Ethanol animal fat emulsions as a diesel engine fuel Part 2: Engine test analysis

Transcription

1 Fuel 85 (26) Ethanol animal fat emulsions as a diesel engine fuel Part 2: Engine test analysis M. Senthil Kumar, A. Kerihuel, J. Bellettre *, M. Tazerout Département Systèmes Energétiques et Environnement, Ecole des Mines de Nantes, 4 rue Alfred Kastler, BP 2722, 4437 Nantes, Cedex 3, France Received 9 March 25; received in revised form 22 May 26; accepted 23 May 26 Available online 23 June 26 Abstract This work aims on the efficient use of animal fat in a diesel engine by making its stable emulsions with ethanol and water. A single cylinder direct injection diesel engine is tested using neat diesel, neat animal fat and animal fat emulsion (optimal emulsion) as fuels under variable load operating conditions. Results show increased peak pressure and ignition delay with ethanol animal fat emulsion as compared to neat fat. Heat release pattern shows improvement in the premixed combustion phase with animal fat emulsion as compared to neat animal fat. Drastic reduction in smoke, nitric oxide, hydrocarbon and carbon monoxide emissions are observed with the emulsion as compared to neat fat and neat diesel mainly at high power outputs. Only, hydrocarbon and carbon monoxide emissions are found as high with the emulsion at light loads. In general, animal fat emulsion shows considerable reduction in all emissions and improvement in engine performance as compared to neat fat. Ó 26 Elsevier Ltd. All rights reserved. Keywords: Diesel engine; Ethanol; Animal fat emulsion 1. Introduction Diesel engines are mainly used in industrial, transport and agricultural applications due to their high efficiency and reliability. However, they suffer from high smoke and nitric oxide emissions [1 3]. The increase in prices of diesel fuel, reduced availability, more stringent governmental regulations on exhaust emissions and the fast depletion of world-wide petroleum reserves provide a strong encouragement to the search for alternative fuels. It is commonly accepted that clean combustion in diesel engines can be achieved only if engine development with fuel reformulation and the use alternative fuels are implemented [4 6]. In the name of energy security, regional air quality and greenhouse gas emissions reduction, use of oxygenated alternative fuels are advocated to reduce emissions in diesel * Corresponding author. Tel.: address: Jerome.Bellettre@emn.fr (J. Bellettre). engines. In this regard, animal fats have come across good choice to use as fuel in diesel engines [7,8]. As a compression ignition engine fuel animal fats have cetane number and calorific value very close to diesel. The added advantage is that animal fats have fixed oxygen present in it [9]. Hence they can increase the local oxygen concentration in the fuel mixture when used as fuel in diesel engines. Contrary to fossil fuels animal fats are free from sulfur. However, the high viscosity and poor vaporization characteristics of animal fats indicate that they need modifications before using them in diesel engines. Animal fats offer the advantage of freely mixing with alcohols (both methanol and ethanol) and these blends can be used in the existing diesel engines without modifications. This is a simple process. The major advantages of the blending are the absence of technical modifications and the ease of implementation. Blending of animal fats with alcohols results in significant improvement in physical properties [1]. Viscosity and density are considerably reduced. Volatility is also improved. Although both methanol and /$ - see front matter Ó 26 Elsevier Ltd. All rights reserved. doi:1.116/j.fuel

2 M.S. Kumar et al. / Fuel 85 (26) ethanol reduce emissions in diesel engines, ethanol has the advantage of having higher miscibility with diesel, vegetable oils and animal fats. Besides being a biomass-based renewable fuel, ethanol has cleaner burning characteristics and a high cetane rating than methanol [11,12]. It has been reported that the application of ethanol as a supplementary compression ignition fuel can reduce environmental pollution, strengthen the agricultural economy and reduce diesel fuel requirements [13 16]. Therefore, the use of ethanol in compression ignition engines has received considerable attention in recent years. Though several research projects have been carried out on a number of alternative fuels in diesel engines, not much data is available on the performance of constant speed stationary diesel engine fuelled with animal fat. Moreover, study of ethanol animal fat emulsions on diesel engines seems to be not done anywhere in the past. In Europe, the production of animal fat is very high. Hence it finds attraction to use as fuel in diesel engines. Since low horsepower stationary diesel engines are commonly used in agricultural and transport sectors, there is a need to study their performance using alternative fuels. This can be further extended to high power output multi cylinder engines also. Therefore, a study is undertaken with the objective of finding out the performance of a diesel engine operated on the fuels completely obtained from renewable energy sources such as animal fat and ethanol. The chemical composition and the different properties of the tested fat and its emulsion have been measured in the first part of this work [17]. 2. Experimental setup and experimental procedure 2.1. Engine test cell A single cylinder air cooled Lister Petter diesel engine developing a power output of 2.8 kw at 15 rev/min is used for the work. The Schematic of the experimental set up is shown in Fig. 1. An electrical dynamometer is used for loading the engine. An orifice meter connected to a large tank is attached to the engine to make air flow measurements. The fuel flow rate is measured on the volumetric basis using a burette. Chromel alumel thermocouples in conjunction with a slow speed digital data acquisition system is used for measuring the exhaust gas temperature Combustion data acquisition A high-speed digital data acquisition system (AVL Indiwin) in conjunction with two AVL piezoelectric transducers is used for the measurement of cylinder pressure and fuel line pressure histories. An optical shaft position encoder is used to give signals at TDC. Engine in cylinder pressure and crank angle are sampled for 1 consecutive cycles at increments of.1 crank angle and averaged to obtain combustion parameters Diesel Diesel Tank 4 Tank Test Engine 11. Fast Data Acquisition Sysytem 2. Dynamometer 12. Slow Data Acquisition system 3. Animal Fat Tank 13. Cylinder Pressure Sensor 4. Diesel Tank 14. Injection Pressure Sensor 5. A/D Card for Pressure 15. Diesel Filter 6. A/D Card for Analyser 16. Animal fat Filter 7. Air Tank 17. TDC Encoder 8. Burette for diesel 18. Speed Sensor 9. Burette for Animal Fat 19 Exhaust gas Analyser 1. Charge Amplifier 2. Smoke Meter Fig. 1. Schematic of experimental setup.

3 2648 M.S. Kumar et al. / Fuel 85 (26) Emission instrumentation An infrared (COSMA) exhaust analyzer is used for measuring hydrocarbon (HC) and carbon monoxide (CO) emissions. NO in the exhaust is measured by using a Beckman chemiluminescence NOx analyzer. Smoke levels are measured using a standard HARTRIDGE smoke meter which works on light absorption technique (passing a light beam through the exhaust sample and the fraction of light is absorbed by the exhaust gas). Light extinction coefficient K is used as the measure of smoke density Experimental procedure Experiments are initially carried out on the engine using diesel and neat fat as fuels. The injection timing is set at 2 before TDC for all the tested fuels. The engine is stabilized before making all measurements. Readings for engine speed, fuel flow, air flow, exhaust gas temperature etc. are recorded for obtaining performance parameters. Exhaust gas analyzers are calibrated before making measurements. Observations are made for smoke, NO, HC and CO to analyze the emission characteristics. In all cases pressure crank angle data are recorded and processed to get combustion parameters. Optimum animal fat emulsion obtained, based on viscosity, stability and micro-structure is finally tested in the same engine at the same operating conditions. Performance, emission and combustion characteristics of the optimum emulsion are analyzed and compared with neat fat and neat diesel. 3. Results and discussion 3.1. Combustion parameters The variation of maximum cylinder gas pressure at different power outputs for neat diesel, neat animal fat and its ethanol emulsion is shown in Fig. 2. Neat animal fat results in lower peak pressure as compared to neat diesel. The maximum cylinder pressure is found as 92 bar with neat diesel and 8.7 bar with neat fat at peak power output. However, except at lightest loads the maximum cylinder pressure increases with the animal fat It is found as 87 bar with animal fat emulsion at peak power output. The increase in peak pressure with the emulsion of animal fat can be explained by the higher premixed burning rate of emulsion due to the long ignition delay (will be seen later). The low cetane number and high latent heat of vaporization of ethanol in the emulsion results in increased ignition delay. The increase in ignition delay results in a strong premixed combustion phase and gives rise to the cylinder gas pressure with the This behavior becomes more obvious at high engine loads. The increase in the ignition delay with the ethanol animal fat emulsion increases the amount of fuel burned within the premixed burning phase. At high engine loads more fuel is burned in the premixed burning phase, causing high value of peak pressure and rate of pressure rise. Peak Pressure (bar) Fig. 2. Variation of cylinder pressure with animal fat ethanol Fig. 3 illustrates the heat release pattern with neat diesel, neat animal fat and its ethanol emulsion at maximum power output. Neat animal fat and its emulsion follow the trend similar to diesel. It can be seen that the combustion is more pronounced at the diffusion phase rather than premixed phase with neat fat. However, ethanol animal fat emulsion indicates improvement in heat release rate at the premixed combustion period. It clearly shows a delay at the starting position of heat release as compared to that of the diesel fuel and neat animal fat. The presence of ethanol and water fraction in the emulsion decreases the cetane number of the emulsion and increases the ignition delay period. This results in increased amount of combustible fuel to be prepared within the period of ignition delay and increases the heat release rate. It is important to note that although more fuel is needed for the emulsion to obtain the same power as compared to diesel, the increase in fraction of the premixed burning phase and shortening in diffusive burning phase could be still achieved with the emulsions. At low engine loads (not shown), the heat release curve revealed a sharp and short premixed burning Heat Release Rate (kj/m 3 deg) Crank Angle ( CA) Inj.Timing : 2 BTDC Load : 1 % Fig. 3. Variation of heat release rate with animal fat ethanol

4 M.S. Kumar et al. / Fuel 85 (26) Ignition delay ( CA) Combustion Duration ( CA) Neat Animal Fat Fig. 4. Variation of ignition delay with animal fat ethanol pattern. This can also be explained by the influence of the ignition delay as long ignition delay will make the combustion to postpone to a late stage. At low power outputs the combustion becomes inferior with the emulsions due to very low temperature of the cylinder. Hence the heat release becomes very weak at low power outputs. Fig. 4 shows the ignition delay for neat diesel, neat animal fat and its emulsion with ethanol and water at all power outputs. As expected, ignition delay decreases with increase in power outputs for all the tested fuels. The decrease in ignition delay with the increase in engine load is due to the influence of cylinder gas temperature within the ignition delay period. The gas temperature is higher at high engine loads than that at low engine loads. It is seen that the ignition delay is more with the emulsions as compared to neat fat and diesel at all power outputs. It is found as 8 CA with neat fat, 6 CA with neat diesel and 1 CA with ethanol animal fat emulsion at peak power output. The increase in ignition delay with the emulsion can be explained by the vaporization of ethanol and water in the emulsion which causes the injected fuel spray into a relatively low gas temperature environment and increases the period of ignition delay. It can be further explained by the low cetane number of ethanol The total combustion duration decreases with the animal fat emulsion as compared to neat fat as seen in Fig. 5. This is mainly due to the increase in rapid burning rate of the The addition of ethanol with the animal fat emulsion promotes combustion and shortens the combustion duration. As being explained in the above section of heat release analysis, the faster combustion rate in the premixed burning phase and shorter diffusive burning phase decrease the total combustion duration of the animal fat ethanol 3.2. Performance parameters The relationship between power output and specific energy consumption with neat animal fat and its ethanol Fig. 5. Variation of combustion duration with animal fat ethanol emulsion is shown in Fig. 6. The specific energy consumption decreases with the increase in engine load. After a certain percentage of maximum load, any further increase in brake load causes only a small increase in brake horsepower. This results in increased specific energy consumption at very high power outputs. It is seen that neat animal fat results in higher SEC as compared to neat diesel. This can be explained by the poor combustion of the injected fat as a result of high viscosity and density. However, there is an improvement in SEC with the emulsions of animal fat. Minimum value of SEC is found at 6% of the maximum load with the The improvement in specific energy consumption with the emulsion is attributed to the changes occurring in the combustion process. The physical and chemical differences in fuel structure of ethanol and fat lead to a combination of changes in the combustion process. The physical properties of animal fat are changed when ethanol is added. The addition of ethanol causes the viscosity of animal fat to decrease. Presence of SEC (kj/kw.hr) Fig. 6. Variation of specific energy consumption with animal fat ethanol

5 265 M.S. Kumar et al. / Fuel 85 (26) Exhaust gas temperature ( C) Hydrocarbon (ppm) Fig. 7. Variation of exhaust gas temperature with animal fat ethanol Fig. 8. Variation of hydrocarbon emission with animal fat ethanol water in the emulsion leads to secondary atomization (micro-explosion) of the fuel and results in more complete combustion and rapid energy release. All these factors result in low specific energy consumption with the The variation of exhaust gas temperature at different power output conditions for neat diesel, neat animal fat and its emulsion with ethanol and water is shown in Fig. 7. It is clear from the figure that as the power increases, the exhaust gas temperature increases with all the fuels. The maximum exhaust gas temperatures of 54 C, 595 C and 48 C are observed at maximum power output when the engine is running on diesel, neat animal fat and ethanol animal fat emulsion respectively. The variations in exhaust gas temperature indicate that the type of fuel and engine brake load have a significant effect on exhaust gas temperature. It is seen that animal fat emulsion has lowest exhaust gas temperature as compared to neat diesel and neat animal fat. This can be explained by the high latent heat of vaporization of water and ethanol which results in lower burning temperatures with the In addition to that, the shorter diffusive combustion reduces the late burning of fuel. due to it s slow burning (late combustion) characteristics produces highest exhaust gas temperature Emission parameters Hydrocarbon emissions emitted from neat diesel, neat animal fat and its emulsions are shown in Fig. 8. Compared to neat diesel, neat animal fat emits more hydrocarbon emissions at all operating conditions. The maximum hydrocarbon emission is found as 126 ppm with neat diesel and 625 ppm with neat fat at peak power output. The main reason for the higher hydrocarbon is the result of incomplete combustion of neat fat. Animal fat emulsion shows lower hydrocarbon emissions (about 215 ppm) as compared to neat fat mainly at high power outputs. Improved vaporization and atomization of the emulsions result in better mixing with air and leads to complete combustion of the fuel at high loads. However, at low power outputs emulsion shows higher hydrocarbon emissions. The hydrocarbon emissions tend to increase because of the quench layer of unburned ethanol present in the combustion chamber at low power outputs. In addition to that the high latent heat of vaporization of water produces slow vaporization and mixing of fuel and air. In homogeneity of the air fuel mixture may also contribute to leaner mixture in some regions of combustion chamber and results in more unburned fuels at low power outputs. Neat animal fat results in higher carbon monoxide emissions as compared to neat diesel as shown in Fig. 9. Neat animal fat results in fuel richness and leads to more carbon monoxide emissions. It is observed that animal fat emulsion also results in higher carbon monoxide emission than neat diesel and neat fat at low power outputs. The increase Carbonmonoxide (ppm) Fig. 9. Variation of carbon monoxide emission with animal fat ethanol

6 M.S. Kumar et al. / Fuel 85 (26) in the carbon monoxide levels with ethanol emulsions is the result of incomplete combustion of the ethanol air mixture at light loads. Factors causing combustion deterioration such as high latent heats of vaporization can be responsible for the poor oxidation reaction rate of carbon monoxide and increased CO production. As mentioned earlier, a thickened quench layer created by the cooling effect of vaporizing alcohol can play a major role on CO production at part loads. Although the CO level is higher at light loads for the ethanol animal fat emulsion, the CO level is fairly lower than that of neat animal fat and neat diesel at high power outputs. Since ethanol has less carbon than diesel fuel and its oxygen content increases the oxygen to fuel ratio in the fuel rich regions. The increased air fuel ratio due to the increased volumetric efficiency leads to more complete combustion of the fuel. The presence of atomic bound oxygen in the fuel satisfies positive chemical control over CO formation. The black smoke emission resulting from combustion of diesel, neat animal fat and its emulsions is plotted in Fig. 1. Smoke levels are high at high power outputs with diesel and neat animal fat. This is due to the presence of fuel rich core at high loads. The maximum smoke level is found as 7.7 K with neat diesel and 3.6 K with neat fat. It is seen that the smoke level is lower with neat animal fat than neat diesel. The result of low smoke emission with neat animal fat is due to the presence of low carbon content in the fat. In addition to that the oxygen present in the fat helps in smoke reduction. Smoke emission is further reduced with animal fat The trend shows drastic reduction (about.3 K) in smoke emissions with ethanol animal fat The reduced smoke at high loads can be explained by the reasons that the use of ethanol, an oxidizer is effectively introduced to the fuel-rich regions and suppress soot formation in combustion chamber. Ethanol does not provide the initial radicals for the formation of aromatic rings. The charge cooling increases ignition delay and thus, enhances the mixing of fuel with air which in turn makes better air utilization. The high oxygen content of the emulsion combined with low C/H ratio and aromatic fractions contributes to the reduction of smoke. High level of oxygen atoms present in the fuel also results in overall leaner mixture. All these factors result in overall reduction in smoke emission. The NO emission of the engine operating on diesel, neat animal fat and ethanol animal fat emulsions is given in Fig. 11. It shows that the NO emission is reduced with neat fat as compared to neat diesel. The maximum NO emission is found as 148 ppm with neat diesel and 965 ppm with neat animal fat. The reduction in NO emission with neat fat is due to the reduced premixed combustion as a result of slow burning. The NO emission is further reduced with the emulsions of animal fat as compared to neat diesel and neat fat. The minimum value of 246 ppm at maximum power output is found with the animal fat The main reason for the drastic reduction in NO emissions is again due to the high latent heat of vaporization of water. In the absence of nitrogen in the tested fuels, the formation of NO mainly depends on thermal NO and prompt NO. The kinetics formation of thermal NO are governed by the extended Zeltovitch mechanisms. Since the latent heat of vaporization of water is high, the charge temperature becomes low when the fuel is injected into the combustion chamber. As a result the peak combustion temperature becomes low and leads NO to diminish. Presence of ethanol in the emulsions also helps to suppress the formation of thermal NO. The formation of prompt NO is initiated by the reaction between hydrocarbon radicals and molecular nitrogen. This kind of NO is principally formed in fuel rich conditions. As the appearance of micro-explosion results in a better air/fuel mixture, it prevents rich pockets. Indeed, with animal fat emulsions the formation of prompt NO is reduced to. Smoke No. (m -1 ) Nitric Oxide (ppm) Fig. 1. Variation of smoke density with animal fat ethanol Fig. 11. Variation of nitric oxide with animal fat ethanol

7 2652 M.S. Kumar et al. / Fuel 85 (26) Conclusions Influence of ethanol on engine performance, emissions and combustion characteristics of a diesel engine fuelled with the optimum animal fat emulsion (explained in Part 1) is studied experimentally. Ethanol animal fat emulsion shows increased cylinder peak pressure and ignition delay. Higher premixed combustion and lower combustion duration are found with the emulsions as compared to neat fat. Further, improvement in performance and significant reduction in smoke, nitric oxide emissions, hydrocarbon and carbon monoxide emissions are achieved mainly at high power outputs. Emulsification of animal fat with ethanol and water can be a promising technique for using animal fat efficiently in diesel engines without any modifications in the engine. Simultaneous reduction in nitric oxide and smoke can be achieved with the use of animal fat emulsions. However, poor part load performance needs attention. Techniques like exhaust gas recirculation, cetane improvers etc. can further improve the emulsion performance at part loads. References [1] Larsen Chris, Oey Frederick, Levendis YA. An optimization study on the control of NOx and particulate emissions from diesel engines. Society of automotive engineers 1996, Paper No [2] Summers JC, Houtte SV, Psaras Dimitrios. Simultaneous control of particulate and NO x emissions from diesel engines. Appl Catal B: Environ 1996;1(1 3): [3] Ladommatos N, Abdelhalim S, Zhao H. Control of oxides of nitrogen from diesel engines using diluents while minimizing the impact on particulate pollutants. Appl Thermal Eng 1998;18(1): [4] Xing-cai Lü, Jian-guang Yang, Wu-gao Zhang, Zhen Huang. Effect of cetane number improver on heat release rate and emissions of high speed diesel engine fueled with ethanol diesel blend fuel. Fuel 24;83(14 15): [5] Satge de Caro P, Mouloungui Z, Vaitilingom G, Berge JC. Interest of combining an additive with diesel ethanol blends for use in diesel engines. Fuel 21;8(4): [6] Canakci M, Van Gerpen JH. Comparison of engine performance and emissions for petroleum diesel fuel, yellow grease biodiesel and soybean oil bio diesel. American society of agricultural engineers 21, Paper No [7] Ali Yusuf, Eskridge KM, Hanna MA. Testing of alternative diesel fuel from tallow and soybean oil in Cummins N14-41 diesel engine. Bioresour Technol 1995;53(3): [8] Ali Yusuf, Hanna MA, Borg JE. Optimization of diesel, methyl tallowate and ethanol blend for reducing emissions from diesel engine. Bioresour Technol 1995;52(3): [9] Senthil Kumar M, Kerihuel A, Bellettre J, Tazerout M. Investigations on the use of preheated animal fat as fuel in a diesel engine. Renewable Energy 25;3: [1] Kerihuel A, Senthil Kumar M, Bellettre J, Tazerout M. Use of animal fats as CI engine fuel by making stable emulsions with water and methanol. Fuel 25;84: [11] Hansen AC, Zhang Q, Lyne PWL. Ethanol diesel fuel blends a review. Bioresour Technol 25;96: [12] He BQ, Shuai Shi-Jin, Wang Jian-Xin, He Hong. The effect of ethanol blended diesel fuels on emissions from a diesel engine. Atmos Environ 23;37(35): [13] Irshad A. Oxygenated diesel: emissions and performance characteristics of ethanol- diesel blends in CI engines. Society of automotive engineers 21, Paper No [14] Czerwinski J. Performance of HD-DI diesel engine with addition of ethanol and rapeseed oil. Society of automotive engineers 1994, Paper No [15] Ajav EA, Singh Bachchan, Bhattacharya TK. Experimental study of some performance parameters of a constant speed stationary diesel engine using ethanol diesel blends as fuel. Biomass Bioenergy 1999;17(4): [16] Ajav EA, Singh Bachchan, Bhattacharya TK. Thermal balance of a single cylinder diesel engine operating on alternative fuels. Energy Conversion Manage 2;41(14): [17] Kerihuel A, Kumar MS, Bellettre J, Tazerout M. Ethanol animal fat emulsions as a diesel engine fuel Part 1: Formulations and influential parameters. Fuel, in press. doi:1.116/j.fuel