particulate matter formation and analysis
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PARTICULATE MATTER
ANALYSIS AND FORMATIONIN CI ENGINE
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Particulate Matter (PM) is defined as any matter excluding water in the exhaustof an internal combustion engine that can be trapped on a sampling filtermedium after having been diluted with air at 125F (52C) or less.
Composition of Diesel particulates:1. solid fraction
a. Elemental carbon
b.ash
2. Soluble organic fraction
a. Fuel fraction
b.lub oil fraction
3.sulfate particles
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Particulates consists of solid and liquid phases. Solid phases
are organically insoluble, whereas liquid phases are
organically soluble.
1.The solid phase consists of
a. Soot in the form of amorphous carbon, ash, oil
additives, corrosion products and abrasion products
b.sulphates
2.The liquid phase consists of
a. Fuel and lubricant contents
b.The hydrocarbons contained in hot exhaust
The size of such particles is approx 0.01 to 1 micron andabove. Most particulates have size below 0.3 micron and
some of them may penetrate into lungs.
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According to that classification, the total
particulate matter (TPM) can be defined as:
TPM = SOL + SOF + SO4
Sulfuric acid in diesel exhaust is derived from
the fuel sulfur.sulfur leaves the combustion
chamber in the form of sulfur dioxide and as a
small portion of sulfur trioxide. In the
presence of water, SO3 reacts to producesulfuric acid.
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1.SOLID FRACTION
1. The solid fraction of diesel particulates is
composed primarily of elemental carbon,
sometimes also referred to as the inorganic
carbon. This carbon, not chemically boundwith other elements, is the finely
dispersed carbon black or soot substance
responsible for black smoke emissions
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b.Ash: Another important component of the solid fraction of
PM is metallic ash. Ash emissions receive a lot of attentionfrom the developers of diesel particulate filter materials, which
must be formulated to resist corrosion by ash compounds
Iron oxides resulting from corrosion of the engine exhaustmanifold and other exhaust system components
Metal oxide impurities resulting from the engine wear, which
are carried into the combustion chamber by the lube oil.These include oxides of iron (Fe), copper (Cu), chromium
(Cr), and aluminum (Al).
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2.SOLUBLE ORGANIC FRACTION
Hydrocarbons adsorbed on the surface of carbon particles
and/or present in the form of fine droplets form the soluble
organic fraction(SOF) of diesel particulates.
Sometimes this fraction is also referred to as VOFvolatile
organic fraction
Particulates with low SOF content are called dryparticulates.
PM of high SOF content is called wetparticulate.
Typically, SOF content is highest at light engine loads when
exhaust temperatures are low
The SOF is typically composed of lube oil derived
hydrocarbons, with a small contribution from the higher
boiling end diesel fuel hydrocarbons
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SOOT FORMATION
Soot particles are made up of roughlyspherical spherules arranged in irregularly-
shaped clusters or chains.Soot formation
occurs at extreme air deficiency. This air or
oxygen deficiency is present locally inside
diesel engines.
Any carbon not oxidized in the cylinder ends
up as soot in the exhaust!
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SULFATE FORMATION
Fuel sulphur is the source for most of the
inorganic remainder.Sulphates concentrationsin the particulate matter are linearly related to
the sulphur concentration in the fuel, with
about 1-2% of fuel sulphur being converted
and subsequently depositedin the Pm.
Reducing the sulphur content of fuel can
thereforereduce the inorganic fraction in the
particulates. 9
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Loss of oil control resulting from improper
cylinder bore honing or piston ring wear canbe a major source of oil consumption and
contribution to unburned oil content in
particulate matter
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SOURCE OF PM EMISSION
Excessive black smoke
inadequate air-fuel ratio
poor combustion
demand for acceleration fuel coupled with turbocharger lag
White smoke
partially evaporated fuel during cold starting partially combusted fuel due to misfire
sources causing HC emissions
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loss of oil control
cylinder bore polishing
inadequate piston ring pack
valve stem sealing issues oil leakage
fuel quality
high sulphur content
high aromatic content low cetane number
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Mixture Formation carbon and fuel
Injection pressure
Combustion chamber shape Intake swirl
Injector / nozzle design
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Oil consumption
Oil leakages in the combustion chamber and / or in
exhaust
Lub oil formulation
Parameters affecting oil consumption
Sulphates
Fuel sulphur content
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STUDY OF FORMATION OF
PARTICULATES IN THE CYLINDER OF
A DIRECT INJECTION DIESEL
ENGINE
Analysis of the composition of particulate matter shows
that it consists of insoluble organic fraction (IOF) and
the soluble organic fraction(SOF).
The IOF consists mainly of carbon soot, measured as
diesel black smoke, while the SOF represents relatively
low molecular weight organic substances whichoriginate from unburnt or partially burnt fuel and
lubricants.
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The SOF particulates is the result of low temperature
which results from light load engine operation.
The IOF is the result of mostly carbon. The quantity isa function of engine load (the amount of fuel supplied
to the engine).
In a swirling direct injection Diesel Engine thecombustion occurs, in the early stages at least in three
distinct modes due to the fact that the fuel is present in
fully vapourized, droplet and un-atomized liquid(on thechamber wall) forms.
High-speed combustion photography, laser shadow-
graphy with narrow band pass filter and in-cylinder
sam lin techni ues are used. 16
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Total particulate was lowest at about or 2/4 load, drysoot increased with the load, while SOF decreased as
the load increased.
It follows consequently that the total particulate is high
at 4/4 load because of a large dry soot emission.
Thus, dry soot and SOF were generally opposite to
each other, and a greater contribution to total
particulate was made by SOF at Light load and dry
soot at High load.
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RESULTS
The particulate density results from the three combustion
regimes show that the fully evaporated combustion gives
peak values of4 g/ml, the droplet condition 17.5 g/ml and
the off-the-wall condition 7.8 g/ml. Off-the-wall results at a second sampling point gave peak
values of17.6 g/ml which may indicate that there is
considerable variability but as the position is much nearer the
spray tip than previous, the result is probably higher eitherbecause the products of droplet burning were being sampled
or as a result of local differences in A/F ratio.
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The results clearly demonstrate that the particulatesformed from the burning of pre-mixed evaporated fuel
are at a much lower level than those formed during the
other combustion regimes.
Also there is a clear trend for both smoke and
particulates to reduce with injection timing advance in a
D.I. Engine.
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Fuel burning from droplets and off-the-wall conditionsproduce much higher levels of particulate than the fuel
burning from fully evaporated conditions.
Instantaneous particulate concentrations peak at levels
in excess of16 g/ml whereas typical tail pipe levels
are 0.25 g/ml, indicating that the particulates are
formed in the cylinder rather than the exhaust systems.
Reductions in peak particulate and tail pipe values may
be achieved by improving the atomization of the fuel
spray.
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REFERENCES:
Norris-Jones, S.R., et al.: A Study of the formation of
particulates in the Cylinder of a Direct Injection DieselEngine SAE Paper No. 840419, 1984.
Masatoshi Shimoda: Observation of the particulate
Formation Process in the cylinder of a direct injection Diesel
Engine SAE Paper No. 870268, 1988. H.Hiroyasu: Soot formation and Oxidation in Diesel
Engines SAE Paper No.800252, 1981.
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THANK YOU!!!!!
QUESTIONS?
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