2001 environ. sci. technol. zervas e. c1 c5 organic acid emissions from an si engine influence of...

7/30/2019 2001 Environ. Sci. Technol. Zervas E. C1 C5 Organic Acid Emissions From an SI Engine Influence of Fuel and Air Fu

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C1-C5 Organic Acid Emissions froman SI Engine: Influence of Fuel andAir/Fuel Equivalence Ratio

E . Z E R V A S , * , , X . M O N T A G N E , A N D

J . L A H A Y E

Institut Francais du Petrole, 1 et 4 avenue du Bois Preau,F - 92500 Rueil-Malmaison Cedex, France and Institut deChimie des Surfaces et Interfaces, 15 rue Jean Starcky,F - 68057 Mulhouse Cedex, France

A spark ignition engine is used to study the impact of fuelcomposition and of the air/fuel equivalence ratio onexhaust emissions of organic acids. Fuel blends arecomposed from eight hydrocarbons (n-hexane, 1-hexene,cyclohexane, n-octane, 2,2,4-trimethylpentane, toluene,o-xylene,andethylbenzene)andfour oxygenatedcompounds(methanol, ethanol, 2-propanol, and MTBE). Exhaustformic acid is slightly enhanced from aromatics andoxygenated compounds; acetic acid is slightly enhancedfromthe oxygenated fuel components;propionic acid comesfromfuel aromatic compounds, and butyric acid originatesfrom fuel o-xylene. Acrylic and isovaleric acids arealso detected in lower concentrations. It is unlikely thatoxygenated compounds are precursors to the formation oforganic acids, but they facilitate their formation becausetheyfacilitatethe oxidationof other fuelcomponents. Exhaustconcentration of formic acid is also related to exhaustoxygen and exhaust temperature. Air/fuel equivalence ratioincreases the exhaust concentration of formic, aceticacid (for the fuels without oxygenated compounds), andacrylic acid and decreases the concentration of isovalericacid. The acetic (for the oxygenated fuels), propionic,and butyric acids are at a maximum at stoichiometry.

In t roduct ion

Correlations between fuel composition and exhaust emis-sions from SI engines have been extensively researched forthe case of regulated pollutants (refs 1-4and many others).However, exhaust gas contains a number of specific pol-lutants, such as aldehydes, alcohols, and organic acids, thathave thus far not been thoroughly investigated.

Organic acids contribute to acid rain formation (5, 6),and many articles describe their distribution and reactions

in urban,rural, andmarine atmospheres(6-14). Atmosphericorganic acids come from many sources, natural or anthro-pogenic (7), and one of which is exhaust emissions (14, 15).Few articles report the emission of these compounds frominternalcombustionengines (15-19) or fromthe combustionof propane on a flat burner (20).

Thispaper presentsthe influence of gasolinecompositionon theemissionsof organicacidsfrom a spark ignition engine.Specific fuel blends, containing hydrocarbons and oxygen-ated compounds, and a commercial fuel are used for thisstudy. Exhaust organic acids are measured using specificanalytical methods. As lean conditions are currently in usein commercial SI engines, the influence of the air/fuel

equivalence ratio (

) is also studied. Relations betweenexhaust organic acidsand fuelparametersand otherexhaustcompounds arealsoresearched.On thebasis of theobtainedresults, some likelyformation paths of these compoundsareproposed.

Experimental SectionEngine and Operating Conditions. A CFR spark ignitionengine (a small experimental monocylinder engine withdisplacement: 6.11 10-4 m3, bore: 0.08255 m, and stroke:0.1143 m) is used for these tests. This type of engine is usedto determine thefuelsoctane numberand usuallyruns undertwo speeds: 10 and 15 Hz (600 and 900 min-1). The air/fuelequivalence ratio used is from 0.83 to 1.25. For these tests,all other engine parameters are kept constant [speed ) 15

Hz, compression ratio)

6:1, indicated mean effectivepressure (IMEP) ) 4.5 105 Pa]. As the subject of this workis to find the correlation between fuel composition andexhaust organic acids,no catalyticconverter is used forthesetests.

Fuels Used. Two fuel matrixes are adopted in this study:the first matrix (called ,synthetic fuels matrix.) containseight representative hydrocarbons: n-hexane, 1-hexene,cyclohexane, n-octane, 2,2,4-trimethylpentane, toluene, o-xylene, and ethylbenzene; the second matrix (called ,oxy-genated fuels matrix.) also contains four oxygenatedcompounds: methanol, ethanol, 2-propanol, and MTBE.Small quantities of benzene (between 0.53 and 0.66%) arealso present in all fuels tested.

An experimental design was used to determine thequantity of each component in the blend of ,synthetic

fuels.. Toavoidverydisperse physicalproperties of thefuelsused, an alkylate (containing basically isooctane) was usedas the base fuel for these blends. Fuel R (the reference fuel),contains an equal content of each of the eight compoundsand is the central point of the experimental matrix. Eachother fuel contains 42% of a major component. Thesematrixes allows one to compare directly each fuel with thereference fuel; if the exhaust concentration of a pollutant isgreater than in thecase of thereferencefuel,one candeducethat themajor component of thisfuel enhancesthe formationof the pollutant in question.

The,oxygenated.matrix was obtained by the additionof 5 or 20% of one of the four oxygenated compounds to thefuel R. Two other fuels were also used. The first fuel, i8, ispure2,2,4-trimethylpentane, andthe second,i8T, is a mixture

of 80% 2,2,4-trimethylpentane and20% toluene. These fuelsallow one to study the addition of an aromatic componentto an alkylate basis. Finally, a commercial gasoline was alsotested.

The chemical composition and the research octanenumber (RON) of each fuel is presented in Tables 1 and 2.More details about these fuels (distillation characteristics)may be found elsewhere (17).

Analysis of Exhaust Gas. Carbon monoxide and carbondioxide were analyzed by nondispersive infrared, nitrogenoxides were analyzed by chemiluminescence, and totalunburnedhydrocarbonswere analyzedby a flame ionizationdetector (FID). Exhaust individual HC, aldehydes, and

* Corresponding author phone: 331-69-27-84-77; fax: 331-69-27-00-49; e-mail: [email protected].

Institut Francais du Petrole. Institut de Chimie des Surfaces et Interfaces. Present Address: Renault - 66123 - CTL L26 0 60, 1, Allee

Cornuel, F - 91510 Lardy, France. E-mail: [email protected]; tel: 331-69 27 84 77; fax: 331-69 27 00 49.

10.1021/es000237v CCC: $20.00 xxxx A meri can Chemical S ociety VOL. xx, N O. xx, xxxx / EN VIRON . S CI. & TECHN OL. 9 APAGE EST: 5.4Published on Web 00/00/0000


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alcohols were also measured, but these results will bepresented in a following article.

Organic acids were collected by passing a sample of rawexhaust gas through two impingersin series, eachcontaining20 mL of deionized water. Typical collection times areapproximately 20 min. The collection efficiency of thismethod is over 90%. The final solution was analyzed by twomethods: ionic chromatography for the analysis of formicacid, and gas chromatography for the analysis of heavieracids. More details about this method can be found in theliterature (20). A standard solution containing 12 organicacids [formic (methanoic), acetic (ethanoic), propionic

(propanoic), acrylic (2-propenoic acid), isobutyric (iso-butanoic), butyric (butanoic), isovaleric (isopentanoic), va-leric (pentanoic), isocaproic (iso-hexanoic), caproic (hex-anoic),heptanoic, andbenzoic] wereused forchromatographcalibration and for the identification of each acid. Six acids:formic, acetic,propionic, acrylic,butyric, andisovaleric,werefound in the exhaust gas in detectable concentrations.

Repeatability Tests. At each air/fuel equivalence ratio,five identical points of the fuel R were used to evaluate therepeatability of the engine and the analytical methods used.All other tests were repeated, and average values were used.The relative standard deviation of the concentration of theregulatedpollutantswas foundto be less than 1%.This valueis below 12% for most of the organic acids detected, but itreaches 20-30% for the propionic and butyric acid at high

.

Results and DiscussionEmission of Regulated Pollutants. The results of theregulated pollutants at stoichiometry show that

(i) CO is increased by the increasing aromatic content inthe fuel, and decreased by the increasing content of hexane,1-hexene, isooctane, and oxygenates.

(ii)HC is increasedby theincreasing contentof aromatics,and decreased by the increasing content of 1-hexene,cyclohexane, and oxygenates.

(iii) NOxis increasedby theincreasing content of hexane,toluene, and ETB, and decreased by the increasing contentof 1-hexene and the addition of oxygenates. The four fuelscontaining low levels of oxygenates decrease NOxemissionsby a larger amount than do the fuels containing high levelsof oxygenates.

Ourresultsare in accordance withthese alreadypresentedin the literature (1-4), and these findings help to validatetheresults of organicacids.The influence of on theregulatedemissions are also in accordance with the literature and asare already well-known, they are not presented here.

Emissions of Organic Acids. F o r m i c a c i d . The bottomgraph of Figure 1 shows that, at stoichiometry, all fuelsproduce comparable concentrations of formic acid, witharomatics, oxygenated compounds, and octane slightlyenhancingthe formationof this compound.The comparisonbetween i8 and i8T fuel (pure isooctane and 80% isooctane/

20% toluene) shows that toluene enhances the formation ofexhaust formic acidmorethanisooctane does (also confirmedfrom the comparison between S5 and S6 fuels, with respec-tively 42% isooctane and toluene). Oxygenated compoundsenhance the formation of formic acid either because theyproduce more precursors of this acid, or because theyfacilitate theformation of theformic acid precursorscomingfrom hydrocarbons. Commercial fuel produces about thesame quantity of formic acid as does the R fuel.

The exhaust concentration of formic acid increases with for allfuelstested(somerepresentative fuels arepresentedin the upper curves of Figure 1), indicating that an excess ofoxygen enhances the formation of this acid. A linearcorrelation, but with high dispersion, between the exhaustoxygen concentration and exhaust formic acid is presented

in the left graph of Figure 2. The decrease of exhaust formicacid concentration at rich conditions, must be due to thepreferable formation of CO. Apparently, it is difficult for amolecule with two atoms of oxygen, as formic acid, to keepboth these atoms at rich conditions, and subsequently anoxidation to CO which is a more stable product occurs. Norelationship between exhaust formic acid and CO concen-tration was found.

Figure2 also shows that theexhaust concentration of thisacid is linked with exhaust temperature (as already reportedin the case of a burner, a natural gas fed SI engine and a CIengine,refs 18-20). Exhaustformicacid is linear withexhausttemperaturefor leanconditionsand stoichiometry. Moreover,when this temperature is low, exhaust formic acid concen-tration is high, indicatingthat thisacid is probably notformed

duringthe combustion processbut duringthe cooling phaseof the exhaust gas, where formic acid comes from theoxidationof other products. Thehigher thetemperature, thefaster the formic acid is decomposed to other products andits concentration decreases. The exhaust concentration ofthis acid is quite independent of temperature at richconditions.

It is likely that formic acid is a product of formaldehydeoxidationas this aldehyde emissionis also linkedwith exhausttemperature (21), but no direct link is found betweenformaldehyde and formic acid exhaust concentration. Norelationship between formic acid and fuel H/C ratio, otherphysical properties of the fuel (octane number, distillationcurve...) or the exhaust concentration of other compounds(CO, CO2, NOx, individualHC, aldehydes,other organicacids)are found. As formic acid is a light compound, it must havemultiple sources not directly linked to the initial fuel

TABLE 1. Fi rs t Fuel Matr ix Synthet ic Fuels (% vol contents)

S1 S2 S3 S4 S5 S6 S7 S8 R

hexane 42 2 2 2 2 2 2 2 71-hexene 2 42 2 2 2 2 2 2 7cyclohexane 2 2 42 2 2 2 2 2 7n-octane 2 2 2 42 2 2 2 2 7isooctane 2 2 2 2 42 2 2 2 7toluene 2 2 2 2 2 42 2 2 7o-xylene 2 2 2 2 2 2 42 2 7ethylbenzene 2 2 2 2 2 2 2 42 7alkylate 44 44 44 44 44 44 44 44 44RON 63.7 83.7 88.7 43.6 93.8 101.3 96.6 100 85.2

TABLE 2. Second Fuel Matrix Oxygenated Fuels (% vol contents)

O1 O2 O3 O4 O5 O6 O7 O8

methanol 5 0 0 0 20 0 0 0ethanol 0 5 0 0 0 20 0 02-propanol 0 0 5 0 0 0 20 0MTBE 0 0 0 5 0 0 0 20fuel R 95 95 95 95 80 80 80 80oxygen (% weight) 3.08 1.98 1.45 0.90 11.89 7.75 5.72 3.60RON 89.4 90.4 87.5 86.8 98.6 97.4 96.6 93.1

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composition. Exhaust oxygen and temperature seems to bemore importantto the formation of this acid than initial fuelcomposition.

No detailed mechanism, based on these results, can beproposed for the formation of formic acid. However, theaddition of an OH radical to an oxygenated C1 radical seemsto be the more probable path to the formation of this acid.Concerning the use of a 3-way catalyst, no detailed data arecurrentlyavailable; from our experience, tail pipe emissions

of formic acid are expected to be higher than the engine outemissions dueto oxidation of other productsin theconverter.

Acetic Acid. Figure3 shows that,at stoichiometry, allfuelsproduce comparative amounts of acetic acid, with fuelcyclohexane, ethanol, and 2-propanol slightly enhancing its

formation. These two oxygenated compounds enhance theformation of this acid probably because they produce moreC2 radicals, or they facilitate the formation of acetic acidprecursors deriving from hydrocarbons. A comparisonbetween i8 and i8T (and also S5 and S6) fuels shows thattoluene enhances the formation of acetic acid over that ofisooctane, but toluene is not one of the major precursors ofthis compound.Commercial fuel produces a little less aceticacid than fuel R.

Air/fuel equivalence ratio increases the exhaust aceticacid in the case of,synthetic. fuels (Figure 3, upper leftcurve). The reasons mustbe the sameas inthecaseof formicacid: excess of exhaust oxygen enhances the formation ofacetic acid at lean conditions and CO formation decreasesitsformation whenrich,butthe introductionof anoxygenatedcompound modifies the shape of these curves at leanconditions; a maximum value at stoichiometry is nowobserved. Two hypothesis can be proposed for this phe-nomenon:

(i) Exhaust temperature has a greater influence thanexhaust oxygen for the formation of acetic acid in the caseof ,oxygenated. fuels. The introduction of oxygenatedcompounds in the fuel modifies the composition of exhaustgas. The precursors of acetic acid originating from ,oxygen-ated. fuels are different than those that come from the,synthetic. fuels, and they probably need a higher tem-perature for their oxidation to acetic acid. As this highertemperatureoccurs at stoichiometry, the,oxygenated. fuelspresent a maximum of the exhaust acetic acid at this .

FIGURE 1. Emissions offormic acid. Bottomgraph: fuel effect atstoichiometry. Mean: mean exhaust concentration; min, max:

minimumandmaximumconcentration fora confidence region of95%.S1)42%hexane,S2)42%1-hexene,S3)42%cyclohexane,S4) 42% octane, S5) 42% isooctane, S6) 42% toluene, S7)42%o-xylene, S8) 42%ethylbenzene, R) reference fuel, O1)5% methanol, O2) 5% ethanol, O3) 5% 2-propanol, O4) 5%MTBE,O5)20%methanol,O6)20%ethanol,O7)20%2-propanol,O8)20%MTBE,i8) pureisooctane,i8T) 80%isooctane+ 20%toluene, C) commercial fuel. Upper curves: effect for somerepresentative fuels.

FIGURE 2. Exhaust concentration of formic acid versus exhaustoxygen (leftgraph)and exhaust temperature (right graph)for allexperimental points used.

FIGURE 3. Emissions ofacetic acid. Bottomgraph: fuel effect atstoichiometry. Mean: mean exhaust concentration; min, max:

minimumandmaximumconcentration for a confidenceregion of95%.S1)42%hexane,S2)42%1-hexene,S3)42%cyclohexane,S4) 42% octane, S5) 42% isooctane, S6) 42% toluene, S7)42%o-xylene, S8) 42%ethylbenzene, R) reference fuel, O1)5% methanol, O2) 5% ethanol, O3) 5% 2-propanol, O4) 5%MTBE,,O5)20%methanol,O6)20%ethanol,O7)20%2-propanol,O8)20%MTBE, i8) pureisooctane,i8T) 80%isooctane+ 20%toluene, C) commercial fuel. Upper curves: effect for somerepresentativefuels(,synthetic. ontheleftand,oxygenated.onthe right).

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(ii) The precursors of acetic acid coming from ,oxygen-ated. fuels arerapidly oxidized to other products dueto theexcess of oxygen at lean conditions.

Our results cannot, for the moment, prove which is thecorrect hypothesis. No relationship between the exhaust

concentration of acetic acid and exhaust concentration ofoxygen or other compounds, exhaust temperature, H/C fuelratio, or other physicalproperties of thefuel havebeen found.On the basis of these results, no detailed mechanism can beproposed for the formation of acetic acid. However, theaddition of an OH radical to an oxygenated C2 radical seemsto be the more probable path to the formation of this acid.No detailed data are currently available for the tail pipeemissions of acetic acid, but, as formic acid, it is expectedthat tail pipe emissions of acetic acid are higher than theengine out emissions due to oxidation of other products inthe converter.

Propionic Acid. The bottom graph of Figure 4 shows thatpropionic acid is clearly produced from fuel aromatics.Kawamura (15) noticed that fuel aromatics enhance theformation of dicarboxylic acids, and Zervas (19) reports thatin the case of a CI engine, a hydrotreated fuel, containingmoremonoaromatics thana non-hydrotreated one,enhancesthe formation of propionic acid. To a lesser extent, ethanoland 2-propanol added at 5% in the fuel (fuels O2 and O3)also enhance its formation, probably because they facilitatethe oxidation of aromatics or they enhance the formation ofthe C3 radicals, as can be the case for 2-propanol. Thecomparison betweeni8 andi8T fuels show the participationof toluene to the formation of this acid; pure isooctaneproduces minimal concentrations of propionic acid incomparison to the isooctane/toluene fuel. As the aromaticscontent of the commercial fuel is higher than that of fuel R,the former produces more propionic acid than the latter.

The maximum exhaust concentration of this acid occursat stoichiometry (Figure 4, upper curves). The hypothesisdescribed previously for the influence of on the acetic acidemissions is also valid in the case of propionic acid: theformation of CO decreases its formation at rich conditions;in the case of lean conditions, the precursors of thiscompound require an increased temperature for theirformation, or the excess of oxygen oxidizes them.

No correlation between the exhaust concentration ofpropionic acidto thatof oxygen or other compounds, exhausttemperature, or fuel properties was found (using all the

experimental points, or even only at lean or rich conditions).A quantitative model can relate the exhaust concentration

of propionic acid with the percentages (in volume) of thefuel components:

The parameters a, b, c, and dare determined for all, butthis model is valid only in the case of the engine used. Thetotal emissions of propionic acid will probably be lower inthe case of more modern engines, so the normalized model:

is to be taken into consideration. According to this model,at stoichiometry, 58% of the exhaust propionic acid comesfrom the fuel benzene, 19% from the fuel toluene, 17% fromthe fuel ETB, and the remaining 6% from the fuel o-xylene.More about this model for other values of can be foundelsewhere (17).

The mechanism of this acid formation must be based onthearomaticring opening andthe formationof twoC3 radicalswhich are further oxidized to propionic acid. The aromaticring is probably partially oxidized to a phenol or aldehydebefore opening, as presented in the following reaction.

More data is necessary to confirm this mechanism.No detailed data are currently available for tail pipe

emissions of propionic acid, but the initial results show thatitstail pipeemissions are lower than theengineout emissionsdue to its oxidation in the converter. This is also applicablefor butyric, acrylic, and isovaleric acid.

Butyric Acid. Evidence suggests that butyric acid isproduced from o-xylene (Figure 5, bottom curve). The othertwo isomers of xylene (p- and m-xylene) are also probablyprecursors of this acid, but these two compounds were nottestedin ourfuel blends. Allotherfuelstested producelowerquantities of butyric acid; the two fuels that did not containo-xylene (i8 and i8T fuels) did not produce it at all (less thanthe detection limits). As commercial fuel contains moreo-xylene than fuel R, it produces more butyric acid than thelatter.

Air/fuel equivalence ratio has the same effect on theformation of butyric acid as propionic acid: a maximumvalue is observed at stoichiometry. The same remarks arevalid here.

No correlation was found between the exhaust concen-tration of this acid and exhaust oxygen or other compoundconcentrations, or exhaust temperature (for all the experi-mental points used or only lean or rich conditions). A goodcorrelation between exhaust butyric acid concentration andexhaust temperature for the five experimental points of the

FIGURE4. Emissions ofpropionic acid.Bottomgraph: fuel effectat stoichiometry. Mean: meanexhaust concentration; min, max:minimumandmaximumconcentration fora confidence region of95%.S1)42%hexane,S2)42%1-hexene,S3)42%cyclohexane,S4) 42% octane, S5) 42% isooctane, S6) 42% toluene, S7)42%o-xylene, S8) 42%ethylbenzene, R) reference fuel, O1)5% methanol, O2) 5% ethanol, O3) 5% 2-propanol, O4) 5%MTBE,,O5)20%methanol,O6)20%ethanol,O7)20%2-propanol,O8)20%MTBE,i8) pureisooctane,i8T) 80%isooctane+ 20%toluene, C) commercial fuel. Upper curves: effect for somerepresentative fuels.

propionic acid ) abenzene + btoluene+cethylbenzene+ d o-xylene

propionic acid ) a/dbenzene + b/dtoluene +c/dethylbenzene+ o-xylene

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o-X fuel is found:

This correlationindicatesthat for the same fuel,therefore

the same precursors, the exhaust concentration of butyricacid depends only on the exhaust temperature. This phe-nomenonwas alsoobserved in thecase of formic acidemittedfromanaturalgasfedSIengine(18). However,this correlationis not valid in the case of the other fuels for the emission ofbutyric acid, nor for the emissions of propionic acid fromthe S6, S7, or S8 fuels.

As in the case of propionic acid, the following model cancorrelate the exhaust concentration of butyric acid with thepercentages (in volume) of the fuel components at stoichi-ometry:

More about this model can be found elsewhere (17).Theformation mechanismof butyric acid must besimilar

to that of propionic acid: oxidation of o-xylene to anoxygenated compound(phenol, biphenol, or cresol),openingof the aromatic ring, and further oxidation to acid. March(ref22, andreferences therein) describes theformation of anacid after a ring opening: the formation of adipic acid fromcyclohexanone over CrO3 as catalyst: C6C11O w HOOC-(CH2)4-COOH. It is likely that exhaust butyric and propionicacids follow a similar reaction path.

Acrylic and Isovaleric Acid. Two other acids are detectedin the exhaust gas of some fuels in concentrations up to 2ppmv: acrylic and isovaleric acid. The obtained results arevery scattered, but acrylic acid is enhanced from 1-hexene,cyclohexane, and octane, while isovaleric acid is enhanced

from o-xylene and ETB (Figure 6). Acrylic acid is mainly

formed at lean conditions; most of the fuels used emittedthis compound in undetectable concentrations at richconditions. Isovaleric acid follows the opposite trend: it ismainly formed at rich conditions. The commercial fuelproduces almost the same concentrations of these acids asfuel R.

Acrylicacid must be linkedwith the formation of acroleine,which is also produced from 1-hexene and octane (21).Cyclohexane enhances the formation of this acid because itenhances the formation of exhaust 1-henexe (17). It is likelythat isovaleric acid is formed after the opening of the ringof o-xylene or ETB and formation of an iC5 radical, but, asalready observed, o-xylene and ETB do not enhance theformation of isopentane (21); this radical must already beoxygenated before its further oxidation to isovaleric acid.

This remark adds support to the hypothesis that propionicand butyric acid are produced after the ring opening of analready oxygenated aromatic compound. The commercialfuel produces almostthe same concentrations of these acidsas fuel R.

Percentageof OrganicAcidsin theotherExhaust Pollutants.The quantity of each acid as a percentage of the total acidsemitted for the commercial fuel at stoichiometry are formic0.8%, acetic 24.6%, propionic 44.0%, butyric 29.6%, acrylic1.0%, andisovaleric0%. These percentages are calculated asthenumber of carbonatoms of each acid divided by thetotalnumber of carbon atoms of all acids detected. Thesepercentages do not differ greatly from those of fuel R. Themajor organic acid emitted is propionic acid (due to fuelaromatics) followed by butyric (due to o-xylene) and aceticacid. Concerningthe otherfuels used,these percentages varyfrom 0.5 to 3% for the formic acid, 12-90% for the acetic,8-80% for the propionic, 0-45% for the butyric, 0-6% forthe acrylic acid, and 0-3% for the isovaleric acid. Propionic,butyric, and acetic acids are still the three major acids.

Concerning the comparison between the organic acidsand the other exhaust pollutants (total unburned hydro-carbons and aldehydes), all fuels used emit the following atstoichiometry: totalHC (measuredby FID): 457-1131 ppm,aldehydes 21-42ppm,acids35-291ppm. Organic acids are4-27%ofthetotalHCand1.2-10 times more than aldehydes.In the case of the commercial fuel at stoichiometry, organicacids are 24% of the total HC and 6.5 times more thanaldehydes. Formic acid corresponds to 0.1% of the total HC,

FIGURE5. Emissions ofbutyric acid.Bottomgraph: fuel effectatstoichiometry. Mean: mean exhaust concentration; min, max:minimumandmaximumconcentration fora confidence region of95%.S1)42%hexane,S2)42%1-hexene,S3)42%cyclohexane,S4) 42% octane, S5) 42% isooctane, S6) 42% toluene, S7)42%o-xylene, S8) 42%ethylbenzene, R) reference fuel, O1)5% methanol, O2) 5% ethanol, O3) 5% 2-propanol, O4) 5%MTBE,O5)20%methanol,O6)20%ethanol,O7)20%2-propanol,O8)20%MTBE,i8) pureisooctane,i8T) 80%isooctane+ 20%toluene, C) commercial fuel. Upper curves: effect for somerepresentative fuels.

FIGURE 6. Emissions of acrylic and isovaleric acid. Effect of.

butyric acid (ppm) )

0.176 * temperature (C) - 134, with r2 ) 0.81

butyric acid ) a o-xylene

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acetic to 3.2%, propionicto 14.8%, butyric to 5.4%, andacrylicto 0.2% (in ppm C).

The air/fuelequivalence ratioinfluences theseratios.TotalHC decreases with (from 2100 to 230 ppm for thecommercial fuel), while the total organic acids and totalaldehydes present a maximum value at stoichiometry(acids: 276 ppmv, against 150 ppmv at ) 0.83 and 244ppmv at ) 1.25; aldehydes: 42 ppmv, against 28 ppmv at) 0.83 and 41 ppmv at) 1.25). These values indicate thata more importantpercentage of exhaust pollutants are foundin oxygenated form under lean conditions (7% at ) 0.83,

27% at ) 1.0, and 55% at ) 1.25).

Literature Cited(1) Jeffrey, J.G.; Elliot N.G. SAETechnicalPaper Series1993,932680.(2) Kaiser, E. W.;Siegel,W. O.;Henig,Y. I.;Anderson, R. W.;Trinker,

F. H. Envir. Sci. Technol. 1991, 25, 2005-2012.(3) Neimark, A.; Kholmer, V.; Sher, E. SAE Technical Paper Series,

1994, 940311.(4) Petit, A.;Montagne,X. SAETechnicalPaper Series, 1993, 932681.(5) Keene, W. C.; Galloway, J. N. Atm. Environ. 1984, 18, 2491-

2497.(6) Lawrence, J. E.; Koutrakis, P. Envir. Sci. Technol. 1994, 28, 957-

964.(7) Chebbi, A.; Carlier, P. Atm. Environ. 1996, 30, 4233-4249.(8) Granby, K.;Christensen,C. S.; Lohse, C.Atm. Environ. 1997, 31,

1403-1415.(9) Grosjean, D. Atm. Environ. 1990, 10, 2699-2702.

(10) Khare, P.; Satsangi, G. S.; Kumar, N.; Maharaj Kumari, K.;Srivastava, S. S. Atm. Environ. 1997, 31, 3867-3875.

(11) Khwara, H. A. Atm. Environ. 1995, 29, 127-139.

(12) Kumar, N.; Kulshrestha, U. C.; Khare, P.; Saxena, A.; Kumari, K.M.; Srivastava, S. S. Atm. Environ. 1996, 30, 3545-3550.

(13) Puxbaum, H.; Rosenberg,C.; Gregori, M.;Lanzerstorfer, C.; Ober,E.; Winiwarter, W. Atm. Environ. 1988, 22, 2841-2850.

(14) Souza, S.; Vasconcellos, P. C.; Carvalho, R. F. Atm. Environ.1999, 33, 2563-2574.

(15) Kawamura, K.; Kaplan, I. R. Environ. Sci. Technol. 1987, 21,105-110.

(16) Kawamura, K.; Ng, L. L.;Kaplan,I. R. Environ. Sci. Techn. 1985,

19, 1082-1086.(17) Zervas, E.; Montagne, X.; Lahaye, J. J. Air Waste Manag. Assoc.1999, 49, 1304-1314.

(18) Zervas, E.; Tazerout, M. Atm. Environ. 2000, 34, 3921-3929.

(19) Zervas, E.; Montagne, X.; Lahaye, J. Atm. Environ. 2001, 35,1301-1306.

(20) Zervas, E.; Montagne, X.; Lahaye, J. Atm. Environ. 1999, 33,4953-4962.

(21) Zervas, E., Ph.D. Dissertation, University of Mulhouse, France,1996.

(22) March J. Advanced Organic Chemistry, 4th ed.; New York: J.Wiley and Sons, 1992; p 1176.

Received for review October 9, 2000. Revised manuscriptreceived March 5, 2001. Accepted March 20, 2001.

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2001 environ. sci. technol. zervas e. c1 c5 organic acid emissions from an si engine influence of...

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