Using Bio-oil Produced by Biomass Pyrolysis as Diesel FuelRenato Cataluna,*,† Pedro M. Kuamoto,† Cesar L. Petzhold,† Elina B. Caramao,† Maria E. Machado,†

and Rosangela da Silva‡

†Federal University of Rio Grande do Sul, Av. Bento Goncalves 9500, 91501-970 Porto Alegre, RS, Brazil‡Pontifical Catholic University of Rio Grande do Sul, Av. Ipiranga 6681, 90619-900 Porto Alegre, RS, Brazil

ABSTRACT: This study evaluated the effect of biomass (soybean oil, eucalyptus sawdust, and coffee grounds) pyrolysis oil onthe formulation of diesel fuels. The parameters analyzed were ignition delay time, emission of particulate matter and unburnedhydrocarbons, and specific fuel consumption. The fraction of pyrolysis oil used as fuel was obtained by vacuum distillation at 80−240 °C. The use of this fraction resulted in a decrease in the ignition delay time in the combustion process, with the resultingincrease in the cetane number due to the presence of phenolic groups in the pyrolysis oil, which modify the formationmechanism of peroxyl radicals by altering the temperature of the flame front. Additionally, particulate matter emissions arereduced significantly by up to 30% when compared with the base fuel. This is probably due to the high solubility of water inpyrolysis oil, which leads to the formation of an azeotropic mixture that lowers the boiling point and contributes to vaporize thefuel inside the combustion chamber, reducing the formation of particulate matter. These results indicate the promising potentialof this fraction for use in the formulation of diesel fuel, decreasing ignition delay and increasing the cetane number, as well assignificantly reducing particulate matter emissions. The main difficulty in using this fraction of pyrolysis oil is its chemicalstability, since it has a strong tendency to form oligomers.

■ INTRODUCION

Today’s energy matrix is largely dependent on fossil fuels,natural gas, and coal. Fossil-based products that supply thetransport sector are expected to be replaced in the short andmedium-term due to high growth rates, mainly in emergingcountries. As a result, the transport sector will account forabout one-third of the future growth in worldwide greenhousegas emissions.1

The first generation biofuels, biodiesel and bioethanol, and,recently, those of the second generation derived from biomass,have shown significant growth in recent years.2−8 Thegeneration of second generation biofuels is favored by thelarge supply of wastes produced in agriculture.9−11

In Brazil, a major producer of agricultural products12 andwith extensive areas of reforestation area, the reuse of residualbiomass plays an important role in the energy matrix, not onlyfor economic reasons but also for environmental issues. Theuse of forest and agricultural residues stands out in the energymatrix, given their characteristic of not contributing to thephenomenon of global warming, and constituting a source ofrenewable fuels and of raw materials for the chemical industry.The use of rice husks, eucalyptus sawdust and fruit seeds inthermal conversion processes (pyrolysis) of biomass is anattractive option for many Brazilian regions, since it can takeadvantage of plentiful locally available residual biomass. Brazilproduces approximately 5 Mton/year of agricultural wastes thatcould easily be converted into biofuels, with an estimatedproduction of 2 Mton/year of bio-oil from thermal ordelignification processes.13−19

The characteristics of fuels play an important role in thecombustion process. The determination of the parameters thataffect self-ignition and air pollutant emissions from diesel fuelsenables the development of new and more efficient combustionprocesses, as well as the addition of new compounds to increase

the performance of the thermal cycle. Oxygenated compoundssuch as biodiesel alter the cetane number (CN) and thecombustion mechanism, reducing the emission of particulatematter (PM).20,21

This paper discusses results of the characterization andperformance of a biofuel, produced by fixed bed slow pyrolysis,using soybean oil, eucalyptus sawdust, and coffee grounds. Thefraction of oil used as fuel was obtained by vacuum distillationat 80 to 240 °C. This fraction was characterized by Fouriertransform infrared spectroscopy (FTIR), proton nuclearmagnetic resonance spectroscopy (1H NMR), comprehensivetwo-dimensional gas chromatography with time-of-flight massspectrometric detection (GC × GC/TOFMS), and watercontent. Additionally, based on a diesel oil (S10) with lowsulfur content (10 mg L−1) and a cetane number (CN) of 50,formulations were prepared with 10% m/m fraction of bio-oiland of soybean biodiesel, which are hereinafter referred to asS10po and S10bd, respectively. Performance tests were carriedout in a diesel cycle engine to evaluate characteristics such asspecific fuel consumption, ignition delay, and emissions ofparticulate matter and unburned hydrocarbons (HCs), usingthe S10 diesel and its S10po, S10bd formulations.

■ EXPERIMENTAL SECTIONCharacterization of the S10 Diesel. The S-10 diesel normally

commercialized in the Brazilian market by Petrobras was used in thisstudy as the base to prepare the two formulations, one containing 10%m/m of bio-oil and the other 10% m/m of soy biodiesel, referred to asS10po and S10bd, respectively.

Received: August 19, 2013Revised: October 28, 2013Published: October 29, 2013

Article

pubs.acs.org/EF

© 2013 American Chemical Society 6831 dx.doi.org/10.1021/ef401644v | Energy Fuels 2013, 27, 6831−6838

The S10, with a maximum sulfur content of 10 mg kg−1, wasdeveloped by Petrobras to meet the requirements of the latestgeneration of diesel engines, which were designed to emit lower levelsof particulate matter and NOx than those manufactured up toDecember 2011. In addition to its low sulfur content, this fuel has ahigh cetane number (at least 48), a narrow range of variation inspecific mass (820 to 850 kg/m3), and a maximum distillation curvetemperature of 370 °C for 95% of the products of evaporation. Theseproperties also favor combustion and cold starting of engines. Table 1describes these physicochemical properties and the respectivemethodologies employed.Characterization of the Bio-oil Produced by Pyrolysis. The

pyrolysis oil was produced in a fixed bed reactor from a mixture of1:1:1 soybean oil, coffee grounds and eucalyptus sawdust, applying aheating rate of 10 °C min−1 from room temperature to 700 °C and aholding time of 15 min. The oil thus produced was separated from thewater and fractionated by vacuum distillation at a pressure of 50 mbarbetween 80 and 240 °C. The oil was characterized by Fouriertransform infrared spectroscopy (FTIR), proton nuclear magneticresonance spectroscopy (1H NMR), and Karl Fischer titration.The infrared spectrum of the pyrolysis oil fraction was obtained in

the form of a film on a potassium bromide (KBr) wafer, using an FTIRspectrophotometer (Varian) in the frequency range of 4000−400cm−1.A nuclear magnetic resonance (NMR) analysis was performed in

deuterated chloroform, using a Varian VRMN-300 MHz spectrometer.The water content of the pyrolysis oil was determined by the KarlFischer titration method, using an 870 Titrino Plus titrator fromMetrohm. The analyses were performed in triplicate.The pyrolysis bio-oil composition was also determined by

comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometric detection (GC × GC/TOFMS), using aPegasus-IV system (LECO, St. Joseph, U.S.A.) equipped with a liquidnitrogen quad-jet modulator and CTC Combi PAL autosampler. Thefollowing columns were employed in the first and second dimension,respectively: a DB5 column (5% phenyl−95% dimethylpolysiloxane)60 m in length, with 250 μm inner diameter (I.D.) and 0.25 μm ofphase thickness, and a DB-17 ms column (50% phenyl−50%dimethylpolysiloxane) 2.15 m in length, with 180 μm I.D, and 0.18μm of phase thickness (Agilent Technologies, J&W Scientific, Agilent,

Folsom, CA, U.S.A.). The carrier gas was helium under a constant flowrate of 1 mL min−1 and the sample injection volume was 1 μL. Theinjector temperature was 300 °C, and samples were injected in thesplitless mode. The temperature program of the first column was set tobegin at 40 °C for 1 min and reach a final temperature of 300 °C at 3°C min−1, with 1 min of holding time. The transfer line was held at300 °C and the electron impact ionization source itself was operated at250 °C with collision energy of −70 eV. The mass range was 45−400amu, and data acquisition rate was 100 Hz. The oven’s modulatorperiod and offset temperatures were 8 s and 15 °C, respectively. Thedata were processed using integrated LECO ChromaTOF software,version 3.32.

Engine Performance Tests. The tests to evaluate specific fuelconsumption, ignition delay time, particulate matter and hydrocarbonemissions of S10 diesel fuel and its S10po and S10bd formulationswere performed in a 250 cm3 Toyama 7.0 Hp single cylinder engine,using an Optrand inductive pressure sensor in the combustionchamber. The engine was run at 80% of maximum power, mechanicalfuel injection at 20° before top dead center (TDC), with 150 baraverage injection pressure, a compression ratio of 21:1, 3600 rpm, and10% of O2 in the exhaust gases. The PM in the exhaust gas wasquantified gravimetrically by direct filtration of the gas in a 47 mmdiameter glass microfiber filter (Macherey-Nagel). The engine wasespecially instrumented22 to optimize its operation during theperformance tests of each fuel. In addition, a differential pressuregauge in the filter was used to assess the accumulation of PM. The gasflow through the filter element was obtained with the aid of a vacuumpump, and after cooling, the flow rate was measured using a flowindicator/recorder (Sensirion), with a maximum rated capacity of 20nL min−1. The quantification of PM in mg m−3 was based on the massof PM trapped on the filter, divided by the volume of sampled gas. Theaverage temperature of the filter element was set at 470 °C to keep thecollected PM dry. The volatile condensable hydrocarbons (HCs) inthe exhaust gases were collected together with the water generated inthe combustion process, after separating the PM.

The liquid fraction from the exhaust of diesel engines is composedof unburned and partially oxidized hydrocarbons (HCs) that condensealong with the water formed in the combustion process. A portion ofthe water vapor in the exhaust gases is condensed by cooling the gasflow after the particulate matter has been collected. The total

Table 1. Physicochemical Properties of Fuel S10

specific gravity(kg m−3)

T 10%(°C)

T 50%(°C)

T 90%(°C)

kinematic viscosity(mm2 s−1)

flash point(°C)

sulfur(mg L−1) CN

polycyclic aromatichydrocarbons (% m)

ASTM D4052 D86 D86 D86 D445 D93 D7039 D613 D6591S10 839.4 209 264 338 2.85 72 10 50 1.61

Figure 1. Representative FTIR spectrum of the pyrolysis oil (film on KBr).

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hydrocarbons in the form of methane were quantified using atechnique similar to that of the ASTM D 659123 standard, by flow-through oxidation of the sample in an oxygen atmosphere. Carbondioxide (CO2) was analyzed in a gas chromatograph equipped with athermal conductivity detector (Shimadzu GC-17A with TCD).

■ RESULTS AND DISCUSSION

Characterization of the Pyrolysis Oil. The results of theKarl Fischer analysis indicated the solubility of 5000 ppm ofwater in the pyrolysis oil. This amount of water, even in smallquantities, strongly affected the initial boiling point of theformulations, causing the fragmentation of the fuel to increaseduring injection because smaller droplets were generated.During the purification process the onset of vaporization isaltered by the presence even of small amounts of water,suggesting that this is one of the determining factors in thereduced formation of particulate matter when pyrolysis bio-oilis used. In addition, albeit to a lesser degree, the presence ofwater in biodiesel may also lead to its hydrolytic oxidation.24

Water not only promotes biodiesel hydrolysis, which resultsin free fatty acids, but is also associated with the proliferation ofmicroorganisms, causing corrosion and sediment deposition instorage tanks. Because biodiesel presents some degree ofhygroscopicity, its water content should be monitored duringstorage.The FTIR spectrum in Figure 1 was used to investigate the

chemical structure of pyrolysis oil. Since the pyrolysis oilobtained from the 1:1:1 mixture of soybean oil, coffee grounds,and eucalyptus sawdust, the absorption bands at 1592, 1453,1414, 1379, 1253, 1236, 1166, and 824 cm−1 are characteristicof lignocellulosic materials and are consistent with the spectrumof pine wood.25

The absorption bands at around 3000 cm−1 are attributed tothe symmetric and asymmetric vibration of saturated CHbonds. The signal at 1704 cm−1 is related to the stretching

vibration of the CO bond of compounds derived from thefragmentation of soybean oil triglycerides. The absorption bandat 1453 cm−1 is associated with the asymmetric deformation ofthe CH methyl and methoxyl26 groups, while the broadenedband at 3367 cm−1 is characteristic of the stretching vibration ofthe OH bond.Figure 2 shows the 1H NMR spectrum of pyrolysis oil.

Because this is a mixture of products, the NMR data confirmthe presence of aromatic and vinylic hydrogens, indicated bythe signals in the region of 5 to 7.5 ppm, as well as of hydrogensbound to oxygenated carbons (CH−O) between 3.5 and 4.8ppm and of hydrogens neighboring carbonyl in the region of1.9 to 2.9 ppm. The intense peaks between 0.7 and 1.5 aretypical of aliphatic hydrogens.The same samples were also analyzed by GC × GC/TOFMS

and the results are described in Table 2. A total of 89compounds were tentatively identified, considering a minimumsignal-to-noise ratio (S/N) of three.The compounds were tentatively identified when the

similarity between the sample and library spectra was greaterthan 750 and after a detailed analysis of the spectra. Since nostandards (reference substances) were used to confirm theidentification, we considered only the indication listed in thelibrary of the device. That is why we consider that thecompounds were “tentatively identified.” For the same reason,the alkyl chains in some compounds were not completelydefined. For example, a compound identified in the library as 2-ethyl pyridine was only “tentatively identified” as C2-pyridine,where C2 represents an ethyl group or two methyl groups in anundefined position in the pyridine ring.In Table 2, the bio-oil composition is grouped by chemical

class: alcohols, ketones, ethers, phenols, aromatics and aliphatichydrocarbons and nitrogen compounds. The sample obtainedby pyrolysis is composed mainly of ketones and nitrogen

Figure 2. 1H NMR spectrum of the pyrolysis oil.

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Table 2. Identification of the Classes of Compounds in Bio-oil of by GC × GC/TOFMS

retention time

TR1D (min) TR

2D (s) compounds similarity reverse formula area (%)

Alcohols9.50 2.96 pentanol 878 878 C5H12O 0,2410.97 3.11 pentanol 501 886 C5H12O 0,0111.10 3.58 pentenol 646 710 C5H10O 2,2413.50 3.72 hexenol 736 818 C6H12O 0,00

Ketones7.63 2.72 pentanone 791 813 C5H10O 0,198.17 2.91 pentanone 887 887 C5H10O 0,658.43 2.96 pentanone 945 945 C5H10O 0,989.50 3.09 hexanone 853 908 C6H12O 0,0311.10 3.34 hexanone 759 902 C6H12O 0,0414.17 3.58 heptanone 775 882 C7H14O 0,0311.23 4.29 cyclopentanone 924 924 C5H8O 1,2113.23 4.29 cyclopentanone, C1(a) 889 906 C6H10O 1,1413.63 4.35 cyclopentanone, C1 905 905 C6H10O 0,5815.77 4.28 cyclopentanone, C2 809 840 C7H12O 0,1816.03 4.25 cyclopentanone, C2 615 842 C7H12O 0,0618.03 4.57 cyclopentanone, C2 825 825 C7H12O 0,3219.10 4.69 cyclopentanone, C2 777 848 C7H12O 0,1013.99 5.1 cyclopentenone, C1 952 952 C6H8O 6,5419.77 5.67 cyclopentenone, C1 937 937 C6H8O 3,4618.17 4.72 cyclopentenone, C2 815 818 C7H10O 0,8521.23 5.16 cyclopentenone, C2 888 888 C7H10O 2,1222.57 5.48 cyclopentenone, C2 868 868 C7H10O 0,4823.37 5.51 cyclopentenone, C2 877 877 C7H10O 6,1625.50 5.69 cyclopentenone, C2 846 869 C7H10O 0,5615.77 4.98 cyclohexanone 869 878 C6H10O 0,6121.10 5.25 cyclohexenone, C1 820 820 C7H10O 1,6615.77 3.73 heptanone 925 925 C7H14O 0,4020.83 3.9 octanone 927 927 C8H16O 0,4421.90 5.37 cycloheptanone 916 924 C7H12O 0,8822.57 4.75 cyclopentenone, C3 745 758 C8H12O 0,3324.97 5.65 acetophenone 863 903 C8H8O 0,1426.03 5.22 cyclohexenyl, ethanone 861 879 C8H12O 1,0126.83 4.78 cyclopentenone, C4 726 789 C9H14O 0,0128.17 5.38 cyclohexanone, ethylidene 774 776 C8H12O 0,7131.50 5.51 cyclopentenone, C3 methylene 789 873 C9H12O 0,2737.50 6.81 indenone, hexahydro 806 854 C9H12O 0,11

Ethers9.23 2.75 ethane, diethoxy 915 925 C6H14O2 1,9917.37 3.73 furanmethanol 853 902 C5H6O2 8,3521.23 5.13 furan, C2 865 884 C6H8O 4,2322.97 4.79 furan, C2 717 828 C6H8O 0,37

Phenols23.37 4.1 phenol 908 914 C6H6O 2,0024.97 4.77 phenol, C1 651 840 C7H8O 0,0626.70 4.59 phenol, C1 714 843 C7H8O 0,78

Hydrocarbons10.3 3.31 toluene 871 871 C7H8 0,2215.633 3.96 benzene, C2 595 790 C8H10 0,0218.567 4.75 cyclopentane, methyl ethylidene 765 779 C8H14 0,5824.967 4.97 cyclopentene, C3 718 747 C8H14 1,4126.033 4.63 cyclopentene, C3 652 741 C8H14 0,7428.3 4.91 cyclohexene, C4 755 755 C10H18 0,35

Nitrogen Compouds9.63 3.56 pyrrole 715 909 C4H5N 0,0310.43 3.74 pyrrole, C1 931 931 C5H7N 8,9711.37 2.91 piperidine, C1 693 846 C6H13N 0,0111.50 2.88 piperidine, C1 787 828 C6H13N 0,14

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compounds, with minor amounts of alcohols, ethers, phenolsand hydrocarbons.The graph in Figure 3a shows the area percentage of different

classes of compounds, while the graph in Figure 3b indicatesthe contribution of each group of compounds by referring tothe number of compounds. As can be seen in these figures, thepredominant classes in the sample were nitrogen and ketonecompounds: 44.19% (41) nitrogen and 32.22% (33) ketonecompounds. C1 pyrrole and C4 pyrazin predominated amongthe various nitrogen and ketone compounds. High percentagesof furanmethanol and of C1 and C2 cyclopentenone were alsoobserved (Table 2).The presence of high amounts of nitrogen compounds in the

composition of pyrolysis oil may lead to the formation ofoligomers and increase the emission of nitrogen oxidecompounds (NOx) during the combustion process. However,the NOx emitted during combustion depends not only on thecomposition of the fuel but also on the mode of operation andthe design of the burners and of the combustion chamber andon the fuel’s other physicochemical characteristics (e.g., its

cetane number (CN)). Each of these parameters is significantin determining the final concentration of NOx emission. Thecombustion control techniques take advantage of the kineticmechanism of NOx formation by using the air flow or fuel flowcontrols (in stages) or by introducing inhibitors. A higher CNin fuels is favored by larger amounts of oxygenates, which, albeitsupplying lower energy content, reduce not only thecombustion flame temperature but also NOx emissions.21,27,28

Engine Performance Tests. Figure 4 illustrates thevariation of chamber pressure as a function of the crankshaftangle with the fuel and its various formulations. As can be seen,with the three fuels evaluated here, the maximum pressure afterthe TDC occurs at a 13° angle, that is, the maximum pressurein the combustion chamber occurs near the 15° angle, whichcorresponds to maximum torque. Note, also, that the fuelsformulated with 10% pyrolysis oil and biodiesel produce higherpressure in the combustion chamber at the TCD than the S10,indicating that the oxidation rates of both the biodiesel and thepyrolysis oil in the proportion of 10% m/m are higher than thatof the base fuel.

Table 2. continued

retention time

TR1D (min) TR

2D (s) compounds similarity reverse formula area (%)

Nitrogen Compouds15.37 3.75 piperidine, C2 696 771 C7H15N 0,0912.83 3.99 pyridine, C1 912 912 C6H7N 0,6515.23 4.32 pyridine, C1 874 882 C6H7N 1,3115.50 4.18 pyridine, C2 891 917 C7H9N 0,8916.57 4.35 pyridine, C2 778 790 C7H9N 0,1618.30 4.38 pyridine, C2 879 880 C7H9N 0,1118.83 4.59 pyridine, C2 882 889 C7H9N 0,0719.50 4.32 pyridine, C3 701 767 C8H11N 0,0521.10 4.42 pyridine, C3 822 826 C8H11N 0,0921.77 4.58 pyridine, C3 633 761 C8H11N 0,0515.77 3.96 imidazole, C4 900 905 C7H12N2 0,1116.43 4.47 pyrazine, C2 681 805 C6H8N2 0,0416.83 4.62 pyrazine, C2 892 931 C6H8N2 0,5516.83 4.66 pyrazine, C2 847 847 C6H8N2 0,1517.23 4.72 pyrazine, C2 869 880 C6H8N2 0,0621.23 4.72 pyrazine, C3 886 886 C7H10N2 0,1421.50 4.76 pyrazine, C3 894 894 C7H10N2 2,6825.37 4.67 pyrazine, C4 921 926 C8H12N2 1,4225.63 4.72 pyrazine, C4 897 905 C8H12N2 2,6025.77 4.81 pyrazine, C4 925 940 C8H12N2 8,0229.50 4.68 pyrazine, C5 885 885 C9H14N2 7,7830.17 4.74 pyrazine, C5 616 753 C9H14N2 0,1029.90 4.65 pyrazine, C6 811 842 C11H18N2 0,2026.83 6.03 pyrrolidinone, C2 857 892 C6H11NO 0,0527.77 6.25 pyrrolidinone, C2 808 810 C6H11NO 0,6727.23 4.88 piperidinone, C4 857 857 C9H17NO 0,2428.30 5.23 pentanamide, C1 819 845 C6H13NO 1,0233.37 4.6 pyrazine, C6 856 861 C10H16N2 0,3031.23 5.45 imidazole, C3 620 789 C6H10N2 0,0833.23 5.02 pyrazole, C3 770 777 C6H10N2 0,3933.37 5.77 pyrazole, C4 809 835 C7H12N2 0,1533.50 5.71 imidazole, C4 829 834 C7H12N2 1,5134.70 5.38 pyrazole, C4 773 784 C7H12N2 0,5535.37 5.15 pyrazole, C4 759 766 C7H12N2 1,6334.97 5.48 pyridine, C1 propenyl 799 801 C10H13N 0,3936.17 6.67 pyrrolidinone, C2 methylidene 800 800 C7H11NO 0,75

aCx: represent an alkyl chain linked to structure where x is the number of carbon atoms.

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According to Shafizadeh,29 eucalyptus biomass is composedof 38−45% cellulose, 16% hemicellulose, 25−37% lignin, and9−15% of other organic and inorganic compounds. Cellulose isa natural high molecular weight polymer with the genericempirical formula of H(C6H10O5)nOH with up to 10 000monomer units and a molecular weight of 1 600 000 a.m.u.30,31

Hemicelluloses are formed with copolymers of glucose and avariety of other monomers, mainly hydrates of carbon. They areamorphous and have a lower degree of polymerization thancellulose.31 During the process of pyrolysis, these compoundsare cracked, producing fractions of lower molecular weightwhile maintaining some of the characteristics of the originalcompounds. Each of these constituents plays a role in thecombustion process. The molecule that has an unpairedelectron, called a free radical, determines the speed of theoxidation reaction. The most important reactive radicals formedduring the combustion process are hydroperoxyl (HOO•),hydroxyl (HO•), alkoxy (RO•), and peroxyl (ROO•). Theseradicals react with N2 and nitrogen oxides, forming N2O. CH•

Figure 3. Distribution of chemical classes for bio-oil produced by biomass pyrolysis according to (a) area percentage and (b) their number ofcompounds tentatively identified.

Figure 4. Pressure profiles in the combustion chamber with S10 dieseland its S10bd and S10po formulations.

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and OH• radicals are formed continuously during thecombustion process. In general, the presence of CH• radicalsindicates low temperature in the inception phase and OH•radicals indicate reactions at high temperatures.32 During thecombustion of biodiesel, the concentration of OH• radicals islower while that of CH• radicals is higher.33 The highconcentration of phenolic constituents in pyrolysis oil, whichhave a high potential for the formation of OH• radicals,explains the decrease in ignition delay and the increase in thespeed of oxidation, with a consequent increase in the CN of theS10po fuel compared to the base fuel (S10).Figure 5 illustrates the differential pressure in the filter

element resulting from the retention of particulate matter (PM)

as a function of the volume of the gas sample for the S10,S10bd, and S10po fuels. The lowest differential pressure as afunction of gas sample volume is observed for the formulationcontaining pyrolysis oil, because it generates less PM. Table 3

shows the mass of PM in mg m−3 and the emissions ofunburned HC in percent (%) of sampled gas. The PM valuesfound here underscore the results shown in Figure 5. Dieselfuels formulated with diphenyl-p-phenylenediamine (DPPD),which has phenolic groups, showed a similar effect in reducingthe formation of PM.27 The use of 10% m/m of pyrolysis oil inthe fuel reduces PM emissions by approximately 30%. Thepresence of aromatic compounds in pyrolysis oil shouldcontribute to increase emissions of PM,34 but the presence ofthe hydroxyl of the phenolic compounds in pyrolysis oilcontributes to augment the efficiency of combustion. The lowerformation of particulate matter is related with the process offuel injection and vaporization in the combustion chamber.Since the injection pressure remains approximately constant,the lower formation of PM with the S10po fuel is due to thepresence of water, which reduces the boiling point of the

mixture, favoring vaporization with the formation of smallerdiameter droplets. The greater the fragmentation of fuel in theinjection process, the lower the formation of PM.35,36

As can be seen, HC emissions show a tendency unlike that ofPM emissions. This is primarily due to the penetration of thejet in the combustion chamber. The higher the penetration thegreater the likelihood of the fuel reaching the cold parts of thewalls of the piston where the speed of oxidation decreases,increasing the emission of HCs. The higher emission of HCsdoes not significantly affect specific fuel consumption, since themaximum pressure in the combustion chamber is observedclose to the 15° angle after TDC, the region of maximumtorque, which keeps the engine’s power stable.During storage, the addition of small amounts of antioxidants

to the fuel serves to suppress the formation of free radicals andinterrupt their propagation for oligomer formation. In general,phenolic antioxidants (TBHQ, BHT, BHA, etc.) are added tobiodiesel to prevent degradation.25 High oligomer formationwas observed during the storage period of the pyrolysis oil andits respective formulation with the commercial diesel oil, evenwhen stored at a low temperature. The addition of antioxidantadditives to the fuel should reduce the formation of oligomerssignificantly and increase the fuel’s storage time.

■ CONCLUSIONSThe pyrolysis oil fraction obtained by vacuum distillation at 80to 240 °C and used in the formulation of diesel fuels showedgood test results in terms of engine performance and aircontaminant emissions. The use of this fraction reduces theignition delay time in the combustion process, hence increasingthe CN. The results obtained here indicate that the increase inthe speed of oxidation at the onset of the combustion processmay be due to the presence of phenolic groups in the pyrolysisoil. The fuels formulated with 10% of pyrolysis oil showed 30%lower formation of PM, which is attributed to the increase inwater solubility in the oil, producing an azeotropic mixture thatincreases the fuel’s volatility during its injection, thus reducingthe diameter of the droplets. The major difficulty in using thepyrolysis oil fraction in the formulation of diesel fuels isattributed to its chemical stability, since it has a strong potentialto form oligomers.

■ AUTHOR INFORMATIONCorresponding Author*Telephone: +55 51 33086308. Fax: +55 51 33087304. E-mail:rcv@ufrgs.br.

NotesThe authors declare no competing financial interest.

■ REFERENCES(1) World Energy Outlook 2004; International Energy Agency (IEA):Brussels, 2004.(2) Beatrice, C.; Di Blasio, G.; Lazzaro, M.; Cannila, C.; Bonura, G.;Frusteri, F.; Asdrubali, F.; Baldinelli, G.; Presciutti, A.; Fantozzi, F.;Bidini, G.; Bartocci, P. Techonologies for energetic exploitation ofbiodiesel chain derived glycerol: Oxy-fuels production by catalyticconversion. Appl. Energy 2013, 102, 63−71.(3) Directive 2009/28/EC of the European Parliament and thecouncil of 23 April 2009 on the promotion of the use of energy fromrenewable sources and amending and subsequently realing Directives2001/77/EC and 2003/30/EC.(4) Zhang, M.; Resende, F. L.P.; Moutsoglou, A.; Raynie, D. E.Pyrolysis of lignin extracted from prairie cordgrass, aspen, and Kraft

Figure 5. Differential pressure in the filter element resulting from theretention of particulate matter (PM) as a function of gas samplevolume with the S10 fuel and its S10bd and S10po formulations.

Table 3. Mass of PM in mg m−3 and the Emissions ofUnburned HCs (%) of Sampled Gas from the CombustionReaction of the S10 Fuel and Its S10bd and S10poFormulations

fuel PM (mg m−3) HCs (%)

S10 33 0.87S10bd 30 0.84S10po 25 0.97

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Energy & Fuels Article

dx.doi.org/10.1021/ef401644v | Energy Fuels 2013, 27, 6831−68386838