- Email: [email protected]
Effect of ternary blends of bio-ethanol, diesel and castor oil on performance, emission and combustion in a CI engine
Renewable Energy 122 (2018) 301e309
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Effect of ternary blends of bio-ethanol, diesel and castor oil on performance, emission and combustion in a CI engine T. Prakash, V. Edwin Geo*, Leenus Jesu Martin, B. Nagalingam Department of Automobile Engineering, SRM University, Kattankulathur, 603203, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 May 2017 Received in revised form 11 December 2017 Accepted 19 January 2018 Available online 20 January 2018
Some properties of castor oil such as extremely high viscosity and high water content complicate the use of neat castor oil (NCO) as a fuel for compression ignition engines. The brake thermal efficiency, emission and combustion characteristics of a diesel engine operation compared with neat castor oil is far inferior. However, neat castor oil has an affinity for alcohol because of high Ricinoleic Acid about 89.5% and hence mixes in any proportion without any phase separation and also diesel easily blends with neat castor oil. The blending of bio-ethanol and diesel enhances the combustion of NCO. The present study aims to obtain an optimum ternary fuel blend with neat castor oil-diesel- bio-ethanol, which can be used in small diesel engines. Experimental investigation reveals that the ternary blend of neat castor oil-dieselbio-ethanol fuel with the volume ratio of NCO40 þ D30 þ E30 is optimum. At full load, the thermal efficiency of the engine operating with NCO40 þ D30 þ E30 is 31.25%, which is closer to diesel operation of 32.94% and specific NO emission for NCO40 þ D30 þ E30 is 6.11 g/kWh, whereas it is 8.17 g/kWh for diesel. NCO40 þ D30 þ E30 has a smoke emission of 68% opacity, but the smoke level of the base diesel engine is 57% opacity. © 2018 Elsevier Ltd. All rights reserved.
Keywords: Neat castor oil Ricinoleic acid Ternary blends Neat castor oil-diesel-bio-ethanol blends Combustion Emission and performance
1. Inroduction Castor oil is a biofuel derived from the biomass of castor beans, which contains 50e55% oil. Among vegetable oils, castor oil is distinguished by its high content of ricinoleic acid over 89.5%. Castor oil is unique among all fats and oils. It has an unusual chemical composition of triglyceride of fatty acids. It is the only source of an 18-carbon hydroxylated fatty acid with one doublebond [1]. The carbon in any biofuel is extracted from atmospheric carbon dioxide by growing plants. Hence, burning it does not result in a net increase of carbon in the Earth's atmosphere. As a result, biofuels are seen as a way to reduce the amount of carbon dioxide released into the atmosphere by using them to replace the current non-renewable source of petroleum based fuels. Properties of castor oil like extremely high viscosity and high water content make neat castor oil (NCO) difficult to use in diesel engines. However, available literature indicates that diesel engine research with neat castor oil and its biodiesel have been carried out only to a limited extent [2e9]. It shows that starting is very difficult
* Corresponding author. E-mail address: [email protected] (V.E. Geo). https://doi.org/10.1016/j.renene.2018.01.070 0960-1481/© 2018 Elsevier Ltd. All rights reserved.
and the brake thermal efficiency, combustion and emission characteristic of a diesel engine operation with neat castor oil is poor compared to diesel operation. However, engine performance improves considerably with castor oil biodiesel operation, but it is still unsatisfactory because of high viscosity of castor oil biodiesel even after transesterification. In addition, biodiesel preparation from neat castor oil needs a laborious two-stage, time-consuming chemical process. Hence, considerable research work was focused on blending low viscous, fast burning fuels with neat castor oil or its biodiesel in order to improve the engine performance closer to base diesel engine [10e16]. In the above context, there are lots of works reported on binary blend, and there has not been much study on the synergistic effect of ternary fuel blends of vegetable oil/biodiesel-diesel-alcohol on engine performance, emission and combustion characteristics. Adding bio-ethanol with castor oil decreases the viscosity and increases the volatility of the blend and thereby air fuel entrainment may improve. Coughlin et al. [17] reported that micro explosions occur when the more volatile component evaporates from the droplet surface, leaving a high concentration of the higher boiling point fuel blend. The droplet then undergoes intense heating that result in superheating of the remaining fuel within the droplet, which in turn substantially lower the boiling point. The lower
302
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
boiling point fuel then boils, causing the droplet to expand and jet secondary droplets. This is advantageous as smaller droplets in reacting sprays have been shown to lead to a more premixed prevaporized reaction, thus improving the overall efficiency and decreasing harmful emissions such as soot and NOx. Blending of ethanol with castor oil is limited to some extent due to knocking. Also, the higher concentration of ethanol may decrease the overall cetane number of the blend. Hence, addition of diesel fuel along with ethanol and castor oil may squarely address the above stated problems. However, satisfactory engine performance and pollutants of the ternary (or three-component) blended fuels need to be proved, which the sole purpose of this work. 1.1. Effect of ricinoleic acid on blending Vegetable oil or its biodiesel is miscible with diesel or alcohol in any proportion to some extent, whereas a major setback in bioethanol and diesel fuel blends is that bio-ethanol is immiscible in diesel over a wide range of temperatures and water content because of their difference in chemical structure and characteristics. This may lead to fuel instability due to phase separation. This phase separation problem can be solved by adding an emulsifier, which helps to suspend small droplets of ethanol within the diesel fuel, or by adding a co-solvent, which acts as a bridging agent through molecular compatibility and bonding to produce a homogenous blend [18]. Emulsification usually requires heating and blending steps to generate the final blend, whereas co-solvents allow fuels to be splash blended, thus simplifying the blending process [19]. There is a number of studies that have been carried out to improve the miscibility of ethanol with diesel fuel, but all those processes need extra effort to make the blend miscible. Neat castor oil has 89.5% of triglycerides of ricinoleic acid, and this fatty acid presents a hydroxyl group at C-12. The hydroxyl group gives castor oil and its derivatives complete miscibility with alcohols at wide range of temperatures. This complete miscibility of bio-ethanol, diesel and castor oil due to Ricinoleic Acid increases the blend stability. Hence, the Ricinoleic Acid plays a major role in blending bio-ethanol and diesel with castor oil.
Table 1 Chemical composition of castor oil. Name of the acid
Percentage
Ricinoleic Acid Linoleic Acid Oleic Acid Stearic Acid Palmitic Acid Dihydroxystearic Acid Linolenic Acid Eicosanoic Acid
89.5 4.2 3 1 1 0.7 0.3 0.3
acid, linoleic acid, stearic acid and palmitic acid as shown in Table 1. However, among various vegetable oils, castor oil is distinguished by its high content (about 89.5%) of Ricinoleic Acid. 3. Experimental set-up and test procedure A single cylinder, 4-stroke, water-cooled, constant speed, compression ignition engine developing power output of 5.2 kW @ 1500 rpm was used for this experimental work. The engine specifications are given in Table 2. The engine cylinder was fitted with piezoelectric transducer for sensing of cylinder pressure at every degree of crank angle. An optical shaft position was used to give signal at TDC and an eddy current dynamometer was fitted to the engine to apply load and measure the power output of the engine at various loads. A high speed data acquisition system was used to record the pressure crank angle data. The intake air and diesel consumption measurements were obtained from pressure transmitter interfaced instruments. The ‘Engine Soft’ software was interfaced with the engine with the help of suitable hardware so that the sensors and transducers provided the required input to the software for the calculation of engine operating parameters. Carbon monoxide, unburnt hydrocarbon and NO emissions were measured using AVL five gas analyzer at various loads on the engine. The smoke emission was measured by AVL smoke meter. A schematic of the experimental setup is shown in Fig. 1.
1.2. Current scenario
3.1. Experiments
In India, a number of small diesel engines with output 3e5 kW are used in rural areas for many agricultural purposes and neat castor oil is available in plenty. Hence, without tedious chemical process of esterification, neat castor oil is investigated as a fuel for small diesel engines. However, neat castor oil cannot be used as a single fuel because of very high viscosity resulting in difficulty in starting and inferior combustion. Neat castor oil has an affinity for alcohol because of high Ricinoleic Acid about 89.5% and hence mixes in any proportion without any phase separation and also diesel blends easily with neat castor oil. Hence, the present study aims to obtain an optimum ternary fuel blend with neat castor oil e diesel-bio-ethanol which can be used in small diesel engines with brake thermal efficiency and other parameters matching very close to base diesel engine.
In the first phase of the research work, experiments were carried out stage by stage from no load to full load operation with diesel and NCO (Neat castor oil). The engine was operated at a constant speed of 1500 rpm for all loads. Torque, engine speed, fuel flow time, HC, CO, NO and smoke emissions were recorded. Performance of the engine was evaluated in terms of brake thermal efficiency, brake power, brake specific energy consumption from the above parameters. Combustion parameters such as ignition delay, combustion duration, peak pressure and maximum rate of pressure rise have been calculated from the pressure e crank angle data. In the second phase of the work, diesel was blended with 10%, 20% and 30% of NCO; experiments were carried out to find the
2. Castor oil India is the leader in global Castor production and dominates in international Castor oil trade. India produces around 10 lakh tons of Castor seed and around 5.5 lakh tons of Castor oil [1]. The Indian variety of castor has an oil content of 48% out of which 42% can be extracted, while the cake retains the rest. Castor oil is one of the very high viscous oils, where the oil content in the seed is relatively high. The oil itself contains a number of fatty acids such as oleic
Table 2 Specification of the test engine. Make
Kirloskar
Model Type of Engine Maximum power Compression ratio Engine bore Stroke Cubic capacity Loading device
TV1 4 stroke single cylinder, CI, Vertical, water cooled 5.2 kW @ 1500 rpm 17.5:1 87.5 mm 110 mm 661.5 cm3 Eddy current dynamometer
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
303
3.2. Error analysis The experimental uncertainty is also taken as the possible value the error may have. The uncertainties in the experiments may arise from instrument type, calibration and observation. These measurements are used to calculate some desired results of the experiments. Estimated the uncertainty in the calculated result on the basis of uncertainties in the primary experiments. The result R is a given function of the independent variable Y1,Y2,Y3, … … … Yn, Thus R¼(Y1,Y2,Y3, … Yn), Let WR be the uncertainty in the result and w1, w2, w3, … wn be the uncertainties in the independent variables. Then the uncertainty in the result is given by WR ¼ {[(vR/vY1)w1]2 þ (vR/vY2)w2]2 þ … þ (vR/vYn)]2}1/2 The percentage of uncertainty of various parameters like load, fuel consumption, air consumption and speed have been calculated by the above-mentioned method [20] is given in Table 5. The uncertainties in fuel consumption, combustion and emission parameters have been calculated by means of the following method.
Fig. 1. Schematic of the experimental setup.
optimum blend. Based on the brake thermal efficiency, emission and combustion parameters, NCO70 þ D30 was selected for next phase of work. It is a known fact that increase in diesel proportion gives better results in terms of performance, emission and combustion compared to NCO. However, the diesel proportion was limited to 30% in the blend to encourage the use of biofuels and also to improve the cold starting problem associated with use of NCO. In the third phase of work, bio-ethanol was blended in different proportions with the binary fuel blend of NCO and diesel, keeping the diesel amount 30% constant. The following three ternary fuel blends were selected for further experiments i) 60% of NCO, 30% of diesel and 10% of bio-ethanol by vol. (NCO60 þ D30 þ E10) ii) 50% of NCO, 30% of diesel and 20% of bio-ethanol by vol. (NCO50 þ D30 þ E20) and iii) 40% of NCO, 30% of diesel and 30% of bio-ethanol by vol. (NCO40 þ D30 þ E30). The ethanol quantity in the binary blend of diesel and NCO was limited by knocking. Results and discussion are presented based the following test fuels: i) Diesel ii) NCO iii) NCO60 þ D30 þ E10 and iv) NCO50 þ D30 þ E20 v) NCO40 þ D30 þ E30. The properties of test fuels are tabulated with ASTM standards in Table 3. Important properties of these test fuels are given in Table 4.
4. Results and discussion 4.1. Combustion characteristics 4.1.1. In-cylinder pressure In-cylinder pressure with crank angle at full load is shown in Fig. 2 for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30. With sluggish combustion and lower heat release rate of NCO, the peak pressure is only 60.49 bar, which is very low compared to diesel operation of 69.79 bar. With blending of diesel and bio-ethanol with NCO, due to combustion enhancement, the peak pressure increases and approaches the same value as that of diesel operation for NCO40 þ D30 þ E30, which is 68.89 bar. Longer ignition delay time and accumulation of oxygenated bio-ethanol during delay gives the injected fuel more oxygen and time to burn. This results in rapid heat release and high peak cylinder pressure. 4.1.2. Rate of pressure rise Fig. 3 indicates the instantaneous rate of pressure rise after the combustion starts. The rate of pressure rise depends strongly on the initial combustion rate in diesel engines, which in turn depends on
Table 3 ASTM standards used for determination of test fuel properties. Property
Test standards
Kinematic viscosity,cSt @ 40 C Density @ 15 C, g/cm3 Lower Heating value kJ/kg Cetane index Flash point, C
ASTM ASTM ASTM ASTM ASTM
D445 D1298 D240 D976 D93
Biodiesel standards ASTM D6751 -02
EN 14,214/14,213
Method
1.9e6.0 e Min 47 Min 93
3.5e5.0 0.860e0.900 Min 35,000 Min 51 Min 120
Redwood Viscometer Pycnometer Bomb calorimeter Calculated based on API gravity & mid boiling point Pensky Martens Apparatus [Closed Cup]
Table 4 Properties of test fuels. Properties
DIESEL
NCO
NCO60 þ D30 þ E10
NCO50 þ D30 þ E20
NCO40 þ D30 þ E30
Density@40 C (g/cc) Kin. Viscosity@40 C (cSt) Gross Calorific Value (kJ/kg) Calculated Cetane Index
0.830 2.6 42,500 47
0.961 226.2 34,696 28
0.905 136 36,385 31
0.889 114 35,734 29.7
0.873 91.59 35,082 27.7
304
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Table 5 List of instruments and their range, accuracy and percentage uncertainties. Parameters
Instrument
Range
Accuracy
Percentage uncertainty
Fuel consumption Load Air flow measurement NO Emission HC Emission CO Emission CO2 Emission Smoke Pressure Speed
Volumetric fuel flow measurement Load sensor Pressure transmitter AVL Gas Analyser AVL Gas Analyser AVL Gas Analyser AVL Gas Analyser AVL Smoke meter Piezo sensor Magnetic pickup type
0-500 mm of water column 0-50 kg 200 mm of water column 0-5000 ppm 0-20000 ppm 0-10% 0-20% 0-100% 0-110 bar 0-2000 rpm
±1 mm of water column ±0.1 kg ±1 mm of water column ±10% ±10 ppm ±0.03% ±0.5% ±1% opacity ±0.5 bar ±10 rpm
1 0.5 1 0.5 0.1 0.3 1 ±1 1 0.5
Fig. 2. In-cylinder pressure with respect to crank angle at full load.
Fig. 4. Variation of peak pressure with brake power for various test fuels.
the amount of fuel prepared during ignition delay. As the viscosity and density of NCO is very high, it reduces the amount of fuel prepared which in turn reduces the initial phase of combustion. Also, the maximum rate of pressure rise occurs at 357 deg. CA (NCO) for which only 44% of fuel mass is burnt. However, 62% of fuel mass is burnt for diesel at the same crank angle. It is seen that combustion of NCO is slower compared to diesel. Rate of pressure rise increases to the level of diesel for NCO40 þ D30 þ E30 as a result of improved fuel properties, leading to better combustion on account of the flame propagation through the bio-ethanol addition.
pressure rise for NCO are 60.49 bar and 4.54 bar/ CA, which are very low compared to other test fuels, since the mass fraction of NCO taking part in the premixed combustion phase is very low resulting in lower heat release. With the blending of diesel and bioethanol with NCO, the peak pressure increases. Experimental values obtained for NCO40 þ D30 þ E30 are very close to the diesel combustion values of 69.79 bar and 6.27 bar/ CA respectively. As shown in Fig. 6, the peak heat release of the blend (NCO40 þ D30 þ E30) is higher which is reflected in the cylinder pressure. The higher flame speed of ethanol in the blend aids in faster premixed combustion which subsequently increases the cylinder peak pressure. This is also due to improved physical properties of the blend. As the volatility is higher and viscosity is lower for ethanol compared to NCO, more amount of fuel is prepared, in addition to diesel and NCO during ignition delay period.
4.1.3. Cylinder peak pressure and maximum rate of pressure rise The cylinder peak pressure and maximum rate of pressure rise for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 test fuels are shown in Fig. 4 and Fig. 5 respectively. Maximum peak pressure and maximum rate of
Fig. 3. Variation of rate of pressure rise with crank angle degree at full load.
Fig. 5. Variation of maximum rate of pressure rise with brake power.
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Fig. 6. Heat release rate with respect to crank angle at full load.
Higher volatility and low viscosity of ethanol aids in more combustible mixture formed during the delay period. Diesel fuel initiates the ignition of fuel mixture, thereafter combustion becomes rapid once the ethanol starts to burn. Rapid heat release is due to high flame velocity of ethanol which in turn reflects in higher peak pressure for ternary blends. 4.1.4. Heat release Fig. 6 represents the heat release rate of various test fuels at full load. It is seen that uncontrolled combustion for diesel is associated with high rate of heat release rate compared to NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30. Due to high viscosity of NCO and subsequently with reduction in fuel air mixing rates, less fuel is prepared for rapid combustion with NCO. Therefore, more burning takes place in the diffusion phase rather than in the premixed phase with NCO. Delayed combustion and higher combustion rates during the later stages with NCO leads to higher exhaust temperature and lower brake thermal efficiency as indicated in Figs. 14 and 14. Maximum heat release for NCO at full load is 44.25 J/deg. CA, where it is 66.42 J/deg. CA for diesel. With bio-ethanol blending for the tri blended fuels, a significant rise in the premixed combustion phase is noticed due to faster combustion rate as a result of lower viscosity and faster burning of bioethanol. From Fig. 7 the percentage mass burnt during premixed combustion and diffusion for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 are 62% & 38%, 46% & 54%, 47% and 53%, 48% & 52% and 52% & 48%. As per our observation, it is very clear that primary combustion occurred in diffusion combustion for NCO and their blends, except in diesel fuel. But
Fig. 7. Variation of percentage of fuel mass burnt with crank angle degree at full load.
305
Fig. 8. Variation of ignition delay with brake power.
maximum work transfer takes place when more fuel burns during premixed phase only. Heat release rate also depends on the accumulation of fuel during the delay period. As seen in Fig. 8, compared to diesel ignition delay for NCO and other ternary blends are higher. Heat release rate is 61.43 J/deg CA for the optimum ternary fuel blend. Premixed phase for NCO40 þ D30 þ E30 is closer to diesel operation results in higher peak pressure and maximum rate of pressure rise with lower smoke level and higher brake thermal efficiency compared to NCO and other ternary blends. 4.1.5. Mass rate of fuel burnt Fig. 7 represents the percentage mass of fuel burnt during the combustion period. The mass fraction burned was calculated by normalizing the cumulative gross heat release at each crank angle to the total heat released. It can be seen that rate of mass of fuel burnt is lower and longer for NCO, indicating a slow combustion when compared to diesel. More fuel is burnt in the second phase of diffusion combustion indicating late combustion subsequently lead to higher exhaust temperature and lower brake thermal efficiency compared to diesel fuel. The combustion starts earlier with NCO40 þ D30 þ E30 than NCO. Also, 100% mass burned with NCO40 þ D30 þ E30 is much earlier than NCO. Higher volatility and flame speed of bio-ethanol increase the rate of combustion at the earliest possibility. Hence, more amount of heat releases during early part of combustion (premixed). These are the reasons for increase in brake thermal efficiency and lower smoke emission with NCO40 þ D30 þ E30 compared to NCO. 4.1.6. Ignition delay Variation of ignition delay with brake power is indicated in Fig. 8. The ignition delay in a diesel engine was defined as the time interval between the start of injection and the start of combustion. The start of injection is usually taken as the time when the injector needle lifts off its seat (determine by a needle e lift indicator). The start of combustion is more difficult to determine precisely. It is best identified from the change in slope of the heat release rate, determined from cylinder pressure data using the techniques [21]. Ignition delay for NCO is higher for all loads, compared to diesel because of very high viscosity, low volatility and high density of NCO. This contributes to poor atomization and fuel air mixture preparation, thereby increasing the ignition delay. Ignition delay increases at all loads with the increase in ethanol concentration in the ternary blends. With NCO, both physical and chemical delay is higher due to high viscosity and low cetane number. Ethanol blending may reduce physical delay due to reduced viscosity and improved volatility. These properties of ethanol causes better atomization, vaporization and mixing with air. However, chemical
306
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Fig. 9. Variation of combustion duration with brake power.
Fig. 11. Variation of NO emission with brake power.
delay for ethanol is slightly higher perhaps due low cetane number. The effects of both the delays are nullified and remain same as NCO. At full load, the ignition delay for NCO is 14 CA, whereas it is 9 CA for diesel operation. Ignition delay for NCO40 þ D30 þ E30 blend increases to the maximum of 14 CA with higher concentration of bio-ethanol in the tri blend.
and NCO40 þ D30 þ E30 at a speed of 1500 rpm. Viscosity of neat castor oil is very high compared to diesel. Hence, spray characteristics of NCO is very poor which leads to sluggish combustion. Smoke opacity increases considerably for NCO, particularly at higher loads compared to diesel. The percentage of smoke opacity exceeds 100% opacity at full load for NCO, but the engine emits less smoke when operating with ternary fuel blends of bio-ethanol, neat castor oil and diesel. There is a reduction in viscosity and density for ternary fuel blend which results in improved combustion. With bio-ethanol blending, smoke emission reduces to a maximum of 68% opacity for NCO40 þ D30 þ E30. Higher concentration of bio-ethanol (E30) in the ternary blend improves volatility, which leads to lower smoke emission. The smoke level of base diesel engine is 57% opacity.
4.1.7. Combustion duration The combustion duration is the time taken from 5% heat release to 95% heat release measured in terms of crank angle degree, which is obtained from heat release analysis. Its variation with brake power for various fuels is shown in Fig. 9. Combustion duration is highest for NCO, indicating slow and sluggish combustion because of poor fuel spray formation characteristics that results in inefficient mixing and poor combustion. Diesel combustion is good, which has shorter combustion duration of 45 oCA, whereas the combustion duration of NCO is 64 oCA. However, the combustion duration for NCO40 þ D30 þ E30 fuel blend improves to 58 oCA by bio-ethanol blending due to lower viscosity, better atomization and higher burning nature of bio-ethanol with its oxygen content in the fuel structure. This is attributed to better combustion and higher heat release of the bio-ethanol, diesel-neat castor oil fuel blend as a result of modified properties. 4.2. Exhaust emission characteristics 4.2.1. Smoke emission Variation of smoke emission with brake power is shown in Fig. 10 for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20
Fig. 10. Variation of smoke emission with brake power.
4.2.2. Nitric oxide emission Fig. 11 shows the variation of specific NO emission with brake power at a speed of 1500 rpm for various fuels tested. Specific NO emission is very low for neat castor oil when compared to diesel operation. Formation of NO depends on in-cylinder temperature and oxygen content in the fuel. With NCO, premixed combustion is very slow due to poor mixture formation during ignition delay period. As a result, heat released during the premixed combustion phase is less, which results in lower combustion temperature and lowers NO emission. At full load, the specific NO emission for NCO is 5.21 g/kWh, whereas it is 8.17 g/kWh for diesel operation. With the addition of ethanol improved premixed combustion is observed ternary blends due to higher flame speed of ethanol, which increases the incylinder temperature, favoring NO formation. It is also observed that NO emission increases with higher ethanol proportion in ternary blends [22]. Specific NO emission for NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 is 6.68 g/kWh, 6.88 g/kWh and 7.58 g/kWh respectively. As the ethanol concentration increases, the NCO concentration decreases in the ternary blend. Due to high volatility of bio-ethanol, more amount of fuel is prepared during the initial phase of combustion. 4.2.3. Carbon monoxide Fig. 12 shows the variation of CO emission with brake power at a speed of 1500 rpm for the test fuels. Diesel engine operating on neat castor oil emits very high CO emissions compared to diesel fuel operation, which is nearly six times higher than base engine CO emission. NCO operation emits 27.54 g/kWh compared to diesel emission value of 4.23 g/kWh at full load. This is mainly attributed to sluggish and incomplete combustion because of poor volatility and viscosity of NCO which causes very less atomization, vaporization and non e uniform air fuel mixture preparation. However,
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Fig. 12. Variation of CO emission with brake power.
CO emission considerably decreases with the blending of diesel and bio-ethanol with NCO. This is mainly due to the improved spray characteristics, better vaporization and mixing of air fuel mixture that leads to better combustion. CO emission of 27.54 g/kWh for NCO decreases to the maximum of 12.53 g/kWh for NCO60 þ D30 þ E10. There is slight increase in CO emission with the optimum blend of NCO40 þ D30 þ E30 (19.04 g/kWh), is still lower than NCO. This may be due to micro explosion of low volatile bio-ethanol leading to better combustion than other blends.
4.2.4. Hydrocarbon emission Fig. 13 indicates the variation of HC emission with brake power for all test fuels at a speed of 1500 rpm. NCO results in higher HC emissions compared to diesel. HC level varies from 2.89 g/kWh at 25% load to 2.07 g/kWh at 100% load for NCO, whereas HC variation for diesel operation is from 1.28 g/kWh at 25% load to 0.53 g/kWh at 100% load. Very high viscosity and density of NCO causes poor atomization and non-uniform mixing of air with bigger size fuel particles. This leads to too rich pockets that can result in higher HC emissions. Neat castor oil, ethanol and diesel ternary fuel blend operation improves the combustion as a result of lower viscosity and better atomization. The HC emissions for NCO60 þ D30 þ E10 operation varies from 2.3 g/kWh at 25% load to 1.29 g/kWh at 100% load, which is closer to diesel operation. However, with a higher concentration of bio-ethanol with NCO and diesel, increases HC emission with a range of 3.42 g/kWh at 25% load to 1.33 g/kWh at 100% load for optimum blend of NCO40 þ D30 þ E30 compared to other ternary blends. Bio-ethanol has lower cetane number and hence weak ignitability. Hence, higher bio-ethanol blending
Fig. 13. Variation of HC emission with brake power.
307
Fig. 14. Variation of brake thermal efficiency with brake power.
produces rich zones, where the flame is not able to burn the fuel air mixtures, resulting in the formation of unburned hydrocarbons. 4.3. Performance characteristics 4.3.1. Brake thermal efficiency Fig. 14 shows the variation of brake thermal efficiency with brake power for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 at a speed of 1500 rpm. Brake thermal efficiency is very poor with NCO compared to diesel. Even though the engine was able to run with NCO after sufficient warm up for nearly 20 min at full load, the combustion is very poor with NCO. NCO has higher viscosity and density compared to diesel. This results in poor spray characteristics, in turn leading to improper atomization, vaporization and mixing of air fuel. The brake thermal efficiency for NCO at full load is 23.47%, whereas it is 32.94% for diesel. The drastic reduction in brake thermal efficiency for NCO is due to less amount of effective energy conversion to useful work, which results in more amount of energy being wasted in the exhaust as seen in Fig. 16. This is also evident from Fig. 7 in which more than 60% of fuel is burnt during diffusion combustion phase. Brake thermal efficiency of the engine operating with NCO40 þ D30 þ E30 is 31.25% which is closer to diesel fuel (32.94%). Blending of bio-ethanol with the binary blend of diesel and neat castor oil improves the combustion due to better atomization and mixture formation. This can be attributed to the rapid pre-mixed combustion component that has mixtures of bioethanol due to an improved mixture upon ignition with oxygen enrichment, resulting in a higher percentage of combustion at constant volume. Moreover, it also results in lower heat loss and slower combustion. In addition, the total duration of combustion of the mixtures is shortened. The heat dissipation process is almost completed in the same angle, which is another aspect that provides evidence to support the rapidly scattering combustion phases of diesel-ethanol-NCO mixtures. Due to these factors, the consumption of mixtures and BTE has increased [23]. 4.3.2. Brake specific energy consumption (BSEC) Fig. 15 indicates the variation of BSEC with brake power for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 at a speed of 1500 rpm. At full load, BSEC for NCO is 15.83 MJ/kWh, whereas it is 10.38 MJ/kWh for diesel. Combustion is enhanced with bio-ethanol blending for the test fuel NCO40 þ D30 þ E30, leading to reduction in BSEC which is 11.87MJ/ kWh. This improvement is due reduced viscosity and density of castor oil with diesel and bio-ethanol blend the improved fuel
308
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Fig. 15. Variation of brake specific energy consumption with brake power.
Fig. 16. Variation of exhaust temperature with brake power.
properties lead to better combustion as a result of good air fuel mixture preparation. 4.3.3. Exhaust temperature Fig. 16 represents the variation of exhaust temperature with brake power for different test fuels at a speed of 1500 rpm. Exhaust temperature is higher for NCO compared to diesel. This is due to the slow combustion of neat castor oil. The poor volatility and high viscosity of castor oil are responsible for this. At full load, the maximum exhaust temperature is 456 C with NCO, whereas it is 420 C for diesel. With diesel and bio-ethanol blending with neat castor oil, combustion improves and more energy is converted into useful work. As a result, the exhaust temperature reduces with diesel and bio-ethanol blending with NCO. The exhaust temperature is 433 C for NCO40 þ D30 þ E30 at full load.
the engine operating with NCO40 þ D30 þ E30 is 31.25%, which is closer to diesel operation of 32.94%. At full load, BSEC for NCO is 15.83 MJ/kWh, whereas it is 10.38 MJ/kWh for diesel. Combustion is further enhanced with bioethanol blending for the test fuel NCO40 þ D30 þ E30, leading to reduction in BSEC which is 11.87 MJ/kW. At full load, the maximum exhaust temperature is 456 C with NCO, whereas it is 420 C for diesel. With diesel and bio-ethanol blending with neat castor oil, combustion improves and more energy is converted into useful work. The exhaust temperature is 433 C for NCO40 þ D30 þ E30 at full load. At full load, the specific NO emission for NCO is 5.21 g/kWh because of poor combustion, whereas it is 8.17 g/kWh for diesel operation. However, specific NO emission reduces to 7.58 g/kWh with blending of bio-ethanol for the optimum blend of NCO40 þ D30 þ E30. NCO operation CO emits 27.54 g/kWh compared to diesel emission value of 4.23 g/kWh at full load. By blending bioethanol with the binary fuel blend of neat castor oil and diesel, CO emission reduces to 12.53 g/kWh for the ternary fuel of NCO40 þ D30 þ E30. NCO results in higher HC emissions compared to diesel. However, by blending bio-ethanol with NCO and diesel, HC emission increases with a range of 2.29 g/kWh at 25% load to 1.23 g/kWh at 100% load for NCO40 þ D30 þ E30 ternary blend. The percentage of smoke opacity exceeds 100% opacity at full load for NCO. With bio-ethanol blending, smoke emission reduces to 68% opacity for NCO40 þ D30 þ E30 tri-blended fuels. The smoke level of base diesel engine is 57% opacity. Maximum heat release for NCO at full load is 44.25 J/deg. CA, whereas it is 66.42 J/deg. CA. for diesel. Heat release rate is 61.43 J/deg. CA for the fuel blend NCO40 þ D30 þ E30, which is closer to diesel operation of 66.42 J/deg. CA. Maximum peak pressure and rate of pressure rise for NCO is 60.49 bar and 4.54 bar/deg. CA, which are very low compared to other test fuels. With the blending of diesel and bio-ethanol, mass fraction of fuel burnt increases with the tri-fuel blend resulting in higher heat release rate in the premixed combustion period. Hence, higher peak pressure and maximum rate of pressure rise values of 68.89 bar and 6.03 bar/deg. CA respectively are obtained for NCO40 þ D30 þ E30, which are very close to the diesel combustion values of 69.79 bar and 6.27 bar/deg. CA respectively. At full load, the ignition delay for NCO is 14oCA, whereas it is 9oCA for diesel operation. Ignition delay for NCO40 þ D30 þ E30 blend increases to 13oCA with bio-ethanol addition. Diesel operation has combustion duration of 45oCA, whereas the combustion duration of NCO is 64oCA. Combustion duration for NCO40 þ D30 þ E30 fuel blend improves to 58oCA by bioethanol blending due to lower viscosity, better atomization and higher burning nature of bio-ethanol with its oxygen content in the fuel structure.
5. Conclusions The objective of the present study is to assess the role of Ricinoleic acid on bio-ethnanol, diesel and neat castor oil ternary blending and also to investigate the combustion, brake thermal efficiency and emissions of a small four-stroke CI engine operating on ternary blends, namely, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 in CI engines. Based on the experimental results, the following conclusions are made: Blending of bio-ethanol with the binary blend of diesel and neat castor oil improves the combustion. Brake thermal efficiency of
In summary, neat castor oil cannot be used as a single fuel because of very high viscosity, resulting in difficulty in starting and inferior performance. The present work indicates that after initial warm up period of 20 min with diesel, the engine could be operated successfully with neat castor oil. The fact that NCO has an affinity for alcohol and diesel because of high Ricinoleic acid of about 89.5%, aids in mixing in any proportion without any phase separation. The optimum ternary fuel blend with neat castor oil-diesel-bio-ethanol, namely, NCO40 þ D30 þ E30 was identified, which can be used in small engines with brake thermal efficiency, emission and combustion matching very close to base diesel engine.
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
References sar, M. Ota vio Batalha, Biodiesel production from castor oil in [1] A. Da Silva Ce Brazil: a difficult reality, Energy Pol. 38 (8) (2010) 4031e4039, https://doi.org/ 10.1016/j.enpol.2010.03.027. [2] V. Scholz, J.N. Da Silva, Prospects and risks of the use of castor oil as a fuel, Biomass Bioenergy 32 (2) (2008) 95e100, https://doi.org/10.1016/ j.biombioe.2007.08.004. [3] N.L. Panwar, H.Y. Shrirame, The emission characteristics of a compression ignition engine operating on castor oil methyl ester, Int. J. Glob. Warming 1 (1/ 2/3) (2009) 368, https://doi.org/10.1504/ijgw.2009.027099. , Fuel con[4] O.S. Valente, M.J. da Silva, V.M.D. Pasa, C.R.P. Belchior, J.R. Sodre sumption and emissions from a diesel power generator fuelled with castor oil and soybean biodiesel, Fuel 89 (12) (2010) 3637e3642, https://doi.org/ 10.1016/j.fuel.2010.07.041. [5] N.L. Panwar, H.Y. Shrirame, N.S. Rathore, S. Jindal, A.K. Kurchania, Performance evaluation of a diesel engine fueled with methyl ester of castor seed oil, Appl. Therm. Eng. 30 (2e3) (2010) 245e249, https://doi.org/10.1016/ j.applthermaleng.2009.07.007. [6] Ch S. Nagaprasad, K. Vijayakumarreddy, P.S.P. Kumar, E. Ramjee, O.D. Heppel, M.C. Nivendgi, Performance and emission characteristics of a diesel engine with castor oil, Indian J. Sci. Technol. ISSN: 0974-6846 2 (10) (Oct 2009). [7] Y.-S. Lin, H.-P. Lin, Spray characteristics of emulsified castor biodiesel on engine emissions and deposit formation, Renew. Energy 36 (12) (2011) 3507e3516, https://doi.org/10.1016/j.renene.2011.05.039. [8] P.R. Wander, C.R. Altafini, A.L. Colombo, S.C. Perera, Durability studies of mono-cylinder compression ignition engines operating with diesel, soy and castor oil methyl esters, Energy 36 (6) (2011) 3917e3923, https://doi.org/ 10.1016/j.energy.2010.10.037. [9] J.M. Dias, J.M. Araújo, J.F. Costa, M.C.M. Alvim-Ferraz, M.F. Almeida, Biodiesel production from raw castor oil, Energy 53 (2013) 58e66, https://doi.org/ 10.1016/j.energy.2013.02.018. [10] W.P. Wicrramanayake, Diesel Substitutes Alternative Fuels for a Diesel Engine, ME Thesis, University of Canterbury, New Zealand, 1981. [11] Mori, M., “Bio-ethanol Blended Fuels for Diesel Engine”,Yanmar diesel engine Co., Ltd.1983.U.S.Patent4,405,337.
309
[12] P. Kwanchareon, A. Luengnaruemitchai, S. Jai-In, Solubility of a dieselebiodieselebio-ethanol blend, its fuel properties, and its emission characteristics from diesel engine, Fuel 86 (7e8) (2007) 1053e1061, https://doi.org/ 10.1016/j.fuel.2006.09.034. f, A. Bereczky, M. Mbarawa, Experimental investigation of [13] F. Lujaji, L. Kristo fuel properties, engine performance, combustion and emissions of blends containing croton oil, butanol, and diesel on a CI engine, Fuel 90 (2) (2011) 505e510, https://doi.org/10.1016/j.fuel.2010.10.004. [14] Y. Yoshimoto, E. Kinoshita, L. Shanbu, T. Ohmura, Influence of 1-butanol addition on diesel combustion with palm oil methyl ester/gas oil blends, Energy 61 (2013) 44e51, https://doi.org/10.1016/j.energy.2012.11.039. [15] N. Yilmaz, F.M. Vigil, A. Burl Donaldson, T. Darabseh, Investigation of CI engine emissions in biodieselebio-ethanol ediesel blends as a function of bioethanol concentration, Fuel 115 (2014) 790e793, https://doi.org/10.1016/ j.fuel.2013.08.012. [16] H. Sharon, P. Jai Shiva Ram, K. Jenis Fernando, S. Murali, R. Muthusamy, Fueling a stationary direct injection diesel engine with diesel-used palm oilebutanol blends e an experimental study, Energy Convers. Manag. 73 (2013) 95e105, https://doi.org/10.1016/j.enconman.2013.04.027. [17] B. Coughlin, A. Hoxie, Combustion characteristics of ternary fuel Blends: pentanol, butanol and vegetable oil, Fuel 196 (2017) 488e496. [18] T.M. Letcher, Diesel blends for diesel engines, S Afr. J. Sci. 79 (1983) 4e7. [19] A.C. Hansen, Q. Zhang, P.W.L. Lyne, Ethanol diesel fuel blends e a review, Bioresour. Technol. 96 (2005) 277e285. [20] J.P. Holman, Experimental Techniques for engineers, 7th Ed, Tata McGraw Hill, New Delhi, 2004. [21] John B. Heywood “internal combustion engine fundamentals” Mcgraw Hill International Editions. ISBN 0-07-100499-8. € [22] S¸. Altun, H. Bulut, C. Oner, The comparison of engine performance and exhaust emission characteristics of sesame oilediesel fuel mixture with diesel fuel in a direct injection diesel engine, Renew. Energy 33 (8) (2008) 1791e1795. [23] R. Sathiyamoorthi, G. Sankaranarayanan, The effects of using ethanol as additive on the combustion and emissions of a direct injection diesel engine fuelled with neat lemongrass oil-diesel fuel blend, Renew. Energy 101 (2017) 747e756.
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Effect of ternary blends of bio-ethanol, diesel and castor oil on performance, emission and combustion in a CI engine T. Prakash, V. Edwin Geo*, Leenus Jesu Martin, B. Nagalingam Department of Automobile Engineering, SRM University, Kattankulathur, 603203, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 May 2017 Received in revised form 11 December 2017 Accepted 19 January 2018 Available online 20 January 2018
Some properties of castor oil such as extremely high viscosity and high water content complicate the use of neat castor oil (NCO) as a fuel for compression ignition engines. The brake thermal efficiency, emission and combustion characteristics of a diesel engine operation compared with neat castor oil is far inferior. However, neat castor oil has an affinity for alcohol because of high Ricinoleic Acid about 89.5% and hence mixes in any proportion without any phase separation and also diesel easily blends with neat castor oil. The blending of bio-ethanol and diesel enhances the combustion of NCO. The present study aims to obtain an optimum ternary fuel blend with neat castor oil-diesel- bio-ethanol, which can be used in small diesel engines. Experimental investigation reveals that the ternary blend of neat castor oil-dieselbio-ethanol fuel with the volume ratio of NCO40 þ D30 þ E30 is optimum. At full load, the thermal efficiency of the engine operating with NCO40 þ D30 þ E30 is 31.25%, which is closer to diesel operation of 32.94% and specific NO emission for NCO40 þ D30 þ E30 is 6.11 g/kWh, whereas it is 8.17 g/kWh for diesel. NCO40 þ D30 þ E30 has a smoke emission of 68% opacity, but the smoke level of the base diesel engine is 57% opacity. © 2018 Elsevier Ltd. All rights reserved.
Keywords: Neat castor oil Ricinoleic acid Ternary blends Neat castor oil-diesel-bio-ethanol blends Combustion Emission and performance
1. Inroduction Castor oil is a biofuel derived from the biomass of castor beans, which contains 50e55% oil. Among vegetable oils, castor oil is distinguished by its high content of ricinoleic acid over 89.5%. Castor oil is unique among all fats and oils. It has an unusual chemical composition of triglyceride of fatty acids. It is the only source of an 18-carbon hydroxylated fatty acid with one doublebond [1]. The carbon in any biofuel is extracted from atmospheric carbon dioxide by growing plants. Hence, burning it does not result in a net increase of carbon in the Earth's atmosphere. As a result, biofuels are seen as a way to reduce the amount of carbon dioxide released into the atmosphere by using them to replace the current non-renewable source of petroleum based fuels. Properties of castor oil like extremely high viscosity and high water content make neat castor oil (NCO) difficult to use in diesel engines. However, available literature indicates that diesel engine research with neat castor oil and its biodiesel have been carried out only to a limited extent [2e9]. It shows that starting is very difficult
* Corresponding author. E-mail address: [email protected] (V.E. Geo). https://doi.org/10.1016/j.renene.2018.01.070 0960-1481/© 2018 Elsevier Ltd. All rights reserved.
and the brake thermal efficiency, combustion and emission characteristic of a diesel engine operation with neat castor oil is poor compared to diesel operation. However, engine performance improves considerably with castor oil biodiesel operation, but it is still unsatisfactory because of high viscosity of castor oil biodiesel even after transesterification. In addition, biodiesel preparation from neat castor oil needs a laborious two-stage, time-consuming chemical process. Hence, considerable research work was focused on blending low viscous, fast burning fuels with neat castor oil or its biodiesel in order to improve the engine performance closer to base diesel engine [10e16]. In the above context, there are lots of works reported on binary blend, and there has not been much study on the synergistic effect of ternary fuel blends of vegetable oil/biodiesel-diesel-alcohol on engine performance, emission and combustion characteristics. Adding bio-ethanol with castor oil decreases the viscosity and increases the volatility of the blend and thereby air fuel entrainment may improve. Coughlin et al. [17] reported that micro explosions occur when the more volatile component evaporates from the droplet surface, leaving a high concentration of the higher boiling point fuel blend. The droplet then undergoes intense heating that result in superheating of the remaining fuel within the droplet, which in turn substantially lower the boiling point. The lower
302
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
boiling point fuel then boils, causing the droplet to expand and jet secondary droplets. This is advantageous as smaller droplets in reacting sprays have been shown to lead to a more premixed prevaporized reaction, thus improving the overall efficiency and decreasing harmful emissions such as soot and NOx. Blending of ethanol with castor oil is limited to some extent due to knocking. Also, the higher concentration of ethanol may decrease the overall cetane number of the blend. Hence, addition of diesel fuel along with ethanol and castor oil may squarely address the above stated problems. However, satisfactory engine performance and pollutants of the ternary (or three-component) blended fuels need to be proved, which the sole purpose of this work. 1.1. Effect of ricinoleic acid on blending Vegetable oil or its biodiesel is miscible with diesel or alcohol in any proportion to some extent, whereas a major setback in bioethanol and diesel fuel blends is that bio-ethanol is immiscible in diesel over a wide range of temperatures and water content because of their difference in chemical structure and characteristics. This may lead to fuel instability due to phase separation. This phase separation problem can be solved by adding an emulsifier, which helps to suspend small droplets of ethanol within the diesel fuel, or by adding a co-solvent, which acts as a bridging agent through molecular compatibility and bonding to produce a homogenous blend [18]. Emulsification usually requires heating and blending steps to generate the final blend, whereas co-solvents allow fuels to be splash blended, thus simplifying the blending process [19]. There is a number of studies that have been carried out to improve the miscibility of ethanol with diesel fuel, but all those processes need extra effort to make the blend miscible. Neat castor oil has 89.5% of triglycerides of ricinoleic acid, and this fatty acid presents a hydroxyl group at C-12. The hydroxyl group gives castor oil and its derivatives complete miscibility with alcohols at wide range of temperatures. This complete miscibility of bio-ethanol, diesel and castor oil due to Ricinoleic Acid increases the blend stability. Hence, the Ricinoleic Acid plays a major role in blending bio-ethanol and diesel with castor oil.
Table 1 Chemical composition of castor oil. Name of the acid
Percentage
Ricinoleic Acid Linoleic Acid Oleic Acid Stearic Acid Palmitic Acid Dihydroxystearic Acid Linolenic Acid Eicosanoic Acid
89.5 4.2 3 1 1 0.7 0.3 0.3
acid, linoleic acid, stearic acid and palmitic acid as shown in Table 1. However, among various vegetable oils, castor oil is distinguished by its high content (about 89.5%) of Ricinoleic Acid. 3. Experimental set-up and test procedure A single cylinder, 4-stroke, water-cooled, constant speed, compression ignition engine developing power output of 5.2 kW @ 1500 rpm was used for this experimental work. The engine specifications are given in Table 2. The engine cylinder was fitted with piezoelectric transducer for sensing of cylinder pressure at every degree of crank angle. An optical shaft position was used to give signal at TDC and an eddy current dynamometer was fitted to the engine to apply load and measure the power output of the engine at various loads. A high speed data acquisition system was used to record the pressure crank angle data. The intake air and diesel consumption measurements were obtained from pressure transmitter interfaced instruments. The ‘Engine Soft’ software was interfaced with the engine with the help of suitable hardware so that the sensors and transducers provided the required input to the software for the calculation of engine operating parameters. Carbon monoxide, unburnt hydrocarbon and NO emissions were measured using AVL five gas analyzer at various loads on the engine. The smoke emission was measured by AVL smoke meter. A schematic of the experimental setup is shown in Fig. 1.
1.2. Current scenario
3.1. Experiments
In India, a number of small diesel engines with output 3e5 kW are used in rural areas for many agricultural purposes and neat castor oil is available in plenty. Hence, without tedious chemical process of esterification, neat castor oil is investigated as a fuel for small diesel engines. However, neat castor oil cannot be used as a single fuel because of very high viscosity resulting in difficulty in starting and inferior combustion. Neat castor oil has an affinity for alcohol because of high Ricinoleic Acid about 89.5% and hence mixes in any proportion without any phase separation and also diesel blends easily with neat castor oil. Hence, the present study aims to obtain an optimum ternary fuel blend with neat castor oil e diesel-bio-ethanol which can be used in small diesel engines with brake thermal efficiency and other parameters matching very close to base diesel engine.
In the first phase of the research work, experiments were carried out stage by stage from no load to full load operation with diesel and NCO (Neat castor oil). The engine was operated at a constant speed of 1500 rpm for all loads. Torque, engine speed, fuel flow time, HC, CO, NO and smoke emissions were recorded. Performance of the engine was evaluated in terms of brake thermal efficiency, brake power, brake specific energy consumption from the above parameters. Combustion parameters such as ignition delay, combustion duration, peak pressure and maximum rate of pressure rise have been calculated from the pressure e crank angle data. In the second phase of the work, diesel was blended with 10%, 20% and 30% of NCO; experiments were carried out to find the
2. Castor oil India is the leader in global Castor production and dominates in international Castor oil trade. India produces around 10 lakh tons of Castor seed and around 5.5 lakh tons of Castor oil [1]. The Indian variety of castor has an oil content of 48% out of which 42% can be extracted, while the cake retains the rest. Castor oil is one of the very high viscous oils, where the oil content in the seed is relatively high. The oil itself contains a number of fatty acids such as oleic
Table 2 Specification of the test engine. Make
Kirloskar
Model Type of Engine Maximum power Compression ratio Engine bore Stroke Cubic capacity Loading device
TV1 4 stroke single cylinder, CI, Vertical, water cooled 5.2 kW @ 1500 rpm 17.5:1 87.5 mm 110 mm 661.5 cm3 Eddy current dynamometer
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
303
3.2. Error analysis The experimental uncertainty is also taken as the possible value the error may have. The uncertainties in the experiments may arise from instrument type, calibration and observation. These measurements are used to calculate some desired results of the experiments. Estimated the uncertainty in the calculated result on the basis of uncertainties in the primary experiments. The result R is a given function of the independent variable Y1,Y2,Y3, … … … Yn, Thus R¼(Y1,Y2,Y3, … Yn), Let WR be the uncertainty in the result and w1, w2, w3, … wn be the uncertainties in the independent variables. Then the uncertainty in the result is given by WR ¼ {[(vR/vY1)w1]2 þ (vR/vY2)w2]2 þ … þ (vR/vYn)]2}1/2 The percentage of uncertainty of various parameters like load, fuel consumption, air consumption and speed have been calculated by the above-mentioned method [20] is given in Table 5. The uncertainties in fuel consumption, combustion and emission parameters have been calculated by means of the following method.
Fig. 1. Schematic of the experimental setup.
optimum blend. Based on the brake thermal efficiency, emission and combustion parameters, NCO70 þ D30 was selected for next phase of work. It is a known fact that increase in diesel proportion gives better results in terms of performance, emission and combustion compared to NCO. However, the diesel proportion was limited to 30% in the blend to encourage the use of biofuels and also to improve the cold starting problem associated with use of NCO. In the third phase of work, bio-ethanol was blended in different proportions with the binary fuel blend of NCO and diesel, keeping the diesel amount 30% constant. The following three ternary fuel blends were selected for further experiments i) 60% of NCO, 30% of diesel and 10% of bio-ethanol by vol. (NCO60 þ D30 þ E10) ii) 50% of NCO, 30% of diesel and 20% of bio-ethanol by vol. (NCO50 þ D30 þ E20) and iii) 40% of NCO, 30% of diesel and 30% of bio-ethanol by vol. (NCO40 þ D30 þ E30). The ethanol quantity in the binary blend of diesel and NCO was limited by knocking. Results and discussion are presented based the following test fuels: i) Diesel ii) NCO iii) NCO60 þ D30 þ E10 and iv) NCO50 þ D30 þ E20 v) NCO40 þ D30 þ E30. The properties of test fuels are tabulated with ASTM standards in Table 3. Important properties of these test fuels are given in Table 4.
4. Results and discussion 4.1. Combustion characteristics 4.1.1. In-cylinder pressure In-cylinder pressure with crank angle at full load is shown in Fig. 2 for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30. With sluggish combustion and lower heat release rate of NCO, the peak pressure is only 60.49 bar, which is very low compared to diesel operation of 69.79 bar. With blending of diesel and bio-ethanol with NCO, due to combustion enhancement, the peak pressure increases and approaches the same value as that of diesel operation for NCO40 þ D30 þ E30, which is 68.89 bar. Longer ignition delay time and accumulation of oxygenated bio-ethanol during delay gives the injected fuel more oxygen and time to burn. This results in rapid heat release and high peak cylinder pressure. 4.1.2. Rate of pressure rise Fig. 3 indicates the instantaneous rate of pressure rise after the combustion starts. The rate of pressure rise depends strongly on the initial combustion rate in diesel engines, which in turn depends on
Table 3 ASTM standards used for determination of test fuel properties. Property
Test standards
Kinematic viscosity,cSt @ 40 C Density @ 15 C, g/cm3 Lower Heating value kJ/kg Cetane index Flash point, C
ASTM ASTM ASTM ASTM ASTM
D445 D1298 D240 D976 D93
Biodiesel standards ASTM D6751 -02
EN 14,214/14,213
Method
1.9e6.0 e Min 47 Min 93
3.5e5.0 0.860e0.900 Min 35,000 Min 51 Min 120
Redwood Viscometer Pycnometer Bomb calorimeter Calculated based on API gravity & mid boiling point Pensky Martens Apparatus [Closed Cup]
Table 4 Properties of test fuels. Properties
DIESEL
NCO
NCO60 þ D30 þ E10
NCO50 þ D30 þ E20
NCO40 þ D30 þ E30
Density@40 C (g/cc) Kin. Viscosity@40 C (cSt) Gross Calorific Value (kJ/kg) Calculated Cetane Index
0.830 2.6 42,500 47
0.961 226.2 34,696 28
0.905 136 36,385 31
0.889 114 35,734 29.7
0.873 91.59 35,082 27.7
304
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Table 5 List of instruments and their range, accuracy and percentage uncertainties. Parameters
Instrument
Range
Accuracy
Percentage uncertainty
Fuel consumption Load Air flow measurement NO Emission HC Emission CO Emission CO2 Emission Smoke Pressure Speed
Volumetric fuel flow measurement Load sensor Pressure transmitter AVL Gas Analyser AVL Gas Analyser AVL Gas Analyser AVL Gas Analyser AVL Smoke meter Piezo sensor Magnetic pickup type
0-500 mm of water column 0-50 kg 200 mm of water column 0-5000 ppm 0-20000 ppm 0-10% 0-20% 0-100% 0-110 bar 0-2000 rpm
±1 mm of water column ±0.1 kg ±1 mm of water column ±10% ±10 ppm ±0.03% ±0.5% ±1% opacity ±0.5 bar ±10 rpm
1 0.5 1 0.5 0.1 0.3 1 ±1 1 0.5
Fig. 2. In-cylinder pressure with respect to crank angle at full load.
Fig. 4. Variation of peak pressure with brake power for various test fuels.
the amount of fuel prepared during ignition delay. As the viscosity and density of NCO is very high, it reduces the amount of fuel prepared which in turn reduces the initial phase of combustion. Also, the maximum rate of pressure rise occurs at 357 deg. CA (NCO) for which only 44% of fuel mass is burnt. However, 62% of fuel mass is burnt for diesel at the same crank angle. It is seen that combustion of NCO is slower compared to diesel. Rate of pressure rise increases to the level of diesel for NCO40 þ D30 þ E30 as a result of improved fuel properties, leading to better combustion on account of the flame propagation through the bio-ethanol addition.
pressure rise for NCO are 60.49 bar and 4.54 bar/ CA, which are very low compared to other test fuels, since the mass fraction of NCO taking part in the premixed combustion phase is very low resulting in lower heat release. With the blending of diesel and bioethanol with NCO, the peak pressure increases. Experimental values obtained for NCO40 þ D30 þ E30 are very close to the diesel combustion values of 69.79 bar and 6.27 bar/ CA respectively. As shown in Fig. 6, the peak heat release of the blend (NCO40 þ D30 þ E30) is higher which is reflected in the cylinder pressure. The higher flame speed of ethanol in the blend aids in faster premixed combustion which subsequently increases the cylinder peak pressure. This is also due to improved physical properties of the blend. As the volatility is higher and viscosity is lower for ethanol compared to NCO, more amount of fuel is prepared, in addition to diesel and NCO during ignition delay period.
4.1.3. Cylinder peak pressure and maximum rate of pressure rise The cylinder peak pressure and maximum rate of pressure rise for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 test fuels are shown in Fig. 4 and Fig. 5 respectively. Maximum peak pressure and maximum rate of
Fig. 3. Variation of rate of pressure rise with crank angle degree at full load.
Fig. 5. Variation of maximum rate of pressure rise with brake power.
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Fig. 6. Heat release rate with respect to crank angle at full load.
Higher volatility and low viscosity of ethanol aids in more combustible mixture formed during the delay period. Diesel fuel initiates the ignition of fuel mixture, thereafter combustion becomes rapid once the ethanol starts to burn. Rapid heat release is due to high flame velocity of ethanol which in turn reflects in higher peak pressure for ternary blends. 4.1.4. Heat release Fig. 6 represents the heat release rate of various test fuels at full load. It is seen that uncontrolled combustion for diesel is associated with high rate of heat release rate compared to NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30. Due to high viscosity of NCO and subsequently with reduction in fuel air mixing rates, less fuel is prepared for rapid combustion with NCO. Therefore, more burning takes place in the diffusion phase rather than in the premixed phase with NCO. Delayed combustion and higher combustion rates during the later stages with NCO leads to higher exhaust temperature and lower brake thermal efficiency as indicated in Figs. 14 and 14. Maximum heat release for NCO at full load is 44.25 J/deg. CA, where it is 66.42 J/deg. CA for diesel. With bio-ethanol blending for the tri blended fuels, a significant rise in the premixed combustion phase is noticed due to faster combustion rate as a result of lower viscosity and faster burning of bioethanol. From Fig. 7 the percentage mass burnt during premixed combustion and diffusion for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 are 62% & 38%, 46% & 54%, 47% and 53%, 48% & 52% and 52% & 48%. As per our observation, it is very clear that primary combustion occurred in diffusion combustion for NCO and their blends, except in diesel fuel. But
Fig. 7. Variation of percentage of fuel mass burnt with crank angle degree at full load.
305
Fig. 8. Variation of ignition delay with brake power.
maximum work transfer takes place when more fuel burns during premixed phase only. Heat release rate also depends on the accumulation of fuel during the delay period. As seen in Fig. 8, compared to diesel ignition delay for NCO and other ternary blends are higher. Heat release rate is 61.43 J/deg CA for the optimum ternary fuel blend. Premixed phase for NCO40 þ D30 þ E30 is closer to diesel operation results in higher peak pressure and maximum rate of pressure rise with lower smoke level and higher brake thermal efficiency compared to NCO and other ternary blends. 4.1.5. Mass rate of fuel burnt Fig. 7 represents the percentage mass of fuel burnt during the combustion period. The mass fraction burned was calculated by normalizing the cumulative gross heat release at each crank angle to the total heat released. It can be seen that rate of mass of fuel burnt is lower and longer for NCO, indicating a slow combustion when compared to diesel. More fuel is burnt in the second phase of diffusion combustion indicating late combustion subsequently lead to higher exhaust temperature and lower brake thermal efficiency compared to diesel fuel. The combustion starts earlier with NCO40 þ D30 þ E30 than NCO. Also, 100% mass burned with NCO40 þ D30 þ E30 is much earlier than NCO. Higher volatility and flame speed of bio-ethanol increase the rate of combustion at the earliest possibility. Hence, more amount of heat releases during early part of combustion (premixed). These are the reasons for increase in brake thermal efficiency and lower smoke emission with NCO40 þ D30 þ E30 compared to NCO. 4.1.6. Ignition delay Variation of ignition delay with brake power is indicated in Fig. 8. The ignition delay in a diesel engine was defined as the time interval between the start of injection and the start of combustion. The start of injection is usually taken as the time when the injector needle lifts off its seat (determine by a needle e lift indicator). The start of combustion is more difficult to determine precisely. It is best identified from the change in slope of the heat release rate, determined from cylinder pressure data using the techniques [21]. Ignition delay for NCO is higher for all loads, compared to diesel because of very high viscosity, low volatility and high density of NCO. This contributes to poor atomization and fuel air mixture preparation, thereby increasing the ignition delay. Ignition delay increases at all loads with the increase in ethanol concentration in the ternary blends. With NCO, both physical and chemical delay is higher due to high viscosity and low cetane number. Ethanol blending may reduce physical delay due to reduced viscosity and improved volatility. These properties of ethanol causes better atomization, vaporization and mixing with air. However, chemical
306
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Fig. 9. Variation of combustion duration with brake power.
Fig. 11. Variation of NO emission with brake power.
delay for ethanol is slightly higher perhaps due low cetane number. The effects of both the delays are nullified and remain same as NCO. At full load, the ignition delay for NCO is 14 CA, whereas it is 9 CA for diesel operation. Ignition delay for NCO40 þ D30 þ E30 blend increases to the maximum of 14 CA with higher concentration of bio-ethanol in the tri blend.
and NCO40 þ D30 þ E30 at a speed of 1500 rpm. Viscosity of neat castor oil is very high compared to diesel. Hence, spray characteristics of NCO is very poor which leads to sluggish combustion. Smoke opacity increases considerably for NCO, particularly at higher loads compared to diesel. The percentage of smoke opacity exceeds 100% opacity at full load for NCO, but the engine emits less smoke when operating with ternary fuel blends of bio-ethanol, neat castor oil and diesel. There is a reduction in viscosity and density for ternary fuel blend which results in improved combustion. With bio-ethanol blending, smoke emission reduces to a maximum of 68% opacity for NCO40 þ D30 þ E30. Higher concentration of bio-ethanol (E30) in the ternary blend improves volatility, which leads to lower smoke emission. The smoke level of base diesel engine is 57% opacity.
4.1.7. Combustion duration The combustion duration is the time taken from 5% heat release to 95% heat release measured in terms of crank angle degree, which is obtained from heat release analysis. Its variation with brake power for various fuels is shown in Fig. 9. Combustion duration is highest for NCO, indicating slow and sluggish combustion because of poor fuel spray formation characteristics that results in inefficient mixing and poor combustion. Diesel combustion is good, which has shorter combustion duration of 45 oCA, whereas the combustion duration of NCO is 64 oCA. However, the combustion duration for NCO40 þ D30 þ E30 fuel blend improves to 58 oCA by bio-ethanol blending due to lower viscosity, better atomization and higher burning nature of bio-ethanol with its oxygen content in the fuel structure. This is attributed to better combustion and higher heat release of the bio-ethanol, diesel-neat castor oil fuel blend as a result of modified properties. 4.2. Exhaust emission characteristics 4.2.1. Smoke emission Variation of smoke emission with brake power is shown in Fig. 10 for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20
Fig. 10. Variation of smoke emission with brake power.
4.2.2. Nitric oxide emission Fig. 11 shows the variation of specific NO emission with brake power at a speed of 1500 rpm for various fuels tested. Specific NO emission is very low for neat castor oil when compared to diesel operation. Formation of NO depends on in-cylinder temperature and oxygen content in the fuel. With NCO, premixed combustion is very slow due to poor mixture formation during ignition delay period. As a result, heat released during the premixed combustion phase is less, which results in lower combustion temperature and lowers NO emission. At full load, the specific NO emission for NCO is 5.21 g/kWh, whereas it is 8.17 g/kWh for diesel operation. With the addition of ethanol improved premixed combustion is observed ternary blends due to higher flame speed of ethanol, which increases the incylinder temperature, favoring NO formation. It is also observed that NO emission increases with higher ethanol proportion in ternary blends [22]. Specific NO emission for NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 is 6.68 g/kWh, 6.88 g/kWh and 7.58 g/kWh respectively. As the ethanol concentration increases, the NCO concentration decreases in the ternary blend. Due to high volatility of bio-ethanol, more amount of fuel is prepared during the initial phase of combustion. 4.2.3. Carbon monoxide Fig. 12 shows the variation of CO emission with brake power at a speed of 1500 rpm for the test fuels. Diesel engine operating on neat castor oil emits very high CO emissions compared to diesel fuel operation, which is nearly six times higher than base engine CO emission. NCO operation emits 27.54 g/kWh compared to diesel emission value of 4.23 g/kWh at full load. This is mainly attributed to sluggish and incomplete combustion because of poor volatility and viscosity of NCO which causes very less atomization, vaporization and non e uniform air fuel mixture preparation. However,
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Fig. 12. Variation of CO emission with brake power.
CO emission considerably decreases with the blending of diesel and bio-ethanol with NCO. This is mainly due to the improved spray characteristics, better vaporization and mixing of air fuel mixture that leads to better combustion. CO emission of 27.54 g/kWh for NCO decreases to the maximum of 12.53 g/kWh for NCO60 þ D30 þ E10. There is slight increase in CO emission with the optimum blend of NCO40 þ D30 þ E30 (19.04 g/kWh), is still lower than NCO. This may be due to micro explosion of low volatile bio-ethanol leading to better combustion than other blends.
4.2.4. Hydrocarbon emission Fig. 13 indicates the variation of HC emission with brake power for all test fuels at a speed of 1500 rpm. NCO results in higher HC emissions compared to diesel. HC level varies from 2.89 g/kWh at 25% load to 2.07 g/kWh at 100% load for NCO, whereas HC variation for diesel operation is from 1.28 g/kWh at 25% load to 0.53 g/kWh at 100% load. Very high viscosity and density of NCO causes poor atomization and non-uniform mixing of air with bigger size fuel particles. This leads to too rich pockets that can result in higher HC emissions. Neat castor oil, ethanol and diesel ternary fuel blend operation improves the combustion as a result of lower viscosity and better atomization. The HC emissions for NCO60 þ D30 þ E10 operation varies from 2.3 g/kWh at 25% load to 1.29 g/kWh at 100% load, which is closer to diesel operation. However, with a higher concentration of bio-ethanol with NCO and diesel, increases HC emission with a range of 3.42 g/kWh at 25% load to 1.33 g/kWh at 100% load for optimum blend of NCO40 þ D30 þ E30 compared to other ternary blends. Bio-ethanol has lower cetane number and hence weak ignitability. Hence, higher bio-ethanol blending
Fig. 13. Variation of HC emission with brake power.
307
Fig. 14. Variation of brake thermal efficiency with brake power.
produces rich zones, where the flame is not able to burn the fuel air mixtures, resulting in the formation of unburned hydrocarbons. 4.3. Performance characteristics 4.3.1. Brake thermal efficiency Fig. 14 shows the variation of brake thermal efficiency with brake power for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 at a speed of 1500 rpm. Brake thermal efficiency is very poor with NCO compared to diesel. Even though the engine was able to run with NCO after sufficient warm up for nearly 20 min at full load, the combustion is very poor with NCO. NCO has higher viscosity and density compared to diesel. This results in poor spray characteristics, in turn leading to improper atomization, vaporization and mixing of air fuel. The brake thermal efficiency for NCO at full load is 23.47%, whereas it is 32.94% for diesel. The drastic reduction in brake thermal efficiency for NCO is due to less amount of effective energy conversion to useful work, which results in more amount of energy being wasted in the exhaust as seen in Fig. 16. This is also evident from Fig. 7 in which more than 60% of fuel is burnt during diffusion combustion phase. Brake thermal efficiency of the engine operating with NCO40 þ D30 þ E30 is 31.25% which is closer to diesel fuel (32.94%). Blending of bio-ethanol with the binary blend of diesel and neat castor oil improves the combustion due to better atomization and mixture formation. This can be attributed to the rapid pre-mixed combustion component that has mixtures of bioethanol due to an improved mixture upon ignition with oxygen enrichment, resulting in a higher percentage of combustion at constant volume. Moreover, it also results in lower heat loss and slower combustion. In addition, the total duration of combustion of the mixtures is shortened. The heat dissipation process is almost completed in the same angle, which is another aspect that provides evidence to support the rapidly scattering combustion phases of diesel-ethanol-NCO mixtures. Due to these factors, the consumption of mixtures and BTE has increased [23]. 4.3.2. Brake specific energy consumption (BSEC) Fig. 15 indicates the variation of BSEC with brake power for diesel, NCO, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 at a speed of 1500 rpm. At full load, BSEC for NCO is 15.83 MJ/kWh, whereas it is 10.38 MJ/kWh for diesel. Combustion is enhanced with bio-ethanol blending for the test fuel NCO40 þ D30 þ E30, leading to reduction in BSEC which is 11.87MJ/ kWh. This improvement is due reduced viscosity and density of castor oil with diesel and bio-ethanol blend the improved fuel
308
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
Fig. 15. Variation of brake specific energy consumption with brake power.
Fig. 16. Variation of exhaust temperature with brake power.
properties lead to better combustion as a result of good air fuel mixture preparation. 4.3.3. Exhaust temperature Fig. 16 represents the variation of exhaust temperature with brake power for different test fuels at a speed of 1500 rpm. Exhaust temperature is higher for NCO compared to diesel. This is due to the slow combustion of neat castor oil. The poor volatility and high viscosity of castor oil are responsible for this. At full load, the maximum exhaust temperature is 456 C with NCO, whereas it is 420 C for diesel. With diesel and bio-ethanol blending with neat castor oil, combustion improves and more energy is converted into useful work. As a result, the exhaust temperature reduces with diesel and bio-ethanol blending with NCO. The exhaust temperature is 433 C for NCO40 þ D30 þ E30 at full load.
the engine operating with NCO40 þ D30 þ E30 is 31.25%, which is closer to diesel operation of 32.94%. At full load, BSEC for NCO is 15.83 MJ/kWh, whereas it is 10.38 MJ/kWh for diesel. Combustion is further enhanced with bioethanol blending for the test fuel NCO40 þ D30 þ E30, leading to reduction in BSEC which is 11.87 MJ/kW. At full load, the maximum exhaust temperature is 456 C with NCO, whereas it is 420 C for diesel. With diesel and bio-ethanol blending with neat castor oil, combustion improves and more energy is converted into useful work. The exhaust temperature is 433 C for NCO40 þ D30 þ E30 at full load. At full load, the specific NO emission for NCO is 5.21 g/kWh because of poor combustion, whereas it is 8.17 g/kWh for diesel operation. However, specific NO emission reduces to 7.58 g/kWh with blending of bio-ethanol for the optimum blend of NCO40 þ D30 þ E30. NCO operation CO emits 27.54 g/kWh compared to diesel emission value of 4.23 g/kWh at full load. By blending bioethanol with the binary fuel blend of neat castor oil and diesel, CO emission reduces to 12.53 g/kWh for the ternary fuel of NCO40 þ D30 þ E30. NCO results in higher HC emissions compared to diesel. However, by blending bio-ethanol with NCO and diesel, HC emission increases with a range of 2.29 g/kWh at 25% load to 1.23 g/kWh at 100% load for NCO40 þ D30 þ E30 ternary blend. The percentage of smoke opacity exceeds 100% opacity at full load for NCO. With bio-ethanol blending, smoke emission reduces to 68% opacity for NCO40 þ D30 þ E30 tri-blended fuels. The smoke level of base diesel engine is 57% opacity. Maximum heat release for NCO at full load is 44.25 J/deg. CA, whereas it is 66.42 J/deg. CA. for diesel. Heat release rate is 61.43 J/deg. CA for the fuel blend NCO40 þ D30 þ E30, which is closer to diesel operation of 66.42 J/deg. CA. Maximum peak pressure and rate of pressure rise for NCO is 60.49 bar and 4.54 bar/deg. CA, which are very low compared to other test fuels. With the blending of diesel and bio-ethanol, mass fraction of fuel burnt increases with the tri-fuel blend resulting in higher heat release rate in the premixed combustion period. Hence, higher peak pressure and maximum rate of pressure rise values of 68.89 bar and 6.03 bar/deg. CA respectively are obtained for NCO40 þ D30 þ E30, which are very close to the diesel combustion values of 69.79 bar and 6.27 bar/deg. CA respectively. At full load, the ignition delay for NCO is 14oCA, whereas it is 9oCA for diesel operation. Ignition delay for NCO40 þ D30 þ E30 blend increases to 13oCA with bio-ethanol addition. Diesel operation has combustion duration of 45oCA, whereas the combustion duration of NCO is 64oCA. Combustion duration for NCO40 þ D30 þ E30 fuel blend improves to 58oCA by bioethanol blending due to lower viscosity, better atomization and higher burning nature of bio-ethanol with its oxygen content in the fuel structure.
5. Conclusions The objective of the present study is to assess the role of Ricinoleic acid on bio-ethnanol, diesel and neat castor oil ternary blending and also to investigate the combustion, brake thermal efficiency and emissions of a small four-stroke CI engine operating on ternary blends, namely, NCO60 þ D30 þ E10, NCO50 þ D30 þ E20 and NCO40 þ D30 þ E30 in CI engines. Based on the experimental results, the following conclusions are made: Blending of bio-ethanol with the binary blend of diesel and neat castor oil improves the combustion. Brake thermal efficiency of
In summary, neat castor oil cannot be used as a single fuel because of very high viscosity, resulting in difficulty in starting and inferior performance. The present work indicates that after initial warm up period of 20 min with diesel, the engine could be operated successfully with neat castor oil. The fact that NCO has an affinity for alcohol and diesel because of high Ricinoleic acid of about 89.5%, aids in mixing in any proportion without any phase separation. The optimum ternary fuel blend with neat castor oil-diesel-bio-ethanol, namely, NCO40 þ D30 þ E30 was identified, which can be used in small engines with brake thermal efficiency, emission and combustion matching very close to base diesel engine.
T. Prakash et al. / Renewable Energy 122 (2018) 301e309
References sar, M. Ota vio Batalha, Biodiesel production from castor oil in [1] A. Da Silva Ce Brazil: a difficult reality, Energy Pol. 38 (8) (2010) 4031e4039, https://doi.org/ 10.1016/j.enpol.2010.03.027. [2] V. Scholz, J.N. Da Silva, Prospects and risks of the use of castor oil as a fuel, Biomass Bioenergy 32 (2) (2008) 95e100, https://doi.org/10.1016/ j.biombioe.2007.08.004. [3] N.L. Panwar, H.Y. Shrirame, The emission characteristics of a compression ignition engine operating on castor oil methyl ester, Int. J. Glob. Warming 1 (1/ 2/3) (2009) 368, https://doi.org/10.1504/ijgw.2009.027099. , Fuel con[4] O.S. Valente, M.J. da Silva, V.M.D. Pasa, C.R.P. Belchior, J.R. Sodre sumption and emissions from a diesel power generator fuelled with castor oil and soybean biodiesel, Fuel 89 (12) (2010) 3637e3642, https://doi.org/ 10.1016/j.fuel.2010.07.041. [5] N.L. Panwar, H.Y. Shrirame, N.S. Rathore, S. Jindal, A.K. Kurchania, Performance evaluation of a diesel engine fueled with methyl ester of castor seed oil, Appl. Therm. Eng. 30 (2e3) (2010) 245e249, https://doi.org/10.1016/ j.applthermaleng.2009.07.007. [6] Ch S. Nagaprasad, K. Vijayakumarreddy, P.S.P. Kumar, E. Ramjee, O.D. Heppel, M.C. Nivendgi, Performance and emission characteristics of a diesel engine with castor oil, Indian J. Sci. Technol. ISSN: 0974-6846 2 (10) (Oct 2009). [7] Y.-S. Lin, H.-P. Lin, Spray characteristics of emulsified castor biodiesel on engine emissions and deposit formation, Renew. Energy 36 (12) (2011) 3507e3516, https://doi.org/10.1016/j.renene.2011.05.039. [8] P.R. Wander, C.R. Altafini, A.L. Colombo, S.C. Perera, Durability studies of mono-cylinder compression ignition engines operating with diesel, soy and castor oil methyl esters, Energy 36 (6) (2011) 3917e3923, https://doi.org/ 10.1016/j.energy.2010.10.037. [9] J.M. Dias, J.M. Araújo, J.F. Costa, M.C.M. Alvim-Ferraz, M.F. Almeida, Biodiesel production from raw castor oil, Energy 53 (2013) 58e66, https://doi.org/ 10.1016/j.energy.2013.02.018. [10] W.P. Wicrramanayake, Diesel Substitutes Alternative Fuels for a Diesel Engine, ME Thesis, University of Canterbury, New Zealand, 1981. [11] Mori, M., “Bio-ethanol Blended Fuels for Diesel Engine”,Yanmar diesel engine Co., Ltd.1983.U.S.Patent4,405,337.
309
[12] P. Kwanchareon, A. Luengnaruemitchai, S. Jai-In, Solubility of a dieselebiodieselebio-ethanol blend, its fuel properties, and its emission characteristics from diesel engine, Fuel 86 (7e8) (2007) 1053e1061, https://doi.org/ 10.1016/j.fuel.2006.09.034. f, A. Bereczky, M. Mbarawa, Experimental investigation of [13] F. Lujaji, L. Kristo fuel properties, engine performance, combustion and emissions of blends containing croton oil, butanol, and diesel on a CI engine, Fuel 90 (2) (2011) 505e510, https://doi.org/10.1016/j.fuel.2010.10.004. [14] Y. Yoshimoto, E. Kinoshita, L. Shanbu, T. Ohmura, Influence of 1-butanol addition on diesel combustion with palm oil methyl ester/gas oil blends, Energy 61 (2013) 44e51, https://doi.org/10.1016/j.energy.2012.11.039. [15] N. Yilmaz, F.M. Vigil, A. Burl Donaldson, T. Darabseh, Investigation of CI engine emissions in biodieselebio-ethanol ediesel blends as a function of bioethanol concentration, Fuel 115 (2014) 790e793, https://doi.org/10.1016/ j.fuel.2013.08.012. [16] H. Sharon, P. Jai Shiva Ram, K. Jenis Fernando, S. Murali, R. Muthusamy, Fueling a stationary direct injection diesel engine with diesel-used palm oilebutanol blends e an experimental study, Energy Convers. Manag. 73 (2013) 95e105, https://doi.org/10.1016/j.enconman.2013.04.027. [17] B. Coughlin, A. Hoxie, Combustion characteristics of ternary fuel Blends: pentanol, butanol and vegetable oil, Fuel 196 (2017) 488e496. [18] T.M. Letcher, Diesel blends for diesel engines, S Afr. J. Sci. 79 (1983) 4e7. [19] A.C. Hansen, Q. Zhang, P.W.L. Lyne, Ethanol diesel fuel blends e a review, Bioresour. Technol. 96 (2005) 277e285. [20] J.P. Holman, Experimental Techniques for engineers, 7th Ed, Tata McGraw Hill, New Delhi, 2004. [21] John B. Heywood “internal combustion engine fundamentals” Mcgraw Hill International Editions. ISBN 0-07-100499-8. € [22] S¸. Altun, H. Bulut, C. Oner, The comparison of engine performance and exhaust emission characteristics of sesame oilediesel fuel mixture with diesel fuel in a direct injection diesel engine, Renew. Energy 33 (8) (2008) 1791e1795. [23] R. Sathiyamoorthi, G. Sankaranarayanan, The effects of using ethanol as additive on the combustion and emissions of a direct injection diesel engine fuelled with neat lemongrass oil-diesel fuel blend, Renew. Energy 101 (2017) 747e756.