SAE TECHNICAL
`PAPER SERIES
`
`2000-01-0188
`
`An Integrated SCR and Continuously
`Regenerating Trap System to Meet
`Future NOx and PM Legislation
`
`Guy R. Chandler, Barry J. Cooper, James P. Harris, James E. Thoss,
`Ari Uusimäki, Andrew P. Walker and James P. Warren
`Johnson Matthey, Catalytic Systems Division
`
`Reprinted From: Diesel Exhaust Aftertreatment 2000
`(SP–1497)
`
`400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A.
`
`Tel: (724) 776-4841 Fax: (724) 776-5760
`
`SAE 2000 World Congress
`Detroit, Michigan
`March 6-9, 2000
`
`BASF-2034.001
`
`

`
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`ISSN 0148-7191
`Copyright © 2000 Society of Automotive Engineers, Inc.
`
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`Printed in USA
`
`BASF-2034.002
`
`

`
`An Integrated SCR and Continuously Regenerating Trap System
`to Meet Future NOx and PM Legislation
`
` 2000-01-0188
`
`Guy R. Chandler, Barry J. Cooper, James P. Harris, James E. Thoss,
`Ari Uusimäki, Andrew P. Walker and James P. Warren
`Johnson Matthey, Catalytic Systems Division
`
`Copyright © 2000 Society of Automotive Engineers, Inc.
`
`ABSTRACT
`
`The tightening NOx and particulate matter (PM) emission
`standards for heavy duty diesel powered vehicles are
`stimulating the development of aftertreatment systems to
`reduce NOx and PM emissions from such vehicles. Here
`we present data on a new system which combines NO2-
`based continuously regenerative trap particulate removal
`technology with
`urea-based Selective Catalytic
`Reduction (SCR) NOx removal technology. There are a
`number of beneficial synergistic effects associated with
`combining these two technologies, including a significant
`improvement in the low temperature NOx removal
`performance of the SCR system. The development of
`this PM/NOx control system is described, and the main
`features of this novel strategy are outlined.
`
`The PM/NOx control system has been evaluated on a
`number of different engines and over a number of
`different drive cycles. During testing we have shown that
`this technology enables simultaneous NOx conversions
`of 75-90% and PM conversions of 75-90% to be obtained
`on current engines using both US and European test
`procedures. These results are presented and discussed.
`
`1. INTRODUCTION
`
`The proposed emissions standards for heavy duty diesel
`engines in North America and in Europe will require
`significant reductions in both NOx and particulate matter
`(PM) emissions from such vehicles. There are a number
`of possible approaches currently being considered to
`achieve these objectives. Many of these include the
`combination of engine modifications to control one
`pollutant with an aftertreatment system to control the
`other. So, for example, the engine can be modified to
`give low NOx and high PM, and this PM can be controlled
`using
`filter
`technology, such as a Continuously
`Regenerating Diesel Particulate Filter (CR-DPF) [1].
`Alternatively, the engine can be calibrated to give low PM
`and high NOx, and this NOx can be controlled using
`Selective Catalytic Reduction (SCR) technology, most
`
`probably using ammonia (derived from urea) as the
`reductant [2].
`
`However, a third alternative is now becoming available,
`which allows the engine to be calibrated for optimum
`performance/fuel economy etc, and which provides very
`high simultaneous conversion of NOx and PM. This
`technology combines advanced SCR NOx control
`catalyst technology with the PM control of a CR-DPF to
`deliver high conversions of HC, CO, NOx and PM. This
`paper describes
`the processes
`involved
`in
`the
`development of
`this combined PM/NOx control
`technology, and demonstrates the potential of this
`technology to deliver very low emissions over different
`test cycles and on different engines.
`
`2. EXPERIMENTAL DETAILS
`
`2.1 CATALYST DETAILS – The Continuously Regenerating
`Diesel Particulate Filter (CR-DPF) used throughout this work
`was
`the
`Johnson Matthey CRT™
`(Continouusly
`Regenerating Trap). Throughout this paper the CRT™ is
`referred to as the "CR-DPF". The CR-DPF comprises an
`oxidation catalyst upstream of a DPF; this oxidation catalyst
`oxidises a proportion of the engine-out NO into NO2, and this
`NO2 combusts the particulate (trapped on the DPF) at low
`temperature.
`
`The catalysts used were coated onto ceramic monolith
`substrates with a cell density of 62 cells.cm-2 (400
`cells.in-2) using standard processing techniques. The
`geometric dimensions of the catalysts used for the
`engine evaluations, given as diameter x length, were
`266.7 x 152.4 mm (10.5 x 6 in) with a wall thickness of
`0.15 mm (0.006 in). The cordierite particulate filters used
`were production standard types, with 15 cells.cm-2 (100
`cells.in-2) and with geometric dimensions (again given as
`diameter x length) of 266.7 x 304.8 mm (10.5 x 12 in),
`with a wall thickness of 0.43 mm (0.017 in).
`
`2.2 BENCH ENGINE EVALUATION ON THE US
`ENGINE – Heavy Duty Transient (HDT) and European
`Steady state Cycle (ESC, OICA) evaluations were
`performed using a 7.2
`liter, 224 kW
`(300 hp)
`
`1
`
`BASF-2034.003
`
`

`
`turbocharged aftercooled engine in a test cell with
`motoring dynometer capability.
`
`Emissions on the HDT and ESC (OICA) tests were
`measured using a full flow dilution tunnel with a
`secondary dilution tunnel and filter holder to measure
`particulate. The NOx emissions were measured using a
`heated chemiluminescence analyzer, but the NOx was
`measured dry. The HC emissions were measured using
`a heated Flame Ionisation Detector. Both of these
`systems sampled continuously. CO and CO2 emissions
`were measured using continuous bag samples read post
`test by NDIR analyzers. N2O emissions were measured
`by gas chromatograph from bag samples and NH3 was
`measured using wet chemistry techniques. All regulated
`emissions during the OICA and HDT tests were
`measured in accordance with US EPA guidelines.
`
`An airless injector with a separate automatic control
`system that varied injector volumes based on engine
`speed and torque was used to inject urea. The urea
`used was a commercially available formulation of 32.5 %
`urea in water. The engine out NOx was mapped over the
`transient and ESC (OICA) cycles and separate urea
`injection maps were developed for these cycles providing
`a 1:1 NOx: NH3 ratio.
`Testing was performed using test fuel with a cetane
`number of 41.6, aromatics content of 15.5 % and sulfur
`content of 15 ppm.
`
`2.3 BENCH ENGINE EVALUATION ON THE
`EUROPEAN ENGINE – The ESC evaluations were
`carried out on a 12
`litre, 310 kW
`turbocharged
`aftercooled engine in a cell with multiple gas stream
`analysis. The temperature window experiments were
`performed on a 10 litre, 210 kW turbocharged engine
`with the same analytical facilities. Two types of fuel were
`used during the evaluations: Swedish MK1 and UK pump
`diesel fuel with sulphur levels of <10 ppm and <50 ppm
`respectively. The MK1 fuel has a cetane number of 53
`and an aromatics content of <4 %, while the UK pump
`diesel fuel has a cetane number of 52 and an aromatics
`content of ~30%. The fuels were purchased from
`existing refinery sources. The engine oil used during the
`evaluations was Shell Myrina 15W 40.
`
`temperature window experiments were
`The engine
`carried out at fixed engine speed, and the temperature
`was increased by increasing the load on the engine. The
`ESC evaluations were carried out using standard
`procedures. The catalysts had all been run on the
`engine for at least 10 hours before ESC evaluations were
`carried out. Prior to each ESC run the system was
`conditioned by running one ESC cycle. The engine was
`operated for the prescribed time in each mode, and
`completed the engine speed and load changes in the first
`20 seconds at each mode. The sampling times were at
`least 4 seconds per 0.01 weighting factor. One PM
`sample was taken over the complete test cycle by means
`of a dilution tunnel. The filter papers were stabilised
`under controlled temperature and humidity conditions for
`
`2
`
`24 hours prior to the testing and then installed for the
`test. After the test cycle had been completed, the filter
`papers, with the collected PM, were again stabilised
`before being weighed.
`
`Gaseous emissions were measured raw before and after
`the catalyst system using a range of analysers:
`chemiluminescence for NO and NO2, heated FID (Flame
`Ionisation Detector) for HC, NDIR (Non-Dispersive Infra
`for CO, CO2 and N2O, and a
`Red) analysers
`paramagnetic detector for O2. A 32.5% aqueous urea
`solution was used as the source of urea; this solution was
`injected into the exhaust directly using a commercially
`available urea injector system. The required urea
`dosage rate was calculated from the engine-out NOx
`levels using dosage rates of NO:NH3 = 1:1 and NO2:NH3
`= 1:1.3. The volumetric flow rate of the urea solution to
`the injector nozzle was measured to check that the urea
`dosing rate was correct. Ammonia was detected using a
`laser-based AltOptronic LD 3000 analyser which
`measures the ammonia sample in situ.
`
`2.4 MICROREACTOR EVALUATION – The microreactor
`(SCAT) experiments were carried out using powder
`catalyst samples at a gas hourly space velocity of 50,000
`hr-1. Two different gas feeds were used, with the
`following compositions: Gas Feed 1: 200ppm NO,
`200ppm NH3, 200ppm CO, 100ppm C3H6, 12% O2, 4.5%
`CO2, 4.5% H2O and 20ppm SO2. The second gas feed
`was identical to the first, except that 100ppm of the NO
`was replaced by 100ppm of NO2 (ie the NOx composition
`of this second gas feed was 100ppm NO and 100ppm
`NO2). The experiments were carried out by increasing
`the temperature at a rate of 5oC/min. NH3 and NOx were
`monitored using a chemiluminescence analyser, while
`the CO and CO2 were monitored using NDIR detectors.
`The O2 and C3H6 were monitored by gas
`chromatography.
`
`3. RESULTS AND DISCUSSION
`
`3.1 DEVELOPMENT OF THE COMBINED PM/NOX
`CONTROL SYSTEM – It is clearly desirable to be able to
`attain high simultaneous conversion of both PM and NOx
`from heavy duty vehicles.
` The CR-DPF
`is well
`established as a particulate control strategy, and also
`offers very high conversions of HC and CO [3]. In
`addition, SCR
`is becoming widely regarded as a
`promising technology to control NOx emissions [4]. SCR
`enables high NOx conversion over a wide temperature
`window. However, the low temperature performance of
`SCR catalysts tends to be very dependent upon the
`space velocity, as illustrated in Figure 1. The Figure
`shows that as the number of SCR catalysts is increased
`from 1 to 2 to 3 the low temperature NOx conversion
`increases significantly. These light-off experiments were
`conducted on a 10 litre, 210 kW turbocharged engine; the
`volume of each of the SCR catalysts was 8.5 litres. It can
`be seen that the 3 catalyst system gives high NOx
`conversion over a very wide temperature window.
`
`BASF-2034.004
`
`

`
`enhancement in the presence of the NO2 can be clearly
`seen.
`
`NO:NH3 = 1:1
`
`NO:NO2:NH3 = 1:1:2
`
`200
`
`250
`
`300
`
`350
`
`400
`
`450
`
`500
`
`550
`
`600
`
`Temperature (C)
`
`100
`
`80
`
`60
`
`40
`
`20
`
`NOx Conversion (%)
`
`0
`150
`
`Figure 2. A Comparison of the NOx Conversion Activity
`of an SCR Catalyst Using a NO:NH3 feed
`(200:200ppm) and a NO:NO2:NH3 feed
`(100:100:200ppm)
`
`the reactions between
`The equations representing
`ammonia and NO and NO2 are as follows:
`4 NO + 4 NH3 + O2 4 N2 + 6 H2O
`6 NO2 + 8 NH3 7 N2 + 12 H2O
`Therefore, the CR-DPF delivers high PM, HC and CO
`control, and an SCR system can provide high NOx
`conversion over a wide temperature window. These two
`emission control strategies have now been combined to
`assess the potential of such systems to deliver high
`simultaneous conversions of PM and NOx (as well as HC
`and CO) [5]. The results presented above suggest that
`there may be a significant NOx conversion enhancement
`associated with placing the CR-DPF upstream of the
`SCR system, since the CR-DPF operates by producing
`NO2 which subsequently combusts the PM. If some of
`this NO2 reaches the SCR catalyst it will lead to an
`improvement in the low temperature NOx conversion of
`the SCR system. The configuration of the combined HC,
`CO, NOx and PM control system is shown schematically
`in Figure 3.
`
`Engine Out Emissions
`
`HC, CO, PM, NOx
`
`Urea
`
`Oxidation
`Catalyst
`(- HC,- CO)
`(NO
` NO2)
`
`Particulate
`Filter
`(- PM)
`
`SCR
`Catalysts
`(- NOx)
`
`NH3 Slip
`Catalyst
`(- Slip NH3)
`
`Figure 3. Schematic Representation of the Combined
`HC, CO, NOx and PM Control System
`
`3
`
`1 SCR Catalyst
`
`2 SCR Catalysts
`
`3 SCR Catalysts
`
`1 Oxicat + 1 SCR Catalyst
`
`250
`
`300
`
`350
`
`400
`
`450
`
`500
`
`Temperature (C)
`
`100
`
`90
`
`80
`
`70
`
`60
`
`50
`
`40
`
`30
`
`20
`
`10
`
`NOx Conversion (%)
`
`0
`200
`
`Figure 1. Effect of Increasing the Number of SCR
`Catalysts on the Activity of the System,
`Compared with the Effect of Placing a Pt-
`based Oxidation Catalyst Upstream of a
`Single SCR Catalyst
`
`However, this 3 catalyst system corresponds to a catalyst
`volume of 25.5 litres on a 10 litre engine, which is a rather
`high catalyst volume. We have found that an alternative
`way to boost the low temperature NOx activity of SCR
`catalyst systems is to place an oxidation catalyst
`upstream of the SCR catalysts. Figure 1 also shows the
`impact of placing a Pt-based oxidation catalyst in front of
`a single SCR catalyst, with urea injection between the
`oxidation catalyst and the SCR catalyst (so that the urea/
`ammonia is not oxidised to NOx over the oxidation
`catalyst). It is clear that the resulting enhancement in low
`temperature activity is significantly greater than that
`obtained by increasing the number of SCR catalysts to 3.
`Therefore, this approach facilitates good low temperature
`activity with a relatively low catalyst volume.
`
`A number of possible explanations can be put forward for
`this low temperature activity enhancement, including:
`
`1. the removal of HC and CO by the Pt-based oxidation
`catalyst
`improves
`the
`low
`temperature SCR
`performance,
`2. the presence of NO2 in the gas stream after the Pt-
`based oxidation catalyst enhances
`the
`low
`temperature SCR activity.
`
`Microreactor (SCAT) experiments have been carried out
`to test these hypotheses, and the experiments showed
`that there is a definite small enhancement in low
`temperature activity associated with the removal of HC
`and CO from the gas feed. This is because these
`species can inhibit the ammonia-NO reaction at low
`temperatures. However, these experiments revealed that
`the major promoting effect is associated with the
`generation of NO2 over the oxidation catalyst. This NO2
`strongly promotes the low temperature activity of the
`SCR catalyst, as shown in Figure 2, which compares the
`NOx conversion efficiency of an SCR catalyst using an
`inlet feed containing 200ppm NO and 200ppm NH3 with
`the efficiency using 100ppm NO, 100ppm NO2 and
` The
`low
`temperature activity
`200ppm NH3.
`
`BASF-2034.005
`
`

`
`The engine emissions are initially treated by the CR-DPF,
`which operates by converting (oxidising) a proportion of
`the engine-out NO into NO2 over an oxidation catalyst;
`this NO2 then reacts with PM trapped by the downstream
`Diesel Particulate Filter
`(DPF) which cleans and
`regenerates
`the
`filter.
` Numerous studies have
`demonstrated that NO2 reacts with PM at much lower
`temperatures than does oxygen (eg [6]). The oxidation
`catalyst also provides very high conversion of HC (into
`CO2 and H2O) and of CO (into CO2). Therefore, the CR-
`DPF removes the PM, HC and CO, and converts some of
`the NO into NO2. The resulting gas stream is then
`treated by the SCR system, which comprises a urea
`injection system followed by the SCR catalyst, followed
`by an oxidation catalyst to minimise ammonia slip from
`the system. This system has been tested on both US
`and European engines, using
`three different SCR
`catalyst formulations. The results of these investigations
`are reported below.
`
`3.2 TEST RESULTS ON A NORTH AMERICAN
`ENGINE – A number of tests have been performed on a
`US engine to evaluate the performance of the CR-DPF
`and SCR technologies in isolation, as well as the
`combined CR-DPF + SCR system. The engine volume
`was 7.2 litres, the CR-DPF volume was 25.5 litres, the
`SCR catalyst volume used was 17 litres and the clean-up
`catalyst had a volume of 8.5 litres. The remainder of the
`exhaust system was 101.6 mm (4 in) diameter tubing; all
`tubing and catalyst cans after the urea injector were
`made of stainless steel. The CR-DPF was tested alone,
`and
`then
`two different SCR catalyst
`formulations
`(designated SCR1 and SCR2) were
`tested alone.
`Following these experiments, each of the SCR catalysts
`was tested in combination with the CR-DPF. The
`systems were tested over the ESC cycle, using 15 ppm S
`fuel and the weighted emission results are presented in
`Table 1.
`
`The HC and CO limits are comfortably met by all of the
`systems. The CR-DPF substantially reduces the PM
`emissions (88% conversion), and, as expected, has no
`significant effect on the NOx emissions. The SCR
`catalysts when tested alone significantly reduce the NOx
`emissions to levels well below the legislated values, and
`appear to increase the PM emissions slightly (perhaps
`due to the presence of small levels of slip ammonia
`reaching and being trapped by the filter paper).
`
`However, the most outstanding results are those of the
`combined CR-DPF + SCR systems. These systems give
`emission
`levels which are substantially below
`the
`legislated values
`for all
`four regulated emissions,
`demonstrating that it is possible to obtain very high
`simultaneous conversions of NOx and PM (as well as HC
`and CO). The NOx results obtained with the combined
`CR-DPF + SCR system are significantly lower than those
`observed with the SCR catalysts alone, which reflects the
`low
`temperature enhancement of NOx conversion
`associated with the production of NO2 by the CR-DPF, as
`discussed above.
`
`4
`
`Table 1. CR-DPF, SCR and Combined CR-DPF + SCR
`Emissions on a US Engine over the ESC
`(OICA) (g/bhp-hr).
`
`Technology
`
`Engine Out
`
`CR-DPF
`
`SCR1
`
`SCR2
`
`CR-DPF + SCR1
`
`CR-DPF + SCR2
`
`HC
`
`0.01
`
`0.00
`
`0.00
`
`0.00
`
`0.00
`
`0.00
`
`CO
`
`NOx
`
`PM
`
`0.79
`
`0.03
`
`0.04
`
`0.12
`
`0.02
`
`0.16
`
`5.39
`
`5.46
`
`0.91
`
`0.84
`
`0.60
`
`0.41
`
`0.050
`
`0.006
`
`0.061
`
`0.069
`
`0.015
`
`0.025
`
`2002 ¾ Limits*
`
`0.50**
`
`15.50
`
`2.50**
`
`0.10
`
`1 g/bhp-hr = 1.341 g/kW-hr
`(* for those manufacturers subject to the Consent Decree.
`Other manufacturers will need to meet these standards in 2004
`** if NMHC > 0.5g/bhp-hr the NMHC + NOx standard is 2.4 g/
`bhp-hr NOx; but if NMHC < 0.5 g/bhp-hr the NMHC + NOx
`standard becomes 2.5 g/bhp-hr)
`
`The two CR-DPF + SCR systems tested above have also
`been tested on the same engine over the US Heavy Duty
`Transient (HDT) cycle, again using 15 ppm S fuel. The
`results of these tests are summarised in Table 2.
`
`Table 2. CR-DPF +SCR Emissions on a US Engine over
`the US HDT Cycle (g/bhp-hr)
`
`Technology
`
`HC
`
`CO
`
`NOx
`
`PM
`
`Engine Out
`
`0.077
`
`1.519
`
`5.633
`
`0.116
`
`CR-DPF + SCR1
`
`0.000
`
`0.161
`
`0.835
`
`0.014
`
`CR-DPF + SCR2
`
`0.000
`
`0.498
`
`0.840
`
`0.007
`
`2002 ¾ Limits*
`
`0.500
`
`15.500
`
`2.500
`
`0.100
`
`1 g/bhp-hr = 1.341 g/kW-hr
`(* for those manufacturers subject to the Consent Decree.
`Other manufacturers will need to meet these standards in
`2004)
`
`Once again, the emissions from the combined CR-DPF +
`SCR systems are substantially below the proposed
`legislated standards.
`
`The PM and NOx emissions of the two CR-DPF + SCR
`systems over the two test cycles are summarised in
`Figure 4, which also shows the 2002 3/4 US standards.
`Note that since the HC emissions of the systems are
`approximately zero, the NOx emission standard becomes
`2.5 g/bhp-hr.
`
`BASF-2034.006
`
`

`
`CR-DPF + SCR1: ESC
`CR-DPF + SCR2: ESC
`CR-DPF + SCR1: HDT
`CR-DPF + SCR2: HDT
`
`Once again, it can be seen that the combined PM/NOx
`control systems give emissions which are substantially
`below the proposed standards for 2005, and also
`comfortably below the proposed 2008 standards. This is
`the case even with a single SCR catalyst. This is further
`demonstrated in Figure 5, which plots the NOx and PM
`results against the proposed future European standards.
`
`0.12
`
`0.1
`
`0.08
`
`0.06
`
`0.04
`
`0.02
`
`PM Emissions (g/bhp-hr)
`
`0
`
`0
`
`EUV (2008)
`
`EUIV (2005)
`
`CR-DPF + SCR2
`CR-DPF + SCR3
`
`0.5
`
`1
`
`1.5
`
`2
`
`2.5
`
`3
`
`3.5
`
`4
`
`NOx Emissions (g/kW-hr)
`
`0.025
`
`0.02
`
`0.015
`
`0.01
`
`0.005
`
`PM Emissions (g/kW-hr)
`
`0
`
`0
`
`Figure 5. PM and NOx Emissions of two Combined
`CR-DPF + SCR Systems over the ESC with
`Respect to the Proposed European Heavy
`Duty Emission Standards.
`
`One of the issues associated with ammonia SCR-based
`NOx control systems is the possibility of ammonia slip
`from the system. As discussed above, the systems used
`in this work contained an oxidation catalyst as the last
`catalyst in the system, to oxidise any slip ammonia and
`therefore minimise ammonia release from the system.
`During the tests the ammonia slip of the system was
`monitored. At the outlet of the SCR catalysts the
`ammonia concentration in the exhaust gas was between
`10 and 45 ppm. The ammonia oxidation catalyst
`removed most of this ammonia, so that the ammonia slip
`from the whole system was only between 5 and 15 ppm.
`It has previously been reported that a fraction of the slip
`ammonia undergoes partial oxidation to N2O, as well as
`undergoing more complete oxidation to NO and NO2 over
`an oxidation catalyst [4]. This was also observed here,
`where the level of N2O after the SCR catalysts was
`between 0 and 7 ppm. This level was increased slightly
`over the ammonia oxidation catalyst, but the tailpipe
`emission was still very low at between 5 and 10 ppm.
`These levels of ammonia and N2O emissions compare
`very favourably with the corresponding levels from
`gasoline-powered passenger cars fitted with three-way
`catalysts, where the levels of ammonia and N2O release
`are around 60-360 and 12-35 ppm respectively [4]. It is
`expected that the low levels observed here could be
`further reduced by better optimising the urea injection
`control strategy.
`
`5
`
`0.5
`
`1
`
`1.5
`
`2
`
`2.5
`
`3
`
`NOx Emissions (g/bhp-hr)
`
`Figure 4. PM and NOx Emissions of the Combined
`CR-DPF + SCR Systems over the ESC
`(OICA) and HDT Cycles With Respect to
`the US Standards.
`
`3.3 TEST RESULTS ON A EUROPEAN ENGINE – Two
`CR-DPF + SCR systems have also been tested over the
`ESC cycle on a European engine. A system based on
`SCR2 catalyst technology was tested, along with a new
`formulation, SCR3. The engine capacity was 12 litres,
`the CR-DPF volume was 25.5 litres, the SCR volume was
`8.5 litres unless stated otherwise and the volume of the
`NH3 slip catalyst was 8.5 litres. During these tests the
`sulphur level in the fuel was approximately 3 ppm
`(Swedish MK1 fuel). The results of the tests are
`summarised in Table 3.
`
`Table 3. CR-DPF + SCR Emissions on a European
`Engine over the ESC (g/kW-hr).
`
`Technology
`
`HC
`
`CO
`
`NOx
`
`PM
`
`Engine Out
`
`0.162
`
`0.989
`
`7.018
`
`0.163
`
`CR-DPF + SCR2
`
`0.005
`
`0.008
`
`1.592
`
`0.008
`
`CR-DPF + SCR3*
`
`0.003
`
`0.000
`
`1.061
`
`0.007
`
`2005 Limits**
`
`0.460
`
`1.500
`
`3.500
`
`0.020
`
`2008 Limits**
`
`0.250
`
`1.500
`
`2.000
`
`0.020
`
`1 g/kW-hr = 0.7457 g/bhp-hr
`(* SCR3 catalyst volume = 17 litres
`** These limits are the proposed limits)
`
`BASF-2034.007
`
`

`
`4. CONCLUSIONS
`
`ACKNOWLEDGEMENTS
`
`By combining the CR-DPF with SCR technology it is
`possible to reach the NOx, PM, HC and CO emissions
`standards proposed to be introduced in Europe in 2008
`and
`in North America
`in 2002 3/4, when using
`conditioned catalyst systems. This is the case over both
`the ESC (OICA) and US HDT test cycles. This combined
`PM/NOx control system potentially enables vehicle
`manufacturers to calibrate their vehicles for optimum
`performance and fuel economy and still be able to reach
`future emissions standards of both PM and NOx.
`Low levels of ammonia slip and N2O release were
`observed over the PM/NOx control system. It is expected
`that these low levels could be even further reduced by
`developing more advanced urea dosing strategies.
`
`to
`required
`trials are now
`Extended durability
`demonstrate that the excellent performance of the
`combined PM/NOx control system is maintained during
`system ageing.
`
`We would like to thank Dr Philip Blakeman and Mr Colin
`Maloney for their help in preparing the catalysts. We
`would also like to thank Dr Raj Rajaram and Dr Isabel
`Jones for carrying out the microreactor experiments. The
`technical assistance of Mr Borje Johansson and Mr
`Anders Andreasson are gratefully acknowledged. We
`are grateful to Johnson Matthey plc for permission to
`publish this paper.
`
`REFERENCES
`
`1. BJ Cooper, HJ Jung and JE Thoss, US Patent
`4,902,487 (1990).
`2. C Havenith, RP Verbeek, DM Heaton and P van
`Sloten, SAE 952652.
`3. JP Warren, R Allansson, PN Hawker and AJJ
`Wilkins, Proc. Diesel Engines - Particulate Control,
`IMechE 1998 S491/006 p.45.
`4. C Havenith and RP Verbeek, SAE 970185.
`5. A Andreasson, G R Chandler, C F Goersmann and
`JP Warren, Patent Application PCT Appln No WO99/
`39809.
`6. BJ Cooper and JE Thoss, SAE 890404
`
`6
`
`BASF-2034.008