Development of waste heat recovery system for internal combustion engine using Organic Rankine Cycle

Negash A. Assmelash,Kim Young Min,Shin Dong Kil 한국자동차공학회 2019 한국자동차공학회 부문종합 학술대회 Vol.2019 No.5

Effect of electrical array configuration of thermoelectric modules on waste heat recovery of thermoelectric generator

Negash, Assmelash A.,Kim, Tae Young,Cho, Gyubaek Elsevier 2017 Sensors and actuators. A Physical Vol.260 No.-

<P><B>Abstract</B></P> <P>An experimental study was undertaken to investigate the effect of the electrical array configuration of thermoelectric modules (TEMs) on thermoelectric power generation. A thermoelectric generator (TEG) was constructed with customized TEMs. Prior to the system-wise power generation experiment, the electrical characteristics of each TEM (a total of ten TEMs) were measured. The sum power output of each TEM was 34.2W, which was set as a reference power output for different system-wise array configuration methods To examine the effect of the array configuration, eight different TEM array configurations were formed using series, parallel, and combination connections to provide different power sources for different applications. The experimental results showed that the system-wise power output of the different array configurations varied up to 59% compared to the reference power. Moreover, a 1.4–36.4% difference in power output was evident compared to the individual array configuration on account of the different ways in which the TEMs were electrically connected. The number of junctions in the circuitry and the unbalanced number of modules in the array configuration were chosen as the possible parameters that mostly affected the power output in various electrical circuitries for a constant temperature difference across the TEM sides. Consequently, the power output of the TEG decreased with the increasing number of circuitry junctions in the TEG. The array configuration with less than two junctions in its circuitry showed a power generation up to 94%, whereas the array configuration with six junctions generated only up to 62.5% compared to the reference power output. Similarly, the power output of the TEG decreased with the increasing unbalanced number of modules in the circuitry. The power generation of TEG array configurations with a balanced number of modules in the array was up to 95.4%, whereas that with four unbalanced number of modules in the array only generated 58.9% compared to the reference power output. Therefore, the array configuration with a minimized number of junctions and balanced number of modules is recommended for maximizing the TEG power output.</P>

다공성 물질과 방열핀을 이용한 열전 에너지 하베스팅 시스템의 유동 및 발전 특성 향상

Assmelash Negash,최영(Young Choi),김태영(Tae Young Kim) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.5

Enhancing Diesel Fuel Plasma Burner`s Combustion efficiency for DPF regeneration

Assmelash Assefa Negash(아스멜라쉬),Junho Lee(이준호),Hongsuk Kim(김홍석) 한국자동차공학회 2014 한국자동차공학회 학술대회 및 전시회 Vol.2014 No.11

Ratio Test Statistics and Multiple Comparisons with the Best for Supplier Selection for a Process with Profiles

Yeneneh Tamirat Negash 대한산업공학회 2020 Industrial Engineeering & Management Systems Vol.19 No.2

For the quality characteristics described by linear profiles and with very low fraction defectives, the usual supplier selection strategies might not work because a sample of a sensible size most likely contains zero defectives. This study provided decision procedures and rules that are easy to implement based on the ratio test statistics. For the ratio test statistics, prior studies are restricted to two suppliers; in practice, more than two suppliers competing for an order is a standard. The Bonferroni correction method is employed to avoid error inflation due to multiple testing. The proposed method is compared with multiple comparisons with the best method. Tables of critical values and the number of profiles required are provided for practitioners. When comparing more than two suppliers, the proposed method provides useful information to rank suppliers and select the supplier with superior process capability. Furthermore, the statistical properties of the proposed method are investigated. A comprehensive simulation study is done to compare the power and the sample size requirement. The result suggests that multiple comparisons with the best method is superior in terms of power and sample size requirement. A real data set is collected from a computer producer to illustrate the applicability of the methods

기후 변화 완화를 위한 열전 발전을 통한 에너지 회수

김태영,Assmelash Negash,조규백 한국에너지학회 2016 한국에너지공학회 학술발표회 Vol.2016 No.10

무인 이동체의 센서 결함 검출과 결함 정보 관리 방법에 대한 연구

김상현,Lebsework Negash,최한림 한국항공우주학회 2015 한국항공우주학회 학술발표회 논문집 Vol.2015 No.4

본 논문에서는 무인 이동체 시스템의 안전성 확보를 위한 센서 검출과 결함 정보의 관리에 대한 연구를 수행하였다. 무인 이동체 시스템에서 발생하는 결함은 결함 유형에 따라 대개 중대 결함 (Major Fault)과 비중대 결함 (Minor Fault)로 구분된다. 결함 검출 및 격리 (FDI)는 중대 결함을 적절하게 처리하지만 비중대 결함을 처리하는데 어려움이 있다. 두 가지 결함 유형을 다루기 위해 결함 검출 및 페널티 (FDP) 알고리듬을 제시하였다. 무인 이동체 시스템 안정성 확보를 위한 결함 검출 및 대응에 대한 성능을 분석하기 위하여 FDI, FDP 를 간단한 UAV 센서 교란 공격 예제에 적용하였다. In this paper, the sensor fault detection and fault information management for securing unmanned vehicle system safety are studied. Faults which occur in the unmanned vehicle system are mainly divided into the major fault and the minor fault depending on fault types. Fault Detection and Isolation (FDI) properly handles the major fault. However it has difficulty in handling the minor fault. To handle two fault types, Fault Detection and Penalty (FDP) algorithm is suggested. FDI and FDP are applied to a simple example of UAV sensor deception attack in order to analyze the performance of the fault detection and response for securing unmanned vehicle system safety.

Waste heat recovery of diesel engine using porous medium-assisted thermoelectric generator equipped with customized thermoelectric modules

Choi, Young,Negash, Assmelash,Kim, Tae Young Elsevier 2019 Energy conversion and management Vol.197 No.-

<P><B>Abstract</B></P> <P>In this study, thirty of customized bismuth-telluride (Bi<SUB>2</SUB>Te<SUB>3</SUB>) thermoelectric modules (TEMs) were fabricated for waste heat recovery of a diesel engine using a thermoelectric generator (TEG). By installing a plate-type porous medium whose porosity ranges from 0.121 to 0.516 in the TEG, the effects of the porosity on energy harvesting performance were investigated. Experimental results show that at the highest engine rotation speed of 1400 rpm, a maximum power output of 98.3 W was obtained using the lowest porosity (0.121), and a maximum energy conversion efficiency of 2.83% was obtained using the optimal porosity (0.416). The most significant improvements in the power output and conversion efficiency compared with the base case without porous media were 44.5% and 10.1% with porosities of 0.121 and 0.416, respectively, at the lowest engine speed of 1000 rpm. We concluded that the conversion efficiency and power output of the present TEG can be maximized via application of porous media with porosities of 0.461 and 0.32, respectively. The use of a porous medium with a porosity of <0.32 in the present TEG configuration should be avoided, as the backpressure would exceed the allowable limit of ~3 kPa for a passenger vehicle.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bi<SUB>2</SUB>Te<SUB>3</SUB> thermoelectric modules were newly constructed for improved open circuit voltages. </LI> <LI> The performance of a thermoelectric generator was investigated for a diesel engine. </LI> <LI> The effects of porosity of the media on the power output and conversion efficiency were determined. </LI> <LI> Pressure drop measurements guide the optimal use of the porous medium. </LI> </UL> </P>

Experimental and numerical study of waste heat recovery characteristics of direct contact thermoelectric generator

Kim, Tae Young,Negash, Assmelash,Cho, Gyubaek Elsevier 2017 Energy conversion and management Vol.140 No.-

<P><B>Abstract</B></P> <P>In this study, waste heat recovery performance of a direct contact thermoelectric generator (DCTEG) is experimentally investigated on a diesel engine. In order to conduct an insightful analysis of the DCTEG characteristics, three experimental parameters—engine load, rotation speed, and coolant temperature—are chosen to vary over ranges during the experiments. Experimental results show that higher temperature differences across thermoelectric modules (TEM), larger engine loads, and rotation speeds lead to an improved energy conversion efficiency of the DCTEG, which lies in the range of approximately 1.0–2.0%, while the output power ranges approximately 12–45W. The increase in the conversion efficiency for an increased engine load becomes more noticeable with a higher engine rotation speed. A 10K decrease in the coolant temperature yields an approximately 0.25% increase in the conversion efficiency for the engine operating conditions tested. In addition, 3D numerical simulations were conducted to investigate the heat transfer and pressure characteristics of the DCTEG. Numerically obtained exhaust gas temperatures exiting the DCTEG were in good agreement with experimental results. It is also revealed that incorporation of the temperature fields from the numerical simulation and an empirical correlation for a temperature-power relationship provides a good predictor for output power from the DCTEG, especially at low engine load conditions, which deviates from experimental results as the engine load increases. Heat recovery efficiency of the DCTEG is found to be in the range of approximately 5.7–11.1%, which is yielded by comparing the heat transfer rate from the exhaust gas to a surface of the TEMs to the total exhaust gas energy entering the DCTEG. Numerical results also show that most exhaust gas thermal energy extracted by the DCTEG is used for thermoelectric energy conversion, and only approximately 1/5 of the energy is wasted to the environment regardless of engine load conditions. Owing to a simple internal geometry without any extended surfaces, the DCTEG features a low exhaust gas pressure drop of smaller than 700Pa even for the maximum exhaust gas flow rate of approximately 322kg/h.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Energy harvesting performance of direct contact thermoelectric generator was studied. </LI> <LI> Power-current and voltage-current curves were given for various operating conditions. </LI> <LI> Output power prediction using numerical results and empirical correlation was verified. </LI> <LI> A 1.0–2.0% conversion efficiency and 5.7–11.1% heat recovery efficiency were obtained. </LI> <LI> A 0.25% increase in efficiency was found with a 10K decrease in coolant temperature. </LI> </UL> </P>

Experimental study of energy utilization effectiveness of thermoelectric generator on diesel engine

Kim, T.Y.,Negash, A.A.,Cho, G. Pergamon Press 2017 ENERGY Vol.128 No.-

This study was devoted to investigating the energy utilization of a thermoelectric generator (TEG). Key factors governing the power generation characteristics of the TEG-the power output, system resistance, and conversion efficiency-are systematically analyzed under various engine operating conditions. The effects of heat rejection conditions on the energy utilization by the TEG are also examined. Experimental results show that a slight coolant temperature reduction of 10 K increases the TEG power output by up to 33.7%, increasing the short-circuit current. The coolant temperature reduction also causes more than 34.8% improvement in the conversion efficiency. Contour maps for the power output and conversion efficiency are proposed as functions of the engine load and speed. A maximum power output and conversion efficiency obtained are ~125.7 W and ~3.0%, respectively. In contrast to the coolant temperature effect, a change in the coolant flow rate has a relatively insignificant effect on energy utilization: the power output variation is only 6.8%-8.5%. The TEG design effectiveness is evaluated by analyzing the flow of exhaust gas energy. The analysis shows that a relatively large portion of exhaust gas energy (37.4%-47.1%) is lost to the environment instead of being used for power generation by the TEG.