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Improving the low temperature properties of biodiesel fuel
Renewable Energy 34 (2009) 794–800
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Improving the low temperature properties of biodiesel fuel Purnanand Vishwanathrao Bhale*, Nishikant V. Deshpande, Shashikant B. Thombre Visvesvaraya National Institute of Technology, Mechanical Engineering, South Ambazari Road, Near Bajaj Nagar, 440011 Nagpur, Maharashtra, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 August 2007 Accepted 11 April 2008 Available online 17 July 2008
The use of biodiesel as a diesel fuel extender and lubricity improver is rapidly increasing. While most of the properties of biodiesel are comparable to petroleum based diesel fuel, improvement of its low temperature flow characteristic still remains one of the major challenges when using biodiesel as an alternative fuel for diesel engines. The biodiesel fuels derived from fats or oils with significant amounts of saturated fatty compounds will display higher cloud points and pour points. This paper is aimed to investigate the cold flow properties of 100% biodiesel fuel obtained from Madhuca indica, one of the important species in the Indian context. In this paper, the cold flow properties of biodiesel were evaluated with and without pour point depressants towards the objectives of identifying the pumping and injecting of these biodiesel in CI engines under cold climates. Effect of ethanol, kerosene and commercial additive on cold flow behavior of this biodiesel was studied. A considerable reduction in pour point has been noticed by using these cold flow improvers. The performance and emission with ethanol blended Mahua biodiesel fuel and ethanol–diesel blended Mahua biodiesel fuel have also been studied. A considerable reduction in emission was obtained. Ethanol blended biodiesel is totally a renewable, viable alternative fuel for improved cold flow behavior and better emission characteristics without affecting the engine performance. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Madhuca indica (Mahua) biodiesel Ethanol Pour point Cloud point Viscosity Performance Emission
1. Introduction Biodiesel is defined as the monoalkyl esters of long chain fatty acids derived from renewable feed stocks like vegetable oils or animal fats. India has vast resources of non-edible, wild seeds from which oil can be derived to develop biodiesel, depending upon the potential and specific needs of the locality. The world is presently confronted with the twin crisis of fossil fuel depletion and environmental degradation. In recent years, systematic efforts were undertaken by many researchers to determine the suitability of vegetable oil and its derivatives as fuel or blend to the diesel [1–6]. This paper is aimed to investigate the cold flow properties of 100% biodiesel fuel obtained from Madhuca indica, one of the important species in the Indian context. M. indica is the botanical name of Mahua in the Indian regional language Hindi. Two major species of the genus M. indica and Madhuca longifolia are found in India [7]. It is a larger, slow growing tree found in many states of the India with wider and round canopy. It is a tree of deciduous nature of the dry tropical and subtropical climate. The tree grows on a wide variety of soils but prefers sandy soils. As a plantation tree, Mahua is an important plant having vital socio-economic value. The * Corresponding author. Tel.: þ91 7122801154; Mobile: þ91 9422182619; fax: þ91 0712 2223230. E-mail address: [email protected] (P.V. Bhale). 0960-1481/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2008.04.037
tree may attain a mean height of 9.19 m and girth 0.5 m in 30 years. The average life span of the tree is 40–50 years. Flowers are fleshy, off white in color, and emit attractive sweet fragrance when the plant is in full bloom. Flowering starts in the month of February and the seeds are obtained during June–July. The kernel of seed contains about 50% of oil. The oil yield in an expeller is nearly 38%. The fresh oil from properly stored seed is yellow in color. M. indica oil is one such tree based seed oil, which have an estimated annual production potential of 181,000 t in India [8]. Fig. 1 shows Mahua tree, fruits and seeds. While most of the properties of biodiesel are comparable to petroleum based diesel fuel, improvement of its low temperature flow characteristic still remains one of the major challenges while using biodiesel as an alternative fuel for diesel engines. The biodiesel fuels derived from fats or oils with significant amounts of saturated fatty compounds will display higher cloud points and pour points. The cloud point, which usually occurs at a higher temperature than the pour point, is the temperature at which a liquid fatty material becomes cloudy due to the formation of crystals and solidification of saturates. Crystallization of the saturated fatty acid methyl ester components of biodiesel during cold seasons causes fuel starvation and operability problems as solidified material clog fuel lines and filters. With decreasing temperature more solids form and material approaches the pour point, the lowest temperature at which it will cease to flow. It has been well established that
P.V. Bhale et al. / Renewable Energy 34 (2009) 794–800
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Fig. 1. Mahua tree, fruits and seeds.
the presence of higher amount of saturated components increases the cloud point and pour point of biodiesel [9]. A field trial conducted by one of the authors on Mahua biodiesel, i.e. Mahua Methyl Ester (MME) fueled CI engine for 200 h resulted in a considerable clogged filter. On the other hand, the diesel fueled CI engine for the same duration shows a considerably clean filter. The clogged MME fueled filter weighed 30% more than that of the diesel fueled CI engine filter after 200 h of operation. Fig. 2 shows the relative comparison of diesel and biodiesel fuel filters over a same period. C.W. Chiu [10] reported that primary solutions to minimize bulk flow and fuel filter block problems include utilization of fuel tank, fuel line and fuel filter heaters; utilization of additives (pour point depressants, anti-gel additives or cold flow improvers) that enhance the impact of crystal morphology; and blending with a fuel like kerosene which causes freezing point depression. Treatment with chemical additives is the most convenient and economical way of improving the low temperature properties of diesel fuels. This technology is also very attractive in biodiesel industries. The chemical additives are generally referred to as pour point depressants, flow improvers or wax modifiers. Most additives promote the formation of small (10–100 mm) needle shaped crystals. These crystals experience significantly reduced growth and agglomeration rates as temperature decreases below cloud point. However, the rate of nucleation is promoted and causes the formation of a large quantity of the relatively small and more compact crystals. Although most of these crystals will be caught in fuel filters, the cake layer formed on the filter surface is considerably more permeable to fuel flow. The performance and emission with ethanol blended Mahua biodiesel fuel (MME E20 and MME E10) have been studied. Apart from blending ethanol with biodiesel, it is reported that the ethanol–diesel–biodiesel fuel blends are stable well below sub-zero temperature and have equal or superior fuel properties to regular
diesel [11]. Hence emission and performance of 10% ethanol–10% diesel and 80% biodiesel were also evaluated and is referred to as MME E10 D10 in the current literature. 2. Materials and methods 2.1. Materials Pure, filtered Mahua oil was supplied by M/s Agrawal Oil Industries, Udaipur, Rajasthan, India. Biodiesel from Mahua was prepared in house using transesterification process. Single stage transesterification process was used for Mahua (M. indica). The following three cold flow improvers were selected for testing: ethanol, kerosene and an experimental pour point depressant which was developed by Lubrizol. The product is sold as Lubrizol 7671 to enhance the cold flow properties of biodiesel and blends with recommended treat levels of 1–2%. Ethanol has been chosen as a cold flow improver since it has a very low solidifying temperature of the order of ()114 C and is highly soluble in biodiesel. Properties of ethanol like density and viscosity match well with that of biodiesel. Same criteria were applicable for kerosene. 2.2. Methods Cloud point and pour point tests characterized the low temperature operability of biodiesel fuels. These measurements for Mahua Methyl Ester (MME) and its blends with ethanol and kerosene were carried out following the ASTM standards D-2500, D-97 procedures, respectively. Four concentrations of ethanol and kerosene blends, i.e. 5%, 10%, 15% and 20%, were tested with MME (Mahua biodiesel) for cold flow studies. To enhance the cold weather functionality of biodiesel fuel, the effect of commercial additive from Lubrizol (Lubrizol 7671) with the amount of 0.5%, 1%, 1.5% 2%, 2.5%, 3%, 3.5% and 4% was also studied. Since the ethanol concentration was up to 20%, its effect on performance and emission was studied. Effects of ethanol–diesel blended biodiesel (MME E10 D 10) were also studied. 2.3. ASTM D-97 pour point procedure [12]
Fig. 2. Filter clogging problem with 100% biodiesel operated engine.
The pour point is defined as the temperature at which the fuel can no longer be poured due to gel formation. The observation of the samples starts at a temperature that is at least 9 C above the expected pour point. The sample was immersed into an 18 C cooling bath. If the sample had not ceased to flow when its temperature has cooled to 6 C, the sample then transferred to 33 C cooling bath. Readings were taken for every 3 C decrease in the temperature until the sample totally ceased to flow (the sample was held in horizontal position for 5 s). Readings of the test thermometer were
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taken and 3 C was added to the temperature recorded as the result of the ASTM D-97 pour point. 2.4 ASTM D-2500 cloud point procedure [13] The cloud point is defined as the temperature at which a cloud of wax crystal first appears in a liquid when it is cooled under controlled conditions during a standard test. The same cooling procedure as described in ASTM D-97 was followed; the samples were examined at intervals of 1 C, until any cloud was observed at the bottom of the test jar. The cloud point was reported to the nearest 1 C as ASTM D-2500 cloud point. 2.5. Mixing procedure of cold flow improvers with biodiesel fuel A 40 ml mixture of biodiesel fuel and cold flow improvers was tested. For more accuracy addition of kerosene, ethanol and additive OS 110050 from Lubrizol (all are cold flow improvers) was carried out using a standard syringe. The mixture was then stirred thoroughly.
Table 1 Engine General details Bore stroke Compression ratio Capacity Rated output
Kirloskar TV1 Four stroke, CI, water cooled, single cylinder 87.5 mm 110 mm 17.5:1 661 cc 5.2 kW at 1500 rev/min
given in Table 1. AVL make 5-gas analyzer was used to measure the concentrations of gaseous emissions such as carbon monoxide, HC, NOx. A smoke meter (AVL make) is employed to measure the smoke intensity of exhaust gas emitted from diesel engine. Performance and emission parameters of MME, MME with 20% ethanol (MME E20), MME with 10% ethanol (MME E10) and MME with 10% diesel and 10% ethanol (MME E10 D 10) were obtained. The base line studies were based on diesel fuel to interpret the data for comparison. The tests were conducted at the rated speed of 1500 rpm at various loads. The BMEP was varied from 0 to 650 kPa for each blend and observations were taken.
3. Experimental set up
4. Results and discussion
3.1. Cloud and pour point set up
4.1. Biodiesel preparation and characterization
The assembly used for the cloud and pour point measurements is shown schematically in Fig. 3. The glass jar was immersed in an ice–salt bath. The glass test jar was thermally isolated from the polished brass cylinder by means of a cork support, stopper and ring assembly. The entire assembly was secured in the bath so as to isolate it from any vibration, because vibrations to the test sample may lead to low and erroneous results. Three trials were conducted for each sample to check the consistency of the results. The difference among all the three measurements was never more than 1 K.
Single stage transesterification process was carried out using KOH catalyst and methanol. In this single stage process, the methanol oil (in the ratio of 0.195–0.3 w/w) and alkali catalyst, KOH (in the ratio of 0.9–1% w/w) were pre-mixed in a flask and added to oil. The mixture was stirred and heated up to 65–70 C and then kept under stirring for another 1.5 h. The rate of stirring in the beginning was more vigorous, i.e. in the range of 650–700 rpm and it was reduced to 450–500 rpm after the mixture temperature attained 70 C. After the reaction was over the mixture was transferred into a separating flask and kept overnight for settling. The upper layer was methyl ester (biodiesel) and lower dark layer was glycerol, by-product of transesterification process. The ester layer was washed using hot water sprayed over its surface for 2–3 times till neutralization, settled overnight and discarded the bottom layer comprising of water, residual catalyst, etc. Finally,
3.2. Engine set up Table 1 shows the specifications of the engine used. A four stroke, single cylinder naturally aspirated diesel engine is employed for the present study. The detailed specifications are
Fig. 3. Cloud and pour point apparatus.
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Table 2 Measured properties of ethanol, kerosene, MME and diesel Properties
Ethanol
Kerosene
MME
Diesel
Density (kg/m3) Calorific value (MJ/kg) Kinematic viscosity (cSt) at 40 C Flash point ( C)
790 27 1.2 40
830 46 1.5 72
860 41.13 5 186
840 42.39 2.67 47.5
ester layer was dried using silica gel by dropping the ester through the silica bed. Various physical and chemical properties such as specific gravity, viscosity, flash point, pour point, calorific value, etc. were obtained. The cloud point is the highest temperature used for characterizing cold flow properties and pour point is the lowest. The properties of Mahua biodiesel have fuel characteristics very close to diesel fuel. The other significant properties in concern with cold flow behavior of biodiesel fuels (apart from cloud point and pour point) were viscosity, density, flash point and fire point. Table 2 indicates the properties of ethanol, kerosene, MME and diesel.
Fig. 5. Variation of kinematic viscosity of kerosene blended biodiesel (MME) in low temperature region.
viscosity was recorded for MME below 20 C as crystallization of the saturated fatty acid methyl ester interferes with the free flow of MME.
4.2. Kinematic viscosity 4.3. Cloud point and pour point Viscosity studies were conducted for biodiesel, ethanol blended biodiesel and kerosene blended biodiesel. The cold climate viscosity of the biodiesel is important when considering the spray characteristics of the fuel within the engine, since the change in spray can greatly alter the combustion properties of the mixture. The esterification of vegetable oils produced a marked decrease in values of viscosity measured and it was found that in general, the measured viscosities of methyl esters were little higher than the values measured for diesel over the higher range of temperatures considered. However, viscosity value of biodiesel fuel in low temperature region is different as compared to petrodiesel and is discussed in subsequent sections. Kinematic viscosity measurements were made with a Redwood viscometer. High viscosity leads to problem in pumping and spray characteristics (atomization and penetration, etc.). The inefficient mixing of oil with air contributes to incomplete combustion. Figs. 4 and 5 show the variation of kinematic viscosity in low temperature region for MME, ethanol and kerosene blended MME. It was observed that kinematic viscosity of MME was found to be 1.6 times of diesel at 40 C. However, as the temperature was decreased below 25 C there was a steep increase in viscosity. This is mainly because of the initiation of the process of crystallization of the saturated fatty acid methyl ester components of biodiesel. No
Although most of the properties of biodiesel fuels are comparable with that of diesel fuel but cloud point and pour point which indicate the cold flow behavior of a fuel are very poor. Fig. 6 shows the reduction in pour point and cloud point of MME when blended with ethanol and kerosene. A cloud point of 291 K (18 C) and pour point of 280 K (7 C) was observed for Mahua Methyl Ester. The reduction in cloud point of MME was from 291 K (18 C) to 281 K (8 C) when blended with 20% of ethanol and up to 278 K (5 C) when blended with 20% of kerosene. Similarly the reduction in pour point was from 280 K (7 C) to 269 K (4 C) when blended with 20% ethanol and up to 265 K (8 C) when blended with 20% kerosene. MME with 10% ethanol and 10% diesel reduces the pour point from 291 K (18 C) up to 268 K (5 C). Thus ethanol and kerosene improve the cold flow properties MME when blended up to 20%. However, higher blends with ethanol are to be discouraged as it may reduce the overall calorific value. Also ethanol has very low value of Cetane number. Crystal growth inhibitors for diesel fuel also known as pour point depressants are available commercially. Though they have been reported to reduce the pour point of biodiesel, these additives usually do not reduce cloud point nor improve the filterability of
Fig. 4. Variation of kinematic viscosity (cSt) of ethanol blended biodiesel (MME) in low temperature region.
Fig. 6. Effect of ethanol and kerosene on cold flow properties of Mahua Methyl Ester.
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Fig. 7. Effect of Lubrizol additive (commercial pour point depressant) on MME.
Fig. 8. Brake thermal efficiency for ethanol blended biodiesel.
biodiesel at low temperatures [14]. Fig. 7 shows the effect of Lubrizol additive on MME pour point. The MME pour point has reduced from 280 K (7 C) to 268 K (5 C) when doped with Lubrizol up to 2%.
match very well for diesel–ethanol blended biodiesel and have similar performance at part load and superior performance at full load to that of the diesel. 5.2. Emissions
4.4. Flash point and fire point Table 3 shows the measured flash point and fire point of biodiesel (methyl ester of M. indica) and its blends with ethanol and kerosene. Although the flash point and fire point of MME are very high as compared to diesel but blending of MME with ethanol or kerosene reduces the flash and fire points. High flash and fire points indicate safety of fuel storage. From Table 3 it can be concluded that higher blends of ethanol should be discouraged as the flash point and fire point reduce considerably. 5. Engine performance and emission parameters 5.1. Engine performance 5.1.1. Brake thermal efficiency The variation of brake thermal efficiency with respect to load for different fuels considered for the present analysis is presented in Fig. 8. The brake thermal efficiency of diesel was almost highest from part load to full load on the other hand MME has the lowest value. This is mainly because of higher viscosity of MME as compared to diesel. Ethanol is a low cost oxygenate with high oxygen content (approximately 35%) that has been used in biodiesel–ethanol blends. It was reported [11] that the ethanol–diesel–biodiesel fuel blends are stable well below sub-zero temperature and have equal or superior fuel properties to regular diesel fuel. Our results also
5.2.1. Carbon monoxide (CO) The emission characteristics of biodiesel and ethanol blended biodiesel are of special interest in order to meet the environmental norms. Fig. 9 shows the plot of carbon monoxide emission of Mahua biodiesel and its various blends with ethanol at the rated engine speed of 1500 rpm at various load conditions. CO emission is higher for diesel as compared to biodiesel (MME) and ethanol blended biodiesel. The no load and full load emissions were higher as compared to part load emission. The reduction in CO emission level with the addition of oxygenates (ethanol) is obvious. The average CO% reduction in 20% ethanol blended biodiesel over diesel was as high as 50%. 5.2.2. HC emission Fig. 10 compares the HC emission of various fuels used in the diesel engine. The HC emission with ethanol blended MME (Mahua biodiesel) were slightly higher than that of the MME level. However, the HC level was on to the lower side than that of the diesel. The MME HC emission on average was 12.4% lower than that of diesel. The reduction in HC emission for ethanol blended
Table 3 Flash point and fire point of biodiesel and its blends Fuel Type
Flash point ( C)
Fire point ( C)
Diesel Mahua oil MME Ethanol Kerosene MME with MME with MME with MME with MME with
60 286 175 40 72 50 52 54 90 95
65 295 186 47 77 55 57 59 97 101
20% ethanol 10% ethanol 10% ethanol and 10% diesel 20% kerosene 10% kerosene
Fig. 9. Co emission for ethanol blended biodiesel.
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Fig. 12. Smoke opacity for ethanol blended biodiesel. Fig. 10. HC emission for ethanol blended biodiesel.
biodiesel (E20 and E10) was lower than 9.15% and 5.25%, respectively. 5.2.3. NOx emission Being an oxygenated fuel, MME has higher value of NOx as compared to diesel. However, the ethanol blended biodiesel has shown low NOx emission and was lowest for MME E20 blend. This is mainly due to the very high value of latent heat of vaporization of ethanol, i.e. 838 kJ/kg as compared to 250 kJ/kg for diesel. The higher rate of latent heat causes drop in temperature which ultimately reduces NOx emission. Fig. 11 shows the variation of NOx for ethanol blended biodiesel. 5.2.4. Smoke emission The variation of smoke opacity with respect to different fuels considered is depicted in Fig. 12. It is obvious that the smoke emissions were reduced with the oxygenated fuels and were decreased most with 20% ethanol blended biodiesel. Adding oxygenates to diesel fuel had a remarkable effect on the reduction of smoke emission, especially at high load. The reduction of smoke emissions can be explained by the enrichment of oxygen content in the fuel by the addition of oxygenates (ethanol) resulting in more complete combustion.
Fig. 11. Nox emission for ethanol blended biodiesel.
5.2.5. Oxygen emission Fig. 13 shows the tail pipe O2 emission. It is clear from the figure that O2 level in case of MME E20 is the highest from no load to full load. This also supports the results obtained such as low CO and high NOx. 6. Conclusions This study experimentally analyzed the characteristics of cold flow performance, and exhaust emissions of MME and ethanol blended MME. Compared with biodiesel, important ethanol properties include low solidifying temperature, high oxygen content, low Cetane number, and low boiling point. The results may be summarized as follows. The low temperature flow properties of Mahua Methyl Ester fuel are less favorable than petroleum diesel fuel. However, blending with ethanol and kerosene has improved the cold flow performance. The effect of 2% commercial additive is similar to that of 20% ethanol blending. The reduction in cloud point of MME was from 291 K (18 C) to 281 K (8 C) when blended with 20% of ethanol and 278 K (5 C) when blended with 20% of kerosene. Similarly the reduction in pour point was from 280 K (7 C) to 269 K (4 C) when blended with 20% ethanol and up to 265 K (8 C) when blended with 20% kerosene. The improved cold flow performance of Mahua biodiesel (MME) by blending with ethanol and kerosene expands the regions where it is usable.
Fig. 13. Oxygen emission for ethanol blended biodiesel.
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A 20 vol% ethanol blending into MME achieves improved combustion with reduction in CO by almost 50% on an average without affecting the thermal efficiency. The NOx emission level is highest for MME. However, with 20% (by vol) ethanol blended MME it is the lowest. This is mainly because of the high latent heat of ethanol which reduces the overall combustion temperature, one of the key parameter for NOx formation. Smoke emissions from diesel combustion of the MME/ethanol blended fuel decrease strongly with increasing percentage of ethanol in MME. The smoke reduction can be attributed to an improved fuel–air mixing by an increased ignition delay due to the lowered Cetane number as a result of the ethanol addition and also to an increase in the oxygen content in the blended fuel. The quite low boiling point of ethanol also promotes the atomization of the fuel spray and reduces soot by a flash boiling effect. Ethanol blended biodiesel is totally a renewable, viable alternative fuel for improved cold flow behavior and better emission characteristics without affecting the engine performance. Acknowledgement The authors wish to thank Institution of Engineers (India) for providing funds to carry out this work. Assistance of Mr. V.C. Bhujade, oil engine mechanic is gratefully acknowledged.
References [1] Agarwal AK, Das LM. Biodiesel development and characterization for use as a fuel in compression ignition engines. J Eng Gas Turbine Power 2001;123. [2] Agarwal Deepak, Agarwal Avinash Kumar. Performance and emission characteristics of Jatropha oil (preheated and blends) in direct injection, compression ignition engine. Appl Therm Eng 2007;27. [3] Ramdhas AS, Muraleedharan C. Performance and emission evaluation of a diesel engine fueled with methyl esters of rubber seed oils. Renew Energy 2005;30. [4] Meher LC, Vidya Sagar D. Technical aspects of biodiesel production by transesterification – a review. Renew Sustain Energy Rev 2000;10. [5] Kalam MA, Masjuki HH. Biodiesel from palm oil – an analysis of its properties and potential. Biomass Bioenergy 2002;23. [6] Barnwall BK, Sharma MP. Prospects of biodiesel production from vegetable oils in India. Renew Sustain Energy Rev 2005;9. [7] Bhatt YC, Murthy NS, Datta RK. Use of mahua oil (Madhuca indica) as a diesel fuel extender. J Inst Eng (India): Agri Eng 2004;85:10–4. [8] Ghadge Shashikant Vilas, Raheman Hifjur. Biodiesel production from Mahua (Madhuca indica) oil having high free fatty acids. Biomass Bioenergy 2005;28: 601–5. [9] Knothe Gerhard. Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters. Fuel Proc Technol 2005;86:1059–70. [10] Chiu CW, Schumacher Leon G. Impact of cold flow improvers on soybean biodiesel blend. Biomass Bioenergy 2004;27. [11] Shi Xiaoyan, Pang Xiaobing. Emission reduction potential of using ethanol– biodiesel–biodiesel–diesel fuel blend on a heavy duty diesel engine. Atmos Environ 2006;40. [12] ASTM standards: ASTM D97. Philadelphia: American Society for Testing Materials; 1991. p. 85. [13] ASTM standards: ASTM D 2500. Philadelphia: American Society for Testing Materials; 1991. p. 268–70. [14] Yori Juan C, Miguel A. Depression of the cloud point of biodiesel by reaction over solid acids. Energy Fuel 2006;20.
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Improving the low temperature properties of biodiesel fuel Purnanand Vishwanathrao Bhale*, Nishikant V. Deshpande, Shashikant B. Thombre Visvesvaraya National Institute of Technology, Mechanical Engineering, South Ambazari Road, Near Bajaj Nagar, 440011 Nagpur, Maharashtra, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 August 2007 Accepted 11 April 2008 Available online 17 July 2008
The use of biodiesel as a diesel fuel extender and lubricity improver is rapidly increasing. While most of the properties of biodiesel are comparable to petroleum based diesel fuel, improvement of its low temperature flow characteristic still remains one of the major challenges when using biodiesel as an alternative fuel for diesel engines. The biodiesel fuels derived from fats or oils with significant amounts of saturated fatty compounds will display higher cloud points and pour points. This paper is aimed to investigate the cold flow properties of 100% biodiesel fuel obtained from Madhuca indica, one of the important species in the Indian context. In this paper, the cold flow properties of biodiesel were evaluated with and without pour point depressants towards the objectives of identifying the pumping and injecting of these biodiesel in CI engines under cold climates. Effect of ethanol, kerosene and commercial additive on cold flow behavior of this biodiesel was studied. A considerable reduction in pour point has been noticed by using these cold flow improvers. The performance and emission with ethanol blended Mahua biodiesel fuel and ethanol–diesel blended Mahua biodiesel fuel have also been studied. A considerable reduction in emission was obtained. Ethanol blended biodiesel is totally a renewable, viable alternative fuel for improved cold flow behavior and better emission characteristics without affecting the engine performance. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Madhuca indica (Mahua) biodiesel Ethanol Pour point Cloud point Viscosity Performance Emission
1. Introduction Biodiesel is defined as the monoalkyl esters of long chain fatty acids derived from renewable feed stocks like vegetable oils or animal fats. India has vast resources of non-edible, wild seeds from which oil can be derived to develop biodiesel, depending upon the potential and specific needs of the locality. The world is presently confronted with the twin crisis of fossil fuel depletion and environmental degradation. In recent years, systematic efforts were undertaken by many researchers to determine the suitability of vegetable oil and its derivatives as fuel or blend to the diesel [1–6]. This paper is aimed to investigate the cold flow properties of 100% biodiesel fuel obtained from Madhuca indica, one of the important species in the Indian context. M. indica is the botanical name of Mahua in the Indian regional language Hindi. Two major species of the genus M. indica and Madhuca longifolia are found in India [7]. It is a larger, slow growing tree found in many states of the India with wider and round canopy. It is a tree of deciduous nature of the dry tropical and subtropical climate. The tree grows on a wide variety of soils but prefers sandy soils. As a plantation tree, Mahua is an important plant having vital socio-economic value. The * Corresponding author. Tel.: þ91 7122801154; Mobile: þ91 9422182619; fax: þ91 0712 2223230. E-mail address: [email protected] (P.V. Bhale). 0960-1481/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2008.04.037
tree may attain a mean height of 9.19 m and girth 0.5 m in 30 years. The average life span of the tree is 40–50 years. Flowers are fleshy, off white in color, and emit attractive sweet fragrance when the plant is in full bloom. Flowering starts in the month of February and the seeds are obtained during June–July. The kernel of seed contains about 50% of oil. The oil yield in an expeller is nearly 38%. The fresh oil from properly stored seed is yellow in color. M. indica oil is one such tree based seed oil, which have an estimated annual production potential of 181,000 t in India [8]. Fig. 1 shows Mahua tree, fruits and seeds. While most of the properties of biodiesel are comparable to petroleum based diesel fuel, improvement of its low temperature flow characteristic still remains one of the major challenges while using biodiesel as an alternative fuel for diesel engines. The biodiesel fuels derived from fats or oils with significant amounts of saturated fatty compounds will display higher cloud points and pour points. The cloud point, which usually occurs at a higher temperature than the pour point, is the temperature at which a liquid fatty material becomes cloudy due to the formation of crystals and solidification of saturates. Crystallization of the saturated fatty acid methyl ester components of biodiesel during cold seasons causes fuel starvation and operability problems as solidified material clog fuel lines and filters. With decreasing temperature more solids form and material approaches the pour point, the lowest temperature at which it will cease to flow. It has been well established that
P.V. Bhale et al. / Renewable Energy 34 (2009) 794–800
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Fig. 1. Mahua tree, fruits and seeds.
the presence of higher amount of saturated components increases the cloud point and pour point of biodiesel [9]. A field trial conducted by one of the authors on Mahua biodiesel, i.e. Mahua Methyl Ester (MME) fueled CI engine for 200 h resulted in a considerable clogged filter. On the other hand, the diesel fueled CI engine for the same duration shows a considerably clean filter. The clogged MME fueled filter weighed 30% more than that of the diesel fueled CI engine filter after 200 h of operation. Fig. 2 shows the relative comparison of diesel and biodiesel fuel filters over a same period. C.W. Chiu [10] reported that primary solutions to minimize bulk flow and fuel filter block problems include utilization of fuel tank, fuel line and fuel filter heaters; utilization of additives (pour point depressants, anti-gel additives or cold flow improvers) that enhance the impact of crystal morphology; and blending with a fuel like kerosene which causes freezing point depression. Treatment with chemical additives is the most convenient and economical way of improving the low temperature properties of diesel fuels. This technology is also very attractive in biodiesel industries. The chemical additives are generally referred to as pour point depressants, flow improvers or wax modifiers. Most additives promote the formation of small (10–100 mm) needle shaped crystals. These crystals experience significantly reduced growth and agglomeration rates as temperature decreases below cloud point. However, the rate of nucleation is promoted and causes the formation of a large quantity of the relatively small and more compact crystals. Although most of these crystals will be caught in fuel filters, the cake layer formed on the filter surface is considerably more permeable to fuel flow. The performance and emission with ethanol blended Mahua biodiesel fuel (MME E20 and MME E10) have been studied. Apart from blending ethanol with biodiesel, it is reported that the ethanol–diesel–biodiesel fuel blends are stable well below sub-zero temperature and have equal or superior fuel properties to regular
diesel [11]. Hence emission and performance of 10% ethanol–10% diesel and 80% biodiesel were also evaluated and is referred to as MME E10 D10 in the current literature. 2. Materials and methods 2.1. Materials Pure, filtered Mahua oil was supplied by M/s Agrawal Oil Industries, Udaipur, Rajasthan, India. Biodiesel from Mahua was prepared in house using transesterification process. Single stage transesterification process was used for Mahua (M. indica). The following three cold flow improvers were selected for testing: ethanol, kerosene and an experimental pour point depressant which was developed by Lubrizol. The product is sold as Lubrizol 7671 to enhance the cold flow properties of biodiesel and blends with recommended treat levels of 1–2%. Ethanol has been chosen as a cold flow improver since it has a very low solidifying temperature of the order of ()114 C and is highly soluble in biodiesel. Properties of ethanol like density and viscosity match well with that of biodiesel. Same criteria were applicable for kerosene. 2.2. Methods Cloud point and pour point tests characterized the low temperature operability of biodiesel fuels. These measurements for Mahua Methyl Ester (MME) and its blends with ethanol and kerosene were carried out following the ASTM standards D-2500, D-97 procedures, respectively. Four concentrations of ethanol and kerosene blends, i.e. 5%, 10%, 15% and 20%, were tested with MME (Mahua biodiesel) for cold flow studies. To enhance the cold weather functionality of biodiesel fuel, the effect of commercial additive from Lubrizol (Lubrizol 7671) with the amount of 0.5%, 1%, 1.5% 2%, 2.5%, 3%, 3.5% and 4% was also studied. Since the ethanol concentration was up to 20%, its effect on performance and emission was studied. Effects of ethanol–diesel blended biodiesel (MME E10 D 10) were also studied. 2.3. ASTM D-97 pour point procedure [12]
Fig. 2. Filter clogging problem with 100% biodiesel operated engine.
The pour point is defined as the temperature at which the fuel can no longer be poured due to gel formation. The observation of the samples starts at a temperature that is at least 9 C above the expected pour point. The sample was immersed into an 18 C cooling bath. If the sample had not ceased to flow when its temperature has cooled to 6 C, the sample then transferred to 33 C cooling bath. Readings were taken for every 3 C decrease in the temperature until the sample totally ceased to flow (the sample was held in horizontal position for 5 s). Readings of the test thermometer were
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taken and 3 C was added to the temperature recorded as the result of the ASTM D-97 pour point. 2.4 ASTM D-2500 cloud point procedure [13] The cloud point is defined as the temperature at which a cloud of wax crystal first appears in a liquid when it is cooled under controlled conditions during a standard test. The same cooling procedure as described in ASTM D-97 was followed; the samples were examined at intervals of 1 C, until any cloud was observed at the bottom of the test jar. The cloud point was reported to the nearest 1 C as ASTM D-2500 cloud point. 2.5. Mixing procedure of cold flow improvers with biodiesel fuel A 40 ml mixture of biodiesel fuel and cold flow improvers was tested. For more accuracy addition of kerosene, ethanol and additive OS 110050 from Lubrizol (all are cold flow improvers) was carried out using a standard syringe. The mixture was then stirred thoroughly.
Table 1 Engine General details Bore stroke Compression ratio Capacity Rated output
Kirloskar TV1 Four stroke, CI, water cooled, single cylinder 87.5 mm 110 mm 17.5:1 661 cc 5.2 kW at 1500 rev/min
given in Table 1. AVL make 5-gas analyzer was used to measure the concentrations of gaseous emissions such as carbon monoxide, HC, NOx. A smoke meter (AVL make) is employed to measure the smoke intensity of exhaust gas emitted from diesel engine. Performance and emission parameters of MME, MME with 20% ethanol (MME E20), MME with 10% ethanol (MME E10) and MME with 10% diesel and 10% ethanol (MME E10 D 10) were obtained. The base line studies were based on diesel fuel to interpret the data for comparison. The tests were conducted at the rated speed of 1500 rpm at various loads. The BMEP was varied from 0 to 650 kPa for each blend and observations were taken.
3. Experimental set up
4. Results and discussion
3.1. Cloud and pour point set up
4.1. Biodiesel preparation and characterization
The assembly used for the cloud and pour point measurements is shown schematically in Fig. 3. The glass jar was immersed in an ice–salt bath. The glass test jar was thermally isolated from the polished brass cylinder by means of a cork support, stopper and ring assembly. The entire assembly was secured in the bath so as to isolate it from any vibration, because vibrations to the test sample may lead to low and erroneous results. Three trials were conducted for each sample to check the consistency of the results. The difference among all the three measurements was never more than 1 K.
Single stage transesterification process was carried out using KOH catalyst and methanol. In this single stage process, the methanol oil (in the ratio of 0.195–0.3 w/w) and alkali catalyst, KOH (in the ratio of 0.9–1% w/w) were pre-mixed in a flask and added to oil. The mixture was stirred and heated up to 65–70 C and then kept under stirring for another 1.5 h. The rate of stirring in the beginning was more vigorous, i.e. in the range of 650–700 rpm and it was reduced to 450–500 rpm after the mixture temperature attained 70 C. After the reaction was over the mixture was transferred into a separating flask and kept overnight for settling. The upper layer was methyl ester (biodiesel) and lower dark layer was glycerol, by-product of transesterification process. The ester layer was washed using hot water sprayed over its surface for 2–3 times till neutralization, settled overnight and discarded the bottom layer comprising of water, residual catalyst, etc. Finally,
3.2. Engine set up Table 1 shows the specifications of the engine used. A four stroke, single cylinder naturally aspirated diesel engine is employed for the present study. The detailed specifications are
Fig. 3. Cloud and pour point apparatus.
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Table 2 Measured properties of ethanol, kerosene, MME and diesel Properties
Ethanol
Kerosene
MME
Diesel
Density (kg/m3) Calorific value (MJ/kg) Kinematic viscosity (cSt) at 40 C Flash point ( C)
790 27 1.2 40
830 46 1.5 72
860 41.13 5 186
840 42.39 2.67 47.5
ester layer was dried using silica gel by dropping the ester through the silica bed. Various physical and chemical properties such as specific gravity, viscosity, flash point, pour point, calorific value, etc. were obtained. The cloud point is the highest temperature used for characterizing cold flow properties and pour point is the lowest. The properties of Mahua biodiesel have fuel characteristics very close to diesel fuel. The other significant properties in concern with cold flow behavior of biodiesel fuels (apart from cloud point and pour point) were viscosity, density, flash point and fire point. Table 2 indicates the properties of ethanol, kerosene, MME and diesel.
Fig. 5. Variation of kinematic viscosity of kerosene blended biodiesel (MME) in low temperature region.
viscosity was recorded for MME below 20 C as crystallization of the saturated fatty acid methyl ester interferes with the free flow of MME.
4.2. Kinematic viscosity 4.3. Cloud point and pour point Viscosity studies were conducted for biodiesel, ethanol blended biodiesel and kerosene blended biodiesel. The cold climate viscosity of the biodiesel is important when considering the spray characteristics of the fuel within the engine, since the change in spray can greatly alter the combustion properties of the mixture. The esterification of vegetable oils produced a marked decrease in values of viscosity measured and it was found that in general, the measured viscosities of methyl esters were little higher than the values measured for diesel over the higher range of temperatures considered. However, viscosity value of biodiesel fuel in low temperature region is different as compared to petrodiesel and is discussed in subsequent sections. Kinematic viscosity measurements were made with a Redwood viscometer. High viscosity leads to problem in pumping and spray characteristics (atomization and penetration, etc.). The inefficient mixing of oil with air contributes to incomplete combustion. Figs. 4 and 5 show the variation of kinematic viscosity in low temperature region for MME, ethanol and kerosene blended MME. It was observed that kinematic viscosity of MME was found to be 1.6 times of diesel at 40 C. However, as the temperature was decreased below 25 C there was a steep increase in viscosity. This is mainly because of the initiation of the process of crystallization of the saturated fatty acid methyl ester components of biodiesel. No
Although most of the properties of biodiesel fuels are comparable with that of diesel fuel but cloud point and pour point which indicate the cold flow behavior of a fuel are very poor. Fig. 6 shows the reduction in pour point and cloud point of MME when blended with ethanol and kerosene. A cloud point of 291 K (18 C) and pour point of 280 K (7 C) was observed for Mahua Methyl Ester. The reduction in cloud point of MME was from 291 K (18 C) to 281 K (8 C) when blended with 20% of ethanol and up to 278 K (5 C) when blended with 20% of kerosene. Similarly the reduction in pour point was from 280 K (7 C) to 269 K (4 C) when blended with 20% ethanol and up to 265 K (8 C) when blended with 20% kerosene. MME with 10% ethanol and 10% diesel reduces the pour point from 291 K (18 C) up to 268 K (5 C). Thus ethanol and kerosene improve the cold flow properties MME when blended up to 20%. However, higher blends with ethanol are to be discouraged as it may reduce the overall calorific value. Also ethanol has very low value of Cetane number. Crystal growth inhibitors for diesel fuel also known as pour point depressants are available commercially. Though they have been reported to reduce the pour point of biodiesel, these additives usually do not reduce cloud point nor improve the filterability of
Fig. 4. Variation of kinematic viscosity (cSt) of ethanol blended biodiesel (MME) in low temperature region.
Fig. 6. Effect of ethanol and kerosene on cold flow properties of Mahua Methyl Ester.
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Fig. 7. Effect of Lubrizol additive (commercial pour point depressant) on MME.
Fig. 8. Brake thermal efficiency for ethanol blended biodiesel.
biodiesel at low temperatures [14]. Fig. 7 shows the effect of Lubrizol additive on MME pour point. The MME pour point has reduced from 280 K (7 C) to 268 K (5 C) when doped with Lubrizol up to 2%.
match very well for diesel–ethanol blended biodiesel and have similar performance at part load and superior performance at full load to that of the diesel. 5.2. Emissions
4.4. Flash point and fire point Table 3 shows the measured flash point and fire point of biodiesel (methyl ester of M. indica) and its blends with ethanol and kerosene. Although the flash point and fire point of MME are very high as compared to diesel but blending of MME with ethanol or kerosene reduces the flash and fire points. High flash and fire points indicate safety of fuel storage. From Table 3 it can be concluded that higher blends of ethanol should be discouraged as the flash point and fire point reduce considerably. 5. Engine performance and emission parameters 5.1. Engine performance 5.1.1. Brake thermal efficiency The variation of brake thermal efficiency with respect to load for different fuels considered for the present analysis is presented in Fig. 8. The brake thermal efficiency of diesel was almost highest from part load to full load on the other hand MME has the lowest value. This is mainly because of higher viscosity of MME as compared to diesel. Ethanol is a low cost oxygenate with high oxygen content (approximately 35%) that has been used in biodiesel–ethanol blends. It was reported [11] that the ethanol–diesel–biodiesel fuel blends are stable well below sub-zero temperature and have equal or superior fuel properties to regular diesel fuel. Our results also
5.2.1. Carbon monoxide (CO) The emission characteristics of biodiesel and ethanol blended biodiesel are of special interest in order to meet the environmental norms. Fig. 9 shows the plot of carbon monoxide emission of Mahua biodiesel and its various blends with ethanol at the rated engine speed of 1500 rpm at various load conditions. CO emission is higher for diesel as compared to biodiesel (MME) and ethanol blended biodiesel. The no load and full load emissions were higher as compared to part load emission. The reduction in CO emission level with the addition of oxygenates (ethanol) is obvious. The average CO% reduction in 20% ethanol blended biodiesel over diesel was as high as 50%. 5.2.2. HC emission Fig. 10 compares the HC emission of various fuels used in the diesel engine. The HC emission with ethanol blended MME (Mahua biodiesel) were slightly higher than that of the MME level. However, the HC level was on to the lower side than that of the diesel. The MME HC emission on average was 12.4% lower than that of diesel. The reduction in HC emission for ethanol blended
Table 3 Flash point and fire point of biodiesel and its blends Fuel Type
Flash point ( C)
Fire point ( C)
Diesel Mahua oil MME Ethanol Kerosene MME with MME with MME with MME with MME with
60 286 175 40 72 50 52 54 90 95
65 295 186 47 77 55 57 59 97 101
20% ethanol 10% ethanol 10% ethanol and 10% diesel 20% kerosene 10% kerosene
Fig. 9. Co emission for ethanol blended biodiesel.
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Fig. 12. Smoke opacity for ethanol blended biodiesel. Fig. 10. HC emission for ethanol blended biodiesel.
biodiesel (E20 and E10) was lower than 9.15% and 5.25%, respectively. 5.2.3. NOx emission Being an oxygenated fuel, MME has higher value of NOx as compared to diesel. However, the ethanol blended biodiesel has shown low NOx emission and was lowest for MME E20 blend. This is mainly due to the very high value of latent heat of vaporization of ethanol, i.e. 838 kJ/kg as compared to 250 kJ/kg for diesel. The higher rate of latent heat causes drop in temperature which ultimately reduces NOx emission. Fig. 11 shows the variation of NOx for ethanol blended biodiesel. 5.2.4. Smoke emission The variation of smoke opacity with respect to different fuels considered is depicted in Fig. 12. It is obvious that the smoke emissions were reduced with the oxygenated fuels and were decreased most with 20% ethanol blended biodiesel. Adding oxygenates to diesel fuel had a remarkable effect on the reduction of smoke emission, especially at high load. The reduction of smoke emissions can be explained by the enrichment of oxygen content in the fuel by the addition of oxygenates (ethanol) resulting in more complete combustion.
Fig. 11. Nox emission for ethanol blended biodiesel.
5.2.5. Oxygen emission Fig. 13 shows the tail pipe O2 emission. It is clear from the figure that O2 level in case of MME E20 is the highest from no load to full load. This also supports the results obtained such as low CO and high NOx. 6. Conclusions This study experimentally analyzed the characteristics of cold flow performance, and exhaust emissions of MME and ethanol blended MME. Compared with biodiesel, important ethanol properties include low solidifying temperature, high oxygen content, low Cetane number, and low boiling point. The results may be summarized as follows. The low temperature flow properties of Mahua Methyl Ester fuel are less favorable than petroleum diesel fuel. However, blending with ethanol and kerosene has improved the cold flow performance. The effect of 2% commercial additive is similar to that of 20% ethanol blending. The reduction in cloud point of MME was from 291 K (18 C) to 281 K (8 C) when blended with 20% of ethanol and 278 K (5 C) when blended with 20% of kerosene. Similarly the reduction in pour point was from 280 K (7 C) to 269 K (4 C) when blended with 20% ethanol and up to 265 K (8 C) when blended with 20% kerosene. The improved cold flow performance of Mahua biodiesel (MME) by blending with ethanol and kerosene expands the regions where it is usable.
Fig. 13. Oxygen emission for ethanol blended biodiesel.
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A 20 vol% ethanol blending into MME achieves improved combustion with reduction in CO by almost 50% on an average without affecting the thermal efficiency. The NOx emission level is highest for MME. However, with 20% (by vol) ethanol blended MME it is the lowest. This is mainly because of the high latent heat of ethanol which reduces the overall combustion temperature, one of the key parameter for NOx formation. Smoke emissions from diesel combustion of the MME/ethanol blended fuel decrease strongly with increasing percentage of ethanol in MME. The smoke reduction can be attributed to an improved fuel–air mixing by an increased ignition delay due to the lowered Cetane number as a result of the ethanol addition and also to an increase in the oxygen content in the blended fuel. The quite low boiling point of ethanol also promotes the atomization of the fuel spray and reduces soot by a flash boiling effect. Ethanol blended biodiesel is totally a renewable, viable alternative fuel for improved cold flow behavior and better emission characteristics without affecting the engine performance. Acknowledgement The authors wish to thank Institution of Engineers (India) for providing funds to carry out this work. Assistance of Mr. V.C. Bhujade, oil engine mechanic is gratefully acknowledged.
References [1] Agarwal AK, Das LM. Biodiesel development and characterization for use as a fuel in compression ignition engines. J Eng Gas Turbine Power 2001;123. [2] Agarwal Deepak, Agarwal Avinash Kumar. Performance and emission characteristics of Jatropha oil (preheated and blends) in direct injection, compression ignition engine. Appl Therm Eng 2007;27. [3] Ramdhas AS, Muraleedharan C. Performance and emission evaluation of a diesel engine fueled with methyl esters of rubber seed oils. Renew Energy 2005;30. [4] Meher LC, Vidya Sagar D. Technical aspects of biodiesel production by transesterification – a review. Renew Sustain Energy Rev 2000;10. [5] Kalam MA, Masjuki HH. Biodiesel from palm oil – an analysis of its properties and potential. Biomass Bioenergy 2002;23. [6] Barnwall BK, Sharma MP. Prospects of biodiesel production from vegetable oils in India. Renew Sustain Energy Rev 2005;9. [7] Bhatt YC, Murthy NS, Datta RK. Use of mahua oil (Madhuca indica) as a diesel fuel extender. J Inst Eng (India): Agri Eng 2004;85:10–4. [8] Ghadge Shashikant Vilas, Raheman Hifjur. Biodiesel production from Mahua (Madhuca indica) oil having high free fatty acids. Biomass Bioenergy 2005;28: 601–5. [9] Knothe Gerhard. Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters. Fuel Proc Technol 2005;86:1059–70. [10] Chiu CW, Schumacher Leon G. Impact of cold flow improvers on soybean biodiesel blend. Biomass Bioenergy 2004;27. [11] Shi Xiaoyan, Pang Xiaobing. Emission reduction potential of using ethanol– biodiesel–biodiesel–diesel fuel blend on a heavy duty diesel engine. Atmos Environ 2006;40. [12] ASTM standards: ASTM D97. Philadelphia: American Society for Testing Materials; 1991. p. 85. [13] ASTM standards: ASTM D 2500. Philadelphia: American Society for Testing Materials; 1991. p. 268–70. [14] Yori Juan C, Miguel A. Depression of the cloud point of biodiesel by reaction over solid acids. Energy Fuel 2006;20.