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*Corresponding author. Present address: Renault - 66123
- CTL L26 1 46, 1, AlleHe Cornuel, F - 91510 Lardy, France. Tel.:
#331-69-27-84-87; fax:#331-69-27-00-49.
E-mail address: [email protected] (E. Zervas).
Atmospheric Environment 35 (2001) 1301}1306
Emission of speci"c pollutants from a compressionignition engine. In#uence of fuel hydrotreatment and fuel/air
equivalence ratio
E. Zervas*, X. Montagne, J. Lahaye
Institut Franc7 ais du Pe&trole, 1 et 4 avenue du Bois Pre&au, F-92500 Rueil-Malmaison cedex, France
Institut de Chimie des Surfaces et Interfaces, 15 rue Jean Starcky, F-68057 Mulhouse cedex, France
Received 19 April 2000; received in revised form 17 July 2000; accepted 20 July 2000
Abstract
A compression ignition engine is used for the study of the fuel (one reference and one hydrotreated) and the fuel/air
equivalence ratio in#uence on the exhaust emissions of speci"c pollutants. Under the experimental conditions used, seven
hydrocarbons, nine aldehydes and three organic acids are detected in the exhaust gas. No alcohols are detected under
these conditions, indicating that these compounds are emitted only if they (or probably other oxygenated compounds)
are introduced in the fuel. Fuel hydrotreatment decreases most of the exhaust pollutants, the four toxics and also the
quantity of the ozone that could be formed from the exhaust gas. It also changes the composition of exhaust gas: it
increases the proportion of methane, benzene, formaldehyde, acetaldehyde, acroleine, and propionic acid, while it
decreases the proportion of all other pollutants detected. Fuel/air equivalence ratio also decreases most of the exhaust
emissions, the emission of the total toxics and the quantity of the ozone that could be formed. It also changes the
proportion of each pollutant in exhaust gas: the percentages of methane, benzene, acetone and acetic acid increase, whilethose of the other pollutants detected decrease. The majority of the speci"c pollutants detected corresponds to organic
acids, followed by hydrocarbons and aldehydes. 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Aldehydes; Compression ignition engines; Hydrocarbons; Organic acids; Ozone
1. Introduction
Since 1 January 2000, the Euro3 emission regulations are
applied in new vehicles of EU member states. These regula-
tions divide almost by two the limits of CI engines for thefour regulated pollutants (CO, NO
V, NO
V#HC, PM).
Although these regulations concern total HC exhaust emis-
sions, all exhaust individual hydrocarbons do not have the
same ozone forming potential or the same e!ects on the
human health; benzene and 1,3 butadiene are known
as toxic pollutants. The study of individual hydrocarbons
exhaust emissions are sometimes necessary to complete
information about total hydrocarbons exhaust emissions.
Aldehydes and ketones are believed to contribute
to the characteristic smell of CI engines exhaust gas, to
participate in the formation of atmospheric ozone, andtwo of them (formaldehyde and acetaldehyde) are known
as toxic pollutants. Some articles present the in#uence of
the fuel and the engine running conditions on the emis-
sions of these pollutants (Bertoli et al., 1993; Montagne et
al., 1991) and others study their atmospheric distribution
(Anderson et al., 1996; Possanzini et al., 1996 and many
others).
Alcohols and other oxygenates are usually added to
the fuel to decrease CO, NOV
and particulate matter
emissions, but they can increase the emission of formal-
dehyde or decrease those of the other aldehydes (Lipari
and Swarin, 1982; Liotta and Montalvo, 1993).
1352-2310/01/$- see front matter 2001 Elsevier Science Ltd. All rights reserved.
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Table 1
Engine and running conditions used
Engine
Type Peugeot XUD9
Prechamber Ricardo Comet V
Cylinders 4Displacement (cm) 1905
Bore (mm) 83
Stroke (mm) 88
Compression ratio 23 : 1
Injection pump BOSCH VER272 type 520
Opening pressure (bar) 130
Running conditions
Engine speed (RPM) and BMEP 2500, 8
Torque (N m) 21
Injection timing 63 BTDC
Coolant temperature (K) 358
Lubri"ant temperature (K) 368
Intake air temperature (K) 313Intake air pressure (bar) 0.993
Fuel/air equivalence ratio 0.24}0.50
Table 2
Main characteristics of the fuels used
Fuel SR HDT2
Density at 288 K (kg m\) 837.2 832.3
Cin. viscosity at 293 K (mm s\) 5.60 5.56
Distillation (3C)
Initial point 482 473
5% 513 508
95% 610 603
Final point 626 621
Chemical analysis (wt%)
Para$ns 46.1 47.5
Naphtenes 32 33.4
Non cond. Naphtenes 22.5 22.3
Condensed Naphtenes 9.5 11.1
Aromatics 21.9 19.1
Mono-aromatics 12.1 16.1
Di-aromatics 9.3 2.9
Tri-aromatics 0.3 0.1
Sulphured aromatics 0.2 *
Sulphur 0.055 0.047
Cetane number 53.8 56
Organic acids are also found in the exhaust gas. They
contribute to acid rain formation (Lawrence and Kou-
trakis, 1994), and many articles study the formation and
reactions of atmospheric organic acids (Chebbi and
Carlier, 1996; Lawrence and Koutrakis, 1994; Souza
et al., 1999 and many others). Some authors study the
exhaust emissions of these pollutants (Kawamura et al.(1985) for a comparison between atmospheric, engine oil
and exhaust gas acids, Kawamura and Kaplan (1987) for
the dicarboxylic organic acids emissions from compres-
sion ignition engines, Zervas et al. (1999a) for the correla-
tions between gasoline composition and exhaust acids
emissions from an SI engine, and Zervas and Tazerout
(2000) for the emission of formic acid from a natural gas
feed SI engine).
Fuel and engine operating conditions in#uence
the speci"c pollutants emissions and their control can
help to decrease the engine out and tailpipe emissions.
This work presents the emission of individual hydrocar-bons, aldehydes, alcohols and organic acids from a
compression ignition engine fed with two di!erent fuels
(a commercial and an hydrotreated one). The in#uence
of the fuel and the fuel/air equivalence ratio on the
emission of these pollutants, on the emission of total
toxics and on the ozone forming potential is presented
and discussed.
2. Experimental section
2.1. Engine and fuels used
The engine used in this work is a PSA XUD9 four-
stroke cycle Diesel Engine. Table 1 presents the main
characteristics of this engine and the experiment running
conditions. Due to low emissions, every experimental
point is doubled and the average value of each pollutant
is taken into account. Table 2 presents the main charac-
teristics of the two fuels used, the reference (SR) and the
hydrotreated (HDT2).
2.2. Exhaust gas analysis
The analysed exhaust gas components are: CO andCO
using nondispersive IR, O
using paramagnetism
and total hydrocarbons by FID. Particulate matter is
collected on a "lter and a balance determines the total
mass. The individual hydrocarbons are analysed on line
by GC/FID. Alcohols are collected in deionised water
and analysed by GC/FID, following the procedure de-
scribed by Siegel et al. (1993) and Smith (1985). Al-
dehydes and ketones are collected in an acidi"ed DNPH
solution and analysed by HPLC/UV, following the pro-
cedure described by Lipari and Swarin (1982) and
Smith (1985). Organic acids are collected in deionised
water and analysed by two methods: ionic chromatogra-
phy/conductimetric detection for the analysis of
formic acid and GC/FID for the analysis of the heavier
acids, following the procedure presented elsewhere
(Zervas et al., 1999b). More details about these
analytical methods can be found elsewhere (Zervas et al.,
1999a, b).
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Fig. 1. In#uence of fuel/air equivalence ratio and fuel on CO
,
CO, HC and PM emissions.
2.3. Repeatability tests
Five identical tests are performed using the SR fuel at
the fuel/equivalence ratio of 0.5 to evaluate the repeata-
bility of engine and of analytical methods.
3. Results and discussion
3.1. Analysis
The following compounds are detected without inter-
ference in the exhaust gas: seven hydrocarbons: methane,
ethylene, propylene, acetylene, 1-butene, 1,3-butadiene
and benzene; ten aldehydes: formaldehyde, acetaldehyde,
acroleine, acetone, propionaldehyde, crotonaldehyde,
methacroleine, butyraldehyde#methylethylketone and
benzaldehyde (the column used cannot separate methyl-
ethylketone and n-butyraldehyde); no alcohol, even fora collection time of 2 h, indicating that these compounds
are emitted only if they are introduced in the fuel (or
probably after the introduction of an oxygenate com-
pound in the fuel); three organic acids: formic, acetic and
propionic acid.
3.2. Repeatability tests
The relative standard deviation of the "ve identical
tests is less than 2% for the CO and CO
emission, 6%
for the particulate matter, from 6 to 12% for the detected
individual hydrocarbons and from 5 to 20% for thealdehydes and organic acids presented here (the heavy
aldehydes show more dispersion due to low concentra-
tion). In these tests, su$cient duration is used for the
aldehydes and organic acids collection, to avoid higher
dispersions due to low quantities collected.
3.3. Emissions of regulated pollutants
Fig. 1 presents the emissions of CO, CO
, total HC
and particulate matter as a function of fuel and fuel/air
equivalence ratio used. Fuel/air equivalence ratio (in the
range 0.24}0.5) increases the emission of CO , becauseof the increased fuel consumption, and the emission of
particulate matter, due to increased fuel injected; the
emissions of HC and CO decrease due to the decrease of
ignition delay (Heywood, 1988; Stone, 1992). Hydro-
genated fuel decreases all these emissions (Bertoli et al.,
1993; Martin and Bigeard, 1992; Montagne, 1991;
Ullman, 1989). Our tests show a decrease of 3}7% for
the CO
, 6}18% for the CO, 15}22% for the total HC
and 7}13% for the particulate matter. All results present-
ed in Fig. 1 are in accordance with those reported in
literature and help to validate those of the speci"c pollu-
tants.
3.4. Emission of individual hydrocarbons
The seven individual hydrocarbons detected in
the exhaust gas are in quite low concentrations: meth-
ane: 2}4.6 ppmv, ethylene: 1.2}5.1ppmv, acetylene:
0.4}1.2 ppmv, propylene: 0.2}0.8 ppmv, 1-butene:
0}0.13 ppmv, 1,3 butadiene: 0.07}0.27ppmv, benzene:
0.07}0.17ppmv. Exhaust hydrocarbons represent only
24}39% (depending on the fuel and fuel/air equivalence
ratio) of the total speci"c pollutants detected (HC, al-
dehydes, organic acids).
All individual hydrocarbons decrease with fuel/air
equivalence ratio, as total HC do. Fuel hydrotreatment
also decreases the emissions of individual hydrocarbons
up to 30% (depending on the hydrocarbon and the
fuel/air equivalence ratio) compared to the reference fuel.
One hydrocarbon, 1-butene, which is detected in the
exhaust gas of the reference fuel in concentrations of
0.05}0.13ppmv, is below the detection limits in the
exhaust gas of the hydrotreated one.
The use of a hydrogenated fuel decreases the HC
emissions, it also changes their distribution. Fig. 2 pres-
ents the percentage of four hydrocarbons (expressed asppmC of each hydrocarbon over the ppmC of the total
emitted HC): the two major ones, methane and ethylene
(which represent more than the half of total hydrocar-
bons), and the two toxic ones, 1,3-butadiene and benzene,
as a function of the fuel and the fuel/air equivalence ratio
used. Fuel/air equivalence ratio increases the percentage
of methane and benzene in total exhaust hydrocarbons
decreasing that of all the other hydrocarbons detected.
This is explained by the increasing temperature of the
higher fuel/air equivalence ratios and the higher resist-
ance of methane and benzene to oxidation than the other
exhaust hydrocarbons. The hydrotreated fuel produces
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Fig. 2. In#uence of fuel/air equivalence ratio and fuel on thepercentage of methane, ethylene, 1,3 butadiene and benzene
(based on the total number of carbons).
Fig. 3. Emission of formaldehyde, acetaldehyde, acetone andacroleine. In#uence of fuel/air equivalence ratio and fuel on
exhaust emissions and percentage of each aldehyde over the
total aldehydes emission.
the same e!ect: an increase of methane and benzene
proportion and a decrease of all the others. This phenom-
enon indicates that fuel hydrotreatment favours the oxi-
dation of hydrocarbons (this is also the reason for the
decrease of total HC emissions), but the hydrotreated fuel
exhaust gas is relatively composed more of toxic com-
pounds (benzene) or more di$cult to treat with a cata-
lytic converter (methane). It must be noted that even the
percentages of methane and benzene in total exhaust HC
of the hydrotreated fuel are increased, the total methane
and benzene emissions of this fuel decreased compared to
those of the reference one.
3.5. Emission of aldehydes and ketones
Fig. 3 presents the in#uence of fuel/air equivalence
ratio on the emission of the four most important
aldehydes (the others are found in exhaust gas in concen-
tration below 0.1 ppmv), where it is shown that most of
these pollutants concentration decreases with fuel/air
equivalence ratio (within the limits of 0.24 to 0.5), exceptthat of acetone that increases (only in the case of the
reference fuel, this pollutant is not detected in the case of
the hydroteated one). The in#uence of fuel/air equiva-
lence ratio is a complex phenomenon: the formation of
aldehydes from hydrocarbons and their further oxidation
depend on the species in the combustion chamber, the
temperature and the time spent under these conditions;
these factors in#uence their "nal concentration in
exhaust gas.
Fuel hydrotreatment decreases the exhaust aldehydes
(Bertoli et al., 1993), up to 80% in our study. The concen-
tration of some aldehydes (acetone and propionaldehyde)
is found below the detection limits in the case of the
HDT2 fuel.
Fuel/air equivalence ratio decreases the percentage of
most aldehydes in exhaust gases except acetone and
propionaldehyde for the SR fuel and crotonaldehyde and
methacroleine for the HDT2 one. On the other hand, fuel
hydrotreatment increases the proportion of formalde-
hyde, acetaldehyde (the two toxics), and also that of
acroleine, methacroleine and crotonaldehyde, while it
decreases the percentage of the others. Fig. 3 presents
also the proportion of formaldehyde, acetaldehyde,
acetone and acroleine. The other aldehydes detected are
not presented in this "gure because their points are very
scattered due to low emissions.
Exhaust aldehydes represent 8}16% of the total speci-
"c pollutants detected. This corresponds to one-third to
half of the hydrocarbons quantity.
3.6. Emission of organic acids
The exhaust concentration of organic acids decreases
with fuel/air equivalence ratio (Fig. 4). A correlation
between the exhaust concentration of organic acids and
exhaust temperature and oxygen concentration is
already reported in the case of spark ignition engines
or burner experiments (Zervas et al., 1999a, b; Zervas and
Tazerout, 2000). The exhaust concentration of these
pollutants increases with the concentration of exhaust
oxygen and the decrease in exhaust temperature. As
exhaust temperature and oxygen concentration decreases
with fuel/air equivalence ratio, these results are con-
"rmed in the case of a CI engine exhaust gas (Fig. 5).
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Fig. 4. Emission of formic, acetic and propionic acid. In#uenceof fuel/air equivalence ratio and fuel on exhaust emissions and
percentage of each acid over the total acids emissions.
Fig. 5. In#uence of exhaust temperature and oxygen on the
formic, acetic and propionic acid exhaust emissions.
Fig. 6. Total toxics and quantity of ozone could be formed bythe exhaust of the two fuels as a function of the fuel/air equiva-
lence ratio.
Fuel hydrotreatment decreases the concentration offormic and acetic acids but increases that of the propionic
one. This con"rms that aromatic hydrocarbons are dir-
ectly responsible for the propionic acid formation
(Zervas et al., 1999a); the hydrotreated fuel contains
about 4% more monoaromatics (16.1% instead of 12.1%
for the SR fuel) and produces 30}100% more propionic
acid.
Fuel/air equivalence ratio increases the proportion of
acetic acid, while it decreases that of the other two,
indicating that formic and propionic acids are more
sensitive to the variations of exhaust temperature and
oxygen concentration than acetic acid. As hydrotreated
fuel increases the emissions of propionic acid, it also
increases its percentage, while it decreases those of formic
and acetic acids (Fig. 4). This last result comes from the
increased content of aromatics of the hydrotreated fuel.
Exhaust organic acids represent more than half of the
total speci"c pollutants detected (53}60%, mainly com-
posed from acetic acid). This high percentage indicates
that organic acids are probably not formed during the
combustion process, but after the oxidation of other
products during the cooling phase of exhaust gas.
3.7. Emissions of toxic pollutants and ozone-forming
potential
Fig. 6 presents the total emission of the four toxic
pollutants (benzene, 1,3-butadiene, formaldehyde and
acetaldehyde) for both fuels as a function of the fuel/air
equivalence ratio. One can see that total toxics concen-
tration decreases with fuel hydrotreatment and with
fuel/air equivalence ratio.
The ozone quantity that could be formed from the
exhaust gas of the reference and hydrotreated fuel, forevery fuel/air equivalence ratio studied, is also presented
in the Fig. 6. This quantity decreases with the fuel/air
equivalence ratio as the unburned hydrocarbons' emis-
sions decrease. Fuel hydrotreatment has also a bene"t
e!ect, as this fuel decreases most of the exhaust gas
pollutants.
4. Conclusions
No alcohols are detected in the exhaust gas under
the experimental conditions used, indicating that these
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compounds are emitted only if an oxygenated compound
is introduced in the fuel.
Fuel/air equivalence ratio decreases the hydrocarbons,
most of the aldehydes and organic acids exhaust emis-
sions. It also decreases the total emissions of toxics and
the quantity of ozone that could be formed. The propor-
tion of each pollutant in exhaust gas changes with fuel/airequivalence ratio: those of methane and benzene increase
while that of the other HC decreases; those of acetone
and acetic acid increase while those of the other
aldehydes and organic acids decrease.
Fuel hydrotreatment decreases most of the exhaust
pollutants, the total emissions of toxic pollutants and
also the quantity of the ozone that could be formed.
More precisely, it decreases all hydrocarbons, aldehydes
(except methacroleine) and organic acids' (except
propionic acid) exhaust emissions. It also changes the
composition of exhaust gas: in the case of hydrocarbons,
it increases the percentage of methane and benzene, in thecase of aldehydes, that of formaldehyde, acetaldehyde
and acroleine, and in the case of organic acids, that of
propionic acid, while it decreases the percentage of all the
other detected pollutants.
The majority of the emissions of the speci"c pollutants
detected corresponds to organic acids (53}60%), fol-
lowed by HC (24}39%) and aldehydes (8}16%).
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