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Effects of biodiesel blend fuel on volatile organic compound (VOC) emissions from diesel engine exhaust
b i o m a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 9 6 e1 0 6
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Effects of biodiesel blend fuel on volatile organic compound (VOC) emissions from diesel engine exhaust Chiung-Yu Peng a,*, Cheng-Hang Lan b, Chun-Yuh Yang a a b
Department of Public Health, College of Health Sciences, Kaohsiung Medical University, Kaohsiung 807, Taiwan Department of Occupational Safety and Health, Chung-Hwa College of Medical Technology, Tainan County 717, Taiwan
article info
abstract
Article history:
Biodiesel has been increasingly used due to its property similarities with diesel and several
Received 7 June 2008
other favorable characteristics with respect to exhaust emissions and biodegradation. For
Received in revised form
better understanding of biodiesel, this study examines the effects of the biodiesel blend
13 October 2011
fuel on VOC emissions from diesel engine exhausts in comparison with those from diesel
Accepted 16 October 2011
fuel. Exhaust emission tests were performed several times for each fuel under the US
Available online 16 November 2011
transient cycle protocol from mileages of 0e80,000 km. VOC samples were collected from diluted exhaust by using thermal desorption tubes, then analyzed by a GC/MS system.
Keywords:
Twenty-two and forty-seven chemicals are identified and quantified in B20 and diesel fuels
Oxygenated VOCs
respectively. Total VOC emissions are in the range of 32.4e71.6 mg kW h1 for B20 fuel, and
Ozone potential
49.6e183.7 mg kW h1 for diesel fuel. Individual VOC emissions are in the ranges of
Thermal desorption
0.1e29.8 mg kW h1 for B20 fuel and 0.1e93.6 mg kW h1 for diesel fuel. Individual VOC
Transit cycle
health risks in terms of hazard quotients are in the ranges of 0.01e1.13, and 0.01e22.79 for
Durability test
B20 and diesel fuels, respectively. B20 has much lower total VOC emissions, decreasing by 61.2% on average; correspondingly, lower total ozone potentials of VOC reduce by 64.0%. The reductions in health risks are also shown in B20 fuel. As a result, use of biodiesel in diesel engines has beneficial effects in terms of VOC emissions. ª 2011 Elsevier Ltd. All rights reserved.
1.
Introduction
Recently there has been increasing interest and application in the use of biodiesel as a substitute for petroleum-based diesel fuel due to high pricing and limited quantities of petroleum oils. Biodiesels are manufactured from the transesterification of vegetable oils or animal fats with alcohols using acids or bases as catalysts, yielding free glycerol as a byproduct [1,2]. Biodiesels can be completely miscible with petroleum diesel fuels in any proportion as blends, and replace diesels in many applications with little or no modification due to having similar properties as petroleum-based diesels [3e7]. Moreover, they are renewable fuels and have characteristics of
biodegradability, a closed carbon cycle, lower volatility, higher cetane number, increasing lubricity, and less CO, SO2and particulate matter (PM) emissions [8e17]. Even though biodiesel has great characteristics, like some other biofuels, some researchers are concerned that exhaust emissions of biofuels would present increased adverse effects on public health [18e20]. Biodiesels have been extensively studied in exhaust emissions of regulated pollutants (CO, HC (hydrocarbons), NOx and PM). Except NO2 emissions, the results favor biodiesel usage in diesel engines [1,4,5,21e24]. Recently, several different measurements that went beyond basic regulated pollutants were performed. Most concentrated on
* Corresponding author. Tel.: þ886 7 3121101x2314; fax: þ886 7 3234691 . E-mail address: [email protected] (C.-Y. Peng). 0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2011.10.016
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composition and quantification of HC and PM. These included measurements of volatile organic compounds (VOCs) and carbonyl compounds from gaseous exhaust, and measurements of polyaromatic hydrocarbons (PAH) from both gaseous and particulate emissions. The limited data showed exhaust emissions were lower in total VOCs, total carbonyl compounds and total PAH when biodiesel fuels were used [16,18,25,26]. However, several un-determined issues were found when unregulated pollutant emissions were examined. For example, an EPA study [25] revealed that the ratio of total VOC (determined by GC) to HC (determined by direct-reading instrument) increased with the biodiesel concentration. The soluble organic fraction of the emitted particles is greater in biodiesel exhaust emissions than that in diesel’s, even though the reductions are shown in total HC and total mass of PM for biodiesel. In terms of individual chemical, biodiesels produced inconsistent results or slightly higher emissions of some chemicals, such as benzene, toluene and acrolein as compared to diesels. Further studies should be carried out to investigate the impacts of biodiesels on emissions of unregulated hazardous air pollutants. Among unregulated air pollutants, carbonyl compounds have been investigated by a study [16] over cumulative mileages of 0e80,000 km and the results indicate that B20 generates lower aldehyde emissions. This mainly results from formaldehyde emissions which drop by 23% on average. In addition to carbonyl chemicals, VOCs are important unregulated air pollutants in vehicle emissions, since vehicles are significant sources of VOCs, different classes of VOCs may have very distinct photochemical activity and adverse health effects [27e29]. Individual VOC information is more important than total HC data with respect to health effects and environmental impacts [25]. Limited data show that biodiesel produces inconsistent results on some chemicals as compared to diesels [1,25]. It seems that definitive studies in this area have not been performed. Therefore, this is clearly an area in need of more extensive research on investigating the effect of this oxygenrich fuel on VOC exhaust emissions. Additionally, several issues, such as whether VOC species in biodiesel exhaust are different from those of diesels, the effects of vehicle/engine age on VOC emissions, and ozone formation potentials of VOC emissions, have been considered in relation to exhaust emissions from biodiesel fuels. The importance of these considerations increases when more vehicles use biodiesel as a fuel and run over long periods of time. Therefore, the present study characterizes and compares VOC emissions in both fuels, estimates corresponding ozone formation potentials, and examines the effects of increased mileage and maintenance procedures on VOC emissions.
2.
Materials and methods
2.1.
Engines, dynamometer and driving cycle
Two new modern diesel engines (Mitsubishi 4M40-2AT1) of exactly the same type which were used in pick-up trucks were employed in this study. These two engines were fueled with diesel and B20, separately; a commercially available synthetic
engine lubricating oil (API SG/CEþ; 15W/40) was used. Changes of lubricating oil took place during maintenance at mileages of 40,000 km and 80,000 km. The engines had 4 cylinders with a bore and stroke of 95 mm 100 mm, a total displacement of 2.84 103 m3. They were turbocharged and indirectly injected. The maximum power was 80.9 kW at 387 rad s1, and maximum torque was 217.6 Nm at 209 rad s1. The tested engines account for 21.3% of diesel cars in terms of total displacement volume in Taiwan [30]. These two engines were mounted and operated on a Schenck DyNAS 335 dynamometer with a DC-IV control system. The DC-current dynamometer with a fully automatic control system was capable of supplying maximum power of 335 kW and maximum torque of 800 N m. Integrated powers over the test period of the two engines were 9.16 0.09 and 9.03 0.13 kW h separately, showing that these two engines had the same performance. Exhaust emission tests were performed under the US transient cycle protocol at cumulative mileages of 0 km, 20,000 km, 40,000 km (before maintenance), 40,000 km (after maintenance), 60,000 km, 80,000 km (before maintenance), and 80,000 km (after maintenance) respectively. The transit cycle and durability test up to 80,000 km are legislated procedures in Taiwan for certification of light heavy-duty diesel cars. This transient cycle sequence took 20 min and included express way, congested urban and uncongested urban driving patterns, which represented a wide variety of speeds and loads to simulate vehicle running conditions [31]. One coldstart cycle and two hot-start ones were carried out with a 20-min soak between starts in each test condition. To mimic actual conditions, the emission factor was estimated based on the composite emission mass which was calculated as oneseventh of cold-start mass and six-sevenths of hot-start mass (average of two hot-start cycles).
2.2.
Fuels
Diesel fuel and the blended fuel B20, containing 20% waste soybean oil biodiesel, and 80% diesel, were used. Diesel was supplied by China Petroleum Company and the waste soybean oil biodiesel was provided by Taiwan New Japan Chemical Corporation. Waste soybean oil biodiesel was produced by transesterification of triglycerides with methanol, and its main fatty acid profile was palmitic fatty acid (12%), oleic fatty acid (23%) and linoleic fatty acid (55%). The properties of tested fuels are listed in Table 1. Diesel and biodiesel fuels meet the specifications of CNS 1471 [32]and CNS 15072 [32]separately.
Table 1 e Properties of tested fuels. Properties Density at 15 C, kg m3 Flash point, C Kinematic viscosity at 40 C, mm2 s1 Cetane index Lubricity, mm Sulfur, mg kg1 Carbon, % (mass fraction) Hydrogen, % (mass fraction) Oxygen, % (mass fraction) Average heat value, MJ kg1
B20
Diesel
840.7 97 3.53 55.7 196 20.5 84.0 13.2 2.8 41.7
830.8 78 3.15 53.1 332 21.8 86.9 13.1 e 42.8
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2.3. Dilution tunnel and constant volume sampling system The exhaust emission sampling system operated on the basis of constant volume sampling (CVS) and fixed dilution ratio, which reduced the temperature of emission exhaust to accommodate sampler requirements. The temperature of the fully diluted exhaust did not exceed 100 C. The system consisted of a dilution air purification device (filters and activated charcoal), a dilution tunnel, a critical flow Venturi, a Spencer blower and a discharge cleaning device (filters and activated charcoal) (Fig. 1). The tunnel was 61cm in diameter and 50 m in length. Diluted air, which was from ambient air and cleaned by a purification device, was drawn into the dilution tunnel by a Spencer blower (Fig. 1). The quantity of air in the dilution tunnel was controlled by the critical flow Venturi. Total engine exhaust gas was fed into the tunnel by a 7.5-m long solid insulated pipe with a 10 cm diameter and mixed with the diluted air in the beginning section of the dilution tunnel. Samples were collected at least 8-diameter long downstream of the mixing point to ensure good mixing. Although no diluted air samples were taken, ambient air which served as diluted air had much lower VOC concentrations in comparison with exhaust air [33e35] and was cleaned by the purification device before entering the dilution tunnel. The VOC contribution from diluted air was minimal. The regulated gaseous pollutants (CO, CO2, NOx, and HC) were measured by computer-controlled analyzers continuously. Volatile organic compound and aldehyde emissions were collected over the transit cycle from the dilution tunnel with 100-L Tedlar bags (SKC Inc., Eighty Four, PA, USA) at a flow rate of 4 L min1 by an in-line pump for the entire cycle (20 min). Pollutant data other than VOCs are not shown here.
range of fuel combustion products. After sampling, the tubes were analyzed with a thermal desorption system (TD4, Scientific Instrument Services, Ringoes, NJ, USA) located directly in the injector/septum area of the GC/MS. The liquidN2-cooled cryofocus trap was mounted in the GC oven, just below the injection port and around the 5-cm section of the capillary column. The cryofocus process concentrated the desorption air flow and provided good resolution in gas chromatograms. A temperature program increasing from 40 to 300 C at a rate of 8 C min1 with a broad mass range (33e400 AMU) was used to detect the compounds with different volatility. Two commercial VOC standards (ASTM D3710 Mix, Supelco Inc., Bellefonte, PA, USA; ASTM D2998 Mix, AccuStandard, New Haven, CT, USA) were used for the calibration of alkanes and aromatics. Some oxygenated chemicals, such as cyclohexanone, phenol, acetophenone and decanal, were identified and quantified in this study. In addition, the internal standard, ethyl benzene-d10, (ASTM aromatic internal standard, Supelco Inc., Bellefonte, PA) was spiked before the analysis to obtain robust and accurate quantification results. Compound identification was based on target ions and qualifier ions of mass spectrum, retention time and comparison with library spectra. Quantification was based on the relative response factor (RFF), which was calculated using the ratio of the test compound response factor to the internal standard (ethyl benzene-d10) response factor. Ranges of recovery, reproducibility (in terms of coefficient of variation), linearity (in terms of the r-square of the regression line) and method of detection limit (MDL, in terms of emission factors) of test chemicals are 77.9%e95.4%, 1.7%e10.45%, 0.971e0.998, and 0.036e0.146 mg kW h1 respectively.
2.5. 2.4.
Statistical analysis and health risk calculation
Analysis of volatile organic compounds (VOCs)
The thermal desorption tube packed with 150 mg of Tenax TA was used for VOC sampling. This is suitable for sampling VOC between C4 w C20 (US EPA, 1997), which is also the carbon
SPSS version 12.0 and Microsoft Office Excel 2003 were used for statistical analysis. T-test, paired t-test, and trend analysis test were carried out for comparing VOC exhaust emissions for both fuels, examining exhaust emissions before and after
Sampling bags Computer Gaseous air pollutant analyzers
Engine & Dynamometer
VOC sampling
7.5 m 10 cm
To discharge cleaning devise
Blower Aldehyde sampling
Ambient air 61 cm
Filter Activated charcoal
Dilution tunnel 50 m
Constant volume sampler
Fig. 1 e Schematic diagram of constant volume sampling system of diesel engine exhaust.
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maintenance, and investigating the effects of increasing mileage and maintenance on engine emissions respectively. Health risks were calculated in terms of non-cancer chronic effect by using California Environmental Protection Agency chronic health benchmarks [36]. It was evaluated by hazard quotient (HQ) as expressed in Eq. (1): HQ ¼
C REFc
(1)
where C is the concentration (mg m3) from the engine exhaust, and REFc is the non-cancer chronic reference concentration (mg m3). Furthermore, the sum of hazard quotients (denoted as hazard index, HI ) of compounds aimed at the same organ was also assessed as per the following equation. HI ¼
3.
X Ci REFci
(2)
Results and discussion
3.1. Characterization of VOC emissions and corresponding ozone potentials According to this study’s results, more chemicals and greater emissions exist in exhaust emissions when using diesel as a fuel. Twenty-two chemicals are found in B20 fuel, and fortyseven chemicals are in diesel fuel. The aggregated emissions of these chemicals are called “total VOC emissions”. Total VOC emissions are in the range of 32.4e71.6 mg kW h1 and 49.6e183.7 mg kW h1, and individual VOC emissions are in the ranges of 0.1e29.8 mg kW h1 and 0.1e93.6 mg kW h1 for B20 and diesel, respectively (Table 2). Compared with diesel, B20 has lower total VOC emissions, decreasing by 61% on average. Dominant VOCs (defined as an emission percentage >5% of total emission) are benzene, heptane, toluene, and phenol with average percentages of 6.1%, 12.2%, 46.1%, and 15.1%, respectively in B20 fuel, accounting for 79.5% of total VOC emissions. For diesel fuel, toluene, xylene, and naphthalene are dominant with average percentages of 37.5%, 5.4% and 19.2%, respectively, accounting for 62.1% of total VOC emissions. Except for toluene, dominant VOCs in both fuels are different. Additionally, we find that more VOCs with emissions greater than 1 mg kW h1are found in diesel fuel; there are twenty seven for diesel fuel, in comparison with thirteen VOCs in B20 fuel. Total ozone formation potentials, based on maximum incremental reactivity (MIR) [37], are in the ranges of 61.4e180.4 mg kW h1 and 124.9e533.4 mg kW h1 for B20 and diesel, respectively. Individual ozone potential emissions are in the ranges of 0.9e88.6 mg kW h1 for B20 and 2.9e252.8 mg kW h1 for diesel. The negative number is due to the negative MIR of acetophenone. The corresponding ozone potential emissions are lower in B20 fuel, decreasing by 64% on average (Table 3), which is almost the same magnitude as the reduction percentage of total VOC emissions. VOC emissions from biodiesels have been reported in few studies. Sharp et al. [18]compare emissions of B20 (20% biodiesel þ 80% diesel) and B100 (100% biodiesel) with those of diesel. Results show total VOCs are 34.9 mg kW h1,
99
31.1 mg kW h1 and 21.6 mg kW h1 for diesel, B20 and B100, respectively. The percent changes relative to diesel are 11 % for B20 and 38% for B100. The EPA study [25] estimates the percent changes relative to diesel in emissions of the sum of eleven organic toxics and refers to these as total toxic emissions at given biodiesel concentrations. Based on the estimations, B20 and B100 fuels’ percent changes of total toxic emissions are 3% and 16%, separately. Correˆa and Aribilla [26] also investigate percent changes of eight mono-aromatic hydrocarbons (MAHs) by comparing with diesel; the average changes of MAHs are 4.2%, 8.2%, and 21.1% for B2, B5, and B20, respectively. Shah et al. [38] find that percent changes in total VOC emissions in comparison with diesel are 14.5% w 73.9% and 39.6% w 57% for B20 and B100, respectively. The four studies in the literature all agree with the present one that B20 fuel has lower total VOC emissions. Lower emissions may result from higher cetane number and oxygen content for B20 fuels. Fuels with high cetane number can reduce ignition delay and help promote more complete combustion, which could lead to reduction in hydrocarbon emissions [39e41]. In addition, higher oxygen content in B20 fuel helps to combust completely and reduces emissions [24,42]. Although our study does not investigate the exhaust emission when using B100 as a fuel, data in the literature show that total VOC emissions decrease with biodiesel concentrations. It is reasonable to conclude that higher biodiesel blends will have lower total VOC emissions.
3.2. Effects of increasing mileage and maintenance on VOC emissions The effects of cumulative mileage and maintenance on engine emissions for both fuels have been examined. Over the test period, the average emissions of individual VOC are in the ranges 0.1e23.0 mg kW h1 and 0.1e47.3 mg kW h1 (Table 2), with variations of 10%e157% and 2%e105% for B20 and diesel fuels, separately. Variations over the test mileages are mainly attributed to fluctuations of exhaust emissions, since they have the same magnitudes as those between duplicate samples (samples from two hot-start cycles with variations of 0.8%e158% and 0.1%e166% for B20 and diesel fuels, individually). Also, time series analysis (auto-regression model) is implemented to test whether there is a trend in total VOC emissions over the test mileages for both fuels. No statistical significance is found. The autocorrelation coefficients ( pvalue) are 0.696 ( p-value ¼ 0.275) for B20 and 0.054 ( pvalue ¼ 0.951) for diesel. Therefore, it is concluded that the engines can run on both fuels for a cumulative mileage up to 80,000 km without having more VOC emissions. Moreover, no significant differences in emissions are found before and after maintenance at both cumulative mileages of 40,000 km and 80,000 km. This indicates that maintenance does not influence VOC emissions (Table 2).
3.3. fuels
Individual VOC comparison between B20 and diesel
Since the effects of increasing mileage and maintenance on VOC emissions are insignificant (as discussed above),
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Table 2 e Exhaust emissions factors of VOCs from engines fueled with B20 and diesel at five different cumulative mileages. VOC
B20 fuel
Diesel fuel 1
Emission facotr (mg kWh1)
Emission factor (mg kWh ) Cumulative mileage (km) 0
3.5 ef 2.7 e 29.8 1.7 e e 1.4 e e 5.3 e e e 2.1 e 5.8 e e e e e 1.3 e e 0.6 e e e e e 0.8 e e e e e e e 0.4 e
1.4 e 6.4 e 23.6 0.3 e 5.5 3.2 6.5 0.9 e 0.9 e 0.6 1.7 e 4.0 e e e e e 1.5 e e e e e e e 1.3 e e e e e e e e e e
40,000 (before maint.)b 3.8 e 4.8 0.1 11.8 0.2 e 0.3 1.8 0.1 0.1 e e e e 0.1 e 12.2 e e e e e e e e e e e e e e e e e e e e e e e e
40,000 (after maint.) 2.3 e 6.8 e 13.5 0.0 e 0.2 1.1 e 0.1 0.1 0.1 e e 0.1 e 8.0 e e e e e e e e e e e e e e e e e e e e e e e e
60,000
3.7 e 1.8 32.8 1.2 e 1.9 6.1 e 2.3 1.3 3.8 e e e e 13.1 e e e 1.1 e e e e 0.9 e e e e e 0.8 e e e 0.5 e e e 0.5 e
Mean 80,000 (before maint.)c 1.6 e 7.9 e 19.8 0.9 e 0.2 2.6 e 0.8 1.0 1.0 e 0.3 1.1 e 3.5 e e 1.9 e e e e e e e e e e e 0.5 e e e e e e e e e
(SD)
80,000 (after maint.) 3.4 e 6.5 e 29.2 0.5 e 0.2 1.5 e 0.1 0.7 0.7 e e 0.8 e 1.4 e e e e e e e e 0.5 e e e e e 0.6 e e e 0.9 e e e 1.1 e
Cumulative mileage (km) 0
2.8 Nag 5.3 0.1 23.0 0.7 Na 1.4 2.5 3.3 0.7 1.7 1.3 Na 0.4 1.0 Na 6.8 Na Na 1.9 1.1 Na 1.4 Na Na 0.7 Na Na Na Na 1.3 0.7 Na Na Na 0.7 Na Na Na 0.7 Na
(1.1) (2.4) (8.5) (0.6) (2.3) (1.8) (4.5) (0.9) (2.3) (1.6) (0.2) (0.9) (4.1)
(0.1)
(0.2)
(0.2)
(0.0)
5.2 0.8 2.9 0.6 22.4 1.3 e 1.4 4.3 0.1 1.4 1.0 1.0 e 0.3 e e 1.7 e 0.5 1.0 e e e e e 0.7 e e e e 0.9 0.8 e e e 0.8 e e e 0.5 e
20,000
2.7 1.0 5.0 e 45.5 1.3 1.1 1.9 5.9 0.8 1.9 2.5 1.6 e 0.4 1.9 e 1.3 3.4 0.5 5.5 e 1.1 4.2 e e 0.9 0.7 e e e 3.0 1.5 0.5 e 0.8 1.3 e e e 1.7 0.5
40,000 (before maint.)d 4.4 0.7 7.8 e 93.6 2.0 1.3 2.8 10.4 1.0 3.4 1.3 1.8 e 0.6 2.4 0.2 4.2 3.3 0.2 7.3 0.7 1.3 4.3 0.1 0.7 1.7 0.9 0.1 1.1 0.7 4.0 2.7 0.8 0.7 1.0 2.9 0.7 0.6 0.4 3.6 1.2
40,000 (after maint.) 5.0 e 3.5 e 37.5 1.8 1.5 2.0 6.9 1.3 2.4 1.6 1.8 e 0.5 1.7 e 4.5 4.1 0.9 5.2 0.7 1.4 5.2 e 0.9 1.7 1.0 0.1 1.0 0.7 49.2 2.9 0.8 0.9 1.4 3.0 0.7 0.8 0.5 3.6 1.1
60,000
0.7 0.6 3.7 0.5 62.1 0.6 1.8 2.7 10.6 2.5 3.7 2.9 2.0 2.7 0.8 1.0 1.0 1.6 3.4 0.7 3.4 0.7 1.2 4.5 e 0.6 2.1 0.8 e 0.8 0.5 9.1 2.1 e 0.5 e 1.5 e 0.4 e 2.2 0.6
80,000 (before maint.)e 2.1 e 2.0 0.4 48.9 1.3 0.6 0.9 3.1 e 1.0 e 0.9 e 0.2 1.1 e 1.5 2.3 e 1.1 e e 3.2 e e 1.0 e e e e 55.6 1.7 e e e 1.6 e e e 2.0 0.5
Mean
(SD)
3.0 0.8 3.7 0.5 47.3 1.3 1.2 1.8 6.5 1.1 2.2 1.7 1.5 2.7 0.4 1.6 0.6 2.4 3.2 0.5 3.5 0.7 1.1 4.2 0.1 0.7 1.3 0.9 0.1 1.0 0.6 25.3 1.9 0.7 0.7 1.0 1.8 0.7 0.6 0.5 2.3 0.7
(1.8) (0.2) (2.0) (0.1) (24.4) (0.5) (0.4) (0.7) (3.1) (0.9) (1.1) (0.8) (0.4) Na (0.2) (0.6) (0.6) (1.5) (0.7) (0.3) (2.5) (0.0) (0.1) (0.7) Na (0.1) (0.6) (0.1) (0.0) (0.2) (0.1) (25.1) (0.8) (0.2) (0.2) (0.3) (0.9) (0.0) (0.2) (0.0) (1.2) (0.3)
80,000 (after maint.) 0.8 e 0.9 e 21.3 1.0 0.7 1.2 4.4 1.0 1.5 0.6 1.1 e 0.3 e e 2.1 2.5 e 1.3 e 0.5 3.7 e e 1.0 e e e 0.5 55.0 1.5 e e e 1.4 e 0.5 e 2.4 0.6
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Benzene 3-Methyl hexane Heptane Methyl cyclohexane Toluenea Octanea 4-Methyl octane Ethyl benzene p-Xylenea Styrene o-Xylenea Cyclohexanone Nonane 1-Methyl ethyl benzene Propyl benzene 1-Ethyl-3-methyl benzene 1,3,5-Trimethyl Benzene Phenola Benzonitrile 2,2,4-Trimethyl heptane 1,2,4-Trimethyl benzene 1-Methyl-3-propyl benzene 2,3,3-Trimethyl octane Acetophenonea 1-Ethyl-2,4-dimethyl benzene 4-Ethyl-1,2-dimethyl benzene Undecanea 2,6-Dimethyl decane 1,2,4,5-Tetramethyl benzene 1,2,3,4-Tetramethyl benzene 3-Methyl undecane Naphthalene Dodecane Decanal 8-Methyl 3-undecene 7-Methyl tridecane Tridecanea 2-Methyl naphthalene 4-Methyl tetradecane 3-Methyl tridecane Tetradecanea 2-Methyl tetradecane
20,000
(0.5) (0.2) (0.1) (1.1) 1.1 0.6 0.5 1.3
1.1 1.7
1.0 0.5 e e 110.9 0.9 0.4 e e 135.9
1.5 1.5
0.8 0.5 e e 139.3 1.6 0.8 0.6 0.1 162.9
0.1
0.6 e e 2.4 104.3 e e e e 49.6
0.6 1.3 e
Na Na Na Na
P < 0.005 (comparison of emissions between B20 and diesel fuel). P ¼ 0.597 (B20 fuel 40,000 km, comparison of emissions before maintenance vs. after maintenance). P ¼ 0.647 (B20 fuel 80,000 km, comparison of emissions before maintenance vs. after maintenance). P ¼ 0.788 (diesel fuel 40,000 km, comparison of emissions before maintenance vs. after maintenance). P ¼ 0.350 (diesel fuel 80,000 km, comparison of emissions before maintenance vs. after maintenance). Not detected. Na: not applicable. a b c d e f g
e
e e e e 48.1 e e e e 42.9
e e
e e e e 71.6 e e e e 32.4
e
e e e e 57.8 e e e e 55.5
e e e
Hexadecane Heptadecane Octadecane Tricosane Total
e e e e 35.4
Na
3.4.
Pentadecane
101
averaging emission factors of individual VOCs over the test mileages are used to calculate emission percent changes of B20 fuel using averages of corresponding diesel emission factors as references. Percent changes are in the range of 95e191%. Most chemical emissions are lower in B20 fuel. Particularly for chemicals, such as toluene, octane, m- &p-xylene, o-xylene, acetophenone, undecane, dodecane and tetradecane, percent changes are in the ranges of 48% to 71%, and statistically significant. However, phenol emission is higher in B20 fuel increasing by 183%, and the difference is significant. Several other studies estimate average percent changes of B20 by comparing with base diesel fuel for benzene, toluene, ethyl benzene, and xylene, respectively. The average percent changes are 16.5%, 19.9%, 44.9%, and 12.3% from the EPA study [25]; 23%, 25%, 9.5% and 20 % according to Correˆa and Aribilla [26] study; 5.7%, 51.5%, 24.5% and 64.5% in this study. Additionally, Shan et al. [38] detect percent change of B20 in comparison with diesel for benzene, toluene, p-&mxylene and o-xylene, and the corresponding percentages are 68.8%, 42.7%, 28.8%, and 14.1%, separately. Although the EPA study shows different results of benzene and toluene from those of the other studies, the latest studies indicate that the B20 fuel has lower emissions of main aromatic compounds. We can conclude that usage of biodiesel has a beneficial effect on aromatic emissions.
1.6 0.8 0.4 1.4 183.7
(0.6)
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Classification of VOC emissions
For better understanding of VOC species in exhaust for both fuels, VOC emissions are categorized into three chemical classes, which are aromatics, oxygenated species, and alkanes & alkenes. Average emissions (SD) of these three classes are 32.6 (12.0) mg kW h1, 8.4 (4.6) mg kW h1, and 8.0 (2.1) mg kW h1, with corresponding percentages of 66.4%, 17.2%, and 16.4%, respectively, for B20 fuel. For diesel, they are 96.7 (33.6) mg kW h1, 7.7 (3.3) mg kW h1, and 22.2 (9.5) mg kW h1, with corresponding percentages of 76.4%, 6.1%, and 17.6%, respectively (Table 4). Both fuels show the highest emissions in the aromatic group. The second highest emission group is the oxygenated one in B20, while it is the alkane & alkene one in diesel. Accordingly, average ozone formation emissions (SD) of these three classes are 100.3 (41.8) mg kW h1, 8.8 (5.3) mg kW h1, and 5.6 (1.4) mg kW h1, with corresponding percentages of 87.4%, 7.7%, and 4.9%, respectively, for B20 fuel. For diesel, they are 298.4 (125.9) mg kW h1, 4.2 (3.6) mg kW h1, and 16.0 (8.3) mg kW h1, with corresponding percentages of 93.7%, 1.3%, and 5.0%, respectively. Higher oxygenated chemical emissions in B20 fuel may be related to the fuel composition, since biodiesel has higher oxygen content (w11% by weight) [16,24], and is prone to produce higher oxygenated chemical emissions in comparison with diesel [1]. Further investigation is carried out by dividing VOCs into non-oxygenated and oxygenated VOCs. Our study shows many non-oxygenated VOCs are lower in B20 fuel with statistical significance, such as toluene, octane, xylenes, tridecane and tetradecane (Table 2). Results of oxygenated chemicals vary a lot. For example, phenol emission increases by 183% with a significant difference when using B20 as a fuel,
102
Table 3 e Ozone formation potentials of VOC exhaust emissions from engines fueled with B20 and diesel at five different cumulative mileages. VOC
B20 fuel
Diesel fuel 1
Ozone formation potential (mg-O3 kW h1)
Ozone formation potential (mg-O3 kW h ) Cumulative mileage (km) 0
1.5 ea 2.2 e 80.5 1.0 e e 9.5 e e 6.3 e e e 17.5 e 6.5 e e e e e 0.7 e e 0.3 e e e e e 0.3 e e e e e e
(SD)
20,000 40,000 40,000 60,000 80,000 80,000 (before (after (before (after maint.) maint.) maint.) maint.) 0.6 e 5.2 e 63.8 0.2 e 14.9 21.2 14.3 6.1 e 0.5 e 1.3 13.6 e 4.4 e e e e e 0.9 e e e e e e e 1.5 e e e e e e e
1.6 e 3.9 0.1 31.9 0.1 e 0.7 11.8 0.3 0.9 e e e e 1.2 e 13.6 e e e e e e e e e e e e e e e e e e e e e
1.0 e 5.5 e 36.5 0.0 e 0.5 7.4 e 0.6 0.1 0.1 e e 0.7 e 9.0 e e e e e e e e e e e e e e e e e e e e e
1.5 e 1.5 e 88.6 0.7 e 5.1 40.3 e 14.6 1.5 2.1 e e e e 14.6 e e e 8.9 e e e e 0.4 e e e e e 0.3 e e e 0.2 e e
0.7 e 6.4 e 53.5 0.5 e 0.5 16.9 e 5.2 1.2 0.5 e 0.6 9.1 e 3.9 e e 16.8 e e e e e e e e e e e 0.2 e e e e e e
1.4 e 5.3 e 78.9 0.3 e 0.4 9.8 e 0.8 0.8 0.4 e e 6.8 e 1.6 e e e e e e e e 0.2 e e e e e 0.2 e e e 0.3 e e
Cumulative mileage (km) 0
1.2 Nab 4.3 0.1 62.0 0.4 Na 3.7 16.7 7.3 4.7 2.0 0.7 Na 0.9 8.1 Na 7.7 Na Na 16.8 8.9 Na 0.8 Na Na 0.3 Na Na Na Na 1.5 0.3 Na Na Na 0.2 Na Na
(0.5) (1.9) (22.9) (0.4) (6.2) (12.1) (9.9) (5.7) (2.7) (0.9) e (0.5) (7.4) (4.6)
(0.1)
(0.1)
(0.1)
2.2 1.1 2.4 1.1 60.3 0.8 e 3.7 28.2 0.2 9.1 1.2 0.5 e 0.6 e e 1.9 e 0.5 9.0 e e e e e 0.3 e e e e 1.1 0.3 e e e 0.3 e e
Mean (SD)
20,000 40,000 40,000 60,000 80,000 80,000 (before (after (before (after maint.) maint.) maint.) maint.) 1.1 1.3 4.0 e 122.8 0.8 1.3 5.1 38.7 1.8 12.5 2.9 0.9 e 0.8 15.8 e 1.4 27.9 0.5 48.5 e 1.4 2.4 e e 0.4 0.9 e e e 3.5 0.6 3.0 e 0.9 0.4 e e
1.8 1.0 6.3 e 252.8 1.2 1.5 7.5 68.4 2.3 22.4 1.6 1.0 e 1.3 20.0 1.5 4.7 27.3 0.2 63.9 5.3 1.8 2.4 0.8 5.4 0.7 1.1 0.8 8.7 0.9 4.7 1.0 5.0 3.1 1.2 1.0 2.4 0.8
2.1 e 2.8 e 101.1 1.1 1.7 5.3 45.7 2.9 15.7 1.9 1.0 6.0 1.0 14.1 e 5.1 33.8 0.9 45.4 5.5 1.9 2.9 e 7.1 0.7 1.2 0.8 8.5 0.9 57.6 1.1 5.2 3.9 1.7 1.0 2.2 1.0
0.3 0.8 3.0 1.0 167.7 0.3 2.0 7.3 69.8 5.6 24.2 3.4 1.1 e 1.6 7.9 10.3 1.8 28.0 0.7 30.0 5.7 1.5 2.5 e 5.1 0.9 1.0 e 6.2 0.6 10.7 0.8 e 2.3 e 0.5 e 0.5
0.9 e 1.6 0.8 132.2 0.8 0.7 2.4 20.2 e 6.8 e 0.5 e 0.5 8.7 e 1.7 18.8 e 9.3 e e 1.9 e e 0.4 e e e e 65.0 0.6 e e e 0.6 e e
0.3 e 0.7 e 57.4 0.6 0.8 3.2 29.1 2.2 9.9 0.7 0.6 e 0.7 e e 2.4 20.4 e 11.4 e 0.7 2.1 e e 0.4 e e e 0.6 64.4 0.6 e e e 0.5 e 0.6
1.2 1.1 3.0 0.9 127.8 0.8 1.3 4.9 42.9 2.5 14.3 2.0 0.8 6.0 0.9 13.3 5.9 2.7 26.0 0.5 31.1 5.5 1.5 2.4 0.8 5.9 0.6 1.1 0.8 7.8 0.7 29.6 0.7 4.4 3.1 1.3 0.6 2.3 0.7
(0.8) (0.2) (1.6) (0.1) (65.9) (0.3) (0.5) (2.0) (20.5) (2.0) (7.0) (0.9) (0.2) Na (0.4) (5.1) (6.2) (1.6) (5.4) (0.3) (22.3) (0.2) (0.2) (0.4) Na (1.1) (0.2) (0.1) (0.0) (1.4) (0.2) (29.4) (0.3) (1.2) (0.8) (0.4) (0.3) (0.1) (0.2)
b i o m a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 9 6 e1 0 6
Benzene 3-Methyl hexane Heptane Methyl cyclohexane Toluene Octane 4-Methyl octane Ethyl benzene p-Xylene Styrene o-Xylene Cyclohexanone Nonane 1-Methyl ethyl benzene Propyl benzene 1-Ethyl-3-methyl benzene 1,3,5-Trimethyl benzene Phenol Benzonitrile 2,2,4-Trimethyl heptane 1,2,4-Trimethyl benzene 1-Methyl-3-propyl benzene 2,3,3-Trimethyl octane Acetophenone 1-Ethyl-2,4-dimethyl benzene 4-Ethyl-1,2-dimethyl benzene Undecane 2,6-Dimethyl decane 1,2,4,5-Tetramethyl benzene 1,2,3,4-Tetramethyl benzene 3-Methyl undecane Naphthalene Dodecane Decanal 8-Methyl 3-undecene 7-Methyl tridecane Tridecane 2-Methyl naphthalene 4-Methyl tetradecane
Mean
e 0.1 e e e e e e 124.8
3-Methyl tridecane Tetradecane 2-Methyl tetradecane Pentadecane Hexadecane Heptadecane Octadecane Tricosane Total
e e e e e e e e 146.8
e e e e e e e e 66.2
e e e e e e e e 61.4
e 0.1 e e e e e e 180.4
e e e e e e e e 116.0
e 0.4 e e e e e e 107.5
Na 0.2 Na Na Na Na Na Na
(0.0)
e 0.2 e e e e e e 124.9
e 0.6 0.6 0.4 0.2 e e 0.8 299.4
0.5 1.1 1.4 0.2 0.5 0.3 0.1 0.4 533.4
0.6 1.1 1.3 0.0 0.5 0.3 0.2 0.0 383.1
e 0.7 0.7 0.5 0.3 0.2 e e 408.3
e 0.7 0.6 0.5 0.3 0.1 e e 272.7
e 0.8 0.7 0.5 0.3 0.2 e e 208.3
0.6 0.7 0.9 0.4 0.3 0.2 0.2 0.4
(0.0) (0.4) (0.4) (0.2) (0.2) (0.1) (0.0) (0.4)
a Not detected. b Na: not applicable.
b i o m a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 9 6 e1 0 6
Table 4 e Exhaust emission factors and corresponding ozone formation potentials of VOC chemical classes from engines fueled with B20 and diesel. VOC class
B20
Diesel
Emission factor (mg kW h1)
Percent (%)
Ozone formation (mg-O3 kW h1)
Percent (%)
Emission factor (mg kW h1)
Percent (%)
Ozone formation (mg-O3 kW h1)
Percent (%)
32.6 (12.0)a 8.4 (4.6) 8.0 (2.1) 49.1
66.4b 17.2 16.4
100.3 (41.8) 8.8 (5.3) 5.6 (1.4) 114.7
87.4 7.7 4.9
96.7 (33.6) 7.7 (3.3) 22.2 (9.5) 126.7
76.4 6.1 17.6
298.4 (125.9) 4.2 (3.6) 16.0 (8.3) 318.6
93.7 1.3 5.0
Aromatics Oxygenated species Alkanes & alkenes Total a Mean (standard deviation). b Percentage of mean.
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Table 5 e Chronic hazard quotients (HQ) and hazard indices (HI) of investigated compounds in exhaust emissions from engines fueled with B20 and diesel. Chemical
Benzene Toluene Ethyl benzene m-& p-Xylene Styrene o-Xylene Phenol Naphthalene
Ref. conc. (mg m3) 60 300 2000 700 900 700 200 9
Ethyl benzene, phenol Phenol Benzene, Toluene, ethyl benzene Benzene Ethyl benzene Ethyl benzene, phenol Benzene, toluene, xylenes, styrene, phenol Toluene, xylenes, naphthalene
HQ
Target organ or system
B20
Diesel
0.38 0.62 0.01 0.03 0.03 0.01 0.28 1.13
0.40 1.28 0.01 0.08 0.01 0.03 0.10 22.79
Developmental, hematologic, nervous Developmental, nervous, respiratory Alimentary, developmental, endocrine, kidney Nervous, respiratory Nervous Nervous, respiratory Alimentary, cardiovascular, kidney, nervous Respiratory
HI 0.28 0.28 1.01 0.38 0.01 0.28 1.35 1.79
0.11 0.10 1.69 0.40 0.01 0.11 1.89 24.17
Alimentary Cardiovascular Developmental Hematologic Endocrine Kidney Nervous Respiratory
and cyclohexanone emission is slightly higher in B20 fuel in this study, while acetophenone emission is lower in B20 with a significant difference. The varied results in oxygenated VOC may be due to the oxygen content in biodiesel. This oxygen-rich fuel increases combustion efficiency [24,43], tending to lower VOC emission, while the additional oxygen increases the probability of oxygenated VOC formation. Basically, the VOC emission results are the net effects of these two mechanisms. This can explain why non-oxygenated VOC emissions are consistently reduced, while oxygenated VOC emissions are varied when biodiesel fuel is compared with diesel.
system. HIs of B20 and diesel fuels are in the ranges of 0.01e1.79 and 0.01e24.17, respectively. For the alimentary, cardiovascular and kidney systems, slightly higher HIs are found in B20 fuel due to higher phenol concentrations. On the contrary, much lower HIs are found in B20 fuel for the developmental, nervous and respiratory systems. Again, this supports the advantage of using the B20 fuel. More reduction in health risks are expected when higher percentages of biodiesel blends are used.
3.5.
In this study, the effects of the B20 fuel on VOC emissions are examined and compared with those of diesel fuel in several measurements over cumulative mileages of 0e80,000 km and two maintenance practices. According to the study’s findings, B20 has lower VOC emissions, correspondingly lower ozone formation potentials, and emission reductions are 61.2% and 64.0% on average for total VOC and ozone potential emissions, respectively. Reduction in health risks in terms of HIs is also found in B20 fuel, especially for the developmental, nervous and respiratory systems. Emission reductions of several VOC chemicals, such as toluene, octane, m-& p-Xylene, o-xylene, acetophenone, undecane, dodecane and tetradecane, are in the range of 48.0%e70.7% with statistical significance. However, phenol emission is higher in B20 fuel and the difference is significant. We also find emission percentage of the oxygenated group is higher in B20 fuel than that in diesel fuel. This results from high oxygen content in B20 fuel. Higher oxygen content in B20 fuel may enhance combustion efficiency, tending to lower VOC emission, while the additional oxygen increases the probability of oxygenated VOC formation. The VOC emission results are the net effects of these two mechanisms. Therefore, emissions of non-oxygenated VOCs are consistently reduced from B20 fuel, while emissions of oxygenated VOCs are varied.
Health risk assessment of exhaust emissions
Health impacts of diesel engine exhausts are investigated in terms of hazard quotients and hazard indices. Engine exhaust emissions likely enter the human body through inhalation and have long-term deleterious health effects [44]; therefore, chronic inhalation reference exposure levels are used for health risk estimations [36]. According to our findings, nine commonly present compounds with significant adverse effects are included, being benzene, toluene, ethyl benzene, xylene (o-, m-, & p-), styrene, phenol and naphthalene. Table 5 shows the hazard quotients and hazard indices of investigated compounds in engine exhausts when fueled with B20 and diesel. HQs of B20 and diesel fuels are in the ranges of 0.01e1.13, and 0.01e22.79, respectively. Except for styrene and phenol, which have slightly higher HQs value in B20 fuel, other compounds show higher HQs in exhausts of the engine fueled with diesel. Basically, HQs reflect exhaust concentration magnitude. Among the investigated compounds, toluene and naphthalene have higher HQs in both fuels; however, their HQs decrease considerably in B20 fuel in comparison with those in diesel fuel. This indicates the beneficial effect of using B20 fuel on health risks. The HI is obtained by the sum of the HQs of compounds aiming at the same target organ or
4.
Conclusions
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Generally, B20 fuel has the beneficial effect in terms of VOC emissions.
Acknowledgments The authors wish to thank China Petroleum Company and Taiwan NJC Corporation for kindly providing diesel and waste cooking oil biodiesel, respectively. This project was partially supported by ARTC of China Petroleum Company and the National Science Council in Taiwan (NSC 94-2314-B-037-102).
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Available online at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
Effects of biodiesel blend fuel on volatile organic compound (VOC) emissions from diesel engine exhaust Chiung-Yu Peng a,*, Cheng-Hang Lan b, Chun-Yuh Yang a a b
Department of Public Health, College of Health Sciences, Kaohsiung Medical University, Kaohsiung 807, Taiwan Department of Occupational Safety and Health, Chung-Hwa College of Medical Technology, Tainan County 717, Taiwan
article info
abstract
Article history:
Biodiesel has been increasingly used due to its property similarities with diesel and several
Received 7 June 2008
other favorable characteristics with respect to exhaust emissions and biodegradation. For
Received in revised form
better understanding of biodiesel, this study examines the effects of the biodiesel blend
13 October 2011
fuel on VOC emissions from diesel engine exhausts in comparison with those from diesel
Accepted 16 October 2011
fuel. Exhaust emission tests were performed several times for each fuel under the US
Available online 16 November 2011
transient cycle protocol from mileages of 0e80,000 km. VOC samples were collected from diluted exhaust by using thermal desorption tubes, then analyzed by a GC/MS system.
Keywords:
Twenty-two and forty-seven chemicals are identified and quantified in B20 and diesel fuels
Oxygenated VOCs
respectively. Total VOC emissions are in the range of 32.4e71.6 mg kW h1 for B20 fuel, and
Ozone potential
49.6e183.7 mg kW h1 for diesel fuel. Individual VOC emissions are in the ranges of
Thermal desorption
0.1e29.8 mg kW h1 for B20 fuel and 0.1e93.6 mg kW h1 for diesel fuel. Individual VOC
Transit cycle
health risks in terms of hazard quotients are in the ranges of 0.01e1.13, and 0.01e22.79 for
Durability test
B20 and diesel fuels, respectively. B20 has much lower total VOC emissions, decreasing by 61.2% on average; correspondingly, lower total ozone potentials of VOC reduce by 64.0%. The reductions in health risks are also shown in B20 fuel. As a result, use of biodiesel in diesel engines has beneficial effects in terms of VOC emissions. ª 2011 Elsevier Ltd. All rights reserved.
1.
Introduction
Recently there has been increasing interest and application in the use of biodiesel as a substitute for petroleum-based diesel fuel due to high pricing and limited quantities of petroleum oils. Biodiesels are manufactured from the transesterification of vegetable oils or animal fats with alcohols using acids or bases as catalysts, yielding free glycerol as a byproduct [1,2]. Biodiesels can be completely miscible with petroleum diesel fuels in any proportion as blends, and replace diesels in many applications with little or no modification due to having similar properties as petroleum-based diesels [3e7]. Moreover, they are renewable fuels and have characteristics of
biodegradability, a closed carbon cycle, lower volatility, higher cetane number, increasing lubricity, and less CO, SO2and particulate matter (PM) emissions [8e17]. Even though biodiesel has great characteristics, like some other biofuels, some researchers are concerned that exhaust emissions of biofuels would present increased adverse effects on public health [18e20]. Biodiesels have been extensively studied in exhaust emissions of regulated pollutants (CO, HC (hydrocarbons), NOx and PM). Except NO2 emissions, the results favor biodiesel usage in diesel engines [1,4,5,21e24]. Recently, several different measurements that went beyond basic regulated pollutants were performed. Most concentrated on
* Corresponding author. Tel.: þ886 7 3121101x2314; fax: þ886 7 3234691 . E-mail address: [email protected] (C.-Y. Peng). 0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2011.10.016
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composition and quantification of HC and PM. These included measurements of volatile organic compounds (VOCs) and carbonyl compounds from gaseous exhaust, and measurements of polyaromatic hydrocarbons (PAH) from both gaseous and particulate emissions. The limited data showed exhaust emissions were lower in total VOCs, total carbonyl compounds and total PAH when biodiesel fuels were used [16,18,25,26]. However, several un-determined issues were found when unregulated pollutant emissions were examined. For example, an EPA study [25] revealed that the ratio of total VOC (determined by GC) to HC (determined by direct-reading instrument) increased with the biodiesel concentration. The soluble organic fraction of the emitted particles is greater in biodiesel exhaust emissions than that in diesel’s, even though the reductions are shown in total HC and total mass of PM for biodiesel. In terms of individual chemical, biodiesels produced inconsistent results or slightly higher emissions of some chemicals, such as benzene, toluene and acrolein as compared to diesels. Further studies should be carried out to investigate the impacts of biodiesels on emissions of unregulated hazardous air pollutants. Among unregulated air pollutants, carbonyl compounds have been investigated by a study [16] over cumulative mileages of 0e80,000 km and the results indicate that B20 generates lower aldehyde emissions. This mainly results from formaldehyde emissions which drop by 23% on average. In addition to carbonyl chemicals, VOCs are important unregulated air pollutants in vehicle emissions, since vehicles are significant sources of VOCs, different classes of VOCs may have very distinct photochemical activity and adverse health effects [27e29]. Individual VOC information is more important than total HC data with respect to health effects and environmental impacts [25]. Limited data show that biodiesel produces inconsistent results on some chemicals as compared to diesels [1,25]. It seems that definitive studies in this area have not been performed. Therefore, this is clearly an area in need of more extensive research on investigating the effect of this oxygenrich fuel on VOC exhaust emissions. Additionally, several issues, such as whether VOC species in biodiesel exhaust are different from those of diesels, the effects of vehicle/engine age on VOC emissions, and ozone formation potentials of VOC emissions, have been considered in relation to exhaust emissions from biodiesel fuels. The importance of these considerations increases when more vehicles use biodiesel as a fuel and run over long periods of time. Therefore, the present study characterizes and compares VOC emissions in both fuels, estimates corresponding ozone formation potentials, and examines the effects of increased mileage and maintenance procedures on VOC emissions.
2.
Materials and methods
2.1.
Engines, dynamometer and driving cycle
Two new modern diesel engines (Mitsubishi 4M40-2AT1) of exactly the same type which were used in pick-up trucks were employed in this study. These two engines were fueled with diesel and B20, separately; a commercially available synthetic
engine lubricating oil (API SG/CEþ; 15W/40) was used. Changes of lubricating oil took place during maintenance at mileages of 40,000 km and 80,000 km. The engines had 4 cylinders with a bore and stroke of 95 mm 100 mm, a total displacement of 2.84 103 m3. They were turbocharged and indirectly injected. The maximum power was 80.9 kW at 387 rad s1, and maximum torque was 217.6 Nm at 209 rad s1. The tested engines account for 21.3% of diesel cars in terms of total displacement volume in Taiwan [30]. These two engines were mounted and operated on a Schenck DyNAS 335 dynamometer with a DC-IV control system. The DC-current dynamometer with a fully automatic control system was capable of supplying maximum power of 335 kW and maximum torque of 800 N m. Integrated powers over the test period of the two engines were 9.16 0.09 and 9.03 0.13 kW h separately, showing that these two engines had the same performance. Exhaust emission tests were performed under the US transient cycle protocol at cumulative mileages of 0 km, 20,000 km, 40,000 km (before maintenance), 40,000 km (after maintenance), 60,000 km, 80,000 km (before maintenance), and 80,000 km (after maintenance) respectively. The transit cycle and durability test up to 80,000 km are legislated procedures in Taiwan for certification of light heavy-duty diesel cars. This transient cycle sequence took 20 min and included express way, congested urban and uncongested urban driving patterns, which represented a wide variety of speeds and loads to simulate vehicle running conditions [31]. One coldstart cycle and two hot-start ones were carried out with a 20-min soak between starts in each test condition. To mimic actual conditions, the emission factor was estimated based on the composite emission mass which was calculated as oneseventh of cold-start mass and six-sevenths of hot-start mass (average of two hot-start cycles).
2.2.
Fuels
Diesel fuel and the blended fuel B20, containing 20% waste soybean oil biodiesel, and 80% diesel, were used. Diesel was supplied by China Petroleum Company and the waste soybean oil biodiesel was provided by Taiwan New Japan Chemical Corporation. Waste soybean oil biodiesel was produced by transesterification of triglycerides with methanol, and its main fatty acid profile was palmitic fatty acid (12%), oleic fatty acid (23%) and linoleic fatty acid (55%). The properties of tested fuels are listed in Table 1. Diesel and biodiesel fuels meet the specifications of CNS 1471 [32]and CNS 15072 [32]separately.
Table 1 e Properties of tested fuels. Properties Density at 15 C, kg m3 Flash point, C Kinematic viscosity at 40 C, mm2 s1 Cetane index Lubricity, mm Sulfur, mg kg1 Carbon, % (mass fraction) Hydrogen, % (mass fraction) Oxygen, % (mass fraction) Average heat value, MJ kg1
B20
Diesel
840.7 97 3.53 55.7 196 20.5 84.0 13.2 2.8 41.7
830.8 78 3.15 53.1 332 21.8 86.9 13.1 e 42.8
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2.3. Dilution tunnel and constant volume sampling system The exhaust emission sampling system operated on the basis of constant volume sampling (CVS) and fixed dilution ratio, which reduced the temperature of emission exhaust to accommodate sampler requirements. The temperature of the fully diluted exhaust did not exceed 100 C. The system consisted of a dilution air purification device (filters and activated charcoal), a dilution tunnel, a critical flow Venturi, a Spencer blower and a discharge cleaning device (filters and activated charcoal) (Fig. 1). The tunnel was 61cm in diameter and 50 m in length. Diluted air, which was from ambient air and cleaned by a purification device, was drawn into the dilution tunnel by a Spencer blower (Fig. 1). The quantity of air in the dilution tunnel was controlled by the critical flow Venturi. Total engine exhaust gas was fed into the tunnel by a 7.5-m long solid insulated pipe with a 10 cm diameter and mixed with the diluted air in the beginning section of the dilution tunnel. Samples were collected at least 8-diameter long downstream of the mixing point to ensure good mixing. Although no diluted air samples were taken, ambient air which served as diluted air had much lower VOC concentrations in comparison with exhaust air [33e35] and was cleaned by the purification device before entering the dilution tunnel. The VOC contribution from diluted air was minimal. The regulated gaseous pollutants (CO, CO2, NOx, and HC) were measured by computer-controlled analyzers continuously. Volatile organic compound and aldehyde emissions were collected over the transit cycle from the dilution tunnel with 100-L Tedlar bags (SKC Inc., Eighty Four, PA, USA) at a flow rate of 4 L min1 by an in-line pump for the entire cycle (20 min). Pollutant data other than VOCs are not shown here.
range of fuel combustion products. After sampling, the tubes were analyzed with a thermal desorption system (TD4, Scientific Instrument Services, Ringoes, NJ, USA) located directly in the injector/septum area of the GC/MS. The liquidN2-cooled cryofocus trap was mounted in the GC oven, just below the injection port and around the 5-cm section of the capillary column. The cryofocus process concentrated the desorption air flow and provided good resolution in gas chromatograms. A temperature program increasing from 40 to 300 C at a rate of 8 C min1 with a broad mass range (33e400 AMU) was used to detect the compounds with different volatility. Two commercial VOC standards (ASTM D3710 Mix, Supelco Inc., Bellefonte, PA, USA; ASTM D2998 Mix, AccuStandard, New Haven, CT, USA) were used for the calibration of alkanes and aromatics. Some oxygenated chemicals, such as cyclohexanone, phenol, acetophenone and decanal, were identified and quantified in this study. In addition, the internal standard, ethyl benzene-d10, (ASTM aromatic internal standard, Supelco Inc., Bellefonte, PA) was spiked before the analysis to obtain robust and accurate quantification results. Compound identification was based on target ions and qualifier ions of mass spectrum, retention time and comparison with library spectra. Quantification was based on the relative response factor (RFF), which was calculated using the ratio of the test compound response factor to the internal standard (ethyl benzene-d10) response factor. Ranges of recovery, reproducibility (in terms of coefficient of variation), linearity (in terms of the r-square of the regression line) and method of detection limit (MDL, in terms of emission factors) of test chemicals are 77.9%e95.4%, 1.7%e10.45%, 0.971e0.998, and 0.036e0.146 mg kW h1 respectively.
2.5. 2.4.
Statistical analysis and health risk calculation
Analysis of volatile organic compounds (VOCs)
The thermal desorption tube packed with 150 mg of Tenax TA was used for VOC sampling. This is suitable for sampling VOC between C4 w C20 (US EPA, 1997), which is also the carbon
SPSS version 12.0 and Microsoft Office Excel 2003 were used for statistical analysis. T-test, paired t-test, and trend analysis test were carried out for comparing VOC exhaust emissions for both fuels, examining exhaust emissions before and after
Sampling bags Computer Gaseous air pollutant analyzers
Engine & Dynamometer
VOC sampling
7.5 m 10 cm
To discharge cleaning devise
Blower Aldehyde sampling
Ambient air 61 cm
Filter Activated charcoal
Dilution tunnel 50 m
Constant volume sampler
Fig. 1 e Schematic diagram of constant volume sampling system of diesel engine exhaust.
b i o m a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 9 6 e1 0 6
maintenance, and investigating the effects of increasing mileage and maintenance on engine emissions respectively. Health risks were calculated in terms of non-cancer chronic effect by using California Environmental Protection Agency chronic health benchmarks [36]. It was evaluated by hazard quotient (HQ) as expressed in Eq. (1): HQ ¼
C REFc
(1)
where C is the concentration (mg m3) from the engine exhaust, and REFc is the non-cancer chronic reference concentration (mg m3). Furthermore, the sum of hazard quotients (denoted as hazard index, HI ) of compounds aimed at the same organ was also assessed as per the following equation. HI ¼
3.
X Ci REFci
(2)
Results and discussion
3.1. Characterization of VOC emissions and corresponding ozone potentials According to this study’s results, more chemicals and greater emissions exist in exhaust emissions when using diesel as a fuel. Twenty-two chemicals are found in B20 fuel, and fortyseven chemicals are in diesel fuel. The aggregated emissions of these chemicals are called “total VOC emissions”. Total VOC emissions are in the range of 32.4e71.6 mg kW h1 and 49.6e183.7 mg kW h1, and individual VOC emissions are in the ranges of 0.1e29.8 mg kW h1 and 0.1e93.6 mg kW h1 for B20 and diesel, respectively (Table 2). Compared with diesel, B20 has lower total VOC emissions, decreasing by 61% on average. Dominant VOCs (defined as an emission percentage >5% of total emission) are benzene, heptane, toluene, and phenol with average percentages of 6.1%, 12.2%, 46.1%, and 15.1%, respectively in B20 fuel, accounting for 79.5% of total VOC emissions. For diesel fuel, toluene, xylene, and naphthalene are dominant with average percentages of 37.5%, 5.4% and 19.2%, respectively, accounting for 62.1% of total VOC emissions. Except for toluene, dominant VOCs in both fuels are different. Additionally, we find that more VOCs with emissions greater than 1 mg kW h1are found in diesel fuel; there are twenty seven for diesel fuel, in comparison with thirteen VOCs in B20 fuel. Total ozone formation potentials, based on maximum incremental reactivity (MIR) [37], are in the ranges of 61.4e180.4 mg kW h1 and 124.9e533.4 mg kW h1 for B20 and diesel, respectively. Individual ozone potential emissions are in the ranges of 0.9e88.6 mg kW h1 for B20 and 2.9e252.8 mg kW h1 for diesel. The negative number is due to the negative MIR of acetophenone. The corresponding ozone potential emissions are lower in B20 fuel, decreasing by 64% on average (Table 3), which is almost the same magnitude as the reduction percentage of total VOC emissions. VOC emissions from biodiesels have been reported in few studies. Sharp et al. [18]compare emissions of B20 (20% biodiesel þ 80% diesel) and B100 (100% biodiesel) with those of diesel. Results show total VOCs are 34.9 mg kW h1,
99
31.1 mg kW h1 and 21.6 mg kW h1 for diesel, B20 and B100, respectively. The percent changes relative to diesel are 11 % for B20 and 38% for B100. The EPA study [25] estimates the percent changes relative to diesel in emissions of the sum of eleven organic toxics and refers to these as total toxic emissions at given biodiesel concentrations. Based on the estimations, B20 and B100 fuels’ percent changes of total toxic emissions are 3% and 16%, separately. Correˆa and Aribilla [26] also investigate percent changes of eight mono-aromatic hydrocarbons (MAHs) by comparing with diesel; the average changes of MAHs are 4.2%, 8.2%, and 21.1% for B2, B5, and B20, respectively. Shah et al. [38] find that percent changes in total VOC emissions in comparison with diesel are 14.5% w 73.9% and 39.6% w 57% for B20 and B100, respectively. The four studies in the literature all agree with the present one that B20 fuel has lower total VOC emissions. Lower emissions may result from higher cetane number and oxygen content for B20 fuels. Fuels with high cetane number can reduce ignition delay and help promote more complete combustion, which could lead to reduction in hydrocarbon emissions [39e41]. In addition, higher oxygen content in B20 fuel helps to combust completely and reduces emissions [24,42]. Although our study does not investigate the exhaust emission when using B100 as a fuel, data in the literature show that total VOC emissions decrease with biodiesel concentrations. It is reasonable to conclude that higher biodiesel blends will have lower total VOC emissions.
3.2. Effects of increasing mileage and maintenance on VOC emissions The effects of cumulative mileage and maintenance on engine emissions for both fuels have been examined. Over the test period, the average emissions of individual VOC are in the ranges 0.1e23.0 mg kW h1 and 0.1e47.3 mg kW h1 (Table 2), with variations of 10%e157% and 2%e105% for B20 and diesel fuels, separately. Variations over the test mileages are mainly attributed to fluctuations of exhaust emissions, since they have the same magnitudes as those between duplicate samples (samples from two hot-start cycles with variations of 0.8%e158% and 0.1%e166% for B20 and diesel fuels, individually). Also, time series analysis (auto-regression model) is implemented to test whether there is a trend in total VOC emissions over the test mileages for both fuels. No statistical significance is found. The autocorrelation coefficients ( pvalue) are 0.696 ( p-value ¼ 0.275) for B20 and 0.054 ( pvalue ¼ 0.951) for diesel. Therefore, it is concluded that the engines can run on both fuels for a cumulative mileage up to 80,000 km without having more VOC emissions. Moreover, no significant differences in emissions are found before and after maintenance at both cumulative mileages of 40,000 km and 80,000 km. This indicates that maintenance does not influence VOC emissions (Table 2).
3.3. fuels
Individual VOC comparison between B20 and diesel
Since the effects of increasing mileage and maintenance on VOC emissions are insignificant (as discussed above),
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Table 2 e Exhaust emissions factors of VOCs from engines fueled with B20 and diesel at five different cumulative mileages. VOC
B20 fuel
Diesel fuel 1
Emission facotr (mg kWh1)
Emission factor (mg kWh ) Cumulative mileage (km) 0
3.5 ef 2.7 e 29.8 1.7 e e 1.4 e e 5.3 e e e 2.1 e 5.8 e e e e e 1.3 e e 0.6 e e e e e 0.8 e e e e e e e 0.4 e
1.4 e 6.4 e 23.6 0.3 e 5.5 3.2 6.5 0.9 e 0.9 e 0.6 1.7 e 4.0 e e e e e 1.5 e e e e e e e 1.3 e e e e e e e e e e
40,000 (before maint.)b 3.8 e 4.8 0.1 11.8 0.2 e 0.3 1.8 0.1 0.1 e e e e 0.1 e 12.2 e e e e e e e e e e e e e e e e e e e e e e e e
40,000 (after maint.) 2.3 e 6.8 e 13.5 0.0 e 0.2 1.1 e 0.1 0.1 0.1 e e 0.1 e 8.0 e e e e e e e e e e e e e e e e e e e e e e e e
60,000
3.7 e 1.8 32.8 1.2 e 1.9 6.1 e 2.3 1.3 3.8 e e e e 13.1 e e e 1.1 e e e e 0.9 e e e e e 0.8 e e e 0.5 e e e 0.5 e
Mean 80,000 (before maint.)c 1.6 e 7.9 e 19.8 0.9 e 0.2 2.6 e 0.8 1.0 1.0 e 0.3 1.1 e 3.5 e e 1.9 e e e e e e e e e e e 0.5 e e e e e e e e e
(SD)
80,000 (after maint.) 3.4 e 6.5 e 29.2 0.5 e 0.2 1.5 e 0.1 0.7 0.7 e e 0.8 e 1.4 e e e e e e e e 0.5 e e e e e 0.6 e e e 0.9 e e e 1.1 e
Cumulative mileage (km) 0
2.8 Nag 5.3 0.1 23.0 0.7 Na 1.4 2.5 3.3 0.7 1.7 1.3 Na 0.4 1.0 Na 6.8 Na Na 1.9 1.1 Na 1.4 Na Na 0.7 Na Na Na Na 1.3 0.7 Na Na Na 0.7 Na Na Na 0.7 Na
(1.1) (2.4) (8.5) (0.6) (2.3) (1.8) (4.5) (0.9) (2.3) (1.6) (0.2) (0.9) (4.1)
(0.1)
(0.2)
(0.2)
(0.0)
5.2 0.8 2.9 0.6 22.4 1.3 e 1.4 4.3 0.1 1.4 1.0 1.0 e 0.3 e e 1.7 e 0.5 1.0 e e e e e 0.7 e e e e 0.9 0.8 e e e 0.8 e e e 0.5 e
20,000
2.7 1.0 5.0 e 45.5 1.3 1.1 1.9 5.9 0.8 1.9 2.5 1.6 e 0.4 1.9 e 1.3 3.4 0.5 5.5 e 1.1 4.2 e e 0.9 0.7 e e e 3.0 1.5 0.5 e 0.8 1.3 e e e 1.7 0.5
40,000 (before maint.)d 4.4 0.7 7.8 e 93.6 2.0 1.3 2.8 10.4 1.0 3.4 1.3 1.8 e 0.6 2.4 0.2 4.2 3.3 0.2 7.3 0.7 1.3 4.3 0.1 0.7 1.7 0.9 0.1 1.1 0.7 4.0 2.7 0.8 0.7 1.0 2.9 0.7 0.6 0.4 3.6 1.2
40,000 (after maint.) 5.0 e 3.5 e 37.5 1.8 1.5 2.0 6.9 1.3 2.4 1.6 1.8 e 0.5 1.7 e 4.5 4.1 0.9 5.2 0.7 1.4 5.2 e 0.9 1.7 1.0 0.1 1.0 0.7 49.2 2.9 0.8 0.9 1.4 3.0 0.7 0.8 0.5 3.6 1.1
60,000
0.7 0.6 3.7 0.5 62.1 0.6 1.8 2.7 10.6 2.5 3.7 2.9 2.0 2.7 0.8 1.0 1.0 1.6 3.4 0.7 3.4 0.7 1.2 4.5 e 0.6 2.1 0.8 e 0.8 0.5 9.1 2.1 e 0.5 e 1.5 e 0.4 e 2.2 0.6
80,000 (before maint.)e 2.1 e 2.0 0.4 48.9 1.3 0.6 0.9 3.1 e 1.0 e 0.9 e 0.2 1.1 e 1.5 2.3 e 1.1 e e 3.2 e e 1.0 e e e e 55.6 1.7 e e e 1.6 e e e 2.0 0.5
Mean
(SD)
3.0 0.8 3.7 0.5 47.3 1.3 1.2 1.8 6.5 1.1 2.2 1.7 1.5 2.7 0.4 1.6 0.6 2.4 3.2 0.5 3.5 0.7 1.1 4.2 0.1 0.7 1.3 0.9 0.1 1.0 0.6 25.3 1.9 0.7 0.7 1.0 1.8 0.7 0.6 0.5 2.3 0.7
(1.8) (0.2) (2.0) (0.1) (24.4) (0.5) (0.4) (0.7) (3.1) (0.9) (1.1) (0.8) (0.4) Na (0.2) (0.6) (0.6) (1.5) (0.7) (0.3) (2.5) (0.0) (0.1) (0.7) Na (0.1) (0.6) (0.1) (0.0) (0.2) (0.1) (25.1) (0.8) (0.2) (0.2) (0.3) (0.9) (0.0) (0.2) (0.0) (1.2) (0.3)
80,000 (after maint.) 0.8 e 0.9 e 21.3 1.0 0.7 1.2 4.4 1.0 1.5 0.6 1.1 e 0.3 e e 2.1 2.5 e 1.3 e 0.5 3.7 e e 1.0 e e e 0.5 55.0 1.5 e e e 1.4 e 0.5 e 2.4 0.6
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Benzene 3-Methyl hexane Heptane Methyl cyclohexane Toluenea Octanea 4-Methyl octane Ethyl benzene p-Xylenea Styrene o-Xylenea Cyclohexanone Nonane 1-Methyl ethyl benzene Propyl benzene 1-Ethyl-3-methyl benzene 1,3,5-Trimethyl Benzene Phenola Benzonitrile 2,2,4-Trimethyl heptane 1,2,4-Trimethyl benzene 1-Methyl-3-propyl benzene 2,3,3-Trimethyl octane Acetophenonea 1-Ethyl-2,4-dimethyl benzene 4-Ethyl-1,2-dimethyl benzene Undecanea 2,6-Dimethyl decane 1,2,4,5-Tetramethyl benzene 1,2,3,4-Tetramethyl benzene 3-Methyl undecane Naphthalene Dodecane Decanal 8-Methyl 3-undecene 7-Methyl tridecane Tridecanea 2-Methyl naphthalene 4-Methyl tetradecane 3-Methyl tridecane Tetradecanea 2-Methyl tetradecane
20,000
(0.5) (0.2) (0.1) (1.1) 1.1 0.6 0.5 1.3
1.1 1.7
1.0 0.5 e e 110.9 0.9 0.4 e e 135.9
1.5 1.5
0.8 0.5 e e 139.3 1.6 0.8 0.6 0.1 162.9
0.1
0.6 e e 2.4 104.3 e e e e 49.6
0.6 1.3 e
Na Na Na Na
P < 0.005 (comparison of emissions between B20 and diesel fuel). P ¼ 0.597 (B20 fuel 40,000 km, comparison of emissions before maintenance vs. after maintenance). P ¼ 0.647 (B20 fuel 80,000 km, comparison of emissions before maintenance vs. after maintenance). P ¼ 0.788 (diesel fuel 40,000 km, comparison of emissions before maintenance vs. after maintenance). P ¼ 0.350 (diesel fuel 80,000 km, comparison of emissions before maintenance vs. after maintenance). Not detected. Na: not applicable. a b c d e f g
e
e e e e 48.1 e e e e 42.9
e e
e e e e 71.6 e e e e 32.4
e
e e e e 57.8 e e e e 55.5
e e e
Hexadecane Heptadecane Octadecane Tricosane Total
e e e e 35.4
Na
3.4.
Pentadecane
101
averaging emission factors of individual VOCs over the test mileages are used to calculate emission percent changes of B20 fuel using averages of corresponding diesel emission factors as references. Percent changes are in the range of 95e191%. Most chemical emissions are lower in B20 fuel. Particularly for chemicals, such as toluene, octane, m- &p-xylene, o-xylene, acetophenone, undecane, dodecane and tetradecane, percent changes are in the ranges of 48% to 71%, and statistically significant. However, phenol emission is higher in B20 fuel increasing by 183%, and the difference is significant. Several other studies estimate average percent changes of B20 by comparing with base diesel fuel for benzene, toluene, ethyl benzene, and xylene, respectively. The average percent changes are 16.5%, 19.9%, 44.9%, and 12.3% from the EPA study [25]; 23%, 25%, 9.5% and 20 % according to Correˆa and Aribilla [26] study; 5.7%, 51.5%, 24.5% and 64.5% in this study. Additionally, Shan et al. [38] detect percent change of B20 in comparison with diesel for benzene, toluene, p-&mxylene and o-xylene, and the corresponding percentages are 68.8%, 42.7%, 28.8%, and 14.1%, separately. Although the EPA study shows different results of benzene and toluene from those of the other studies, the latest studies indicate that the B20 fuel has lower emissions of main aromatic compounds. We can conclude that usage of biodiesel has a beneficial effect on aromatic emissions.
1.6 0.8 0.4 1.4 183.7
(0.6)
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Classification of VOC emissions
For better understanding of VOC species in exhaust for both fuels, VOC emissions are categorized into three chemical classes, which are aromatics, oxygenated species, and alkanes & alkenes. Average emissions (SD) of these three classes are 32.6 (12.0) mg kW h1, 8.4 (4.6) mg kW h1, and 8.0 (2.1) mg kW h1, with corresponding percentages of 66.4%, 17.2%, and 16.4%, respectively, for B20 fuel. For diesel, they are 96.7 (33.6) mg kW h1, 7.7 (3.3) mg kW h1, and 22.2 (9.5) mg kW h1, with corresponding percentages of 76.4%, 6.1%, and 17.6%, respectively (Table 4). Both fuels show the highest emissions in the aromatic group. The second highest emission group is the oxygenated one in B20, while it is the alkane & alkene one in diesel. Accordingly, average ozone formation emissions (SD) of these three classes are 100.3 (41.8) mg kW h1, 8.8 (5.3) mg kW h1, and 5.6 (1.4) mg kW h1, with corresponding percentages of 87.4%, 7.7%, and 4.9%, respectively, for B20 fuel. For diesel, they are 298.4 (125.9) mg kW h1, 4.2 (3.6) mg kW h1, and 16.0 (8.3) mg kW h1, with corresponding percentages of 93.7%, 1.3%, and 5.0%, respectively. Higher oxygenated chemical emissions in B20 fuel may be related to the fuel composition, since biodiesel has higher oxygen content (w11% by weight) [16,24], and is prone to produce higher oxygenated chemical emissions in comparison with diesel [1]. Further investigation is carried out by dividing VOCs into non-oxygenated and oxygenated VOCs. Our study shows many non-oxygenated VOCs are lower in B20 fuel with statistical significance, such as toluene, octane, xylenes, tridecane and tetradecane (Table 2). Results of oxygenated chemicals vary a lot. For example, phenol emission increases by 183% with a significant difference when using B20 as a fuel,
102
Table 3 e Ozone formation potentials of VOC exhaust emissions from engines fueled with B20 and diesel at five different cumulative mileages. VOC
B20 fuel
Diesel fuel 1
Ozone formation potential (mg-O3 kW h1)
Ozone formation potential (mg-O3 kW h ) Cumulative mileage (km) 0
1.5 ea 2.2 e 80.5 1.0 e e 9.5 e e 6.3 e e e 17.5 e 6.5 e e e e e 0.7 e e 0.3 e e e e e 0.3 e e e e e e
(SD)
20,000 40,000 40,000 60,000 80,000 80,000 (before (after (before (after maint.) maint.) maint.) maint.) 0.6 e 5.2 e 63.8 0.2 e 14.9 21.2 14.3 6.1 e 0.5 e 1.3 13.6 e 4.4 e e e e e 0.9 e e e e e e e 1.5 e e e e e e e
1.6 e 3.9 0.1 31.9 0.1 e 0.7 11.8 0.3 0.9 e e e e 1.2 e 13.6 e e e e e e e e e e e e e e e e e e e e e
1.0 e 5.5 e 36.5 0.0 e 0.5 7.4 e 0.6 0.1 0.1 e e 0.7 e 9.0 e e e e e e e e e e e e e e e e e e e e e
1.5 e 1.5 e 88.6 0.7 e 5.1 40.3 e 14.6 1.5 2.1 e e e e 14.6 e e e 8.9 e e e e 0.4 e e e e e 0.3 e e e 0.2 e e
0.7 e 6.4 e 53.5 0.5 e 0.5 16.9 e 5.2 1.2 0.5 e 0.6 9.1 e 3.9 e e 16.8 e e e e e e e e e e e 0.2 e e e e e e
1.4 e 5.3 e 78.9 0.3 e 0.4 9.8 e 0.8 0.8 0.4 e e 6.8 e 1.6 e e e e e e e e 0.2 e e e e e 0.2 e e e 0.3 e e
Cumulative mileage (km) 0
1.2 Nab 4.3 0.1 62.0 0.4 Na 3.7 16.7 7.3 4.7 2.0 0.7 Na 0.9 8.1 Na 7.7 Na Na 16.8 8.9 Na 0.8 Na Na 0.3 Na Na Na Na 1.5 0.3 Na Na Na 0.2 Na Na
(0.5) (1.9) (22.9) (0.4) (6.2) (12.1) (9.9) (5.7) (2.7) (0.9) e (0.5) (7.4) (4.6)
(0.1)
(0.1)
(0.1)
2.2 1.1 2.4 1.1 60.3 0.8 e 3.7 28.2 0.2 9.1 1.2 0.5 e 0.6 e e 1.9 e 0.5 9.0 e e e e e 0.3 e e e e 1.1 0.3 e e e 0.3 e e
Mean (SD)
20,000 40,000 40,000 60,000 80,000 80,000 (before (after (before (after maint.) maint.) maint.) maint.) 1.1 1.3 4.0 e 122.8 0.8 1.3 5.1 38.7 1.8 12.5 2.9 0.9 e 0.8 15.8 e 1.4 27.9 0.5 48.5 e 1.4 2.4 e e 0.4 0.9 e e e 3.5 0.6 3.0 e 0.9 0.4 e e
1.8 1.0 6.3 e 252.8 1.2 1.5 7.5 68.4 2.3 22.4 1.6 1.0 e 1.3 20.0 1.5 4.7 27.3 0.2 63.9 5.3 1.8 2.4 0.8 5.4 0.7 1.1 0.8 8.7 0.9 4.7 1.0 5.0 3.1 1.2 1.0 2.4 0.8
2.1 e 2.8 e 101.1 1.1 1.7 5.3 45.7 2.9 15.7 1.9 1.0 6.0 1.0 14.1 e 5.1 33.8 0.9 45.4 5.5 1.9 2.9 e 7.1 0.7 1.2 0.8 8.5 0.9 57.6 1.1 5.2 3.9 1.7 1.0 2.2 1.0
0.3 0.8 3.0 1.0 167.7 0.3 2.0 7.3 69.8 5.6 24.2 3.4 1.1 e 1.6 7.9 10.3 1.8 28.0 0.7 30.0 5.7 1.5 2.5 e 5.1 0.9 1.0 e 6.2 0.6 10.7 0.8 e 2.3 e 0.5 e 0.5
0.9 e 1.6 0.8 132.2 0.8 0.7 2.4 20.2 e 6.8 e 0.5 e 0.5 8.7 e 1.7 18.8 e 9.3 e e 1.9 e e 0.4 e e e e 65.0 0.6 e e e 0.6 e e
0.3 e 0.7 e 57.4 0.6 0.8 3.2 29.1 2.2 9.9 0.7 0.6 e 0.7 e e 2.4 20.4 e 11.4 e 0.7 2.1 e e 0.4 e e e 0.6 64.4 0.6 e e e 0.5 e 0.6
1.2 1.1 3.0 0.9 127.8 0.8 1.3 4.9 42.9 2.5 14.3 2.0 0.8 6.0 0.9 13.3 5.9 2.7 26.0 0.5 31.1 5.5 1.5 2.4 0.8 5.9 0.6 1.1 0.8 7.8 0.7 29.6 0.7 4.4 3.1 1.3 0.6 2.3 0.7
(0.8) (0.2) (1.6) (0.1) (65.9) (0.3) (0.5) (2.0) (20.5) (2.0) (7.0) (0.9) (0.2) Na (0.4) (5.1) (6.2) (1.6) (5.4) (0.3) (22.3) (0.2) (0.2) (0.4) Na (1.1) (0.2) (0.1) (0.0) (1.4) (0.2) (29.4) (0.3) (1.2) (0.8) (0.4) (0.3) (0.1) (0.2)
b i o m a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 9 6 e1 0 6
Benzene 3-Methyl hexane Heptane Methyl cyclohexane Toluene Octane 4-Methyl octane Ethyl benzene p-Xylene Styrene o-Xylene Cyclohexanone Nonane 1-Methyl ethyl benzene Propyl benzene 1-Ethyl-3-methyl benzene 1,3,5-Trimethyl benzene Phenol Benzonitrile 2,2,4-Trimethyl heptane 1,2,4-Trimethyl benzene 1-Methyl-3-propyl benzene 2,3,3-Trimethyl octane Acetophenone 1-Ethyl-2,4-dimethyl benzene 4-Ethyl-1,2-dimethyl benzene Undecane 2,6-Dimethyl decane 1,2,4,5-Tetramethyl benzene 1,2,3,4-Tetramethyl benzene 3-Methyl undecane Naphthalene Dodecane Decanal 8-Methyl 3-undecene 7-Methyl tridecane Tridecane 2-Methyl naphthalene 4-Methyl tetradecane
Mean
e 0.1 e e e e e e 124.8
3-Methyl tridecane Tetradecane 2-Methyl tetradecane Pentadecane Hexadecane Heptadecane Octadecane Tricosane Total
e e e e e e e e 146.8
e e e e e e e e 66.2
e e e e e e e e 61.4
e 0.1 e e e e e e 180.4
e e e e e e e e 116.0
e 0.4 e e e e e e 107.5
Na 0.2 Na Na Na Na Na Na
(0.0)
e 0.2 e e e e e e 124.9
e 0.6 0.6 0.4 0.2 e e 0.8 299.4
0.5 1.1 1.4 0.2 0.5 0.3 0.1 0.4 533.4
0.6 1.1 1.3 0.0 0.5 0.3 0.2 0.0 383.1
e 0.7 0.7 0.5 0.3 0.2 e e 408.3
e 0.7 0.6 0.5 0.3 0.1 e e 272.7
e 0.8 0.7 0.5 0.3 0.2 e e 208.3
0.6 0.7 0.9 0.4 0.3 0.2 0.2 0.4
(0.0) (0.4) (0.4) (0.2) (0.2) (0.1) (0.0) (0.4)
a Not detected. b Na: not applicable.
b i o m a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 9 6 e1 0 6
Table 4 e Exhaust emission factors and corresponding ozone formation potentials of VOC chemical classes from engines fueled with B20 and diesel. VOC class
B20
Diesel
Emission factor (mg kW h1)
Percent (%)
Ozone formation (mg-O3 kW h1)
Percent (%)
Emission factor (mg kW h1)
Percent (%)
Ozone formation (mg-O3 kW h1)
Percent (%)
32.6 (12.0)a 8.4 (4.6) 8.0 (2.1) 49.1
66.4b 17.2 16.4
100.3 (41.8) 8.8 (5.3) 5.6 (1.4) 114.7
87.4 7.7 4.9
96.7 (33.6) 7.7 (3.3) 22.2 (9.5) 126.7
76.4 6.1 17.6
298.4 (125.9) 4.2 (3.6) 16.0 (8.3) 318.6
93.7 1.3 5.0
Aromatics Oxygenated species Alkanes & alkenes Total a Mean (standard deviation). b Percentage of mean.
103
104
b i o m a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 9 6 e1 0 6
Table 5 e Chronic hazard quotients (HQ) and hazard indices (HI) of investigated compounds in exhaust emissions from engines fueled with B20 and diesel. Chemical
Benzene Toluene Ethyl benzene m-& p-Xylene Styrene o-Xylene Phenol Naphthalene
Ref. conc. (mg m3) 60 300 2000 700 900 700 200 9
Ethyl benzene, phenol Phenol Benzene, Toluene, ethyl benzene Benzene Ethyl benzene Ethyl benzene, phenol Benzene, toluene, xylenes, styrene, phenol Toluene, xylenes, naphthalene
HQ
Target organ or system
B20
Diesel
0.38 0.62 0.01 0.03 0.03 0.01 0.28 1.13
0.40 1.28 0.01 0.08 0.01 0.03 0.10 22.79
Developmental, hematologic, nervous Developmental, nervous, respiratory Alimentary, developmental, endocrine, kidney Nervous, respiratory Nervous Nervous, respiratory Alimentary, cardiovascular, kidney, nervous Respiratory
HI 0.28 0.28 1.01 0.38 0.01 0.28 1.35 1.79
0.11 0.10 1.69 0.40 0.01 0.11 1.89 24.17
Alimentary Cardiovascular Developmental Hematologic Endocrine Kidney Nervous Respiratory
and cyclohexanone emission is slightly higher in B20 fuel in this study, while acetophenone emission is lower in B20 with a significant difference. The varied results in oxygenated VOC may be due to the oxygen content in biodiesel. This oxygen-rich fuel increases combustion efficiency [24,43], tending to lower VOC emission, while the additional oxygen increases the probability of oxygenated VOC formation. Basically, the VOC emission results are the net effects of these two mechanisms. This can explain why non-oxygenated VOC emissions are consistently reduced, while oxygenated VOC emissions are varied when biodiesel fuel is compared with diesel.
system. HIs of B20 and diesel fuels are in the ranges of 0.01e1.79 and 0.01e24.17, respectively. For the alimentary, cardiovascular and kidney systems, slightly higher HIs are found in B20 fuel due to higher phenol concentrations. On the contrary, much lower HIs are found in B20 fuel for the developmental, nervous and respiratory systems. Again, this supports the advantage of using the B20 fuel. More reduction in health risks are expected when higher percentages of biodiesel blends are used.
3.5.
In this study, the effects of the B20 fuel on VOC emissions are examined and compared with those of diesel fuel in several measurements over cumulative mileages of 0e80,000 km and two maintenance practices. According to the study’s findings, B20 has lower VOC emissions, correspondingly lower ozone formation potentials, and emission reductions are 61.2% and 64.0% on average for total VOC and ozone potential emissions, respectively. Reduction in health risks in terms of HIs is also found in B20 fuel, especially for the developmental, nervous and respiratory systems. Emission reductions of several VOC chemicals, such as toluene, octane, m-& p-Xylene, o-xylene, acetophenone, undecane, dodecane and tetradecane, are in the range of 48.0%e70.7% with statistical significance. However, phenol emission is higher in B20 fuel and the difference is significant. We also find emission percentage of the oxygenated group is higher in B20 fuel than that in diesel fuel. This results from high oxygen content in B20 fuel. Higher oxygen content in B20 fuel may enhance combustion efficiency, tending to lower VOC emission, while the additional oxygen increases the probability of oxygenated VOC formation. The VOC emission results are the net effects of these two mechanisms. Therefore, emissions of non-oxygenated VOCs are consistently reduced from B20 fuel, while emissions of oxygenated VOCs are varied.
Health risk assessment of exhaust emissions
Health impacts of diesel engine exhausts are investigated in terms of hazard quotients and hazard indices. Engine exhaust emissions likely enter the human body through inhalation and have long-term deleterious health effects [44]; therefore, chronic inhalation reference exposure levels are used for health risk estimations [36]. According to our findings, nine commonly present compounds with significant adverse effects are included, being benzene, toluene, ethyl benzene, xylene (o-, m-, & p-), styrene, phenol and naphthalene. Table 5 shows the hazard quotients and hazard indices of investigated compounds in engine exhausts when fueled with B20 and diesel. HQs of B20 and diesel fuels are in the ranges of 0.01e1.13, and 0.01e22.79, respectively. Except for styrene and phenol, which have slightly higher HQs value in B20 fuel, other compounds show higher HQs in exhausts of the engine fueled with diesel. Basically, HQs reflect exhaust concentration magnitude. Among the investigated compounds, toluene and naphthalene have higher HQs in both fuels; however, their HQs decrease considerably in B20 fuel in comparison with those in diesel fuel. This indicates the beneficial effect of using B20 fuel on health risks. The HI is obtained by the sum of the HQs of compounds aiming at the same target organ or
4.
Conclusions
b i o m a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 9 6 e1 0 6
Generally, B20 fuel has the beneficial effect in terms of VOC emissions.
Acknowledgments The authors wish to thank China Petroleum Company and Taiwan NJC Corporation for kindly providing diesel and waste cooking oil biodiesel, respectively. This project was partially supported by ARTC of China Petroleum Company and the National Science Council in Taiwan (NSC 94-2314-B-037-102).
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