kinetically limited.
`This reaction rate is accelerated by the catalytic coating
`of the filter, however, the reaction rate is not only
`determined by NOx exhaust gas concentration and
`temperature. There is also an impact of engine speed (i.
`e. space velocity over CDPF).
`
`At 1400 rpm, NOx concenfrationin the engine exhaust is
`lower than at 1800 rpm (see Fig. 4). Standard kinetic
`expressions for NO oxidation predict that this should lead
`to lower reaction rates at a given temperature [6].
`Nevertheless, NO conversion at 1400 rpm is higher than
`at 1800 rpm as shown in Fig. 8. The reason for this
`phenomenon is the higher exhaust gas flow at 1800 rpm
`resulting in a lower residence time of the exhaust gas
`in turn
`leads to decreased
`inside the CDPF. This
`reaction rates associated with mass diffusion limitations
`at the catalytic sites.
`
`Despite the decreased reaction rates at 1800 rpm, the
`N02 concentration is higher at 1800 rpm due to the
`higher NOx raw emissions (see Fig. 9).
`
`The highest N02 concentration within the exhaust gas
`was measured at 350 oc with the lowest exhaust gas
`flow. In this case all considered rate influencing factors
`are beneficial with regard to N02 formation: high NOx
`concentration, high theoretical limit for N02/NO ratio, and
`long
`residence
`time
`in CDPF. However,
`for
`the
`determination of the final amount of N02 that is available
`for soot oxidation according to equation (1) the influence
`of the exhaust gas flow has to be included. The N02
`mass flows generated at each of the investigated engine
`operating points are shown in Fig.1 0.
`
`- -
`··-~
`I .,800rpm
`I "'""""""
`
`I
`
`500
`
`A
`
`0
`250
`
`300
`
`Fig. 10 N02 Flow as a Function of Temperature and
`Engine Speed
`
`Although the highest N02 concentration was generated
`at 1 000 rpm and 350 oc, the N02 mass flow is
`comparatively
`flow was
`low. A higher N02 mass
`lower N02 concentrations but higher
`generated at
`exhaust gas flow at 1800 rpm. Since the mass of soot
`being converted according to equation (1) depends on
`the mass flow of N02, this should result in higher soot
`burning rates for 1800 rpm as compared to 1 000 rpm.
`Summary of these results are given in Fig.11.
`
`liOII
`tiO
`
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`
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`
`•"
`:411
`
`Zll
`
`II
`-
`
`- .............
`---~
`
`/
`
`/
`
`/
`/
`/ . /
`//"""
`/'"
`
`~""" -
`
`, •" -
`
`~·~ -
`
`----
`-----
`
`11o· m
`
`-
`
`1101
`
`J&o
`
`liC m
`:m1
`JGIJ
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`
`«HH
`
`•fll
`
`-
`
`-
`
`440
`
`4510
`
`Fig. 11 Average Soot Burning Rate as a Function of
`Temperature and Engine Speed
`
`Interestingly, the soot-burning rate for this experimental
`setup is independent of the engine speed up to a
`temperature of 380 oc. Although according to Fig. 1 0
`almost twice as much N02 is available at 1800 rpm, this
`does not result in higher soot burning rates. Regardless
`
`BASF-2013.005
`
`

`
`of N02 mass flow rates and engine speed, the results
`indicate only ·an effect of temperature on soot burning
`rate up to 380 oc. This indicates that for the given
`temperature window, up to 380 oc the kinetics of the
`soot burning rate (equation 1) are not limited by the
`kinetics of the N02 formation step (equation 3) catalysed
`by the oxidation function of the CDPF.
`
`In the higher temperature region (T > 380 °C}, there is an
`inflection point in the curve indicating a sharp increase in
`soot burning rate, especially at 1800 rpm. This behavior
`may be explained by an
`increased contribution of
`oxygen-based soot combustion (equation 2). This also
`helps explain the sharp increase in SBR from 380 - 450
`oc at 1800 rpm, even
`is
`though N02 mass flow
`decreasing.
`
`Investigation of the Combined Impact of Aged CDPF and
`Lower NOx/Soot Ratio on Soot Burning Rate
`
`To generate a
`filter
`for
`"worst case scenario"
`regeneration, the 300 hour engine-aged CDPF was
`evaluated at two different NOx emission levels, one at
`the original engine-out emission level and the other with
`a 70 % lower NOx level. An uncoated filter at the original
`NOx level was also tested as a reference. The average
`soot-burning rate of CDPF, fresh and after aging is
`plotted versus temperature for the two threshold NOx
`levels (original and 70% decrease) in Fig. 12.
`
`350
`
`400
`«.ill
`Temperahn alPFl"CJ
`Fig.12 Comparison of Average Soot Burning Rate for
`CDPF (Conditioned), CDPF (Aged At 70 % Reduced
`NOx Emission) and an Uncoated DPF
`
`!00
`
`5lill
`
`Even at low NOx levels projected for the future, the aged
`low
`temperature soot
`CDPF supported N02-based
`combustion. While oxygen-based regeneration in the
`uncoated filter is only initiated above temperatures of
`about 480 oc, the engine bench-aged CDPF is active
`above 350 oc, giving a maximum soot burning rate of
`about 50 g/hour. As outlined earlier in the dynamic stop(cid:173)
`and-go city cycle test, this will help to extend the time
`until an active, oxygen-based soot regeneration would be
`needed.
`
`Therefore, these results indicate that a coated CDPF will
`be beneficial with respect to fuel efficiency, even at the
`lower engine-out NOx emission levels projected for the
`future.
`
`CONCLUSION
`
`Two major challenges for the passive regeneration of
`catalysed particulate filters are the long term durability
`requirement for the NO oxidation function, and the
`reduction in NOx/soot ratio anticipated in future engine
`applications. The results of this study support the use of
`CDPF systems in future HD applications.
`
`ratios have
`low NOx/soot
`investigations of
`The
`demonstrated that a CDPF is beneficial with respect to
`passive soot regeneration, even at a level of 1.0-1.5
`g/kWh engine-out NOx emissions. Even under "worst
`case" conditions, use of the engine aged CDPF and a
`low NOx emission level, a soot burning rate of 50 g/hour
`was measured at 450 oc - a temperature where an
`uncoated filter would be ineffective.
`
`Thus, under real world conditions an advanced filter such
`as CDPF should help extend the time· between active,
`oxygen-based soot regenerations, even in conjunction
`with future low NOx emitting engines.
`
`ACKNOWLEDGMENTS
`
`The authors like to thank all their colleagues from ICT.
`Co Ltd., ICT Inc. and Umicore who contributed to this
`study.
`
`REFERENCES
`
`1. P. Spurk, M. Pfeifer, B.V. Setten, N. Seeger, G.
`Hohenberg, C. Gietzelt, G. Garr, 0. Bailey, "Examination
`of Engine Control Parameters for the Regeneration of
`Catalytic Activated Diesel Particulate Filters
`in
`Commercial Vehicles", SAE 2003-3177
`2. J. Gieshoff, M. Pfeifer, A. Schafer-Sindlinger, U.
`Hackbarth, 0. Teysset, C. Colignon, C. Rigaudea"u, 0.
`Salvat, H. Krieg, B. W. Wenclawick, "Regeneration of
`Catalytic Diesel Particulate Filters", SAE paper 2001-01-
`0907
`3. H.C. Vergeer, A. Lawson, W. M. Jones, W. Robinson,
`SAE paper 860133
`4. T.V. Johnson, "Diesel Emission control: 2001 in Review",
`SAE 2002-01-0285
`5. K. Kimura, T. L. Alleman, S. Chatterjee, Kevin Hallstrom,
`"Long-Term Durability of Passive Diesel Particulate Filters
`on Heavy-Duty Vehicles, SAE2004-01-0079
`6. M.Crocoll,
`"Modellierung und Simulation der Pt(cid:173)
`katalysierten NO-Oxidation in sauerstoffreichen Abgasen",
`Dissertation, Universitat Karlsruhe (TH), 2003
`
`BASF-2013.006