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Comparative profile of pollutants generated by a stationary engine fueled with diesel, biodiesel, and ethanol
Author’s Accepted Manuscript Comparative profile of pollutants generated by a stationary engine fueled with diesel, biodiesel, and ethanol Beatriz Silva Amaral, Fábio Júnior Moreira Novaes, Maria da Conceição Klaus V.Ramos, Francisco Radler de Aquino Neto, Adriana Gioda www.elsevier.com/locate/jaerosci
PII: DOI: Reference:
S0021-8502(16)30243-9 http://dx.doi.org/10.1016/j.jaerosci.2016.07.009 AS5024
To appear in: Journal of Aerosol Science Received date: 16 March 2015 Revised date: 1 July 2016 Accepted date: 6 July 2016 Cite this article as: Beatriz Silva Amaral, Fábio Júnior Moreira Novaes, Maria da Conceição Klaus V.Ramos, Francisco Radler de Aquino Neto and Adriana Gioda, Comparative profile of pollutants generated by a stationary engine fueled with diesel, biodiesel, and ethanol, Journal of Aerosol Science, http://dx.doi.org/10.1016/j.jaerosci.2016.07.009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Comparative profile of pollutants generated by a stationary engine fueled with diesel, biodiesel, and ethanol
Beatriz Silva Amaral1,2, Fábio Júnior Moreira Novaes³, Maria da Conceição Klaus V.Ramos3, Francisco Radler de Aquino Neto3, Adriana Gioda1*
¹Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Departamento de Química, Rio de Janeiro, Brasil. ²Instituto Federal do Rio de Janeiro (IFRJ), Rio de Janeiro, Brasil ³Universidade Federal do Rio de Janeiro, Instituto de Química, LPCC – LADETEC. Rio de Janeiro, Brasil.
Corresponding author: Prof. Dr. Adriana Gioda ([email protected]) Department of Chemistry, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Marquês de São Vicente, 225, 22451-900, Gávea, Rio de Janeiro-RJ, Brasil. Phone: +55 21 3527-1328 Fax: +55 21 3114-1637
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Abstract Fossil fuel emissions derived from crude oil have a significant impact on the environment, climate change, air pollution, and others. Under these circumstances, there is a great interest in alternative energy resources, especially those that are able to reduce the emission of atmospheric pollutants. The aim of this study is to evaluate the burning emissions of the following binary mixture and biofuels: commercial diesel (diesel with 5 % of biodiesel, B5), pure soy biodiesel (B100), additivated biodiesel (B100 adt) stored at 40 °C for 1, 2, and 3 weeks, and additivated ethanol (Ethanol adt). The burning emissions were evaluated by the levels of benzene, toluene, ethylbenzene, and xylenes (BTEX) and total particulate matter (TPM). The quality of the biofuels was given by oxidative stability during storage. The combustion products were originated from a diesel cycle stationary engine, operating in 1800 rpm and 0 % load. For a greater reliability in the results, some figures of merit were evaluated for the determination BTEX by gas chromatography and flame ionization detection (GC-FID) and the particulate matter was determined by gravimetric analysis. Results show that operating time of the engine influences combustion efficiency. During the initial 15 minutes, cold engine start, there was increasing in BTEX and TPM emissions, when comparing B100 and B5. Regarding to the storage period of 1-2 weeks, B100, B100 adt, and B5 showed reduction of approximately 36, 16, and 4 % for TPM, respectively. Evaluating each component of BTEX, the benzene emissions were greater for biofuels, which is in agreement with previous studies. As observed for TPM, the storage time of 1-2 weeks was beneficial for the mitigation of aromatic emissions. A reduction about 60 % percent was measured for benzene and ethylbenzene. However, these emissions can also be influenced by the engine operating conditions (load and speed), engine type, and characteristics of biofuels. Additivated ethanol also presented low emissions for these pollutants as well as the lowest percentage of emissions of TPM. It is noteworthy that Ethanol adt present the lowest percentage of benzene emission.
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Keywords: vehicular emission; diesel; biodiesel; BTEX; particulate matter; oxidative process
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1. Introduction
The impacts caused by global warming and the search for alternative energy resources are a worldwide concern. Currently, great part of the energy consumed in the world is originated from non-renewable sources like natural gas, coal, and oil (Corrêa and Arbilla, 2008). Diesel, one of the derivatives of crude oil, is extensive used in internal combustion vehicle engines. It contains paraffinic hydrocarbons, aromatics, olefins, sulfurous, nitrogen and oxygenous compounds, and metals (Aleme and Barbeira, 2012). The use of this fuel on the automotive industry is increasing due to its high efficiency, durability, and flexibility (Guarieiro, et al., 2011; Santos, 2008). In spite of that, during the combustion process, there is an immense production of particles and gases (Gauer, et al., 2013). In the present scenario, biofuels gained great importance as alternative to the current global energy matrix, once it offers a clean energy model. Biodiesel use reduces the emission of some air pollutants and it help to close the carbon cycle due to its vegetal origin. Moreover, when added to diesel, it has a synergetic effect of biodegradation by cometabolism (Quintella, et al., 2009). Even though biodiesel is a renewable source of energy, which is highly advantageous, its effects on environment and on public health must also be considered. The use of this biofuel present some disadvantages such as high NOx emissions, high viscosity, problems related to low temperatures, and low oxidative stability. The latter is the major responsible for the biodiesel degradation during long storage (Singh and Singh, 2010). The chemical nature of biodiesel, a mixture of unsaturated fatty acid, facilitates the oxidation processes. These processes may be accelerated in the presence of metals, contact with air, and high temperatures (Dos Reis Albuquerque, 2009). In order to prevent or minimize the oxidation, antioxidants are added to biodiesel, they may be natural or synthetic (Karavalakis, et al., 2011). However, storage conditions are key factors to prevent the degradation of biodiesel.
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Given the importance of storage conditions, several authors conducted experiments in order to identify the principal factors to the quality of biodiesel. A study carried out in 2007 reports that the biodegradability of biodiesel was superior to diesel in 28 days (Demirbas, 2007). Leung et al. (2006) noted that the biodiesel at 20 ºC degraded less than 10 % in comparison with 40 % of degradation, when the fuel was stored at 40 ºC. Ethanol is another important renewable fuel source that is produced mainly by sugar cane. Currently, this hydrated fuel is used directly in the supply of automotive vehicles. It has physicochemical properties that differ from gasoline such as lower combustion heat, higher vaporization heat, single boiling point, and a different air/fuel stoichiometric ratio (Vianna et al., 2008). On the one hand, this biofuel is both non-toxic and biodegradable (Guarieiro, et al., 2011) but it emits oxidation products during its combustion, i.e., aldehydes, ketones, and carboxylic acids. These pollutants have an important role in the processes of photo-oxidation in the atmosphere; therefore, the impact caused by the use of ethanol has also been evaluated and discussed in several studies (Teixeira, et al., 2008). Brazil has been the pioneer in the use of renewable fuels. In the early 1970s, the use of ethanol was implemented, and since the year of 2008 biodiesel has been used as an additive in diesel engines. The addition of biodiesel to diesel began with 2 % (B2), in 2008, it increased to 5 % (B5), and it reached 6 % (B6) in July 2014. In November 2016, the proportion of biodiesel is going to reach 7 % (B7). In Brazil, soy biodiesel is the most used due to the large-scale production. Besides, oil with high calorific value is obtained from soy (Schlesinger and Noronha, 2006). The combustion of any fuel emits a range of pollutants to the atmosphere that may be harmful to the environment, including human health. Among these pollutants, particulates can be listed, whose composition include elemental carbon, sulfates, metal oxides, trace gases (e.g., NOx, SOx, CO, and CO2), polycyclic aromatic hydrocarbons (PAH), and benzene, ethylbenzene,
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toluene, and xylenes (BTEX). To establish new air quality guidelines, based on a renewable energetic matrix, the level of gases and particulates emitted from the combustion of vehicles, as well as their chemical composition, must be investigated. The knowledge of emission levels leads the implementation of mitigation measures. The objective of this study was to quantify BTEX and total particulate matter (TPM) generated by a stationary engine supplied with renewable and non-renewable fuels in order to compare their emission profiles. The engine, a diesel cycle mono cylinder of 10 HP, operating in 1800 rpm and 0 % load, was fueled with additivated ethanol adt (Ethanol adt), commercial diesel (B5), pure soybean biodiesel (B100), and soybean biodiesel additive (B100 adt). The engine was attached to a generator (Toyama T6000 CXE3) at 1800 rpm and 60 Hz set. To evaluate the biofuels resistance to oxidation, the PetroOXI technique was applied and the results are indicated by the induction period (IP) in hours.
2. Materials and methods
2.1 Sample systems
The sampling was planned in order to concentrate the pollutants emitted by the engine and prevent contamination of the outside air. An acrylic chamber (1 m³) with collectors (filters, cartridges, and sensors), positioned inside, was used. All samples were collected in triplicate under the same engine operating conditions: no load (0 %) and speed of 1800 rpm. To ensure the quality of measurements, the engine was rinsed for 10 minutes with the fuel to be tested and the generated emissions discarded. The measurements initiated with a cold start of the engine of 30 minutes, supplied with the fuel to be tested. Six hundred milliliters of each fuel, on average, were used for each test. Temperature and relative humidity were controlled throughout the collecting
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process using a digital Thermohygrometer (Temperature and Relative Humidity sensor, Cole Pamer Thermohygrometer, Model 37951-00, USA) (Figure F1, supplementary information). The emissions generated by the fuel combustion were collected during the operation of the stationary engine, diesel cycle mono cylinder of 10 HP, connected to a generator (Toyama, T6000 CXE3) at 1800 rpm and 60 Hz set. In order to evaluate background contamination, samples were taken from the chamber before sampling with fuels. Outdoor air samples were also collected in order to verify influence of the surroundings on the samples within the chamber.
2.2 Fuels and Biofuels
Four types of fuels were used in this study: Commercial diesel – fossil diesel 95 % and 5 % biodiesel (B5) samples were collected at fuel distribution stations in the João Pessoa city, Paraíba state, Brazil. Pure soybean biodiesel (B100) and additivated pure soybean (B100 adt) with butilhydroxyanisol (BHA) were provided by the biodiesel division of the
Strategic
Technologies Center of the Northeast (CETENE), in the Pernambuco state, Brazil. Additivated ethanol (Ethanol adt) was prepared in the Federal University of Paraíba from 91.06 % ethanol, the additives were nitrate of tetrahydro-furfuryl (NTHF) 7.92 % and castor oil 0.99 %. One liter amber bottles of B100, B100 adt, and B5 fuels were storage in an oven at 40 ºC to verify the oxidation process. The samples were stored for 7, 14, and 21 days, characterized as T1, T2, and T3, respectively. Fuels were also not aged, characterizing the instant as time zero of storage (T0). This study was conducted in the northeast of Brazil, where the temperature of 40 °C is usual, especially in summer. Other studies conducted at lower temperatures did not succeed to significantly oxidize biofuels. Before and during storage time of the biofuels, the PetroOXY
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method measured the variation of oxidative stabilityPetroOXY. The Ethanol adt samples were not used in the oxidation experiments.
2.3 Sampling
The samplings were carried out in triplicate with three distinct times of 15, 30, and 60 minutes. These different sampling times were used to evaluate the development emissions during the operating time of the engine. BTEX were collected based on the EPA TO-1 method (1988), using activated charcoal tubes (Anasorb CSC, catalog 22601 2000, SKC. Eighty-four, PA) containing two beds (Bed A: 100 mg and Bed B: 50 mg) at a flow of approximately 1.0 L min -1. The TPM was collected in parallel with BTEX. Polycarbonate filters with porosity of 0.4 µm and diameter equal to 37 mm (Millipore HTTP 03700) were coupled to the vacuum pump at a flow rate of 10.0 L min-1. .
2.4 Analysis 2.4.1 Total particulate matter
For the determination of the mass of TPM, filters were previously conditioned in a desiccator with a solution of 80 % glycerol (v/v) for at least 24 hours. They were weighed before and after sampling on a precise balance (Mettler Toledo - Model XP 205, maximum capacity 220 g and readability 0.01 mg) at constant weight, until they presented standard deviation equal to or less than 0.00002 g.
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2.4.2 Determination of BTEX by GC-FID
For greater reliability in the results, the method for determination of BTEX considered some figures of merit commonly used in validation of chromatographic methods such as analytical curves, limits of detection (LOD), limits of quantification (LOQ), linearity, selectivity, recovery, and repeatability (Causon, 1997; Ribani, et al., 2004). The standard solutions were prepared from the standard mixture (mix) of BTEX with concentration of 2000 µg mL-1 per analyte (Sigma – Aldrich, São Paulo, Brazil). Initially, a work solution of 1000 µg mL-1 was prepared. After that, the analytical curve with concentrations of 1.0 µg mL-1, 10.0 µg mL-1, 20.0 µg mL-1, 30.0 µg mL-1, 50.0 µg mL-1 e 100.0 µg mL-1 was prepared in dichloromethane (Tedia, Brazil) with 99.9 % of purity. The LOD determination considered 3 sb/S, and LOQ considered 10 sb/S, where sb is the standard deviation between the linear coefficients and S is the sensitivity determined by the average slope of the analytical curve. For the desorption of analytes, firstly, the glass cartridge containing the adsorbent material was transferred to a 2.0 mL glass vials, properly identified with specifications of bed A and B. To avoid losses, the glass vials were immediately closed and placed in an ice bath and 1.5 mL of dichloromethane (99.9 %) was slowly added. Secondly, bottle caps were exchanged, the vials were homogenized for about 1 minute in a vortex and conditioned at 0 °C for 24 hours, a period that ensures the extraction of analytes. Finally, the samples were analyzed by GC-FID. Each sample was analyzed in triplicate. In this study, BTEX were determined with the use of a gas chromatograph (Agilent Technologies, Hewlett-Packard 7890, Series II, Palo Alto, CA, USA), equipped with automatic sampler and flame ionization detector. An innowax column of 25 m, diameter of 0.2 mm and 0.4 µm film thickness (Agilent Technologies) was used. The defined conditions of BTEX analysis were: automatic injector at 250 °C, initial oven temperature at 40 °C, ramp of 40 °C per minute
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until 53 °C, 40 °C per minute until 200 °C, detector at 260 °C, carrier gas was hydrogen, injection split 1:20 and injection volume 1.0 µL.
3. Results and Discussion
3.1 Total Particulate Matter
The pollutant profiles, in percentage, were evaluated considering: 1) engine operating time for B100, B100 adt, and B5 that was not stored (T0) in periods of 15, 30, and 60 minutes; 2) considering the storage at 40 °C in the periods T1, T2, and T3 for the same fuels sampled during 30 minutes. Both biodiesel pollutant profiles were compared with the emissions originating from the engine fueled with Ethanol adt sampled during 30 minutes. The levels of TPM varied with the operating time of the engine. In the initial 15 minutes, the highest TPM concentrations for all the fuels were registered, with the exception of additivated Ethanol. The high particle emission in the initial instants may be related to the fact that the engine was still cold, as it was not acting under ideal working conditions, leading to an incomplete combustion of the fuels. Considering the motor operation time, the percentage profiles of particulate matter are presented in Figure 1a, where the value of 100 % was attributed to B100. B100 presents the highest concentration in the period of 15 minutes, while the lowest percentage was measured for Ethanol adt (15 %). Comparing the percentages of TPM emissions, during the periods of 15 and 30 minutes of engine operation, it was observed a significant decrease of circa 60, 23, and 17 % for B100, B100 adt, and B5, respectively. Comparing the emission percentages between 30 and
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60 minutes, the reduction was 6 % and 2 % for B100 and B100 adt and 5 % for B5 (Table S1, Supplementary information). As expected, the TPM levels associated with ethanol were lower in comparison with biodiesel. This is attributed to the molecular structure of ethanol, the high degree presence of unsaturations, which relates to a high viscosity and better stability. Comparing B100 adt, B100, and B5 with Ethanol adt, it was observed that TPM emissions increased 32 % for B100 adt, 21 % for B100 and B5 for the period of 30 minutes of engine operation. Some authors found no differences in PM emissions for biodiesel relative to diesel (Qi et al., 2010), others reported a slight increase (Armas et al., 2010). These findings are associated with the higher viscosity of biodiesel, which causes a worse combustion quality (Aydin and Bayindir, 2010). The increase of PM can be attributed to the emission of unburned or partially burned hydrocarbons (HC). These HC are condensed and absorbed on the PM surface, which increases the soluble organic fraction (SOF), the main component of PM (Xue, J. and Hansen, 2011). Some studies report that particulate matter emissions were associated to the engine operating conditions (load and speed). Varying load and speed of an engine, Zhang et al. (2011) compared the PM2.5 emissions of diesel, soybean biodiesel, and biodiesel made from waste oil. The results showed that petroleum diesel emissions were higher at low speed and high load (1400 rpm, 100 %) as compared to biofuels. At high speed and low load (2300 rpm, 25 %), the diesel emissions were reduced (Zhang, et al., 2011). In this study, the emission profile showed similar behavior to the period of greatest stability of the engine, in other words, 60 minutes, where the emissions percentage for TPM of B5, B100 and B100 adt were 30 %, 32 % and 45 %, respectively. Thus, under low engine loads, biodiesel application increased PM emissions compared to petroleum diesel. Under high loads, biodiesel application decreased PM emissions. However, some authors found opposite results. Gauer et al. (2013) reported mass concentration of particulate material from the emission of diesel and soybean biodiesel under different engine
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load conditions. It was not observed significant differences in the emissions considering different loads (0.5 and 1.5 kW). Besides, diesel emitted more PM in comparison with soybean biofuel (Gauer et al., 2013). Several authors reported the reduction of PM by comparing the use of diesel and biodiesel, which is related to the oxygen level present in the biodiesel molecule (Haas, et al., 2001; Kado and Kuzmicky, 2003; Di, Cheung, and Huang, 2009). However, a few authors found no significant differences in particulate matter emissions between pure diesel (B0) to pure biodiesel (B100). In this case, the explanation may be due to the reduction of the insoluble fraction of the particulate matter, composed of soot, in consequence of an increase of the soluble organic fraction. The increase of the soluble organic fraction are ascribable to the generation of low volatility unburned HC., These compounds have the potential to condense and to adsorb onto surface particles (Lapuerta, et al., 2008). Since a significant difference between emissions in 30 and 60 minutes of engine operation were not detected, the period of 30 minutes was chosen to compare pollutants levels, using fuel with no storage. With regarding to storage, similar profiles were observed for B100 and B100 adt, presenting higher TPM emission for T1 (7 days storage), where the value of 100 % was attributed to the biofuel B100 T1 (Table S2, Supplementary information). Comparing T1 and T2, reductions of 36 %, 16 %, and 4 % were observed for B100, B100 adt, and B5, respectively (Figure 1b). These results suggest that the storage of biodiesel in the tank of vehicles or in distribution stations can suffer oxidation even under appropriate conditions, resulting in a reduction in particulate emissions. Monyem and Van Gerpen (2001) found significant reductions in smoke number of oxidized biodiesel, when compared with not oxidized one. Our results show thatB100 presented a greater reduction of TPM in comparison to B100 adt, which was expected since B100 does not contain the oxidant agent BHT.
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This is in agreement with the induction period (IP) results obtained via the PetroOXY method, which evaluated the oxidative stability of biofuels before and during storage. The IP of biofuels before storage were approximately 2 hours for B100 and 4 hours for the B100 adt. After 21 days of storage, these values decreased to approximately 1 hour for B100 and 3 hours to the B100 adt (Figure F2, Supplementary information). The data indicate that in the absence of antioxidants biodiesel quickly oxidize at typical temperatures of diesel engines. This oxidation increases the peroxide value, acid value, and viscosity. There is a great concern among producers, suppliers, and users of biodiesel due to its oxidative instability. The existence of unsaturated fatty acids in the biodiesel favors the development of oxidative rancidity and thus it decreases the quality of biodiesel during its storage (Ferrari and Souza, 2009). Atmospheric air, temperature variation, and light are some factors that have a direct influence on the oxidation of biofuels. Regarding B5, this fuel has many HC in the structure that could undergo oxidation during the storage, resulting in a better combustion. Studies have been executed to increase the oxidation resistance of biodiesel (Knothe and Dunn, 2003), which is pointed out as the main disadvantage of using this biofuel. In this context, the commercialization of biodiesel obtained from soybean oil is complicated due its low oxidative stability (Santos, 2008). With respect to particle emissions, among the four tested fuels (B100, B100 adt, B5, and Ethanol adt), Ethanol adt presented the lowest particle emission. This is may be due to its simple molecular structure and the lack of other components in the mixture, which allows it generate a cleaner and complete combustion (Vianna et al., 2008). TPM concentration was higher for B100 and B100 adt. This may be associated to other factors related to the combustion of biodiesel such as engine operational aspects, the synthesis route of biodiesel, and oilseed origin (Bakeas, et al., 2011). These particles were also analyzed by toxicological essay and the results showed that biodiesel is less toxic than diesel (Gioda et al., 2016).
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3.2 BTEX
The results of the analytical parameters limit of detection, limits of quantification, coefficient of determination (R2) and repeatability found for the method evaluation to determine the concentration of BTEX present in the emissions are shown in Table 1. Coefficient of determination (R2) value close to 1.0 indicates less dispersion of the set of data points (Jardim, et al., 2004). The results were satisfactory for R2 values ranging from 0.9993 to 0.9997 and for repeatability with deviations less than 1.0 μg mL-1. The recovery results were 62.1 % (p-xylene), 66.0 % (o-xylene), 75.6 % (toluene), 84.9 % (ethyl benzene), 94.1 % (m-xylene) and 98.9 % (benzene). Acceptable values for recovery are normally between 70 % and 120 % with an accuracy of ± 20 % (Jardim et al., 2004). Therefore, the obtained results are acceptable. Regarding the selectivity parameter, the method also presented acceptable results, and it is able to assess, in an unequivocal manner, the analytes of interest in the matrix. The selectivity obtained ensures that the peak of response was only from the analytes of interest, without compromising the linearity of the method. After the method evaluation, the BTEX concentrations were evaluated considering the time of engine operation (Figure 2a) and storage time of the fuel (Figure 2b). Regarding the time of engine operation (Figure 2a), the highest percentage (100 %) of benzene and ethylbenzene emissions were assigned to the biofuel B100 in the period of 30 minutes. The highest percentage for toluene and p-o-xylenes were assigned for B5, in the period 30 minutes, and the highest percentage of m-Xylene was also assigned for B5 but in the period of 15 minutes (Table S3, Supplementary information). During the cold engine start, benzene and ethylbenzene showed high percentage of emissions from ranging from 93 and 87 % for B100 and
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67 and 74 % for B100 adt considering that the highest percentage (100 %) of emissions of those compounds was the B100 / 30 minutes. This fact could be related with some HC from biodiesel that could condense in the engine due to the lower exhaust gas temperature, which tend to increase at low engine loads. The lower volatility of biodiesel compared with the diesel fuel might be the major factor for the large difference of HC emissions (Cheung, Zhu and Huang, 2009). The lowest percentage emissions for this group of pollutants were measured in B5 / 60 minutes, which may be associated with a better burning. The additivated ethanol presented emissions of 6 , 14, and 81 % for benzene, toluene, and o-xylene, respectively. This fact may be related to additives added to this biofuel. Regarding storage, the B5-T1, related to 7 days of storing, showed the highest percentage (100 %) of BTEX components, except for the ethylbenzene where 100 % was assigned to B100T1 (Table S4, Supplementary information). The BTEX emission profiles showed similar behavior at zero time of storage. Studies showed that in general, regardless of the biodiesel origin, BTEX emissions from the combustion of pure B100 or in binary mixtures, decrease compared to diesel (B0) (Di, Y Cheung and Huang, 2009). However, when pollutants are compared individually, the profile changes. BTEX emissions were individually compared using biodiesel originated from used cooking oil - B100, B20, B40, B80, and diesel with low sulfur - in an engine with 4 cylinders with rotation of 1800 rpm, varying the load. Results point out that benzene emissions for mixtures and B100 from kitchen oil were higher than low sulfur diesels in all the loads (Cheung, Zhu and Huang, 2009). Similar results regarding the concentration of benzene, which were higher in B100 and in B100 adt, were also observed in this study, which was not expected. Studies indicate that the main source of benzene in these fuels may not be from the emissions of biodiesel exhaust but from the presence of non- esterified oils in the synthesis of biodiesel
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(Krahl, et al., 2002). Another factor that influences the reduction of aromatic compounds emission is the increase of the oxygen content present in the biodiesel molecule, which increases the temperature in the combustion of both the pure fuel and mixtures. A tangible reduction in the concentration of BTEX emitted by the engine powered by diesel (B5) was observed compared to the emissions from the engine powered by B100 and B100 adt, except for benzene and ethyl benzene (Krahl, et al., 2002). Another factor that must be taken into account for the emission of this group of pollutant is the origin of oilseed and engine operating conditions. This fact may be observed by the study carried out by Gauer et al. (2012), which compared the emissions from an engine generator with direct injection, powered by fossil diesel. The fuels used were soybean B100 (BS 100), animal fat B100 (BG 100) and the binary mixtures, BG 5, BG 20, BG 50, and BS 50, varying the load from 0.5 kW to 1.5 kW. The results showed that there were decreasing in benzene emissions with the increase of the load added to the motor as observed by others (Di, Y Cheung and Huang, 2009; Cheung, Zhu and Huang, 2009). The explanation for this reduction with increased load may be related to the higher temperature that was reached with more loads in the combustion chamber. Another observation in this study was that, overall, animal fat B100 showed lower emissions for these pollutants compared to soybean B100, confirming that the origin of the oilseed may influence the emissions of these compounds. It is noteworthy that benzene emissions are higher for soybean B100 when compared to animal fat B100 and fossil diesel with both loads presented. These results are in agreement with the percentage profile of benzene emissions found in this study, where the percentages of benzene emissions for B100 and B100 adt are higher compared to those found in engine emission powered with B5. The storage periods contributed to the reduction of benzene and ethylbenzene percentages for B100 and B100 adt, while there were reductions for all BTEX compounds in B5. The percentage reduction was more significant between periods T1 and T2 (Figure 2b), where
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benzene and ethylbenzene achieved reductions of 65 % and 71 % for B100 and 57 % and 65 % for B100 adt, respectively. Regarding B5, the percentage reductions for these compounds were 63 % for benzene and 45 % for ethylbenzene. These differences in the percentage reduction can be attributed to the fact that the oxidative stability of pure soybean biodiesel is influenced by the presence of unsaturations, and thus becoming more susceptible to both thermal and oxidative degradation. This could explain a reduction in B100 greater than B100 adt, as it does not present the antioxidant BHT. The B5 presents 95 % of the fossil fuel, it is more stable; however, its structure presentes HC which can also undergo oxidation during the storage. These results are consistent with those found by Monyem and Van Gerpen (2001). The authors reported that biodiesel blends produced lower emissions of unburned HC compared with pure biodiesel. They found that the oxidized biodiesel reduces HC emissions significantly compared with non-oxidized biodiesel. ABesides, they showed that HC emissions were greater in the low load engine condition than in the full-load engine condition. In this study, the additivated ethanol showed the best results for BTEX emission, a fact confirmed in other works. Niven (2005) evaluated mixtures of ethanol and gasoline. The results showed that ethanol reduces air pollutants emissions such as volatile organic compounds |(VOC), emissions of greenhouse gases, but there is a tremendous increase in emissions of formaldehyde and acetaldehyde.. Another study done with six small vehicle engines fueled with gasoline or gasoline/ethanol mixture showed that E85 (gasoline with 85 % ethanol) presented a reduction of total hydrocarbon (THC) emissions compared to pure gasoline. About BTEX emissions, individually assessed, although values were very low, the emissions of formaldehyde and acetaldehyde were high.
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The results in this study are in agreement with those found in other works for emissions of benzene and toluene at low levels, xylenes at higher levels and undetectable ethylbenzene (Karavalakis, et al., 2012). In general, the increase of ethanol in gasoline presents a reduction of unburned hydrocarbons, but an increase in fuel consumption. Among the fuels used in this study, B5 showed higher emissions of BTEX, which contributes to a greater impact on health and the environment, since VOC are precursors for ozone formation and contributors to the formation of secondary pollutants.
4. Conclusion
The combustion of fossil fuels by vehicles releases a large quantity of pollutants into the atmosphere, including TPM and BTEX. In the present study, the biodiesel and additivated biodiesel emitted a higher concentration of particles than the commercial diesel. This may be attributed to engine operational aspects of, synthetic route of biodiesel, and oilseed origin. The storage time, monitored at 40 °C, reduced the emissions of all pollutants. This fact may be related to the oxidation that occurs during storage along with the high temperature, which improves the combustion. Evaluating the operation time, we conclude that the more the engine is heated, the less pollutant it will emit. This study evaluated a method for the identification and quantification of the BTEX present in biodiesel, diesel, and ethanol emissions. All parameters evaluated were within the recommended criteria. Regarding the BTEX compounds, benzene was present in all samples. In the biodiesel, this fact may be related to either the incomplete combustion of this fuel or the presence of fatty acids with a high unsaturation degree. However, the additivated Ethanol
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showed the best environmental performance with the lowest emission rate of particles. Ultimately, we conclude that the effect of biodiesel is specific for each of the different pollutant species. It depends on the type of engine, on the engine speed and load conditions, on the ambient conditions, on the origin and quality of biodiesel.
Acknowledgements
The authors are grateful to the FAPERJ, CNPq, and CAPES-PROCAD for financial support for the research. The authors also thank to the staff of the Department of Chemistry of the Federal University of Paraíba.
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Dos Reis Albuquerque, Anderson. (2009). Autoxidação de ésteres metílicos de ácidos graxos: estudo teórico-experimental. Journal of the American Oil Chemists Society 86(7) 699-706. Ferrari, R. A., & Souza, W. L. D. (2009). Evaluation of oxidation stability of sunflower oil biodiesel with antioxidants. Química Nova, 32(1), 106-111. Gioda, A., Rodríguez-Cotto, R. I., Amaral, B. S., Encarnación-Medina, J., Ortiz-Martínez, M. G., Jiménez-Vélez, B. D. (2016) Biodiesel from soybean promotes cell proliferation in vitro. Toxicology in Vitro 34, 283 – 288. Gomes, S., Gauer, M. A., Schirmer, W. N., De Souza, S. N. M. (2013). Análise da concentração mássica de materiais particulados provenientes da combustão de diesele biodiesel Analysis of the mass concentration of particulate matter from the combustion of diesel and biodiesel. Ambiência 9(2), 335-348. Guarieiro, L. L. N., Vasconcellos, P. C., & Solci, M. C. (2011). Poluentes Atmosféricos Provenientes da Queima de Combustíveis Fósseis e Biocombustíveis: Uma Breve Revisão. Revista Virtual de Química 3(5), 434-445. Haas, M. J., Scott, K. M., Alleman, T. L., & McCormick, R. L. (2001). Engine Performance of Biodiesel Fuel Prepared from Soybean Soap stock: A High Quality Renewable Fuel Produced from a Waste Feedstock||. Energy & Fuels, 15(5), 1207- 1212. Kado, N. Y., & Kuzmicky, P. A. (2003). Bioassay Analysis of Particulate Matter from a Diesel Bus Engine Using Various Biodiesel Feedstock Fuels: Final Report. National Renewable Energy Laboratory. Karavalakis, G., Bakeas, E., Fontaras, G., & Stournas, S. (2011). Effect of biodiesel origin on regulated and particle-bound PAH (polycyclic aromatic hydrocarbon) emissions from a Euro 4 passenger car. Energy, 36(8), 5328-5337.
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Karavalakis, G., Durbin, T. D., Shrivastava, M., Zheng, Z., Villela, M., & Jung, H. (2012). Impacts of ethanol fuel level on emissions of regulated and unregulated pollutants from a fleet of gasoline light-duty vehicles. Fuel (93), 549-558. Knothe, G., & Dunn, R. O. (2003). Dependence of oil stability index of fatty compounds on their structure, concentration, and presence of metals. Journal of the American Oil Chemists' Society 80 (10), 1021-1026. Krahl, J., Bünger, J., Schröder, O., Munack, A., & Knothe, G. (2002). Exhaust emissions and health effects of particulate matter from agricultural tractors operating on rapeseed oil methyl ester. Journal of the American Oil Chemists' Society 79(7), 717-724. Lapuerta, M., Armas, O., & Rodriguez-Fernandez, J. (2008). Effect of biodiesel fuels on diesel engine emissions. Progress in energy and combustion science 34(2), 198-223. Monyem, A., & Van Gerpen, J. H. (2001). The effect of biodiesel oxidation on engine performance and emissions. Biomass and Bioenergy, 20(4), 317-325. Niven, R. K. (2005). Ethanol in gasoline: environmental impacts and sustainability review article. Renewable and Sustainable Energy Reviews 9(6), 535-555. Qi, D. H., Chen, H., Geng, L. M., & Bian, Y. Z. (2010). Experimental studies on the combustion characteristics and performance of a direct injection engine fueled with biodiesel/diesel blends. Energy Conversion and Management, 51(12), 2985-2992. Quintella, C. M., Teixeira, L. S., Korn, M. G. A., Costa Neto, P. R., Torres, E. A., Castro, M. P., & Jesus, C. A. (2009). Cadeia do biodiesel da bancada à indústria: uma visão geral com prospecção de tarefas e oportunidades para P&D&I. Química Nova 32(3), 553 793-808. Ribani, M., Bottoli, C. B. G., Collins, C. H., Jardim, I. C. S. F., & Melo, L. F. C. (2004). Validação em métodos cromatográficos e eletroforéticos. Química Nova 27, 771-780.
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Santos N. A. (2008). Propriedades Termo-oxidativas e de Fluxo do Biodiesel de Babaçu (Orbignya phalerata). Dissertação de Mestrado, Universidade Federal da Paraíba, Centro de Ciências Exatas e da Natureza. Departamento de Química. Schlesinger, S., & Noronha, S. (2006). O Brasil está nu! o avanço da monocultura da soja, o grão que cresceu demais. FASE. Singh, S. P., & Singh, D. (2010). Biodiesel production through the use of different sources and characterization of oils and their esters as the substitute of diesel: a review. Renewable and Sustainable Energy Reviews, 14(1), 200-216. Teixeira, E. C., Feltes, S., & Santana, E. R. R. D. (2008). Estudo das emissões de fontes móveis na região metropolitana de Porto Alegre, Rio Grande do Sul. Química Nova 31(2), 244-248. Vianna, J. D. S., Duarte, L. M., & Wehrmann, M. (2008). Contribuição do etanol para mitigação das mudanças climáticas. Encontro Nacional da ANPPAS 4. Xue, J., Grift, T. E., & Hansen, A. C. (2011). Effect of biodiesel on engine performances and emissions. Renewable and sustainable energy reviews, 15(2), 1098-1116. Zhang, J., He, K., Shi, X., & Zhao, Y. (2011). Comparison of particle emissions from an engine operating on biodiesel and petroleum diesel. Fuel 90(6), 2089-2097.
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Figure Captions
Figure 1. Average percentage of TPM considering (Figure a) - Considering operation engine time: Pure soybean biodiesel (B100), additivated soybean biodiesel (B100 adt), diesel with 5 % of biodiesel (B5), and additivated ethanol (Ethanol adt). (Figure b) - Considering the storage at 40 °C in the periods T1 (7 days), T2 (14 days), and T3 (21 days): Pure soybean biodiesel (B100), additivated soybean biodiesel (B100 adt), diesel with 5 % of biodiesel (B5), and additivated ethanol (Ethanol adt).
Figure 2. Average percentages of BTEX considering (Figure a) considering operation engine time: Pure soybean biodiesel (B100), additivated soybean biodiesel (B100 adt), diesel with 5 % of biodiesel (B5), and additivated ethanol (Ethanol adt). (Figure b) - Considering the storage at 40 °C in the periods T1 (7 days), T2 (14 days), and T3 (21 days): Pure soybean biodiesel (B100), additivated soybean biodiesel (B100 adt), diesel with 5 % of biodiesel (B5), and additivated ethanol (Ethanol adt).
25
Figure 1
Note 1: Considering the value of 100 % for the biofuel B100 in the period of 15 minutes (figure a). Note 2: Considering the value of 100 % for the biofuel B100-T1 (7 days) (figure b).
26
Figure 2
Note 1 -Figure a: Considering the value of 100 % for the Benzene and Ethylbenzene (B100/30 min); Toluene (B5/30 min); p-Xylene and m-Xylene (B5/15 min); o- Xylene (B5/30 min) for motor operation, prior to storage of biofuels. Note 2- Figure b: Considering the value of 100 % for the Benzene; Toluene; p-Xylene; mXylene; o- Xylene (B5 – T1 (7 days) and Ethylbenzene (B100 – T1 (7 days).
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Table 1 Values obtained for limit of detection (LOD), limit of quantification (LOQ), coefficient of determination (R2), and repeatability with the deviation of measurements found during the method validation. Analytes
LOD
LOQ -1
R² -1
Repeatability
Deviation
(µg mL-1)
(µg mL-1)
(µg mL )
(µg mL )
Benzene
0.51
1.68
0.9993
31.41
0.70
Toluene
0.30
1.01
0.9997
30.93
0.66
Ethylbenzene
0.27
0.90
0.9997
30.55
0.61
p-Xylene
0.40
1.32
0.9997
30.52
0.60
m-Xylene
0.33
1.12
0.9997
30.46
0.60
o-Xylene
0.35
1.16
0.9997
30.52
0.60
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Highlights
- Comparison among biodiesel, diesel and ethanol emissions - Evaluation of the operating of the engine and oxidation processes of fuels - BTEX and TPM levels
PII: DOI: Reference:
S0021-8502(16)30243-9 http://dx.doi.org/10.1016/j.jaerosci.2016.07.009 AS5024
To appear in: Journal of Aerosol Science Received date: 16 March 2015 Revised date: 1 July 2016 Accepted date: 6 July 2016 Cite this article as: Beatriz Silva Amaral, Fábio Júnior Moreira Novaes, Maria da Conceição Klaus V.Ramos, Francisco Radler de Aquino Neto and Adriana Gioda, Comparative profile of pollutants generated by a stationary engine fueled with diesel, biodiesel, and ethanol, Journal of Aerosol Science, http://dx.doi.org/10.1016/j.jaerosci.2016.07.009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Comparative profile of pollutants generated by a stationary engine fueled with diesel, biodiesel, and ethanol
Beatriz Silva Amaral1,2, Fábio Júnior Moreira Novaes³, Maria da Conceição Klaus V.Ramos3, Francisco Radler de Aquino Neto3, Adriana Gioda1*
¹Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Departamento de Química, Rio de Janeiro, Brasil. ²Instituto Federal do Rio de Janeiro (IFRJ), Rio de Janeiro, Brasil ³Universidade Federal do Rio de Janeiro, Instituto de Química, LPCC – LADETEC. Rio de Janeiro, Brasil.
Corresponding author: Prof. Dr. Adriana Gioda ([email protected]) Department of Chemistry, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Marquês de São Vicente, 225, 22451-900, Gávea, Rio de Janeiro-RJ, Brasil. Phone: +55 21 3527-1328 Fax: +55 21 3114-1637
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Abstract Fossil fuel emissions derived from crude oil have a significant impact on the environment, climate change, air pollution, and others. Under these circumstances, there is a great interest in alternative energy resources, especially those that are able to reduce the emission of atmospheric pollutants. The aim of this study is to evaluate the burning emissions of the following binary mixture and biofuels: commercial diesel (diesel with 5 % of biodiesel, B5), pure soy biodiesel (B100), additivated biodiesel (B100 adt) stored at 40 °C for 1, 2, and 3 weeks, and additivated ethanol (Ethanol adt). The burning emissions were evaluated by the levels of benzene, toluene, ethylbenzene, and xylenes (BTEX) and total particulate matter (TPM). The quality of the biofuels was given by oxidative stability during storage. The combustion products were originated from a diesel cycle stationary engine, operating in 1800 rpm and 0 % load. For a greater reliability in the results, some figures of merit were evaluated for the determination BTEX by gas chromatography and flame ionization detection (GC-FID) and the particulate matter was determined by gravimetric analysis. Results show that operating time of the engine influences combustion efficiency. During the initial 15 minutes, cold engine start, there was increasing in BTEX and TPM emissions, when comparing B100 and B5. Regarding to the storage period of 1-2 weeks, B100, B100 adt, and B5 showed reduction of approximately 36, 16, and 4 % for TPM, respectively. Evaluating each component of BTEX, the benzene emissions were greater for biofuels, which is in agreement with previous studies. As observed for TPM, the storage time of 1-2 weeks was beneficial for the mitigation of aromatic emissions. A reduction about 60 % percent was measured for benzene and ethylbenzene. However, these emissions can also be influenced by the engine operating conditions (load and speed), engine type, and characteristics of biofuels. Additivated ethanol also presented low emissions for these pollutants as well as the lowest percentage of emissions of TPM. It is noteworthy that Ethanol adt present the lowest percentage of benzene emission.
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Keywords: vehicular emission; diesel; biodiesel; BTEX; particulate matter; oxidative process
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1. Introduction
The impacts caused by global warming and the search for alternative energy resources are a worldwide concern. Currently, great part of the energy consumed in the world is originated from non-renewable sources like natural gas, coal, and oil (Corrêa and Arbilla, 2008). Diesel, one of the derivatives of crude oil, is extensive used in internal combustion vehicle engines. It contains paraffinic hydrocarbons, aromatics, olefins, sulfurous, nitrogen and oxygenous compounds, and metals (Aleme and Barbeira, 2012). The use of this fuel on the automotive industry is increasing due to its high efficiency, durability, and flexibility (Guarieiro, et al., 2011; Santos, 2008). In spite of that, during the combustion process, there is an immense production of particles and gases (Gauer, et al., 2013). In the present scenario, biofuels gained great importance as alternative to the current global energy matrix, once it offers a clean energy model. Biodiesel use reduces the emission of some air pollutants and it help to close the carbon cycle due to its vegetal origin. Moreover, when added to diesel, it has a synergetic effect of biodegradation by cometabolism (Quintella, et al., 2009). Even though biodiesel is a renewable source of energy, which is highly advantageous, its effects on environment and on public health must also be considered. The use of this biofuel present some disadvantages such as high NOx emissions, high viscosity, problems related to low temperatures, and low oxidative stability. The latter is the major responsible for the biodiesel degradation during long storage (Singh and Singh, 2010). The chemical nature of biodiesel, a mixture of unsaturated fatty acid, facilitates the oxidation processes. These processes may be accelerated in the presence of metals, contact with air, and high temperatures (Dos Reis Albuquerque, 2009). In order to prevent or minimize the oxidation, antioxidants are added to biodiesel, they may be natural or synthetic (Karavalakis, et al., 2011). However, storage conditions are key factors to prevent the degradation of biodiesel.
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Given the importance of storage conditions, several authors conducted experiments in order to identify the principal factors to the quality of biodiesel. A study carried out in 2007 reports that the biodegradability of biodiesel was superior to diesel in 28 days (Demirbas, 2007). Leung et al. (2006) noted that the biodiesel at 20 ºC degraded less than 10 % in comparison with 40 % of degradation, when the fuel was stored at 40 ºC. Ethanol is another important renewable fuel source that is produced mainly by sugar cane. Currently, this hydrated fuel is used directly in the supply of automotive vehicles. It has physicochemical properties that differ from gasoline such as lower combustion heat, higher vaporization heat, single boiling point, and a different air/fuel stoichiometric ratio (Vianna et al., 2008). On the one hand, this biofuel is both non-toxic and biodegradable (Guarieiro, et al., 2011) but it emits oxidation products during its combustion, i.e., aldehydes, ketones, and carboxylic acids. These pollutants have an important role in the processes of photo-oxidation in the atmosphere; therefore, the impact caused by the use of ethanol has also been evaluated and discussed in several studies (Teixeira, et al., 2008). Brazil has been the pioneer in the use of renewable fuels. In the early 1970s, the use of ethanol was implemented, and since the year of 2008 biodiesel has been used as an additive in diesel engines. The addition of biodiesel to diesel began with 2 % (B2), in 2008, it increased to 5 % (B5), and it reached 6 % (B6) in July 2014. In November 2016, the proportion of biodiesel is going to reach 7 % (B7). In Brazil, soy biodiesel is the most used due to the large-scale production. Besides, oil with high calorific value is obtained from soy (Schlesinger and Noronha, 2006). The combustion of any fuel emits a range of pollutants to the atmosphere that may be harmful to the environment, including human health. Among these pollutants, particulates can be listed, whose composition include elemental carbon, sulfates, metal oxides, trace gases (e.g., NOx, SOx, CO, and CO2), polycyclic aromatic hydrocarbons (PAH), and benzene, ethylbenzene,
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toluene, and xylenes (BTEX). To establish new air quality guidelines, based on a renewable energetic matrix, the level of gases and particulates emitted from the combustion of vehicles, as well as their chemical composition, must be investigated. The knowledge of emission levels leads the implementation of mitigation measures. The objective of this study was to quantify BTEX and total particulate matter (TPM) generated by a stationary engine supplied with renewable and non-renewable fuels in order to compare their emission profiles. The engine, a diesel cycle mono cylinder of 10 HP, operating in 1800 rpm and 0 % load, was fueled with additivated ethanol adt (Ethanol adt), commercial diesel (B5), pure soybean biodiesel (B100), and soybean biodiesel additive (B100 adt). The engine was attached to a generator (Toyama T6000 CXE3) at 1800 rpm and 60 Hz set. To evaluate the biofuels resistance to oxidation, the PetroOXI technique was applied and the results are indicated by the induction period (IP) in hours.
2. Materials and methods
2.1 Sample systems
The sampling was planned in order to concentrate the pollutants emitted by the engine and prevent contamination of the outside air. An acrylic chamber (1 m³) with collectors (filters, cartridges, and sensors), positioned inside, was used. All samples were collected in triplicate under the same engine operating conditions: no load (0 %) and speed of 1800 rpm. To ensure the quality of measurements, the engine was rinsed for 10 minutes with the fuel to be tested and the generated emissions discarded. The measurements initiated with a cold start of the engine of 30 minutes, supplied with the fuel to be tested. Six hundred milliliters of each fuel, on average, were used for each test. Temperature and relative humidity were controlled throughout the collecting
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process using a digital Thermohygrometer (Temperature and Relative Humidity sensor, Cole Pamer Thermohygrometer, Model 37951-00, USA) (Figure F1, supplementary information). The emissions generated by the fuel combustion were collected during the operation of the stationary engine, diesel cycle mono cylinder of 10 HP, connected to a generator (Toyama, T6000 CXE3) at 1800 rpm and 60 Hz set. In order to evaluate background contamination, samples were taken from the chamber before sampling with fuels. Outdoor air samples were also collected in order to verify influence of the surroundings on the samples within the chamber.
2.2 Fuels and Biofuels
Four types of fuels were used in this study: Commercial diesel – fossil diesel 95 % and 5 % biodiesel (B5) samples were collected at fuel distribution stations in the João Pessoa city, Paraíba state, Brazil. Pure soybean biodiesel (B100) and additivated pure soybean (B100 adt) with butilhydroxyanisol (BHA) were provided by the biodiesel division of the
Strategic
Technologies Center of the Northeast (CETENE), in the Pernambuco state, Brazil. Additivated ethanol (Ethanol adt) was prepared in the Federal University of Paraíba from 91.06 % ethanol, the additives were nitrate of tetrahydro-furfuryl (NTHF) 7.92 % and castor oil 0.99 %. One liter amber bottles of B100, B100 adt, and B5 fuels were storage in an oven at 40 ºC to verify the oxidation process. The samples were stored for 7, 14, and 21 days, characterized as T1, T2, and T3, respectively. Fuels were also not aged, characterizing the instant as time zero of storage (T0). This study was conducted in the northeast of Brazil, where the temperature of 40 °C is usual, especially in summer. Other studies conducted at lower temperatures did not succeed to significantly oxidize biofuels. Before and during storage time of the biofuels, the PetroOXY
8
method measured the variation of oxidative stabilityPetroOXY. The Ethanol adt samples were not used in the oxidation experiments.
2.3 Sampling
The samplings were carried out in triplicate with three distinct times of 15, 30, and 60 minutes. These different sampling times were used to evaluate the development emissions during the operating time of the engine. BTEX were collected based on the EPA TO-1 method (1988), using activated charcoal tubes (Anasorb CSC, catalog 22601 2000, SKC. Eighty-four, PA) containing two beds (Bed A: 100 mg and Bed B: 50 mg) at a flow of approximately 1.0 L min -1. The TPM was collected in parallel with BTEX. Polycarbonate filters with porosity of 0.4 µm and diameter equal to 37 mm (Millipore HTTP 03700) were coupled to the vacuum pump at a flow rate of 10.0 L min-1. .
2.4 Analysis 2.4.1 Total particulate matter
For the determination of the mass of TPM, filters were previously conditioned in a desiccator with a solution of 80 % glycerol (v/v) for at least 24 hours. They were weighed before and after sampling on a precise balance (Mettler Toledo - Model XP 205, maximum capacity 220 g and readability 0.01 mg) at constant weight, until they presented standard deviation equal to or less than 0.00002 g.
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2.4.2 Determination of BTEX by GC-FID
For greater reliability in the results, the method for determination of BTEX considered some figures of merit commonly used in validation of chromatographic methods such as analytical curves, limits of detection (LOD), limits of quantification (LOQ), linearity, selectivity, recovery, and repeatability (Causon, 1997; Ribani, et al., 2004). The standard solutions were prepared from the standard mixture (mix) of BTEX with concentration of 2000 µg mL-1 per analyte (Sigma – Aldrich, São Paulo, Brazil). Initially, a work solution of 1000 µg mL-1 was prepared. After that, the analytical curve with concentrations of 1.0 µg mL-1, 10.0 µg mL-1, 20.0 µg mL-1, 30.0 µg mL-1, 50.0 µg mL-1 e 100.0 µg mL-1 was prepared in dichloromethane (Tedia, Brazil) with 99.9 % of purity. The LOD determination considered 3 sb/S, and LOQ considered 10 sb/S, where sb is the standard deviation between the linear coefficients and S is the sensitivity determined by the average slope of the analytical curve. For the desorption of analytes, firstly, the glass cartridge containing the adsorbent material was transferred to a 2.0 mL glass vials, properly identified with specifications of bed A and B. To avoid losses, the glass vials were immediately closed and placed in an ice bath and 1.5 mL of dichloromethane (99.9 %) was slowly added. Secondly, bottle caps were exchanged, the vials were homogenized for about 1 minute in a vortex and conditioned at 0 °C for 24 hours, a period that ensures the extraction of analytes. Finally, the samples were analyzed by GC-FID. Each sample was analyzed in triplicate. In this study, BTEX were determined with the use of a gas chromatograph (Agilent Technologies, Hewlett-Packard 7890, Series II, Palo Alto, CA, USA), equipped with automatic sampler and flame ionization detector. An innowax column of 25 m, diameter of 0.2 mm and 0.4 µm film thickness (Agilent Technologies) was used. The defined conditions of BTEX analysis were: automatic injector at 250 °C, initial oven temperature at 40 °C, ramp of 40 °C per minute
10
until 53 °C, 40 °C per minute until 200 °C, detector at 260 °C, carrier gas was hydrogen, injection split 1:20 and injection volume 1.0 µL.
3. Results and Discussion
3.1 Total Particulate Matter
The pollutant profiles, in percentage, were evaluated considering: 1) engine operating time for B100, B100 adt, and B5 that was not stored (T0) in periods of 15, 30, and 60 minutes; 2) considering the storage at 40 °C in the periods T1, T2, and T3 for the same fuels sampled during 30 minutes. Both biodiesel pollutant profiles were compared with the emissions originating from the engine fueled with Ethanol adt sampled during 30 minutes. The levels of TPM varied with the operating time of the engine. In the initial 15 minutes, the highest TPM concentrations for all the fuels were registered, with the exception of additivated Ethanol. The high particle emission in the initial instants may be related to the fact that the engine was still cold, as it was not acting under ideal working conditions, leading to an incomplete combustion of the fuels. Considering the motor operation time, the percentage profiles of particulate matter are presented in Figure 1a, where the value of 100 % was attributed to B100. B100 presents the highest concentration in the period of 15 minutes, while the lowest percentage was measured for Ethanol adt (15 %). Comparing the percentages of TPM emissions, during the periods of 15 and 30 minutes of engine operation, it was observed a significant decrease of circa 60, 23, and 17 % for B100, B100 adt, and B5, respectively. Comparing the emission percentages between 30 and
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60 minutes, the reduction was 6 % and 2 % for B100 and B100 adt and 5 % for B5 (Table S1, Supplementary information). As expected, the TPM levels associated with ethanol were lower in comparison with biodiesel. This is attributed to the molecular structure of ethanol, the high degree presence of unsaturations, which relates to a high viscosity and better stability. Comparing B100 adt, B100, and B5 with Ethanol adt, it was observed that TPM emissions increased 32 % for B100 adt, 21 % for B100 and B5 for the period of 30 minutes of engine operation. Some authors found no differences in PM emissions for biodiesel relative to diesel (Qi et al., 2010), others reported a slight increase (Armas et al., 2010). These findings are associated with the higher viscosity of biodiesel, which causes a worse combustion quality (Aydin and Bayindir, 2010). The increase of PM can be attributed to the emission of unburned or partially burned hydrocarbons (HC). These HC are condensed and absorbed on the PM surface, which increases the soluble organic fraction (SOF), the main component of PM (Xue, J. and Hansen, 2011). Some studies report that particulate matter emissions were associated to the engine operating conditions (load and speed). Varying load and speed of an engine, Zhang et al. (2011) compared the PM2.5 emissions of diesel, soybean biodiesel, and biodiesel made from waste oil. The results showed that petroleum diesel emissions were higher at low speed and high load (1400 rpm, 100 %) as compared to biofuels. At high speed and low load (2300 rpm, 25 %), the diesel emissions were reduced (Zhang, et al., 2011). In this study, the emission profile showed similar behavior to the period of greatest stability of the engine, in other words, 60 minutes, where the emissions percentage for TPM of B5, B100 and B100 adt were 30 %, 32 % and 45 %, respectively. Thus, under low engine loads, biodiesel application increased PM emissions compared to petroleum diesel. Under high loads, biodiesel application decreased PM emissions. However, some authors found opposite results. Gauer et al. (2013) reported mass concentration of particulate material from the emission of diesel and soybean biodiesel under different engine
12
load conditions. It was not observed significant differences in the emissions considering different loads (0.5 and 1.5 kW). Besides, diesel emitted more PM in comparison with soybean biofuel (Gauer et al., 2013). Several authors reported the reduction of PM by comparing the use of diesel and biodiesel, which is related to the oxygen level present in the biodiesel molecule (Haas, et al., 2001; Kado and Kuzmicky, 2003; Di, Cheung, and Huang, 2009). However, a few authors found no significant differences in particulate matter emissions between pure diesel (B0) to pure biodiesel (B100). In this case, the explanation may be due to the reduction of the insoluble fraction of the particulate matter, composed of soot, in consequence of an increase of the soluble organic fraction. The increase of the soluble organic fraction are ascribable to the generation of low volatility unburned HC., These compounds have the potential to condense and to adsorb onto surface particles (Lapuerta, et al., 2008). Since a significant difference between emissions in 30 and 60 minutes of engine operation were not detected, the period of 30 minutes was chosen to compare pollutants levels, using fuel with no storage. With regarding to storage, similar profiles were observed for B100 and B100 adt, presenting higher TPM emission for T1 (7 days storage), where the value of 100 % was attributed to the biofuel B100 T1 (Table S2, Supplementary information). Comparing T1 and T2, reductions of 36 %, 16 %, and 4 % were observed for B100, B100 adt, and B5, respectively (Figure 1b). These results suggest that the storage of biodiesel in the tank of vehicles or in distribution stations can suffer oxidation even under appropriate conditions, resulting in a reduction in particulate emissions. Monyem and Van Gerpen (2001) found significant reductions in smoke number of oxidized biodiesel, when compared with not oxidized one. Our results show thatB100 presented a greater reduction of TPM in comparison to B100 adt, which was expected since B100 does not contain the oxidant agent BHT.
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This is in agreement with the induction period (IP) results obtained via the PetroOXY method, which evaluated the oxidative stability of biofuels before and during storage. The IP of biofuels before storage were approximately 2 hours for B100 and 4 hours for the B100 adt. After 21 days of storage, these values decreased to approximately 1 hour for B100 and 3 hours to the B100 adt (Figure F2, Supplementary information). The data indicate that in the absence of antioxidants biodiesel quickly oxidize at typical temperatures of diesel engines. This oxidation increases the peroxide value, acid value, and viscosity. There is a great concern among producers, suppliers, and users of biodiesel due to its oxidative instability. The existence of unsaturated fatty acids in the biodiesel favors the development of oxidative rancidity and thus it decreases the quality of biodiesel during its storage (Ferrari and Souza, 2009). Atmospheric air, temperature variation, and light are some factors that have a direct influence on the oxidation of biofuels. Regarding B5, this fuel has many HC in the structure that could undergo oxidation during the storage, resulting in a better combustion. Studies have been executed to increase the oxidation resistance of biodiesel (Knothe and Dunn, 2003), which is pointed out as the main disadvantage of using this biofuel. In this context, the commercialization of biodiesel obtained from soybean oil is complicated due its low oxidative stability (Santos, 2008). With respect to particle emissions, among the four tested fuels (B100, B100 adt, B5, and Ethanol adt), Ethanol adt presented the lowest particle emission. This is may be due to its simple molecular structure and the lack of other components in the mixture, which allows it generate a cleaner and complete combustion (Vianna et al., 2008). TPM concentration was higher for B100 and B100 adt. This may be associated to other factors related to the combustion of biodiesel such as engine operational aspects, the synthesis route of biodiesel, and oilseed origin (Bakeas, et al., 2011). These particles were also analyzed by toxicological essay and the results showed that biodiesel is less toxic than diesel (Gioda et al., 2016).
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3.2 BTEX
The results of the analytical parameters limit of detection, limits of quantification, coefficient of determination (R2) and repeatability found for the method evaluation to determine the concentration of BTEX present in the emissions are shown in Table 1. Coefficient of determination (R2) value close to 1.0 indicates less dispersion of the set of data points (Jardim, et al., 2004). The results were satisfactory for R2 values ranging from 0.9993 to 0.9997 and for repeatability with deviations less than 1.0 μg mL-1. The recovery results were 62.1 % (p-xylene), 66.0 % (o-xylene), 75.6 % (toluene), 84.9 % (ethyl benzene), 94.1 % (m-xylene) and 98.9 % (benzene). Acceptable values for recovery are normally between 70 % and 120 % with an accuracy of ± 20 % (Jardim et al., 2004). Therefore, the obtained results are acceptable. Regarding the selectivity parameter, the method also presented acceptable results, and it is able to assess, in an unequivocal manner, the analytes of interest in the matrix. The selectivity obtained ensures that the peak of response was only from the analytes of interest, without compromising the linearity of the method. After the method evaluation, the BTEX concentrations were evaluated considering the time of engine operation (Figure 2a) and storage time of the fuel (Figure 2b). Regarding the time of engine operation (Figure 2a), the highest percentage (100 %) of benzene and ethylbenzene emissions were assigned to the biofuel B100 in the period of 30 minutes. The highest percentage for toluene and p-o-xylenes were assigned for B5, in the period 30 minutes, and the highest percentage of m-Xylene was also assigned for B5 but in the period of 15 minutes (Table S3, Supplementary information). During the cold engine start, benzene and ethylbenzene showed high percentage of emissions from ranging from 93 and 87 % for B100 and
15
67 and 74 % for B100 adt considering that the highest percentage (100 %) of emissions of those compounds was the B100 / 30 minutes. This fact could be related with some HC from biodiesel that could condense in the engine due to the lower exhaust gas temperature, which tend to increase at low engine loads. The lower volatility of biodiesel compared with the diesel fuel might be the major factor for the large difference of HC emissions (Cheung, Zhu and Huang, 2009). The lowest percentage emissions for this group of pollutants were measured in B5 / 60 minutes, which may be associated with a better burning. The additivated ethanol presented emissions of 6 , 14, and 81 % for benzene, toluene, and o-xylene, respectively. This fact may be related to additives added to this biofuel. Regarding storage, the B5-T1, related to 7 days of storing, showed the highest percentage (100 %) of BTEX components, except for the ethylbenzene where 100 % was assigned to B100T1 (Table S4, Supplementary information). The BTEX emission profiles showed similar behavior at zero time of storage. Studies showed that in general, regardless of the biodiesel origin, BTEX emissions from the combustion of pure B100 or in binary mixtures, decrease compared to diesel (B0) (Di, Y Cheung and Huang, 2009). However, when pollutants are compared individually, the profile changes. BTEX emissions were individually compared using biodiesel originated from used cooking oil - B100, B20, B40, B80, and diesel with low sulfur - in an engine with 4 cylinders with rotation of 1800 rpm, varying the load. Results point out that benzene emissions for mixtures and B100 from kitchen oil were higher than low sulfur diesels in all the loads (Cheung, Zhu and Huang, 2009). Similar results regarding the concentration of benzene, which were higher in B100 and in B100 adt, were also observed in this study, which was not expected. Studies indicate that the main source of benzene in these fuels may not be from the emissions of biodiesel exhaust but from the presence of non- esterified oils in the synthesis of biodiesel
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(Krahl, et al., 2002). Another factor that influences the reduction of aromatic compounds emission is the increase of the oxygen content present in the biodiesel molecule, which increases the temperature in the combustion of both the pure fuel and mixtures. A tangible reduction in the concentration of BTEX emitted by the engine powered by diesel (B5) was observed compared to the emissions from the engine powered by B100 and B100 adt, except for benzene and ethyl benzene (Krahl, et al., 2002). Another factor that must be taken into account for the emission of this group of pollutant is the origin of oilseed and engine operating conditions. This fact may be observed by the study carried out by Gauer et al. (2012), which compared the emissions from an engine generator with direct injection, powered by fossil diesel. The fuels used were soybean B100 (BS 100), animal fat B100 (BG 100) and the binary mixtures, BG 5, BG 20, BG 50, and BS 50, varying the load from 0.5 kW to 1.5 kW. The results showed that there were decreasing in benzene emissions with the increase of the load added to the motor as observed by others (Di, Y Cheung and Huang, 2009; Cheung, Zhu and Huang, 2009). The explanation for this reduction with increased load may be related to the higher temperature that was reached with more loads in the combustion chamber. Another observation in this study was that, overall, animal fat B100 showed lower emissions for these pollutants compared to soybean B100, confirming that the origin of the oilseed may influence the emissions of these compounds. It is noteworthy that benzene emissions are higher for soybean B100 when compared to animal fat B100 and fossil diesel with both loads presented. These results are in agreement with the percentage profile of benzene emissions found in this study, where the percentages of benzene emissions for B100 and B100 adt are higher compared to those found in engine emission powered with B5. The storage periods contributed to the reduction of benzene and ethylbenzene percentages for B100 and B100 adt, while there were reductions for all BTEX compounds in B5. The percentage reduction was more significant between periods T1 and T2 (Figure 2b), where
17
benzene and ethylbenzene achieved reductions of 65 % and 71 % for B100 and 57 % and 65 % for B100 adt, respectively. Regarding B5, the percentage reductions for these compounds were 63 % for benzene and 45 % for ethylbenzene. These differences in the percentage reduction can be attributed to the fact that the oxidative stability of pure soybean biodiesel is influenced by the presence of unsaturations, and thus becoming more susceptible to both thermal and oxidative degradation. This could explain a reduction in B100 greater than B100 adt, as it does not present the antioxidant BHT. The B5 presents 95 % of the fossil fuel, it is more stable; however, its structure presentes HC which can also undergo oxidation during the storage. These results are consistent with those found by Monyem and Van Gerpen (2001). The authors reported that biodiesel blends produced lower emissions of unburned HC compared with pure biodiesel. They found that the oxidized biodiesel reduces HC emissions significantly compared with non-oxidized biodiesel. ABesides, they showed that HC emissions were greater in the low load engine condition than in the full-load engine condition. In this study, the additivated ethanol showed the best results for BTEX emission, a fact confirmed in other works. Niven (2005) evaluated mixtures of ethanol and gasoline. The results showed that ethanol reduces air pollutants emissions such as volatile organic compounds |(VOC), emissions of greenhouse gases, but there is a tremendous increase in emissions of formaldehyde and acetaldehyde.. Another study done with six small vehicle engines fueled with gasoline or gasoline/ethanol mixture showed that E85 (gasoline with 85 % ethanol) presented a reduction of total hydrocarbon (THC) emissions compared to pure gasoline. About BTEX emissions, individually assessed, although values were very low, the emissions of formaldehyde and acetaldehyde were high.
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The results in this study are in agreement with those found in other works for emissions of benzene and toluene at low levels, xylenes at higher levels and undetectable ethylbenzene (Karavalakis, et al., 2012). In general, the increase of ethanol in gasoline presents a reduction of unburned hydrocarbons, but an increase in fuel consumption. Among the fuels used in this study, B5 showed higher emissions of BTEX, which contributes to a greater impact on health and the environment, since VOC are precursors for ozone formation and contributors to the formation of secondary pollutants.
4. Conclusion
The combustion of fossil fuels by vehicles releases a large quantity of pollutants into the atmosphere, including TPM and BTEX. In the present study, the biodiesel and additivated biodiesel emitted a higher concentration of particles than the commercial diesel. This may be attributed to engine operational aspects of, synthetic route of biodiesel, and oilseed origin. The storage time, monitored at 40 °C, reduced the emissions of all pollutants. This fact may be related to the oxidation that occurs during storage along with the high temperature, which improves the combustion. Evaluating the operation time, we conclude that the more the engine is heated, the less pollutant it will emit. This study evaluated a method for the identification and quantification of the BTEX present in biodiesel, diesel, and ethanol emissions. All parameters evaluated were within the recommended criteria. Regarding the BTEX compounds, benzene was present in all samples. In the biodiesel, this fact may be related to either the incomplete combustion of this fuel or the presence of fatty acids with a high unsaturation degree. However, the additivated Ethanol
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showed the best environmental performance with the lowest emission rate of particles. Ultimately, we conclude that the effect of biodiesel is specific for each of the different pollutant species. It depends on the type of engine, on the engine speed and load conditions, on the ambient conditions, on the origin and quality of biodiesel.
Acknowledgements
The authors are grateful to the FAPERJ, CNPq, and CAPES-PROCAD for financial support for the research. The authors also thank to the staff of the Department of Chemistry of the Federal University of Paraíba.
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Figure Captions
Figure 1. Average percentage of TPM considering (Figure a) - Considering operation engine time: Pure soybean biodiesel (B100), additivated soybean biodiesel (B100 adt), diesel with 5 % of biodiesel (B5), and additivated ethanol (Ethanol adt). (Figure b) - Considering the storage at 40 °C in the periods T1 (7 days), T2 (14 days), and T3 (21 days): Pure soybean biodiesel (B100), additivated soybean biodiesel (B100 adt), diesel with 5 % of biodiesel (B5), and additivated ethanol (Ethanol adt).
Figure 2. Average percentages of BTEX considering (Figure a) considering operation engine time: Pure soybean biodiesel (B100), additivated soybean biodiesel (B100 adt), diesel with 5 % of biodiesel (B5), and additivated ethanol (Ethanol adt). (Figure b) - Considering the storage at 40 °C in the periods T1 (7 days), T2 (14 days), and T3 (21 days): Pure soybean biodiesel (B100), additivated soybean biodiesel (B100 adt), diesel with 5 % of biodiesel (B5), and additivated ethanol (Ethanol adt).
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Figure 1
Note 1: Considering the value of 100 % for the biofuel B100 in the period of 15 minutes (figure a). Note 2: Considering the value of 100 % for the biofuel B100-T1 (7 days) (figure b).
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Figure 2
Note 1 -Figure a: Considering the value of 100 % for the Benzene and Ethylbenzene (B100/30 min); Toluene (B5/30 min); p-Xylene and m-Xylene (B5/15 min); o- Xylene (B5/30 min) for motor operation, prior to storage of biofuels. Note 2- Figure b: Considering the value of 100 % for the Benzene; Toluene; p-Xylene; mXylene; o- Xylene (B5 – T1 (7 days) and Ethylbenzene (B100 – T1 (7 days).
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Table 1 Values obtained for limit of detection (LOD), limit of quantification (LOQ), coefficient of determination (R2), and repeatability with the deviation of measurements found during the method validation. Analytes
LOD
LOQ -1
R² -1
Repeatability
Deviation
(µg mL-1)
(µg mL-1)
(µg mL )
(µg mL )
Benzene
0.51
1.68
0.9993
31.41
0.70
Toluene
0.30
1.01
0.9997
30.93
0.66
Ethylbenzene
0.27
0.90
0.9997
30.55
0.61
p-Xylene
0.40
1.32
0.9997
30.52
0.60
m-Xylene
0.33
1.12
0.9997
30.46
0.60
o-Xylene
0.35
1.16
0.9997
30.52
0.60
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Highlights
- Comparison among biodiesel, diesel and ethanol emissions - Evaluation of the operating of the engine and oxidation processes of fuels - BTEX and TPM levels