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doi:10.1016/j.at

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Atmospheric Environment ] (]]]]) ]]]–]]]

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Particulate emission characterization of a biodiesel vsdiesel-fuelled compression ignition transport engine:

A comparative study

Dipankar Dwivedia, Avinash Kumar Agarwalb,�, Mukesh Sharmaa

aDepartment of Civil Engineering, IIT Kanpur, Kanpur 208016, IndiabDepartment of Mechanical Engineering, IIT Kanpur, Kanpur 208016, India

Received 9 March 2006; received in revised form 1 May 2006; accepted 2 May 2006

Abstract

This study was set out to characterize particulate emissions from diesel engines fuelled by (i) mineral diesel and (ii) B20

(a blend of 20% biodiesel with diesel); in terms of metals and benzene soluble organic fraction (BSOF), which is an

indicator of toxicity and carcinogenicity.

A medium duty, transport diesel engine (Mahindra MDI 3000) was operated at idling, 25%, 50%, 75% and rated load

at maximum torque speed (1800 rpm) and samples of particulate were collected using a partial flow dilution tunnel for both

fuels. Collected particulate samples were analyzed for their metal contents. In addition, metal contents in mineral diesel,

biodiesel and lubricating oil were also measured to examine and correlate their (metals present in fuel) impact on

particulate characteristics. Results indicated comparatively lower emission of particulate from B20-fuelled engine than

diesel engine exhaust. Metals like Cd, Pb, Na, and Ni in particulate of B20 exhaust were lower than those in the exhaust of

mineral diesel. However, emissions of Fe, Cr, Ni Zn, and Mg were higher in B20 exhaust. This reduction in particulate and

metals in B20 exhaust was attributed to near absence of aromatic compounds, sulphur and relatively low levels of metals in

biodiesel. However, benzene soluble organic fraction (BSOF) was found higher in B20 exhaust particulate compared to

diesel exhaust particulate.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Particulate; Biodiesel; Metals; Benzene soluble organic fraction; Toxicology

1. Introduction

Diesel engines are a major source of nitrogenoxides and particulate, which mainly consist of sootand metals. The composition varies depending onengine type, operating conditions, fuel and lubricat-

e front matter r 2006 Elsevier Ltd. All rights reserved

mosenv.2006.05.005

ing author. Tel.: +91512 2597982;

97982.

ess: akag@iitk.ac.in (A.K. Agarwal).

ing oil composition and whether an emissioncontrol system is present. Recent studies havefocused on the composition and toxicity of dieselexhaust (DE) and diesel particulate matter (DPM)(USEPA, 2002; Sharma et al., 2005). The USEPAand other agencies, engine and vehicle manufac-turers, emission control system manufacturers, andfuel refiners have been working for the past fewdecades to substantially reduce emissions fromdiesel engines. The chemistry and properties of

.

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Fuel Tank

Air Box

Engine

Dynamometer Controller

Eddy Current

D. Dwivedi et al. / Atmospheric Environment ] (]]]]) ]]]–]]]2

diesel fuel have a direct effect on emissions andformation of pollutants from diesel engines (EPA,2001).

Scientists are constantly working on alternativefuels, which are clean and efficient in combustion.These fuels include compressed natural gas (CNG),biodiesel, alcohols, gas-to-liquid fuels (GTL), di-methyl-ether (DME), etc. For example, CNG hasbeen extensively used as a clean fuel in Delhi andseveral other cities of the world. There is a need tostudy possible usage of other alternative fuels atlarge scale and their impact on human health andenvironment. It is not feasible to replace dieselengines with CNG engines in cities all overthe world. Other alternative fuels need to beexamined for engine performance and emissioncharacteristics.

Biodiesel is one such fuel which is a carbon-neutral fuel from bio-origin. B20 is a blend of 20%biodiesel and 80% mineral diesel, which maypartially replace mineral diesel and can be imple-mented without significant changes in the existingengine hardware. Biodiesel has also shown potentialto reduce the problem of CO2 emissions and canpartly meet energy needs in rural areas (Wedel,1999). It needs to be recognized that biodiesel doesprovide an effective alternative to diesel, but unlessit is ensured that emissions from biodiesel (espe-cially toxic pollutants) will be lower, or same asdiesel, acceptability of biodiesel as a fuel on a largescale may not be forthcoming.

Biodiesel for the present experimental study hasbeen made from rice-bran oil using the process oftransesterification using methanol and basic catalyst(KOH). The physical properties of biodiesel (rice-bran oil methyl ester), mineral diesel and B20 areshown in Table 1.

Out of metals studied in this research (Cr, Ni, Pb,Cd, Na, Al, Mg and Fe) Cr, Ni, Pb, and Cd aretoxic metals having a limit of maximum allowableexposure. The acceptable ambient air concentrationfor Ni is 5 ngm�3, Pb is 1000 ngm�3 and for Cd, it

Table 1

Physical properties of diesel and biodiesel

Fuel property Diesel B100 B20

Specific gravity at 30 1C 0.839 0.877 0.847

Viscosity (cSt) at 40 1C 3.18 5.30 3.48

Calorific value (MJkg�1) 44.8 42.2 44.1

Flash point (1C) 48 265 —

Sulfur content (ppm) 500 10 400

is 20 ngm�3. Fe, Al, and Mg are generally present insoil in the form of crust metals but excess of thesemetals in atmosphere is of concern. In addition,profiling of metal content in engine exhaust isnecessary to identify and apportion air-pollutionsources.

The focus of this paper is on comparativeassessment and characterization of emissions fromtraditional diesel and B20 (20% biodiesel blend) fuelexhausts in terms of (i) particulate, (ii) metals inparticulate, and (iii) benzene soluble organic frac-tion (BSOF; a toxicity indicator) in particulate.

2. Materials and methods

To characterize the emissions from mineral dieseland B20, a typical medium duty transport engine(Model: MDI 3000 A; Make: Mahindra andMahindra Ltd., India) was used in present experi-mental investigations (Fig. 1). This is a four-cylinder,four-stroke, variable-speed, transport engine withdirect-injection of fuel. Detailed specifications of theengine are given in Table 2. This engine is installedwith an eddy-current dynamometer (Model: ASE-70;Make: Shenck-Avery India Ltd.). The eddy-currentdynamometer is equipped with a dynamometercontroller capable of loading the engine at thedesired speed/load. For collection of particulate forcharacterization, the engine was operated at loadsranging from idling, 25%, 50%, 75%, to ratedengine load at a constant speed of 1800 rpm (ratedspeed for maximum torque). Particulate sampleswere collected iso-kinetically using a partial flowdilution tunnel, which was designed and fabricated

Exhaust Calorimeter

Fig. 1. Mahindra (MDI-3000 A) engine and dynamometer

system.

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Table 2

Engine specifications

Manufacturer Mahindra & Mahindra

Ltd., India

Model MDI 3000 A

No. of cylinders, configuration Four, in-line

Combustion system Direct injection

Bore/stroke (mm) 88.9/101.6

Engine displacement (cc) 2520

Compression ratio 18:1

Maximum speed at full load (RPM) 2300

Rated power (RPM) 40hp (2300)

Table 3

Sampling details

Samples collected for

analysis

Load Sampling

duration (min.)

Benzene soluble organic

fraction (single sample)

Idle 30

25% 25

50% 25

75% 25

100% 25

Metals (duplicate sample) Idle 30

25% 25

50% 25

75% 25

100% 25

D. Dwivedi et al. / Atmospheric Environment ] (]]]]) ]]]–]]] 3

in-house for this purpose (Dwivedi, 2005), describedlater. The gaseous emissions were measured using araw exhaust gas emission analyzer (Model: EXSA-1500; Make: HORIBA Ltd., Japan) however thispaper discusses the results of particulate and BSOFonly.

2.1. Diesel engine and dynamometer system

Particulate sample were collected on filter paper(GF/A, 47mm. Make: Nupore Filtration System,Batch No. 1720704) for analyzing various metalsand BSOF. Sampling details are given in Table 3.

2.2. Standard sampling method: dilution tunnel

The particulate leaving the exhaust pipe are atrelatively high temperature. These particulate andgases which contain hydrocarbons also cool downduring the mixing and dilution process with theatmospheric air, and the associated condensation ofhydrocarbons takes place on the particulate surface

layer, which changes the structure, composition anddensity of the particulate. Partial flow dilutiontunnel is used to simulate this near field (o3m)mixing, condensation and adsorption process in thepresent study. When the diesel engine is operated,carbonaceous soot particles and high boiling pointhydrocarbons are emitted from the tailpipe. Thesehydrocarbons condense on soot to form particulatematter (PM) after being diluted with preheated airinside the partial flow dilution tunnel. The dilutionratio is typically kept at 10:1.

2.3. Test procedure

The first step in the sampling procedure ispreparation of filter papers. The filter papers weredesiccated for 12 h and then weighed. One filterpaper was placed in the filter holder and then thefilter assembly was installed in the partial flowdilution tunnel. After running the engine at desiredload and speed condition and collecting theparticulate through partial flow dilution tunnel fora predetermined period of time, the filter paperswere removed from the filter assembly and againkept in desiccators for 12 h and then weighed.Particulate emission was found gravimetrically bymeasuring difference in weights of filter paper,before and after the particulate sampling. Thesefilter papers were then analyzed for characterizationof particulate for metals and BSOF.

2.4. Instruments and measurement systems

2.4.1. Extraction of samples for metal analysis in

particulate

Extraction of samples for metals analysis wascarried out using the hot plate method. In hot acidextraction (USEPA, 1995), the filter strips areplaced in a beaker and extracted by refluxing on ahot plate, using 10mL hydrochloric acid (8%) nitricacid (3%) solution. The digested solution wasfiltered before analysis.

2.4.2. Sample preparation for analyzing metals in

diesel and lubricating oil

Sample preparation for metals analysis wascarried out using acid digestion of oils for metalsanalysis by atomic absorption spectrometry (AAS).A representative 0.5 g sample was mixed with 0.5 gof finely ground potassium permanganate and then1.0mL of concentrated sulfuric acid was addedwhile stirring. A strong exothermic reaction takes

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15

25

35

45

55

50% 75% 100%

Par

ticu

late

s (

mg

/m3 )

Diesel

Biodiesel

Engine Load (%)

25%0%

Fig. 2. Variation in particulate emission with engine load.

Table 4

Concentration of various metals in diesel, biodiesel and lubricat-

ing oil samples

Diesel Biodiesel Lubricating oil

(mg g�1)

Na 1393.75 247.5 1770

Zn 152.1 180.5 656.55

Fe 7 10.2 20.1

Mg 9.2 15.8 27.3

Ni ND ND ND

Pb 0.93 ND ND

Cd 0.52 ND ND

Al 1.55 2.2 35.1

Cr 1.3 1.85 1.45

D. Dwivedi et al. / Atmospheric Environment ] (]]]]) ]]]–]]]4

place. The sample was then treated with 2mLconcentrated nitric acid. Ten mL of concentratedHCl was added and the sample was heated until thereaction was complete and then the metalextract was filtered for further analysis using AAS(USEPA, 2002).

2.4.3. Estimation of BSOF in particulate

Analysis for BSOF of the particulate samples wascarried out using ASTM test method D 4600-87(ASTM, 2001). This method is also recommendedby the National Institute of Occupational Safetyand Health, USA to represent the toxic organiccompounds in the particulate. This test methoddescribes the sampling and gravimetric determina-tion of benzene-soluble PM.

2.5. Metal analysis using AAS

AAS (Model: GBC Avanta S, Australia) wasused to carry out analysis of samples of diesel,biodiesel and lubricating oil along with particulatesamples collected on filter papers. Metals analyzedincluded Fe, Mg, Cr, Ni, Pb, Zn, Cd, Al, and Na.For analyzing these metals, first standard solutionsof known concentration of salts containing thesemetals were prepared and instrument was cali-brated.

3. Results and discussion

Particulate samples were collected from thecompression ignition engine using diesel and B20and were analyzed for metals and BSOF as per thesampling plan shown in Table 3. This sectionpresents a summary and interpretations of theexperimental results for DE and 20% biodieselexhaust (BDE).

3.1. Particulate

One of the objectives of this study was to examineparticulate emission in DE and BDE undervarying engine load conditions. Fig. 2 showsvariations of particulate emission under varyingengine loads for diesel and B20 fuel at constantengine speed. Shobokshy (1984) and Sharmaet al. (2005) have reported that particulate concen-tration increases with increased engine load;the same trend is obtained in present study forboth the fuels (Fig. 2). However, it is noteworthythat particulate emission is higher in DE

(22–59mgm�3) than B20 exhaust (17–48mgm�3).Studies by Sharp (1996) and Wedel (1999)established that a B20 blend (approximately 2%oxygen for RME-20) reduces particulate by ap-proximately 30% compared to particulate in theDE. Fig. 2 shows that rate of increase (withincreasing load) of particulate emission is lowerfor B20 exhaust.

This lower increase in particulate concentration inB20 exhaust can be attributed to (i) higher oxygencontent in B20 and (ii) lower C/H ratio; in B20 C/Hratio 6.53 compared to diesel 6.82 (Turrio-Baldas-sarri et al., 2004; Canakci and Van Gerpen, 2001),and (iii) near absence of sulphur and aromaticcontent of biodiesel.

3.2. Metals in mineral diesel, biodiesel and

lubricating oil

Table 4 shows measured levels of Fe, Cr, Ni, Pb,Zn, Cd, Na, and Al in diesel, biodiesel (beforeblending with mineral diesel) and lubricating oil.

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The basic metal content in the fuels and lubri-cating oil are variable e.g. iron is found to behigher in biodiesel, whereas lead and cadmiumis not detected. The variable metal contents willhave an impact on the metal in the parti-culate exhaust of diesel and biodiesel. There areother factors like lubricity of the fuel, whichaffects the wear of fuel injection system andpresence of wear metals in particulate to a minordegree.

3.3. Metals in particulate collected from DE and

BDE

The experimental study showed that concentra-tions of Fe, Mg, and Na (crust elements) were muchhigher than those of Cr, Ni, Pb, Zn, Al and Cd(anthropogenic elements) in both the fuels. Thesimilar trend has also been reported by Wang et al.(2000). The results of present experimental investi-gation for metals in particulate are divided in twosections based on (i) relatively higher concent-ration in DE and (ii) relatively higher concentrationin BDE.

0.4

1

0% 100%

Lea

d (

mg

/g)

Diesel

B20

Diesel

B20

0

2

4

6

8

10

12

50% 75% 100%

So

diu

m (m

g/g

)

0.9

0.8

0.7

0.6

0.5

0.3

0.2

25% 50% 75%

Engine Load (%)

0% 25%

Engine Load (%)

Fig. 3. Concentration of various metals present in highe

3.4. Metals present in higher concentration in DE

Four metals namely lead, cadmium, sodium andnickel are present in higher concentration in theparticulate collected from DE compared to BDE(Fig. 3). Metal-wise emissions are discussed below.

3.4.1. Lead

It may be noted from Fig. 3 that there are loweremissions of lead in BDE than in DE(0.9–0.30mg g�1 for DE, 0.7–0.25mg g�1 forBDE). The analysis of lead concentration in diesel,biodiesel and lubricating oil depicted that it waspresent only in diesel and was not present inbiodiesel and lubricating oil (Table 4). With B20blend, the emission of lead decreased becauseabsence of lead in biodiesel.

3.4.2. Cadmium

There is a slight reduction in emissions ofcadmium for BDE compared to DE(0.13–0.027mg g�1 for DE, 0.12–0.024mg g�1 forBDE). The analysis of cadmium concentration indiesel, biodiesel and lubricating oil showed that itwas present in diesel but was non-detectable in

Diesel

B20

Diesel

B20

0.01

Cad

miu

m (

mg

/g)

0

0.2

0.4

0.6

0.8

1

1.2

0% 100%

Nic

kel (

mg

/g)

0.13

0.09

0.05

0% 25% 50%

Engine Load (%)75% 100%

1.4

25% 50%

Engine Load (%)75%

r concentration in particulate from diesel exhaust.

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biodiesel and lubricating oil (Table 4). The source ofcadmium in DE and BDE is possibly from fuel(mineral diesel) and engine wear.

3.4.3. Sodium

It may be noted that sodium shows highestemissions (12–2mg g�1 for DE, 9–1mg g�1 forBDE) amongst all crust metals. This is due to thefact that sodium is present in abundance in diesel,biodiesel and lubricating oil (Table 4). Presence ofsodium was found highest in lubricating oilfollowed by diesel and biodiesel. With B20 fuel,the emission of sodium decreased because biodieselcontains lower amount of sodium as compared tomineral diesel. It is seen in Fig. 3 that there issignificant difference in sodium content in particu-late from DE and BDE at idling.

In this study, a small bore (88.9mm) engine isused. In smaller engines, there is always a possibilityof fuel dilution of lubricating oil because of fuelspray impingement on lubricated cylinder walls.This is an undesirable situation however thisinvariably happens in smaller diesel engines. Fuellubricity plays an important role in injection systemwear and additional lubricity properties of fuel(biodiesel) leads to lower injection system wear(Bijwe et al., 2004).

3.4.4. Nickel

Nickel shows emissions in DE and was notdetected in case of BDE (1.3–0.7mg g�1 for DE,Not detected for BDE). As shown in Fig. 3, nickelwas either absent or was below detection level inboth the fuels and lubricating oil. It can therefore beinferred that whatever nickel is coming out in DEmay be from engine wear. With B20, the emission ofnickel in particulate is not observed possibly due toself-lubricity property of biodiesel, which results inreduced engine and fuel injection system wear.

3.5. Metals present in higher concentration in BDE

Other metals such as iron, aluminum, zinc,chromium and magnesium are found in higherconcentration in the particulate collected from BDEcompared to DE (Fig. 4).

3.5.1. Iron

Fig. 4 presents iron content in particulate drawnfrom DE and BDE at different engine loads. It maybe noted that iron shows highest emission(7–2mg g�1 for DE, 8–3mg g�1 for BDE) amongst

all anthropogenic metals. This is due to the fact thatiron is present in abundance in diesel, biodiesel andlubricating oil. In addition, iron may also becontributed from engine wear (Agarwal et al.,2003). With B20, the emission of iron is found tobe higher because biodiesel contains higher amountof iron compared to mineral diesel (Table 4).

3.5.2. Aluminum

It may be noted that aluminum shows higheremissions for biodiesel operation (2.2–0.9mg g�1 forDE, 2.3–1.5mg g�1 for BDE; Fig. 4). Aluminumcontent is higher in biodiesel compared to mineraldiesel (Table 4); hence it is reflected in highercontent in particulate from BDE.

3.5.3. Zinc

It may be noted that zinc concentrations varyfrom 7.8 to 2.3mg g�1 for DE and 8.2–3.1mg g�1

for BDE (Fig. 4). With B20, the emission of zincincreased because biodiesel contains more zinccompared to mineral diesel. There is no significantdifference in zinc concentration in particulatefrom DE and BDE at idling. As load increasesthe difference seems to be more pronouncedbecause at idling, consumption of lubricating oil islower for biodiesel due to self-lubricity property ofbiodiesel.

3.5.4. Chromium

It may be noted that chromium shows higheremissions for BDE compared to DE (1.2–0.4mg g�1

for DE, 1.5–0.6mg g�1 for BDE; Fig. 4). Theanalysis of chromium concentration in diesel,biodiesel and lubricating oil shows that its presencein biodiesel is higher than mineral diesel (Table 4).With B20, the emission of chromium increased ascompared to diesel because of its higher concentra-tion in fuel itself (Table 4). Difference between theconcentration of lubricating oil and biodiesel is notvery high so lubricating oil does not play anysignificant role in emission of chromium.

3.5.5. Magnesium

Magnesium concentration varies from 8.7 to5mg g�1 for DE and 9.12–6.2mg g�1 for BDE(Fig. 4). This is due to the fact that magnesium ispresent in abundance in diesel, biodiesel andlubricating oil (Table 4). It is clear from Fig. 4 thatthere is not much difference in magnesium contentfor DE and BDE at idling. As load increases thisdifference gets pronounced. As load further in-

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1

2

3

4

5

6

7

8

Iro

n (

mg

/g)

Diesel

B20

0.8

1.2

1.6

2

2.4

2.8

Alu

min

ium

(m

g/g

) DieselB20

2

3

4

5

6

7

8

50%

Engine Load(%)

ZIn

c (m

g/g

)

DieselB20

1

Ch

rom

ium

(m

g/g

)

Diesel

B20

e

55.5

66.5

77.5

88.5

9

100%

Mag

nes

ium

(m

g/g

) Diesel

B20

Engine Load (%)

100%75%50%25%0% 0%

Engine Load (%)

25% 50% 75% 100%

100%75%

Engine load (%)

50%25%0%0.2

0.4

1.6

1.4

1.2

0.8

0.6

100%75%0% 25%

9.5

0%

Engine Load (%)

25% 50% 75%

Fig. 4. Concentration of various metals present in higher concentration in particulate from B20 exhaust.

D. Dwivedi et al. / Atmospheric Environment ] (]]]]) ]]]–]]] 7

creases, the consumption of lubricating oil alsoincreases. Lubricating oil has a large content ofmagnesium in organo-metallic additives, which areresponsible for the increase in magnesium content inDE and BDE.

3.6. Source of metals in DE and BDE: overall

characterization of metal emissions

Fig. 5 presents metal levels in particulate from DEand BDE and metals present in fuels. Fe, Mg, Cr, Pb,Al and Cd show a good association between metals in

fuels and metals in exhaust particulate. In B20 fuel,concentration of metals is calculated by mass balance(80% metal content in diesel added with 20% metalcontent of biodiesel). Zn and Na do not show anysuch association, it can be inferred from thisinvestigation that sources of Zn and Na in exhaustparticulate may be from sources other than fuel.

The metal concentration results presented inFigs. 3 and 4 reflect that as load increases, themetal content in particulate gradually decreases.This can be explained by the fact that at higherengine load, combustion takes place at higher

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0

1

2

3

4

5

6

7

8

9

10

Fe Mg Cr Ni Pb Al Cd

Met

al C

on

ten

t in

Par

ticu

late

s(m

g/g

)

0

1

2

3

4

5

6

Met

al C

on

ten

t in

Die

sel (

ug

/g)

DieselDiesel Exhaust

0

2

4

6

8

10

12

Fe Mg Cr Ni Pb Al Cd

Met

al C

on

ten

t in

Par

ticu

late

s(m

g/g

)

0

1

2

3

4

5

6

7

Met

al C

on

ten

t in

Die

sel (

ug

/g)

B20Biodiesel Exhaust

Metals Metals

Fig. 5. Sources of metals in diesel and biodiesel exhaust.

0

10

20

30

40

50

60

0% 25% 50% 75%

BS

OF

(%

w/w

)DieselBiodiesel

Load (%)

100%

Fig. 6. Variation of BSOF with engine load.

D. Dwivedi et al. / Atmospheric Environment ] (]]]]) ]]]–]]]8

temperature; leading to improved thermal effi-ciency. In other words, it is known that the emissionof particulate matter is strongly affected by theoperating conditions of the engine. In particular,lower engine load/ speed might result in lowerthermal efficiency and hence lead to higher particleformation and emission. Brake specific fuel con-sumption of diesel engine decreases with increasingload/ speed and this is reflected in reduced emissionof metals with increasing engine load. It is alsoreported by Sharma et al. (2005) that overallparticulate formation increases in the form ofelemental carbon with increase in engine load.Particulate matter emission is higher for higherengine loads because higher amount of fuel is beinginjected and burnt in the engine. For this reason, theparticulate emission from the diesel engine is higherbut the corresponding metal content is lower forhigher engine load as evident for almost all metals.It must be recognized that at higher engine loads,particulate emission is more in terms of elementalcarbon; thereby reducing metal content (mg g�1) inparticulate (Ullman, 2004). This is noteworthy thatthe thermal efficiency of the engine increases withincreasing engine load and after a threshold limit (inpresent study it corresponds to approximately75–85% of rated load), efficiency starts decreasing.Emission of metals increases at 100% load (com-pared to 75% load) for almost all metals, due tohigher specific brake fuel consumption at full load(Figs. 3 and 4).

In view of the above discussions, this can beconcluded that metal content in diesel, biodiesel andlubricating oil play an important role in theemission of metals in the engine exhaust and

blending with biodiesel is likely to result in loweremissions of metals.

3.7. BSOF in particulate

BSOF has been taken as indicator of organicfraction of particulate which represents the toxiccompounds. It can be observed from Fig. 6 that atidling, BSOF was about 48% in DE and 55% inBDE and BSOF gets lowered with increase in engineload. At idling condition, the mineral diesel andlubricating oil undergo partial combustion (pyro-lysis) due to low temperature conditions prevailingin the combustion chamber. This leads to higherunburnt hydrocarbon species formation andemissions, which is detected as BSOF (Sharmaet al., 2005).

Although the exact mechanism for presence ofBSOF varies depending on the engine’s operating

ARTICLE IN PRESSD. Dwivedi et al. / Atmospheric Environment ] (]]]]) ]]]–]]] 9

condition, generally accepted explanation for BSOFin exhaust is that soot particles that are formed infuel-rich portions of the diesel (spray) collecthydrocarbons through condensation and adsorp-tion (Finch et al., 2002). Higher molecular weightcompounds will form small liquid droplets and getadsorbed and deposited on the carbonaceous sootparticles. These small droplets may be adsorbed bysoot particles or simply be trapped on the filtersused to collect particulate. Operating conditionswhich increase the fraction of the fuel and lubricat-ing oil that remains unburned or partially burned;will increase the BSOF of the particulate. For B20particulate, this value of BSOF is higher than thatof diesel particulate. This is primarily because oflower volatility of constituents of biodiesel; biodie-sel can be expected to increase the amount ofsoluble organic fraction emitted by a compressionignition engine. However, the increased mass con-sists mostly of unburned esters from the fuel itself(Sharp et al., 2000). Since biodiesel is nontoxic, theincreased level of soluble organic fraction may notbe hazardous (Finch et al., 2002). However in orderto clearly establish the organic toxicity of BDE,more investigations are required through furtherspeciation of exhaust.

4. Conclusions

Oxygenated fuel B20 (biodiesel blend) showedsuperior engine performance in reducing particulateemissions at all operating conditions compared tomineral diesel (particulate in DE; 22–59mgm�3 andin BDE; 17–48mgm�3) at constant speed. This maybe due to lower sulphur and aromatic content ofbiodiesel. Along with reduction in particulatematter, there is an overall reduction in metalemissions from the biodiesel exhaust. It was alsofound that metals in particulate mainly originatefrom fuel and lubricating oil and in addition someof the metals can originate from engine wear. Thereduced metal emissions in BDE are because of (i)inherent lubricity property of biodiesel leading toreduction of emissions of certain metals in BDE dueto lower fuel injection system wear and (ii) lowermetal levels (Pb and Cd) in biodiesel compared tomineral diesel.

There is a net increase in BSOF for B20 fuel ascompared to mineral diesel, however biodiesel isnontoxic, hence the increased level of solubleorganic fraction may not be viewed as hazardous(Finch et al., 2002). However hazardous nature of

biodiesel exhaust needs further investigations byspeciating organic species in biodiesel exhaust. Thisnecessitates that speciation of organic compounds isdone for both the fuel exhausts to clearly establishcomparative organic toxicity. Nonetheless, thisresearch suggests that overall toxicity of emissionsin terms of metals reduces in BDE compared to DE.

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