Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-1986-2
RESEARCH ARTICLE
Studies on the effects of storage stability of bio-oil obtained from pyrolysis of Calophyllum inophyllum deoiled seed cake on the performance and emission characteristics of a direct-injection diesel engine Sakthivel Rajamohan 1,2
&
Ramesh Kasimani 3
Received: 9 January 2018 / Accepted: 9 April 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract The highly unbalanced nature of bio-oil composition poses a serious threat in terms of storage and utilization of bio-oil as a viable fuel in engines. So it becomes inevitable to study the variations in physicochemical properties of the bio-oil during storage to value its chemical instability, for designing stabilization methodologies. The present study aims to investigate the effects of storage stability of bio-oil extracted from pyrolyzing Calophyllum inophyllum (CI) deoiled seed cake on the engine operating characteristics. The bio-oil is produced in a fixed bed reactor at 500 °C under the constant heating rate of 30 °C/min. All the stability analysis methods involve an accelerated aging procedure based on standards established by ASTM (D5304 and E2009) and European standard (EN 14112). Gas chromatography-mass spectrometry was employed to analytically characterize the unaged and aged bio-oil samples. The results clearly depict that stabilizing Calophyllum inophyllum bio-oil with 10% (w/w) methanol improved its stability than that of the unstabilized sample thereby reducing the aging rate of bio-oil to 0.04 and 0.13 cst/ h for thermal and oxidative aging respectively. Engine testing of the bio-oil sample revealed that aged bio-oil samples deteriorated engine performance and increased emission levels at the exhaust. The oxidatively aged sample showed the lowest BTE (24.41%), the highest BSEC (20.14 MJ/kWh), CO (1.51%), HC (132 ppm), NOx (1098 ppm) and smoke opacity (34.8%). Keywords Calophyllum inophyllum . Stability . Methanol . Emission . Performance
Nomenclature CI Calophyllum inophyllum ASTM American Society for Testing Materials GC-MS Gas chromatography coupled with mass spectrometry PTFE Polytetrafluoroethylene
PID OSI BTE BSEC
Proportional-integral-derivative Oil stability index Brake thermal efficiency Brake specific energy consumption
Introduction Responsible editor: Philippe Garrigues * Sakthivel Rajamohan
[email protected] Ramesh Kasimani
[email protected] 1
Department of Mechanical Engineering, Research Scholar, Government College of Technology, Coimbatore 641013, India
2
Thanjavur, India
3
Department of Mechanical Engineering, Faculty of Engineering, Government College of Technology, Coimbatore 641013, India
In the present situation, fossil fuels play a vital role in satisfying the energy needs of the transportation sector which is one of the major backbones of a country’s economic growth. However, the worldwide attentiveness towards climatic changes owing to environmental pollution and exhaustion of fossil reserves has provided a rising attention towards biofuels. In past decades, a number of research works have been carried out in biodiesels obtained from vegetable oils which directly constitute the first and second generations of the biofuel era. Owing to the Bfood vs fuel^ challenge faced by the biodiesel utilization, the researchers are in a situation to
Environ Sci Pollut Res
find a suitable third-generation biofuel that does not compete with food. In these circumstances, biomass appears to be a potential source which has benefits of being available in large reserves, environmentally friendly and carbon neutral (Xiu and Shahbazi 2012; Bilgili 2012). Pyrolysis is a thermochemical conversion procedure under the absence of oxygen at elevated temperatures which produces liquid (bio-oil), gaseous (fuel gas) and solid products (biochar) (Iribarren et al. 2012). The yield of various pyrolysis products is affected by operating conditions such as temperature, heating rate, particle size, etc. Among the parameters, pyrolysis temperature influences the product properties to a wide extent (Chen et al. 2016a; Chen et al. 2016b). In recent decades, bio-oil attracts the researchers in satisfying energy needs of assorted sectors since bio-oil possesses high energy density and low sulphur content. In this view, bio-oil is utilized as a straight fuel for boilers and furnaces without any processing, whereas it also finds its application in engines after proper upgradation (Hossain and Davies 2013; Czernik and Bridgewater 2004; Butler et al. 2011; Mortensen et al. 2011). Also, from the long-term perspectives, bio-oil obtained from biomass has a wider market prospect as fuel for the transportation sector (Isahak et al. 2012). Although bio-oil provides numerous merits, several obstacles must be crossed before it can be employed efficiently and reliably as a transportation fuel in the commercial sector. Some of the negative aspects of bio-oil are its augmented moisture content, acidic nature, elevated viscosity, high oxygen content, low calorific value and most of all deprived storage stability (Jacobson et al. 2013). Thermal and oxidative degradation of bio-oil during storage limits its utilization in the transportation sector and other commercial applications. Thermal degradation causes biased decomposition of components and diminishes volatile organic contents which can lead to amplification in viscosity of bio-oil. On the other hand, oxidation catalyzes a polymerization reaction resulting in the gumming of storage containers due to augmented viscosity (Diebold and Czernik 1997; Oasmaa et al. 1997). In addition to that, during long-term storage, the aging not only downgrades the quality but also influences the refining process of bio-oil and its chemical components (Oasmaa and Kuoppala 2003; Oasmaa et al. 2003a,b; Oasmaa et al. 2004). On the whole, these thermo chemical degradations elevate the viscosity as well as change the composition of bio-oil which is unfavourable for most of the commercial applications. Therefore, the storage stability of the bio-oil needs to be enhanced before utilizing it for commercial purposes. The term storage stability refers to the capability of bio-oil to preserve its unique physical and chemical properties while storing at diversified environmental conditions. Unlike fossil fuels, storing bio-oil is complicated due to its deprived stability. In general, the storage stability of bio-oil comprises two major stability criteria, namely thermal stability and oxidative
stability. Some of the generally used stability assessment parameters are kinematic viscosity, insoluble solid content and water content. Also, analytical techniques like FT-IR and GCMS can be used to evaluate the storage stability of bio-oil (Lievens et al. 2013; Ba et al. 2004). A wide range of literatures suggests some techniques to enhance bio-oil stability like adding solvent, emulsification, biomass drying, ash and char removing, catalytic cracking, adding an antioxidant and catalytic hydrogenation (Chen et al. 2014). Chen et al. (2015) analysed the effects of torrefaction temperature on the properties of the fuel obtained from cotton stalks and observed that torrefaction temperature enhanced the heating value of pyrolytic gas and bio-oil accompanied with a reduction of acids in bio-oil. Yuxin et al. (2011) showed that Pt supported mesoporous ZSM-5 as a better catalyst than Pt/ZSM-5 and Pt/Al2O3 in dibenzofuran hydrodeoxygenation process. Wanjin et al. (2011) suggested 5% Pd/Al2(SiO3)3 as the best catalyst to convert unstable constituents of bio-oil to esters and alcohols through hydrogenation-esterification reaction. Gu et al. (2013) demonstrated that acid pretreatment of biomass promotes lower molecular products, furfural compounds and phenolic formation. Chiaramonti et al. (2003) emulsified bio-oil with diesel at different ratios with the aid of different surfactants. The results clearly showed that the stability of emulsified oil improved with the concentration of surfactants. The optimal concentration of the surfactants prescribed by the authors was 0.5–2%. Das et al. (2004) observed no improvements in the stability of bio-oil after deashing the bagasse due to a significant increase of polar components of the bio-oil. Chen et al. (2011) characterized bio-oil from rice husk after hot vapor filtration and observed that filtered bio-oil had high water content, lower yield and low acidity and alkali content. Lu et al. (2008) found that viscosity dropped to 21.7, 16.3 and 11.9% for the bio-oil ages at 50 °C for 120 h after the addition of 5, 10 and 15 wt% of methanol. Zhang et al. (2006) used a solid acid catalyst for esterification of bio-oil and observed the augmentation of ester concentration in bio-oil which in turn improved the stability of bio-oil. Whenever bio-oil is exposed to an oxygen atmosphere, active components of bio-oil react with oxygen and form peroxides which in turn catalyze the polymerization reaction of olefins. In order to inhibit the free radical formation, suitable oxidation inhibitors can be added to bio-oil (Hong and Shurong 2009).Chen et al. (2017) employed a novel approach of combining aqueous phase bio-oil washing combined with torrefaction pretreatment to enhance the quality of pyrolysis products. The results showed that aqueous phase washing decreased the water and acid content of bio-oil along with augmenting the heating value of pyrolytic gas as compared to that of torrefaction pretreatment. Meanwhile, Chen et al. (2016c) observed a sharp decrease in the acid and aldehyde content of bio-oil obtained from torrified pinewood using HZSM-5 catalyst. Hilten and Das 2010 found that both
Environ Sci Pollut Res
initial oxidation onset temperature and stability of pine bio-oil were higher than that of peanut shell bio-oil. The authors also observed that addition of organic solvents not only promoted oxidative stability but also reduced particulate matter formation. Xiong et al. 2009a utilized ionic liquid catalyst to catalyze the esterification of bio-oil which results in greater reduction of water and acid contents in bio-oil. Also reduction in lignin content, as well as viscosity, was also observed by the authors. Xiong et al. 2009b found significant changes in the concentration of various components at GC-MS spectra of bio-oil after the aging reaction. The authors also observed that pH of bio-oil was not affected due to aging and it remains unchanged in the range of 2.9–3.0. Among the methods mentioned in previous literature studies, adding mutually soluble organic solvents to bio-oil is most efficient and simplest method of improving bio-oil stability. This research work is novel in terms of analysing the effects of bio-oil aging in the performance and emission aspects of diesel engine. Even though a number of works have been reported for stability improvements of bio-oil obtained from various feedstocks, no works discussed the storage stability of bio-oil extracted from CI deoiled cake and its effects on engine operating characteristics. The main aim of this study is to analyse the storage stability of bio-oil obtained from CI deoiled seek cake and improving it by methanol stabilization. The changes in chemical composition of raw bio-oil were studied by GCMS. With a meagre amount of work done in revealing the potential of bio-oil as an engine fuel, the present research focuses on analysing the effects of aging on the performance and emission attributes of a direct injection diesel engine.
Materials and methods Materials The raw material used in this current study is a CI deoiled cake. A CI deoiled cake is the by-product obtained from the cold pressing of CI seed kernels in a mechanical screw press. The seed cakes are procured from a local vendor named Tamil Traders Pvt. Ltd., Coimbatore, Tamil Nadu, India, at a cost of Rs.10/kg. The obtained cakes were crushed in a grinder and sieved to obtain an average particle size of 1.4 mm. Analytical-grade chemicals used in this study such as sodium sulphate (used in bio-oil phase separation), N,Obis(trimethylsilyl) trifluoroacetamide (derivatizing agent) and hexane (solvent) were purchased from Sigma Aldrich Chemicals Private Limited (Bangalore, India).
Bio-oil production Pyrolysis of selected feedstock was carried out in a fixed bed batch type reactor with a capacity of 2 kg. The line diagram of
the reactor is shown in Fig. 1. The reactor core was equipped with an electrical heater of 240 V and 9.5 A rating. The temperature of the reactor was maintained at 500 °C by a PID controller integrated with a K-type thermocouple. The reactor core was cleaned in order to eliminate the residual char contaminants produced by previous pyrolysis runs. For pyrolysis experiments, the reactor was filled with 2 kg of feedstock and the chamber was sealed with a PTFE gasket to avoid the leakage of organic vapors. The heating rate was adjusted to 30 °C/min by using a Dimmerstat arrangement. Upon reaching the biomass temperature of 500 °C, a holding period of 30 min was sustained. The organic vapor evolved during pyrolysis was passed into the shell and tube condenser arrangement. Pyrolytic gas is a complex mixture of condensable and non-condensable gases. Once the gas was passed through the condenser, the condensable gases were condensed as liquid and got collected into a collector vessel. Sample preparation To ensure the reliability of quantitative analytical measurement techniques, sufficient sample pretreatment steps are adopted with the principal objective of imparting selectivity and specificity in the analysis. The bio-oil obtained was found to be a mixture of aqueous and viscous organic phases. In order to analyse the stability, the organic phase was separated immediately after the pyrolysis experiment. Approximately 100 mL of bio-oil sample was taken in an Erlenmeyer flask and 10 g sodium sulphate was added to it. The sample was mixed thoroughly by manual shaking and then centrifuged at 10,000 rpm for 20 min (Remi R-12C plus centrifuge). After centrifugation, the upper aqueous layer was separated from the organic bottom layer with the help of a syringe. The resulting lower layer was further centrifuged at 10,000 rpm for 30 min which separates the less viscous upper portion, leaving thick lower portion. The upper less viscous layer (organic) was separated with the help of pipette and used in this study. Two samples of bio-oil were produced including CI bio-oil with 0% CH3OH (named CI) and CI with 10% CH3OH (CIM). All the samples were stored at 4 °C until analysed for their stability. Derivatization Derivatization generally imparts thermal stability to compounds and enhances their chromatographic properties. For polar bio-oil components, silylation followed by GC-MS is reported in a large number of literature studies (Kanaujia et al. 2013). The silylation process involves the substitution of acidic hydrogen on the compound with an alkyl silyl group. One hundred microlitres of the organic phase was collected in a separate vial through a calibrated pipette. Silylation was carried out by adding 100 μL of BSTFA into the vial, sealing
Environ Sci Pollut Res Fig. 1 Line diagram of the pyrolysis reactor. 1, K-type thermocouple; 2, heater coil; 3, reactor core; 4, cooling water in; 5, cooling water out; 6, condenser; 7, bio-oil collecting vessel; 8, airtight bladder
the vial, heating it at 70 °C for 1 h, cooling it to ambient temperature and analysing with GC-MS (Kanaujia et al. 2016; Naik et al. 2016).
Characterization of bio-oil Ultimate analysis Bio-oil samples were analysed for elemental carbon, hydrogen, nitrogen, sulphur and oxygen composition using a PerkinElmer 2400 Series II CHNSO elemental analyser and following protocols formulated by ASTM D5291-96. In the ultimate analysis of samples, C, H, N, S and O were determined on a dry basis. Viscosity The kinematic viscosity of the obtained bio-oil samples was determined by using a SimpleVIS automated kinematic viscometer. The method used is ASTM D445 for determining the viscosity of samples before and after the accelerated aging procedure at 40 °C. Water content The bio-oil sample was analysed for water content using the volumetric Karl Fischer titration method following the ASTM E203 and ASTM D1744 methods. The solvent used was Aquastar Solvent KC which contains dichloromethane for improved solubility with fats and oils. Calorific value The determination of the calorific value of bio-oil samples was accomplished by using an Isoperibol bomb calorimeter (model 6200) following guidelines laid by ASTM D240.
pH value The pH of the bio-oil samples before and after the accelerated aging process was determined by an Omega DP24-pH meter by adhering to the ASTM E70 protocol. The pH meter was calibrated with buffer solutions of pH 4,7 and 10 to ensure reliability in measurements. FTIR analysis Fourier transform infrared spectroscopy was used to analyse the organic functional group present in the bio-oil samples before and after the accelerated aging process. A PerkinElmer FTIR spectrometer with a resolution of 4 cm−1 was used for analysing the test samples. For analysing bio-oil samples, the sample was spread on a horizontal attenuated total reflectance (HATR) plate with zinc selenide crystal and the spectrum was developed in reflectance mode with a wave number range of 650–4000 cm−1. GC-MS analysis Gas chromatography-mass spectrometry analysis of pure pyrolytic oil samples before and after the aging process was carried out by the Thermo Trace Ultra GC system equipped with a TriPlus RSH autosampler DSQ II mass selective detector (Thermo Scientific Co.) using a (0.25 mm × 30 m) nonpolar DB 35-MS capillary standard column with a film thickness of 0.25 μm to identify the volatile organic compounds present in the bio-oil. Helium (99.99995% pure) was used as carrier gas for carrying out the analysis. The GC oven temperature was programmed to hold at 75 °C for 2 min, and then, the temperature was ramped up at a rate of 6 °C/min and held there for 10 min. The final oven temperature was set to 260 °C. A splitless injection of 1 μL sample with an injection temperature of 250 °C was adopted. The MS was fixed with a
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mass electron (m/z) range of 15–650 at an ionization energy of 70 eV. The components were identified based on the comparison of obtained mass spectra with those of the NIST and Wiley mass spectral libraries.
Bio-oil stability analysis Thermal stability The thermal stability of bio-oil can be determined as the percentage change of the viscosity of fresh and aged bio-oil samples. The kinematic viscosity of fresh bio-oil samples (Vfresh) was determined within 24 h of production, whereas the viscosity of aged bio-oil was measured after storing it in a sealed container at 80 °C for 24 h, which is equivalent to storing at ambient temperature for 1 year (Oasmaa and Peacocke 2010). The change in viscosity and the aging rate were calculated by Eq. (1) and Eq. (2). Δviscosity ¼
V aged −V fresh 100% V fresh
ð1Þ
aging rate ¼
V aged −V fresh cst=h 24
ð2Þ
An increase in viscosity after accelerated aging indicates that larger molecules have formed due to polymerization reactions. The bio-oil sample that shows less change in viscosity and aging rate is expected to demonstrate greater thermal stability during long-term storage for commercial usage. Oxidation stability The oxidation stability of bio-oil refers to the capacity to resist auto-oxidation in the presence of heat and an oxidizing agent. In the present study, oxidation stability was determined for the bio-oil test samples using a Metrohm 873 Rancimat instrument adhering to the guidelines provided by the EN14214 standard. The line diagram of the Rancimat instrument is illustrated in Fig. 2. The testing procedure involves heating 5 g of bio-oil sample at a constant temperature of 110 °C over which a stream of air is passed. As the bio-oil sample is heated, the air carrying secondary oxidation products is passed into a conductivity cell containing ultra pure water. Accumulation of water-soluble oxidation products leads to a rise in conductivity of ultra pure water, which is illustrated by a graph plotted between time (h) and conductivity (μS/ cm). A steady climb in the conductivity curve with respect to time indicates the augmentation of organic compounds in ultra pure water. The point at which the conductivity curve starts to rise suddenly accompanied by a drop in the second derivative curve is termed as an Binduction period (IP),^ which is calculated by the
automated Rancimat software Stabnet. The induction period refers to the time at which the bio-oil sample starts to degrade with respect to the temperature at which the oxidation occurs. The induction period is the direct measure of the sample’s oxidation stability. The bio-oil sample possessing high IP demonstrates higher oxidation stability during storage in the oxygen atmosphere. Another effective method to analyse oxidation stability is to determine the solid contents of bio-oil according to the ASTM D7579 standard. Approximately 10 g of bio-oil sample was mixed thoroughly with 100 g of acetone. The solution was filtered by a pre-dried and pre-weighed Whatman filter paper with a mean pore size of 1 μm. The filtrate was dried for 15 min at room temperature followed at 105 °C for 30 min. After drying, the filtrate was weighed by a measuring scale with an accuracy of ± 0.0001 g. Chemical changes during accelerated aging Changes in the chemical composition of fresh and aged bio-oil samples were analysed by using GC-MS and FTIR analyses. The main aim of this analysis is to show the changes in the concentration of certain organic groups of bio-oil after the accelerated aging process. The GC-MS analysis was expected to show the variations in concentration of higher molecular weight organic compounds after the aging process. The sample size was 1 μL and used for GC-MS analysis by diluting with hexane. It is one of the most convenient ways to observe the formation and variation of oxygenated groups formed due to oxidation of bio-oil during storage.
Engine testing Experimental setup The engine testing was carried out in a vertical single-cylinder direct-injection-type diesel engine test rig coupled with electrical loading arrangement through an eddy current dynamometer. The emission at the tailpipe was measured by using an AVL Modular diagnostic system gas analyser. The engine tests were carried out at a standard compression ratio (17.5:1) and injection timing (23°bTDC). As from our previous work (Rajamohan and Kasimani 2018), it was observed that 20% of bio-oil addition showed better engine output and was set as a reference mark in this study. So the test fuels were prepared with 20% of bio-oil concentrations in this study with the help of surfactants (Span 80 + Tween 80) and labelled as follows: fresh bio-oil (CI), unstabilized thermally aged bio-oil (CI-T), methanol-stabilized thermally aged bio-oil (CI-MT), unstabilized oxidatively aged bio-oil (CI-O) and methanolstabilized oxidatively aged bio-oil (CI-MO).
Environ Sci Pollut Res Fig. 2 Line diagram of the Rancimat apparatus
Results and discussion Characterization of biomass The properties of the feedstocks employed in this study are given in Table 1. The proximate analysis was used to evaluate the volatile matter, fixed carbon, ash and moisture content present in the feedstock. A fair amount of volatile matter present in feedstock indicates that the materials were more suitable for pyrolysis. This is due to the fact that the organic volatile matter present in the biomass was decomposed and evaporated into short-chain organic vapors which contain condensable and non-condensable gaseous components. Higher ash and moisture contents have negative effects on the calorific value and fuel conversion efficiency of the biomass. The ash content comprises a broad array of minerals such as potassium,
calcium, magnesium and silica. The elevated moisture content of biomass improves the rate of decomposition during storage and reduces the energy content. Mere amount of moisture in the CI seed cake showed promising odds to utilize the biomass as fuel. On the other hand, the ash content of a biomass mainly depends on the environmental condition of plantation and soil quality from which the biomass was derived. The less fixed carbon content of the CI cake also supports their potential to be employed as raw material for pyrolysis (Sakthivel and Ramesh 2017). The ultimate analysis of CI cake powder showed that the cake primarily contains oxygen followed by carbon, hydrogen and nitrogen with traces of sulphur. A lower O/C molar ratio shows that CI cake can be utilized as solid fuel directly due to its higher calorific value.
Characterization of bio-oil Table 1
Properties of feedstocks
Property
Biomass CI cake
Physical appearance Proximate analysis Volatile matter (wt%) Ash (wt%) Fixed carbon (wt%) Moisture (wt%) Ultimate analysis
Brown powder
C H O N S H/C molar ratio O/C molar ratio Calorific value (MJ/kg)
72.61 2.73 21.1 3.56 43.82 6.35 45.98 3.15 0.695 1.73 0.78 18.865
Table 2 depicts the results of compositional and property analysis of bio-oil samples used in the present study. The compositional analysis results clearly showed that CI-M oil contains low carbon and high oxygen content as compared to bio-oil derived from the CI cake. Also, both bio-oil samples seemed to be free of sulphur content which clearly shows that usage of bio-oil as fuel will restrict harmful oxides of sulphur. The theoretical values of C, H, O, N and S for methanol are 37.5, 12.6, 49.9, 0 and 0. Therefore, the addition of methanol decreased the carbon content and increased the oxygen content, assuming no chemical reactions were occurring between the constituents of bio-oil and methanol. On the other hand, the physicochemical properties of bio-oil were altered with the addition of methanol. Kinematic viscosity was significantly reduced by the addition of methanol: 12.2 to 3.6 cst for CI bio-oil. This reduction of viscosity was also accompanied by a slight increase of water content of both bio-oil samples with the addition of methanol. An appreciable reduction in density was also observed by the addition of methanol: 1.17 to 1.08 g/
Environ Sci Pollut Res Table 2
Properties of bio-oil samples
Property
Bio-oil CI
CI-M
Solvent (%, w/w) C
0 72.34
10 68.69
H
8.26
9.14
O N
19.4 0
22.17 0
S H/C molar ratio
0 1.37
0 1.59
O/C molar ratio
0.20
0.24
Calorific value (MJ/kg) Kinematic viscosity at 40 °C (cst)
36.84 12.2
34.21 3.6
pH Density at 30 °C (g/cm3) Water content (%)
4.3 1.17
4.6 1.08
23.3
35.2
cm3 for CI bio-oil. These substantial changes in property values with the addition of alcohol cannot be achieved by simple mixing of alcohol with bio-oil. Thus, it is expected that reactions such as acetalization, transacetalization, esterification and transesterification are occurring as observed by Diebold et al. (Diebold and Czernik 1997).
Stability assessment of bio-oil Thermal stability Table 3 summarizes the results of viscosity measurements at 40 °C for test samples analysed in this study. In order to ensure that there were no losses in volatile matters, the samples were weighed before and after the accelerated aging procedure. On analysing the results, it can be clearly seen that unstabilized CI bio-oil showed deprived thermal stability as compared to the methanol-stabilized bio-oil sample CI-M. For unstabilized CI bio-oil, an increase in viscosity from 12.20 to 20.36 cst was observed during accelerated aging with an aging rate of 0.34 cst/h. This elevated trend in viscosity may be attributed to complex chemical reactions like polymerization that occurred during storage period at high temperature (Oasmaa et al. 1997). This, in turn, signifies that raw bio-oil cannot be stored a long time for commercial purposes which is one of the Table 3 Viscosity changes in biooil samples during thermal aging
Bio-oil sample
CI CI-M
major setbacks of bio-oil commercialization. On the other hand, the methanol-stabilized fresh bio-oil showed promising values of viscosity compared to unstabilized CI oil. The result shows that methanol addition of bio-oil decreased viscosity over time and increased the stability of bio-oil relative to unstabilized CI bio-oil. For stabilized bio-oil, an increase in viscosity from 3.60 to 4.62 cst was observed during accelerated aging with an aging rate of 0.04 cst/h. The percentage change in viscosity is an effective measure for analysing the thermal stability of bio-oil. In the present work, unstabilized and methanol-stabilized bio-oil showed a change in viscosity values of 66.88 and 28.33% respectively. The variations in change are mainly due to the stabilization effect of methanol which is consistent with results obtained by Diebold et al. (Diebold and Czernik 1997). The addition of methanol reduces change in viscosity and increases the stability of bio-oil by the following mechanism: (1) physical dilution of bio-oil, (2) decreasing the reactant concentration or changing the micro structure of bio-oil components to lessen the rate of reaction and (3) formation of lower molecular weight ester compounds or acetal-based compounds on reacting with active components in bio-oil to prevent generation of large-chain polymers. Oxidation stability The value of the oil stability index (OSI) was obtained by a Rancimat instrument with respect to the guidelines prescribed by EN 14112 (Ramalho et al. 2011). The experiment is carried out at 110 °C thrice, and the OSI values were averaged to ensure the reliability of results. The OSI values of CI and CI-M bio-oil samples were of 0.94 and 3.97 h respectively. Figure 3 shows the induction period results of CI and CI-M through Rancimat experiments. The OSI value of the CI-M sample was in accordance with ASTM D6751 which prescribes a minimum OSI value of 3 h. The lower OSI value of unstabilized CI oil may be due to the polymerization process which induces the formation of active oligomers of the fatty acid methyl esters. Also, there may be the formation of higher molecular weight products due to the tendency of unsaturated double bonds to polymerization-type reactions. This complex reaction within bio-oil leads to the formation of insoluble double bonds and increases the viscosity of bio-oil. The viscosity changes of bio-oil subjected to oxidative aging are given in Table 4. The increase in viscosity from 12.2 to
Kinematic viscosity at 40 °C (cst) Fresh bio-oil
Aged bio-oil
12.2 3.6
20.36 4.6
Change in viscosity (%)
Aging rate (cst/h)
66.58 27.77
0.34 0.04
Environ Sci Pollut Res Fig. 3 Induction period obtained through the Rancimat apparatus. a Unstabilized bio-oil, b methanol-stabilized bio-oil
26.24 cst at an aging rate of 0.58 cst/h indicates that complete oxidation occurred with the formation of heavy molecular compounds due to polymerization reactions as explained above. Being complex in composition, specific chemical reactions in bio-oil are difficult to discern during the addition of solvent to improve stability. For example, if the solvent is an alcohol, esterification reactions are prone to occur by the Table 4 Viscosity changes in biooil samples during oxidative aging
Bio-oil sample
CI CI-M
reactions with acid compounds present in it. It is worth noting that alcohol additives convert reactive oligomeric compounds in the bio-oil to non-reactive oligomers. Also, on the other hand, additives apparently slow down the polymerization reactions of aromatics by dilution effects and by creating fewer reactive sites available for polymerization reaction to take place (Diebold and Czernik 1997). This chain termination of
Kinematic viscosity at 40 °C (cst) Fresh bio-oil
Aged bio-oil
12.2 3.6
26.24 6.75
Change in viscosity (%)
Aging rate (cst/h)
115.08 87.5
0.58 0.13
Environ Sci Pollut Res
oligomers leads to an increase in the OSI value of stabilized bio-oil. This chain termination of the polymerization reaction can be clearly explained by the viscosity change observed for CI-M oil which showed 87.5% hike after oxidative aging which was 27.58% less than that of unstabilized CI bio-oil. The aging rate of stabilized bio-oil was found to be 0.13 cst/h which was less than that of unstabilized bio-oil by 77.58%. Another method to evaluate the oxidation stability of biooil is the analysing of the solid formation pre- and post-oxidation. Table 5 illustrates the results of insoluble solids present in bio-oil samples. It is evident from the results that both fresh bio-oil samples adhere to the ASTM D7579 standard which prescribes the minimum solids should be below 1% by weight of bio-oil. On analysing the unstabilized bio-oil sample, it can be observed that there was an increase in insoluble solid content by 193.33 and 335.55% after thermal aging and oxidative aging respectively. It clearly validates the increase in kinematic viscosity of respective samples during the aging process. On the other hand, methanol-stabilized bio-oil showed relatively less increase in solid content during the aging process which is in the order of 83.14 and 202.5% after thermal aging and oxidative aging respectively. From the results, it can be clearly seen that stabilized bio-oil showed improved oxidation stability compared to unstabilized bio-oil.
Chemical changes during accelerated aging The chemical composition of unstabilized CI bio-oil sample before and after the accelerated aging process was analysed by using GC-MS. While analysing relative peak areas, recognized compounds with a substantial peak area and similarity index greater than 80% were included. To ensure the trustworthiness of results, relative peak areas were calculated as the average of the obtained peak areas from the duplicate experiment. The identified compounds were classified into individual functional groups. Figure 4 depicts the variations observed in individual functional groups of unstabilized bio-oil during the accelerated aging process. From the figure, it is clear that the concentration of functional groups varies greatly with the accelerated aging procedure and it can be noted that there was a diminishment in the major functional groups like alcohol, phenols, aldehydes, ketones and aromatics whereas steep increase was found in the concentration of carboxylic acids. In addition, the GC-MS results for unstabilized bio-oil in Table 6 show that the concentration of all the ester compounds Table 5 Insoluble solid formation for bio-oil samples during oxidative aging
Bio-oil sample
CI CI-M
increased with the aging process. Higher concentration of esters was found in oxidatively degraded samples due to its complete degradation than that of the thermally aged sample. The presence of a higher concentration of ester compounds in aged samples may be attributed to the esterification of organic acids and decomposition of large esters. The highest concentration was observed for octadecanoic acid, methyl ester with an area of 2.87% followed by 9, 12-octadecadienoic acid (Z, Z)-, methyl ester with an area of 2.67% in the oxidatively aged sample. This trend of increase in ester compounds is an indication intense oxidation occurred during aging (Czernik et al. 1994). Also, the detection of acetic acid and cycloheptanone in aged bio-oil samples is worth noting. The presence of acetic acid in aged samples indicates that esterification reaction occurred during aging. In addition, the concentration of active carbonyl compounds such as aldehydes and ketones decreased during the aging process. According to Diebold (2000), the reduced reactive carbonyl compounds (aldehydes and ketones) could have been converted to moderate molecular weight ester, acetals and hemiacetals, which attributed to stabilize bio-oil during accelerated aging. Also, during the aging process, reactive aldehyde compounds such as 2hydroxy acetaldehyde, but-2-enal and benzaldehyde could produce some large molecular weight products by reactions such as hydration, homopolymerization, hemiacetal formation and acetalization (Chen et al. 2014). All ketonic compounds decreased in concentration during the accelerated aging process which can be attributed to aldehyde and ketone reactions mentioned above. On the whole, the clear declination of oxygenated compounds showed an oxidation reaction had occurred and the reduction in carbonyl groups suggested that a complex polymerization reaction took place during the accelerated aging process. Meanwhile, it is interesting to note that changes occurred in the methanol-stabilized bio-oil sample during the accelerated aging process. The addition of methanol to bio-oil not only reduced viscosity but also changed the concentration of various compounds as compared to the unstabilized bio-oil sample. Figure 5 depicts the variations in concentration of functional groups present in methanol-stabilized bio-oil after the accelerated aging process. From the figure, it can be noted that aging affects the functional groups of stabilized bio-oil similar to that of unstabilized bio-oil but the only difference is the variations in concentration of the compounds. Lesser
Insoluble solid formation (wt%) Fresh bio-oil
Thermal aged bio-oil
Oxidative aged bio-oil
0.45 0.40
1.32 0.82
1.96 1.21
Environ Sci Pollut Res 35
Fig. 4 Variations in functional groups of unstabilized bio-oil after the accelerated aging process
30
Area %
25 20 15 Pre-aging 10
Post-Thermal aging
5
Post-Oxidave aging
0
Compounds
variations in the area percentage of individual components were observed for stabilized bio-oil as compared to that of the unstabilized bio-oil sample. During the accelerated aging process, augmentation in the concentration of carboxylic acids accompanied with a diminishment in the concentration of active carbonyl compounds, aromatic compounds and oxygenated compounds was observed for the stabilized bio-oil sample. It is worth noting that the increase in area percentage of the carboxylic acid group was observed to be less for methanol-stabilized bio-oil as compared to unstabilized bio-oil for both aging processes. In the oxidative aging process, the percentage reduction of ketones was found to be 53.32 and 36.70% in unstabilized bio-oil and methanol-stabilized bio-oil respectively. Also, aldehydes showed percentage reduction of 50.42 and 45.06% in unstabilized bio-oil and methanolstabilized bio-oil respectively. It clearly shows that reduction of active carbonyl compounds was less in the case of methanol stabilization which in turn implies that complex reactions such as polymerization and condensation were inhibited due to methanol stabilization. On the other hand, the area percentage of alcoholic compounds reduced by 35.92 and 22.36% in unstabilized bio-oil and methanolstabilized bio-oil respectively which implies less oxidative degradation occurred in the stabilized bio-oil sample. A fair decrease in alkanes and olefins was observed in both bio-oil samples which can be attributed to breakage of the C–H bond during aging. Table 7 shows the GC-MS result of methanol-stabilized CI bio-oil. From the table, it is clear that compounds detected in methanol-stabilized bio-oil were not the same as those of unstabilized biooil. Some new compounds like furancarboxylic acid methyl ester, octadecynoic acid methyl ester, methanol, acetic acid and cycloheptanone were detected in methanol-stabilized bio-oil. An augmentation in ester compounds in stabilized bio-oil may be to esterification reaction due to the addition of a primary alcohol (methanol). Most of the compounds were the same for both bio-
oil samples; the area percentage of all the compounds varies in large extent due to methanol stabilization. Among the oxidatively degraded samples, octadecanoic acid methyl ester detected at the retention time of 34.48 min showed a maximum area of 2.19% followed by dodecanoic acid methyl ester detected at 13.38 min with an area of 2.15%. Among carbonyl compounds, formaldehyde showed a maximum area percentage of 0.88% followed by cycloheptanone,2,3,9-trimethoxy (0.78%). On the whole, it can be seen clearly that variations in concentration of compounds were found to be less in the case of methanol-stabilized bio-oil when compared to unstabilized bio-oil. The obtained results were on par with previous research works (Diebold and Czernik 1997; Oasmaa et al. 2004; Hilten and Das 2010; Li et al. 2015).
Engine testing Performance characteristics Brake thermal efficiency (BTE) is the measure of thermal energy conversion while burning a certain quantity of fuel which is the ratio between brake power to the fuel power. Figure 6 shows a clear relationship between brake thermal efficiency with respect to brake mean effective pressure (BMEP). From the figure, it can be observed that BTE increased with increase in load for all the test fuels. Meanwhile, a drop in BTE was observed for all aged samples as compared to the fresh bio-oil blend. On analysing the aged samples, thermally aged and oxidatively aged samples showed a decrease in BTE by 3.1 and 5.8% respectively at no load whereas at peak loading condition, the drop was observed to be 2.8 and 6.29% respectively. This can be attributed to the degree of oxidation undergone by the samples during accelerated aging which depletes the oxygen content in the bio-oil. Due to the insufficient oxygen in the test fuel, the completeness of combustion is affected which in turn resulted in decreased BTE. On the other hand, the stabilized sample
Environ Sci Pollut Res Table 6
GC-MS results for unstabilized CI bio-oil pre- and post-aging process
Compounds
Molecular formula
Retention time (min)
Area % Preaging
Post-thermal aging
Post-oxidative aging
Alkanes Cyclopropane Undecane 1,3,3-Trimethyltricyclo(2.2.1.02,6)heptane Dodecane Pentadecane,2,6,10,14-tetramethyl Dodecane, 2,6,10-trimethyl Tetradecane Pentadecane Hexadecane Octadecamethyl cyclononasiloxane Heptadecane Eicosamethyl cyclodecasiloxane Nonadecane Docosane Nonacosane Alkenes Dec-1-ene Undec-1-ene Dodec-1-ene Cycloheptene, 1-methyl Tetradec-1-ene Pentadec-1-ene Hexadec-1-ene Heptadec-1-ene Octadecene Carboxylic acids Acetic acid 17-Octadecynoic acid 14-Pentadecynoic acid, methyl ester Dodecanoic acid, methyl ester Hexadecanoic acid, methyl ester 9,12-Octadecadienoic acid (Z,Z)-, methyl ester cis-11-Eicosenoic acid, methyl ester 3-Furancarboxylic acid, tetrahydro-4-methyl Octadecanoic acid, butyl ester Docosanoic acid, methyl ester 15-Tetracosenoic acid, methyl ester Octadecanoic acid, methyl ester 5-Heptenoic acid 9-Hexadecenoic acid, 9-octadecenyl ester Aromatics Toluene Ethylbenzene p-Xylene m-Xylene
C3H6
4.84 6.44 7.82 7.87 8.89 10.28 10.87 12.05 12.89 14.31 16.10 17.02 19.16 27.02 36.19
0.54 1.34 0.79 1.64 0.58 0.35 0.72 0.88 0.41 0.57 0.58 0.52 0.82 0.24 0.34
0.38 0.97 0.49 1.14 0.42 0.31 0.67 0.77 0.34 0.51 0.48 0.41 0.66 0.22 0.18
0.24 0.67 0.32 0.85 0.31 0.15 0.47 0.62 0.12 0.36 0.27 0.19 0.47 0.15 0.12
C10H20 C11H22
4.86 6.51
1.48 1.74
1.39 1.45
0.94 0.87
C12H24 C8H14 C18H36 C15H30 C16H32 C17H34 C14H28
7.94 8.12 10.98 12.16 12.97 16.23 16.75
1.38 0.41 0.82 0.86 0.74 0.51 1.76
1.23 0.47 0.63 0.78 0.63 0.47 1.36
0.86 0.41 0.40 0.52 0.39 0.27 0.79
C2H4O2 C18H32O2 C17H34O2 C13H26O2 C17H34O2 C19H34O2 C21H40O2 C14H24O4 C34H68O2 C23H46O2
2.87 4.69 9.61 13.38 21.72 25.53 28.23 29.56 29.82 31.26
ND 0.23 0.52 1.07 0.46 0.74 0.24 0.17 0.64 0.61
0.95 0.33 1.68 1.96 1.65 1.88 1.32 0.59 1.96 1.67
1.21 0.67 2.24 2.63 2.41 2.67 1.97 1.21 2.57 2.50
C25H48O2 C19H38O2 C24H47NO5Si2 C34H64O2
34.13 34.48 37.89 39.18
0.24 0.62 0.23 0.32
1.66 2.14 0.69 1.74
2.43 2.84 0.87 2.36
4.06 6.16 6.35 6.38
1.48 1.68 1.28 1.42
1.21 1.42 0.98 0.99
1.15 1.31 0.92 0.97
C11H24 C10H16 C12H26 C19H40 C15H32 C14H30 C15H32 C16H34 C18H54O9Si9 C17H36 C20H60O10Si10 C19H40 C22H46 C29H60
C7H8 C8H10 C8H10 C8H10
Environ Sci Pollut Res Table 6 (continued) Compounds
Molecular formula
Retention time (min)
Area % Preaging
Styrene
C8H8
Benzene, 1-ethyl-2-methyl Benzene, 1,3,5-trimethyl Benzene, 1-ethyl-3-methyl Benzene, 1-methyl-2-(1-methyl ethyl)
C9H12 C9H12 C9H12 C10H14
1-H Indene, 3-methyl 3,5-Bis(p-dimethylaminostryl)-2,2-dimethyl-2H-pyrrole1-oxide Flavone 4′-OH,5-OH,7-di-o-glucoside Tocopheryl methyl ether Ketones Ethanone,1-cyclopropyl 3-Hexanone 2-Cyclopenten-1-one, 3-methyl Ethanone,1-(2-furanyl) Cyclopentanone,2-methyl 2-Cyclopenten-1-one, 3-methyl2-Cyclopenten-1-one,2-methyl Piperidine-2,5-dione 2-Cyclohexen-1-one Cycloheptanone Cycloheptanone,2,3,9-trimethoxy Alcohols 2-Furanmethanol 1-Tetradecanol 1-Heptadecanol 2-Methyl-E,E-3,13-octadecadien-1-ol Ergost-5-en-3-ol, acetate, (3á,24R)Phenols Phenol Phenol, 2-methyl Phenol, 4-methyl Phenol, 2-methoxy Phenol, 2,3-dimethyl Phenol, 3,5-dimethyl Phenol, 2,4-dimethyl Phenol, 2-methoxy,4-methyl 2-Methoxy-5-methyl phenol Phenol, 4-ethyl-2-methoxy Phenol,2-methoxy-4-propyl 3-Phenyl-5-t-butylpyridazine Phenol,4-(ethoxymethyl-2-methoxy) 2,7-Di-tert-butyl-3,6-diphenylbiphenylene Polycyclic aromatic hydrocarbons Naphthalene,2-methyl Naphthalene,2,3-dimethyl
Post-thermal aging
Post-oxidative aging
6.85 8.47 9.18 9.81 9.85
1.79 1.87 2.34 2.38 2.22
1.12 1.14 1.89 1.93 1.78
1.03 0.99 1.69 1.86 1.62
C10H10 C26H33N3O
11.45 30.47
0.72 0.88
0.86 0.74
0.93 0.68
C27H30O15 C29H50O2
31.43 40.39
0.73 1.65
0.61 1.96
0.58 2.12
C5H8O C6H12O C6H8O C6H6O2 C6H10O C6H8O C6H8O C5H7NO2 C6H8O C7H12O
3.56 4.5 4.56 4.8 5.69 5.93 7.24 8.72 14.52 31.09
0.92 0.82 1.32 1.24 1.52 1.21 0.99 1.42 0.93 ND
0.56 0.47 0.64 0.70 0.69 0.74 0.42 0.99 0.87 0.44
0.47 0.36 0.58 0.53 0.35 0.42 0.24 0.49 0.63 0.56
C18H18O4
33.22
1.05
0.81
0.70
C5H6O2 C14H30O C17H36O C19H36O C30H50O2
3.72 12.22 14.07 26.74 32.06
2.95 1.25 1.67 1.91 0.32
1.78 0.96 0.83 0.93 0.98
1.63 0.85 0.64 0.75 1.32
C6H6O C7H8O C7H8O C7H8O2 C8H10O C8H10O C8H10O C8H10O2 C8H10O2 C9H12O2 C10H14O2
9.3 10.75 11.23 11.32 11.67 12.57 13.16 13.33 13.43 14.87 16.36
1.44 1.49 1.46 1.31 1.34 1.29 1.71 1.28 1.46 1.44 1.56
1.12 1.03 0.98 0.85 1.02 1.14 1.36 1.15 1.09 1.35 1.29
0.98 0.87 0.83 0.76 0.93 0.85 1.02 0.86 0.78 1.03 1.09
C14H16N2 C10H14O3 C32H32
18.23 19.61 35.62
1.79 1.76 1.44
1.11 1.36 0.91
0.80 0.81 0.67
C11H10 C12H12
15.11 16.97
0.88 0.86
0.69 0.73
0.60 0.59
Environ Sci Pollut Res Table 6 (continued) Compounds
Molecular formula
Retention time (min)
Area % Preaging
Naphthalene, 2,7 dimethyl Amines Benzenemethanamine, N-hydroxy-N-(4-methylphenyl)Paromomycin 1H-Purin-6-amine, [(2-fluorophenyl)methyl]
Post-thermal aging
Post-oxidative aging
C12H12
17.21
0.62
0.46
0.25
C14H15NO C23H45N5O14 C12H10FN5
6.83 7.62 24.05
0.53 0.24 1.58
0.62 0.37 1.47
0.74 0.48 1.59
CH2O C2H4O2 C4H6O C7H6O
5.87 7.38 8.65 12.36
1.87 0.87 0.32 0.43
1.26 0.52 0.16 0.31
1.02 0.36 0.12 0.23
Aldehydes Formaldehyde 2-Hydroxy acetaldehyde But-2-enal Benzaldehyde ND not detected
showed improved BTE as compared to unstabilized samples. BTE decreased for methanol-stabilized bio-oil that underwent thermal and oxidative aging, at 1.65 and 4.03% respectively at no load whereas at peak load the drop was observed at 1.96 and 4.74%. It is crystal clear the reduction in BTE was retarded with the addition of methanol to bio-oil, and also, it is worth noting that the BTE values were still lower than those of the fresh sample. This implies that addition of methanol only reduces the aging rate and cannot stop the aging completely. Since the fuels with different calorific values and densities cannot be compared with brake specific fuel consumption (BSFC) for performance evaluation, a new performance index named break specific energy consumption (BSEC) was employed. It is the product of BSFC and the calorific value of the fuel. Figure 7 clearly explains the relationship between the BMEPandBSECforallthetestfuels.Fromthefigure,itcanbe observed that the BSEC of all the test fuels decreased with the increase in load as expected. At no load condition, the
thermally aged bio-oil sample showed a 7.1% increase in BSEC whereas the oxidatively aged bio-oil sample showed a 9.8% hike as compared to fresh bio-oil sample. At the same time,theBSECwasincreasedby17.3and38.3%forthermally and oxidatively aged samples at peak load condition. This augmented energy consumption can be attributed to the increased viscosity and reduced oxygen content of aged samples which cause poor atomization characteristics during injection. Meanwhile, the stabilized bio-oil showed a decreased rate of energy consumption when subjected to both thermal and oxidative aging process as compared to that of unstabilized samples. After stabilization, the augmentation of BSEC by 11.3 and 25.06% was recorded for thermally and oxidatively aged samples at peak load. So, it is evident that methanol addition not only decreased the viscosity but also enhanced the stability of bio-oil which in turn results in oxygen availability for better combustion than unstabilized bio-oil samples.
25
Fig. 5 Variations in functional groups of methanol-stabilized bio-oil after the accelerated aging process
20
Area%
15
10
Pre-aging Post-Thermal aging
5
Post-Oxidave aging
0
Compounds
Environ Sci Pollut Res Table 7 GC-MS results for methanol-stabilized CI bio-oil pre- and post-aging process
Compounds
Alkanes Cyclopropane Undecane 1,3,3-Trimethyltricyclo (2.2.1.02,6)heptane Dodecane Pentadecane,2,6,10,14-tetramethyl Dodecane, 2,6,10-trimethyl Tetradecane Pentadecane Hexadecane Heptadecane Nonadecane Docosane Nonacosane Alkenes Dec-1-ene Undec-1-ene Dodec-1-ene Cycloheptene, 1-methyl Tetradec-1-ene Pentadec-1-ene Hexadec-1-ene Heptadec-1-ene Octadecene Carboxylic acids Acetic acid 17-Octadecynoic acid 14-Pentadecynoic acid, methyl ester Dodecanoic acid, methyl ester Hexadecanoic acid, methyl ester 9,12-Octadecadienoic acid (Z,Z)-, methyl ester cis-11-Eicosenoic acid, methyl ester 3-Furancarboxylic acid, tetrahydro-4-methyl Octadecanoic acid, butyl ester Furancarboxylic acid methyl ester Docosanoic acid, methyl ester 15-Tetracosenoic acid, methyl ester Octadecanoic acid, methyl ester Octadecynoic acid, methyl ester 5-Heptenoic acid 9-Hexadecenoic acid, 9-octadecenyl ester
Molecular formula
C3H6
Retention time (min)
Area % Preaging
Postthermal aging
Postoxidative aging
C11H24 C10H16
4.84 6.44 7.82
0.49 1.28 0.83
0.42 1.15 0.76
0.35 0.89 0.68
C12H26 C19H40 C15H32 C14H30 C15H32 C16H34 C17H36 C19H40 C22H46 C29H60
7.87 8.89 10.28 10.87 12.05 12.89 16.10 19.16 27.02 36.19
1.70 0.48 0.33 0.74 0.76 0.49 0.63 0.77 0.32 0.26
1.59 0.41 0.28 0.68 0.61 0.42 0.55 0.69 0.29 0.22
1.40 0.36 0.21 0.52 0.49 0.37 0.39 0.51 0.19 0.15
C10H20 C11H22 C12H24 C8H14 C18H36 C15H30 C16H32
4.86 6.51 7.94 8.12 10.98 12.16 12.97
1.51 1.63 1.46 0.43 0.76 0.95 0.53
1.44 1.56 1.38 0.31 0.59 0.82 0.47
1.32 1.39 1.18 0.23 0.42 0.68 0.35
C17H34 C14H28
16.23 16.75
0.62 0.88
0.53 0.72
0.31 0.54
C2H4O2 C18H32O2 C17H34O2
2.87 4.69 9.61
0.44 0.68 1.46
0.58 0.76 1.58
0.71 0.92 1.73
C13H26O2 C17H34O2 C19H34O2
13.38 21.72 25.53
1.93 1.27 1.35
2.03 1.41 1.48
2.15 1.58 2.06
C21H40O2
28.23
0.98
1.16
1.25
C14H24O4
29.56
0.86
0.98
1.21
C34H68O2 C6H6O3 C23H46O2 C25H48O2 C19H38O2 C19H34O2 C24H47NO5 Si2 C34H64O2
29.82 30.87 31.26 34.13 34.48 36.65 37.89
1.42 1.33 1.05 1.06 1.47 1.21 0.59
1.59 1.47 1.13 1.19 1.53 1.39 0.70
1.73 1.66 1.35 1.29 2.19 1.52 0.89
39.18
0.87
0.94
1.14
Environ Sci Pollut Res Table 7 (continued)
Compounds
Aromatics Toluene
Molecular formula
C7H8
Retention time (min)
Area % Preaging
Postthermal aging
Postoxidative aging
Ethylbenzene p-Xylene m-Xylene
C8H10 C8H10 C8H10
4.06 6.16 6.35 6.38
1.37 1.54 1.02 1.14
1.26 1.42 0.92 0.87
1.12 1.31 0.83 0.76
Styrene
C8H8 C9H12 C9H12 C9H12 C10H14
6.85 8.47 9.18 9.81 9.85
1.53 1.32 1.47 1.14 1.01
1.26 1.08 1.26 0.99 0.82
1.09 0.92 0.98 0.75 0.66
C10H10 C27H30O15
11.45 31.43
0.81 0.38
0.69 0.27
0.53 0.19
C29H50O2
40.39
1.86
1.57
1.41
C5H8O C6H12O C6H8O C6H6O2 C6H10O C6H8O C6H8O C5H7NO2 C6H8O C7H12O C18H18O4
3.56 4.5 4.56 4.8 5.69 5.93 7.24 8.72 14.52 31.09 33.22
0.71 0.69 0.91 0.87 0.82 0.93 0.79 0.85 0.78 0.63 1.12
0.53 0.50 0.77 0.71 0.69 0.81 0.57 0.65 0.56 0.47 0.91
0.42 0.38 0.57 0.63 0.52 0.59 0.43 0.57 0.49 0.38 0.78
CH4O C5H6O2 C6H14O C8H18O C14H30O C17H36O C19H36O
2.15 3.72 6.32 9.14 12.22 14.07 26.74
0.86 1.96 1.35 1.68 1.47 1.89 1.99
0.68 1.78 1.03 1.42 1.31 1.78 1.83
0.57 1.61 0.89 1.30 1.17 1.54 1.65
C30H50O2
32.06
0.83
0.72
0.61
C6H6O C7H8O C7H8O C7H8O2 C8H10O C8H10O C8H10O C8H10O2 C8H10O2
9.3 10.75 11.23 11.32 11.67 12.57 13.16 13.33 13.43
1.34 1.52 1.54 1.31 1.44 1.36 1.63 1.31 1.20
1.22 1.34 1.38 1.14 1.29 1.23 1.46 1.18 1.02
1.13 1.20 1.24 1.01 1.08 1.10 1.20 0.98 0.86
Benzene, 1-ethyl-2-methyl Benzene, 1,3,5-trimethyl Benzene, 1-ethyl-3-methyl Benzene,1-methyl-2-(1-methyl ethyl) 1-H Indene, 3-methyl Flavone 4′-OH,5-OH,7-di-o-glucoside Tocopheryl methyl ether Ketones Ethanone,1-cyclopropyl 3-Hexanone 2-Cyclopenten-1-one, 3-methyl Ethanone,1-(2-furanyl) Cyclopentanone,2-methyl 2-Cyclopenten-1-one, 3-methyl2-Cyclopenten-1-one,2-methyl Piperidine-2,5-dione 2-Cyclohexen-1-one Cycloheptanone Cycloheptanone,2,3,9-trimethoxy Alcohols Methanol 2-Furanmethanol 1-Hexanol 1-Octanol 1-Tetradecanol 1-Heptadecanol 2-Methyl-E,E-3,13octadecadien-1-ol Ergost-5-en-3-ol, acetate, (3á,24R)Phenols Phenol Phenol, 2-methyl Phenol, 4-methyl Phenol, 2-methoxy Phenol, 2,3-dimethyl Phenol, 3,5-dimethyl Phenol, 2,4-dimethyl Phenol, 2-methoxy,4-methyl 2-Methoxy-5-methyl phenol
Environ Sci Pollut Res Table 7 (continued)
Compounds
Molecular formula
Phenol, 4-ethyl-2-methoxy Phenol,2-methoxy-4-propyl Phenol,4-(ethoxymethyl-2methoxy) 2,7-Di-tert-Butyl-3,6diphenylbiphenylene Polycyclic aromatic hydrocarbons Naphthalene,2-methyl Naphthalene,2,3-dimethyl Naphthalene, 2,7 dimethyl
C9H12O2
Retention time (min)
Area % Preaging
Postthermal aging
Postoxidative aging
C10H14O2 C10H14O3
14.87 16.36 19.61
1.52 1.48 1.38
1.31 1.22 1.19
1.14 1.08 1.03
C32H32
35.62
1.36
1.10
0.82
C11H10 C12H12 C12H12
15.11 16.97 17.21
0.83 0.78 0.55
0.62 0.56 0.43
0.53 0.47 0.36
6.83
0.56
0.41
0.29
C23H45N5O14 C12H10FN5
7.62 24.05
0.31 1.47
0.23 1.24
0.12 1.13
CH2O C2H4O2 C4H6O C7H6O
5.87 7.38 8.65 12.36
1.28 0.53 0.24 0.28
1.07 0.38 0.14 0.16
0.88 0.21 0.09 0.10
Amines Benzenemethanamine, N-hydroxy-N-(4-methylphenyl)Paromomycin 1H-Purin-6-amine, [(2-fluorophenyl)methyl] Aldehydes Formaldehyde 2-Hydroxy acetaldehyde But-2-enal Benzaldehyde
Emission characteristics
2017). On analysing the results in Fig. 10, it is evident that CO increased for aged samples at all loading conditions as compared to that of fresh bio-oil sample. At no load condition, an increase in CO emission by 17.1 and 39.47% was noted for thermally and oxidatively aged samples respectively as compared to that of the fresh sample. For methanol-stabilized aged bio-oil samples at no load condition, the CO emission showed an augmentation by 6.5 and 25.6% after thermal and oxidative aging. This clearly showed that augmentation of CO emission decreased for aged samples after methanol stabilization but is still greater than that of the fresh bio-oil sample. Methanol stabilization of bio-oil inhibits the oxidation to a great extent
35
40
30
35
25
30 CI
20
CI-T 15
CI-MT
10
CI-O CI-MO
5
BSEC (MJ/kWhr)
BTE (%)
Carbon monoxide (CO) emission is one of the major air pollutants generated by vehicles due to incomplete combustion of fuel. The inefficient combustion may be due to several reasons such as oxygen availability, combustion temperature, compression ratio, injection timing, fuel quality, etc. Figure 8 reveals the relationship between the CO emission and BMEP at various loading conditions. It is clear that the CO emission was more at low load conditions due to low temperature and poor mixing of air-fuel which was reported at previous literature works (Rajamohan and Kasimani 2018, Pradhan et al.
C14H15NO
25
CI
20
CI-T
15
CI-MT
10
CI-O CI-MO
5 0
0 1.16
2.07
3.16
BMEP (bar)
Fig. 6 Variations of BTE vs BMEP
4.11
1.16
2.07
3.16
BMEP (bar)
Fig. 7 Variations of BSEC vs BMEP
4.11
Environ Sci Pollut Res 2.5
10 9
2
8 6
CI
5
CI-T
4
CI-MT
CI-O
3
CI-O
CI-MO
2
CI-T 1
CI-MT
0.5
CI-MO
1
0 1.16
2.07
3.16
0
4.11
1.16
BMEP (bar)
250 200 CI
150
CI-T 100
CI-MT CI-O
50
CI-MO
0 2.07
3.16
BMEP (bar)
Fig. 10 Variations of HC vs BMEP
3.16
4.11
Fig. 9 Variations of CO2 vs BMEP
by reducing the formation of active oligomers which results in an increase in oxygen availability for carbon oxidation thereby decreasing CO emission as compared to that of the unstabilized sample. Carbon dioxide is one of the most important greenhouse gases emitted by vehicles due to perfect combustion of fuel. The augmentation of CO2 shows the degree of completeness of combustion of the fuel during power stroke. Figure 9 shows the variation of CO2 emission with respect to the loads for all test fuel blends. The figure clearly depicts the tradeoff behaviour of CO2 with CO emission at all loads. The aged bio-oil showed a drop in CO2 values at all loads as compared to the fresh bio-oil sample. At peak loading condition, the reduction in CO2 by 8.4 and 19.14% was observed for thermally and oxidatively aged bio-oil samples. Meanwhile, the methanolstabilized aged bio-oil showed a reduction of CO2 by 3.7 and 16.4% after thermal and oxidative aging. When comparing the magnitude of CO2 emission for aged samples, the methanolstabilized samples showed higher CO2 than the unstabilized samples. This is due to the oxygen availability and reduced viscosity of the stabilized sample that enhanced the combustion process, thereby increasing CO2 at the exhaust. Hydrocarbon emission is the major by-product of incomplete combustion of hydrocarbon. High levels of HC in the exhaust signify the incomplete combustion of the fuel during the combustion phase. Figure 10 illustrates the variations of the
1.16
2.07
BMEP (bar)
Fig. 8 Variations of CO vs BMEP
HC (ppm)
CO2 (%vol)
CO (% vol)
7 CI
1.5
4.11
HC level with respect to BMEP for all bio-oil samples. From the figure, it is clear that unaged bio-oil sample results in cleaner combustion as compared to other aged samples. It can also be observed that HC magnitude was high in lower engine loads due to inefficient combustion and reduced turbulence at injection. At the peak engine loading condition, the oxidatively and thermally aged bio-oil sample showed high HC values of 132 and 129 ppm which are 30.69 and 27.72% higher than that of the unaged sample. This trend of elevated HC level may be attributed to lack of oxygen content and the formation of higher molecular weight hydrocarbons during aging which result in incomplete burning during the combustion phase. Oxides of nitrogen are the major products generated by high combustion flame temperature which can be explained by the Zeldovich mechanism. NOx emission increased with respect to engine load as expected. Figure 11 shows the variations of NOx with respect to BMEP for all test fuels. For all loading conditions, the lowest NOx values were recorded for the unaged fresh bio-oil blend whereas the oxidatively aged bio-oil blend showed the highest NOx emission. At peak load, the oxidatively aged bio-oil blend emits 25.05% higher NOx emission whereas thermally aged bio-oil generates 9.79% higher NOx as compared to fresh bio-oil. It may be due to the reduction of the quenching effect produced by water content of bio-oil since the water content is reduced in aged oil accompanied with augmentation of viscosity. It can also be noted that methanol stabilization reduced the NOx emission due to the quenching effect provided by methanol. Unlike other engine exhaust emissions, the smoke opacity relies on different factors like fuel-rich zones, oxygen availability and completeness of combustion. Figure 12 depicts the changes in smoke opacity with respect to BMEP. It can be seen that the aged bio-oil samples generated more smoke at the exhaust due to lack of oxygen content for sufficient soot oxidation. The highest opacity was recorded for the oxidatively aged bio-oil sample at low load condition which is 24.28% higher than that of the unaged sample. Also, methanol stabilization improved smoke opacity values by enhancing the combustion and soot oxidation at all engine loads.
Environ Sci Pollut Res 1400 1200
NOx (ppm)
1000 CI
800
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BMEP (bar)
Fig. 11 Variations of NOx vs BMEP
Conclusion Three different stability analysis methodologies were employed to evaluate the storage stability of CI seed cake bio-oil. The influence of methanol addition on the shelf life of bio-oil was also analysed. From thermal stability analysis, it can be seen that the least change in viscosity of 27.77% with an aging rate of 0.04 cst/h was observed for the methanolstabilized bio-oil sample whereas the change was 66.58% and the aging rate was 0.34 cst/h for the unstabilized bio-oil. Meanwhile, a higher OSI value of 3.94 h was obtained for the CI-M sample which is on par with the ASTM D6751 standard. This undoubtedly shows that methanol stabilization inhibited the formation complex polymer chain during aging by terminating the chain reactions. Meanwhile, methanol addition to the bio-oil lowered insoluble solid formation by 61.98%. Compositional analysis by GC-MS indicated the distinct changes in the chemical composition of bio-oil during the aging process. For both bio-oil samples, augmentation in ester content accompanied by a reduction in aldehyde, ketone and alcohol concentrations was detected after aging. Methanol addition clearly decreased the deviation in concentration of organic groups after aging which revealed that fewer reactions took place during the aging process which in turn confirmed that the bio-oil was stable. The engine testing results showed that the unaged CI sample showed superior performance and 50 45 Smoke opacity (%)
40 35 30
CI
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20
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15
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10
CI-MO
5 0 1.16
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3.16 BMEP (bar)
Fig. 12 Variations of smoke opacity vs BMEP
4.11
emission characteristics at all loading conditions whereas all aged samples showed deteriorated engine characteristics. Since oxidative aging completely deteriorated the quality of oil, the CI-O sample showed poor BTE of 24.41% and increased emissions of CO (1.51%), HC (132 ppm), NOx (1098 ppm) and smoke opacity (34.8%) at full load. From the results, it can also be seen that methanol addition not only enhanced the storage stability but also improved performance and emission aspects of the aged sample. For example, the methanol-stabilized oxidatively aged sample CI-MO showed enhanced BTE (25.96%) and reduced emissions of CO (1.43%), HC (124 ppm), NOx (1019 ppm) and smoke opacity (32.7%) as compared to the CI-O sample. From these experimental results, it is recommended to employ 10% methanol addition to the bio-oil obtained from slow pyrolysis of CI deoiled seed cake to improve the storage stability so that the bio-oil can be utilized effectively in commercial sectors. Acknowledgements The authors would like to acknowledge Dr. T. Meenambal, Former Principal Advisor, TEQIP II - Centre of Excellence for Environmental Studies (COE-Es), Government College of Technology, Coimbatore 641013, Tamil Nadu, India, for support in conducting the series of experiments.
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