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Optimization of the effect of thermal barrier coating (TBC) on diesel engine performance by Taguchi method
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Full Length Article
Optimization of the effect of thermal barrier coating (TBC) on diesel engine performance by Taguchi method Serkan Özela, , Erdinç Vuralb, Murat Binicic ⁎
a
Bitlis Eren University, Department of Mechanical Engineering, Bitlis, Turkey Aydın Adnan Menders University, Germencik Yamantürk Vocational School, Aydın, Turkey c Bitlis Eren University, Department of Industrial Engineering, Bitlis, Turkey b
ARTICLE INFO
ABSTRACT
Keywords: Thermal barrier coating Diesel engine performance Taguchi ANOVA
In this study, thermal barrier layers were coated on piston and valve surfaces using plasma spray method. The effects of coated layers on torque, power and brake specific fuel consumption (BSFC) were investigated experimentally, and statistically using the Taguchi optimization method. Coating materials used in this study were Al2O3 + 13% TiO2, Cr2O3, and Cr2O3 + 25% Al2O3. Each coating material was tested at different speeds, which were 1400 rpm, 2000 rpm, 2600 rpm and 3200 rpm. The results showed that engine torque and BSFC reached their optimum values with the use of Al2O3 + 13% TiO2 at the speed of 2600 rpm. However, engine power showed the best performance with the same coating material but at the speed of 3200 rpm. The results of the experiment were also tested using Taguchi optimization method with coating material and engine speed parameters. The design of Taguchi analysis was carried out with L16 (42) orthogonal array. The highest S/N ratios of engine torque and BSFC were observed with the coating material of Al2O3 + 13% TiO2 at the speed of 2600 rpm. However, the highest S/N ratio of engine power was seen with the use of Al2O3 + 13% TiO2 at the speed of 3200 rpm. In order to determine the statistical significance of experimental parameters on engine torque and power and BSFC, ANOVA and F-test were carried out. The results of statistical analysis showed that the coating materials (P < 0.05) and engine speed (P < 0.05) parameters were statistically significant on the engine torque, power and BSFC.
1. Introduction Diesel engines have an important role in the automotive industry. They are widely used in both transport and agriculture industries because they have higher fuel saving and lower fuel consumption than other types of engines [1]. However, due to increases in fuel costs, decreases in supplying high-quality fuels to the markets and concerns for environmental issues, researchers in the industry have begun to research on more productive engines [2]. Efficiency and emissions of engines are crucial. There are two ways to make a diesel engine more productive and efficient with lower emission levels [3]. First way is the reduction of losses such as heat loss from the cylinder, wall, cooling water and friction losses in order to make the engine more efficient mechanically and indicatively, and the second one is the usage of a suitable alternative fuel in the engine [3–6]. Regarding the first way, thermal barrier coating (TBC) is one of the most commonly used technologies to keep the heat inside the engine so that it can improve the thermal efficiency of the engines. TBC
⁎
has been used to make improvements on the efficiency and performance of different types of machine tools for a long time and it can be applied to the areas having high temperatures or heat transfer surfaces of gas tribunes. TBC technology can be applied by insulating the engine with ceramic-based coating [7–10]. Ceramic coating layers such as Zr2O, Y2O3, Al2O3, TiO2 and Cr2O3 can be obtained using TBC methods. These layers can be used in aircraft engines and power generation gas turbines to ensure that metal alloy components are not damaged from high-temperature [11–14]. There are some advantages of using TBC in a diesel engine. The heat inside the engine can be kept and thermal fatigue and shocks can be avoided. It can also reduce the emission levels of Hydrocarbon and Carbon Monoxide. Additionally, a piston can be protected from corrosion attack, thermal stress, and high heat emissions by reducing heat flux into the piston and fuel consumption. Moreover, due to the high increase in fuel prices and decreasing the quality of fuels, TBC can be an advantage to get more efficient engine performance. In relation to the low-quality fuels, TBC can keep much more heat inside the engine even
Corresponding author. E-mail address: [email protected] (S. Özel).
https://doi.org/10.1016/j.fuel.2019.116537 Received 11 April 2019; Received in revised form 23 October 2019; Accepted 29 October 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Serkan Özel, Erdinç Vural and Murat Binici, Fuel, https://doi.org/10.1016/j.fuel.2019.116537
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though the fuel is low quality [1–4,7–10,15]. Taguchi design method, which is one of the experimental design methods, is successful in solving optimization problems as it increases processing performance with a lower number of experiments and less cost, and by using Taguchi, the number of experiments can be decreased significantly and thus the loss of time and cost can be prevented [16]. In addition to solving the problems with a few experiments, Taguchi supports developing high-quality process and product from every angle. It has minimum sensitivity to the process or manufacturing conditions of products and uncontrollable factors. Therefore, both the necessary tolerances can be provided with the lowest cost and Taguchi lost function can bring a new understanding to the quality process [17,18]. The Taguchi optimization method has previously been used in many experimental design studies [19–22]. In this study, thermal barrier layers were coated on a piston and valve surfaces by using plasma spraying method. The effects of coated materials and engine speed on engine torque, power and BSFC were investigated experimentally, and statistically using the Taguchi optimization method.
Table 2 Technical properties of the test engine.
- Higher the better, - Nominal to better, - Lower the better,
2.2. Engine tests
Information of each parameter can be retrieved using Analysis of Variance (ANOVA) [27]. In this study, L16 (42) orthogonal array was employed for the robust design of the experimentations. The parameters presumed to affect engine torque and power and BSFC are coating materials and engine speeds. Table 3 presents the standard engine, Al2O3 + 13% TiO2, Cr2O3, and Cr2O3 + 25% Al2O3 coating materials levels; 1400, 2000, 2600 and 3200 engine speed levels. Models employed for the experiment of this research are ''higher the better'' for engine torque and power and smaller the better'' for BSFC. Signal to Noise ratios (S/N) can be obtained using the equations underneath.
Motor tests were carried out with a single cylinder, compressionignition, air-cooled, four-stroke diesel engine. The technical properties of the engine used in the experiments are given in Table 2. For the loading of the engine, an electric dynamometer which is capable of operating at 26 kW, 80 Nm torque and max 5000 rpm ( ± 50) was used. A schematic view of the test engine is shown in Fig. 1. The data obtained during the engine tests were recorded to the computer by the interface of the engine test device depending on the time. In-cylinder pressures were measured with Kistler 4065A piazza electric pressure sensor and 4618A type amplifier compatible with the sensor. The pressure sensor was mounted on the cylinder head with a steel apparatus. OPKON brand optical encoder was used for the determination of the crankshaft angle. The data obtained from the internal cylinder pressure sensor was recorded to the computer with a Pico digital oscilloscope, which corresponds to the 0.5 Crankshaft Angle (°CA) of the crankshaft sensor in millivolts. 100 cycle values were averaged for each cylinder pressure value to be measured. The average electrical signal values were multiplied by the coefficient value of the internal cylinder pressure sensor and the data were converted to pressure (bar) units. Simultaneously with these measurements, emission values were measured from the emission device and recorded by printing out. All experiments were repeated three times and the results were averaged. The data obtained are graphically analyzed in the next
Higher the better S/N =
Nominal the better S/N = Lower the better S/N =
1 n
10 x log10
n i 1
1 Yi2
10x log10 (s 2) 10x log10
1 n
n
Yi2
i 1
where Yi = the result of the each experiment, i = number of repetitions 3. Results and discussions
Table 1 The powders coated on piston and valve surfaces.
Piston and Valve
1 70 57 219 20/1 3.72 13 Top cam, 2 valves 3600 2.2 185 0.75
Taguchi method is a very useful technique for improving the design of experiments. It was introduced by Genichi Taguchi, who was a Japanese engineer. He thought that quality can be defined as losses that a product yields to a society. In this method, he introduced orthogonal arrays, robust designs and signal-to-noise (S/N) ratios [26]. In an analysis, the response of the experimental trials can be obtained using signal-to-noise (S/N) ratios, which are very significant. Concepts for analyzing data are given below.
Ceramic powders were coated on piston and valve by using the plasma spraying method. Al2O3 + 13% TiO2, Cr2O3, and Cr2O3 + 25% Al2O3 were used as ceramic coating powders (Table 1). The reason why these powders were selected was that they form coating layers with high corrosion and abrasion resistance and thermal insulation properties [23,24,25].
Standard Engine Al2O3 + 13% TiO2 Cr2O3 Cr2O3 + 25% Al2O3
Number of cylinders Cylinder diameter (mm) Stroke (mm) Cylinder Displacement (cc) Compression ratio Maximum power (kW) Max. Torque (N.M/rpm) Valve regulation Maximum engine speed (rpm) Warehouse volume (L) Fuel Consumption (g/Hp.hour) Oil Capacity (L)
2.3. Statistical method
2.1. Coating materials
Substrate
Diesel
section. Engine experiments were performed at four throttle speeds of 1400 rpm, 2000 rpm, 2600 rpm and 3200 rpm at full throttle position.
2. Materials and method
Coating Materials
Technical Properties
3.1. Experimental results The experiments were carried out with four different types of diesel engine at four different speeds. One of the engine type was standard engine and the other three were the coated engines mentioned in Section 2. Coated powders were Al2O3 + 13%TiO2, Cr2O3 and Cr2O3 + 25%Al2O3. The purpose of these experiments was to measure 2
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Fig. 1. A schematic view of the test setup. Table 3 Control factors and levels. Control Factors
Level 1
Level 2
Level 3
Level 4
Coating Materials
Standard
Al2O3 + 13% TiO2
Cr2O3
Engine Speed
1400 rpm
2000 rpm
2600 rpm
Cr2O3 + 25% Al2O3 3200 rpm
and define the optimum values of engine torque, power and brake spesific fuel consumption. 3.1.1. Torque values of diesel engines Torque values measured on the engine are given in Table 4, depending on the coating materials and engine speeds. The highest torque values were observed with the coating material of Al2O3 + 13%TiO2 at each speed. In addition, the highest torque value was obtained as 13.1 at the speed of 2600 rpm with the coating material of Al2O3 + 13% TiO2. Compared to engines coated with other powders, Al2O3 + 13%TiO2 coated engine has the highest torque values due to the low thermal conductivity coefficient of Al2O3 + 13%TiO2 powder [28,29]. On the other hand, the standard engine had the lowest torque values at each speed and the lowest one was 3.6 at the speed of 1400 rpm. In comparison with the standard engine, the engine torque has an increase of 1.75% in the Cr2O3 sample, 4.21% in the Cr2O3 + 25% Al2O3 sample and 14.91% in the Al2O3 + 13%TiO2 sample. When we look at the Fig. 2, which was created using the values of Table 4, the engine torque increases as the engine speed increases in each type of coating materials. However, there is a slight decrease after the speed of 2600 rpm in each coating material. As the engine speed increases in internal combustion engines, an increase in engine torque is observed and this increase decreases again at a maximum point [30]. The reason for this decrease in engine torque might be because of the
Fig. 2. Effects of the coating materials and engine speed on engine torque.
decrease in volumetric efficiency caused by the increase in cylinder walls and gas temperatures as a result of thermal barrier coating and increasing friction losses at high speeds. Engines which are coated with a thermal barrier are generally known with their high combustion and temprature. Also, as a result of spraying fuel into the clyinders, reaction time decreases and this makes firing time very short [31]. However, short spraying time causes an increase in the amount of air falling on the fuel and this makes volumetric efficiency high as a result of the complete combustion of the fuel. Therefore, the engine torque increases. 3.1.2. Power values of diesel engines Power values measured on the engine are given in Table 5, depending on coating materials and engine speeds. Fig. 3 shows the effect
Table 4 Experimental results of coating materials and engine speeds on engine torque at different levels. Engine Speeds
1400 rpm 2000 rpm 2600 rpm 3200 rpm
Table 5 Experimental results of coating materials and engine speeds on engine power at different levels.
Coating Materials
Engine Speeds
Standard Engine
Al2O3 + 13%TiO2
Cr2O3
Cr2O3 + 25%Al2O3
3.6 5.4 11.4 10.5
5.1 8.97 13.1 12.43
3.7 5.3 11.6 10.4
3.86 5.44 11.88 10.7
1400 rpm 2000 rpm 2600 rpm 3200 rpm
3
Coating Materials Standard Engine
Al2O3 + 13%TiO2
Cr2O3
Cr2O3 + 25%Al2O3
0.53 1.13 3.10 3.52
0.75 1.88 3.57 4.17
0.54 1.11 3.16 3.49
0.57 1.14 3.23 3.59
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Table 6 Experimental results of the coating materials and engine speeds on engine BSFC at different levels. Engine Speeds
1400 rpm 2000 rpm 2600 rpm 3200 rpm
Coating Materials Standard Engine
Al2O3 + 13%TiO2
Cr2O3
Cr2O3 + 25%Al2O3
333.48 303.32 270.28 298.87
325.28 296.26 258.73 289.47
324.65 299.47 262.36 288.38
328.27 302.25 266.82 292.82
standard and the coated engines. This is due to an increase in engine speed which causes an increase in fuel consumption, thus increasing fuel consumption resulting in increased engine power [33]. In comparison with the standard engine, the motor power has an increase of 1.72% in the Cr2O3 sample, 4.84% in the Cr2O3 + 25%Al2O3 sample and 12.97% in the Al2O3 + 13%TiO2 sample.
Fig. 3. Effects of the coating materials and engine speed on engine power.
3.1.3. BSFC values of diesel engines Brake Specific Fuel Consumption (BSFC) values measured on the engine are given in Table 6, depending on coating materials and engine speeds. Fig. 4 shows the effect of coatings on brake specific fuel consumption. It is known that more pressure is applied to the piston surface with the increase of combustion and temperature in coated engines [34]. This means more useful work with the same amount of fuel. In general, engines with thermal barriers have less fuel consumption than standard engines [35,36]. However, as an engine reaches high speeds, it decreases momentum and increases BSCF because fuel inside a cylinder cannot be fully burned due to any decrease in volumetric efficiency, the shortening of combustion time and the reduction of fuel injection interval. In comparison with the standard engine, it was determined that the BSFC had a decrease of 1.07% in the Cr2O3 sample, 2.34% in the Cr2O3 + 25%Al2O3 sample and 11.82% in the Al2O3 + 13%TiO2. For all the test engines, the BSFC decreased due to the increased engine speed. With the increase in the engine speed, the high turbulence of the air swept into the cylinder helped to create a homogeneous mixture in the cylinder following fuel injection. This improved combustion efficiency and reduced fuel consumption. However, as the engine speed increased too much, the fuel in the cylinder reduced the time required for the entire air mixture to burn, resulting in an increase in the BSFC after 2600 rpm. In the engines with thermal barrier coating, the ignition delay time was shortened due to the increase in the cylinder gas temperatures and this improved the combustion efficiency.
Fig. 4. Effects of the coating materials and engine speed on engine BSFC.
of coatings on engine power. In internal combustion engines, the engine power is generated by the combustion of the fuel in the cylinders, resulting in a useful work in unit time. The combustion reaction in diesel engines starts with the injection of fuel. The fuel needs the ignition temperature in order to be burnt. The reaction time at the time of the combustion of the fuel takes place slowly in the first place with the injection of fuel from the injectors, and a certain amount of time is required to fully burn the fuel. For this reason, the ignition of the diesel engines is delayed, thus more fuel consumption into the cylinders during the ignition delay. Therefore, the temperature inside the cylinder is an important parameter for the ignition temperature of the fuel and ignition delay [31,32]. In the range where the fuel is most efficient, it is thought that both the fuel consumption is reduced and the engine power is the maximum according to the unit fuel consumption. The results obtained in Figs. 4 and 6 also seem to support this situation. Referring to Fig. 4, it is seen that engine power increases with increasing engine speed for all types of coated materials. Depending on the increasing speed, the number of cycles per unit time increased and this led to an increase in engine power. The engine power increased rapidly up to 2600 rpm, but then increased slowly. This was because the engine speed was too high and there was not enough time to burn all the fuel that was sprayed into the cylinder. When the increase in engine power for all test engines is examined, it is seen that thermal barrier effect resulting from ceramic coating improves combustion efficiency and coated engine produces better engine power under same conditions compared to uncoated diesel engine. It was determined that the highest engine power was 3200 rpm on
3.1.4. Exhaust gas temperature of diesel engines The experiments showed that the applied coatings formed a thermal barrier and increased exhaust gas temperatures (Fig. 5). Increases in exhaust gas temperatures at all engine speeds were detected. This might be due to the increases in the combustion temperature of thermal barrier coated engines, also combustion products increased the temperature and exhaust gas temperature was therefore affected. Furthermore, the increases in the engine cycle, the amount of fuel burned in the cylinder at the time of the unit and the heat energy produced at the end of combustion might be other reasons of the increasing exhaust gas temperature. As a result, the increasing engine speed increased both exhaust gas temperature and flow rate. The heat energy that was prevented from passing to the cooler fluid and cylinder walls in thermal coating engines increased the exhaust gas temprature by passing to exhaust gases. In comparison with the standard engine, the exhaust gas temperature had an increase of 2.04% in the Cr2O3 sample, 4.16% in the Cr2O3 + 25%Al2O3 sample and 17.27% in the Al2O3 + 13%TiO2 sample. 4
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Fig. 7. Effect of coated pistons on pressure changes in cylinder.
Fig. 5. Change of exhaust gas temperature according to engine speed.
engine pistons, it is seen that the pressure values inside the cylinder change in similar profiles. With the use of all coated pistons, the internal cylinder pressure values have changed. The highest internal cylinder pressure value is 45.70 bar, which was obtained by using Al2O3 + 13% TiO2 piston at 361 °CA angle. The lowest internal cylinder pressure was obtained by using the standard engine piston at a pressure of 40.46 bar. Fig. 7 illustrates the effect of changes in heat release depending on the crankshaft angle of the use of standard engine piston and coated engine piston. It is seen that with the use of coated pistons with respect to the standard engine piston, the combustion time changes and the total combustion time is shortened but the onset of combustion is slightly delayed. Also, the highest heat release rate is 20.89 (j/°CA), which was obtained by using Al2O3 + 13% TiO2 piston at 377 °CA. 3.2. Statistical results The experiments mentioned in previous section were performed using the Taguchi design method and ANOVA and F-test were carried out in order to define the statistical significance of the test parameters. The statistical analysis was conducted using the trial version of Minitab 18.1 program.
Fig. 6. Effect of coated pistons on pressure changes in cylinder.
3.1.5. Combustion analysis of diesel engines In the combustion analysis, the pressure changes occurring in the cylinder were recorded according to the crankshaft position. Combustion analysis is an important parameter used to determine the combustion characteristics of internal combustion engines. To perform the combustion analysis, it is necessary to know the changes in instantaneous cylinder pressure and cylinder volume. Using the pressure and volume data, parameters such as heat generation, cylinder temperatures, pressure increase rate and ignition delay were calculated. In this study, the calculations were made according to the following assumptions:
3.2.1. The statistical results of engine torque Table 7 shows the S/N ratios determined for the experimental control parameters mentioned in Section 2.3. This table records figures maximizing the results under the influence of the test parameters. Furthermore, these figures were employed to plot the influence of the parameters of coating material and engine speeds on the engine torque in Fig. 8. The statistical analysis, which has two independent parameters as coating material and engine speeds, depicted the result that the variations in the coating material and engine speed were statistically significant on the engine torque. Table 8 demonstrates that the engine torque is significantly affected at different levels of the coating materials and engine speeds.
• Heat generation was determined according to the average values in • • •
the cylinder volume and regional combustion characteristics were ignored. Compression leaks in the cylinders were neglected. Mixtures in the cylinder were assumed to have thermal and chemical equilibrium. It was assumed that the gas fuels taken into the mixing chamber were at a pressure of 100 kPa and a temperature of 25 °C.
Table 7 S/N ratios of factor levels for Engine Torque. Control Factors
In this study, it was decided to investigate the changes at the engine speed of 2600 rpm where maximum engine torque was obtained. Fig. 6 illustrates the effect of pressure changes in the cylinder depending on the crankshaft angle of the use of standard engine piston and coated engine piston. With the use of coated pistons compared to standard
Coating Materials Engine Speeds
Engine Torque Level 1
Level 2
Level 3
Level 4
16.83 12.09
19.36* 15.73
16.87 21.57*
17.13 20.81
*Levels which are maximazing the results. 5
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Fig. 8. S/N ratio graph of experimental parameters for Engine Torque.
Fig. 9. S/N ratio graph of experimental parameters for Engine Power.
Table 8 Analysis of Variance (ANOVA) for the S/N ratios of engine torque.
Table 10 Analysis of Variance (ANOVA) for the SN Ratios of Engine Power.
Source
DF
Seq SS
Adj SS
Adj MS
F
P
Source
DF
Seq SS
Adj SS
Adj MS
F
P
Coating Materials Engine Speed Residual Error Total
3 3 9 15
17.712 239.494 5.395 262.601
17.712 239.494 5.395
5.9042 79.8313 0.5994
9.85 133.18
0.003 0.000
Coating Materials Engine Speed Residual Error Total
3 3 9 15
17.712 669.658 5.395 692.765
17.712 669.658 5.395
5.904 223.219 0.599
9.85 372.39
0.003 0.000
The S/N ratios of engine torque are revealed by Table 7. Level 2 for the coating materials and level 3 for the engine speed have the highest ratios. Conversely, level 1 for the coating materials and engine speed has the lowest ratios. Finally, the results from Fig. 8 shows that the engine torque reaches its maximum point with the coating material of Al2O3 + 13% TiO2 at the speed of 2600 rpm. Also, P-values for coating materials and engine speed are below 0.05, which means that they are both statistically significant parameters influencing the engine torque.
Table 11 S/N ratios of factor levels for BSFC.
3.2.2. The statistical results of engine power Table 9 records the S/N ratios determined for the experimental control parameters mentioned in Section 2.3 for the engine power. This table has figures maximizing the results under the influence of the test parameters. In addition, in Fig. 9, these figures are used to plot the influence of the parameters of the coating material and engine speeds on the engine power.Table 10. Table 9 exhibits the S/N ratios of the engine power. The S/N ratios of the engine power have more different trend than the engine torque and BSFC because the level 2 of the coating materials and level 4 of the engine speed parameters have the highest ratios. The reason behind this change are explained in Section 3.1.2. On the other hand, level 1 for the coating materials and engine speed have the lowest ratios, which are as same as the engine torque and BSFC. To sum up, the results from Fig. 9 demostrates that the engine power reaches its maximum point with the coating material of Al2O3 + 13% TiO2 at the speed of 3200 rpm. In addition, P-values for the coating materials and engine speed are under 0.05, which means they are both the statistically significant parameters affecting the
engine power.
Control Factors
Coating Materials Engine Speeds
Brake Specific Fuel Consumption (BSFC) Level 1
Level 2
Level 3
Level 4
−49.56 −50.31
−49.29* −49.55
−49.33 −48.45*
−49.45 −49.23
*Levels which are minimazing the results
3.2.3. The statistical results of BSFC Table 11 demonstrates the S/N ratios determined for the experimental control parameters mentioned in Section 2.3 for the BSFC. In this table, there are figures that are minimizing the results under the influence of the test parameters. Moreover, in Fig. 10, these figures are plotted to see the influence of the parameters of the coating material and engine speeds on the BSFC. The S/N ratios of the BSFC are given by Table 11. Level 2 for the coating materials and level 3 for the engine speed have the highest
Table 9 S/N ratios of factor levels for Engine Power. Control Factors
Coating Materials Engine Speeds
Engine Power Level 1
Level 2
Level 3
Level 4
4.071 −4.583
6.598* 2.147
4.107 10.268
4.369 11.314*
Fig. 10. S/N ratio graph of experimental parameters for BSFC.
*Levels which are maximazing the results 6
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References
Table 12 Analysis of Variance (ANOVA) for the SN Ratios of BSFC. Source
DF
Seq SS
Adj SS
Adj MS
F
P
Coating Materials Engine Speed Residual Error Total
3 3 9 15
0.17647 7.08381 0.02367 7.28395
0.17647 7.08381 0.02367
0.05882 2.36127 0.00263
22.37 898.00
0.000 0.000
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[17] Naik AB, Reddy AC. Optimization of tensile strength in TIG welding using the Taguchi method and analysis of variance (ANOVA). Thermal Sci Eng Prog 2018;8:327–39. https://doi.org/10.1016/j.tsep.2018.08.005. [18] Özel S, Turhan H, Gönel E. Optimization of effect of production parameters on wear resıstance of coated layer on the surface of copper alloy by taguchi method. Int J Adv Res Innovative Ideas Educ 2017;3(4):1517–23. DUI:16.0415/IJARIIE-6161. [19] Park IC, Kim SJ. Cavitation erosion behavior in seawater of electroless Ni-P coating and process optimization using Taguchi method. Appl Surf Sci 2018;477:37–43. https://doi.org/10.1016/j.apsusc.2018.02.033. [20] Tabaraki R, Nateghi A. Application of taguchi L16 orthogonal array design to optimize hydrazine biosorption by Sargassum ilicifolium. Environ Prog Sustainable Energy 2016;35(5):1450–7. https://doi.org/10.1002/ep.12377. [21] Moganapriya C, Rajasekar R, Ponappa K, Venkatesh R, Jerome S. Influence of coating material and cutting parameters on surface roughness and material removal rate in turning process using taguchi method. Mater Today: Proc 2018;5(2):8532–8. https://doi.org/10.1016/j.matpr.2017.11.550. [22] Trivedi HK, Bhatt DV. An experimental investigation on friction and wear test parameters of cylinder liner and piston ring pair using Taguchi technique. Ind Lubrication Tribol 2018;70(9):1721–8. https://doi.org/10.1108/ILT-10-20170310. [23] Jia SK, Yong ZOU, Xu JY, Jing WANG, Lei YU. Effect of TiO2 content on properties of Al2O3 thermal barrier coatings by plasma spraying. Trans Nonferrous Metals Soc China 2015;25(1):175–83. https://doi.org/10.1016/S1003-6326(15)63593-2. [24] Toma FL, Stahr CC, Berger LM, Saaro S, Herrmann M, Deska D, et al. Corrosion resistance of APS-and HVOF-sprayed coatings in the Al2O3-TiO2 system. J Therm Spray Technol 2010;19(1-2):137–47. https://doi.org/10.1007/s11666-009-9422-2. [25] Bolleddu V, Racherla V, Bandyopadhyay PP. 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ratios while level 1 for both the coating materials and the engine speed has the lowest ratios. This shows that the minimum specific fuel consumption can be seen at the level 2 for the coating materials and level 3 for the engine speed, while level 3 for the coating materials and level 1 for the engine speed causes the maximum fuel consumption. To summarize, according to the Fig. 10, the BSFC reaches its minimum point with the coating material of Al2O3 + 13% TiO2 at the speed of 2600 rpm, which is similar to the results of the engine torque. Also, the statistical results of the BSFC in Table 12 showes that P-value for the coating materials and engine speed parameters are 0, which are under 0.05. Therefore, it can be argued that they are important parameters for the BSFC. 4. Conclusions - According to the experimental studys, it was seen that the coating materials (Al2O3 + 13% TiO2, Cr2O3, and Cr2O3 + 25% Al2O3) could be coated on piston surfaces. Also, the engine tests at four different speeds (1400 rpm, 2000 rpm, 2600 rpm and 3200 rpm) could be applied to the coated pistons. As a result, a better engine torque, power, and BSFC can be achieved with the use of different types of the coating material and engine speed. - Maximum experimental engine torque value was measured as 13.1 Nm with the use of Al2O3 + 13% TiO2 at the speed of 2600 rpm. Maximum experimental engine power value was measured as 3.59 kW with the use of Al2O3 + 13% TiO2 at the speed of 3200 rpm. The minimum experimental BSFC value was measured as 258.73 g/kW.h with the use of Al2O3 + 13% TiO2 at the speed of 2600 rpm. - Maximum exhaust gas temperature was measured as 445 °C with the use of Al2O3 + 13% TiO2 at the speed of 3200 rpm. - Maximum cylinder pressure and heat release rate were measured as 45.70 bar at 361 °CA and 20.89 (j/oCA) at 377 °CA angle respectively with the use of Al2O3 + 13% TiO2 at the speed of 2600 rpm. - Taguchi design method showed that maximum engine torque and minimum engine BSFC values were achieved using the coating material of Al2O3 + 13% TiO2 at the speed of 2600 rpm. Maximum engine power value, on the other hand, was achieved using the coating material of Al2O3 + 13% TiO2 at the speed of 3200 rpm. - The statistical study have demonstrated that all of the P values of coating material and engine speed parameters are smaller than 0.05 and this means that they are statistically significant on the engine torque, power and BSFC. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This study was supported by Bitlis Eren University Scientific Research Projects Coordination Unit. Project Number: BEBAP-2014.15. The authors would like to thank the Bitlis Eren University Science and Technology Research and Application Center for the tests of specimens. 7
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S. Özel, et al. [26] Maghsoodloo S, Ozdemir G, Jordan V, Huang C-H. Strengths and limitations of Taguchis contributions to quality, manufacturing, and process engineering. J Manuf Syst 2004;23(2):73–126. https://doi.org/10.1016/S0278-6125(05)00004-X. [27] Montgomery DC, Design and Analysis of Experiments, 9th Edition, 1 review, Publisher: Wiley, Release Date: May 2017. ISBN: 978-1-119-11347-8. [28] Arboleda JA, Serna CM, Cadavid E, Barrios AC, Vargas F, Toro A. Effect of flame spray deposition parameters on the microstructure of Al2O3-13%TiO2 coatings applied Onto 7075 aluminum alloy. Mater Res 2018;21(5):1–12. https://doi.org/10. 1590/1980-5373-mr-2018-0038. [29] Garcia EM. Optimizing the sintering of Cr2O3-nano powders for HVOF applications. Spain: Universidad Carlos III de Madrid, Career Project; 2012. [30] Gürbüz H. An experimental study on the effects of the thermal barrier plating over diesel engine performance and emissions MSc. Thesis Graduate School of Natural and Applied Sciences, Department of Mechanical Engineering, Karabük University; 2011. [31] Safgönül B, Ergeneman M, Arslan HE, Soruşbay C, Internal combustion engines, Birsen Yayınevi, Istanbul, p. 218, 2008.
[32] Hazar H, Ozturk U. The effects of Al2O3-TiO2 coating in a diesel engine on performance and emission of corn oil methyl ester. Renewable Energy 2010;35(10):2211–6. https://doi.org/10.1016/j.renene.2010.02.028. [33] Och SH, Moura LM, Mariani VC, Coelho LDS, Domingues JAVE. Volumetric efficiency optimization of a single-cylinder D.I. diesel engine using differential evolution algorithm. Appl Therm Eng 2016;108:660–9. https://doi.org/10.1016/j. applthermaleng.2016.07.042. [34] Yao C, Hu J, Geng P, Shi J, Zhang D, Ju Y. Effects of injection pressure on ignition and combustion characteristics of diesel in a premixed methanol/air mixture atmosphere in a constant volume combustion chamber. Fuel 2017;206:593–602. https://doi.org/10.1016/j.fuel.2017.06.058. [35] Venkadesan G, Muthusamy J. Experimental investigation of Al2O3/8YSZ and CeO2/ 8YSZ plasma sprayed thermal barrier coating on diesel engine. Ceram Int 2019;45(3):3166–76. https://doi.org/10.1016/j.ceramint.2018.10.218. [36] Jena SP, Acharya SK, Das HC, Bajpai S. Investigation of the effect of FeCl3 on combustion and emission of diesel engine with thermal barrier coating. Sustainable Environ Res 2018;28(2):72–8. https://doi.org/10.1016/j.serj.2017.10.002.
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Full Length Article
Optimization of the effect of thermal barrier coating (TBC) on diesel engine performance by Taguchi method Serkan Özela, , Erdinç Vuralb, Murat Binicic ⁎
a
Bitlis Eren University, Department of Mechanical Engineering, Bitlis, Turkey Aydın Adnan Menders University, Germencik Yamantürk Vocational School, Aydın, Turkey c Bitlis Eren University, Department of Industrial Engineering, Bitlis, Turkey b
ARTICLE INFO
ABSTRACT
Keywords: Thermal barrier coating Diesel engine performance Taguchi ANOVA
In this study, thermal barrier layers were coated on piston and valve surfaces using plasma spray method. The effects of coated layers on torque, power and brake specific fuel consumption (BSFC) were investigated experimentally, and statistically using the Taguchi optimization method. Coating materials used in this study were Al2O3 + 13% TiO2, Cr2O3, and Cr2O3 + 25% Al2O3. Each coating material was tested at different speeds, which were 1400 rpm, 2000 rpm, 2600 rpm and 3200 rpm. The results showed that engine torque and BSFC reached their optimum values with the use of Al2O3 + 13% TiO2 at the speed of 2600 rpm. However, engine power showed the best performance with the same coating material but at the speed of 3200 rpm. The results of the experiment were also tested using Taguchi optimization method with coating material and engine speed parameters. The design of Taguchi analysis was carried out with L16 (42) orthogonal array. The highest S/N ratios of engine torque and BSFC were observed with the coating material of Al2O3 + 13% TiO2 at the speed of 2600 rpm. However, the highest S/N ratio of engine power was seen with the use of Al2O3 + 13% TiO2 at the speed of 3200 rpm. In order to determine the statistical significance of experimental parameters on engine torque and power and BSFC, ANOVA and F-test were carried out. The results of statistical analysis showed that the coating materials (P < 0.05) and engine speed (P < 0.05) parameters were statistically significant on the engine torque, power and BSFC.
1. Introduction Diesel engines have an important role in the automotive industry. They are widely used in both transport and agriculture industries because they have higher fuel saving and lower fuel consumption than other types of engines [1]. However, due to increases in fuel costs, decreases in supplying high-quality fuels to the markets and concerns for environmental issues, researchers in the industry have begun to research on more productive engines [2]. Efficiency and emissions of engines are crucial. There are two ways to make a diesel engine more productive and efficient with lower emission levels [3]. First way is the reduction of losses such as heat loss from the cylinder, wall, cooling water and friction losses in order to make the engine more efficient mechanically and indicatively, and the second one is the usage of a suitable alternative fuel in the engine [3–6]. Regarding the first way, thermal barrier coating (TBC) is one of the most commonly used technologies to keep the heat inside the engine so that it can improve the thermal efficiency of the engines. TBC
⁎
has been used to make improvements on the efficiency and performance of different types of machine tools for a long time and it can be applied to the areas having high temperatures or heat transfer surfaces of gas tribunes. TBC technology can be applied by insulating the engine with ceramic-based coating [7–10]. Ceramic coating layers such as Zr2O, Y2O3, Al2O3, TiO2 and Cr2O3 can be obtained using TBC methods. These layers can be used in aircraft engines and power generation gas turbines to ensure that metal alloy components are not damaged from high-temperature [11–14]. There are some advantages of using TBC in a diesel engine. The heat inside the engine can be kept and thermal fatigue and shocks can be avoided. It can also reduce the emission levels of Hydrocarbon and Carbon Monoxide. Additionally, a piston can be protected from corrosion attack, thermal stress, and high heat emissions by reducing heat flux into the piston and fuel consumption. Moreover, due to the high increase in fuel prices and decreasing the quality of fuels, TBC can be an advantage to get more efficient engine performance. In relation to the low-quality fuels, TBC can keep much more heat inside the engine even
Corresponding author. E-mail address: [email protected] (S. Özel).
https://doi.org/10.1016/j.fuel.2019.116537 Received 11 April 2019; Received in revised form 23 October 2019; Accepted 29 October 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Serkan Özel, Erdinç Vural and Murat Binici, Fuel, https://doi.org/10.1016/j.fuel.2019.116537
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though the fuel is low quality [1–4,7–10,15]. Taguchi design method, which is one of the experimental design methods, is successful in solving optimization problems as it increases processing performance with a lower number of experiments and less cost, and by using Taguchi, the number of experiments can be decreased significantly and thus the loss of time and cost can be prevented [16]. In addition to solving the problems with a few experiments, Taguchi supports developing high-quality process and product from every angle. It has minimum sensitivity to the process or manufacturing conditions of products and uncontrollable factors. Therefore, both the necessary tolerances can be provided with the lowest cost and Taguchi lost function can bring a new understanding to the quality process [17,18]. The Taguchi optimization method has previously been used in many experimental design studies [19–22]. In this study, thermal barrier layers were coated on a piston and valve surfaces by using plasma spraying method. The effects of coated materials and engine speed on engine torque, power and BSFC were investigated experimentally, and statistically using the Taguchi optimization method.
Table 2 Technical properties of the test engine.
- Higher the better, - Nominal to better, - Lower the better,
2.2. Engine tests
Information of each parameter can be retrieved using Analysis of Variance (ANOVA) [27]. In this study, L16 (42) orthogonal array was employed for the robust design of the experimentations. The parameters presumed to affect engine torque and power and BSFC are coating materials and engine speeds. Table 3 presents the standard engine, Al2O3 + 13% TiO2, Cr2O3, and Cr2O3 + 25% Al2O3 coating materials levels; 1400, 2000, 2600 and 3200 engine speed levels. Models employed for the experiment of this research are ''higher the better'' for engine torque and power and smaller the better'' for BSFC. Signal to Noise ratios (S/N) can be obtained using the equations underneath.
Motor tests were carried out with a single cylinder, compressionignition, air-cooled, four-stroke diesel engine. The technical properties of the engine used in the experiments are given in Table 2. For the loading of the engine, an electric dynamometer which is capable of operating at 26 kW, 80 Nm torque and max 5000 rpm ( ± 50) was used. A schematic view of the test engine is shown in Fig. 1. The data obtained during the engine tests were recorded to the computer by the interface of the engine test device depending on the time. In-cylinder pressures were measured with Kistler 4065A piazza electric pressure sensor and 4618A type amplifier compatible with the sensor. The pressure sensor was mounted on the cylinder head with a steel apparatus. OPKON brand optical encoder was used for the determination of the crankshaft angle. The data obtained from the internal cylinder pressure sensor was recorded to the computer with a Pico digital oscilloscope, which corresponds to the 0.5 Crankshaft Angle (°CA) of the crankshaft sensor in millivolts. 100 cycle values were averaged for each cylinder pressure value to be measured. The average electrical signal values were multiplied by the coefficient value of the internal cylinder pressure sensor and the data were converted to pressure (bar) units. Simultaneously with these measurements, emission values were measured from the emission device and recorded by printing out. All experiments were repeated three times and the results were averaged. The data obtained are graphically analyzed in the next
Higher the better S/N =
Nominal the better S/N = Lower the better S/N =
1 n
10 x log10
n i 1
1 Yi2
10x log10 (s 2) 10x log10
1 n
n
Yi2
i 1
where Yi = the result of the each experiment, i = number of repetitions 3. Results and discussions
Table 1 The powders coated on piston and valve surfaces.
Piston and Valve
1 70 57 219 20/1 3.72 13 Top cam, 2 valves 3600 2.2 185 0.75
Taguchi method is a very useful technique for improving the design of experiments. It was introduced by Genichi Taguchi, who was a Japanese engineer. He thought that quality can be defined as losses that a product yields to a society. In this method, he introduced orthogonal arrays, robust designs and signal-to-noise (S/N) ratios [26]. In an analysis, the response of the experimental trials can be obtained using signal-to-noise (S/N) ratios, which are very significant. Concepts for analyzing data are given below.
Ceramic powders were coated on piston and valve by using the plasma spraying method. Al2O3 + 13% TiO2, Cr2O3, and Cr2O3 + 25% Al2O3 were used as ceramic coating powders (Table 1). The reason why these powders were selected was that they form coating layers with high corrosion and abrasion resistance and thermal insulation properties [23,24,25].
Standard Engine Al2O3 + 13% TiO2 Cr2O3 Cr2O3 + 25% Al2O3
Number of cylinders Cylinder diameter (mm) Stroke (mm) Cylinder Displacement (cc) Compression ratio Maximum power (kW) Max. Torque (N.M/rpm) Valve regulation Maximum engine speed (rpm) Warehouse volume (L) Fuel Consumption (g/Hp.hour) Oil Capacity (L)
2.3. Statistical method
2.1. Coating materials
Substrate
Diesel
section. Engine experiments were performed at four throttle speeds of 1400 rpm, 2000 rpm, 2600 rpm and 3200 rpm at full throttle position.
2. Materials and method
Coating Materials
Technical Properties
3.1. Experimental results The experiments were carried out with four different types of diesel engine at four different speeds. One of the engine type was standard engine and the other three were the coated engines mentioned in Section 2. Coated powders were Al2O3 + 13%TiO2, Cr2O3 and Cr2O3 + 25%Al2O3. The purpose of these experiments was to measure 2
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Fig. 1. A schematic view of the test setup. Table 3 Control factors and levels. Control Factors
Level 1
Level 2
Level 3
Level 4
Coating Materials
Standard
Al2O3 + 13% TiO2
Cr2O3
Engine Speed
1400 rpm
2000 rpm
2600 rpm
Cr2O3 + 25% Al2O3 3200 rpm
and define the optimum values of engine torque, power and brake spesific fuel consumption. 3.1.1. Torque values of diesel engines Torque values measured on the engine are given in Table 4, depending on the coating materials and engine speeds. The highest torque values were observed with the coating material of Al2O3 + 13%TiO2 at each speed. In addition, the highest torque value was obtained as 13.1 at the speed of 2600 rpm with the coating material of Al2O3 + 13% TiO2. Compared to engines coated with other powders, Al2O3 + 13%TiO2 coated engine has the highest torque values due to the low thermal conductivity coefficient of Al2O3 + 13%TiO2 powder [28,29]. On the other hand, the standard engine had the lowest torque values at each speed and the lowest one was 3.6 at the speed of 1400 rpm. In comparison with the standard engine, the engine torque has an increase of 1.75% in the Cr2O3 sample, 4.21% in the Cr2O3 + 25% Al2O3 sample and 14.91% in the Al2O3 + 13%TiO2 sample. When we look at the Fig. 2, which was created using the values of Table 4, the engine torque increases as the engine speed increases in each type of coating materials. However, there is a slight decrease after the speed of 2600 rpm in each coating material. As the engine speed increases in internal combustion engines, an increase in engine torque is observed and this increase decreases again at a maximum point [30]. The reason for this decrease in engine torque might be because of the
Fig. 2. Effects of the coating materials and engine speed on engine torque.
decrease in volumetric efficiency caused by the increase in cylinder walls and gas temperatures as a result of thermal barrier coating and increasing friction losses at high speeds. Engines which are coated with a thermal barrier are generally known with their high combustion and temprature. Also, as a result of spraying fuel into the clyinders, reaction time decreases and this makes firing time very short [31]. However, short spraying time causes an increase in the amount of air falling on the fuel and this makes volumetric efficiency high as a result of the complete combustion of the fuel. Therefore, the engine torque increases. 3.1.2. Power values of diesel engines Power values measured on the engine are given in Table 5, depending on coating materials and engine speeds. Fig. 3 shows the effect
Table 4 Experimental results of coating materials and engine speeds on engine torque at different levels. Engine Speeds
1400 rpm 2000 rpm 2600 rpm 3200 rpm
Table 5 Experimental results of coating materials and engine speeds on engine power at different levels.
Coating Materials
Engine Speeds
Standard Engine
Al2O3 + 13%TiO2
Cr2O3
Cr2O3 + 25%Al2O3
3.6 5.4 11.4 10.5
5.1 8.97 13.1 12.43
3.7 5.3 11.6 10.4
3.86 5.44 11.88 10.7
1400 rpm 2000 rpm 2600 rpm 3200 rpm
3
Coating Materials Standard Engine
Al2O3 + 13%TiO2
Cr2O3
Cr2O3 + 25%Al2O3
0.53 1.13 3.10 3.52
0.75 1.88 3.57 4.17
0.54 1.11 3.16 3.49
0.57 1.14 3.23 3.59
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Table 6 Experimental results of the coating materials and engine speeds on engine BSFC at different levels. Engine Speeds
1400 rpm 2000 rpm 2600 rpm 3200 rpm
Coating Materials Standard Engine
Al2O3 + 13%TiO2
Cr2O3
Cr2O3 + 25%Al2O3
333.48 303.32 270.28 298.87
325.28 296.26 258.73 289.47
324.65 299.47 262.36 288.38
328.27 302.25 266.82 292.82
standard and the coated engines. This is due to an increase in engine speed which causes an increase in fuel consumption, thus increasing fuel consumption resulting in increased engine power [33]. In comparison with the standard engine, the motor power has an increase of 1.72% in the Cr2O3 sample, 4.84% in the Cr2O3 + 25%Al2O3 sample and 12.97% in the Al2O3 + 13%TiO2 sample.
Fig. 3. Effects of the coating materials and engine speed on engine power.
3.1.3. BSFC values of diesel engines Brake Specific Fuel Consumption (BSFC) values measured on the engine are given in Table 6, depending on coating materials and engine speeds. Fig. 4 shows the effect of coatings on brake specific fuel consumption. It is known that more pressure is applied to the piston surface with the increase of combustion and temperature in coated engines [34]. This means more useful work with the same amount of fuel. In general, engines with thermal barriers have less fuel consumption than standard engines [35,36]. However, as an engine reaches high speeds, it decreases momentum and increases BSCF because fuel inside a cylinder cannot be fully burned due to any decrease in volumetric efficiency, the shortening of combustion time and the reduction of fuel injection interval. In comparison with the standard engine, it was determined that the BSFC had a decrease of 1.07% in the Cr2O3 sample, 2.34% in the Cr2O3 + 25%Al2O3 sample and 11.82% in the Al2O3 + 13%TiO2. For all the test engines, the BSFC decreased due to the increased engine speed. With the increase in the engine speed, the high turbulence of the air swept into the cylinder helped to create a homogeneous mixture in the cylinder following fuel injection. This improved combustion efficiency and reduced fuel consumption. However, as the engine speed increased too much, the fuel in the cylinder reduced the time required for the entire air mixture to burn, resulting in an increase in the BSFC after 2600 rpm. In the engines with thermal barrier coating, the ignition delay time was shortened due to the increase in the cylinder gas temperatures and this improved the combustion efficiency.
Fig. 4. Effects of the coating materials and engine speed on engine BSFC.
of coatings on engine power. In internal combustion engines, the engine power is generated by the combustion of the fuel in the cylinders, resulting in a useful work in unit time. The combustion reaction in diesel engines starts with the injection of fuel. The fuel needs the ignition temperature in order to be burnt. The reaction time at the time of the combustion of the fuel takes place slowly in the first place with the injection of fuel from the injectors, and a certain amount of time is required to fully burn the fuel. For this reason, the ignition of the diesel engines is delayed, thus more fuel consumption into the cylinders during the ignition delay. Therefore, the temperature inside the cylinder is an important parameter for the ignition temperature of the fuel and ignition delay [31,32]. In the range where the fuel is most efficient, it is thought that both the fuel consumption is reduced and the engine power is the maximum according to the unit fuel consumption. The results obtained in Figs. 4 and 6 also seem to support this situation. Referring to Fig. 4, it is seen that engine power increases with increasing engine speed for all types of coated materials. Depending on the increasing speed, the number of cycles per unit time increased and this led to an increase in engine power. The engine power increased rapidly up to 2600 rpm, but then increased slowly. This was because the engine speed was too high and there was not enough time to burn all the fuel that was sprayed into the cylinder. When the increase in engine power for all test engines is examined, it is seen that thermal barrier effect resulting from ceramic coating improves combustion efficiency and coated engine produces better engine power under same conditions compared to uncoated diesel engine. It was determined that the highest engine power was 3200 rpm on
3.1.4. Exhaust gas temperature of diesel engines The experiments showed that the applied coatings formed a thermal barrier and increased exhaust gas temperatures (Fig. 5). Increases in exhaust gas temperatures at all engine speeds were detected. This might be due to the increases in the combustion temperature of thermal barrier coated engines, also combustion products increased the temperature and exhaust gas temperature was therefore affected. Furthermore, the increases in the engine cycle, the amount of fuel burned in the cylinder at the time of the unit and the heat energy produced at the end of combustion might be other reasons of the increasing exhaust gas temperature. As a result, the increasing engine speed increased both exhaust gas temperature and flow rate. The heat energy that was prevented from passing to the cooler fluid and cylinder walls in thermal coating engines increased the exhaust gas temprature by passing to exhaust gases. In comparison with the standard engine, the exhaust gas temperature had an increase of 2.04% in the Cr2O3 sample, 4.16% in the Cr2O3 + 25%Al2O3 sample and 17.27% in the Al2O3 + 13%TiO2 sample. 4
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Fig. 7. Effect of coated pistons on pressure changes in cylinder.
Fig. 5. Change of exhaust gas temperature according to engine speed.
engine pistons, it is seen that the pressure values inside the cylinder change in similar profiles. With the use of all coated pistons, the internal cylinder pressure values have changed. The highest internal cylinder pressure value is 45.70 bar, which was obtained by using Al2O3 + 13% TiO2 piston at 361 °CA angle. The lowest internal cylinder pressure was obtained by using the standard engine piston at a pressure of 40.46 bar. Fig. 7 illustrates the effect of changes in heat release depending on the crankshaft angle of the use of standard engine piston and coated engine piston. It is seen that with the use of coated pistons with respect to the standard engine piston, the combustion time changes and the total combustion time is shortened but the onset of combustion is slightly delayed. Also, the highest heat release rate is 20.89 (j/°CA), which was obtained by using Al2O3 + 13% TiO2 piston at 377 °CA. 3.2. Statistical results The experiments mentioned in previous section were performed using the Taguchi design method and ANOVA and F-test were carried out in order to define the statistical significance of the test parameters. The statistical analysis was conducted using the trial version of Minitab 18.1 program.
Fig. 6. Effect of coated pistons on pressure changes in cylinder.
3.1.5. Combustion analysis of diesel engines In the combustion analysis, the pressure changes occurring in the cylinder were recorded according to the crankshaft position. Combustion analysis is an important parameter used to determine the combustion characteristics of internal combustion engines. To perform the combustion analysis, it is necessary to know the changes in instantaneous cylinder pressure and cylinder volume. Using the pressure and volume data, parameters such as heat generation, cylinder temperatures, pressure increase rate and ignition delay were calculated. In this study, the calculations were made according to the following assumptions:
3.2.1. The statistical results of engine torque Table 7 shows the S/N ratios determined for the experimental control parameters mentioned in Section 2.3. This table records figures maximizing the results under the influence of the test parameters. Furthermore, these figures were employed to plot the influence of the parameters of coating material and engine speeds on the engine torque in Fig. 8. The statistical analysis, which has two independent parameters as coating material and engine speeds, depicted the result that the variations in the coating material and engine speed were statistically significant on the engine torque. Table 8 demonstrates that the engine torque is significantly affected at different levels of the coating materials and engine speeds.
• Heat generation was determined according to the average values in • • •
the cylinder volume and regional combustion characteristics were ignored. Compression leaks in the cylinders were neglected. Mixtures in the cylinder were assumed to have thermal and chemical equilibrium. It was assumed that the gas fuels taken into the mixing chamber were at a pressure of 100 kPa and a temperature of 25 °C.
Table 7 S/N ratios of factor levels for Engine Torque. Control Factors
In this study, it was decided to investigate the changes at the engine speed of 2600 rpm where maximum engine torque was obtained. Fig. 6 illustrates the effect of pressure changes in the cylinder depending on the crankshaft angle of the use of standard engine piston and coated engine piston. With the use of coated pistons compared to standard
Coating Materials Engine Speeds
Engine Torque Level 1
Level 2
Level 3
Level 4
16.83 12.09
19.36* 15.73
16.87 21.57*
17.13 20.81
*Levels which are maximazing the results. 5
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Fig. 8. S/N ratio graph of experimental parameters for Engine Torque.
Fig. 9. S/N ratio graph of experimental parameters for Engine Power.
Table 8 Analysis of Variance (ANOVA) for the S/N ratios of engine torque.
Table 10 Analysis of Variance (ANOVA) for the SN Ratios of Engine Power.
Source
DF
Seq SS
Adj SS
Adj MS
F
P
Source
DF
Seq SS
Adj SS
Adj MS
F
P
Coating Materials Engine Speed Residual Error Total
3 3 9 15
17.712 239.494 5.395 262.601
17.712 239.494 5.395
5.9042 79.8313 0.5994
9.85 133.18
0.003 0.000
Coating Materials Engine Speed Residual Error Total
3 3 9 15
17.712 669.658 5.395 692.765
17.712 669.658 5.395
5.904 223.219 0.599
9.85 372.39
0.003 0.000
The S/N ratios of engine torque are revealed by Table 7. Level 2 for the coating materials and level 3 for the engine speed have the highest ratios. Conversely, level 1 for the coating materials and engine speed has the lowest ratios. Finally, the results from Fig. 8 shows that the engine torque reaches its maximum point with the coating material of Al2O3 + 13% TiO2 at the speed of 2600 rpm. Also, P-values for coating materials and engine speed are below 0.05, which means that they are both statistically significant parameters influencing the engine torque.
Table 11 S/N ratios of factor levels for BSFC.
3.2.2. The statistical results of engine power Table 9 records the S/N ratios determined for the experimental control parameters mentioned in Section 2.3 for the engine power. This table has figures maximizing the results under the influence of the test parameters. In addition, in Fig. 9, these figures are used to plot the influence of the parameters of the coating material and engine speeds on the engine power.Table 10. Table 9 exhibits the S/N ratios of the engine power. The S/N ratios of the engine power have more different trend than the engine torque and BSFC because the level 2 of the coating materials and level 4 of the engine speed parameters have the highest ratios. The reason behind this change are explained in Section 3.1.2. On the other hand, level 1 for the coating materials and engine speed have the lowest ratios, which are as same as the engine torque and BSFC. To sum up, the results from Fig. 9 demostrates that the engine power reaches its maximum point with the coating material of Al2O3 + 13% TiO2 at the speed of 3200 rpm. In addition, P-values for the coating materials and engine speed are under 0.05, which means they are both the statistically significant parameters affecting the
engine power.
Control Factors
Coating Materials Engine Speeds
Brake Specific Fuel Consumption (BSFC) Level 1
Level 2
Level 3
Level 4
−49.56 −50.31
−49.29* −49.55
−49.33 −48.45*
−49.45 −49.23
*Levels which are minimazing the results
3.2.3. The statistical results of BSFC Table 11 demonstrates the S/N ratios determined for the experimental control parameters mentioned in Section 2.3 for the BSFC. In this table, there are figures that are minimizing the results under the influence of the test parameters. Moreover, in Fig. 10, these figures are plotted to see the influence of the parameters of the coating material and engine speeds on the BSFC. The S/N ratios of the BSFC are given by Table 11. Level 2 for the coating materials and level 3 for the engine speed have the highest
Table 9 S/N ratios of factor levels for Engine Power. Control Factors
Coating Materials Engine Speeds
Engine Power Level 1
Level 2
Level 3
Level 4
4.071 −4.583
6.598* 2.147
4.107 10.268
4.369 11.314*
Fig. 10. S/N ratio graph of experimental parameters for BSFC.
*Levels which are maximazing the results 6
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References
Table 12 Analysis of Variance (ANOVA) for the SN Ratios of BSFC. Source
DF
Seq SS
Adj SS
Adj MS
F
P
Coating Materials Engine Speed Residual Error Total
3 3 9 15
0.17647 7.08381 0.02367 7.28395
0.17647 7.08381 0.02367
0.05882 2.36127 0.00263
22.37 898.00
0.000 0.000
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ratios while level 1 for both the coating materials and the engine speed has the lowest ratios. This shows that the minimum specific fuel consumption can be seen at the level 2 for the coating materials and level 3 for the engine speed, while level 3 for the coating materials and level 1 for the engine speed causes the maximum fuel consumption. To summarize, according to the Fig. 10, the BSFC reaches its minimum point with the coating material of Al2O3 + 13% TiO2 at the speed of 2600 rpm, which is similar to the results of the engine torque. Also, the statistical results of the BSFC in Table 12 showes that P-value for the coating materials and engine speed parameters are 0, which are under 0.05. Therefore, it can be argued that they are important parameters for the BSFC. 4. Conclusions - According to the experimental studys, it was seen that the coating materials (Al2O3 + 13% TiO2, Cr2O3, and Cr2O3 + 25% Al2O3) could be coated on piston surfaces. Also, the engine tests at four different speeds (1400 rpm, 2000 rpm, 2600 rpm and 3200 rpm) could be applied to the coated pistons. As a result, a better engine torque, power, and BSFC can be achieved with the use of different types of the coating material and engine speed. - Maximum experimental engine torque value was measured as 13.1 Nm with the use of Al2O3 + 13% TiO2 at the speed of 2600 rpm. Maximum experimental engine power value was measured as 3.59 kW with the use of Al2O3 + 13% TiO2 at the speed of 3200 rpm. The minimum experimental BSFC value was measured as 258.73 g/kW.h with the use of Al2O3 + 13% TiO2 at the speed of 2600 rpm. - Maximum exhaust gas temperature was measured as 445 °C with the use of Al2O3 + 13% TiO2 at the speed of 3200 rpm. - Maximum cylinder pressure and heat release rate were measured as 45.70 bar at 361 °CA and 20.89 (j/oCA) at 377 °CA angle respectively with the use of Al2O3 + 13% TiO2 at the speed of 2600 rpm. - Taguchi design method showed that maximum engine torque and minimum engine BSFC values were achieved using the coating material of Al2O3 + 13% TiO2 at the speed of 2600 rpm. Maximum engine power value, on the other hand, was achieved using the coating material of Al2O3 + 13% TiO2 at the speed of 3200 rpm. - The statistical study have demonstrated that all of the P values of coating material and engine speed parameters are smaller than 0.05 and this means that they are statistically significant on the engine torque, power and BSFC. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This study was supported by Bitlis Eren University Scientific Research Projects Coordination Unit. Project Number: BEBAP-2014.15. The authors would like to thank the Bitlis Eren University Science and Technology Research and Application Center for the tests of specimens. 7
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