Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX
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Selected Physicochemical Properties of Diethyl Ether/Rapeseed Oil Blends and Their Impact on Diesel Engine Smoke Opacity Krzysztof Górski*,† and Ruslans Smigins‡ †
Kazimierz Pulaski University of Technology and Humanities in Radom, Chrobrego 45 Street, Radom, PL 26-600 Poland Latvia University of Agriculture, Liela 2 Street, Jelgava, LV3001 Latvia
‡
S Supporting Information *
ABSTRACT: In this paper, selected physicochemical properties such as kinematic viscosity (ν), density (ρ), lower heating value (LHV), cold filter plugging point (CFPP), miscibility, flash point (FP), coefficient of friction (μ), lubricity (WS1.4), surface tension (σ), and copper strip corrosion (CSC) of diethyl ether/rapeseed oil blends were experimentally determined. Diethyl ether (DEE) was blended with rapeseed oil (RO) in volumetric ratios of 10, 20, 30, and 40%. The values of the LHV, kinematic viscosity, surface tension, and density of the blends were lower than the values obtained for the tested rapeseed oil. Especially, it was found that DEE has significant influence on the rapeseed oil viscosity value. The addition of merely 10% DEE to rapeseed oil decreased its viscosity by 50%. It was shown that the lubricity of all tested blends is reduced, but not as significantly as viscosity. Also, we confirmed that tested blends do not promote the corrosion processes. What is more, it was found that the temperature of the CFPP decreased when DEE was added to RO and the miscibility of all tested fuel blends is excellent in a wide range of temperature changes. For this reason the results of our research suggest that DEE/RO blends seem to be usable for engines operated in the winter season. However, it should be confirmed in further engine research carried out in low temperature conditions. In this study the diesel smoke opacity (SO) was also measured in the condition of a free acceleration test according to requirements of the United Nations Economic Commission for Europe (ECE) Regulation No. 24. Results of these tests demonstrate that the diesel smoke opacity is reduced even by 55% for DEE40 blend compared with RO.
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INTRODUCTION The use of plant oils as a fuel for diesel engines dates back to the beginning of the 20th century. It is well-known that the first diesel engine, shown by Rudolf Diesel at the World Exhibition in Paris in 1900, was powered with peanut oil. However, over the next few decades the history of the internal combustion (IC) engines was not related to renewable fuels. Until the oil shock in the early 1970s the prices of crude oil were relatively low. Also, knowledge on environmental problems associated with burning fossil fuels in IC engines was limited. It seems that both these factors were to become critical issues for the engine development process based on combustion of fossil fuels. In consequence, air quality has become more and more unacceptable, not only in urban areas but also on a global scale. According to Cook et al.1 about 97% of climate scientists agree that climate-warming trends over the past century are very likely due to human activities. This means that anthropogenic sources of greenhouse gases impact the current global warming trend and the combustion process of fossil fuels seems to be a significant part of this phenomenon. For this reason the idea of environmentally friendly fuels for IC engines is still being developed not only in Europe but also in many other advanced countries in the world. In this area much research is still focused on application of plant oils, selected alcohols, and ethers as alternative fuels for IC engines. Plant oils have some advantages and disadvantages compared to fossil fuels. It is known that plant oils and their derivatives such a fatty acid methyl esters (FAME) can significantly improve the lubricity of diesel oils. Anastopoulos et al.2 stated that a very small amount of the selected biodiesel types and © XXXX American Chemical Society
tertiary amides dramatically improves the low-sulfur diesel lubricity. Also Knothe et al.3 suggest that commercial biodiesel is required at a level of 1−2% in low-sulfur diesel oils. Their research carried out on neat C3 compounds with OH, NH2, and SH groups showed that oxygen enhances lubricity more than nitrogen and sulfur. In the case of plant oils, due to their high viscosities and poor low-temperature properties, they are usually converted into smaller, straight-chain molecules of fatty acid methyl esters (FAME). The entire chemical process is known as transesterification or alcoholysis of triglycerides. It allows production of a biodiesel meeting necessary quality requirements of ASTM D6751 or the European standard EN 14214. In particular, the transesterification process of plant oils allows reduction of their viscosities to levels comparable for a diesel fuel described in the EN 590 or ASTM D975 standard. Even so, there are many problems with the physicochemical properties of FAME. For example, low-temperature properties of such a fuel is still unacceptable for an engine operated in the winter season. This is because FAME tend to gel up and clog filters at low temperatures. For this reason such a fuel in winter application must contain a special additive that prevents the formation of solid crystals. Also, it was found that the oxidation stability of FAME rapidly decreases even after a short storage period.4 As FAME are oxidized, many changes in their physicochemical properties occur. For example, the acid value, peroxide value, and viscosity increase, while the iodine Received: October 20, 2017 Revised: January 20, 2018 Published: January 24, 2018 A
DOI: 10.1021/acs.energyfuels.7b03225 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels value and content of methyl esters decrease.5 These selected drawbacks of FAME can be inhibited by the right composition of fuel additives. It also stimulates the further research policy. For example, in Europe such actions are supported by the Horizon 2020 program. It should be noted that research on alternative fuels for diesel engines is focused not only on biodiesel and its blends with diesel oil. There are many papers describing other possibilities. One of these depends on application of the dual-fuel technology for diesel engines. The primary fuel such as liquefied petroleum gas (LPG), liquefied natural gas (LNG), compressed natural gas (CNG), or ethanol is injected into the intake manifold of the engine. Mixture of such a fuel with air is ignited by diesel oil or biodiesel as the secondary fuel injected directly into the combustion chamber. The dual-fuel diesel technology is not very popular because new management systems as well as technical modifications of the engine are required. However, a dual-fuel system allows reduction of exploitation costs of the engine and emission of selected harmful gases. Lu et al.6 conducted a study evaluating the emissions and combustion characteristics of a direct injection dual-fuel engine fueled with biodiesel and anhydrous ethanol. The authors of this paper showed that CO and hydrocarbon (HC) emissions are higher than those of diesel mode but NOx and smoke emissions simultaneously decrease remarkably. Similar results were also presented by Kowalewicz.7 Addition of ethanol to biodiesel or diesel oil also has been investigated by some researchers paying attention to engine performance and exhaust emission characteristics from diesel engines. Although ethanol blending with diesel oil is problematic, ethanol usage in two-component (ethanol/biodiesel) or even three-component (diesel/biodiesel/ethanol) fuels has become more popular in scientific research. It is related not only to the ability of ethanol to reduce some exhaust components such as NOx, which is not possible with biodiesel use, but also to the implementation of the Renewable Energy Directive 2009/28/EC in EU Member States requiring substitution of 10% of consumed fossil fuels by renewable fuels by 2020. A review of different scientific research studies in the years 2000−2017 done by Zaharin et al.8 on biodiesel− alcohol and biodiesel−alcohol−diesel blends confirms that usage of such blends improves diesel engine performance and mostly reduces hazardous exhaust components (HC, CO, particulate matter (PM), and NOx) through their enhancement of physicochemical properties compared to other twocomponent fuels with the presence of diesel oil or even diesel oil alone. The above-presented references briefly confirm the common knowledge that renewable plant oils are acceptable but not the best fuels for a diesel engine. For this reason new ways of converting plant oils into a better diesel fuel are still developed. Application of diethyl ether (DEE) seems to be one such way. DEE has a high energy content and the possibility of producing it by ethanol conversion through a dehydration process.9 The fundamental difference between alcohols and ethers is related to the presence of OH groups in the alcohol, which are missing in the ethers. Such an absence leads to important consequences on chemical properties. Ethers are mostly inert to chemical reactions, stable to most acids and bases with exceptions at high temperatures and with the most common use as solvents. Addition of ethers to conventional fossil fuels and also biodiesel was realized by some researchers. Most of them have found the decrease of NOx and increase of
HC with increase of the DEE additive ratio testing karanja oil methyl ester or Thevetia peruviana oil methyl ester blends with up to 20% by volume DEE at various loads.10,11 Straight vegetable oil could be a more acceptable fuel due to its advantages over diesel oil. It has a higher flash point and lubricity and also minimal sulfur and aromatic content, but also very high viscosity and pour point, which could be reduced by an appropriate oxygenate, such as diethyl ether.12 The main advantages of DEE for blending with other diesel fuels are high cetane number, high oxygen content, low autoignition temperature, and excellent miscibility.12,13 There are no practically works on detailed analysis of physicochemical properties of different fuel blends, such as rapeseed oil with DEE. Therefore, the objective of this study was to test the effect of DEE addition with rapeseed oil on the physicochemical properties of these mixtures as a possible diesel fuel.
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SELECTED PHYSICOCHEMICAL PROPERTIES OF RAPESEED OIL Rapeseed oil (RO) is formed by a mixture of about 6% saturated, 73% monounsaturated, and 21% polyunsaturated fatty acids.14 The composition of these acids in vegetable oils varies with a few factors such as agroclimatic conditions of growth as well as the seed species. For this reason some rapeseed genotypes contain even 78% erucic acid whereas oleic acid is dominant in other oils such as Canola.15 Selected physicochemical properties of these two acids, that is, erucic and oleic, are listed in Table 1. The high-erucic rapeseed oil is a Table 1. Selected Physicochemical Properties of Erucic and Oleic Acids16−19,a value property
erucic acid
oleic acid
CAS RN PubChem no. EINECS no. ChemSpider no. M (g/mol) ρ (g/mL) η (cP) ν (mm2/s) bp (°C) σ (mN/m) mp (°C) FP (°C) AV (mg of KOH/g)
112-86-7 5281116 204-011-3 4444561 339 0.86b 32.3d − 381 − 33.8 349.9 165
112-80-1 445639 204-007-1 393217 282 0.897c 17.7d 18.8e 222 32.8 13 190 200
Abbreviations and acronyms: M, molar mass; ρ, density; η, dynamic viscosity; ν, kinematic viscosity at 40 °C; bp, boiling point at 1 atm; σ, surface tension; mp, melting point; FP, flash point; AV, acid value; −, unmeasurable for solid state chemicals. bTested at 55 °C. cTested at 15 °C. dTested at 100 °F. eTested at 40 °C. a
valuable and renewable raw material in industry for the manufacture of a wide array of products such as nylon, petroleum-based lubricants, and biodiesel. It should be pointed out that erucic acid is considered as antinutritional for human, but the latest results of the European Food Safety Authority (EFSA) research seem to not confirm these findings.16 The level of erucic acid has been reduced significantly in the rapeseeds that are used in the food industry.20 It is known that the fatty acid composition of rapeseed oils varies widely depending on the seed species, the variety, and the climatic B
DOI: 10.1021/acs.energyfuels.7b03225 Energy Fuels XXXX, XXX, XXX−XXX
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number (CN) of RO can vary. The determined cetane numbers of rapeseed oil samples from decentralized oil mills predominantly ranged from 38 to 42.29 Šimácě k et al.30 evaluated the impact of the hydroprocessing of rapeseed oil as a source of hydrocarbon-based biodiesel. They found that hydroprocesed rapeseed oil has a higher cetane number; however its low-temperature properties are still unacceptable. Lubrication properties of RO are also confirmed by a triacylglycerol structure containing long fatty acid chains and polar groups, in such a way giving RO amphiphilic character.31 This structure of RO promotes the arrangement of molecules making a closed packed monomolecular layer, which enhances the surface film, and the high molecular weight provides low volatility and improves viscosity properties.31 In any case, the use of RO as an industrial lubricant is limited due to poor thermooxidation, which is related to the presence of bis-allylic protons, and could be resulting from increase of oil viscosity and acid content, and therefore will promote corrosion of metal parts.31 In the case of vegetable oils it is an important parameter to find out the long-term durability of fuel injection equipment, because vegetable oils contain unsaturated acids and are easily oxidized during use, in such a way causing corrosion.32 Corrosion could be promoted also by different variable properties related to RO obtaining conditions. For example, different ash constituents are harmful for the engine and can increase wear, but water content in the long term causes cavitation events in the combustion chamber.33 Besides that also relevant characteristics can cause corrosion, and one of them is sulfur content. Neat rapeseed oil sulfur content usually is close to zero, while fossil diesel sulfur content according EN 590 is fixed at 10 mg/kg. This ws confirmed by Soltic et al.34 during tests with different fuel types, where they remarked that the content of sulfur in neat rapeseed oil is 3.6 mg/kg, but in diesel market fuel it is about 10.1 mg/kg. The heating value of RO is close to that of diesel, but still lower in range between 10 and 15%. This means that it will leave an impact on fuel consumption, which is proportional to the volumetric energy density of RO based on the lower heating value (LHV).28,35 The higher heating value (HHV) is strongly related to HHVs of their pure fatty acids and can be used to predict the heating value of RO with an absolute error less than 2%.36 Similarly, it is possible to predict HHVs of esters produced from vegetable oils and improve them if in used oil containing unsaturated acids with relatively small molecular weights.37
conditions under which it is grown. This means that the physicochemical properties of rapeseed oil are not constant. As we mentioned earlier, rapeseed oil density is higher than that of conventional diesel fuel. Noureddini et al.17 studied the impact of temperature on rapeseed oil density. Their results confirmed that the density of RO decreases when the temperature increases. In particular, the RO density values measured at the temperatures 23.9 and 100 °C were 0.9073 and 0.8579 g/mL, respectively. According to the EN 590 standard the density of diesel oil measured at 15 °C must be set in the range between 0.82 and 0.86 g/mL. Also, the viscosity of vegetable oils is temperature dependent. Stanciu21 confirmed an exponential relationship between temperature and the RO kinematic viscosity. Her research indicated that the RO viscosity reduces when the temperature increases. The RO kinematic viscosity measured by Stanciu at 40 °C was approximately 37 mm2/s, which is 10 times higher than that for conventional diesel fuel. High values of the RO kinematic viscosity and density have a negative impact on the quality of fuel atomization as well as on the combustion process and may lead to choking of the injectors.22 Fuel viscosity has a similar effect on droplet size distribution as surface tension. Too high values of surface tension together with high values of the RO viscosity can result in worse fuel atomization and larger diameter of spray droplets. It is known that the surface tension value is increased with an increase in the chain length.23 On the other hand, the surface tension value is a temperature dependent parameter. For this reason, based on adequate heating of RO, it is possible to reduce the surface tension value closer to that of conventional diesel fuel.24 However, the transesterification process seems to be the most popular method allowing reduction of the viscosity, density, and surface tension of all vegetable oils. During the transesterification chemical reaction the long chain fatty acids are converted into monoalkyl esters. Anastopoulos et al.25 confirmed that the properties of ethyl esters do not differ significantly from those of methyl esters. They stated that the densities, viscosities, and heating values of these alternative fuels were comparable with those of diesel oil. On the other hand, these esters as well as fatty acids still have poor lowtemperature properties. Several methods such as fuel heating, addition of cold flow improver, and blending allow partially overcoming this problem. The knowledge on the efficiency of these different methods is widely described for different FAME. However, in the case of rapeseed oil this knowledge is very limited. Dukulis et al.26 examined the impact of blending rapeseed oil and Arctic diesel oil. They stated that it is possible to run diesel engines with a second Arctic class diesel fuel blended with rapeseed oil (mixture ratio 50% by volume) even at a temperature of −20 °C. They also concluded that the cold filter plugging point (CFPP) value is mostly affected by the higher viscosity of rapeseed oil than the crystal formation process. The suitability of RO as an alternative for diesel fuel is confirmed by triacylglycerols contained in the oil and explained by the cetane scale. Long, unbranched chains of fatty acids are similar to those of the n-alkanes of conventional diesel fuel.27 The majority of the fatty acids of most oils have 16 and 18 carbon length chains, and RO could contain also a high percentage of the monounsatured C22 erucic acid.28 Consequently, the cetane number will be lower with increasing unsaturation and higher with increasing chain length. Experimental research has shown that the value of the cetane
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MATERIALS AND METHODS
Rapeseed oil used in this study was produced by Kruszwica Co., which is the one of the largest manufacturers of vegetable fats in Central Europe. All necessary tests were performed for a commercial refined low erucic RO containing 8, 26, and 66 wt % saturated, polyunsaturated, and monounsaturated fatty acids, respectively. Details of the fatty acid composition required for the tested RO are listed in Table 2. In our study DEE with purity over 99.5% was blended with RO in volumetric ratios of 10, 20, 30, and 40%. In this paper these fuel blends are coded as follows: DEE10, DEE20, DEE30, and DEE40, respectively. Figure S1, available in the Supporting Information, presents a view of all tested fuel samples. DEE was purchased from the Poch S.A. a Polish chemical company. Selected physicochemical properties of the tested RO and DEE are listed in Table 3. Measurements of selected physicochemical properties of DEE/RO blends were carried out in the Chemical Laboratory at the Kazimierz C
DOI: 10.1021/acs.energyfuels.7b03225 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels Table 2. Main Components of Low Erucic Rapeseed Oil Expressed as Percentage of Total Fatty Acids fatty acid name
C:Da
contentsb (%)
palmitic acid stearic acid arachidic acid linoleic acid linolenic acid oleic acid eicosenoic acid erucic acid
16:0 18:0 20:0 18:2 18:3 18:1 20:1 22:1
2.5−7.0 0.8−3.0 0.2−1.2 15.0−30.0 5.0−14.0 51.0−70.0 0.1−4.3 max 2
Table 4. Selected Physicochemical Properties of Tested DEE/RO Blendsa value
a
Number of carbon atoms (C) and of double bonds (D) in the fatty acid chain. bData taken from ref 38.
Table 3. Physicochemical Characteristics of Tested RO and DEEa RO
DEE
CN ν (mm2/s) ρ (g/mL) LHV (MJ/kg) FP (°C) CFPP (°C) bp (°C) σ (mN/m) WS1.4 (μm)
37 34 0.92 36.9 >300 28 >350 45.8 120c
>125b 0.23 0.71 33.9 −40 − 34.6 16.9 614d
DEE10
DEE20
DEE30
DEE40
17.5 0.904 33.0 36.5 13 solid 20 0.103 158 1 40.9
10.2 0.887 32.1 36.2 −4 liquid −2 0.112 188 1 36.9
6.3 0.869 31.3 36.0 −20 liquid −11 0.119 215 1 30.6
3.2 0.845 30.1 35.6 −29 liquid −20 0.153 265 1 26.7
a Abbreviations and acronyms: ν, kinematic viscosity at 40 °C; ρ, density at 15 °C; LHV, lower heating value; CFPP, cold filter plugging point; FP, flash point; μ, coefficient of friction; WS1.4, wear scar diameter corrected to normalize the standard water vapor pressure of 1.4 kPa; CSC, copper strip corrosion; σ, surface tension. bTested at −12 °C.
fuel property
property ν (mm2/s) ρ (g/mL) LHV (MJ/m3) LHV (MJ/kg) CFPP (°C) appearanceb FP (°C) μ WS1.4 (μm) CSC (class) σ (mN/m)
be reduced. Also too high viscosity of a diesel fuel is not favorable due to increasing resistance of fuel flow as well as poor atomization of the fuel droplets injected into the combustion chamber. Mainly for this reason according to the EN 590 standard the viscosity of the diesel fuels must be set in the range between 2.0 and 4.5 mm2/s. It is well-known that the viscosities of all plant fuels are approximately 10 times higher than that for typical diesel fuel and increase with decreasing temperature.21 Figure 1 confirms that the viscosity of rapeseed
a Abbreviations and acronyms: CN, cetane number; ν, kinematic viscosity at 40 °C; ρ, density; LHV, lower heating value; FP, flash point; CFPP, cold filter plugging point; bp, boiling point; σ, surface tension; WS1.4, wear scar diameter corrected to normalize the standard water vapor pressure of 1.4 kPa; −, too low to be measured. b Data taken from ref 9. cTested at 25 °C. dData taken from ref 39.
Pulaski University of Technology and Humanities in Radom. In particular, the kinematic viscosity and density of the blends were measured according to requirements of EN ISO 3104 and EN ISO 3838 standards, respectively. The heat of combustion of all tested fuels was expressed by the lower heating value measured in accordance with ASTM procedure D240-02:2007. Lubricity tests were performed using the high frequency reciprocating rig (HFRR) under conditions specified in EN ISO 12156-1:2006. Temperature-dependent parameters such as the cold filter plugging point and flash point of the blends were measured in agreement with EN 116:2015 and EN ISO 2719 standards, respectively. Surface tension measurements were performed in accordance with ISO 304:1985, which conforms in substance to DIN 53914. Moreover, in this study the smoke opacity was measured for a three-cylinder, four-stroke, water-cooled, naturally aspirated direct-injection Perkins AD3.152 diesel engine fueled with DEE/RO blends and neat RO. Details of the AD3.152 engine are listed in Table S1 in the Supporting Information. Smoke measurements were carried out using an AVL 465 diGas analyzer in the condition of a free acceleration test, according to requirements of Regulation No. 24 of the United Nations Economic Commission for Europe (ECE). The engine test stand is illustrated in Figure S2 in the Supporting Information.
Figure 1. Kinematic viscosity (ν) of rapeseed oil and DEE/RO blends tested at 40 °C.
oil is very high compared with that of diesel oil, but it is also visible that addition of DEE allows reduction of this viscosity significantly. In particular, 10% DEE added reduces the viscosity of RO by 50%.Therefore, the addition of DEE to RO can improve the atomization of fuel during the injection process as there will be a wider injection spray angle, smaller fuel droplets, and a higher quality of vaporization compared with neat RO. Overall, reduction of RO viscosity by DEE addition could help to avoid preheating of RO for reaching the necessary viscosity for usage in a diesel engine without any conversion of it. The next parameter tested in this research was fuel density. Usually diesel oil, with higher density, has a higher heating value, too. For this reason an engine can reach higher power.
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RESULTS AND DISCUSSION Physicochemical properties of all tested DEE/RO blends are listed in Table 4 and discussed below. The viscosity of diesel fuel impacts the performance of engine work. It is known that too low fuel viscosity promotes excessive pump leakage. For this reason the engine power may D
DOI: 10.1021/acs.energyfuels.7b03225 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels On the other hand, a denser fuel tends to increase engine deposits and smoke emission. It is known that the EN 590 standard requires keeping density in the range between 0.820 and 0.845 g/mL. It should be pointed out that the RO density of 0.92 g/mL does not meet this requirement. However, addition of a larger volume of DEE allows reduction of the density of RO. As diethyl ether has a lower density than RO, then addition of DEE to the fuel mixture reduces the density with increasing the additive ratio (see Figure 2), up to 8% in the case of DEE40.
Figure 4. Lower heating value (LHV) by mass of tested rapeseed oil and its blends with DEE.
Also, the cold filter plugging point (CFPP) is one of the main factors which characterize the biofuel application efficiency. Theoretically it is the lowest temperature used to characterize how fuel passes through a filter under cooled conditions. This is an important factor for countries with cold climate to allow avoiding clogging of filters. The measurements of the CFPP carried out in line with the EN 116:2015 standard show that the addition of DEE improves low temperature properties of RO (see Figure 5). The base value of the CFPP for RO was 28
Figure 2. Density (ρ) of rapeseed oil and DEE/RO blends tested at 15 °C.
Variation of the DEE/RO blend density impacts the LHV. As shown in Figure 3, it is visible that increasing the content of
Figure 5. Impact of DEE addition to RO on CFPP value.
°C, and it showed a dramatic reduction below −20 °C for DEE40. Also, it should be pointed out that low temperature does not promote phase separation of DEE/RO blends (see Figure S3 in the Supporting Information). The flash point can be characterized as the lowest temperature at which evaporation of fluid can form a combustible concentration. Our research demonstrates that DEE has a lower flash point compared with RO, which makes it more hazardous and flammable than RO. Figure 6 illustrates changes of flash point value based on DEE/RO ratio. As shown in Figure 6, it is visible that even 10% addition of DEE can reduce the flash point of DEE/RO blend more than 16 times. For this reason Hazardous Material Regulations (HMR) must be considered to ensure safe transport of DEE/RO blends. It should be pointed out that diesel fuels must meet necessary lubricity requirements. For this reason in our work the high frequency reciprocating rig (HFRR) test was used to characterize the lubricity of the fuel samples. In this test the load is applied as a high-frequency alternating load and the result is given as the diameter of the wear scar (WS1.4) visible under a microscope on the steel ball. This scar size is reported in micrometers. According to the EN 590 standard the scar diameter cannot excide 460 μm for tests performed at 60 °C. In
Figure 3. Lower heating value (LHV) by volume of tested RO and its blends with DEE.
DEE in RO reduces the LHV by volume. For this reason an older diesel engine equipped with a mechanically controlled fuel injection system can reach lower power and torque compared to the same engine powered with RO or with diesel oil. However, it should be pointed out that the LHV by mass of RO and DEE is almost the same (Table 3). For this reason LHV by mass of RO is not significantly changed with the addition of 10, 20, 30 or even 40% DEE (see Figure 4). It is known that the LHV of vegetable oils is nearly 90% that of diesel oil and usually increases with chain length, but fatty alcohols possess heats of combustion in the same range.27 A similar situation is observed also in the case of DEE. This property together with lower viscosity of the DEE should result in higher engine brake power. However, in this matter additional engine tests are necessary. E
DOI: 10.1021/acs.energyfuels.7b03225 Energy Fuels XXXX, XXX, XXX−XXX
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on the DEE/RO ratio. Straight vegetable oil itself contains molecular species promoting film formation increase in the wear due to unsaturated fatty acid chains; particularly linolenic and linoleic acid chains form due to polymerization of heavy polyunsaturated lipids.41,42 For this reason all tested DEE/RO blends have lubricity WS1.4 values significantly below the limit of 380 μm. As we mentioned earlier, DEE reduces the viscosity of RO. In this way DEE addition will promote a better fuel atomization process. This process is also affected by the surface tension value of the blend injected into the combustion chamber. As a general rule, a lower surface tension supports fluid breakup into smaller droplets. Figure 9 illustrates that even small addition of
Figure 6. Impact of DEE addition to RO on flash point (FP) value.
the case of the measurements carried out at 25 °C, the value of WS1.4 cannot be higher than 380 μm.40 Our work in this area demonstrates that DEE stimulates increase of the friction coefficient even by 50% in the case of DEE40 (Figure 7). A too
Figure 9. Surface tension (σ) value of DEE/RO blends.
DEE to RO can reduce the surface tension of the blend. In the case of DEE10 the surface tension value was reduced by 12% compared with RO. Moreover, our research confirms that changes of surface tension have a trend similar to that of density. Both parameters have a linear relationship and decrease with higher content of DEE in the blend. Besides that, the value of the surface tension of the oil could be affected by the length of the fatty acid hydrocarbon chain and the number of unsaturated bonds.24 Neat RO has a long fatty acid chain, which gives it a higher surface tension than that with blends with DEE. In our work corrosion properties of DEE/RO blends were also evaluated according to requirements of ASTM D130. Results (see Figure S4 in the Supporting Information) confirm that tested blends meet the requirements of Class 1 specified in the EN 590 standard. In this study the diesel engine smoke opacity was also measured in the condition of a free acceleration test according to requirements of the United Nations Economic Commission for Europe (ECE) Regulation No. 24. Results of these tests are depicted in Figure 10. Results demonstrate that the diesel engine smoke opacity varies from 34 to 77% depending on the DEE/RO ratio. The highest 55% reduction in smoke opacity was achieved for the DEE40 blend compared with RO. Such results can be justified on the basis of earlier presented physicochemical properties of DEE/RO blends. DEE addition reduces the kinematic viscosity and surface tension of RO. It impacts the quality of the fuel droplet atomization process and improves evaporation and mixing with air. Both these factors improve combustion efficiency and decrease harmful pollution emission from diesel engines. Moreover, the high cetane number of DEE should reduce the ignition delay period. In this way DEE promotes complete combustion, thereby reducing the smoke opacity.
Figure 7. Impact of DEE addition on lubrication properties (μ, friction coefficient) of RO tested at 25 °C.
large value of the friction coefficient indicates that diesel fuel can fail the lubricity evaluation. Moreover, a larger increase of the friction coefficient value would not be valuable as it can reduce the normal service life of fuel pumps and injectors. It is known that the chemical composition and physical properties of a fuel blend can affect the wear of the main components of the injection system. As shown in Figure 8, DEE addition to RO modifies the lubricity of the blend. The value of the WS1.4 parameter measured for DEE10 is increased by 26% compared with RO. In the case of DEE40 the value of WS1.4 was 2 times higher compared with neat RO. Performed measurements confirm that the trend of wear changes is progressive and based
Figure 8. Impact of DEE addition on lubrication properties (WS1.4, wear scar diameter) of RO tested at 25 °C. F
DOI: 10.1021/acs.energyfuels.7b03225 Energy Fuels XXXX, XXX, XXX−XXX
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of DEE/RO blends; technical specifications of Perkins AD3.152 diesel engine (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Krzysztof Górski: 0000-0003-0951-3147 Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. K.G. contributed 75% in the manuscript. R.S. contributed 25% in the manuscript.
Figure 10. Impact of DEE addition to RO on diesel smoke opacity (SO) measured in condition of a free acceleration test.
Notes
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The authors declare no competing financial interest.
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CONCLUSIONS A literature review suggests that DEE with its high cetane number can improve some properties of different diesel fuels such as diesel oil, fatty acid methyl esters, and their mixtures. Against this background, knowledge about the impact of DEE on properties of vegetable oil such as rapeseed oil is still insufficient. For this reason in this paper we have researched the physicochemical properties of renewable fuel blends of DEE/RO. In particular, we have demonstrated the impact of DEE blended with RO on the variation of the kinematic viscosity, density, lower heating value, cold filter plugging point, miscibility, flash point, coefficient of friction, lubricity, surface tension, and corrosion resistance. Results of our study showed that DEE is miscible with RO in all tested concentrations. We found that DEE addition improves some physicochemical properties of RO as a diesel fuel. In particular, DEE significantly reduces the kinematic viscosity and surface tension of RO, however, without an important impact on density values of these blends. The LHV of DEE/RO blends is approximately 10% lower compared with that of diesel oil. Moreover, we have demonstrated that the CFPP decreases with the higher content of DEE in mixtures with RO. In particular, the CFPPs of DEE30 and DEE40 meet the EN 590 standard requirements for Class F winter fuel. Reduced DEE content in RO is recommended for a diesel engine operating at temperatures above 0 °C. We found that excellent lubricity properties of RO are reduced by DEE addition. However, despite this the lubricities of all tested blends meet the necessary requirements described in the EN 590 standard. Unfortunately, addition of DEE reduces the flash points of the blends that are more dangerous in transportation. For this reason the safety rules in transportation of DEE/RO blends must be the same as for gasoline. Our research confirms that DEE/RO blends are not corrosive to copper. Moreover, our work proves that increasing the DEE content in tested blends significantly reduces the smoke opacity from the diesel engine.
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REFERENCES
(1) Cook, J.; Nuccitelli, D.; Green, S. A.; Richardson, M.; Winkler, B.; Painting, R.; Way, R.; Jacobs, P.; Skuce, A. Quantifying the consensus on anthropogenic global warming in the scientific literature. Environ. Res. Lett. 2013, 8 (2), 024024. (2) Anastopoulos, G.; Lois, E.; Serdari, A.; Zanikos, F.; Stournas, S.; Kalligeros, S. Lubrication properties of low-sulfur diesel fuels in the presence of specific types of fatty acid derivatives. Energy Fuels 2001, 15 (1), 106−112. (3) Knothe, G.; Steidley, K. R. Lubricity of Components of Biodiesel and Petrodiesel. The Origin of Biodiesel Lubricity. Energy Fuels 2005, 19 (3), 1192−1200. (4) Sendzikiene, E.; Makareviciene, V.; Janulis, P. Oxidation Stability of Biodiesel Fuel Produced from Fatty Wastes. Pol. J. Environ. Stud. 2005, 14 (3), 335−339. (5) Knothe, G. Some aspects of biodiesel oxidative stability. Fuel Process. Technol. 2007, 88 (7), 669−677. (6) Lu, X.; Ma, J.; Ji, L.; Huang, Z. Simultaneous reduction of NOx emission and smoke opacity of biodiesel-fueled engines by port injection of ethanol. Fuel 2008, 87 (7), 1289−1296. (7) Kowalewicz, A. Eco-diesel engine fuelled with rapeseed oil methyl ester and ethanol. Part 1: Efficiency and emission. Proc. Inst. Mech. Eng., Part D 2006, 220, 1283−1291. (8) Zaharin, M. S. M.; Abdullah, N. R.; Najafi, G.; Sharudin, H.; Yusaf, T. Effects of physicochemical properties of biodiesel fuel blends with alcohol on diesel engine performance and exhaust emissions: A review. Renewable Sustainable Energy Rev. 2017, 79, 475−493. (9) Bailey, B.; Eberhardt, J.; Goguen, S.; Erwin, J. Diethyl ether (DEE) as a renewable diesel fuel. SAE Tech. Pap. Ser. 1997, DOI: 10.4271/972978. (10) Iranmanesh, M.; Subrahmanyam, J. P.; Babu, M. K. G. Potential of diethyl ether as a blended supplementary oxygenated fuel with biodiesel to improve combustion and emission characteristics of diesel engines. SAE Tech. Pap. Ser. 2008, DOI: 10.4271/2008-01-1805. (11) Kannan, T. K.; Marappan, R. Study of performance and emission characteristics of a diesel engine using Thevetia Peruviana biodiesel with diethyl ether blends. Eur. J. Sci. Res. 2010, 43, 563−570. (12) Rakopoulos, D. C. Combustion and emissions of cottonseed oil and its bio-diesel in blends with either n-butanol or diethyl ether in HSDI diesel engine. Fuel 2013, 105, 603−613. (13) Rakopoulos, D. C.; Rakopoulos, C. D.; Giakoumis, E. G.; Dimaratos, A. M.; Kyritsis, D. C. Effects of butanol−diesel fuel blends on the performance and emissions of a high-speed DI diesel engine. Energy Convers. Manage. 2010, 51 (10), 1989−1997. (14) Orsavova, J.; Misurcova, L.; Ambrozova, J. V.; Vicha, R.; Mlcek, J. Fatty Acids Composition of Vegetable Oils and Its Contribution to Dietary Energy Intake and Dependence of Cardiovascular Mortality on Dietary Intake of Fatty Acids. Int. J. Mol. Sci. 2015, 16, 12871−12890. (15) Nath, U. K.; Kim, H.; Khatun, K.; Park, J.; Kang, K.; Nou, I. Modification of Fatty Acid Profiles of Rapeseed (Brassica napus L.)
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.7b03225. Views of tested fuel samples stored at 20 and −12 °C; Perkins AD3.152 engine test stand equipped with AVL 465 diGas analyzer; results of copper strip corrosion test G
DOI: 10.1021/acs.energyfuels.7b03225 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels Oil for Using as Food, Industrial Feed-Stock and Biodiesel. Plant Breed. Biotechnol. 2016, 4 (2), 123−134. (16) Knutsen, H. K.; Alexander, J.; Barregård, L.; Bignami, M.; et al. Erucic acid in feed and food. EFSA J. 2016, 14 (11), e04593. (17) Noureddini, H.; Teoh, B. C.; Clements, L. D. Densities of Vegetable Oils and Fatty Acids. J. Am. Oil Chem. Soc. 1992, 69 (12), 1184−1188. (18) Rabelo, J.; Batista, E.; Cavaleri, F. W.; Meirelles, A. J. A. Viscosity Prediction for Fatty Systems. J. Am. Oil Chem. Soc. 2000, 77 (12), 1255−1261. (19) Sajjadi, B.; Raman, A. A. A.; Arandiyan, H. A. Comprehensive review on properties of edible and non-edible vegetable oil-based biodiesel: Composition, specifications and prediction models. Renewable Sustainable Energy Rev. 2016, 63, 62−92. (20) Matthaus, B.; Ö zcan, M. M.; Al Juhaimi, F. Some rapeseed/ canola seed oils: fatty acid composition and tocopherols. Z. Naturforsch., C: J. Biosci. 2016, 71 (3−4), 73−77. (21) Stanciu, I. Viscosity Indices of Rapeseed Oil. J. Chem. Chem. Eng. 2012, 6, 668−671. (22) Shay, E. G. Diesel fuel from vegetable oils: status and opportunities. Biomass Bioenergy 1993, 4, 227−242. (23) Melo-Espinosa, E. A.; Sánchez-Borroto, Y.; Errasti, M.; PilotoRodríguez, R.; Sierens, R.; Roger-Riba, J.; Christopher-Hansen, A. Surface tension prediction of vegetable oils using artificial neural networks and multiple linear regression. Energy Procedia 2014, 57, 886−895. (24) Esteban, B.; Riba, J. R.; Baquero, G.; Puig, R.; Rius, A. Characterization of the surface tension of vegetable oils to be used as fuel in diesel engines. Fuel 2012, 102, 231−238. (25) Anastopoulos, G.; Zannikou, Y.; Stournas, S.; Kalligeros, S. Transesterification of Vegetable Oils with Ethanol and Characterization of the Key Fuel Properties of Ethyl Esters. Energies 2009, 2, 362−376. (26) Dukulis, I.; Birkavs, A.; Birzietis, G. Investigation of Flowability of Rapeseed Oil and Diesel Fuel Blends in Winter Conditions. Res. Pap. Lith. Univ. Agric. 2010, 42 (2−3), 204−213. (27) Knothe, G.; Van Gerpen, J.; Krahl, J. The Biodiesel Handbook; AOCS Press: 2005. (28) Graboski, M. S.; McCormick, R. L. Combustion of fat and vegetable oil derived fuels in diesel engines. Prog. Energy Combust. Sci. 1998, 24, 125−164. (29) Attenberger, A.; Remmele, E. Development of a test method for a Cetane number determination of rapeseed oil fuel. Landtechnik 2003, 58 (5), 312−313. (30) Šimácě k, P.; Kubička, D.; Šebor, G.; Pospíšil, M. Fuel properties of hydroprocessed rapeseed oil. Fuel 2010, 89 (3), 611−615. (31) Darminesh, S. P.; Sidik, N. A. C.; Najafi, G.; Mamat, R.; Ken, T. L.; Asako, Y. Recent development on biodegradable nanolubricant: a review. Int. Commun. Heat Mass Transfer 2017, 86, 159−165. (32) Kuliev, R. Sh.; Kuliev, F. A.; Mutalibova, A. A.; Kulieva, S. R. Improving the antioxidant and anticorrosion properties of vegetable oils. Chem. Technol. Fuels Oils 2006, 42, 55−59. (33) Blin, J.; Brunschwig, C.; Chapuis, A.; Changotade, O.; Sidibe, S. S.; Noumi, E. S.; Girard, P. Characteristics of vegetable oils for use as fuel in stationary diesel engines − Towards specifications for a standard in West Africa. Renewable Sustainable Energy Rev. 2013, 22, 580−597. (34) Soltic, P.; Edenhauser, D.; Thurnheer, T.; Schreiber, D.; Sankowski, A. Experimental investigation of mineral diesel fuel, GTL fuel, RME and neat soybean and rapeseed oil combustion in a heavy duty on-road engine with exhaust gas aftertreatment. Fuel 2009, 88, 1− 8. (35) Corsini, A.; Marchegiani, A.; Rispoli, F.; Sciulli, F.; Venturini, P. Vegetable oils as fuels in Diesel engine. Engine performance and emissions. Energy Procedia 2015, 81, 942−949. (36) Fassinou, W. F. Higher heating value (HHV) of vegetable oils, fats and biodiesels evaluation based on their pure fatty acids’ HHV. Energy 2012, 45, 798−805.
(37) Hong, I. K.; Lee, J. R.; Lee, S. B. Fuel properties of canola oil and lard biodiesel blends: Higher heating value, oxidative stability, and kinematic viscosity. J. Ind. Eng. Chem. 2015, 22, 335−340. (38) Codex Alimentarius Commission. Codex standard for named vegetable oils. CODEX STAN-210, 1999; www.fao.org/input/ download/standards/74/CXS_019e_2015.pdf. (39) Sivebæk, I. M.; Jacobsen, J. The lubricity of diethyl ether (DEE). Proceedings of 16th Nordic Symposium on Tribology - NORDTRIB; Danish Technological Institute: 2014; pp 41−46. (40) Lacey, P. I.; Mason, R. L. Fuel lubricity: Statistical analysis of literature data. SAE Tech. Pap. Ser. 2000, DOI: 10.4271/2000-01-1917. (41) Nettles-Anderson, S. L.; Olsen, D.B. Survey of Straight Vegetable Oil Composition Impact on Combustion Properties. SAE Tech. Pap. Ser. 2009, DOI: 10.4271/2009-01-0487. (42) Reddy, M. S.; Sharma, M. N.; Agarwal, A. K. Effect of straight vegetable oil blends and biodiesel blends on wear of mechanical fuel injection equipment of a constant speed diesel engine. Renewable Energy 2016, 99, 1008−1018.
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DOI: 10.1021/acs.energyfuels.7b03225 Energy Fuels XXXX, XXX, XXX−XXX
