Testing Waste Olive Oil Methyl Ester as a Fuel in a Diesel Engine

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Energy & Fuels 2003, 17, 1560-1565

Testing Waste Olive Oil Methyl Ester as a Fuel in a Diesel Engine M. P. Dorado,*,† E. Ballesteros,‡ J. M. Arnal,§ J. Go´mez,§ and F. J. Lo´pez Gime´nez# Department of Mechanics and Mining and Department of Physical and Analytical Chemistry, EUP de Linares, University of Jae´ n, C/. Alfonso X el Sabio 28, 23700 Linares (Jae´ n), Spain, Department of Mechanization, CIFA “Alameda del Obispo”, Junta de Andalucı´a, Apdo. 3092, 14080 Co´ rdoba, Spain, and Department of Agricultural Engineering, ETSIAM, University of Co´ rdoba, Avda. Mene´ ndez Pidal s/n, 14080 Co´ rdoba, Spain Received October 27, 2002. Revised Manuscript Received August 25, 2003

The importance of the recycling of vegetable oils that have been used for frying has led the scientific community to provide viable options; among them is the transesterification in biodiesel. Biodiesel is one of the most popular and accepted diesel-fuel alternatives. In this sense, to gain knowledge about the implications of its use, waste olive oil methyl ester was evaluated as a fuel for diesel engines during a 50-h short-term performance test in a diesel direct-injection Perkins engine. Engine-performance tests indicated a slight power loss and brake-specific fuel consumption increase, although statistical analysis showed no significant differences between biodiesel and No. 2 diesel fuel (EN 590) tests. In this sense, energy conversion efficiency remained constant or showed a slight increase when waste olive oil methyl ester was used instead of No. 2 diesel fuel. Carbon deposits and wear seemed normal. During the test, no difficulties were experienced, in regard to engine starting, and the engine performed satisfactorily on the biodiesel throughout the entire test. On the basis of this study, waste olive oil methyl ester can be considered as a fuel candidate, thus providing an interesting alternative for the recycling of used frying oil, which is essentially a waste product. Biodiesel from used olive oil can be recommended as a diesel-fuel alternative if long-term diesel-engine tests provide satisfactory results.

Introduction At the beginning of the last century, Rudolph Diesel fueled a diesel engine with the oil of an African groundnut (peanut), thus demonstrating the idea of using vegetable oil as a substitute for No. 2 diesel fuel. Since that time, several approaches have been described concerning the use of neat, blended, or modified vegetable oils as No. 2 diesel fuel. Among them, the transesterification of vegetable oils seems to be the more attractive alternative, because it provides a fuel with chemical properties that are similar to those of No. 2 diesel fuel. Otherwise, the use of neat vegetable oils or their blends with No. 2 diesel fuel supplies a fuel with high viscosity and high molecular weight, which cause poor fuel atomization (leading to incomplete combustion) and low volatility, respectively.1 * Author to whom correspondence should be addressed. E-mail: [email protected]. † Department of Mechanics and Mining, EUP de Linares, University of Jae´n. ‡ Department of Physical and Analytical Chemistry, EUP de Linares, University of Jae´n. § Department of Mechanization, CIFA ‘Alameda del Obispo’, Junta de Andalucı´a. # Department of Agricultural Engineering, ETSIAM, University of Co´rdoba. (1) Bagby, M. O. Vegetable Oils for Diesel Fuel: Opportunities for Development. Presented at the 1987 International Winter Meeting of the American Society of Agricultural Engineers, Chicago, IL, Dec. 1518, 1987; ASAE Paper No. 87-1588.

Short- and long-term performance tests in diesel engines using biodiesel (ethyl or methyl esters from vegetable oils such as soybean oil, rapeseed oil, sunflower oil, etc.) reveal an increase in volumetric brakespecific fuel consumption, because of the lower volumetric calorific value. Power and torque differ lightly or remain constant, whereas smoke emissions of biodiesel are much lower, compared to No. 2 diesel fuel.2-7 To improve combustion and decrease exhaust emissions, several researchers have recommended blending biodiesel with No. 2 diesel fuel in different percentages.8-13 Moreover, some researchers have found that biodiesel (2) Pischinger, G.; Siekmann, R. W.; Falcon, A. M.; Fernandes, F. R. Results of Engine and Vehicle Tests with Methyl Esters of Plant Oils as Alternative Diesel Fuels. Presented at the International First Symposium on Alcohol Fuel Technology, Auckland, New Zealand, 1982; pp 1-9. (3) Kaufman, K. R.; Ziejewski, M. Trans. ASAE 1984, 1626-1633. (4) Einfalt, J.; Goering, C. E. Trans. ASAE 1985, 70-74. (5) De Zanche, C.; Friso, D.; Belli, A.; Baldoin, C. Trials of the Performance of an Agricultural Tractor Fueled by Biodiesel. Presented at AgEnd ‘96, Madrid, Spain, 1996; pp 1-7. (6) Peterson, C. L.; Reece, D. On-Road Testing of BiodieselsA Report of Past Research Activities; Department of Agricultural Engineering, University of Idaho: Moscow, ID, 1997. (Available via the Internet at http://biodiesel.ag.uidaho.edu/research/past_research.html.) (7) Wo¨rgetter, M. Pilot Project “Biodiesel”. Presented at the 7th European Conference on Biomass for Energy and Environment, Florence, Italy, 1992; pp 1-7. (8) Sims, R. E. H. Trans. ASAE 1985, 28, 716-721. (9) Staat, F.; Vallet, E. Chem. Ind. 1994, 7, 863-865. (10) Ali, Y.; Hanna, M. A.; Borg, J. E. Trans. ASAE 1996, 39, 799804.

10.1021/ef0202485 CCC: $25.00 © 2003 American Chemical Society Published on Web 10/02/2003

Waste Olive Oil Methyl Ester as a Diesel Fuel

has higher cloud and pour points than does No. 2 diesel fuel and, hence, may experience some difficulty with engine starting in cold weather.3,14 Also, one must not to forget the importance of the recycling of waste vegetable oils that have been obtained from restaurants, hospitals, and household fryers, which otherwise contribute to environmental damage. In fact, only a very small percentage of the used frying oils has been processed into soap; most of it is usually a disposal problem. In Spain, the consumption of edible vegetable oil totals ∼6 × 108 L per year. Most (70%) of this oil is olive oil and is primarily used for deep-frying processes.15 According to the INE (Spanish National Institute of Statistics), ∼7.4 × 107 L of waste olive oil is collected per year, which is an approximate value because most household waste frying oil is discarded through the drainage. The advantage of the used frying oil is that it can be used as a very cheap and useful alternative fuel source. In this sense, in 2001, the consumption of No. 2 diesel fuel in Spain was ∼2.4 × 1010 L. There are only a few biodiesel plants in the world that are dedicated to processing only recycling oils. The usual model is to establish a multi-feedstock plant, which can process any feedstock of virgin or recycled oil and fat of vegetable and animal origin. Such plants exist mainly in the United States, Germany, France, and Austria. Currently, in Austria, biodiesel plants can be found in Bruck (total capacity is 2.5 × 104 t, processing topdegummed rapeseed oil plus an ∼10% share of recycling oils), Mureck (total capacity is 6 × 103 t, processing warm-pressed rapeseed oil and recycling oils up to ∼60%, depending on supply), and Arnoldstein (still under construction, with startup projected by the end of 2003; total capacity will be 2.5 × 104 t, to be expanded to 5 × 104 t in 2006, processing mainly recycling oils and fats), as reported by the Austrian Biofuels Institute. In the year 2000, France produced >2.5 × 105 t of biodiesel, whereas Germany exceeded 2.3 × 105 t of biodiesel. Today, forecasts for the year 2003 show an overall biodiesel capacity of more than 1 × 106 t per year in Germany. By comparison, the production capacity from dedicated biodiesel plants operating in the United States in 2002 was estimated to be between 2.4 × 105 t and 3.2 × 105 t (∼10% of the total biodiesel originates from yellow grease), as reported by the National Biodiesel Board. This capacity is mostly modular and can be doubled or tripled in a short time frame (46 from -10 to 0 0.15

EN 14214b

waste olive oil methyl ester

860-900 3.5-5 >120

882.3 5.29 169

>51.0 depends on the climate

58.7 -9 -2 -6 1.38 39.67

a The data for diesel fuel are generic. The particular diesel fuel samples used were a mixture obtained from different suppliers and, thus, had different properties. However, all of them met the European EN 590 standard. b European standard. Automotive fuels-fatty acids methyl esters (FAME) for diesel fuel-requirements and tests methods.

The engine dynamometer was an electric testing device (Froment, model XT200), with a maximum engine power of 136 kW, with an accuracy of (1.44 kW at 100% of the engine speed (as reported by the National Institute of Agricultural Engineering, in the United Kingdom), as described by Dorado et al.23 The fuel was metered by a positive-displacement gear-type sensor, using an electronic fuel flow monitor (Froment, model FM502) that had been fitted in the fuel line between the tank and the engine fuel filter. The return fuel from the engine was recirculated back into the engine supply line, as described by Dorado et al.23 The engine speed was measured by the Froment testing device and monitored electronically to the nearest 5 rpm. Data under several atmospheric conditions were collected to correct the brake-specific fuel consumption and power, following SAE standard J1349 (revised June 1990). 4. Engine Performance Tests. The engine running conditions were in the range of 8-15 kW (concerning ∼25%-50% of the maximum engine power) and 1800-2100 rpm (in the range of 75%-90% of the maximum engine speed), simulating the usual operating conditions of this engine. The performance curves were obtained at different loads and speed settings, including the maximum values. A first baseline test was run with straight No. 2 diesel fuel at the beginning, followed by the waste oil methyl ester test run. After the engine had been running for 50 h, a final test was performed with waste oil methyl ester, followed by the No. 2 diesel fuel test, to compare engine performance with the two fuels and to determine whether the use of the biodiesel had affected the engine performance. Each test consisted of measuring the speed ω (recorded in units of rpm), fuel consumption cf (in units of kg/m3), torque M (in units of N m), room temperature Tr (in Kelvin), and room pressure Pr (in units of kPa). Statistical analysis was applied to determine if any deterioration of engine performance occurred throughout the test period.

Results 1. Fuel Properties. According to Table 1, most of the biodiesel properties were very similar to those of No. 2 diesel fuel (EN-590). However, Table 1 reveals a slight increase in kinematic viscosity and Conradson carbon residue (CCR). A higher viscosity value can lead to problems related to incomplete combustion or excessive smoke emissions. However, in the present work, no evidence of the aforementioned problems was found. (23) Dorado, M. P.; Arnal, J. M.; Go´mez, J.; Gil, A.; Lo´pez, F. J. Trans. ASAE 2002, 45, 519-523.

According to the CCR content, which represents the carbon-forming tendency of fuels, a value greater than the No. 2 diesel-fuel specification was found. Sims8 observed a good correlation between the carbon content of the fuel and deposit formation at the injector. Hence, combustion problems could occur when waste olive oil methyl esters are used. Although the engine probably will require a more frequent cleaning after long-term performance tests, during the present work, no problems related to incomplete combustion or abnormal carbon deposits have been noticed. The differences in the fatty acid composition of both unused and used oil are not very great, as reported by Mittelbach et al.24 In comparison with the fatty acid composition of sunflower oil, canola oil, and soybean oil methyl esters, used olive oil represented up to 15% of the saturated chains, whereas the saturated chains from canola oil are in the range of 5%-7%, those from soybean oil are in the range of 4.7%-17%, and those from sunflower oil are in the range of 4.8%-12.1%. According to Knothe and Dunn,20 saturated hydrocarbon chains, as they are found in fatty compounds, are especially suitable for conventional diesel fuel, thus indicating that olive oil methyl ester presents a more suitable value to be considered as a diesel-fuel alternative. The cold filter plugging point (CFPP) is related to operating conditions during cold weather. Table 1 shows a CFPP value of -9 °C, which indicates that waste olive oil can provide a suitable fuel for cold-weather use, more appropriate than the waste vegetable oil used in central Europe (which has a value of -5 °C, probably because of the large amount of saturated components).24 One of the major problems associated with the use of biodiesel is its poor low-temperature flow properties, which are documented by a relatively high cloud point (CP) and pour point (PP). The CP is the temperature at which a fatty material becomes cloudy because of the formation of crystals and the solidification of saturates. The PP is the lowest temperature at which it will still flow. In fact, as the temperature decreases, more material solidifies, clogging fuel lines and filters and causing major operating problems. It is recommended by engine (24) Mittelbach, M.; Pokits, B.; Silberholz, A. Production and Fuel Properties of Fatty Acid Methyl Esters from Used Frying Oil. Liquid Fuel from Renewable Resources, Proceedings of Alternative Energy Conference; American Society of Agricultural Engineers: St. Joseph, MI, 1992; pp 74-78.

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manufacturers that the CP be below the temperature of use and not more than 6° above the PP.20 The CP, however, is more important than the PP, in regard to improving the low-temperature flow properties.25 According to Table 1, the CP of used olive oil methyl ester is -2 °C, which is the same as that for rapeseed oil methyl ester and lower than that of soybean oil methyl ester (+2 °C) and sunflower methyl ester (0 °C).20 However, instead of the CP and PP, the European Standard EN 14214 includes the CFPP. Also, during the test on the waste oil methyl ester, no difficulties were experienced with engine starting, thus indicating that the CP and PP values were suitable. In contrast to our results, other researchers observed some difficulties with engine starting3,26 when using biodiesel from sunflower oil and curcas oil, respectively. Equations for predicting the cetane number (CN) are not applicable to biodiesel. An alternative parameter for biodiesel is the cetane index (CI). According to this parameter, as shown in Table 1, used olive oil methyl ester presents an appropriate value in comparison to the CN for No. 2 diesel fuel. In addition to the CN, the gross heating value (GHV) is another essential property that provides the heat content of the fuel. In this sense, used olive oil methyl ester presents a value of 39.67 MJ/ kg, which is similar to that of biodiesel from rapeseed oil, soybean oil and sunflower oil but is smaller than that of No. 2 diesel fuel (47 MJ/kg).20 However, neither the European Standard EN 14214 nor the EN 590 diesel fuel include the GHV for certification. 2. Engine Power. Results revealed that engine power was similar, using either No. 2 diesel fuel or biodiesel from waste oil. However, during the start-up tests, the maximum engine power slightly increased (5.7%) using biodiesel instead of No. 2 diesel fuel. After the engine was run for 50 h, however, a minor loss in maximum power occurred (2%) when biodiesel was used instead of No. 2 diesel fuel. However, this seems to be normal, given the acuracy of the engine dynamometer. Mittelbach and Tritthart17 found similar results using biodiesel from waste oils, whereas several researchers observed engine-power losses up to 10% using biodiesel from straight vegetable oil.3,5,6 The performance curves were obtained at different loads and speed settings. The N-ω surface at maximum load, when burning each fuel, was integrated considering an engine speed of 1300-2300 rpm, using the expression23 ωf

S)

Ni ∆ωi ∑ ω

(1)

0

where Ni is the engine power (in kilowatts). This method helps to clarify the percentage differences between each test, compared to No. 2 diesel fuel. Results are shown in Table 2, where Si is the power-speed area value for each test and S0 corresponds to that of diesel fuel at the beginning of the test. As shown in Table 2, results revealed slight differences (8%) between biodiesel tests and the No. 2 diesel-fuel test at 0 h, as found by other researchers.3,17 This reduced power output is consistent (25) Dunn, R. O.; Shockley, M. W.; Bagby, M. O. J. Am. Oil Chem. Soc. 1996, 73, 1719-1728. (26) Ishii, Y.; Takeuchi, R. Trans. ASAE 1987, 30, 605-609.

Table 2. Percentage Change in the Engine Power Output (S), Brake-Specific Fuel Consumption (V) and Energy Output/Input (R) over 50 h of Testing for No. 2 Diesel Fuel and Waste Olive Oil Methyl Estera Change at 0 h (%) Si/S0 Vi/V50 Ri/R0

Change after 50 h (%)

diesel fuel

biodiesel

biodiesel

diesel fuel

1.00 1.09 1.00

0.92 1.16 1.06

0.92 1.26 1.05

0.93 1.00 1.05

a S , engine power-speed area using No. 2 diesel fuel at 0 h; 0 R0, energy output/input area using No. 2 diesel fuel at 0 h; and V50, brake-specific fuel consumption-engine power-speed volume using No. 2 diesel fuel after 50 h (this value was chosen because this test showed the minimum value).

with the lower biodiesel energy delivery. A power loss of 7% was also observed between No. 2 diesel fuel (0 h) and diesel fuel (50 h). However, Bradin27 observed a power loss of >19%, whereas other researchers found that the engine power was similar using either biodiesel or No. 2 diesel fuel.2,4,28 Graphic results of the N-ω curves at different loads and speed settings are shown in Figure 1 (panel a1 represents data for diesel fuel at 0 h, whereas panel a2 represents data for waste olive oil methyl ester after 50 h). In addition, the one-way analysis of variance (ANOVA) test showed that the differences in engine power between each test were not significant. In addition, statistical analysis showed that the experimental error was not relevant. 3. Brake-Specific Fuel Consumption. The brakespecific fuel consumption volume (V) was calculated following eq 2, as in Dorado et al.:23 Nf)25 ωf)2300

V)

∑ ∑

N0)10 ω0)1300

qjk ∆Nj ∆ωk

(2)

where qjk is the brake-specific fuel consumption (in units of g (kW h)-1) related to each ωk and Nj value, integrated considering only the usual working values for each parameter. The working values were chosen to simulate the usual requirements of this engine. In this way, we obtained a volume value for each trio of working values, making a brake-specific fuel consumption comparison between different tests or fuels possible, as shown in Table 2, where Vi is the volume value for each test and V50 corresponds to that of No. 2 diesel fuel after 50 h (the test that showed the minimum value). Table 2 illustrates a slight decrease (up to 9%) between the initial and final diesel-engine tests. This is probably due to the change in the atmospheric conditions, as well as the accuracy of the engine dynamometer. For this reason, it seems to be more attractive to make the comparison between those tests performed under the same atmospheric conditions (both tests performed at the beginning and both performed after the engine had been running for 50 h). In this sense, it can be noticed that the biodiesel test (0 h) showed an increase in the brake-specific fuel consumption (6.4%), compared to that in the No. 2 diesel-fuel test (0 h). Comparison of both tests after the engine had been running for 50 h, (27) Bradin, D. S. Biodiesel Fuel. U.S. Patent 5,578,090, Nov. 26, 1996. (28) Pryor, R. W.; Hanna, M. A.; Schinstock, J. L.; Bashford, L. L. Trans. ASAE 1983, 26, 333-337.

1564 Energy & Fuels, Vol. 17, No. 6, 2003

Dorado et al.

Figure 1. Comparison between No. 2 diesel fuel at 0 h and waste olive oil methyl ester at 50 h, at different loads and speed settings, including the maximum values, related to engine power ((a1) No. 2 diesel fuel and (a2) waste olive oil methyl ester), brake-specific fuel consumption ((b1) No. 2 diesel fuel and (b2) waste olive oil methyl ester), and energy delivery/energy consumption ((c1) No. 2 diesel fuel and (c2) waste olive oil methyl ester).

however, showed a larger increase (26%) in the brakespecific fuel consumption for biodiesel. Several authors found similar results using biodiesel from straight vegetable oils.4,5 Graphic results are shown in Figure 1 (panel b1 shows data for diesel fuel at 0 h, whereas panel b2 shows data for waste olive oil methyl ester after 50 h). ANOVA testing showed that specific fuel consumption variation between each test and the No. 2 diesel fuel

was not significant. In addition, statistical analysis showed that the experimental error was not relevant. 4. Energy Delivery/Energy Consumption. The relationship between energy output and energy input is an efficient method to determine whether the use of the biodiesel has affected the engine performance. In this sense, any loss of energy was reported, i.e., in the injection pump or in the combustion chamber, because of the higher viscosity of the biodiesel.

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Energy & Fuels, Vol. 17, No. 6, 2003 1565

The energy output and input were calculated using eqs 3 and 4. Equation 5 represents the quotient (R) between them, according to each cycle, considering only engine speeds of 1300-2300 rpm (Table 2):

EDELIVERY )

60 × 103N ω

106cfLHV ECONSUMPTION ) 60ω R)

∫j ∫i

(

EDELIVERY

ECONSUMPTION

)

dωi dNj

(3)

seemed to be lower than those from the use of No. 2 diesel fuel. However, it should be indicated that a 50-h test has been conducted. For this reason, although the results are encouraging, to assess deposits and wear accurately, a long-term performance test should be performed. Discussion

(4)

(5)

where EDELIVERY is the energy delivered per cycle by the engine (in joules per cycle) and ECONSUMPTION is the energy provided per cycle by the fuel (in joules per cycle), considering that the engine has three cylinders and that a cycle consists of two revolutions. LHV is the lower heating value of the fuel (given in units of J/kg). As shown in Table 2, a slight increase (6%) was observed using waste olive oil methyl ester during the engine-start tests. However, no differences were achieved after the engine had been running for 50 h, when comparing both No. 2 diesel fuel and waste olive oil methyl ester tests, thus indicating that the energy conversion efficiency was similar for both fuels. Graphic results are shown in Figure 1 (panel c1 shows data for diesel fuel at 0 h, whereas panel c2 shows data for waste olive oil methyl ester after 50 h). ANOVA tests showed that the differences in the energy output/input between each test and No. 2 diesel fuel were not significant. In addition, carbon deposits and wear seemed normal, without visual differences between the engine fueled with either No. 2 diesel fuel or waste oil methyl ester. All injector needles were in good condition after the test. Visually, smoke emissions from the use of biodiesel

A diesel direct-injection Perkins engine was fueled with waste olive oil methyl ester while simulating its usual operating service, in the range of 8-15 kW and 1800-2100 rpm, for a total of 50 h. Engine-performance tests indicated a slight power loss (