The study of Thermoelectric Module with Various Thermal Conditions of Exhaust Gas from Diesel Engine

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1 The study of Thermoelectric Module with Various Thermal Conditions of Exhaust Gas from Diesel Engine Byungdeok In, Kihyung Lee* Abstract Internal combustion engines rejects 30-40% of the energy supplied by fuel to the environment through exhaust gas. Thus, there is a possibility for further significant improvement of efficiency with the utilization of exhaust gas energy and its conversion to mechanical energy or electrical energy. The Thermo-Electric Generator (TEG) will be located in the exhaust system and will make use of an energy flow between the warmer exhaust gas and the external environment. Predict to the optimum position of temperature distribution and the performance of TEG through numerical analysis. The experimental results obtained show that the power output significantly increases with the temperature difference between cold and hot sides of thermoelectric generator. Keywords Thermoelectric generator, Numerical analysis, Seebeck coefficient, Figure of merit T I. INTRODUCTION he worldwide trend intends to tighten even vehicle fuel consumption with regulations to reduce CO2 gas which is a main factor of global warming. In case of internal combustion engines, only 30-40% of fuel energy can be converted into useable power and the others are wasted as cooling loss from coolant and exhaust gas. Therefore vehicle engine efficiency could be improved with minimizing the loss of coolant and exhaust gas. In present day, technologies to use the wasted energies of the vehicle have been attracting. 1) Hi-Z Technology Inc. developed an 1kW-thermoelectric generation system using a wasted thermal energy of a heavy duty diesel engine instead of using mechanical electric generator and as a result, they finally improved fuel consumption. 2) Douglas et al. studied a combination technology of a generator and TEG using a passenger car. 3) Richard drew a result of increasing in 6% of fuel consumption with numerical analysis using a thermo-electric regenerator of a passenger car. 3) Thermoelectric generator to improve fuel economy is an energy converting device which can directly convert thermal energy into electric energy and so it could be one of the environmental - friendly technologies generating electric power without using any other extra energy source and mechanical equipment. The principle of thermoelectric generating is an electric flow from heat absorption and generation phenomena of thermoelectric module using Seebeck effect which Byungdeok In is with the Department of mechanical engineering Hanyang university, 1271, Sa3-dong, Sangrok-gu, Ansan, Republic of Korea (phone: ; fax: ; sirusony@ hanmail.net). Kihyung Lee is with the Department of mechanical engineering Hanyang university, 1271, Sa3-dong, Sangrok-gu, Ansan, Republic of Korea ( hylee@ hanyang.ac.kr). electromotive force is occurred by temperature difference between both ends of two different thermoelectric devices. In this study, we could expect the efficiency of thermoelectric generator using a simulation modeling before taking an experiment with real thermoelectric generator. II. NUMERICAL ANALYSIS AND METHOD A. Modeling of numerical analysis In this study, WAVE simulation modeling of Ricardo was used to expect the performance of the thermoelectric generator with 2 liter common rail type diesel engine shown in Figure 1. The engine bore and stroke were set as 83mm and 92mm, the compression ratio was set as 18.4 appeared in Table 1. The temperature of the air-fuel mixture was set as 350K. The injector nozzle size and spray angle were 0.1mm and 40. Fig. 1 Diagram of simulation modeling Table 1 Specification of engine Contents Displacement Bore Stroke Injection duration (msec) Condition 2000 cc 83 mm 92 mm 18.4 ISBN:

2 B. Theory We organized several test conditions to carry out a simulation modeling as follows. At first, the target engine speed was increased from 1000rpm to 4000rpm and the data was acquired every 500rpm increased while the exhaust gas temperature was varied at 4 different positions of the exhaust pipe line. The first setting position was for the pure combustion gas condition and the others were set at further positions of ducts from the exhaust port. For the second, we drew results from the exhaust gas obtained under the estimation, which the thermoelectric module was belonging to the same chain as Bi 2 Te 3, to explain the principle of thermoelectric generating, which an electric flow occur from heat absorption and generation phenomena of thermoelectric module. The temperature of the lower temperature part of the module was selected as 120. The performance equations of thermoelectric generating appear as following equations. 5)-7) The Seebeck coefficient (α) and electric resistance (R) could be calculated experimentally from equations(1). 8) The Seebeck coefficient was calculated with the temperature difference between both ends of thermoelectric device and the voltage (V) at non-load condition (I=0). The electric resistance of the thermoelectric device module was calculated from the average value of the electric resistance appeared. Fig. 2 Photograph of thermo-electric module showing the cold side (left) and hot side (right) Table 2. Properties of HZ-20 Physical Properties Width & Length Thickness Weight Compressive Yield Stress Number of active couples Electrical Properties Value 7.5 cm 0.5 cm 115 grams 70 MPa 71 couples Value (2) (1) Power Load Voltage Current Open Circuit Voltage 19 Watts 2.38 Volts 8 Amps 5 Volts Efficiency 4.5 % (3) C. Method of thermoelectric module experiment In this study, we were examined characteristics of thermoelectric module (HZ-20 of Hi-Z Inc) by change of exhaust gas temperature for investigated possibility of that can be applied to actual engine. In low-temperature part, considering the characteristics of the engine coolant temperature, as well as a constant flow rate can also be regulated by 12L/min water bath (CPT Inc. CDRC-8) was used. The module size was 75mm square by 5 mm thick and contained 71 couples of hot pressed bismuth telluride-based materials. The performance of thermoelectric power generation was measured by electric loader device (KIKUSUI PLZ334W). Voltage, temperature and air flow were recorded by data gathering device (cdaq-9178). Thermoelectric module machined grooves on both ends and using the thermocouples (K-type) measured temperature of hot and low temperature part. Amount of heat absorption is calculated by measuring temperature of between heat sink and module. Thermal compound plaster contacts of aluminum block and module for thermal resistance minimized. D. Method of actual engine experiment Experiment proceeds using engine exhaust gas in order to evaluate performance of thermoelectric module. 2L diesel engine used in the experiment and specifications of engine are shown in Table 3. Fig. 3 Photograph of diesel engine As shown in Fig. 6 thermoelectric module attached in the exhaust gas line considered characteristics and structures of the exhaust gas line as possible rear of catalysis. Table 3. Engine specifications ISBN:

3 Description Displacement Bore Stroke Specification 1988cc 83mm 92mm Compression ratio 18.4 Exhaust gas flow rate and temperature are the most important factors of waste heat recovery system. In low-temperature part, considering the characteristics of the engine coolant temperature, as well as a constant flow rate can also be regulated by 12L/min water bath (CPT Inc. CDRC-8) was used. The performance of thermoelectric power generation was measured by electric loader device (KIKUSUI PLZ334W). Voltage, temperature and air flow were recorded by data gathering device (cdaq-9178). In addition rpm and torque of engine were adjusted by dynamometer controller. Low-temperature heat source temperature fixed at 80 was studied. Measuring performance of module by fixed at 1500rpm and engine load increasing 2kg m from 2kg m to 18kg m. Positions of measured temperature are shown in Fig. 3. Experimental condition was fixed 1500rpm because temperature difference of 1500rpm and 2000rpm were little. The experimental conditions are shown in Table 4. Exhaust gas temperature data was measured after exhaust gas temperature stabilized at each experimental condition. Table 4. Conditions of engine experiment CASE RPM Torque (kg m) anticipated using the temperature of duct 777. Accordingly, when the thermoelectric module was applied to a commercial vehicle, advantages of efficiency and performance could be expected from the duct 777 position. Fig. 4 Diagram of simulation modeling Figure 5 and 6 show the Seebeck coefficient and Electrical resistance of thermoelectric module, and Figure 7 shows the figure of merit to thermoelectric module. Seebeck coefficient was decreased according to RPM increased, thereafter the values of Seebeck coefficient were almost same over 3000 rpm. Also Electrical resistance and Figure of merit was kept similar after decreasing. Accordingly, Figure of merit with Seebeck coefficient and Electrical resistance of thermoelectric module was excellent at lower RPMs Fig. 5 Seebeck coefficient of TEM III. RESULT AND DICUSSION A. Results of numerical analysis Figure 4 shows the variation of exhaust gas temperature according to various thermal conditions. As shown in Figure 4, Duct 777 has a little temperature variation but other conditions have big temperature variation. Therefore when the thermoelectric module was applied; it was possible to predict a high consistent temperature could be used at the duct 777. So the performance result of the thermoelectric module was Fig. 6 Electrical resistance of TEM ISBN:

4 Fig. 7 Figure of merit Figure 8 shows the performance curve of thermoelectric generator according to the temperature difference of thermoelectric module. Output voltage was linearly decreased according to current value increased; the value of output power was decreased after increasing and also maximum power was indicated in process of output power. Because temperature of high heat source is constant, maximum value by each condition hardly has variation. In the thermoelectric generation, thermal condition of both ends temperature differential is important factor to result of generation (electric power) performance. (c) Engine speed: 2000 rpm (d) Engine speed: 2500 rpm (a) Engine speed: 1000 rpm (e) Engine speed: 3000 rpm (b) Engine speed: 1500 rpm (f) Engine speed: 3500 rpm ISBN:

5 (g) Engine speed: 4000 rpm Fig. 8 Performance curves according to RPM Prediction result value is very difficult to (the application of) reality but if it(thermoelectric generator) enhance the development of material and efficiency, Thermoelectric generator(it) can be used as a part of heat recovery system. B. Results of engine experiment It shows exhaust gas temperature by position on exhaust line as each experimental condition. Exhaust gas temperature increases as engine load increased. As shown in Fig. 10, temperature of exhaust gas on exhaust port was measured about 200 to 560 and temperature of exhaust gas on front of thermoelectric module was measured about 155 to 470. Also temperature of exhaust gas on rear of thermoelectric module was measured about 130 to 450. The difference of temperature was measured about 30 on exhaust port and front of thermoelectric module and was measured about 30 on front of thermoelectric module and rear of thermoelectric module. Performance of thermoelectric module declined at under 250 on front of thermoelectric module. Thus, performance was measured more than 250. In this study performance of thermoelectric module was measured by external resistance. Resistance offer from 0.25Ω to 22Ω. Fig. 10 Exhaust gas temperature of conditions Fig. 11 shows performance of thermoelectric module according to resistance. As shown in Fig. 13 (a), voltage increased rapidly under 3Ω but increment of increase sharply reduced more than 3Ω. In addition, decrement of current increased rapidly under 3Ω. Current and power measured value was negligible more than 3Ω. Therefore, this thermoelectric module s optimal external resistance is under 3Ω. Fig. 9 Diagram of simulation modeling Fig. 9 shows the maximum value and minimum value of voltage and power of thermoelectric generator according to conditions. As shown in the figure the difference between the maximum and the minimum value is few. Because of high temperature is steady that values of thermoelectric generator are little difference. In the thermoelectric generation, thermal condition of both ends temperature differential is important factor to result of generation (electric power) performance. (a) Feature of voltage ISBN:

6 (b) Feature of current factor to result of generation(electric power ) performance. therefore thermoelectric module need to material development and efficiency increase for the prediction result value apply to reality. 4) Investigate the performance of thermoelectric module by exhaust gas through engine experiment. The difference of temperature was measured about 30 on exhaust port and front of thermoelectric module and was measured about 30 on front of thermoelectric module and rear of thermoelectric module. 5) Voltage, current and power can be investigated under 3Ω. Therefore, this thermoelectric module s optimal external resistance is under 3Ω. ACKNOWLEDGMENT This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(mest) (No ). (c) Feature of power Fig. 11 Performance of thermoelectric module by resistance IV. CONCLUSION From this research, exhaust gas temperature was anticipated by simulation modeling and thus performance of thermoelectric module was understood. Constant temperature position of exhaust line was found and thus Seebeck coefficient and Electrical resistance of thermoelectric module was understood and Figure of merit for thermoelectric module was understood with electric power and voltage. 1) Exhaust gas temperature was surveyed from various parts of exhaust line. From exhaust line, duct 777 was maintained low variation temperature and constant temperature. Therefore thermoelectric module will get constant performance and efficiency at duct ) Figure of merit and Electrical resistance and Seebeck coefficient of thermoelectric module was kept after decrease according to RPM increase. In case of low RPM, Electrical resistance and Seebeck coefficient and figure of merit had large value. 3) Output voltage was linearly decreased according to current increase and output power was decreased after increase also maximum power was indicated in process of output power. Because temperature of high heat source is constant, maximum value by each condition hardly have variation. In the thermoelectric generation, thermal condition of both ends temperature differential is important REFERENCES [1] Endo, T., Kwajiri, S., Kojima, Y., Takahashi, K. et al., Study on Maximizing Exergy in Automotive Engines, SAE Technical Paper , [2] Aleksandr, S.K., John, C.B., Saeid, G., Norbert, B.E., Richard, A.B., David, F., Mike, M. Thermoelectric Development ay Hi-Z Technology, Technical Paper, 2001 [3] Crane, D., Jackson, G., and Holloway, D., Towards Optimization of Automotive Waste Heat Recovery Using Thermoelectrics, SAE Technical Paper , 2001B. Smith, An approach to graphs of linear forms (Unpublished work style), unpublished. [4] Stobert, R. and Milner, D., The Potential for Thermo-Electric Regeneration of Energy in Vehicles, SAE Technical Paper , [5] Rowe, D. M., Thermoelectric Handbook Macro to Nano, Taylor and Francis Group Press, Wales, [6] Bass, J. C., Elsner, N. B. and Leavitt, F. A., Performance of the 1kW thermoelectric generator for diesel engines, Proceedings of the 13th International Conference on Thermoelectrics, pp , [7] Wu, C., Analysis of waste-heat thermoelectric power generators, Applied Thermal Eng., Vol. 16, No. 1, pp , [8] Huang, B. J. Chin, C. J., and Duang, C. L., A design method of thermoelectric cooler, Int. J. Refrigeration, Vol. 23, pp , [9] MYRIAM LAZARD Heat Transfer in Thermoelectricity: Modelling, Optimization and Design, Proceedings of the 7th IASME / WSEAS International Conference on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT, Available: HTE/HTE19.pdf [10] ELENA-OTILIA VIRJOGHE, DIANA ENESCU, MARCEL IONEL,MIHAIL-FLORIN STAN, Numerical simulation of Thermoelectric System, LATEST TRENDS on SYSTEMS (Volume II), Available: STEMS/SYSTEMS2-48.pdf [11] ANDERSON W. SPENGLER, ELNATAN C. FERREIRA, JOSÉ A. SIQUEIRA DIAS, Precision Table-Top Portable Thermal Chamber with Double Thermoelectric Module, Available: RCS/CIRCS-18.pdf [12] Nikos E. Mastorakis, Andreea Jeles, Cornelia A Bulucea, Carmen A. Bulucea, Constantin Brindusa, Evaluating the environmental impact of ISBN:

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