Automotive Thermoelectric Generator Research Articles

Segmented Thermoelectric Generator under Variable Pulsed Heat Input Power

In this paper, we consider the transient state behavior of a segmented thermoelectric generator (STEG) exposed to a variable heat input power on the hot side while the transfer of heat on the cold side is by natural convection. Numerical analysis is used to calculate the power generation of the system. A one-dimensional STEG model, which includes Joule heating, the Peltier effect with constant properties of materials, is considered and governing equations are solved using the finite differences method. The transient analysis of this model is typical for energy harvesting applications. A novel design methodology, formulated on the ratio of the figure of merit of the thermoelectric materials, is developed including segmentation on the legs of the thermoelectric generator, which does not consider previous studies. In our approach, the figure of merit is an advantageous parameter to analyze its impact on thermal and electrical efficiency. The transient state of the thermoelectric generator is analyzed, considering two and three heat input sources. We obtain the temperature profiles, voltage generation, and efficiency of the STEG under pulsed heat input power. The results showed that the temperature drop along the semiconductor elements was more considerable when three pulses were applied, and when the thermal conductivity in the first segment was higher than that of the second segment. Furthermore, we show that the generated voltage and the maximum efficiency in the system occur when the value of the figure of merit in the first segment, which is in contact with the temperature source, is lower than the figure of merit for the second thermoelectric segment of the leg. The model investigated in this paper offers an essential guide on the thermal and electrical performance behavior of the system under transient conditions, which are present in many variable thermal phenomena such as solar radiation and the normalized driving cycles of an automotive thermoelectric generator.

Optimum Design, Heat Transfer and Performance Analysis for Thermoelectric Energy Recovery from the Engine Exhaust System

Thermoelectric waste heat recovery can improve the thermal efficiency of internal combustion engines and reduce CO2 emissions. In this study, a mathematical optimization using a genetic algorithm method is applied to obtain the optimal fin parameters of a rectangular offset-strip fin heat exchanger, used with an automotive thermoelectric generator (TEG) system. Three fin parameters are considered (fin spacing, fin thickness and fin height). Their effect on the exhaust pumping power, the exhaust heat transfer coefficient and the system performance is explored. The main goal is to maximize the net power output of the system. Results show that fin spacing has the most significant effect on the system performance. Moreover, when fin spacing is reduced below 0.5 mm, a negative net power output is obtained. By comparing the performance of stainless-steel (SS) and copper heat exchangers, it was found that the SS heat exchanger requires smaller fin spacing and fin height, which induces a higher pressure drop. TEGs with higher maximum operating temperature will allow further utilization of the exhaust heat, without a decline in performance due to overheating. Finally, a maximum net power output of 553.3 W is achieved using the copper heat exchanger and commercial bismuth-telluride (Bi2Te3) thermoelectric modules.

Suppressed secondary phase generation in thermoelectric higher manganese silicide by fabrication process optimization

Abstract Controlling the generation of secondary phases in thermoelectric higher manganese silicides is crucial to enhance their thermoelectric performance for use in automotive thermoelectric generators. However, the effect of different synthesis and sintering procedures on the secondary phase formation and thermoelectric properties has not yet been investigated. In this study, we demonstrate that fabricating Mn11Si19 via arc melting and spark plasma sintering results in a figure of merit (ZT) of 0.43 at 823 K, which is 15% higher than for a sample fabricated by a solid-state reaction and spark plasma sintering. We found that the presence of secondary MnSi phases in the Mn11Si19 samples was significantly reduced when using arc melting instead of solid-state reaction, which suggests that the phase formation behavior could be controlled by optimizing the fabrication process.

Thermal and acoustic performance of an integrated automotive thermoelectric generation system

In recent years, the use of thermoelectric generators (TEGs) to recover secondary energy from exhaust heat has increased speedily with applications ranging from microwatts to kilowatts. In terms of automotive exhaust system, there are compatibility problems among automotive TEG, catalytic converter and muffler. An integrated automotive thermoelectric generator (IATEG) which contains automotive TEG, catalytic converter and muffler that converts engine exhaust waste heat into electricity is constructed and simulated. Through comparison of steel, aluminum and copper heat exchangers, it is found that both the average interface temperature and the maximum output power increase are highly dependent on the thermal conductivity of the heat exchanger material. An engine bench test and an acoustic bench test are developed to analyze the performance of the IATEG system characteristics, which are undertaken to assess the feasibility of automotive applications. The numerical simulations and experiment results indicate that the IATEG has better sound reduction performance in high frequency noise and higher temperature distribution which can generate a high power while the power output of the TEG can reach 515 W. Through these experiments, thermal, electrical and acoustic performance of the system is characterized. The results establish the fundamental development of IATEG system that enhances the TEG efficiency for vehicles.

Fuel economy analysis under a WLTP cycle on a mid-size vehicle equipped with a thermoelectric energy recovery system

Automotive thermoelectric generators (ATEG) have become a promising technology for exhaust heat recovering in vehicles. Many models and prototypes have been developed and validated with very promising results. Most of them have been analysed in both steady-state and transient conditions in engine test benches. However, only a few have been tested on a real vehicle while injecting the power generated by the ATEG into the electric system of the vehicle. The objective of this work is to test and analyse the behaviour of an ATEG in a mid-size vehicle under a World Harmonized Light Vehicle Test Procedure WLTP. The results show that the alternator is responsible of up to 4.26% of the vehicle fuel consumption. Then, with the incorporation of the ATEG presented, a fuel consumption savings and CO2 emissions reduction of 0.53% can be achieved.

Analysis of an automotive thermoelectric generator on a gasoline engine

This study determined the heat, flow, and electrical power values of and automotive thermoelectric generation system integrated in the exhaust system of an internal combustion gasoline engine. The combustion analyses of the engine integrated with and without automotive thermoelectric generation were carried out. The 20 thermoelectric modules were placed on the rectangular structure which was made of the aluminum 6061 material. The thermoelectric modules were electrically connected to each other in series. The gasoline engine was operated at full load at 1250, 1750, and 2250 rpm, and the electrical energy generated by the automotive thermoelectric generation system was calculated. At the same time, the heat and flow analyses of the automotive thermoelectric generation system were performed using the ANSYS FLUENT commercial software.

Validation of a fuel economy prediction method based on thermoelectric energy recovery for mid-size vehicles

Automotive thermoelectric generators (ATEG) have become a promising technology for exhaust heat recovering in vehicles. Many models and prototypes have been developed and validated with very encouraging results. Most of them have been analyzed in both steady-state and transient conditions in engine test benches. However, only very few have been tested on a real vehicle while injecting the power generated by the ATEG to the electrical system. The first part of this work deals with a real test of a new concept of ATEG in a mid-size vehicle under different steady-state engine regimes. The second part, which goes beyond the state-of-the-art of ATEGs, is focused on the validation of a new mathematical method for predicting the expected fuel economy.The ATEG presented allows for saving up to 1.08% of fuel and CO2 emissions. In addition, the results show that the model enables the estimation of the ATEG savings accurately, with an average error of 11.27%. This data represents the accomplishment of the main objective of this paper providing original and unique data, and a useful tool for ATEG designers.

Development of the Automotive Thermoelectric Generator Electrical Network

The automotive thermoelectric generator (ATEG) produces electrical power by converting heat energy of engine exhaust gasses. The transfer of this electrical energy to a vehicle’s electrical system should be done with minimum losses. The electrical parameters of thermoelectric modules (TEMs), which are installed in the ATEG, are changing due to non-stationary ATEG operating conditions. This fact leads to a mismatch between ATEG resistance and equivalent electrical load resistance, causing the issue of generating maximum energy. One potential solution to this problem is a maximum power point tracking (MPPT) method. MPPT controllers provide harvesting maximum power from the ATEG. In this way, MPPT application is required for thermoelectric systems with variable heat flow. However, any MPPT controller has its own conversion losses, which affect overall ATEG system efficiency. These losses depend on MPPT controller working conditions, i.e. TEMs output voltages and currents. Therefore, the simulation of the electrical circuit should be done during driving cycles to evaluate the total efficiency of the entire system. This evaluation helps to estimate the effectiveness of each element of the electrical network. In this paper, we elaborate our theoretical and experimental studies of the ATEG electrical network and do comprehensive discussion over the design for it.

Optimization of Thermoelectric Modules’ Number and Distribution Pattern in an Automotive Exhaust Thermoelectric Generator

Thermoelectric generators are efficient devices to recover energy from the automotive exhaust gas. In this paper, conversion efficiency of automotive thermoelectric generator (ATEG) and the maximum electrical power generated by the ATEG, defining as the power output of the ATEG excluding the energy loss caused to the engine improved by optimizing the number of thermoelectric modules (TEMs) and its distribution pattern in an ATEG. An advanced numerical model of ATEG considering the effect of the heat transfer among the adjacent TEMs' rows is developed with Simulation-X software. In order to acquire the ATEG's optimal electrical performance, a 3-step optimization is applied. First, 17 independent factors (the number of TEMs in each row from 1 to 18) are assessed and the significant parameters are screened using Plackett-Burman design. Second, an experiment designed with a central composite design is performed to analyze the sensitivity of six selected factors and a surrogate model is built through response surface method. Then, conflicts in two objectives are settled with a multi-objective genetic algorithm. According to the optimization results of a given ATEG, the maximum electrical power generated by the ATEG is 139.47 W and the conversion efficiency is 2.51% under steady engine condition. Finally, the performances of the optimized design under different engine conditions are discussed. The results show that the maximum power generated by the ATEG and efficiency respectively increase by 49.8% and 106.5% after optimization when the exhaust inlet temperature is 805 K and the mass flow rate is 0.5 kg/s.

Combined Numerical and Experimental Investigation on the Optimum Coolant Flow Rate for Automotive Thermoelectric Generators

In a water-cooled thermoelectric generator (TEG) system, there is an energy-consuming circulating water pump. In order to reduce pump energy consumption caused by backpressure and increase the output power of the entire system, combining numerical simulation and experimentation is adopted to explore the suitable coolant flow rate. Due to the limitations of the experimental conditions, numerical simulation is used to compute the temperature distribution and flow field inside the TEG. Base on the numerical results and the empirical formula, the circulating pump energy consumption is calculated. The maximum power output of the thermoelectric module (TEM) at the corresponding temperature difference is obtained by experiment. Finally, the maximum net output power of the module is revealed and the relationship between the coolant flow rate and average temperature of the hot end of the TEMs is proposed, which can serve as a theoretical basis for cooling water flow rate management of the TEG system.

Effects of Design Parameters on Fuel Economy and Output Power in an Automotive Thermoelectric Generator

The need for more sustainable mobility promoted research into the use of waste heat to reduce emissions and fuel consumption. As such, thermoelectric generation is a promising technique thanks to its robustness and simplicity. Automotive thermoelectric generators (ATEGs) are installed in the tailpipe and convert heat directly into electricity. Previous works on ATEGs mainly focused on extracting the maximum amount of electrical power. However, the back pressure caused by the ATEG heavily influences fuel consumption. Here, an ATEG numerical model was first validated with experimental data and then applied to investigate the effects that modifying the main ATEG design parameters had on both fuel economy and output power. The cooling flow rate and the geometrical dimensions of the heat exchanger on the hot side and the cold side of the ATEG were varied. The design that produced the maximum output power differed from that which maximized fuel economy. Back pressure was the most limiting factor in attaining fuel savings. Back pressure values lower than 5 mbar led to a < 0.2% increase in fuel consumption. In the ATEG design analyzed here, the generation of electrical output power reduced fuel consumption by a maximum of 0.5%.

Power and Fuel Economy of a Radial Automotive Thermoelectric Generator: Experimental and Numerical Studies

Recent developments of high performance thermoelectric (TE) materials have increased the interest of using this technology to directly convert waste heat into electricity. In the automotive sector, many automotive thermoelectric generators (ATEGs) designs use TE modules (TEMs) with high hot side temperatures to cope with high engine load regimes. Here, we develop a new concept of a radial ATEG that is specifically designed to work with low temperature TEMs, which enables the use of Pb-free modules and reduces the thermal stress of the device. A prototype is built and tested at different regimes in an engine test bench. A numerical model of the ATEG is developed and validated. The consequences of modifying (1) the exchange area between the heat absorber and the exhaust gases and (2) the effective figure of merit of TEMs on the electrical output power and fuel economy are investigated by means of simulations. Results indicate that the maximum fuel economy (1.3%) is not attained at the point of maximum output power (228 W). In terms of fuel economy, the back pressure at the exhaust penalizes high mass flow regimes. We use a dimensionless parameter to analyze the potential of the ATEG for reducing fuel consumption.

A method to assess the fuel economy of automotive thermoelectric generators

For the widespread application of thermoelectric generators, it is of vital importance to have convenient simulation tools in order to test the behavioral consequences of a thermoelectric generator in almost real conditions. The simulation by numerical methods of the performance of automotive thermoelectric generators (ATEG) allows for time- and cost-saving assessment of material combinations and variations of crucial design parameters. However, even in the case of promising simulation results, it is complicated to guarantee the ATEG capacity for reducing the vehicle’s fuel consumption. This work presents a method to assess the fuel economy of an ATEG design. The procedure, which takes into account the ATEG power generation, backpressure, weight and the coolant pumping power, reveals that the maximum fuel economy value does not occur with the maximum ATEG power generation point. The method applied to the ATEG presented predicts a maximum fuel economy value of 0.18%.

Performance evaluation of an automotive thermoelectric generator with inserted fins or dimpled-surface hot heat exchanger

A virtual evaluation method that computational fluid dynamics combines with a mathematical model was proposed to compute the temperature distribution and final power output of an onboard automotive thermoelectric generator (ATEG), which was configured for an off-road vehicle called Mengshi. A road test was conducted to validate the accuracy and reliability of the virtual evaluation method. The output power and voltage of the ATEG in the road test showed that the virtual evaluation method exhibited satisfactory accuracy in predicting the performance of the ATEG and could provide effective guidance for the design of the ATEG. Furthermore, dimpled surfaces were introduced to replace the inserted fins in the conventional hot heat exchanger to reduce the pressure drop but maintain the temperature difference between the hot and cold end of the ATEG. Computational results showed that, compared with the ATEG with inserted fins, the pressure drop in the ATEG with dimpled surface was reduced by 20.57%, and the net power output was increased by 173.60%.

Numerical Investigation on the Performance of an Automotive Thermoelectric Generator with Exhaust-Module-Coolant Direct Contact

Energy conservation and environmental protection have typically been a concern of research. Researchers have confirmed that in automotive engines, just 12–25% of the fuel energy converts into effective work and 30–40% gets wasted in the form of exhaust. Saidur et al. (Energy Policy 37:3650, 2009) and Hasanuzzaman et al. (Energy 36:233, 2011). It will be significant to enhance fuel availability and decrease environmental pollution if the waste heat in the exhaust could be recovered. Thermoelectric generators (TEGs), which can translate heat into electricity, have become a topic of interest for vehicle exhaust waste heat recovery. In conventional automotive TEGs, the thermoelectric modules (TEMs) are arranged between the exhaust tank and the coolant tank. The TEMs do not contact the hot exhaust and coolant, which leads to low heat transfer efficiency. Moreover, to provide enough packing force to keep good contact with the exhaust tank and the coolant tank, the framework required is so robust that the TEGs become too heavy. Therefore, in current study, an automotive TEG was designed which included one exhaust channel, one coolant channel and several TEMs. In the TEG, the TEMs which contacted the exhaust and coolant directly were inserted into the walls of each coolant channel. To evaluate the performance of the automotive TEG, the flow field and temperature field were computed by computational fluid dynamics (CFD). Based on the temperature distribution obtained by CFD and the performance parameters of the modules, the total power generation was obtained by some proved empirical formulas. Compared with conventional automotive TEGs, the power generation per unit volume exhaust was boosted.

Transient behavior under a normalized driving cycle of an automotive thermoelectric generator

Thermoelectric generators (TEGs) have become a promising technology for vehicle exhaust heat recovery. Many models and prototypes have been developed and validated with very promising results. The majority of them have been tested under steady-state engine conditions. However, light-duty vehicles operate under wide variable loads, causing significant variation of TEG performance. The purpose of this study is to test and analyze an automotive thermoelectric generator (ATEG) under different steady-state engine conditions and under the transient New European Driving Cycle (NEDC). Results show that both thermal inertia and pressure drop play a key role in designing an ATEG for real applications. Variations on exhaust temperature and mass flow rate prevent achievement of thermal steady state. Consequently, total energy generated during the NEDC is lower than that expected from a steady-state analysis. On the other hand, excessive pressure loss on the exhaust considerably minimizes engine performance.Results show that the overall power generation of the ATEG can be significantly improved by maximizing the heat transfer through TEMs using a finned geometry, employing lower temperature thermoelectric materials and including a hot-side temperature control.

Development of a mathematical model for optimizing the design of an automotive thermoelectric generator taking into account the influence of its hydraulic resistance on the engine power

A complex of models for optimizing the design and operation modes of an automotive thermoelectric generator is developed within the proposed approach taking into account the influence of hydraulic resistance of the generator on the internal combustion engine. Several designs of generators for converting the thermal energy of exhaust gases (EGs) of internal combustion engines into electricity due to the Seebeck effect in semiconductor elements, which have different geometries of the continuous-flow part of the generator with different hydraulic resistances, are considered. Models for calculating the thermoelectric elements, gas heat exchanger, and automotive engine are considered jointly. Simulation is performed using the example of a VAZ-21126 engine, which demonstrated that up to 500 W of electric power can be obtained using semiconductor thermoelectric elements based on germanium and lead tellurides.

Numerical investigation on the performances of automotive thermoelectric generator employing metal foam

The automotive thermoelectric generator (TEG) can recover the thermal energy of automotive exhaust and convert it into electric energy. The metal foam can provide a high heat transfer performance as well as sound absorption function, when it is applied in heat exchanger in TEG. The heat exchanger whose wall is attached with metal foam is modeled, and the temperature distribution and acoustic performance are calculated. The numerical simulations indicate that the TEG with metal foam has better sound reduction performance in high frequency noise and higher temperature distribution which can generate a high power while the power output of the TEG can reach 323.424W. Then three parameters of the metal foam, including porosity, thickness of the foam that attached to the eight surfaces and the octagonal foam attached to the outlet are calculated to invest their impacts. The results reveal that temperature distribution and output power gradual peak and decline as the porosity decreases, which will also lead to a deteriorative acoustic performance. The increase of metal foam thickness will contribute to enhance the thermal performance of the TEG, and better sound reduction can be obtained.

Experimental analysis of an automotive thermoelectric generator under different engine operating regimes

Experimental analysis of an automotive thermoelectric generator under different engine operating regimes

Design and Preparation of High-Performance Bulk Thermoelectric Materials with Defect Structures

Thermoelectric is a key technology for energy harvesting and solid-state cooling by direct thermal-to-electric energy conversion (or vice versa); however, the relatively low efficiency has limited thermoelectric systems to niche applications such as space power generation and small-scale or high-density cooling. To expand into larger scale power generation and cooling applications such as ATEG (automotive thermoelectric generators) and HVAC (heating, ventilation, and air conditioning), high-performance bulk thermoelectric materials and their low-cost processing are essential prerequisites. Recently, the performance of commercial thermoelectric materials including Bi2Te3-, PbTe-, skutterudite-, and half-Heusler-based compounds has been significantly improved through non-equilibrium processing technologies for defect engineering. This review summarizes material design approaches for the formation of multi-dimensional and multi-scale defect structures that can be used to manipulate both the electronic and thermal transport properties, and our recent progress in the synthesis of conventional thermoelectric materials with defect structures is described. Key words: Thermoelectric, Solid-state cooling, Energy harvesting, Defect engineering