Vegetable Oils of Soybean, Sunflower and Tung as Alternative Fuels for Compression Ignition Engines

Year 2013, Volume: 16 Issue: 2, 87 - 96, 01.06.2013

Ricardo Hartmann , Nury Garzon Eduardo Hartmann Amir Oliveira Edson Bazzo

Abstract

This paper deals with the use of straight vegetable oil as fuel for compression ignition engine applied to distributed electric generation. It was studied three typical oils from southern of the Brazil, soybean oil, sunflower oil and tung oil. For this purpose it was designed and assembled a conversion kit that allows the use of the selected oils directly in the engine. The kit preheats the fuel to a temperature where their physical properties, mainly viscosity, reaches the diesel oil levels. This kit is electronic controlled and it was used standardized measurements of some physical properties of the fuels, for the design of their control software. The straight vegetables oils, its blends 50/50 v/v with petrodiesel fuel and neat petrodiesel fuel were tested in dynamometer bench. It was obtained results of brake power, torque, specific fuel consumption and emissions as function of the rotation of the engine. The discussions about the results in terms of efficiency first law showed the technical feasibility of the using of straight vegetable oils and the effectiveness of the developed conversion kits.

Keywords

Renewable energy, vegetable oils, biofuels, compression ignition engine.

References

• Edible Oils Soybean (Glycine max) Altin et al. (2001); Engelman et al. (1978); Pryor et al. (1983).
• Rapeseed (Brassica napus) Bialkowski et al. (2005); Hazar & Aydin (2010); Kleinova et al. (2009); Nwafor (2003); Peterson et al. (1983); Yilmaz & Morton (2011).
• Palm (Elaeis guineensis) Almeida et al. (2002); Antwi (2008); Bari & Roy (1995); Belchior & Pimentel (2005); Sapaun et al. (1996).
• Coconut (Cocos nucifera) Antwi (2008); Kalam et al. (2003); Thaddeus et al. (2001).
• Cottonseed (Gossypium hirsutum and Gossypium herbaceum) Altin et al. (2001); Amba & Rama (2003); He & Bao (2005); Fontaras et al. (2007); Sarada et al. (2010); Balafoutis et al. (2011); Martin & Prithviraj (2011).
• Corn (Zea mays) Altin et al. (2001).
• Olive (Olea europaea) Rakopoulos et al. (2011).
• Sunflower (Helianthus annuus) Altin et al. (2001); Karaosmanoglu et al. (2000); Maziero et al. (2007); Yilmaz & Morton (2011).
• Peanut (Arachis hypogaea) Barsic & Humke (1981); Yilmaz & Morton (2011).
• Safflower (Carthamus tinctorius) Bettis et al. (1982); Isigigur et al. (1993).
• Sesame (Sesamum indicum) Altun & Oner (2009).
• Rice bran (Oryza sativa) Agarwal (2007); Bari & Roy (1995); Raghu et al. (2011).
• Linseed (or flaxseed) (Linum usitatissimum) Agarwal (2007).
• Poppy seed (Papaver somniferum) Aksoy (2010).
• Mahua (Madhuca longifolia) Agarwal & Agarwal (2007); Pugazhvadivu & Sankaranarayanan (2010).
• Neem (Azadirachta indica or Antelaea azadirachta) Sivalakshmi & Balusamy (2011). Nonedible Oils
• Castor seed (Ricinus communis) Naga et al. (2009).
• Jatropha (Jatropha curcas) Agarwal & Agarwal (2007); Antwi (2008); Chalatlon et al. (2011); Chauhan et al. (2010); Forson et al. (2004); Kumar et al. (2003); Pramanik (2003); Yaodong et al. (2010).
• Pongam (or indian beech, karanja, honge) (Pongamia pinnata) Agarwal & Rajamanoharan (2009); Venkanna et al. (2009).
• Tobacco seed (Nicotiana tabacum) Giannelos et al. (2002).
• Tung (Aleurites fordii) Chang & Wan (1947). Most of these (and others) have already been tested as neat fuels for CI engines. Table 1 lists oil producing crops that have been tested as straight vegetable oil (SVO) fuel in CI engines in recent years. The references for their use as biodiesel far outnumber those shown and are omitted.
• Vegetable oils present, comparatively to diesel oil, lower LHV (from 10% to 17% lower, leading to lower energy release per mass burned), higher viscosity (leading to poor atomization), higher boiling temperatures (delaying evaporation and formation of a combustible mixture), higher bulk modulus (causing injector to open earlier), higher flash point (delaying mixture ignition), higher oxidation instability (leading to higher tendency to degradation during storage), and a tendency for thickening with time (Babu & Devaradjane, 2003; Franco
• & Nguyen, 2011). When using the same injectors and settings adjusted for diesel fuel, the higher viscosity, surface tension and density of the vegetable oils result in changes in injected oil volumes, injection delay after injector opening, spray patterns (cone and penetration) and atomization (droplet size distribution) (Bialkowski et al., 2005). As a result of poor atomization, mixing and ignition there are: (a) Longer ignition delay, smaller pressure rise, lower cylinder peak pressure and a longer combustion duration (Venkanna et al., 2009), resulting in 5% to 25% (Chalatlon et al., 2011) reduction in thermal efficiency at maximum power when compared to pure diesel oil.
• (b) Blending vegetable oil with diesel also decreases viscosity and improves volatility. These improved properties result in better mixture formation and spray penetration. A number of investigators tried the vegetable oils in varying proportions with diesel. Most remarkably, few studies (Forson et al., 2004) show engine performance even above that of operation with neat diesel oil.
• (c) Advanced injection timing compensates the effects of the longer delay period and slower burning rate that is exhibited by vegetable oils (Nwafor & Rice, 1996). Staged injection may not lead to improvement in fuel/air mixing when it occurs too late along the expansion cycle (Bialkowski et al., 2005). Most of the recent work was developed using low power single cylinder CI engines fuelled by mechanical pumps (Aksoi, 2010; Altin et al., 2001; Forson et al., 2004; Martin & Prithviraj, 2011; Pugazhvadivu &
• Sankaranarayanan, 2010; Raghu et al., 2011; Sarada et al., 2010; Sivalakshmi & Balusamy, 2011; Venkanna et al., 2009) in the context of the application of small engines for rural and remote areas. Fewer works were developed with larger engines for general use (Bialkowski et al. , 2005), for use in agriculture (Maziero et al., 2007), and for transportation (Chalatlon et al., 2011; Kleinova et al., 2009). Usually, large indirect injection compression ignition engine (IDI) operate better during long duration tests while small IDI and direct injection compression ignition engine (DI) present problems (Bialkowski et al., 2005; He & Bao, 2005). Only Kleinova et al. (2009) and Bialkowski et al. (2005) have developed their studies using common rail injection systems. Most modern CI engines nowadays employ common rail injection. The use of a central electronic unit and the common rail has enabled great advances in performance and in-cylinder emissions control using diesel oil and these improvements could also be expected when using straight vegetable oils.
• For example, Venkanna et al. (2009) investigated the effect of the injection pressure in a mechanical system, varying the injection pressure from 200 bar to 280 bar.
• Even in this small range they measured differences in thermal efficiency that point out to an optimum operation pressure for a given combustion chamber, injector and oil temperature. They argue that, for their engine, a further increase in pressure would cause an excessive diminution of droplet sizes and insufficient spray penetration. They also noticed that smoke reduces continually with the increase in pressure. This indicates the need to explore further the effects of injection pressure, injection timing, and split injection. Here, tests of a mechanical injected engine in a dynamometric bench operating with straight vegetable oils of Soybean, Sunflower and Tung and their mixtures with diesel oil are reported. This work relies on the assumption that oil heating and higher injection pressure contribute to a better spray development and atomization, leading to better performance, efficiency and smaller emission of smoke. The basic strategy for pre-heating consists in bringing the straight vegetable oil before the injector to a temperature in which the viscosity of the oil approaches that of the diesel oil at ambient temperature. To allow for the control of the fuel heating an electronically controlled heating unit was developed and adapted to the engine. This set up is described next. Experiment 1 Engine and instrumentation The study was carried out in a single cylinder, four strokes, direct injection, mechanically pumped and controlled, CI engine. Table 2 lists the main characteristics of the engine. This is a sturdy, small engine, typically used for electrical energy generation in isolated communities. The engine was coupled to a Schenck W70, eddie current dynamometer. The torque was measured with an Hbm Wagezelle extensometer type load cell and the speed was measured with an incremental encoder with resolution of 60 steps. The temperature of the exhaust gases was measured in the exhaust manifold, close to the exhaust valve. The concentration of the exhaust gases were measured with a Testo Portable Gas Analyzer, model 350-XL. The mass of fuel consumed was measured gravimetrically with a Shimadzu electronic balance model UX 8200S. The entire experiment was controlled using the LabVIEW software.
• Table Engine basic characteristics. Manufacturer Yanmar Model YT22 Bore [mm] 115 Stroke [mm] 115 Compression Ratio 3 Displacement volume [cm³] 1194 Nominal conditions: Speed [rpm] 2000 Power [kW] 7 BSFC [g (kWh) -1 ] 238
• Injection pressure [bar] 200 Injection time [°BTDC] 18 The mechanical speed control system uses a flyball governor for fuel control and as speed limiter, as shown in Figure 1. The engine was adjusted to full load by setting the load handle to its maximum (top) position. The load handle is connected to a spindle that directly acts in the injection pump, controlling the fuel flow. A tensioned spring keeps the spindle arms in contact against the sliding balls. When the engine speed increases, the sliding balls move outwards, releasing the spindle arms. The tensioned spring pulls the spindle in the direction of closing the fuel flow. Figure 1. Drawing of the governor subsystem and synchronizing gears. As the speed reduces, the sliding balls move back towards the center of the flyball governor, pressing the spindle arms up against the spring and opening the fuel flow. The sensitivity of the control is provided by the design of the curvature of the lever arms, their position in respect to the sliding balls, and the tension of the spring. 2 Fuels analysis Three vegetable oils and their blends with commercial Brazilian diesel oil were used. Brazilian diesel oil has a volumetric addition of 5% of biodiesel, as required by law and regulated by ANP, the National Petroleum Agency. The fuels used are labeled following Table 3. Table Nomenclature for the fuel mixtures used. Nomenclature Fuel 100% SW Straight Sunflower Oil 100% SY Straight Soybean Oil 100% TG Straight Tung Oil 50%SW-50%D 50/50 v/v Sunflower Oil and diesel oil 50%SY-50%D 50/50 v/v Soybean Oil and diesel oil 50%TG-50%D 50/50 v/v Tung Oil and diesel oil 100% D Brazilian commercial diesel oil The straight vegetable oils and their respective mixtures were preheated before injection in the engine. The strategy was to bring the fuel kinematic viscosity to a value close to that of diesel oil at ambient temperature. For that, the viscosities of the fuel mixtures were measured as a function of temperature by standardized viscosity experiments carried out in the Brazilian National Institute of Technology (INT), Rio de Janeiro, RJ. Table 4 summarizes the injection temperature, the kinematic viscosity and the density of the fuel blends. The density was measured gravimetrically using a Kern electronic balance model EW 220 – 3 NW. The fuel temperature was kept sufficiently low to avoid thermal degradation. Table Injection temperatures and kinematic viscosities. Fuel Injection Temperature [°C] Table Energy content of the fuels and fuel blends. Fuel LHV (kJ/kg) Ratio in respect to diesel oil 100% SW 36150 ± 30 (1) 0.86 100% SY 36270 ± 20 (1) 0.86 100% TG 35750 ± 30 (1) 0.85 50%SW-50%D 38932 (2) 0.93 50%SY-50%D 38975 (2) 0.93 50%TG-50%D 38946 (2) 0.93 100% D 42000 (3) 00
• Methods: (1) ASTM D 4809, (2) Blending rule, (3) ANP Standard .
• Table 6. Elementary analysis of the straight vegetable oils. Soybean Sunflower Tung Diesel C (wt %) (1) 9 6 5 6 (4) H (wt %) (1) 4 3 4 4 (4) N (wt %) (1) 0 0.0 0.0 -O (wt%) (3) 7 11,1 1 -S (mg/kg) (2) 2 5 0.6 1800
• (1) ASTM D 5291, (2) ASTM D 5453, (3) Balance, (4) As C 16 H 34 .
• The solution was pumped to a second heat exchanger, where the vegetable oils were heated to the selected temperature. The temperature of the vegetable oil was measured at the outlet of the heat exchanger. This value was sent to the ECU that controlled the temperature of the vegetable oils by controlling the flow of the thermal fluid. A second conversion kit that will allow the use of a common rail system is under development. The results reported here were obtained with the mechanical governor. 3 Test procedure A typical test began with the engine warm up at full load using neat diesel oil until the temperature of its coolant reached 70°C. Then, the fuel was switched to the fuel of interest and the engine operation at zero load was allowed to stabilize for 10 min. After stabilizing at zero load, the brake was applied, the engine speed reduced and the engine was allowed to reach steady-state operation at a new speed. The procedure was repeated until the engine speed reached 1500 rpm. About 10 operation points were recorded for each fuel and fuel blend.
• Each complete run took about 2 hours. After each steady-state, the engine speed, torque, coolant temperature, fuel mass, fuel temperature, inlet air humidity and temperature, exhaust gas temperature and concentration of CO, CO 2 , and NO x were recorded. Each complete run was repeated at least three times, until statistical repeatability was observed. 4 Measurement uncertainties The uncertainty of the reported measurements was estimated based on the uncertainty of each instrument used for the measurement of the base variables and with the statistical uncertainty related to the number of experiments. Table 7 summarizes the expanded uncertainties. It can be observed that the measurement of emissions has the greater expanded uncertainty while the results obtained in the dynamometric bench are associated to smaller uncertainties. Table Expanded uncertainty (1) of each measurement. Measurement Expanded Uncertainty [%] Engine speed ± 5 Torque ± 8 Power ± 2 Fuel mass flow rate ± 5 Specific fuel consumption ± 4 First law efficiency ± 4 CO mole fraction ± 9 CO 2 mole fraction ± 5 NO x mole fraction ± 8 Exhaust gas temperature ± 0.8 (1) Expanded uncertainty as a percentage of the mean value for a probability of 95%. Results and discussion In this section, the results obtained in the dynamometric bench are shown. Figures 2 and 3 present power, figures 4 and 5 present fuel consumption, figure 6 presents the thermal efficiency, and figures 7 to 9 present emissions and exhaust gas temperature. Figure 2 presents the engine power as a function of engine speed for the three SVO and their blends with diesel oil. The measurements are represented by the symbols. The interpolating continuous lines are used only as a guide to the eyes. The measurements for speeds above 2000 rpm are affected by the governor and the curves for all fuels fall to similar values. Therefore, in the figures that follow all measurements taken above 2000 rpm are not presented. Figure 3 presents the percentage variation in engine power when compared to neat diesel oil. Figure 2. Engine power versus engine speed.
• Figure 3. Percentage reduction in power when compared to the operation with diesel fuel. In order to better understand the results of performance in Figures 2 and 3, initially, the mass of fuel injected is discussed. 1 Engine control and fuel consumption Figure 4 presents the mean fuel mass injected per cycle as a function of engine speed. Within the measurement uncertainty, all fuels presented the same values, indicating the good match of the kinematic viscosities. This fixes a basis for comparison, i.e., all measurements at a given engine speed occurred with approximately the same mass of fuel injected per cycle. In Figure 4, it is also noticed that the fuel mass increased approximately linearly with the decrease of the engine speed. The mechanical control of the fuel injection acted in the direction of keeping a constant engine speed. Therefore, as the load in the engine was increased and the speed reduced, the mass of fuel injected per cycle was increased. This increase was approximately linear due to the design of the governor. However, we note that the fuel mass flow rate increases with engine speed, as shown in Figure 5. Figure 4. Fuel mass injected per cycle versus engine speed. Figure 5. Fuel mass flow rate versus engine speed. 2 Engine performance The results in Figure 2 can be separated in four groups, from the higher to the lower performance, formed by, respectively: (1) The diesel oil, (2) the blends of soybean and sunflower oils, (3) the straight soybean, sunflower and the blend of tung oil, and (4) the straight tung oil. This is in accordance with the distribution of 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 Engine speed (rpm) 2 4 6 8 10 12 14 16 18 1300 1400 1500 1600 1700 1800 1900 2000 P er ce n ta g e re d u ct io n i n r esp ec t to d ie se l o il ( %) Engine speed (rpm) 50 52 54 56 58 60 62 64 66 1300 1400 1500 1600 1700 1800 1900 2000 F u el mass in je ct ed p er c y cl e (mg /c y cl e) Engine speed (rpm) 100% SW 100% SY 100% TG 100% D 50% SW - 50% D 50% SY - 50% D 50% TG - 50% D 0.6 0.7 0.8 0.9 0 1300 1400 1500 1600 1700 1800 1900 2000 F u el mass fl o w r at e (g /s) Engine speed (rpm) 100% SW 100% SY 100% TG 100% D 50% SW - 50% D 50% SY - 50% D 50% TG - 50% D
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