International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
Scope for Improvements in Design and Development of
Diesel Particulate Filter
Vishwajit Patil#1, Dr M.Talib*2, Dr.L.G.Navale#3
#
Assist Prof., Mech Dept,SITS,Narhe,Pune, India; Dr.L.G.Navale,Prof.,Mech Dept.,DYP
COE,Pimpri,Pune,India
Abstract — Global warming is the major concern
nowadays and diesel engines are the major
contributors for exhaust pollutions. These exhaust
emissions are hazardous to human health and to the
environment. To minimise the exhaust pollutants and
to meet the stringent emission norms from the diesel
engines some arrangement must have to done and the
answer was filters called as Diesel Particulate
Filter(DPF). From then the research is going on for
different substitute materials to optimise its
performance, cost. This paper describes research
conducted by a group of researchers considering
some of the important parameters that should be taken
into account while designing the diesel particulate
filter and the impact of particulate matter on engine
performance in terms of back pressure for
conventional particulate filter thereby improving the
design parameter that can be applied to different
materials also .
Europe and America. Particularly for the PM issue,
the adoption of diesel particulate filters has enabled us
to obtain certain prospective solutions. However, as is
typically seen in Europe, regulations have been more
and more stringent, and thus development of higher
performance DPFs is the need of the situation which
can perform better.
A wall-flow type filter structure is mainly used in
DPFs. This type of filter is mainly made from
ceramics, and the inlet and outlet of the honeycomb
structure are alternately plugged, and the honeycomb
wall face is used as a filtration area. The honeycomb
wall has a porous structure, and PM is removed from
the exhaust gases as it passes through this porous layer
as shown in Fig1. However, it is said that the fuel
efficiency will be reduced by 1% to 3% once a DPF is
installed because the exhaust gas pressure loss will be
higher due to the PM accumulation on the DPF, hence
PM accumulation on the DPF must be periodically
burned and removed.[1]
Keywords — Diesel Particulate filter, diesel filter
materials, DPF parameters.
I. INTRODUCTION
A diesel particulate filter, sometimes called a DPF, is
a device which is meant to remove diesel particulate
matter or soot from the exhaust gas from a diesel
engine. Diesel particulate filters have contributed to
decreasing particulate matter (PM) in the exhaust gas
of diesel cars, and they have become standard diesel
exhaust gas after-treatment devices. Silicon carbide
(SiC) is currently used as a material in these filters due
to its high thermal stability.
In order to halt the progress of global warming,
attention has been increasingly given to technologies
for reducing carbon dioxide (CO2) emissions, and the
reduction of CO2 discharged from automobiles has
garnered a lot of interest. It is considered that for the
next two decades the internal combustion engine will
be an appropriate selection as a power train for
automobiles. Especially, diesel-powered automobiles
have better fuel efficiency than gasoline-fueled
automobiles, and thus they are recognized part of the
―eco-car‖ category. However, it is crucial to
implement environmental measures for dieselpowered automobiles also, including the reduction of
particulate matter (PM) and nitrogen oxide (NOx)
discharged from diesel engines. As part of these
environmental measures, studies of the exhaust gas
after-treatment systems for diesel engines have been
actively conducted for quite some time, mainly in
ISSN: 2231-5381
Fig1: Ceramic Wall flow filter
Currently, silicon carbide (SiC) having outstanding
heat resistance properties is the principal material used
for DPFs. Because SiC has a high coefficient of
thermal expansion. The DPFs are bind in segments.
With this type, units with specific dimensions are
bonded to each other, and the thermal expansion of the
whole DPF is absorbed by the conjugation layers as
shown in Fig 2. However, because the manufacturing
cost for this type of DPFs is high and material loss is
significant as compared to ―monolith‖ type DPFs, it is
one of the high cost factors for DPFs. Furthermore, it
also has a disadvantage in terms of performance as the
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segmented layers do not perform its function in PM
removal.[2]
Fig 2: Segmented Filter
II. PRESENT STATUS
Direct oxidation catalysts have been of interest in the
field for more than five years. These catalysts use
oxygen conducting materials (such as ceria, zirconia,
or manganate) to burn the soot at the soot-catalyst
interface, rather than by oxygen in the gas phase.
Complex ceria material can begin oxidizing soot with
model gas phase oxygen at 160°C with completion at
220°C using no or very little precious metal.[3]
Diesel oxidation catalysts (DOC) were once the
premier choice for diesel exhaust after-treatment,
however with ever tightening emissions standards,
they are quickly becoming obsolete. DOCs are very
effective in reducing CO, HC, aldehydes, and the
soluble organic fraction (SOF), however they have
little effect on NOX and limited effect on particulate
emissions.[4]. Also, at high temperature it produces
sulfates.
Although DPFs have been in commercial production
for more than 10 years, there is still much
optimization activity in the field. The research is going
on to find different materials for better performance
and cost efficient.[5]
Warner, et al., investigated present diesel filter
regeneration dynamics and found that Passive
regeneration is more efficient than Active
regeneration.[6]
DPF substrates are also improving. For low-soot
applications, Heibel A shows that low-mass DPF
prototype cordierite substrates can allow a
downstream SCR catalyst to heat-up faster, dropping
NOx emissions by 15% in cold start testing. Back
pressure is also reduced 35% relative present US
DPFs.[5][7]
Cheng A S, studied Contribution of Lubrication Oil to
Particulate Emissions from a Diesel Engine, when
wear produces larger gaps that contribute to transport
of lubrication oil into the combustion chamber and out
the exhaust port. The consumption of oil is a concern
for proper engine operation. The sensitivity of modern
emission control catalysts, to sulphur poisoning has
led to increased interest in determining the quantity of
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oil transported through the cylinder and out the
exhaust port. Also, although the mass of lubrication
oil consumption is quite low, it has been implicated as
a source of nanoparticles which are harmful for human
health.[8]
According to study conducted by Timothy V., for
review on diesel exhaust in which he had reviewed
various developments in the field of exhaust emission
after treatment systems where Cu-Zeolite filter used,
reported that A DPF with Cu-zeolite behaves similarly
to the uncoated filter, and has minimal impact on DPF
regeneration when used with SCR system.[5]
In selective catalytic reduction, ammonia is commonly
injected into the waste gas stream and the combination
is passed across a catalyst to reduce nitrogen oxides to
nitrogen and water. Disadvantages of this approach
include high cost, narrow temperature range of
applicability, and ammonia emissions into the
atmosphere. In selective noncatalytic reduction,
ammonia or urea is injected into the engine or
combustor itself or into the gas leaving the engine
where temperatures are very high.[9]
Disadvantages of this approach are low NOx removals
and the problems associated with the handling of
ammonia or urea. Reaction of the oxides with water or
alkali has seen only limited success because of NO,
the principal NOx species in most gases, does not
readily dissolve in water or react with alkali in
aqueous solutions. [10]
Sidney C. et.al. conducted study on Activated carbon.
Few materials sorb NOx well. An exception is
activated carbon under certain conditions. The
specially prepared activated carbons can sorb 10
percent or more of their weight in NOx under ideal
conditions. After NOx is sorbed at a low temperature,
heating the carbon to a higher temperature can release
it. This process of sorbing NOx at a low temperature
with activated carbon and releasing it at a high
temperature has been used commercially in the past.
This approach was pursued in treating exhaust gases
from mobile sources and the study reported says of
about 54 to 64 percent were achieved for mobile
engine. Though, in the study it has not elaborated
about the control of particulate matter and the
regeneration of filter. Also the effect on back pressure
is not mentioned.[11]
Nett Technologies Inc. developed DPF based on
zeolite also known as molecular sieves, which are
most frequently used as the hydrocarbon trap. These
zeolites traps and store diesel exhaust hydrocarbons
during periods of low exhaust temperature, such as
during engine idling.
Then, when the exhaust
temperature increases, the hydrocarbons are released
from the washcoat and are oxidized on the catalyst.
Zeolite is capable of 40-50% HC conversion and
effective diesel odor control at very low exhaust
temperatures[12].
ML Stewart et.al. conducted study on a silicate
mineral which is processed to obtain the required filter
material called Acicular Mullite, in his study he found
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International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
the filter can be able to reduce the back pressure effect
and exhaust emission of a diesel engine. The study
also reported to have sufficient reduction in pressure
drop across diesel filter.[13].
The research is going on various materials to find
better possible alternatives which can reduce the
exhaust emission (PM) by improving the engine
performance.
III. DPF DESIGN PARAMETERS
DPF design items consist of the following factors:
a) Material: DPF material will affect the thermal
stability, thermal shock resistance, mechanical
strength and reactivity with the base material of the
exhaust gases.
b) Cell structure: This will affect the pressure drop,
thermal shock resistance and ash resistance
characteristics which can sustain
physical
accumulation of ash.
c) Pore size: This will affect the filter’s basic
properties, namely the pressure drop and filtration
efficiency. As the substrate material’s wall is used as a
filtration area.
a) Material
The parts used for vehicle emission gas lines are
exposed to various harsh conditions. For example,
severe thermal conditions due to sudden changes in
the engine operating status, vibrations from the engine
and road surface, and coming into contact with
chemical compositions such as ash having high
reactivity and originating from fuel or oil.
Above all, when using a DPF, the PM collected inside
the filter must be burned and removed after
accumulating for a certain period of time which is
generally called as ―regeneration‖. The combustion
heat generated during this process will cause the DPF
to be exposed to more severe thermal conditions than
any other part. Although DPF regeneration is normally
conducted under relatively mild and controlled
conditions, on rare occasions it is performed under an
uncontrollable condition. Under such conditions, the
greater the PM amount is, the more severe the
combustion will be. Therefore, the regeneration start
timing is set according to actual vehicles so as not to
damage filters. The larger the SML (Smoke Mass
Limit) value is, the greater is the PM amount that can
be burned and removed at once, thus causing
regeneration to occur less frequently, thereby
improving the fuel efficiency. The thermal shock
parameter (TSP) and heat capacity of a base material
can be considered as factors that would affect the
SML value. The TSP can be simply calculated as a
correlation equation of material properties as shown
below: Regarding MOR/eMod in this equation, since
values usually fluctuate in sync with each other and
the MOR/eMod ratio is nearly a constant value, it is
assumed that reducing the coefficient of thermal
expansion (CTE) is most effective to improve the
TSP.
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TSP = MOR / (CTE × eMod)
TSP ; Thermal shock parameter
MOR ; Bending strength
eMod; Young modulus
CTE ; Coefficient of thermal expansion
Furthermore, the heat capacity of the DPF can be
considered as a material property that directly
contributes to the SML. The temperature of the DPF
itself will increase due to the heat generated during the
DPF regeneration. The larger the heat capacity is, the
milder the heating behavior will be during the
regeneration so the sudden temperature change is
minimal. When comparing ceramic materials having
identical volume, ―the material density is large‖ can be
rephrased as ―the heat capacity is large.‖
The present available filter are SiC and Cordierite
filter the following Table-I shows material properties
which are also helpful to get favourable smoke mass
limit properties.
Table-I: Material Properties and its effect on SML
Parameter
SiC
Cordierite
Theoretical density
3.2
2.6
[g/cc]
SML
High
Heat Capacity [J/L ·K]
1900
1300
High
CTE/×10–6 [1/K]
4
1
High
Thermal Conductivity
[W/m·K]
50
2
Low
b) Cell Structure
Cell structure is one the important factor as it can
affect contact surface area there by the pressure drop
may vary causing the influence on engine performance.
The cell structure also affects the ash resistant ability
of the filter.
Contribution of Cell Structure to Ash Capacity solid
components (other than PM) contained in exhaust gas
include non-organic components mixed in from the
fuel and/or lubricating oil, as well as metal
components mixed in due to the frictional wear of
syringes. These solid components are collectively
called ash components. Ash components gradually
accumulate in the DPF, decreasing the effective
filtration area, and can therefore cause an increase in
pressure drop. According to the study conducted
Hexagonal structure was found to be better in terms of
performance for controlling back pressure.
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(a)
Hexagonal Cell Structure
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International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
(b)
(c)
Squqre Cell Structure
Octa square Cell Structure
Fig 4: Effect of pore size
Fig.3: Different Cell Structure of diesel particulate filter
IV. EFFECT OF PARTICULATE MATTER
c) Pore Size
DPF partition wall possesses a ―pore structure‖ that
consists of minute pores in the order of microns. This
structure (i.e. pore size and distribution) greatly affects
the filtration efficiency and pressure drop
characteristics. This means that in order to efficiently
collect PM, it is preferable that the porosity and pore
diameter are as small as possible. Contrastingly, in
order to reduce the pressure drop (= allow gas to flow
efficiently), larger porosity and pore diameter are
better. The optimal pore structure can be determined
by taking both characteristics into account. We
conducted pore structure optimization on DPF
products already on the market, through a small-scale
experiment using the filtration efficiency and pressure
drop characteristics as parameters (Fig. 2). Fig. 2
shows the pore characteristics (porosity and mean pore
diameter) of each product and the characteristics of
the filtration efficiency.
Fig. 4 also indicates the pressure drop characteristics
using the value of Serial (A) as a standard.
Additionally, Serial (A), Serial (B) and Serial (C) are
DPF products obtained from the market. Of all those
products, Serial (A) is made of the material that can be
considered to be the most popular in the current global
market.
Fig. 5 depicts the measurement results of the pressure
drop characteristics during PM accumulation. The PM
accumulation mode after passing the initial PM
accumulation region (where the amount of deposited
PM is less than 1g/L) is considered as the cake
filtration region. In this region a linear increase in
pressure drop, which occurred in proportion to the
amount of deposited PM, was observed.
Additionally, the initial PM accumulation region was
referred to as the transient region. It is considered that
in this region the PM infiltrate into the pores of the
partition wall and accumulates in them. Regarding SiC
having relatively small pores which means low
porosity, small mean pore diameter, it was surmised
that the pressure drop increased sharply because the
pore channels tend to be overlapped by PM.[14]
Fig 5: Effect of particulate matter on back pressure
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International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
V. PARTICULATE MATTER CHARACTERISTICS
According to the study conducted by Akiyoshi
NEMOTO et al., to find PM charactorystics.The PM
collection properties called as filtration efficiency
were measured using a PM generator and a particle
counter. Also, in order to obtain a preparative gas in
the measurement range that could detect the amount of
PM, the gas was diluted first using a diluter and then
introduced to the particle counter.
The filtration efficiency was obtained using the
equation shown below, denoting the start time needed
to allow the gas containing PM to flow into the DPF
as t = 0s:
Filtration efficiency (%) = 100 (1 – N600s/N0)
N0 : The PM number concentration generated by the
apparatus (number/cm3)
N600s: The PM number concentration passing
through the DPF after 600s (number/cm3)
parameters and influences are compared. New
catalysts and substrates are described which are being
used for forming the substrate of a filter. In short,
regeneration temperatures are going down, catalysts
are getting less expensive, and system back pressure
and fuel efficiency are improving.
As we can see from the above results there remains a
vast scope in improving the diesel particulate filter by
selecting different substitute materials so that overall
improvement can be achieved. Thereby there remains
a wide scope to search for other possible options
which can reduce the cost of the filter can also be
reduced to some extent.
ACKNOWLEDGMENT
I would like to acknowledge Prof P.D.Darade for
his valuable guidance and timely help whenever and
wherever required.
REFERENCES
1.
2.
Fig.6 shows the chronological change in the PM
number concentration in the calculation of the
filtration efficiency. For each DPF, the PM number
concentration decreased chronologically for particles
of any diameter, and the PM was efficiently filtered by
the
DPFs. When the filtration efficiency of each DPF was
calculated using equation (4), the results were 96% for
SC-AT (HEX) and 94% for SiC (OS), thus indicating
that SC-AT (HEX) possessed a PM collection
capability equivalent to or greater than that of SiC
(OS).
3.
4.
5.
6.
7.
8.
9.
10.
11.
Fig. 6 Changes in PM number distribution on downstream filter.
12.
VI. CONCLUSION
To meet the ever changing demands of exhaust
emission regulations the design of diesel particulate
filters is undergoing a drastic change and requires a
search for cost efficient substrate materials. DPF
studies are showing improved understanding of
regeneration. Passive and active regeneration
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13.
14.
Ezio Alfieri, Emissions-Controlled Diesel Engine, Ph.D,
Swiss Federal Institute of Technology Zurich,2009.
Tree D.R. and Svensson K.I., ―Soot processes in compression
ignition engines,‖ Progress in Energy and Combustion Science,
vol. 33, no. 3, pp. 272–309, 2007.
Southward, B.W.L., Basso, S., and Pfeifer, M., ―On the
Development of Low PGM Content Direct Soot Combustion
Catalysts for Diesel Particulate Filters,‖ SAE Technical Paper
2010-01-0558, 2010, doi:10.4271/2010-01-0558.
Zelenka, P., Kriegler, W., Herzog, P., Cartellieri, W. (1990).
Ways Toward theClean Heavy-Duty Diesel (SAE 900602).
Timothy V. Johnson Corning Inc., Diesel Emissions in
Review, 2011 SAE International.
Warner, J.R., Dobson, D., and Cavataio, G., ―A Study of
Active and Passive Regeneration Using Laboratory Generated
Soot on a Variety of SiC Diesel Particulate Filter
Formulations,‖ SAE Int. J. Fuels Lubr. 3(1): 149-164, 2010,
doi:10.4271/2010-01-0533.
Heibel, A., ―Advancements in Substrate Technology,‖
Presentation at SAE 2010 Heavy Duty Diesel Emissions
Control Symposium, September, 2010.
Cheng A.S., Rich D., Dibble R.W., Buchholz B.A.,
Quantifying the Contribution of Lubrication Oil to Particulate
Emissions from a Diesel Engine, 3' Joint Meeting of the U.S.
Sections of the Combustion Institute, Chicago, ILL, March 1619, 2003.
Kamasamudram, K., Currier, N., Szailer, T., and Yezerets, A.,
―Why Cu- and Fe-Zeolite SCR Catalysts Behave Differently
at Low Temperatures,‖ SAE Int. J. Fuels Lubr. 3(1):664-672,
2010, doi:10.4271/2010-01-1182.
Nova, I., Colombo, M., Tronconi, E., Schmeisser, V., Weibel,
M., ―Transient Kinetic Study and Modelling of the NO/NO2
NH3-SCR Reactions over Cu- and Fe-Zeolite Catalysts for
Diesel Exhaust Aftertreatment‖, 3rd International IAV
MinNOx Conference, Berlin, June 2010.
Sidney C. Nelson and Rick A. Babyak, Sorbent Technologies
Corporation, ―Activated Carbon use in treating diesel engine
exhausts‖, 1664 East Highland Road Twinsburg, OH
44087.Pg 298-301
―Diesel Exhaust Catalytic Converters‖ Nett Technologies Inc.
2-6707 Goreway Drive, Mississauga, Ontario Canada L4V
1P7.
Stewart M.L., Maupin G D, Gallant T R, Zelenyuk A, Kim D
H, ―Fuel Efficient Diesel Particulate Filter (DPF) Modeling
and Development‖ Prepared for the U.S. Department of
Energy under Contract DE-AC05-76RL01830, August 2010.
Akiyoshi NEMOTO et al., Development of Innovative Diesel
Particulate Filters based on Aluminum Titanate: Design and
Validation, SUMITOMO KAGAKU 2011-II.
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