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Energy & Fuels 2007, 21, 1878-1882
Performance and Emission of the Emulsified Fuel in a DI Diesel Engine Using Oxygenated Additive Diethyl Ether with Surfactant of Span-80 M. P. Ashok* and C. G. Saravanan† Department of Mechanical Engineering, Faculty of Engineering & Technology, Annamalai UniVersity, Tamil Nadu, India ReceiVed NoVember 17, 2006. ReVised Manuscript ReceiVed March 6, 2007
In this present work, investigations are carried out to study the performance and emission characteristics of adding diethyl ether as an oxygenated additive with the selected ratio of 70D:30E. For this experiment, a single-cylinder, four-stroke, water-cooled diesel engine is used. Initially, the engine is run with diesel no. 2 fuel and the readings are recorded. Then, the engine is run with the emulsified fuel ratio of 70D:30E by a volume basis and the readings are taken in to an account. Finally, along with the emulsified fuel 70D:30E, the oxygenated additive diethyl ether is added on a 10% by volume basis and the readings are also being observed. On the basis of the test results, the oxygenated additive diethyl ether added emulsified fuel shows increase in brake thermal efficiency and decrease in specific fuel consumption, smoke density, particulate matter, and oxides of nitrogen comparted to the diesel fuel no. 2 and the emulsified fuel.
1. Introduction Diesel engines, due to their dominant advantages of high thermal efficiency, rigid and simple in structure and fuel economy, are the major power sources for inland transportations and industrial power plants. They are the most fuel combustion efficient engines known and are expected to remain widely used in the foreseeable future. However, the pollutants emitted from the diesel engines are detrimental to human health and to the ecological environment. Hence, diesel engines have been considered to be one of the major air pollution sources. The major pollutants emitted from diesel engines are particulate matter (PM), smoke density (SD), oxides of nitrogen (NOx), etc., These pollutants cause damage to the ozone layer, enhance the greenhouse effect, and produce acid rain. The photochemical smog formed from the reaction of NOx with ultraviolet sunlight might also damage the respiratory system, throat, and eyes and hinder the environmental field of vision. Inhalation of the particulate matter laden with Polycyclic Aromatic Hydrocarbons (PAH) or metallic compounds may even cause carcinogen diseases.1 The emulsification technique is one of the possible approaches to the improvement of fuel economy and the reduction of the pollutants emission of diesel engines.2 In this technique, ethanol has a higher miscibility with diesel fuel. Therefore, the use of ethanol in compression ignition (CI) engines has received considerable attention in recent years.3 Ethanol addition to the diesel fuel results in different physicochemical changes in diesel * Corresponding author. E-mail:
[email protected]. † E-mail:
[email protected]. (1) Pischinger, F. F. Compression Ignition Engines. In Handbook of Air Pollution from Internal Combustion Engines; : Sher, E., Ed.; Academic Press: London, UK; 1998; pp 261-3. (2) Mohammadi, A.; Ishiyama, T.; Kakuta, T.; Kee, S.-S. Fuel Injection Strategy for Clean Diesel Engine Using Ethanol Blended Diesel Fuel; SAE technical paper no. 2005-01-1725, SAE: Warrendale, PA, 2005. (3) Koganti, R. B.; Maheshwari, M.; Swami, K. K. Performance EValuation of Ethanol Diesel Blend; SAE technical paper no. 2004-280085, SAE: Warrendale, PA, 2004.
fuel properties, particularly, a reduction in the cetane number, viscosity, and heating value.4 Therefore, different techniques involving ethanol-diesel fuel operation have been developed to make the diesel engine technology compatible with the properties of ethanol based fuels. Several ratios of emulsified fuels 50D:50E, 60D:40E, 70D: 30E, 80D:20E, and 90D:10E are prepared based on the waterin-oil type emulsion method. It is found that the best performance and least pollution results are given by the emulsified fuel ratio of 70D:30E.5 This ratio is selected for the continuation of this present work. Even though this emulsified fuel gives better brake thermal efficiency, gives less specific fuel consumption, and has given a lesser value of smoke density, particulate matter based on the performance and emissions, respectively, when compared with the diesel no, 2, there is a significant increase in oxides of nitrogen (NOx) emission over diesel no. 2. This is due to the lower cetane number of ethanol, which causes high temperature, resulting in a longer ignition delay. This increases the NOx emission for this fuel. This emission of NOx can be controlled by adding a suitable additive, which must have the property of a high cetane number. This leads to a reduction of high temperature, resulting in a smaller ignition delay, thus reducing emission of NOx. Hence for this present work, diethyl ether (DEE) has been selected as an additive, because of its high cetane number, noncorrosiveness, and low volatility.6 This additive is added on a 10% by volume basis with the selected emulsified fuel ratio of 70D:30E, and (4) Faria, M. D. C.; da Cunha Pinto, R. R.; Valle, M. L. M. The Influence of Physico-Chemical Properties of Diesel/Biodiesel Mixtures on Atomization Quality in Direct Injection Diesel Engines; SAE technical paper no. 200501-4154, SAE: Warrendale, PA, 2005. (5) Ashok, M. P.; Saravanan, C. G. Study the Performance and Emission characteristics of different ratios of Emulsified Fuels in a Diesel Engine. Proceedings of the National conference on Bio-Fuels for Internal Combustion Engines, March 23-25, 2006; NITK: Karnataka, Surathkal, India, 2006, pp 24-29. (6) Subramanian, K. A.; Ramesh, A. Use of Diethyl Ether along with Water-Diesel Emulsion in a DI Diesel Engine; SAE technical paper no. 2002-01-2720, SAE: Warrendale, PA, 2002.
10.1021/ef060584b CCC: $37.00 © 2007 American Chemical Society Published on Web 05/19/2007
Emulsified Fuel in a DI Diesel Engine
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Table 1. Properties of Diethyl Ether, Ethanol, and Diesel No. 2 #
diethyl ether
ethanol (100% proof)
diesel no. 2
chemical formula boiling point (°C) cetane number self-ignition temperature (°C) stoichiometric air/fuel ratio lower heating value (kJ/kg) viscosity at 20 °C (cP) specific gravity density (kg/m3)
C4H10O 34.4 > 125 160 11.1 wt/wt 33900 0.23 0.714 713
CH3CH2OH 78 8 420 9 wt/wt 27000 1.2 0.783 794
C12H26 180 to 330 50 200 to 420 14.6 wt/wt 42800 3.9 0.894 830
the performance and emission tests are carried out. Similarly, the diesel no. 2 and the emulsified fuel 70D:30E are tested based on the performance and emission and all the three results are compared. Table 1 indicates the properties of diethyl ether, ethanol, and diesel no. 2. 2. Present Work The objective of this work is to study the performance and emission characteristics of diethyl ether added on a 10% by volume basis to the selected emulsified fuel ratio 70D:30E. And, the results are to be compared with the same emulsified fuel ratio of 70D:30E and the diesel no. 2. In the earlier work,5 it has been identified that the emulsified fuel has given the best performance and reduction of pollutants except NOx. The aim of the present work is to reduce NOx by adding the required percentage of the additive diethyl ether because of its high cetane number. A higher cetane number reduces the effect of the delay period. From this, it is clear that reduction of the delay period reduces the gas temperature, which can control NOx emission.7
Table 2. Specifications of Span 80 Surfactant
Table 3. Specifications of the Test Engine type of engine: 4-stroke, water-cooled, single-cylinder, DI diesel bore × stroke: 87.5 × 110 mm injection timing: 23° BTDC (static) compression ratio: 17.5:1 rated power: 5.2 kW @ 1500 rpm dynamometer: eddy current dynamometer injection pressure: 220 kg f/cm2
4. Experimental Setup Details of the engine are given in the Table 3. The fuel flow rate is obtained on a gravimetric basis, and the airflow rate is obtained on a volumetric basis. NOx emission is obtained using an analyzer working on the chemiluminescence principle. The particulate matter from the exhaust is measured with the help of the micro high volume sampler. An AVL smoke meter is used to measure the smoke capacity. An AVL DIGAS 444 {DITEST} fivegas analyzer is used to measure the rest of the pollutants. All the measurements are collected and recorded by a data acquisition system. The experimental set up is indicated in Figure 1.
3. Preparation of the Emulsified Fuel For the preparation of the emulsified fuel, initially, the known quantity of 10% by volume of diethyl ether is added to the 63% volume based diesel no. 2. Then, the ethanol of 27% is mixed along with the mixture. In the ethanol-in-diesel emulsion fuel preparation method, diesel and ethanol are the dispersion and dispersed media, respectively. Hence, the dispersed medium is added slowly to the dispersion medium. In this mixture, the surfactant span-80 is also added to reduce the interfacial tension between the two liquid phases to form a homogenized stable solution.8 Span-80 is selected based on its HLB (Hydrophile-Lipophile Balance) of 4.3 (specific gravity 0.98). After adding all of the above, the mixture is placed in a special type of mechanical stirrer, which has the specifications of being 3-phase and having an AC power supply, 0-10 000 rpm variable speed, a vertical motor having twin blades, a helical shape attached with the vertical shaft of the motor, and four zigzag shaped blades which are fixed in the emulsified fuel containing drum vessel to obtain swirl motion for better mixing. After a required time interval, a good emulsion is formed due to the sharing effects produced by the helical blades of the shaft and fixed blades in the emulsified fuel vessel. Surfactant (1% by weight) is used, and the stability time is about 1.5 days. All the tests are carried out at a constant speed of 1500 rpm under variable load conditions. Performance and emission tests has been carried out for the additive added emulsified fuel to find the optimum quality of diethyl ether, and results are compared with normal emulsified fuel and the diesel no. 2. Throughout the experiment, the static injection timing has been maintained at 23° before top dead center (BTDC), which is optimal for the base diesel engine (Table 2). (7) Herzog, P.; Burgler, L. L.; Winklhofer, E.; Zelenka, P.; Wolfgang, C. NOx reduction strategies for DI Diesel Engines; SAE technical paper no. 920470, SAE: Warrendale, PA, 1992. (8) Lin, C.-Y.; Wang, K.-H. Effects of an Oxygenated Additive on the Emulsification Characteristics of Two and Three phase Diesel Emulsions. Fuel 2004, 83, 507-515.
Figure 1. Experimental setup.
5. Results and Discussion Results obtained by the 10% diethyl ether added emulsified fuel have been compared with emulsified fuel 70D:30E and diesel no. 2 and are as shown in Figures 2-7. From Figure 2 the brake thermal efficiency is almost equal for all the fuels at lower loads. This is due to increase in the ignition delay and the adverse effect of ethanol on the combustion process when the engine temperature is low.9 At the higher load condition, the brake thermal efficiency slightly increases for the diethyl ether added emulsified fuel than the remaining two fuels. In view of this point, at the higher load condition, the longer ignition delay leads to a rapid increase in the premixed heat release rate that affects brake thermal efficiency favorably. The ignition delay period is slightly decreased for the emulsified fuel and the diesel no. 2. On this basis, there is a small decrease in brake thermal efficiency for the emulsified fuel, then to diesel no. 2 fuel, compared to the diethyl ether added emulsified fuel. (9) Gunnerman, R. W.; Russel, R. L. Emission and efficiency benefits of emulsified fuels to internal combustion engines; SAE technical paper no. 972099, SAE: Warrendale, PA, 1997.
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Figure 2. Comparison of brake thermal efficiency.
Figure 3. Comparison of specific fuel consumption.
The difference in value between the diesel no. 2 and the diethyl ether added emulsified fuel is 4.5%, at the maximum load condition. Figure 3 shows that diethyl ether added emulsified fuel attains less specific fuel consumption. The next consecutive roles are taken by the emulsified fuel 70D:30E and the diesel no. 2, respectively. This is based on the energy content of the fuel.10 Normally, ethanol has less energy content than the diesel fuel. On this basis, the emulsified fuel shows a lesser value of specific fuel consumption than the diesel fuel. Also, diethyl ether has the property of a lesser energy content value than ethanol.11 Hence, the lesser specific fuel value is attained by the diethyl ether added emulsified fuel, then the emulsified fuel and the diesel no. 2, as shown in Figure 3. The difference in the values obtained between the diesel no. 2 and the diethyl ether added emulsified fuel at the maximum load is 0.14 kg/kW h. The smoke density level decreases for the emulsified fuel compared to the diesel no. 2 fuel due to better mixing of the air and fuel and increase in the OH radical concentration.12 The (10) Likos, B.; Callahan, T. J.; Moses, C. A. Performance and Emissions of Ethanol and Ethanol-Diesel Blends in Direct-Injected and Pre-Chamber Diesel Engines; SAE technical paper no. 821039, SAE: Warrendale, PA, 1982. (11) Bailey, B.; Eberhardt, J.; Goguen, S.; Erwin, J. Diethyl ether (DEE) as a Renewable Diesel Fuel; SAE technical paper no. 972978, SAE: Warrendale, PA, 1997. (12) Murayama, T.; Morishima, Y.; Tsukahara, M.; Miyamoto, N. Experimental Reduction of NOx, smoke and BSFC in a Diesel Engine using uniquely Produced Water to Fuel Emulsion; SAE technical paper no. 780224, SAE: Warrendale, PA, 1978.
Ashok and SaraVanan
Figure 4. Comparison of smoke density.
Figure 5. Comparison of particulate matter.
peak value attained by the diesel no. 2 at the maximum load condition is 20.2 HSU (Hartridge smoke units). Similarly, the peak value attained by the emulsified fuel at the maximum load condition is 13.9 HSU. The smoke density is further decreased with the diethyl ether addition due to the presence of oxygen in the additive. The difference in values between the emulsified fuel and the diethyl ether added emulsified fuel is 9 HSU. As the smoke density and the particulate matter are directly proportional with each other, the same result is obtained. Particulate matter is reduced for the emulsified fuel due to the fact that ethanol can be combusted essentially soot free under typical combustion conditions.13 It is much more reduced for the diethyl ether added emulsified fuel due to the presence of oxygen. Hence, more soot free combustion occurs under typical conditions for the additive than the ethanol. On that basis, the diesel no. 2 has taken the peak value, next to the role of emulsified fuel; finally, diethyl ether added emulsified fuel has taken the least role of particulate matter. The low cetane depressing properties cause increase in ignition delay and greater rates of pressure rise, resulting in high peak cylinder pressures and high peak combustion temperatures. The peak temperature always increases NOx formation.14 Due to this fact, the emulsified fuel containing ethanol, which has a low cetane number (8), emits higher NOx formation than the (13) EPAA Report: Automobile Emissions: An OVerView and Science Topics: Particulate Matter: Back ground; National center for Environmental research, US Environmental Protection Agency, Washington, D.C., 1994.
Emulsified Fuel in a DI Diesel Engine
Figure 6. Comparison of oxides of nitrogen.
Figure 7. Comparison of exhaust gas temperature.
diesel fuel no. 2, which has a high cetane number (50). But, the additive diethyl ether having higher cetane number (>125) than those two fuels emits much lower NOx formation. This is due to the reduction in ignition delay. This reduced ignition delay lowers the mass of the fuel accumulated before combustion and lowers the initial combustion rates, hence decreasing the peak temperature thus reducing the NOx formation.15 On the basis of the above reference, the emulsified fuel emits more NOx than the diesel fuel no. 2 and the diethyl ether added emulsified fuel emits a lower value than the diesel no. 2, based on its cetane number. Since the latent heat of evaporation of ethanol is higher than that of the diesel no. 2, it causes increase in the combustion temperature.16 This increases the values of the exhaust gas temperature for the emulsified fuel over that of the diesel no. 2. Similarly, the diethyl ether has a lower latent heat of evaporation value than the diesel no. 2 and ethanol, and hence, it emits a lower exhaust gas temperature. According to this order, the respective curves have taken the place in Figure 7. (14) Tsukahara, M.; Yoshimoto, Y.; et al. Reduction of NOx, Smoke, BSFC, and Maximum Combustion Pressure by Low compression ratios in a Diesel Engine Fueled by Emulsified fuel; SAE technical paper no. 920464, SAE: Warrendale, PA, 1992. (15) Miyamoto, N.; et al. Significant NOx reductions with direct water injection in to the sub chamber of an IDI Diesel engine; SAE technical paper no. 950609, SAE: Warrendale, PA, 1995. (16) Corkwell, K. C.; Jackson, M. M.; Daly, D. T. Review of Exhaust Emissions of Compression Ignition Engines Operating on E Diesel Fuel Blends; SAE technical paper no. 2003-01-3283, SAE: Warrendale, PA, 2003.
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Figure 8. Comparison of ignition delay.
Figure 9. Comparison of peak pressure.
Ignition delay is the highest at all loads for the emulsified fuels as compared to diesel no. 2 and the diethyl ether added emulsified fuel. The lowest ignition delay value is obtained by the diethyl ether added emulsified fuel at all loads. The diesel no. 2 ignition delay values are obtained in between these two curves as shown in Figure 8. Normally, a low cetane number increases the delay period.17 Here, the emulsified fuel 70D:30E consists of ethanol, which has a low cetane number. Hence, the emulsified fuel curve has taken the higher value of the delay period. The next role has been taken by the diesel no. 2 fuel, which has a higher cetane number than the emulsified fuel ratio. At least the 10% diethyl ether added emulsified fuel has the comparatively best cetane number. Hence, it has taken the least value of the delay period. With the introduction of diethyl ether, the dynamic injection timing is retarded. This leads the fuel to being injected closer to TDC (top dead center), where the air temperature is high. This phenomenon and the high cetane number of diethyl ether leads to lower ignition delay.5,18 The peak pressure is higher for the emulsified fuel as shown in Figure 9. It is reduced at high out put with the introduction of diethyl ether due to reduction in ignition delay and retarded injection.19 However, it is increased at lower outputs. The diesel no. 2 fuel gives a lesser peak pressure value than the two fuels. (17) Orlee, R. M.; Lenane, D. L. Diesel Combustion Cetane Number Effects; SAE technical paper no. 840108, SAE: Warrendale, PA, 1984. (18) Afify, E. M.; Korah, N. S.; Dickey, D. W. The Effect of Air Charge Temperature on Performance, Ignition delay and Exhaust Emissions of Diesel Engines using W/O emulsions as fuel; SAE technical paper no. 870555, SAE: Warrendale, PA, 1987.
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Figure 10. Comparison of the maximum rate of pressure rise.
The difference between the diethyl ether added emulsified fuel and the diesel no. 2 at a higher output is 12 bar. As in the previous category, similar trends are seen in the case of a maximum rate of pressure rise as shown in Figure 10. It is also reduced at high outputs with the introduction of diethyl ether due to reduction in ignition delay and retarded injection. Conclusions The performance and emission characteristics of the diethyl ether added emulsified fuel is compared with the emulsified fuel ratio 70D:30E and the diesel no. 2. The following results are obtained. • Use of emulsified fuel increases the brake thermal efficiency and reduces the specific fuel consumption, smoke density, and particulate matter. However, there is much rising of NOx. (19) Hountalas, D. T.; Rakopoulos, C. D.; Zannis, T. C.; Koutroubousis, A. P. Application and EValuation of a Detailed Friction Model on a Di Diesel Engine With Extremely High Peak Combustion Pressures; SAE technical paper no. 2002-01-0068, SAE: Warrendale, PA, 2002.
Ashok and SaraVanan
• Addition of diethyl ether to the emulsified fuel improves the performance and reduces the emissions. It also reduces the NOx and ignition delay. - Higher brake thermal efficiency is achieved by the diethyl ether added emulsified fuel. Brake thermal efficiency increases from 36% (emulsified fuel) to 38% (diethyl ether added emulsified fuel). - Lower specific fuel consumption is achieved by the diethyl ether added emulsified fuel. There is a difference in the specific fuel consumption of 0.068 kg/kW h between the diethyl ether added emulsified fuel and the emulsified fuel. - The best decrease in the smoke density value is obtained for the diethyl ether added emulsified fuel than the other two fuels. The value for the diethyl ether added emulsified fuel and the emulsified fuels are 9 and 13.4 HSU, respectively. - Particulate matter emission is low at lower outputs and equal to the emulsified fuel values at higher outputs for the diethyl ether added emulsified fuel. - The NOx value is drastically reduced because of the diethyl ether additive. It is usually higher for the emulsified fuel. It is reduced from 653 to 240 ppm (parts per million) for 70D:30E emulsified fuel and the diethyl ether added emulsified fuel, respectively. - The exhaust gas temperature is lower for the diethyl ether added emulsified fuel than for the other two fuels. - The ignition delay is decreased in value for the diethyl ether added emulsified fuel compared to the other two fuels. At lower output, the difference in value is 4.9 ca. deg. - The peak pressure and the maximum rate of pressure rise decrease high output due to reduction in ignition delay. On the whole, the emulsified fuel 70D:30E increases the brake thermal efficiency and decreases the specific fuel consumption, particulate matter, and smoke density. However, there is a rise in NOx and ignition delay. By adding the diethyl ether as an additive to the emulsified fuel (70D:30E), the NOx and ignition delay are significantly decreased. Also, the performance of the fuel increased and emission characteristics decreased. EF060584B
