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									      Busan Engine International Symposium 2001                                                                                                                                             ENSY 2001-CE-
      Busan, Korea, December 13∼14, 2001
                           The trend of exhaust emission standard and diesel particulate filter
                                      trap technology for diesel powered vehicles
                                                                                                       Youngil Jeong*


               The CO2 automotive emission standard will start from year 2008, and diesel engine especially high speed direct
            injection (HSDI) diesel engine has an advantageous position in holding the next passenger car market because of its
            superiority in high efficiency. But particulate matters (PM) and NOx emissions from diesel engine are much heavier
            than those of gasoline engines. Therefore, it is an essential requirement to find the measure against PM and NOx
            emissions in order to maintain this valuable opportunity. The diesel vehicle policy in USA and EU is after lowing the
            level of PM and NOx emission the same as those of gasoline vehicles to positively promote diesel powered vehicles.
            The diesel particulate filter trap (DPF) is recognized as the most efficient technology for the reduction of PM at
            present. The current 2nd generation DPF technology is mostly the passive type, using catalyst or fuel additives, but it
            is expected that passive and active combination DPF system - 3rd generation DPF technology – will be available for
            the year 2005 EURO4 standard.

              Key Words : CO2, Particulate Matters (PM), Diesel Particulate Filter Trap (DPF), Regeneration, Continuous
            regeneration Trap (CRT), Diesel Vehicles

1. CO2 emission standard and its influence on                                                                       The CO2 automotive emission standard was first adopted in
   diesel vehicles                                                                                               1998 by EU environment committee of 140g/km from year 2008
                                                                                                                 and 120g/km in 2012. Korea and Japan signed an agreement to
                                                                                                                 satisfy 140g/km from 2009 and in addition, as an interim
   Medium and small size diesel powered vehicles have recently                                                   evaluation, 165g/km in 2004. This agreement is, in the wide
been actively developed from automotive companies in Korea.                                                      view, for the protection of global environment, but on the other
They newly launched the commonrail type direct injection                                                         hand, it could also be understood as the beginning of another
diesel engine to SUV and are preparing the diesel passenger car                                                  new trade barrier. In Europe, the technical measures against CO2
market as well. All of these are derived from the provision for                                                  regulation have been developed for long time and the ultra fuel
the new era of diesel vehicles driven by Europe, which is                                                        economy vehicle – the three liter car that drives 100km per one
supposed to cope with CO2 regulation and the competition of                                                      liter fuel - is already available in the market.
ultra fuel economy vehicles. As shown in Fig. 1, the increase of                                                    When taking into consideration of the high level of CO2 from
diesel passenger cars started from the mid 90’s, and the number                                                  current domestic vehicles - 200g/km from medium size
of cars is expected to double before 2005, mostly with high                                                      passenger cars and even 160g/km from mini-cars as shown in
speed direct injection engines.                                                                                  Fig. 2 - CO2 regulation is expected to be a very difficult target to
                                     Trend of EU Market for Diesel Passenger Car
     Million Unit
       7                                                                                               70%

       6                                                                                               60%
      5                                                                                                50%

       4                                                                                               40%
       3                                                                                               30%
                                                                                                                         CO2 (g/km)

      2                                    90%                                                         20%                                          Diesel
      0                                                                                                10%
       0                                                                                               0%
           89   90   91    92   93    94   95    96   97     98    99   00    01   02   03   04   05                                  400

           Fig. 1 EU market trend of diesel passenger car                                                                             200

                                                                                                                                            0   5            10       15       20      25    30   35
  * Korea Institute of Machinery and Materials                                                                                                                    Fuel Consumption (km/l)
    Engine R&D Group
    171, Jang-dong, Yusung, Taejeon, 305-600
    TEL: +82-42-868-7312                                                                                             Fig. 2 CO2 emission level according to fuel consumption
     Http://                                                                                      Moreover, if we look at CO2 level of year 2000 in table 1, the
                                                                                                                 average is 191g/km which is only 3% reduced value during 5

Busan Engine International Symposium 2001                                                                                                                                                E NSY 2001-CI-
Busan, Korea, December 13∼14, 2001

years. So, even the value of 165g/km in 2004 requiring 14%                                 is inevitably expected to demand aftertreatment devices, such as
reduction is too heavy a burden to overcome in the current status.                         diesel particulate filter trap or NOx trap to satisfy these strong
       Table 1 CO2 average of exported vehicles to EU                                         Korea already decided to adopt the EUOR3 for the 2003
              1995 1996 1997 1998 1999 2000                                                standard and is considering applying the EURO4 standard in
   Gasoline   195     197     201     198     189     185                                  2006 or 2007 for heavy duty diesel engines.
    Diesel    309     274     246     248     253     245
                                                                                                                                                                        HD Diesel Vehicle
    Total     197     199     203     202     194     191                                                                   0.4

   Since the more efficient fuel combustion, the more CO2
emission production, any possible technologies able to reduce
CO2 from engine combustion or aftertreatment are not proposed                                                                                                                            Japan(97)

yet. The only available approach at present is to curtail the
amount of CO2 formation during combustion by using less fuel                                                                                                              Japan(03)
                                                                                                                                      EURO2(96)                                                          Korea(00)
consumption.                                                                                                                                       Japan(07)                          USA(98)
   Therefore, development of the ultra low fuel consumption                                                                 0.1
                                                                                                                                      EURO3(00)               USA(04)              Korea(03)

vehicle, satisfying the continuously stringent exhaust emission
standard at the same time, is the kernel direction for the next                                                                                                                                 USA(98 BUS)
                                                                                                                                      EURO4(05)                         Korea(next)
coming automotive technology.                                                                                                              USA(07)
                                                                                                                                  0            1         2          3          4           5         6          7         8
   Among the current engines popular for vehicles, the thermal                                                                                                            NOx(g/kwh)
efficiency of a diesel engine is 20-30% higher, therefore, 20%
less CO2 emission than that of a gasoline engine. Especially the
                                                                                                                            Fig. 4 PM and NOx standard for HD diesel vehicle
high speed direct injection (HSDI) diesel engine is in the center
of attention to develop because of its superiority in high
                                                                                              When it comes to the diesel passenger car, there was no diesel
efficiency. Fig. 3 explains the advantageous potential of direct
                                                                                           passenger car in Korea’s market for a while, and the policy will
injection (DI) diesel. In addition, it shows gasoline direct
                                                                                           maintain the same situation for the present. As shown in Fig. 5,
injection (GDI) has the same position as indirect injection (IDI)
                                                                                           the 2001 standard of the diesel passenger car in Korea is very
                                                                                           strict with PM (0.01g/km) and NOx (0.02g/km) standards,
                                                                                           which is quite stronger than the EURO4 and almost the same
                                                                                           level as the ULEV in LEV-2 of California. Korean government
   Fuel Consumption (L/100km)

                                                                                           is understanding the current situation that the domestic diesel
                                                                   Gasoline                passenger car market needs some time in order to comply with
                                                                                           CO2 regulation and deal with trade problems. We are under a
                                                                                           serious debate about the emission standard - applying standard
                                 6                       GDI
                                                                   IDI Diesel              value and time - for diesel passenger cars taking into
                                                                                           consideration of measure technologies, environmental and
                                                                      DI Diesel            industrial circumstance.

                                     0    1000   1200   1400   1600       1800    2000                                                                       Diesel Passenger Car

                                                        GVW (kg)                                                            EURO1(92)

                                         Fig. 3 Comparison of fuel consumption                            0.12


2. PM and NOx standard

                                                                                                          0.08                                                  Japan(97)                Korea(98)

   Even though diesel engine is in a favorable position for                                                                 EURO3(00)                Japan(02)                           Tier-I(USA 94)
                                                                                                                                         LEV                                             Korea(00)
holding the next passenger car market, it is essential to find a                                          0.04

measure against particulate matters (PM) and NOx emissions                                                                  EURO4(05) ULEV(LEV-1)
which are emitted quite heavier from diesel engines than                                                                     Korea(01)
gasoline engines in order to keep this valuable opportunity.                                              0.0
                                                                                                                        0         0.1      0.2     0.3        0.4        0.5       0.6    0.7      0.8    0.9       1.0
Moreover, according to recent studies supporting the suspicion                                                                                                      NOx(g/km)
that the risk of lung cancer is increased in work environments
with an exposure to diesel soot, the concern about the health
                                                                                                                 Fig. 5 PM and NOx standard for diesel passenger car
effect of PM was increased with an extra weight.
   Therefore, the policy of diesel vehicles in USA and EU is
after developing the level of PM and NOx the same as those of                              3. Trend of DPF technology
gasoline vehicles, to positively promote diesel powered vehicles.
For example, as shown in Fig. 4, EU strengthened the PM                                       According to the definition of PM in CARB, “particulates are
standard steeply for heavy duty diesel engines - from 0.1g/kwh                             all exhaust components (with the exception of condensed water)
to 0.02g/kwh, which is the same level as gasoline and natural                              that are deposited on a defined filter after having been diluted
gas fuelled vehicles, in the 2005 EURO4 standard, and NOx                                  with air to a temperature below 51.7oC”. The main component
from 3.5g/kwh to 2.0g/kwh in the 2008 EURO5. USA also                                      of PM is the unburned carbon – solid particle phase of 15-30nm
sharply cut the 2007 standard - 90% cut of PM from 0.1g/bhph                               diameter, gas phase- from fuel and partly from lubricant, and all
to 0.01g/bhph, 95% cut of NOx from 4.0g/bhph to 0.2g/bhph. It                              named as fines, dust, soot, mist, fog, and smog are a part of PM.

Busan Engine International Symposium 2001                                                                                                         E NSY 2001-CI-
Busan, Korea, December 13∼14, 2001

Besides, soluble organic fraction (SOF) removable by organic                             The fuel burner and throttling system were subsequently
solvent is adsorbed and sulfuric acid (sulfates), which is                            developed, which mostly uses dual traps and burns PM with the
inorganic species, are condensed in PM (Fig. 6).                                      assistance of an exterior heater source. These systems are called
The diesel particulate filter trap (DPF) is recognized as the most                    an active regeneration system and could be assumed as the 1st
efficient technology for the reduction of PM at present. A large-                     generation DPF technology. Because of complexity and
scale fleet test on DPF is under operation and its                                    unreliability of system, and fuel economy penalty caused by the
commercialization is on the beginning stage. The principle of                         increased filter pressure drop, this 1st generation DPF
the DPF technology is simple - collect the PM inside trap filter                      technology has not succeeded in application.
and then incinerate it, which is called regeneration, repeatedly.                        DPF technology has distinctly advanced into a new phase, a
The core technology is, first how to efficiently trap the PM by                       passive regeneration of 2nd generation DPF technology, which
using what kind of filter, second how to regenerate PM with                           regenerates PM with engine exhaust gas temperature only by
assistance of what type of thermal energy without damage to the                       using catalyst and fuel additive. CRT from Johnson Matthey and
filter and, third how to make an electronic controller managing                       DPX from Engelhard are paid the most promising attention for
the trapping, regeneration and matching with vehicle operation                        the heavy duty vehicles. Besides Peugeot installed fuel additive
conditions.                                                                           system in diesel passenger car from 2000.
                                                                                         The principle of CRT regeneration is based on the fact that
                                                                                      PM is easily oxidized by nitrogen dioxide (NO2). Carbon is
                                                                                      oxidized by oxygen at a temperature above 550oC, but with
      Carbon                                                                          NO2 the regeneration process begins at 250oC. The CRT is
                                                                                      composed of two filters – an oxidation catalyst upstream and a
                                                                        0.01-0.08     ceramic wall-flow filter downstream as shown in Fig. 8. The
                                                                                      NO2 is generated in the oxidation catalyst from nitric oxide (NO)
    Soluble Organic                                                                   present in diesel exhaust, and, once the NO2 enters the
     Fraction(SOF)                                                                    downstream filter, it reacts with soot. The CRT system is
                                                                                      commercially available as an aftermarket kit and retrofits for
                                                                                      heavy duty engines as fully passive systems. Eventhough more
                                                                                      than 20,000 vehicles have been equipped with CRT up to now,
                                                                                      CRT requires the application limits for a successful passive
                                                                                      operation, such as higher than 275oC of exhaust gas temperature,
                                                                                      less than 50ppm of sulfur content in the fuel, and more than 20
                                                                                      of exhaust NOx/PM ratio.

                        Fig. 6 Components of PM

    The electric heater type DPF was first fleet tested at 400
buses of New York city by Donaldson in 1992, which was the
first introduction of DPF technology to the world. Fig. 7 depicts
the schematics of the electric heater DPF system. The trap
system filters the exhaust gas and periodically disposes the
collected particulate by controlled oxidation. The filters fill with
PM until the optimum loading is reached and then, the blower
system and the heater perform the regeneration. The particulate
loading is determined from measurement of the intake air flow,
filter pressure drop, and the filter inlet temperature. The two
traps facilitate uninterrupted gas filtering during regeneration by
switching the exhaust flow between filters.
                                                                                                                              Fig. 8 CRT system from JM
        Intake Manifold Pressure
                  Air Flow Rate
                                                                                          PM Conversion Rate (%)

                                                              Battery                                               0
                                                           Back Pressure Sensor                                    -200
       Engine                                                                                                      -300
                                        Blow er
                             Shut-off    Valve
                                                                                                                        100   200      300        400     500         600
                                                                                                                                       Temperature ( C)

        Fig. 7 Schematics of electric heater DPF system
                                                                                                    Fig. 9 Effect of fuel sulfur on PM conversion in the CRT

Busan Engine International Symposium 2001                                                                                              E NSY 2001-CI-
Busan, Korea, December 13∼14, 2001

    The mechanism of the fuel additive type regeneration is
similar to that of the catalyzed filter, except the use of additives                                       Insufficient temperature
                                                                                                               for regeneration
provides better contact between the catalyst and the carbon
particles. Fuel additives for diesel trap regeneration
commercially available are iron (Fe/ferrocene), iron-strontium

                                                                             Distribution (%)
(Fe/Sr), cerium (Ce), platinum (Pt), and copper (Cu).                                                                                 ETC
    There are some drawbacks and unsolved issues for the fuel                                                           USFTP
additive system; the necessity of introducing the catalyst to fuel,
like on-board automated dozing devices; ash deposits on the                                     40
filter; ash emissions due to limited filtration efficiency or filter                                   Field test
failure; impact on engine-out emissions such as PM size                                         20
distribution; impact on the engine or its components specially
fuel injector and fuel stability.                                                                0
    PSA Peugeot Citroen developed a diesel particulate filter                                         50          150           250         350     450
system fitting on 2.2liter, 98kW, commonrail, passenger car                                                                         o
                                                                                                                        Temperature ( C)
diesel engine. This system includes a porous silicon carbide trap
and an oxidation catalyst upstream. Cerium based fuel additive
                                                                         Fig. 10 Exhaust temperature distribution in HD diesel engine
is used to lower the regeneration temperature below 450oC and
multiple post injection controlled by the commonrail injection
system is applied as an assistant active means achieving the rise        4.2 Ash deposits on the filters
of exhaust temperature by 200oC to 250oC.                                 Most of the additive is trapped on the filter in the form of an
                                                                       inorganic oxide and/or salt. Even in the catalyst filter, the ash
                                                                       from engine oil is accumulated inside of the filter. With time, it
4. Issues and countermeasures                                          accumulates to considerable quantities. The ash deposits
                                                                       contribute to increased pressure drop. It is became known
   Passive, catalytic or fuel additive DPF system is generally         recently that ash is a very fine and high surface area material
favored for heavy duty diesel engine applications due to its           prone to interaction with substrate materials. Therefore, at
simplicity and relatively low cost. However several important          excessive temperature higher than 1000oC, ash can sinter and
issues still remains in order to apply passive filters in light duty   eventually plug channels (Fig. 11) resulting in cracking and
engines and, also, expand wide scale application in heavy duty         melting of the filter.
engines.                                                                  In order to avoid this problem, the filter must be periodically
                                                                       cleaned from the ashes by flushing it with pressurized water or
                  Table 2 Regeneration type                            air. Also, filter material has to be upgraded to enhanced thermal
      Regeneration                                                    durability
     Active                 Electric Heater
                            Fuel Burner
     Passive                Fuel Additive
                            Catalyzed Trap
     Passive-Active         Engine Management
     Combination            Electric Heater

  4.1 Regeneration temperature
   In retrofit applications particulate filters have been mostly
applied in heavy duty vehicles within the limits. But in new
engine applications, they must provide reliable operation under
any operating conditions - whether in heavy duty or light duty
   The exhaust gas temperature is the kernel of a question for the
passive type filters application because PM is regenerated by the
thermal source of exhaust gas. The exhaust gas temperature of
light duty engines is too low to ensure proper filter regeneration
and, though the exhaust temperature from heavy duty engine as            Fig. 11 Ash segment sintered and plugged in monolith filter
shown in Fig. 10, is higher than that of light duty engines, it is
generally not sufficient to support continuous regeneration.             4.3 Uncontrolled Regeneration
   There are two ways to countermeasure in this issue; one way            In an ideal regeneration, particulates that enter the filter are
is to develop the catalyst or fuel additive to be able to decrease     oxidized in a continuous manner. Such continuous operation
the regeneration temperature of PM as low as 150oC, another            mode requires a certain minimum of exhaust temperature. If the
way is to use additional subsidiary heating source, such as            temperature is too low, poor regeneration leads to increasing
electric heater, fuel burner, and engine management. The former        soot load in the filter and, hence, increasing pressure drop.
case is more desirable for competitive potential, but it is            Eventually, it may lead to complete clogging of the filter. This is,
necessary to approach it with long terms because it is not easy to     unfortunately, the common problem with many passive systems.
anticipate the time of technology completion. The latter case is          When a high load of soot becomes ignited, the soot load burns
more complicated but realistic in a short view. It is expected that    rapidly, releasing high quantities of heat, raising filter
passive and active combination DPF system may be available             temperature and eventually causing damage by melting or
for the EURO4 standard.                                                cracking to the filter material. This uncontrolled regeneration is
                                                                       called “stochastic regeneration” - to emphasize its random,

Busan Engine International Symposium 2001                                                                    E NSY 2001-CI-
Busan, Korea, December 13∼14, 2001

unpredictable character - and Fig. 12 is the picture of a melted      advanced countries by 2005 to 2007. The price of DPF is
filter by stochastic regeneration tested in KIMM.                     currently more than $6,000 but could be cut down sharply when
   There is no means to solve this problem in the current passive     mass produced. EPA prospects the cost of heavy duty DPF to be
system, which is a technical weakness of the passive filter. Thus,    $1,200 in 2007 and $690 in 2010.
it may essentially necessary to devise a combustion control               The exhaust gas temperature of light duty engines is too low
technology during regeneration.                                       for current DPF system to operate as passive mode, and even
                                                                      filter systems for heavy duty vehicles are also likely to require
                                                                      some form of active regeneration support - most likely through
                                                                      engine management or electric heater. However, it is the general
                                                                      prospect that DPF is inevitably necessary in order to meet the
                                                                      year 2005 EURO4 standard for heavy duty diesel engine, and
                                                                      expected to be applied in 2008 for the EURO5 standard for light
                                                                      duty diesel vehicles.
                                                                          In Korea, more than 1,400 DPF, mostly active filters of
                                                                      electric heater and fuel burner, had been retrofitted at the
                                                                      garbage trucks of Seoul in 1997. After this program, several
                                                                      technologies, such as fuel additive, catalyst, and plasma system,
                                                                      have been continuously developed. The Korean government is
                                                                      preparing a DPF demonstration program again to promote DPF
                                                                      in new engines for the next EURO4 level standard.

                                                                      6. References
 Fig. 12 Melted sintered metal filter by stochastic regeneration
                                                                         (2) Particulate traps for heavy duty vehicles, Environmental
                                                                             documentation No. 130, SAEFL, 2000.
  4.4 Filter                                                             (3) Application particulate trap systems for diesel engines,
   Filter configurations and materials are an important factor               VERT TTM W04/4/98, 1998.
determining the performance of the DPF system. Wall flow                 (4) Presentation from Corning.
monolithic cell – honeycomb - is the most popular shape, and             (5) Presentation from DaimlerChrysler
cartridge, knitted and cross flow filters are used as well.              (6) Presentation from Bosch
Cordierite - synthetic ceramics - is the most popular, and silicon
carbide, fibers and sintered metal are also important materials.
   Filtration capacity, porosity, pressure drop, heat capacity,
thermal durability, thermal expansion and strength, thermal
shock resistance, chemical durability, melting point, and also
cost are the important parameters judging the performance of the
                         Table 3 Filter type
         Filter
         - Ceramic Wall-flow Monolithic Cell (Honeycomb)
         - SiC Monolith
         - Fiber Wound Cartridge
         - Knitted Fiber
         - Sintered Metal
         - Ceramic Foam
         - Glass/Ceramic Fiber
         - Cross-flow Ceramic Filter

5. Prospect of DPF market
Considering the DPF development situation up to now, the
passive, catalyst filter is considered as practical use for heavy
duty vehicles. DPF retrofit programs in EU and USA have been
promoted in earnest with more than 20,000 DPF units already
retrofitted in Europe and USA. Japan also announced a very
energetic and challenging program that retrofitting will
commence in 2003 and be completed in 2006, and after April
2006 diesel vehicles without traps cannot operate in Tokyo.
   The most difficult obstacles for the promotion of the catalyst
DPF system are preparing ultra low sulfur diesel (ULSD) fuel
with less than 50ppm sulfur content and the price of the DPF
   The manufacturing technology of ULSD is already in
practical use and price difference is expected to be less than 10
cents per gallon. The supply of ULSD is gradually expanding
centered around big cities and is expected to be used at all of the


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