Article pubs.acs.org/est
The Effects of Neat Biodiesel and Biodiesel and HVO Blends in Diesel Fuel on Exhaust Emissions from a Light Duty Vehicle with a Diesel Engine Adam Prokopowicz,*,† Marzena Zaciera,† Andrzej Sobczak,†,‡ Piotr Bielaczyc,§ and Joseph Woodburn§ †
Institute of Occupational Medicine and Environmental Health, Koscielna 13, 41-200 Sosnowiec, Poland School of Pharmacy with Division of Laboratory Medicine in Sosnowiec, Medical University of Silesia, Poniatowskiego 15, 40-055 Katowice, Poland § BOSMAL Automotive Research and Development Institute Ltd, Sarni Stok 93, 43-300 Bielsko-Biala, Poland ‡
S Supporting Information *
ABSTRACT: The influence of fatty acid methyl esters (FAME) and hydrotreated vegetable oil (HVO) diesel blends on the exhaust emissions from a passenger car was examined. The impact of FAME for the cold urban phase (UDC) was increased CO and HC emissions, probably due to blend physical properties promoting incomplete combustion. The HVO blend caused the lowest CO and HC emissions for the UDC. NOx emissions did not change significantly with the fuel used, however the UDC was characterized by lower NOx emission for FAME blends. Particle emissions were highest with standard diesel. Emissions of carbonyl compounds increased as fuel biodiesel content increased, especially during the UDC. HVO in diesel fuel decreased carbonyl emissions. Formaldehyde and acetaldehyde were the most abundant carbonyl compounds in the exhaust gas. Total particle-bound PAH emissions were variable, the emission of heavier PAHs increased with blend biodiesel content. The HVO blend increased emission of lighter PAHs. Nitro-PAHs were identified only during the UDC and not for all blends; the highest emissions were measured for pure diesel. The results showed that emission of nitro-PAHs may be decreased to a greater extent by using biodiesel than using a HVO blend.
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consumption needs.4,5 The transesterification process decreases the viscosity and increases the cetane number and heating value in comparison to the feedstock, so FAMEs properties do not differ significantly from petroleum diesel fuel, and may be used in unmodified diesel engines. However, the high percentage of unsaturated bonds in the fatty acids’ structure causes biodiesel to be more prone to oxidation compared to diesel, which decreases its long-term stability properties. Much research has indicated that their addition to diesel fuel reduces the toxicity of exhaust emissions by lowering the emission of particulate matter, carbon monoxide, and total hydrocarbons, although some increase in emission of nitrogen oxides is observed.6−9 Hydrotreated vegetable oil (HVO) is another renewable fuel for diesel engines, which is produced from vegetable oils and composed mainly of liquid paraffinic hydrocarbons. A pathway to their production is conventional hydrotreating catalysis, in which hydrogen is used to remove oxygen atoms and double bonds from the structure of triglicerides. The physical and
INTRODUCTION In the past decade interest in usage of renewable fuels has increased sharply, due to limited fossil fuel resources and the opportunity to reduce greenhouse gas emissions. This also involves transport fuels, which for example, in the EU, have the highest contribution to general energy consumption (about 40%) and of which 5−6% originate from renewable sources.1 In the case of diesel engines, commonly used both in heavy transportation vehicles and passenger cars, fatty acid methyl esters (FAMEs), known as biodiesel, are the main biocomponents which are blended and used with conventional petroleum diesel fuel.2 FAMEs are produced mainly by transestrification of vegetable oils such as soybean, rapeseed, and palm oils with glycerol as a byproduct in an alkali-catalyzed process.3 Although methanol and ethanol are most frequently used as a alcohol, the former is mainly employed because of its low cost and physicochemical advantages but, in contrast to ethanol, methanol originates mostly from fossil feedstock. Production may lead to the presence of some catalyst poisons in biodiesel, like Na, K, or P. The fats for FAME production also may originate from postfrying oils, waste animal fats, or microalgae oil, which fulfill the greenhouse gas emission criteria better than edible vegetable oils and do not compete with food © 2015 American Chemical Society
Received: Revised: Accepted: Published: 7473
February 5, 2015 April 30, 2015 May 20, 2015 May 20, 2015 DOI: 10.1021/acs.est.5b00648 Environ. Sci. Technol. 2015, 49, 7473−7482
Article
Environmental Science & Technology Table 1. Main Physicochemical Properties of the Test Fuelsa fuel parameter density at 15 °C (kg/dm3) viscosity at 40 °C (mm2s) flash point (°C) sulfur content (ppm) cetane number water content (ppm) CFPP °C E250 (evaporated at 250 °C) [% v/v] E350 (evaporated at 350 °C) (% v/v) T95(95% vol. evaporated at) (°C) LHV (MJ/kg) PAHs (% m/m) a
B0 (100% DF)
B7 (93.1% DF + 6.9% FAME)
B15 (85% DF + 15% FAME)
B30 (70% DF + 30% FAME)
B100(100% FAME)
HVO30 (70% DF + 30% HVO)
0.836 2.632 59.5 8.0 55.2 70 −28 38.7
0.838 2.637 61.0 7.1 52.5 82 −27 41.1
0.842
0.847
0.816 2.737
−25
−17
0.875 4.64 178 6.0 56.1 350 −8
98.8
95.7
339.8
347.5
42.6 3.0
37.0
42.9
2.2
−17
DF, diesel fuel; FAME, fatty acid methyl esters; HVO, hydrotreated vegetable oil.
condition, which may change the emission profile of most harmful pollutants, probably due to the higher viscosity and lower volatility of biodiesel in comparison to conventional diesel fuel. Concerning paraffinic fuels, it was observed that emission of formaldehyde and PAHs can decrease with this fuel.16,19 Diesel engine operation is very sensitive to fuel properties; crucially, a number of physical properties change when biodiesel or paraffinic fuel are added to diesel fuel. Thus, changes in emissions may not be just due to the change in chemical composition, but also to changes in other properties such as density, volatility, and cetane number.20 The purpose of the present study was a comparison of regulated and unregulated (carbonyl, PAH and nitro-PAH compounds) emissions in relation to fuels containing different proportions of FAMEs and HVO in diesel fuel. The European legislative NEDC test cycle (Supporting Information page S3), introduced in Directive 98/69/EC, was selected as a representative test for this study. The emission tests were performed on a chassis dynamometer and conducted on a passenger car equipped with a modern direct injection turbocharged diesel engine meeting Euro 4 emission standards.
functional properties of this fuel are very comparable to petroleum diesel fuel so their importance increases, including the possibility of usage as aviation fuel.10 However, aside from cold flow properties, which may be improved by alkane isomerization, due to its low lubricity and high cetane number it is not recommend to use HVO blends with concentrations above 50% in diesel fuel.11 The sooting reduction tendency observed in the same study indicated potential reductions in particulate matter (PM) emissions in most recent model year vehicles. The toxicity of exhaust emission and changes in the profile of emitted pollutants when using renewable fuels is a very important issue, due to the influence on air pollution and the attending possible health effects. Diesel engine exhaust consists of many toxic compounds and has been classified in group 1, according to IARC, as carcinogenic to humans.12 Despite many studies which concern the emissions profile using biodiesel, most of them were conducted with test engines under steady state driving condition, and not on in-use cars, operating with exhaust after treatment devices over transient cycles, for example the New European Driving Cycle (NEDC). A recent investigation indicated a marginal increase in HC, CO, and PM emission under these conditions, due to certain physical properties of biodiesel blends and cold-start occurring in the cycle.13 However, previous studies showed significant increases in CO, HC, and even PM when using biodiesel blends and pure biodiesel, which was explained by higher viscosity and lower volatility of these fuels in comparison to conventional diesel fuel.14,15 In turn, usage of paraffinic biofuels caused reductions of emissions of these pollutants under similar test conditions.16 There are, however, growing concerns regarding unregulated pollutants emitted from diesel engines, which mostly include carbonyl compounds, polycyclic aromatic hydrocarbons (PAHs), and their nitrated derivatives (nitro-PAHs). Recent studies have reported increasing carbonyl compound emissions with increased biodiesel content in the diesel fuel, which is in agreement with the majority of investigations conducted in engine test cells.17,18 In turn, the emission of PAHs was shifted toward lighter PAH compounds and was clearly dependent on the feedstock origin for FAME production, showing that oxidized fuel increased emissions of some PAHs and nitroPAHs compared to when using standard diesel fuel.13 Moreover, these emissions were affected by the cold-start
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MATERIAL AND METHODS The experiment was carried out on midsize passenger car of European manufacture, produced in 2009 and with a compression ignition engine of displacement 1920 cm3. The vehicle’s engine also featured typical technology for a Euro 4 diesel passenger car: a turbocharger, cooled exhaust gas recirculation controlled by an air flow meter, and a commonrail fuel injection system with high-pressure injectors. A diesel particulate filter was not present, but an oxidation catalyst was fitted, again, typical for a Diesel car meeting the Euro 4 standard. The emission tests were carried out in BOSMAL’s Emission Testing Laboratory using an AVL48″ single roll chassis dynamometer. This chassis dynamometer is situated within a climatic chamber (Supporting Information Figure S1). As per the European legislative test method, the test commenced from a cold start at a temperature of 20 °C to 30 °C (24 °C was targeted) with the oil, coolant and all elements of the engine at ambient temperature (24 °C ± 2 °C). The vehicle speed versus time plot for the NEDC is presented in the Supporting Information in Figure S2. Each test on each 7474
DOI: 10.1021/acs.est.5b00648 Environ. Sci. Technol. 2015, 49, 7473−7482
Article
Environmental Science & Technology
Figure 1. Relative emissions of CO, HC, NOx, PM, CO2, and absolute values of fuel consumption for the fuels tested. * p < 0.05.
A HORIBA CVS 7400S system with a full-flow dilution tunnel and DLS 7100EPM sampling system, a set of HORIBA MEXA HTRLE and the HORIBA VETS7000NT management system were all used to measure exhaust emission levels.21 An average dilution ratio of 1:20 and 1:10 was used during UDC and EUDC phases, respectively. Fuel consumption was calculated by the carbon balance method.
blend was performed in triplicate. Six different fuels were used, whose general compositions and densities with some others parameters are listed in Table 1. Pure petroleum diesel fuel, neat rapeseed methyl ester (RME) and B7 were purchased from PKN ORLEN. Pure HVO produced using NExBTL technology was obtained from Neste Oil Oyj. In addition, conventional diesel was blended to obtain the remaining fuels (B15, B30, HVO30). 7475
DOI: 10.1021/acs.est.5b00648 Environ. Sci. Technol. 2015, 49, 7473−7482
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Environmental Science & Technology Table 2. Regulated emissions over the NEDC (UDC + EUDC)a emissions (mg/km) NEDC
a
CO2 emission (g/km)
UDC
EUDC
fuel
CO
NOx
HC
PM
CO
NOx
HC
PM
CO
NOx
HC
PM
NEDC
UDC
EUDC
B0 B7 B15 B30 B100 HVO30
121 159 145 167 426 59
221 211 219 220 211 224
30 36 40 45 97 25
33 29 29 26 16 30
323 428 391 448 1152 154
257 234 241 249 206 266
69 83 90 103 246 51
34 32 27 25 31 30
4 4 4 4 4 5
201 197 207 204 213 200
8 8 11 12 10 10
33 27 31 26 8 31
162.8 164.3 161.4 163.4 169.7 161.9
214.0 212.1 207.9 211.3 226.9 207.3
133.4 136.7 134.6 135.7 136.6 135.6
Euro 4 limits (mg/km): CO 500; NOx 250; (NOx+HC) 300; PM 25.
a near-linear relationship between this reduction and the increase in the H/C ratio of the fuel. However, the main reason for the observed reduction is probably the lower boiling point, which has a beneficial impact on complete vaporization of the fuel in the combustion chamber at low load and cold start conditions.11In turn, Lim et al. indentified the increased cetane number with HVO addition to diesel fuel as an important factor for reducing the CO emission level.30During the EUDC phase, emissions of CO were at a very low level, due to the high effectiveness of the vehicle’s diesel oxidation catalyst at removing CO, and comparable for all tested fuels. No reductions in CO emissions during the EUDC phase were observed for any of the fuels containing FAME, nor for HVO blend. A similar tendency as for CO emission was observed for total HC emissions, which were also the highest in the case of B100 in the UDC phase. In reference to conventional diesel fuel, a significant increase occurred also for B30, but for the other biodiesel blends, the increase in HC emissions was only marginally significant. As reported previously, benzene was the most abundant among the light aromatic hydrocarbons, and benzene emissions showed a similar trend to that of total HC.31 This trend was especially visible during the UDC phase and it is undoubtedly the result of the cold start conditions and the physicochemical parameters of fuels containing FAME. Diesel engine cold start is affected by many interacting processes during mixture formation inside the cylinder that lead to autoignition and combustion. Emissions during DI diesel engine cold-start and warm up are significant for overall emissions, (however not as significant as in a spark-ignition engine), since the conditions for fuel atomization, mixture formation and combustion are poor.32 Moreover, aftertreatment devices (e.g., an oxidizing catalyst) do not work effectively under these conditions. A previous investigation concerning HC emissions when using standard diesel fuel indicated that during the first of the four elementary phases of the UDC, this emission is 100−150% higher than during the last elementary phase of the UDC.33 Poorer atomization and vaporization due to the higher density, viscosity and boiling point of FAME and its blends than for pure petroleum diesel fuel lead to an increase in HC emissions during the UDC, which during the following EUDC phase did not show such a significant differentiation (only for B30, marginally). As discussed by Giacoumis and coworkers,9 a diesel oxidation catalyst may seem to operate less efficiently with biodiesel and biodiesel blends not only under cold conditions, but also throughout the whole cycle. The reason for this behavior is the lower biodiesel exhaust gas temperature causing lower available exhaust gas thermal energy. It was evident that HC emissions decreased for the HVO30
Carbonyl compounds in the engine exhaust gas were determined using 2,4-dinitrophenylhydrazine (2,4-DNPH) method after collection of diluted exhaust in Tedlar bags. Particle bound PAHs and nitro-PAHs collected onto Pallflex (T60A20) filters were determined by HPLC with fluorescence detection and GC-MS method, respectively.14,15 Methodological details and QA/QC data including recoveries, precision and accuracy for carbonyl, PAH and nitro-PAH compounds are presented in the Supporting Information, (pages S3−S4 and Table S1). t test analyses were used to assess differences in emission results. P values 70) and its addition to diesel fuel increases the cetane number linearly. It was found that increased cetane number also reduced emissions of HC and CO, probably due to improvement of ignition performance.30Another cause for the observed reduction may be a decrease in concentration of precursors for carbonyl compound formation and the degree of molecular unsaturation. The ability of paraffinic fuel to reduce emission of carbonyl compounds was also found in some earlier studies. Yuan et al.50 evaluated emissions from a heavy-duty diesel engine in a transient test using a paraffinic and biodiesel blend and they obtained a significant reduction of carbonyls in exhaust gases, equaling 24% and 30% for 20% and 5% biodiesel paraffinic blend, respectively. Zervas et al.16tested two types of paraffinic fuel and also obtained significant reductions of formaldehyde, acetaldehyde and total carbonyl compounds, which reached 69% and 89% in comparison to when using conventional diesel fuel. PAH Emissions. PAH emissions in vehicular diesel exhaust are the focus of much attention because many of these compounds have been identified as potential cancer causing compounds. According to IARC, there is sufficient evidence of the carcinogenicity of benzo(a)pyrene in humans (group 1A). Additionally, dibenzo(a,h)anthracene, benzo(a)anthracene, benzo(b)fluorantene, benzo(k)fluorantene, chrysene, and indeno(1,2,3-c,d)pyrene are recognized as animal carcinogens (IARC groups 2A and 2B). Regarding diesel exhaust emissions, there are especially suitable conditions for adsorption of these compounds on simultaneously emitted particulate matter. Very fine particulate matter containing particles B7 > HVO30 > B100 and with B15 and B30 all of the 6 nitro-PAHs analyzed were below the limit of detection. These decreasing nitro-PAH emissions with biodiesel and biodiesel blends in comparison to diesel fuel is in agreement with previous studies.13,17,58,59 The main reason for this reduction was attributed to lower emission of nitro-PAH precursors, that is, parent PAHs, which therefore resulted in the higher emission of nitro-PAHs measured with oxidized biodiesel blends, whose use were related to higher PAH emissions than with diesel fuel. In this study a reduction was found in most cases, despite the increase in emission of parent PAHs. This may suggest less favorable conditions for the
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AUTHOR INFORMATION
Corresponding Author
*Phone: +48326341195; e-mail: a.prokopowicz@imp. sosnowiec.pl. Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding
This work was supported by the Polish Ministry of Science and Higher Education, grant number N N404 311540. Notes
The authors declare no competing financial interest.
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ABBREVIATIONS CVS constant volume sampling EUDC Extra Urban Driving Cycle NEDC New European Driving Cycle UDC Urban Driving Cycle
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DOI: 10.1021/acs.est.5b00648 Environ. Sci. Technol. 2015, 49, 7473−7482
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Environmental Science & Technology (47) Nelson, P. F.; Tibbett, A. R.; Day, S. J. Effects of vehicle type and fuel quality on real world toxic emissions from diesel vehicles. Atmos. Environ. 2008, 42, 5291−5303. (48) Guariero, L. L. N.; Pereria, P. A. P.; Torres, E. A.; Rocha, G. O.; Andrade, J. B. Carbonyl compounds emitted by a diesel engine fuelled with diesel and biodiesel-diesel blends: Sampling optimization and emissions profile. Atmos. Environ. 2008, 42, 8211−8218. (49) Ballesteros, R.; Hernandez, J. J.; Guillen-Flores, J. Carbonyl speciation in a typical European automotive diesel engine using bioethanol-diesel blends. Fuel 2012, 95, 136−145. (50) Yuan, C. S.; Lin, Y. C.; Tsai, C. H.; Wu, C. C.; Lin, Y. S. Reducing carbonyl emissions from a heavy-duty diesel engine at US transient cycle test by use of paraffinic/biodiesel blends. Atmos. Environ. 2009, 43, 6175−6181. (51) Selected Nitro- and Nitro-Oxy-Polycyclic Aromatic Hydrocarbons, Environmental Health Criteria 229; World Health Organization: Geneva, 2003. (52) He, C.; Ge, Y.; Tan, Y.; You, K.; Han, X.; Wang, J. Characteristics of polycyclic aromatic hydrocarbons of diesel engine fueled with biodiesel and diesel. Fuel 2010, 89, 2040−2046. (53) Casal, C. S.; Arbilla, G.; Correa, S. M. Alkyl polycyclic aromatic hydrocarbons emissions in diesel/biodiesel exhaust. Atmos. Environ. 2014, 96, 107−116. (54) Correa, S. M.; Arbilla, G. Aromatic hydrocarbons emissions in diesel and biodiesel exhaust. Atmos. Environ. 2006, 40, 6821−6826. (55) Turrio-Baldassarri, L.; Battistelli, C. L.; Conti, L.; Crebelli, R.; De Berardis, B.; Iamiceli, A. L.; Gambio, M.; Iannaccone, S. Emission comparison of urban bus engine fueled with diesel oil and ‘biodiesel’ blend. Sci. Total Environ. 2004, 327, 147−162. (56) Ballesteros, R.; Hernández, J. J.; Lyons, L. An experimental study of the influence of biofuel origin on particle-associated PAH emissions. Atmos. Environ. 2010, 44, 930−938. (57) Szewczynska, M.; Posniak, M. Polycyclic aromatic hydrocarbons and soluble organic fraction in fine particles from solid fraction of biodiesel exhaust fumes. Med. Pr. 2012, 63, 659−666 (in Polish).. (58) Kooter, I. M.; Vugt, M.A.T. M.; Jedynska, A. D.; Tromp, P. C.; Houtzager, M. M. G.; Verbeek, R. P.; Kadijk, G.; Mulderij, M.; Krul, C. A. M. Toxicological characterization of diesel engine emissions using biodiesel and closed soot filter. Atmos. Environ. 2011, 45, 1574−1580. (59) Huang, L.; Bohac, S. V.; Chernyak, S. M.; Batterman, S. A. Effects of fuels, engine load and exhaust after-treatment on diesel engine SVOC emissions and development of SVOC profiles for receptor modeling. Atmos. Environ. 2015, 102, 228−238.
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The Effects of Neat Biodiesel and Biodiesel and HVO Blends in Diesel Fuel on Exhaust Emissions from a Light Duty Vehicle with a Diesel Engine Adam Prokopowicz,*,† Marzena Zaciera,† Andrzej Sobczak,†,‡ Piotr Bielaczyc,§ and Joseph Woodburn§ †
Institute of Occupational Medicine and Environmental Health, Koscielna 13, 41-200 Sosnowiec, Poland School of Pharmacy with Division of Laboratory Medicine in Sosnowiec, Medical University of Silesia, Poniatowskiego 15, 40-055 Katowice, Poland § BOSMAL Automotive Research and Development Institute Ltd, Sarni Stok 93, 43-300 Bielsko-Biala, Poland ‡
S Supporting Information *
ABSTRACT: The influence of fatty acid methyl esters (FAME) and hydrotreated vegetable oil (HVO) diesel blends on the exhaust emissions from a passenger car was examined. The impact of FAME for the cold urban phase (UDC) was increased CO and HC emissions, probably due to blend physical properties promoting incomplete combustion. The HVO blend caused the lowest CO and HC emissions for the UDC. NOx emissions did not change significantly with the fuel used, however the UDC was characterized by lower NOx emission for FAME blends. Particle emissions were highest with standard diesel. Emissions of carbonyl compounds increased as fuel biodiesel content increased, especially during the UDC. HVO in diesel fuel decreased carbonyl emissions. Formaldehyde and acetaldehyde were the most abundant carbonyl compounds in the exhaust gas. Total particle-bound PAH emissions were variable, the emission of heavier PAHs increased with blend biodiesel content. The HVO blend increased emission of lighter PAHs. Nitro-PAHs were identified only during the UDC and not for all blends; the highest emissions were measured for pure diesel. The results showed that emission of nitro-PAHs may be decreased to a greater extent by using biodiesel than using a HVO blend.
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consumption needs.4,5 The transesterification process decreases the viscosity and increases the cetane number and heating value in comparison to the feedstock, so FAMEs properties do not differ significantly from petroleum diesel fuel, and may be used in unmodified diesel engines. However, the high percentage of unsaturated bonds in the fatty acids’ structure causes biodiesel to be more prone to oxidation compared to diesel, which decreases its long-term stability properties. Much research has indicated that their addition to diesel fuel reduces the toxicity of exhaust emissions by lowering the emission of particulate matter, carbon monoxide, and total hydrocarbons, although some increase in emission of nitrogen oxides is observed.6−9 Hydrotreated vegetable oil (HVO) is another renewable fuel for diesel engines, which is produced from vegetable oils and composed mainly of liquid paraffinic hydrocarbons. A pathway to their production is conventional hydrotreating catalysis, in which hydrogen is used to remove oxygen atoms and double bonds from the structure of triglicerides. The physical and
INTRODUCTION In the past decade interest in usage of renewable fuels has increased sharply, due to limited fossil fuel resources and the opportunity to reduce greenhouse gas emissions. This also involves transport fuels, which for example, in the EU, have the highest contribution to general energy consumption (about 40%) and of which 5−6% originate from renewable sources.1 In the case of diesel engines, commonly used both in heavy transportation vehicles and passenger cars, fatty acid methyl esters (FAMEs), known as biodiesel, are the main biocomponents which are blended and used with conventional petroleum diesel fuel.2 FAMEs are produced mainly by transestrification of vegetable oils such as soybean, rapeseed, and palm oils with glycerol as a byproduct in an alkali-catalyzed process.3 Although methanol and ethanol are most frequently used as a alcohol, the former is mainly employed because of its low cost and physicochemical advantages but, in contrast to ethanol, methanol originates mostly from fossil feedstock. Production may lead to the presence of some catalyst poisons in biodiesel, like Na, K, or P. The fats for FAME production also may originate from postfrying oils, waste animal fats, or microalgae oil, which fulfill the greenhouse gas emission criteria better than edible vegetable oils and do not compete with food © 2015 American Chemical Society
Received: Revised: Accepted: Published: 7473
February 5, 2015 April 30, 2015 May 20, 2015 May 20, 2015 DOI: 10.1021/acs.est.5b00648 Environ. Sci. Technol. 2015, 49, 7473−7482
Article
Environmental Science & Technology Table 1. Main Physicochemical Properties of the Test Fuelsa fuel parameter density at 15 °C (kg/dm3) viscosity at 40 °C (mm2s) flash point (°C) sulfur content (ppm) cetane number water content (ppm) CFPP °C E250 (evaporated at 250 °C) [% v/v] E350 (evaporated at 350 °C) (% v/v) T95(95% vol. evaporated at) (°C) LHV (MJ/kg) PAHs (% m/m) a
B0 (100% DF)
B7 (93.1% DF + 6.9% FAME)
B15 (85% DF + 15% FAME)
B30 (70% DF + 30% FAME)
B100(100% FAME)
HVO30 (70% DF + 30% HVO)
0.836 2.632 59.5 8.0 55.2 70 −28 38.7
0.838 2.637 61.0 7.1 52.5 82 −27 41.1
0.842
0.847
0.816 2.737
−25
−17
0.875 4.64 178 6.0 56.1 350 −8
98.8
95.7
339.8
347.5
42.6 3.0
37.0
42.9
2.2
−17
DF, diesel fuel; FAME, fatty acid methyl esters; HVO, hydrotreated vegetable oil.
condition, which may change the emission profile of most harmful pollutants, probably due to the higher viscosity and lower volatility of biodiesel in comparison to conventional diesel fuel. Concerning paraffinic fuels, it was observed that emission of formaldehyde and PAHs can decrease with this fuel.16,19 Diesel engine operation is very sensitive to fuel properties; crucially, a number of physical properties change when biodiesel or paraffinic fuel are added to diesel fuel. Thus, changes in emissions may not be just due to the change in chemical composition, but also to changes in other properties such as density, volatility, and cetane number.20 The purpose of the present study was a comparison of regulated and unregulated (carbonyl, PAH and nitro-PAH compounds) emissions in relation to fuels containing different proportions of FAMEs and HVO in diesel fuel. The European legislative NEDC test cycle (Supporting Information page S3), introduced in Directive 98/69/EC, was selected as a representative test for this study. The emission tests were performed on a chassis dynamometer and conducted on a passenger car equipped with a modern direct injection turbocharged diesel engine meeting Euro 4 emission standards.
functional properties of this fuel are very comparable to petroleum diesel fuel so their importance increases, including the possibility of usage as aviation fuel.10 However, aside from cold flow properties, which may be improved by alkane isomerization, due to its low lubricity and high cetane number it is not recommend to use HVO blends with concentrations above 50% in diesel fuel.11 The sooting reduction tendency observed in the same study indicated potential reductions in particulate matter (PM) emissions in most recent model year vehicles. The toxicity of exhaust emission and changes in the profile of emitted pollutants when using renewable fuels is a very important issue, due to the influence on air pollution and the attending possible health effects. Diesel engine exhaust consists of many toxic compounds and has been classified in group 1, according to IARC, as carcinogenic to humans.12 Despite many studies which concern the emissions profile using biodiesel, most of them were conducted with test engines under steady state driving condition, and not on in-use cars, operating with exhaust after treatment devices over transient cycles, for example the New European Driving Cycle (NEDC). A recent investigation indicated a marginal increase in HC, CO, and PM emission under these conditions, due to certain physical properties of biodiesel blends and cold-start occurring in the cycle.13 However, previous studies showed significant increases in CO, HC, and even PM when using biodiesel blends and pure biodiesel, which was explained by higher viscosity and lower volatility of these fuels in comparison to conventional diesel fuel.14,15 In turn, usage of paraffinic biofuels caused reductions of emissions of these pollutants under similar test conditions.16 There are, however, growing concerns regarding unregulated pollutants emitted from diesel engines, which mostly include carbonyl compounds, polycyclic aromatic hydrocarbons (PAHs), and their nitrated derivatives (nitro-PAHs). Recent studies have reported increasing carbonyl compound emissions with increased biodiesel content in the diesel fuel, which is in agreement with the majority of investigations conducted in engine test cells.17,18 In turn, the emission of PAHs was shifted toward lighter PAH compounds and was clearly dependent on the feedstock origin for FAME production, showing that oxidized fuel increased emissions of some PAHs and nitroPAHs compared to when using standard diesel fuel.13 Moreover, these emissions were affected by the cold-start
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MATERIAL AND METHODS The experiment was carried out on midsize passenger car of European manufacture, produced in 2009 and with a compression ignition engine of displacement 1920 cm3. The vehicle’s engine also featured typical technology for a Euro 4 diesel passenger car: a turbocharger, cooled exhaust gas recirculation controlled by an air flow meter, and a commonrail fuel injection system with high-pressure injectors. A diesel particulate filter was not present, but an oxidation catalyst was fitted, again, typical for a Diesel car meeting the Euro 4 standard. The emission tests were carried out in BOSMAL’s Emission Testing Laboratory using an AVL48″ single roll chassis dynamometer. This chassis dynamometer is situated within a climatic chamber (Supporting Information Figure S1). As per the European legislative test method, the test commenced from a cold start at a temperature of 20 °C to 30 °C (24 °C was targeted) with the oil, coolant and all elements of the engine at ambient temperature (24 °C ± 2 °C). The vehicle speed versus time plot for the NEDC is presented in the Supporting Information in Figure S2. Each test on each 7474
DOI: 10.1021/acs.est.5b00648 Environ. Sci. Technol. 2015, 49, 7473−7482
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Figure 1. Relative emissions of CO, HC, NOx, PM, CO2, and absolute values of fuel consumption for the fuels tested. * p < 0.05.
A HORIBA CVS 7400S system with a full-flow dilution tunnel and DLS 7100EPM sampling system, a set of HORIBA MEXA HTRLE and the HORIBA VETS7000NT management system were all used to measure exhaust emission levels.21 An average dilution ratio of 1:20 and 1:10 was used during UDC and EUDC phases, respectively. Fuel consumption was calculated by the carbon balance method.
blend was performed in triplicate. Six different fuels were used, whose general compositions and densities with some others parameters are listed in Table 1. Pure petroleum diesel fuel, neat rapeseed methyl ester (RME) and B7 were purchased from PKN ORLEN. Pure HVO produced using NExBTL technology was obtained from Neste Oil Oyj. In addition, conventional diesel was blended to obtain the remaining fuels (B15, B30, HVO30). 7475
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Environmental Science & Technology Table 2. Regulated emissions over the NEDC (UDC + EUDC)a emissions (mg/km) NEDC
a
CO2 emission (g/km)
UDC
EUDC
fuel
CO
NOx
HC
PM
CO
NOx
HC
PM
CO
NOx
HC
PM
NEDC
UDC
EUDC
B0 B7 B15 B30 B100 HVO30
121 159 145 167 426 59
221 211 219 220 211 224
30 36 40 45 97 25
33 29 29 26 16 30
323 428 391 448 1152 154
257 234 241 249 206 266
69 83 90 103 246 51
34 32 27 25 31 30
4 4 4 4 4 5
201 197 207 204 213 200
8 8 11 12 10 10
33 27 31 26 8 31
162.8 164.3 161.4 163.4 169.7 161.9
214.0 212.1 207.9 211.3 226.9 207.3
133.4 136.7 134.6 135.7 136.6 135.6
Euro 4 limits (mg/km): CO 500; NOx 250; (NOx+HC) 300; PM 25.
a near-linear relationship between this reduction and the increase in the H/C ratio of the fuel. However, the main reason for the observed reduction is probably the lower boiling point, which has a beneficial impact on complete vaporization of the fuel in the combustion chamber at low load and cold start conditions.11In turn, Lim et al. indentified the increased cetane number with HVO addition to diesel fuel as an important factor for reducing the CO emission level.30During the EUDC phase, emissions of CO were at a very low level, due to the high effectiveness of the vehicle’s diesel oxidation catalyst at removing CO, and comparable for all tested fuels. No reductions in CO emissions during the EUDC phase were observed for any of the fuels containing FAME, nor for HVO blend. A similar tendency as for CO emission was observed for total HC emissions, which were also the highest in the case of B100 in the UDC phase. In reference to conventional diesel fuel, a significant increase occurred also for B30, but for the other biodiesel blends, the increase in HC emissions was only marginally significant. As reported previously, benzene was the most abundant among the light aromatic hydrocarbons, and benzene emissions showed a similar trend to that of total HC.31 This trend was especially visible during the UDC phase and it is undoubtedly the result of the cold start conditions and the physicochemical parameters of fuels containing FAME. Diesel engine cold start is affected by many interacting processes during mixture formation inside the cylinder that lead to autoignition and combustion. Emissions during DI diesel engine cold-start and warm up are significant for overall emissions, (however not as significant as in a spark-ignition engine), since the conditions for fuel atomization, mixture formation and combustion are poor.32 Moreover, aftertreatment devices (e.g., an oxidizing catalyst) do not work effectively under these conditions. A previous investigation concerning HC emissions when using standard diesel fuel indicated that during the first of the four elementary phases of the UDC, this emission is 100−150% higher than during the last elementary phase of the UDC.33 Poorer atomization and vaporization due to the higher density, viscosity and boiling point of FAME and its blends than for pure petroleum diesel fuel lead to an increase in HC emissions during the UDC, which during the following EUDC phase did not show such a significant differentiation (only for B30, marginally). As discussed by Giacoumis and coworkers,9 a diesel oxidation catalyst may seem to operate less efficiently with biodiesel and biodiesel blends not only under cold conditions, but also throughout the whole cycle. The reason for this behavior is the lower biodiesel exhaust gas temperature causing lower available exhaust gas thermal energy. It was evident that HC emissions decreased for the HVO30
Carbonyl compounds in the engine exhaust gas were determined using 2,4-dinitrophenylhydrazine (2,4-DNPH) method after collection of diluted exhaust in Tedlar bags. Particle bound PAHs and nitro-PAHs collected onto Pallflex (T60A20) filters were determined by HPLC with fluorescence detection and GC-MS method, respectively.14,15 Methodological details and QA/QC data including recoveries, precision and accuracy for carbonyl, PAH and nitro-PAH compounds are presented in the Supporting Information, (pages S3−S4 and Table S1). t test analyses were used to assess differences in emission results. P values 70) and its addition to diesel fuel increases the cetane number linearly. It was found that increased cetane number also reduced emissions of HC and CO, probably due to improvement of ignition performance.30Another cause for the observed reduction may be a decrease in concentration of precursors for carbonyl compound formation and the degree of molecular unsaturation. The ability of paraffinic fuel to reduce emission of carbonyl compounds was also found in some earlier studies. Yuan et al.50 evaluated emissions from a heavy-duty diesel engine in a transient test using a paraffinic and biodiesel blend and they obtained a significant reduction of carbonyls in exhaust gases, equaling 24% and 30% for 20% and 5% biodiesel paraffinic blend, respectively. Zervas et al.16tested two types of paraffinic fuel and also obtained significant reductions of formaldehyde, acetaldehyde and total carbonyl compounds, which reached 69% and 89% in comparison to when using conventional diesel fuel. PAH Emissions. PAH emissions in vehicular diesel exhaust are the focus of much attention because many of these compounds have been identified as potential cancer causing compounds. According to IARC, there is sufficient evidence of the carcinogenicity of benzo(a)pyrene in humans (group 1A). Additionally, dibenzo(a,h)anthracene, benzo(a)anthracene, benzo(b)fluorantene, benzo(k)fluorantene, chrysene, and indeno(1,2,3-c,d)pyrene are recognized as animal carcinogens (IARC groups 2A and 2B). Regarding diesel exhaust emissions, there are especially suitable conditions for adsorption of these compounds on simultaneously emitted particulate matter. Very fine particulate matter containing particles B7 > HVO30 > B100 and with B15 and B30 all of the 6 nitro-PAHs analyzed were below the limit of detection. These decreasing nitro-PAH emissions with biodiesel and biodiesel blends in comparison to diesel fuel is in agreement with previous studies.13,17,58,59 The main reason for this reduction was attributed to lower emission of nitro-PAH precursors, that is, parent PAHs, which therefore resulted in the higher emission of nitro-PAHs measured with oxidized biodiesel blends, whose use were related to higher PAH emissions than with diesel fuel. In this study a reduction was found in most cases, despite the increase in emission of parent PAHs. This may suggest less favorable conditions for the
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AUTHOR INFORMATION
Corresponding Author
*Phone: +48326341195; e-mail: a.prokopowicz@imp. sosnowiec.pl. Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding
This work was supported by the Polish Ministry of Science and Higher Education, grant number N N404 311540. Notes
The authors declare no competing financial interest.
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ABBREVIATIONS CVS constant volume sampling EUDC Extra Urban Driving Cycle NEDC New European Driving Cycle UDC Urban Driving Cycle
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DOI: 10.1021/acs.est.5b00648 Environ. Sci. Technol. 2015, 49, 7473−7482
