Automotive Waste Heat Recovery Research Articles

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.

Power generation of annular thermoelectric generator with silicone polymer thermal conductive oil applied in automotive waste heat recovery

The annular thermoelectric generator (ATEG) matches the shape of the exhaust pipe. To improve the power generation efficiency of the ATEG in automobiles, a scheme is proposed to use a silicone polymer-based thermal conductive oil to transfer heat from the exhaust. Based on this concept, a new type of concentric tube heat exchanger is designed. A finite element model of the new system is established by considering temperature gradients, temperature dependence, and fluid resistance characteristics. Numerical simulations are performed to investigate the effects of exhaust parameters, thermal oil parameters, and heat exchanger structure on thermoelectric performance. The findings demonstrate a 15.2% increase in maximum output power of the new generator compared to a conventional ATEG, accompanied by a 19% decrease in the optimal thermoelectric module area. Furthermore, the net power first increases and then decreases with increasing thermal oil mass flow rate. The thermal oil mass flow rate can be adjusted in real-time based on fluctuations in exhaust parameters to achieve peak net output power. Finally, optimal fitting relationships between the heat exchanger dimensionless diameter and the total diameter, as well as between exhaust parameters and the optimal thermal oil mass flow rate, are obtained through parameter analysis and derivation.

Thermal and Electrical Performances of Thermoelectric Generator System for Different Internal Fin Structures

In the present study, the thermal and electrical performances of automotive waste heat recovery thermoelectric generator system are investigated for different internal fin structures in hot heat exchanger. A coupled numerical model integrated with heat transfer and thermoelectric effects is developed to simulate the Multiphysics behavior of thermoelectric generator system. The coupled numerical model is validated with experimental results for both thermal and electrical performances within maximum error of ± 8%. The temperature difference, pressure drop, power, conversion efficiency, exergy efficiency, and net efficiency of thermoelectric generator system are compared for hot heat exchanger without internal fin structure and that with 12 different internal fin structures. The 12 different internal fin structures comprise of straight fins, perpendicular fins, fishbone fins, triangular guide fins, and combination of fins. The results reveal that, an Internal structure11 depicts superior thermal and electrical performances of thermoelectric generator system among all internal fin structures. Despite of higher pressure drop of 0.04571 bar, the Internal structure11 shows superior power, conversion efficiency, exergy efficiency, and net efficiency of 70.79 W, 7.76%, 14.10%, and 0.996%, respectively. The hot heat exchanger with Internal structure11 is proposed as the best configuration for the optimum performance of thermoelectric generator system.

Development and validation of thermal performances in a novel thermoelectric generator model for automotive waste heat recovery systems

Integrated thermoelectric generators (TEGs) and heat exchangers (HEX) can transform heat into electrical power by converting temperature gradients between heat sources and cold sinks. Predicting TEG thermal performances with compact HEX is crucial to designing efficient TEGs for automotive waste heat recovery. However, previous investigations mainly concentrated on TEG electrical performance, neglecting the thermal performances under high Reynolds numbers (Re) of exhaust gasses. This study utilizes the model-based development (MBD) method to develop a novel 1D TEG model, focusing heat transfer coefficient α and pressure drop ΔP inside a louvered corrugated fin HEX, component temperatures, and boundary heat flux, which affect electrical power from thermoelectric modules (TEM). The performance data are measured from 36 tests under different fin pitches Fp = 1.0 - 2.0 mm, Re = 4,000–14,000, and inlet gas conditions. Two methods are used to develop the model using user-defined functions (UDFs) for friction coefficient Cf and α, accounting for actual fin geometries. In Method 1, UDF multipliers for each Fp are required to calibrate the TEG model. In Method 2, simplified UDFs for Cf and α are implemented. Method 1 shows that the model is well-calibrated with maximum average relative errors δa< 6.7% but requires model fitting for each Fp. The fast-predictive TEG model with the novel calibration Method 2 can reproduce the thermal and electrical performances with δa< 20% without model tuning, which can be used for TEG redesign and integrated into vehicle-level MBD with a conventional and electrified powertrain, leveraging a fast driving-cycle simulation.

LTCC-based Y-type thermoelectric generator with an improved heat flow guide for automotive waste heat recovery

An improved heat guide Ag/AgPd metal-based Y-type thermoelectric generator (TEG) for converting automotive waste heat into electricity has been designed, analyzed, and manufactured with a low-cost LTCC technology.

Novel designs of thermoelectric generator for automotive waste heat recovery: A review

&lt;abstract&gt; &lt;p&gt;Many worldwide scientists have concentrated on using waste heat recovery technology in automotive applications because of increasingly strict fuel consumption. The thermoelectric generator (TEG) has garnered significant interest in the automobile sector as a viable waste heat recovery solution over the past several decades. A short survey of thermoelectric materials and heat exchangers for TEG systems is initially presented in this paper. To overcome the heat exchanger's current shortcomings, some previous studies designed a variety of the heat exchanger geometry of the TEG system. They suggested concentric cylindrical TEG system utilizes an annular thermoelectric module instead of the traditional square-shaped one. It uses the heat pipe's benefits to improve radial heat transmission. A comparison of the water-inside and gas-inside arrangements indicated that the water-inside concentric cylindrical TEG system provided a greater power output in our simulations to test the performance of the proposed system.&lt;/p&gt; &lt;/abstract&gt;

Experimental investigation and comparative analysis of selected thermoelectric generators operating with automotive waste heat recovery module

A thermoelectric generator (TEG) is a device that converts waste heat into electricity which can have a rapid rise in the coming years. Different types of thermoelectric generators like wearable, flexible, Liquid metal, foam-based, and solar-based are being explored for different applications such as Low power (Micro-milliwatts), Intermediate power (watts hundreds of watts), Parasitic application, High power (hundred to megawatts). In this work, the experimental investigation has been carried out with a TEG module (TEC1-12715) integrated with a waste heat recovery module with help of an Aluminum heat sink on one side and a Copper Heat Sink on another end. This complete waste heat recovery module is attached to the Engine Honda GX120 exhaust and is used for conversion and storage the purpose. The highest voltage achieved by using a set of two TEG’s (TEC1- 12715) is 1.4 V at 3000 rpm. Also, the comparative analysis on the performance evaluation of thermoelectric generators i.e., TEC1-12715 and TEG-27145 integrated with exhaust waste heat recovery module, depicts that the TEG module (TEG-27145) shows better performance than the TEG module (TEC1-12715) where the voltage of 9.2 V and current of 0.98 A has been generated with Thermoelectric generator (TEG-27145) at an engine rpm of 3000 under no-load conditions. Furthermore, the waste heat recovery module coupled with the thermoelectric generator (TEG-27145) can be readily used to charge the 9 V rating batteries of the two-wheelers. Also, as per the comparative analysis of TEGs as the maximum power generated by TEG-27145 is 1.062 kW at an engine rpm of 3000.

Tubular ring thermoelectric module for exhaust pipes: From Skutterudite nanopowders to the final device

There is an important number of thermoelectric applications in the range of medium temperatures (between 200 and 600 °C), such as heat recovery in automotive applications, where these temperatures are easily reached in the exhaust or the motor. Among the various materials which exhibit good thermoelectric properties in this range, Skutterudites (with the general formula CoSb3) stand out as some of the most used. In recent years, different improvements have been done to decrease their thermal conductivity, from using rattler atoms inside their structure to nanostructuring by sintering nanoparticles and increasing the number of grain boundaries. In this work, we present the subsequent development of the nanopowder ball-milling fabrication method, to obtain a scalable production of n-type and p-type nanostructured Skutterudites. The sintering of these powders into nano-composites was done by different pressing and annealing treatments, which not only could substitute other sintering processes such as Spark Plasma Sintering, giving competitive values of the thermoelectric properties of the final nanostructured material, but can also be used to directly obtain different geometries to be used in certain implementations. This procedure has been tested by fabricating thermoelectric legs of the thermoelectric nanostructured material in the shape of rings, in contrast with the more generally available thermoelectric modules, which have a planar architecture. The ring-shaped architecture was obtained by pressing the nano-powders between copper rings, and from them, cylindrical thermoelectric generators were implemented, which present several of advantages for their use in automotive waste heat recovery from the exhaust, for instance. The optimal parameters, as far as geometry and the materials used in the final device, can be extracted from simulations based on the actual measurements obtained in the fabricated thermoelectric rings. Taking all these into account, in this work we present a route to fabricate low-cost nano-structured Skutterudite in an easily scalable way, suitable for the implementation of different architectures of thermoelectric generators for mid-range temperature applications.

Nonlinear model predictive control of organic Rankine cycles for automotive waste heat recovery: Is it worth the effort?

Using organic Rankine cycles (ORC) for waste heat recovery in vehicles promises significant reductions in fuel consumption. Controlling the organic Rankine cycle, however, is difficult due to the highly transient exhaust gas conditions. To tackle this issue, nonlinear model predictive control (NMPC) has been proposed and approximate NMPC solutions have been investigated to reduce computational demand. Herein, we compare (i) an idealized economic NMPC (eNMPC) scheme as a benchmark to (ii) a NMPC enforcing minimal superheat and (iii) a PI controller with dynamic feed-forward term (PI-ff) in a control case study with highly transient disturbances. We show that, for an ORC system with supersonic turbine, the economic control problem can be reduced to a single-input single-output superheat tracking problem combined with a decoupled steady-state real-time optimization (RTO) of turbine operation, assuming an idealized condenser. Our results indicate that the NMPC enforcing minimal superheat provides good control performance with negligible losses in average power compared to the full solution of the economic NMPC problem and that even PI-ff only results in marginal losses in average power compared to the model-based controllers.

Review of Small Gas Turbine Engines and Their Adaptation for Automotive Waste Heat Recovery Systems

Current commercial and heavy-duty powertrains are geared towards emissions reduction. Energy recovery from exhaust gases has great potential, considering the mechanical work to be transferred back to the engine. For this purpose, an additional turbine can be implemented behind a turbocharger; this solution is called turbocompounding (TC). This paper considers the adaptation of turbine wheels and gearboxes of small turboshaft and turbojet engines into a two-stage TC system for a six-cylinder opposed-piston engine that is currently under development. The initial conditions are presented in the first section, while a comparison between small turboshaft and turbojet engines and their components for TC is presented in the second section. Based on the comparative study, a total number of 7 turbojet and 8 turboshaft engines were considered for the TC unit.

Designing Regenerators of Thermoacoustic Engines for Automotive Waste Heat Recovery

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Extraction and utilization of automotive waste exhaust heat is an effective way to save fuel and protect the environment. One promising technology for this purpose is the thermoacoustic engine, where thermal energy is converted to mechanical energy in terms of high amplitude oscillations. The core component in a travelling-wave thermoacoustic engine is its regenerator where the process of energy conversion is mainly realized. This paper introduces a strategy for the design of the regenerator for applications in typical light- and heavy-duty vehicles. Starting from 1-D linear thermoacoustic theory, the nonlinear effects (given by the high amplitude oscillations) are modelled as acoustic resistances and introduced into the basic linear equations to estimate the nonlinear dissipations in the regenerator. Then, a few dimensionless parameters are derived by normalizing these thermoacoustic equations. This yields a good overview of how different design parameters such as the geometrical dimensions, operating temperature, and thermal boundary conditions influence the performance of the regenerator. For the application of automotive waste heat recovery, the thermal properties of the actual exhaust gas are accepted to be the boundary condition for the heat matching. The results obtained in the current work show that the optimum designs for the regenerators in travelling-wave thermoacoustic engines aimed at light- and heavy-duty applications widely differ due to the different thermal properties of their exhaust gas. Finally, two possible optimal designs of the regenerators in travelling-wave thermoacoustic engines for the typical light- and heavy-duty applications are presented. The designs are based on heat matching between the required heat by the regenerators and the available heat from the exhaust gases.&lt;/div&gt;&lt;/div&gt;

Automotive Waste Heat Recovery after Engine Shutoff in Parking Lots

&lt;div class="section abstract"&gt;&lt;span class="label"&gt;1&lt;/span&gt;&lt;div class="htmlview paragraph"&gt;The efficiency of internal combustion engines remains a research challenge given the mechanical friction and thermodynamic losses. Although incremental engine design changes continue to emerge, the harvesting of waste heat represents an immediate opportunity to address improved energy utilization. An external mobile thermal recovery system for gasoline and diesel engines is proposed for use in parking lots based on phase change material cartridges. Heat is extracted via a retrofitted conduction plate beneath the engine block after engine shutoff. An autonomous robot attaches the cartridge to the plate and transfers the heat from the block to the Phase Change Material (PCM) and returns later to retrieve the packet. These reusable cartridges are then driven to a Heat Extraction and Recycling Tower (HEART) facility where a heat exchanger harvests the thermal energy stored in the cartridges. A series of mathematical models are created to estimate the recoverable heat from a standard parking lot configuration. A representative case study that considered 500 cars with periodic traffic flow over a period of 16 hours can heat approximately 25 kiloliters of potable water from 15°C to 50°C. Future development will involve the creation of strategies to extract heat during engine idling at traffic stops and drive through lanes.&lt;/div&gt;&lt;/div&gt;

A Study of Exhaust Waste Heat Recovery in Internal Combustion Engines

This research presents an investigation of an energy recovery solution from exhaust gases in internal combustion based on the heat exchange to distil fresh water from the sea water. Consequently, an optimization of the flow field design of the heat exchanger was performed using the commercial computational fluid dynamics (CFD) software. The result of this research showed that the energy recovery performance of the exchanger strictly depends on the engine load, which can reach a value of approximately 33% at the full load condition of the research engine. These results might forecast a future application of the optimized exchanger’s flow-field design in automotive waste heat recovery in order to improve the internal combustion engine efficiency.

Model predictive control of an automotive waste heat recovery system

This paper proposes a model predictive control strategy for an Organic Rankine Cycle based waste heat recovery system. The control strategy uses a prediction model based on gain scheduling of local models, which results in a quadratic program to efficiently calculate the optimal control inputs. To ensure an optimal system operation, the reference values are obtained from a steady-state optimization. To capture a model-plant mismatch, the control concept features an EKF-based estimator of the model uncertainties. Simulations on a validated simulation model show that this control strategy can track the optimal reference very well, even for a large model-plant mismatch.

Effect on TEG performance for waste heat recovery of automobiles using MgO and ZnO nanofluid coolants

Present study deals with the theoretical analysis for the performance comparison of automotive waste heat recovery system with EG-W, ZnO and MgO nanofluidas coolants for TEG system. Effects on performance parameters i.e power output, conversion efficiency and circuit voltage of TEG system with exhaust inlet temperature, total area of TEG, Reynolds number and particle concentration of nanofluids for TEG system have been investigated. Theoretical performance analysis revealed enhancement in output power, conversion efficiency and voltage of the TEG system for MgO nanofluid, followed by ZnO and EG-W coolants. The power output and the conversion efficiency using 1% vol. fraction MgO nanofluid at an inlet exhaust temperature of 500 K, were enhanced by 11.38% and 10.95% respectively, as compared to EG-W coolants. The further increase in nanofluid concentration exhibited a progressive effect on output performance of the TEG system. Further analysis shows that there exists an optimal total area of TEGs for maximum output performance of the system. With MgO nanofluid as a coolant, total area of TEGs can be reduced by up to 33% as compared to EG-W, which would bring significant convenience for the arrangement of TEGs and reduce the cost of TEG system.

Thermodynamic analysis of compound cycle system for automotive waste heat recovery and air conditioning refrigeration

A compound cycle system, which integrates an automotive waste heat recovery (WHR) and air conditioning (A/C) refrigeration functions, is proposed in this paper. The models of this compound cycle system, independent organic Rankine cycle (ORC) system and independent A/C system are built by Aspen Plus software. R134a and R1234yf are selected as working fluids because of their common use in air conditioning system. R245fa is employed as working fluid for independent ORC system as a comparison. The targets of this analysis are more power output and smaller heat transfer area. Linear weighted method is applied to optimize this multi-objective problem using the working fluid flow rate and WHR evaporating pressure as variables. The simulation results indicate that the compound system behaves better than independent system both in the power output and heat transfer area with the same working fluid. The independent system with R245fa-R134a generates the most power output of 13.01 kW. The compound system with R1234yf shows the smallest total heat transfer area and total heat transfer area decreasing ratios (THTADRs) are 6.2–14.8% comparing with independent systems.

A Novel Design of Thermoelectric Generator for Automotive Waste Heat Recovery

With progressively stringent fuel consumption regulations, many researchers and engineers are focusing on the employment of waste heat recovery technologies for automotive applications. Regarded as a promising method of waste heat recovery, the thermoelectric generator (TEG) has been given increasing attention over the whole automotive industry for the last decade. In this study, we first give a brief review of improvements in thermoelectric materials and heat exchangers for TEG systems. We then present a novel design for a concentric cylindrical TEG system that addresses the existing weaknesses of the heat exchanger. In place of the typical square-shaped thermoelectric module, our proposed concentric cylindrical TEG system uses an annular thermoelectric module and employs the advantages of the heat pipe to enhance the heat transfer in the radial direction. The simulations we carried out to verify the performance of the proposed system showed better power output among the existing TEG system, and a comparison of water-inside and gas-inside arrangements showed that the water-inside concentric cylindrical TEG system produced a higher power output.

Performance Analysis of Thermoelectric Based Automotive Waste Heat Recovery System with Nanofluid Coolant

Output performance of a thermoelectric-based automotive waste heat recovery system with a nanofluid coolant is analyzed in this study. Comparison between Cu-Ethylene glycol (Cu-EG) nanofluid coolant and ethylene glycol with water (EG-W) coolant under equal mass flow rate indicates that Cu-EG nanofluid as a coolant can effectively improve power output and thermoelectric conversion efficiency for the system. Power output enhancement for a 3% concentration of nanofluid is 2.5–8 W (12.65–13.95%) compared to EG-Water when inlet temperature of exhaust varies within 500–710 K. The increase of nanofluid concentration within a realizable range (6%) has positive effect on output performance of the system. Study on the relationship between total area of thermoelectric modules (TEMs) and output performance of the system indicates that optimal total area of TEMs exists for maximizing output performance of the system. Cu-EG nanofluid as coolant can decrease optimal total area of TEMs compared with EG-W, which will bring significant advantages for the optimization and arrangement of TEMs whether the system space is sufficient or not. Moreover, power output enhancement under Cu-EG nanofluid coolant is larger than that of EG-W coolant due to the increase of hot side heat transfer coefficient of TEMs.

Design Optimization of A Small Scale High Expansion Ratio Organic Vapour Turbo Expander for Automotive Application

Environmental concern on a global scale and the concept of energy conservation in heavy duty trucks nowadays have attracted the increasing attention among researchers on the automotive waste heat recovery applications based on Organic Rankine Cycle (ORC) system. However, the system efficiency is theoretically low because of comparatively small temperature difference between exhaust gas and atmosphere, which brings about increasing expansion ratio as a feasible method to improve system performance. However, turbo expander, the most significant component in the system, might generate huge losses due to supersonic flow caused by high expansion ratio, therefore study on supersonic organic vapor turbo expander design emerged as required.In this paper, a single-stage radial-inflow organic vapor turbo expander with pressure-ratio up to 8 is preliminarily designed, and its performance and internal flow are numerically studied. The performance is simulated with three dimensional computational fluid dynamic (CFD) method at operating conditions. Several geometry modifications are conducted in order to learn their influence on turbine performance. Shock waves and trailing edge losses are observed as main losses in the nozzles. In addition, flow separations are the main losses in the rotors. Turbine blade is accordingly optimized after the analysis, and the nozzle total pressure loss coefficient decrease clearly, meanwhile a rise of 3.4% on turbine efficiency can be obtained. Shock waves and reflected waves are suppressed, and a more uniform stream at nozzle outlet can be observed.

Temperature Control of Evaporators in Automotive Waste Heat Recovery Systems

This paper presents a control strategy for the steam generation process in automotive waste heat recovery systems that are based on the subcritical Rankine cycle. The central question is how to regulate the flow of water into the evaporator such that dry steam is generated at its outlet, subject to large variations in the heat input. Tight control of this process increases the amount of recovered energy while ensuring safe system operation. The method consists of inversion-based feedforward combined with output feedback on the temperature of the evaporator, which is estimated using exhaust gas measurements. As this method does not require a high fidelity evaporator model, it is easy to implement. It is demonstrated on an experimental setup, where the exhaust flow is imitated by electrically heated air. On an automotive driving cycle, steam was generated reliably with a superheating temperature of 10-20 [K].