Automotive Thermoelectric Generator Research Articles

A novel mathematical optimization method to obtain the maximum-power electrical configuration of thermoelectric generators for energy harvesting

Waste thermal energy recovery with thermoelectric generators has been widely studied as a method to make systems that produce hot exhaust gases, such as aircrafts, ground vehicles and factories, more sustainable. In this type of applications, the mismatch in hot and cold side temperatures of thermoelectric modules (TEMs) creates a mismatch in the electrical output. For each situation, there is a certain electrical interconnection between the modules that gives the maximum global power output. Three optimization models to find what is the best way of connecting the TEMs without a trial-and-error process, as usually done in previous literature, based on mathematical programming are proposed: single branch of series-connected TEMs, multiple parallel-connected branches of series-connected TEMs, and multiple groups of independent series-connected TEMs. The main novel contributions of this paper are: (i) a mathematical optimization approach that provides how to connect the thermoelectric modules one by one, (ii) the application of the above-mentioned method in a common case study: an automotive thermoelectric generator, (iii) information about how the optimal connection between modules changes if the heat source changes its operation (iv) a method for selecting a fixed optimal connection even when the heat source operation changes, e.g. different operation modes in a thermal engine, based on introducing weighting parameters in the optimization mathematical model. The optimization approach followed here is novel and has not been applied before to thermoelectric generators.

Performance improvement of the automotive thermoelectric generator by extending the hot side area of the heat exchanger through heat pipes

In pursuit of enhancing the utilization of exhaust heat in the automotive thermoelectric generator (ATEG), this study introduces a novel heat exchanger with integrated heat pipes to extend the effective hot-side surface area. Meanwhile, a numerical model containing multiphysical fields is developed, and the quantity and arrangement of heat pipes are optimized based on this model. Results suggest that (i) The incorporation of heat pipes markedly enhances the recovery of heat energy from the ATEG, leading to a substantial increase in its output power; (ii) With an increasing heat pipe quantity, the ATEG’s output power exhibits a continuous upward trend before eventually reaching stability; (iii) The arrangement of heat pipes also influences system performance, and through optimizations, the optimal quantity of heat pipes is determined to be N = 11 and toleration to be d = 1 mm. At an exhaust temperature of 550 K and a mass flow rate of 60 g/s, the ATEG achieves an output power of 213.19 W and a heat absorption of 4318.02 W, which increased by 42.95 % and 55.6 % respectively, compared with the traditional structure without heat pipes. This structural optimization concept for the heat exchanger provides a new approach to performance improvements of ATEGs. This study provides a design basis and guidance for optimizing the design of ATEG systems with integrated heat pipes.

A novel maximum power point tracking with hybrid control algorithm for automotive thermoelectric generator system.

To dynamically track the maximum power of an automotive thermoelectric generator (ATEG) system in real-time, this study introduces a novel maximum power point tracking (MPPT) algorithm that integrates Kalman filtering and fuzzy control. Employing a two-phase interleaved parallel DC-DC boost converter in the MPPT controller effectively reduces current ripple and switch loss. Results demonstrated a significant improvement in tracking time compared to the traditional incremental conductance algorithm, attributed to the elimination of high-frequency components in output power by the Kalman filter. The novel algorithm exhibits enhanced tracking stability through the application of fuzzy control. Ultimately, the tracking accuracy of the novel algorithm surpasses that of the incremental conductance algorithm by 5.2%, achieving an impressive 94.9%. This study, therefore, presents a valuable contribution to a novel MPPT algorithm for precisely and rapidly tracking the global maximum power points of the ATEG system throughout the entire vehicle driving cycle.

Advancements in Thermoelectric Generator Design: Exploring Heat Exchanger Efficiency and Material Properties

This paper presents a comprehensive study on the application and optimization of automotive thermoelectric generators (ATEGs), focusing on the crucial role of heat exchangers in enhancing energy conversion efficiency. Recognizing the substantial waste of thermal energy in internal combustion engines, our research delves into the potential of TEGs to convert engine waste heat into electrical energy, thereby improving fuel efficiency and reducing environmental impact. We meticulously analyze various heat exchanger designs, assessing their influence on the TEG’s output power under different exhaust gas flow rates and temperatures. Furthermore, we explore the impact of TEG material properties on the overall energy conversion effectiveness. Our findings reveal that specific heat exchanger designs significantly enhance the efficiency of waste gas heat exchange, leading to an improved performance of the TEG system. We also highlight the importance of thermal insulation in maximizing TEG output. This study not only contributes to the ongoing efforts to develop more sustainable and efficient vehicles but also provides valuable insights into the practical application of thermoelectric technology in automotive engineering. Through this research, we aim to pave the way for more environmentally friendly transportation solutions, aligning with global efforts to reduce fossil fuel dependence and mitigate environmental pollution.

Taguchi optimization and thermoelectrical analysis of a pin fin annular thermoelectric generator for automotive waste heat recovery

Enhancing thermoelectric performance while minimizing exhaust back pressure is a crucial step in advancing the commercial viability of automotive thermoelectric generators. To achieve high overall performance in a thermoelectric generator, an annular thermoelectric generator equipped with circular pin fins is proposed. A comprehensive three-dimensional numerical model is established to accurately predict thermoelectric performance and thermomechanical behavior. Detailed multi-physics field distribution characteristics are analyzed. Using an L25 orthogonal array, we examine five influencing factors and their five levels: exhaust temperature, exhaust mass flow rate, fin height, fin diameter, and the number of fins. The Taguchi analysis suggests that exhaust temperature is the most influential factor in determining thermoelectric performance, followed by mass flow rate, fin height, fin diameter, and fin number. The optimal values for these parameters are 673 K, 30 g/s, 20 mm, 3 mm, and 420, respectively. Under the optimal design parameters, the net power reaches 34.11 W, representing an 18.7% increase compared to the original design. Moreover, a comparative study is conducted between plate fins and pin fins, showing that the pin fin-based thermoelectric generator exhibits a 5.83% increase in output power and a 4.82% increase in maximum thermal stress compared to the plate fin-based thermoelectric generator.

Identification of the most influential variables on the power generation of an automotive thermoelectric generator through a global sensitivity analysis

A methodology to determine the most influential independent input variables on the maximum power generation of an automotive thermoelectric generator is developed. A validated numerical model is used to predict the maximum power generation of a thermoelectric generator composed of several thermoelectric modules installed in the exhaust pipe of an internal combustion engine. The Morris sensitivity analysis and the least absolute shrinkage and selection operator feature selection approach are employed to identify the most influential variables. The amount of independent variables selected to carry out the analysis are 18 and they are embedded in different fields such as hydraulic, thermal, electrical, chemical, geometrical and design. Results show that the most influential variables are the inlet temperature of the hot fluid and the Seebeck coefficient and electric resistance of the thermoelectric modules. The thickness of the thermoelectric modules has the least influence on the maximum power generation. These findings could be useful to other researchers to develop simpler mathematical models without compromising the accuracy.

Experimental validation and numerical assessment of a temperature-controlled thermoelectric generator concept aimed at maximizing performance under highly variable thermal load driving cycles

Although the internal combustion engine (ICE) dominance in mobility is being challenged, ICE R&D enables a non-disruptive transition towards sustainable transportation through hybridization and carbon neutral fuels. The efficiency improvement of ICE-based mobility through Waste Heat Recovery (WHR) is thus a priority, especially in the area of hybrid, plugin hybrid and long-haul transportation, where the recovery potential is high, and ICEs will still be used for a long time. Thermoelectric (TE) Generators (TEGs) have been assessed as a possible low maintenance WHR solution for long. However, viable market solutions are still not a reality. While material costs are steadily being overcome with novel affordable TE materials, there is still the issue of low average conversion efficiency under realistic driving conditions. This is caused by the fact that the efficiency of TEGs is further deprecated by the big challenge of thermally optimizing the TEGs under highly variable conditions of exhaust flow rate and exhaust temperature during real-world driving. This thermal optimization mainly means that the hot side temperature should be as close as possible to the maximum allowable temperature of the modules, but not higher.The authors have been exploring exhaust heat exchanger (HX) concepts that allow achieving this thermal optimization under highly variable thermal loads by using phase change. The strategy used incorporates the spreading of excess heat along the HX by variable conductance heat pipes (VCHPs) embedded in it, thus enabling to maximize the energy conversion without thermal dilution under low thermal loads or overheating risk under high thermal loads. This was done by pre-regulating the pressure of the non-condensable gas (NCG) present inside the VCHPs so that these devices would start performing the spreading of excess heat from over-heated to under-heated regions of the HX at a precise phase change temperature, optimized to the optimal thermal level of the thermoelectric generators.The merit of the aforementioned strategy was confirmed through modelling and illustrated in previous work. The scientific novelty of present study relatively to previous work by the authors or other researchers is that it finally provides a full experimental validation of this concept with two different prototypes attached to a light duty engine. The experimental proof-of-concept results were successfully compared against predictions. Finally, theoretical performance analysis of the impact of the application on a light duty vehicle in terms of fuel economy and GHG emissions during the WLTC class 3 b was assessed with the help of driving cycle and engine simulations performed with AVL Suite software.The unique heat spreading and temperature control features of the concept were confirmed experimentally. In addition, predictions made by the model were far beyond the current state of the art for light duty automotive TEG generators. Namely, maximum output powers exceeding 2 kW and 1.2 kW were predicted during the WLTC cycle when using commercial bismuth telluride and the silicide-Tetrahedrite modules explored by the authors, respectively. Average fuel/CO2 savings of 4% were predicted for the WLTC cycle, with these savings raising to 12% during the highway portion of the cycle. This unparalleled performance is explained by the possibility of achieving both an optimized hot face temperature and a high heat exchanger effectiveness even under highly variable thermal loads.

Optimal design of a heat exchanger for automotive thermoelectric generator systems applied to a passenger car

The heat exchanger determines the overall performance of automotive thermoelectric generator (ATEG) systems. To obtain the accurate performance of the ATEG system under actual driving conditions, a fluid-thermal-electric multiphysics numerical model is established. Considering the backpressure loss, weight loss, and pumping power loss, a net power model of the ATEG system is established. The performance of the two heat exchangers with and without fins is investigated and compared. Through optimizations, the optimal parameters for the heat exchanger with fins are NW = 2 rows, H = 30 mm, and NL = 5 columns, and those of the heat exchanger without fins are NW = 2 rows, H = 10 mm, and NL = 4 columns. The output power, net power, conversion efficiency, and net efficiency of the optimal ATEG system with fins are 35.49 W, 22.93 W, 1.89%, and 1.22%, respectively, and those of the optimal ATEG system without fins are 16.49 W, 8.67 W, 1.51%, and 0.79%, respectively. Through the use of fins, the net power and net efficiency of the ATEG system can be increased by 164.48% and 54.43% respectively. The results are helpful to guide the optimization and design of ATEG systems.

Towards compliance with the prospective EURO VII NOx emissions limit using a thermoelectric aftertreatment heater

In this study, the use of a thermoelectric aftertreatment heater (TATH) to reduce NOx emissions in low demanding regimes of diesel-powered Heavy-Duty vehicles (HDV) has been analysed. This system is composed by an Exhaust Gas Heater (EGH) that heats up the exhaust gases in low engine regimes, in order to shorten the time that urea is injected. Besides, the TATH is fed by an Automotive Thermoelectric Generator (ATEG) that converts the waste heat from exhaust gases into electricity, so the system can work energetically autonomous. Experimental results show that under low-speed regimes, a Euro VI certified HDV emits NOx 5 times above the Euro VI limit value. Results demonstrate that the use of a TATH reduces NOx emissions by up to 97.2% in a long-haul diesel-powered MAN Euro VI TGX 18.480 Efficient Line 2 and may help to fulfil the prospective EURO VII regulation. Apart from that, it is also demonstrated that an ATEG can produce the energy required by the EGH in a long-haul mission profile. However, the added weight and the back pressure caused by the TATH is expected to increase the fuel consumption of the vehicle in 0.35%.

Performance study on a thermoelectric generator with exhaust-module-coolant direct contact

The Automotive Thermoelectric Generator (ATEG) aims to recycle the heat in vehicle exhaust, and transforms it into electricity. This paper proposes a specific structure of an automotive direct contact thermoelectric generator (ADCTEG) system. With no space among the TEMs, exhaust gas and coolant water, this automotive direct-contact configuration works in favor of system integration, minimizing the contact thermal resistance, and maximizing thermal efficiency. In this new TEG system, the thermoelectric modules (TEMs) expose the hot side surface on the automotive waste gas, while another surface directly contact with the cooling water. For the purpose of revealing output characteristics of the ADCTEG and the heat transfer performance, several numerical simulations and bench test are carried out to predict the temperature distribution, flow field and output power generation. Meanwhile, the influence of experimental parameters on ADCTEG power generation performance is studied also, the output characteristics of ADCTEG under vehicle on-board environment are discussed. The net output power of ADCTEG under different engine rotation speed is calculated. The researches on output characteristics of liquid–solid–gas ADCTEG system has guiding significance for the structure design of heat exchanger and the optimization design of thermal resistance and heat transfer of the system, and also has reference value for the potential application of automotive TEG.

NOx Emissions below the Prospective EURO VII Limit on a Retrofitted Heavy-Duty Vehicle

In this study, a EURO VI heavy-duty vehicle (HDV) has been retrofitted with an exhaust gas heater (EGH) with the objective to reduce its NOx emissions below the current EURO VI and EURO VII limits. Results show that an EGH of 5 kW is enough to produce a significant NOx emissions abatement below the EURO VI and EURO VII limits. A conventional after-treatment system heated using a 5 kW EGH could work at its maximum catalytic conversion efficiency of 95% regardless of the engine operating speed. Consequently, exhaust gas heaters are a potential solution to high NOx emission at low engine regimes. With the use of an EGH, urea can be injected sooner, and catalytic reactions could cut much more NOx emissions. However, its incorporation would increase the vehicle’s fuel consumption by 1.47% if it is connected directly to the vehicle’s electrical system. Finally, it is also demonstrated that an automotive thermoelectric generator (ATEG) can supply the energy required by the EGH through the conversion of the waste heat from exhaust gases into electricity. This system could work electrically autonomous so there is no extra consumption of fuel.

Performance evaluation of an automotive thermoelectric generator with a non-isometric distributed fin heat exchanger

A novel non-isometric distributed fin structure for a heat exchanger is proposed, which can effectively improve the thermoelectric generator's output performance.

Energy, exergy, environmental sustainability and economic analyses for automotive thermoelectric generator system with various configurations

The objective of the present study is to evaluate the characteristics of energy and exergy performances, environmental sustainability, and economic aspect for three configurations namely, single stage, two stage and segmented thermoelectric generator systems. The experimental study is conducted on single stage thermoelectric generator system to evaluate the energy and exergy performances under various temperature and mass flow rate conditions of working fluids. The Multiphysics coupled numerical approach is proposed for the detail comparison which is validated with experimental results within ± 10% error. The two stage parallel thermoelectric generator system with Skutterudite + Bismuth Telluride presents superior energy and exergy performances, higher environmental sustainability and lower economic. The maximum values of power, energy efficiency, exergy efficiency, net energy efficiency and net exergy efficiency of two stage parallel thermoelectric generator system with Skutterudite + Bismuth Telluride show 220.17 W, 25.42%, 42.01%, 15.38% and 23.36%, respectively. The same configuration shows minimum CO2 emission of 0.0717 g/W, maximum net CO2 mitigation of 43.41 tones, maximum carbon credit of 1078.6 $, minimum levelized cost of energy of 0.0196 $/kWh and minimum energy payback time of 4 months 1 day.

Analysis of an automotive thermoelectric generator coupled to an electric exhaust heater to reduce NOx emissions in a Diesel-powered Euro VI Heavy Duty vehicle

This study presents a new approach to minimize the amount of NOx emitted by diesel engines of Heavy-Duty Vehicles during low engine regimes and low gases temperature conditions. We propose the addition of an electric Exhaust Gas Heater (EGH) to make the SCR system inject the urea solution at low engine regimes. The second part of this study focuses on the viability to use an Automotive Thermoelectric Generator (ATEG) to generate the energy required by the EGH and thus avoiding the need to consume electrical energy from the vehicle’s system. This EGHATEG system is designed to be energetically closed, so there is no extra consumption of fuel. Experimental results show that NOx emissions reduce up to 80% when an EGH is added to a standard diesel-powered Euro VI Heavy Duty truck configuration. Simulations show that an ATEG installed downstream of the aftertreatment system can produce the energy required by the EGH. This system can improve SCR efficiency up to 55% during low engine regimes.

Transient numerical modelling of a thermoelectric generator system used for automotive exhaust waste heat recovery

The automotive thermoelectric generator system is a promising technology of exhaust waste heat recovery, but reasonable theoretical models to predict its dynamic performance are lacking. In this work, a transient fluid-thermal-electric multiphysics coupling field numerical model is proposed for the first time, and the model is used to evaluate the dynamic performance of a simplified automotive thermoelectric generator system under vehicle driving cycles. The transient numerical model, which takes into account the dynamic characteristics, fluid-thermal-electric multiphysics field coupling effects, and material temperature dependence, is thus far the most complete model ever. Numerical results reveal that there is a delay in output response with the change of exhaust temperature, and the change of output voltage and output power is often accompanied by the change of exhaust mass flow rate. The small and short-term fluctuation of exhaust gases has a slight influence on output performance. With the transient variation of exhaust characteristics, the output voltage and output power show more stable changes and slower responses, but the situation is the opposite for conversion efficiency. The output power predicted by steady-state numerical simulation is 12.6% higher than that of transient numerical simulation. Moreover, the proposed transient numerical model is recommended to investigate the dynamic performance of automotive thermoelectric generator systems.

Nox emissions reduction analysis in a diesel Euro VI Heavy Duty vehicle using a thermoelectric generator and an exhaust heater

Selective Catalytic Reduction systems (SCR) are very efficient on reducing NOx. However, they only perform properly when exhaust gas temperature is higher than 180 °C. This means that for low engine regimes combined with cold engine temperatures, SCR systems remains inactive.This study presents a new approach to minimize the amount of NOx emitted by diesel engines of Heavy-Duty Vehicles during low engine regimes and low exhaust gases temperature conditions. We propose the addition of an Automotive Thermoelectric Generator (ATEG) coupled to an electric Exhaust Gas Heater (EGH) to make the SCR system inject the urea solution at low engine regimes. This EGH-ATEG system, which can be retrofitted in any existing vehicle, is designed to be energetically closed, so there is no extra consumption of fuel. Experimental results show that NOx emissions can be reduced up to 80% when an EGH is added to a standard diesel-powered Euro VI Heavy Duty truck configuration. Apart from that, the use of an ATEG installed downstream of the aftertreatment system can produce the energy required by the EGH, which means that the EGH-ATEG system can work energetically autonomous and independent from the vehicle’s electrical system. This system can improve SCR efficiency up to 55% during low engine regimes.

Effects of Module Spatial Distribution on the Energy Efficiency and Electrical Output of Automotive Thermoelectric Generators

Automotive thermoelectric generators (ATEGs) are devices used to harvest waste energy from the exhaust gases of internal combustion engines. An ATEG is essentially formed by three main elements: (1) heat absorber in contact with exhaust gases; (2) thermoelectric modules that directly convert heat into electricity; (3) heat sink to increase the heat transfer through the system. Thermoelectric modules (TEM) are commonly based on small-scale commercial units, with tenths of them needed to assemble a full ATEG device. Thus, several thermal and electrical connections between TEMs can be implemented. Previous studies focused on the implications on the output power. Here, we investigated the effects of using different module connections on the energy efficiency and on the electrical outputs (voltage and current). The study was carried out numerically with ATEGs that used from 4 to 100 individual TEMs. Series, parallel and square connections were investigated under two different engine operating points. The maximum output power was obtained with overall energy conversion efficiencies on the order of 3%. Though the series connection provided the highest output power, the square configuration was the best compromise between output power and electrical characteristics (voltage and current) to successfully integrate the ATEG into the vehicle management system.

Improving transient performance of thermoelectric generator by integrating phase change material

Thermoelectric generator (TEG) based on Seebeck effect, which is well regarded as an effective way for waste heat recovery, has stepped into vision of automotive researchers in the past decades in terms of electricity generation from vehicle exhaust gases. Various driving conditions of the vehicles and fluctuating temperature of the exhaust gases are crucial factors that obstruct the development of automotive TEG. In this study, a novel concept of integrating phase change material (PCM) with TEG for improving transient performance and total efficiency is presented. PCM, as a commonly utilized material for thermal energy storage, reduces the impact of exhaust gas temperature fluctuations on the automotive TEG, thereby improving the efficiency under various driving conditions. According to the thermal properties of the exhaust gases, Pentaerythritol (PE) is selected as the appropriate PCM for the automotive TEG, because of the suitable temperature range for phase transition and extremely low rate of volume change during the phase transition (due to its solid-solid phase change). Experiments are conducted to explore the feasibility of PE integrating with TEG and the capability of improving transient performance of TEG. Results showed that the improvement of open circuit voltage and power output are 0.7% and 1.16%, respectively. The present study provided a guideline for the design and further research of PCM integrated automotive TEG.

Thermoelectric Generators for Automotive Applications: Holistic Optimization and Validation by a Functional Prototype

Current research has led to a significant improvement at the system level of thermoelectric generators (TEG) for automotive applications. The previously low power density could be increased considerably up to 267 W/kg and 478 W/dm3. In addition, the cost–benefit ratio of the technology in the overall system of the vehicle was improved through intensive optimizations on system level. The results presented so far are based on measurement data of single thermoelectric modules (TEM) and simulation of the TEG system. In this paper the high simulative increases at the system level, achieved through a holistic optimization method, are validated by a functional prototype, completely equipped with TEM. Thereby, a functional prototype has been developed and built successfully and measured on a hot gas test bench. In the experiment all TEM show a stable power output and the highest gravimetric power density of automotive TEG systems known to the authors could be measured. Further tests will be performed with the functional prototype as described in the outlook. In addition to the successful tests, the simulation is validated with the detailed measurement data. After adapting the measurement method of the TEM for providing more accurate TEM measurement data as input for the simulation, a suitable match could be achieved between the TEG simulation and the experiment. In the measurement points performed so far, the accuracy of the simulated temperatures reaches more than 95%. The accuracy of the simulated output power is more than 97%.

Selection of the design of a hot heat exchanger of an automotive thermoelectric generator for an urban driving cycle

It is considered for combustion engines to have nearly 60-70% of fuel energy to be dissipated to the environment by the exhaust gases. Automobile thermoelectric generator (ATEG) application is proved to be a solution for increasing vehicle fuel economy by exhaust gas waste heat recovery. The overall efficiency of ATEG system highly depends on its hot heat exchanger, which is designed to remove heat from the exhaust gases to thermoelectric modules that generate electricity. Intensification of heat transfer in ATEG prototypes is usually achieved by using finning and tabulators. However, the modification of inner side of hot heat exchanger increases the hydraulic resistance of the exhaust system, which adversely affects the power and efficiency of the engine. In this work, we investigate the designs of hot heat exchangers with different configurations of the inner surface and evaluate their impact on the engine power during the modern urban driving cycle.