Aqueous Aluminum Nanofluid Combustion in Diesel Fuel

Transcription

1 Journal of Testing and Evaluation, Vol. 36, No. 2 Paper ID JTE Available online at: Mu-Jung Kao, 1 Chen-Ching Ting, 2 Bai-Fu Lin, 1 and Tsing-Tshih Tsung Aqueous Aluminum Nanofluid Combustion in Diesel Fuel ABSTRACT: This paper presents a significant chemical reaction of hydrogen combustion during aqueous aluminum nanofluid combustion in diesel fuel. The results show that hydrogen burns in a diesel engine in the presence of an active aqueous aluminum nanofluid. The nano particles are made by applying a plasma arc to aluminum nanopowder submerged in water. The average diameter of the aluminum nanoparticles is about nm and they are covered with thin layers of aluminum oxide due to the high oxidation activity of pure aluminum. This provides a large contact surface area with water and high activity for the decomposition of hydrogen from water during the combustion process. During combustion the alumina serves as a catalyst and the coated aluminum nanoparticles are denuded and decompose the water to yield the hydrogen. The combustion of the diesel fuel mixed with aqueous aluminum nanofluid shows the following phenomena: total combustion heat increases while the concentration of smoke and nitrous oxide in the exhaust emission from diesel engine are decreased. KEYWORDS: aqueous aluminum nanofluid, combustion, diesel fuel, aluminum nanopowder Introduction Manuscript received April 19, 2006; accepted for publication October 17, 2007; published online November Department of Vehicle Engineering, National Taipei University of Technology, Taiwan 2 Department of Mechanical Engineering, National Taipei University of Technology, Taiwan, chchting@ntut.edu.tw Research on the topic of water/diesel mixtures in compression ignition engines is aimed at fuel conservation and reduction of undesirable emissions and has been presented in several papers [1 3]. Experiments have shown that the water/diesel emulsion can reduce the concentrations of NOx, smoke, BSFC, etc. during combustion, and these results agree with the theoretical prediction [4,5]. Additives of metal oxide in the water/diesel emulsion are normally used as the catalyst to activate the molecular bonding of the water/diesel mixture and produce a chemical reaction [6]. The photoelectrocatalytic effect for generation of hydrogen from water using metal oxide, e.g., TiO 2, as the catalyst is well known [7]. Recently, scientists and engineers have applied nanotechnologies to human lives in a wide variety of subjects such as biomedical, material, computer, and fuel engineering fields. Adding metallic powder to ordinary fossil fuel usually increases the combustion efficiency and improves combustion stability, e.g., adding 0.5 % aluminum nanopowder to a rocket s solid fuel can improve combustion efficiency by 10 to 25 % and increase combustion speed by an order of magnitude [8]. Studies have shown that water can react with aluminum powder during combustion to generate hydrogen and hence increase aqueous aluminum fossil fuel s combustion heat. Hydrogen is clearly a promising alternative to hydrocarbon fossil fuels since it has higher energy efficiencies and is associated with lower emissions [9]. The catalytic activity of a metal oxide catalyst Fe/Al 2 O 3 can cause water to yield hydrogen through decomposition [7,9]. Aluminum nanopowder has a very high activity and can react with water at temperatures from 400 to 660 C to generate hydrogen and improve fuel combustion [2]. The cited studies have shown that aluminum nanopowder promotes fuel combustion. Therefore, in this study, homemade nanofluid in the form of aluminum nanoparticles coated by alumina submerged in water is added to diesel fuel to explore the effects on fuel consumption, exhaust emission, and combustion features of a diesel engine [10]. Aluminum nanopowder can react with water at high temperature and generate hydrogen, promoting the combustion of the fuel [11,12]. Because the aluminum is nanometer size, it has more surface area and higher activity to decompose the hydrogen from water and increase combustion heat. Making aqueous aluminum nanofluid for combustion involves the use of an ultrasonic vibrator to produce emulsified nano-aluminum liquid in a molecule structure of H 2 O Al 2 O 3. An agitator is applied to constantly agitate the nano-aluminum solution and diesel fuel before the mixed fuel is injected into the combustion cylinder. When the H 2 O Al 2 O 3 is mixed with the diesel fuel and burns in the combustion chamber, the focused burning energy with aid of the Al 2 O 3 catalyst breaks the O-H bond with H 2 O. The combustion procedure creates OH and causes denuded aluminum to react with it. According to the Department of Energy, University of Chicago [3], OH and H 2 O can react with aluminum powder to generate hydrogen and promote the combustion of fuel; the reaction equation is described as 2Al +2OH + H 2 O Al 2 O 3 +2H 2. Diesel fuel C n H m is a stable organic molecule. Its electronic structure, its lack of polarity, and in the absence of any functional group make it difficult to decompose into its constituent parts. However, high temperature processes for the thermal decomposition of diesel fuel have been researched [9]. Some studies show that the hydrogen is a high quality fuel that burns rapidly and cleanly [13]. Accordingly, hydrogen can be obtained in the proposed manner from water to burn cleanly and efficiently in diesel engines. Experiments In this experiment, a single-cylinder diesel engine with the specifications indicated in Table 1 is used in a dynamometer. After the engine s operating temperature reached approximately 80 C its power output is tested. During the test the engine is cooled continu- Copyright 2008 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA

2 2 JOURNAL OF TESTING AND EVALUATION TABLE 1 Experimental diesel engine specifications. Type YANMAR TF110-F 1 Cycle 4 2 Number of Cylinder Horizontal Single 3 Bore Stroke (mm) Displacement Volume (cc) Compression Intake System Naturally Aspirated, Single Valve 7 Exhaust System Single Valve 8 Diameter of Plunger (mm) 8 Type of Injection 4-Hole Nozzle Opening Pressure (MPa) 19.6 Injection Timing BTDC 17 Injection Angle Power(HP/r/min) 11/ 2400 FIG. 2 Photo of the used NOx and smoke meter. ously to maintain it in a certain temperature range. The cooling water is circulated and the output power measured under these controlled test conditions. First, the engine s r/min is set to the specified test range, then increased full-throttle to increase engine load to a maximum value under steady state. Experimental data are then collected regarding various exhaust emission concentrations and combustion curves determined after 200 sampling combustion cycles. The same procedure is repeated under reduced loads from nm in 5nm increments till the minimum test load of 12 nm is reached. We measure the fuel consumption and sample exhaust emission concentration values as well as plotting combustion analysis curves at the different test loads. The test fuel employed in this experiment is a high-quality diesel product, the aluminum nanofluid (AN) additive is from the 40 to 60 nm added from 30 cc to 50 cc into 1 litre of diesel fuel, and then an ultrasonic vibrator is used to vibrate the mixture for 15 min to form the experimental nano-aluminum diesel fuel. Figure 1 shows the experimental setup used. The mixer will continuously agitate the diesel fuel and aluminum nanofluid to make sufficient mixing; the mixed fuel then passes through the three-way diverting valve and is sent to the fuel pump, it then enters the injector of the single-cylinder diesel engine. The combustion status of the cylinder in the engine cylinder is transmitted to the combustion analyzer through the pressure transducer and the rotary encoder; it is transformed there and finally sent to the computer. The screen displays the mean combustion pressure inside the engine cylinder for 200 combustion cycles and automatically plots the heat release rate curve. Meanwhile, the engine s exhaust emission concentrations are measured by an NOx meter and a smoke meter as the exhaust passes through the exhaust gas tank. Figure 2 shows a photo of the used NOx and smoke meter. Figure 3 shows the photos of experimental equipment. The left photo is the testing part and right photo is the measuring instrument. Results and Discussions This work uses the experimental equipment described above and follows the specified test procedure to add aqueous aluminum FIG. 1 Layout of experimental equipment. 1 mixer; 2 fuel tank and mixed fuel; 3 three-way valve; 4 oil meter, fuel pump with regulator; injector; 7 single-cylinder diesel engine; 8 transducer; 9 rotary encoder; AVL combustion analyzer; 11 mirco computer; 12 monitor; 13 exhaust gas tank; 14 NOx meter; smoke meter; 16 surge tank; 17 U gage; 18 exhaust thermal sensor. FIG. 3 Photos of experimental equipment.

3 KAO ET AL. ON COMBUSTION IN DIESEL FUEL 3 FIG. 4 BSFC deviation rate of AN+D fuel and D fuel under varied loads. nanofluid additive to diesel fuel to form the mixed fuel AN+D. The experiments were performed by using an engine dynamometer, an exhaust emission analyzer, and other relevant test instruments. The measured values are brake specific fuel consumption (BSFC), exhaust emission concentrations of smoke and NOx, heat released, and pressure inside the engine cylinder with varied values of brake mean effective pressure (BMEP) at varied For comparison, combustion tests at the same conditions using pure diesel fuel (D) are also carried out. Figure 4 presents results on BSFC for values of both diesel (D) and aqueous aluminum nanofluid mixed diesel fuels AN+D at three The engine s speed determines the frequency of the injected fuel into the combustion cylinder the greater the speed the greater the injecting frequency. Greater engine speeds cause greater concentration of fuel in the combustion chamber. As shown in Fig. 4, the values for D fuel and AN+D fuel show an increasing tendency with increasing engine speed. At 1200 and 1800 r/min results show that the trend for using AN+D fuel is to lower BSFC values compared with D fuel. Figure 5 shows another comparison for other varied engine FIG. 5 BSFC mean value deviation rate of AN+D fuel and D fuel at various FIG. 6 Smoke concentrations for AN+D fuel and D fuel under varied loads. speeds using BSFC mean values. The results seem to reverse at higher engine speeds and Fig. 5 illustrates the fact that at greater speeds the chemical reaction of hydrogen decomposition from water during combustion is incomplete. At greater engine speeds the combustion with D fuel is more efficient than with AN+D fuel because of the too large moisture content in AN+D fuel, which causes the decomposing energy to become insufficient. This result agrees also with the previous observation of reduced variation at higher engine speeds due to the increasing concentration of aqueous aluminum nanofluid in diesel fuel. Hydrogen decomposition from water by aqueous aluminum nanofluid combustion does not exist because of too large a concentration of aqueous aluminum nanofluid in the injected fuel. Figure 6 shows the smoke percent for both diesel (D) and aqueous aluminum nanofluid mixed diesel fuels AN+D at three engine speeds. The reduced smoke concentrations at 1200 and 1800 r/min indicate clearly that the combustion with AN+D fuel is more complete at these speeds than with D fuel. This agrees also with the reduced BSFC values. At 2400 r/min the smoke concentration shows no significant difference between AN+D fuel and D fuel. In comparison to the results shown in Fig. 5, the mean values for smoke concentration in Fig. 7 show good agreement. As seen in Fig. 7, the mean smoke concentration of AN+D fuel is lower than that from D fuel in all loads for engine speeds less than 2200 r/min. The reason is that adding aqueous aluminum nanofluid in diesel fuel promotes more complete combustion and the aluminum nanopowder additive contains moisture that produces a microexplosion on the emulsified fuel drains and hence reduces the smoke concentration [12 15]. At 2200 and 2400 r/min the smoke concentration of AN+D fuel does not show a difference in comparison with D fuel, because at these points the catalytic effect of aqueous aluminum nanofluid does not occur. Figure 8 indicates the NOx concentration for D fuel and AN +D fuel of all loads at three It can be seen that the NOx concentration for AN+D fuel is lower than that of D fuel at all loads at 1200 and 1800 r/min, because the aluminum nanopowder additive contains moisture causing micro-explosions in the emulsified fuel drains [16,17]. At 1200 r/min at maximum load hydrogen burning results in the more complete combustion and thus makes the NOx concentration caused by AN+D fuel to be less than that

4 4 JOURNAL OF TESTING AND EVALUATION FIG. 7 Smoke mean value deviation rate of AN+D fuel and D fuel at various caused by D fuel [11]. The latent heat of evaporation of water and its high thermal capacity also reduce the temperatures in the combustion chamber, thus retarding nitrogen oxide build-up. Figure 9 shows the NOx mean values of measurements and indicates that the NOx concentration of AN+D fuel is less than D fuel for engine speeds less than 1800 r/min except for 1400 r/min. In comparison with Fig. 7, the reduction of the NOx concentration with AN+ D fuel is not clear. The aluminum nanopowder additive mixed in D fuel causes a clear smoke reduction and for engine speeds less than 1800 r/min the NOx concentration also shows a decreasing trend. The consumption of AN+D fuel is slightly lower than that of D fuel. The exhaust emission from AN+D fuel is less than from D fuel in all respects. To verify that the fuel consumption and exhaust emission result compare with the actual combustion result, analysis of the combustion heat release rate and the combustion pressure inside the engine cylinder were conducted. Figures 10 and 11 show the combustion heat release rate, Q, and the combustion pressure inside the engine cylinder for D and AN+D fuels at 1200 r/min at FIG. 9 NOx mean value deviation rate of AN+D fuel and D fuel at various the specific load BMEP about 8.4 kg/cm 2. Figure 10 reveals that at a particular concentration of aluminum powder, the combustion heat release rate area under curve increases slightly with the amount of water added, from 3 to 6 %. The combustion heat release rate of D fuel is lower than that of any AN+D fuel, suggesting that the burning of hydrogen contributes slightly to the combustion heat release rate by thermocatalytic decomposition at water concentrations from 3 to 6 %. The AN+D fuel has a slightly greater heat release rate for a given amount of water added. Therefore, less fuel is consumed. Although D fuel yields a higher peak combustion pressure inside the engine cylinder at 1200 r/ min, emissions from AN+ D are slightly lower in NOx concentration because nitrogen oxide is formed at the higher pressures and temperatures. Conclusions Experimental measurements and analysis of aqueous aluminum nanofluid combustion in diesel fuel using a single-cylinder engine FIG. 8 NOx deviation rate of AN+D fuel and D fuel under varied loads. FIG. 10 Heat release rate inside engine cylinder for various added volumes of water.

5 KAO ET AL. ON COMBUSTION IN DIESEL FUEL 5 for engine performance, exhaust emission, and combustion characteristics were conducted. The fixed parameters are fuel injection pressure, injection timing, compression ratio, and geometry of the combustion chamber. The results show that BSFC for AN+D fuel is less than the D fuel at lower engine speeds less than 1800 r/min. The aluminum nanopowder additive mixed in D fuel causes a clear smoke reduction and for engine speeds less than 1800 r/min the NOx concentration has also a decreasing tendency. Adding a particular quantity of aluminum nanofluid to diesel fuel not only reduces fuel consumption, but also improves the exhaust emission concentration from the diesel engine. Acknowledgments The authors would like to acknowledge the financial support from the National Science Foundation of Taiwan under Grant No. NSC S and the Department of Vehicle Engineering, National Taipei University of Technology. References FIG. 11 Combustion pressure inside engine cylinder. [1] Abu-Zaid, M., Performance of Single Cylinder Direct Injection Diesel Engine Using Water Fuel Emulsions, Energy Convers. Manage., Vol. 45, No. 5, 2004, pp [2] Barnaud, F., Schmelzle, P., and Schulz, P., Aquazole: An Original Emulsified Water-Diesel Fuel for Heavy Duty Applications, Society of Automotive Engineerers, Inc., , pp [3] Harbach, J. and Agosta, V., Effects of Emulsified Fuel on Combustion in a Four-Stoke Diesel Engine, J. Ship Res, Vol. 35, No. 4, 1991, pp [4] Tsukahara, M. and Yoshimoto, Y., Reduction of NOx, Smoke, BSFC, and Maximum Combustion Pressure by Low Compression Ratio in a Diesel Engine Fueled by Emulsion Fuel, International Congress and Exposition, Detroit, 1992, pp [5] Law, C. K., A Model for the Combustion of Oil/Water Emulsion Droplets, Combust. Sci. Technol., Vol. 17, Nos. 1 and 2, 1977, pp [6] Mimani, T. and Patil, K. C., Solution Combustion Synthese of Nanoscale Oxide and Their Composites, Mater. Phys. Mech., Vol. 4, 2001, pp [7] Ichikawa, S., Photoelectrocatalytic Production of Hydrogen from Natural Seawater Under Sunlight, Int. J. Hydrogen Energy, Vol. 22, No. 7, 1997, pp [8] Interagency Working Group on Nanoscience, National Nanotechnology Initiative: Leading to the Next Industrial Revolution, Technology National Science and Technology Council, U.S.A., February, [9] Grégoire-Padró, C. E. and Lau, F., Advances in Hydrogen Energy, Kluwer Academic/Plenum Publishers, New York, [10] Kao, M. J., Lin, B. F., and Tsung, T. T., The Study of High- Temperature Reaction Responding to Diesel Engine Performance and Exhaust Emission by Mixing Aluminum Nanofluid in Diesel Fuel, 18th Internal Combustion Engine Symposium Jeju, Korea, [11] Calder, V., Aluminum Combustion, Chicago University, [12] Mench, M. M., Yeh, C. L., and Kuo, K. K., Propellant Burning Rate Enhancement and Thermal Behavior of Ultra-Fine Aluminum Powder (Alex), Proceedings of the 29th International Annual Conference of ICT, Karlsruhe, Federal Republic of Germany, 1998, pp. 30/1 30/15. [13] Hydrogen Power: Theoretical and Engineering Solutions: Proceedings of the HYPOTHESIS II Symposium, T. O. Saetre, Ed., Grimstad, Norway, August 1997, Kluwer Academic Publishers, Boston. [14] Mench, M. M., Yeh, C. L., and Lu, Y. C., Comparison of Thermal Behavior of Regular and Ultra-Fine Aluminum Powder (Alex) Made from Plasma Explosion Process, Combust. Sci. Technol., Vol. 135, No. 1 6, 1998, pp [15] Ritter, H., Braun, S., and Scharf, M., Analyse des thermischen Verhaltens von hochfeinem Alex, ISL publication PU 375/99, [16] Park, J. W., Huh, K. Y., and Park, K. H., Experimental Study on the Combustion Characteristics of Emulsified Diesel in a RCEM, Seoul 2000 FISITA World Automotive Congress, Korea, June, [17] Nadeem, M., Rangkuti, C., Anuar, K., Haq, M. R. U., Tan, I. B., and Shah, S. S., Diesel Engine Performance and Emission Evaluation Using Emulsified Fuels Stabilized by Conventional and Gemini Surfactants, Fuel, Vol. 85, No , 2006, pp