Exhaust Waste Heat Recovery Research Articles

Enhanced Heat Transfer in Thermoelectric Generator Heat Exchanger for Sustainable Cold Chain Logistics: Entropy and Exergy Analysis

This study investigates the application of thermoelectric power generation devices in conjunction with cold chain logistics transport vehicles, focusing on their efficiency and performance. Our experimental results highlight the impact of thermoelectric module characteristics, such as thermal conductivity and the filling thickness of copper foam, on the energy utilization efficiency of the system. The specific experimental setup involved a simulated logistics cold chain transport vehicle exhaust waste heat recovery thermoelectric power generation system, consisting of a high-temperature exhaust heat exchanger channel and two side cooling water tanks. Thermoelectric modules (TEMs) were installed between the heat exchanger and the water tanks to use the temperature difference and convert heat energy into electrical energy. The analysis demonstrates that using high-performance thermoelectric modules with a lower thermal conductivity results in better utilization of the temperature difference for power generation. Additionally, the insertion of porous metal copper foam within the heat exchanger channel enhances convective heat transfer, leading to an improved performance. Furthermore, the study examines the concepts of exergy and entropy generation, providing insights into the system energy conversion processes and efficiency. Overall, this research offers valuable insights for optimizing the design and operation of thermoelectric generators in cold chain logistics transport vehicles to enhance energy utilization and sustainability.

Performance analysis of a multi-tube exhaust waste heat recovery methanol reforming to hydrogen reactor

Performance analysis of a multi-tube exhaust waste heat recovery methanol reforming to hydrogen reactor

A Hybrid Heavy Duty Diesel Power System for Off-Road Applications—Concept Validation

Abstract A multiyear power system R&D program was completed with the objective of developing an off-road hybrid heavy duty diesel engine with front end accessory drive-integrated energy storage. This system was validated to deliver 10.5–25.6% reduction in fuel consumption over current Tier 4 Final-based 18L diesel engines, over various off-road machine application cycles. The power system consisted of a downsized heavy-duty diesel 13L engine containing advanced combustion technologies, capable of elevated peak cylinder pressures and thermal efficiencies, thermal barrier coatings, exhaust waste heat recovery via SuperTurbo™ turbocompounding, and hybrid energy assisting and recovery through both mechanical and electrical systems. Following the concept definition, design, and analysis phases of the program, the final phase focused on building and validating the performance and efficiency in laboratory tests. While aspects of the system such as start/stop and reduced off-road cooling package energy losses were only analytically evaluated, the main 13L concept engine with full hybrid system was successfully built and tested in steady-state and in transient certification and real-world application cycles. Extensive simulations in Caterpillar's DYNASTY™ software environment utilized the validation test data to assess performance more fully and confidently over varied cycles and strategies. An average fuel consumption reduction of 17.9% was realized, and the majority (∼13%) of the benefit stemmed from the core concept 13L engine. To conclude, a total cost of ownership analysis provides context to commercial viability and where adoption focus should be placed.

Cost-Effective Design of Exhaust Waste Heat Recovery System: A Numerical and Optimization Approach

Cost-Effective Design of Exhaust Waste Heat Recovery System: A Numerical and Optimization Approach

Prediction of electric power performance of the exhaust waste heat recovery system of an automobile with thermoelectrical generator under real driving conditions by means of machine learning algorithms

In internal combustion engines, approximately 40% of the thermal power obtained from fuel burning is thrown out to the environment from the exhaust system. Implementations of waste heat recovery systems with thermoelectrical generator over exhaust system have become widespread as it is the waste heat resource with the highest temperature in a vehicle. During literature research, experiments related to waste heat recovery under real road conditions are very few and no study on estimation of system performance by machine learning algorithms has been found; therefore, Toyota Corolla has designed an air-cooled waste heat recovery system using 3 thermoelectrical generators for the exhaust system of the automobile. During the road tests, temperature and electric power generation values obtained as per gear, vehicle speed and engine speed have been recorded. In the study, a dataset consisting of 10 attributes was created with each record as a result of the path test. Using this dataset, Random Forest, Support Vector Machine (SVM) and Naive Bayes machine learning algorithms estimated the electrical power to be generated from the thermoelectric generator recovery system. In the study, 7 electric power classification estimates were made. In the estimation process, 76% of the dataset was used for training and 24% was used for testing. In terms of estimation success; an estimation success of 96.6% has been achieved by Random Forest method; 94.6% by Support Vector Machine (SVM) method; and 76.7% by Naive Bayes method. The results show that prospective electricity generation estimation can be achieved with high level of accuracy.

Energy and exergy analysis of a thermoelectric generator system for automotive exhaust waste heat recovery

Thermoelectric generators are a viable solution for recovering and producing energy utilizing wasted energy in automotive exhaust. Exergy analysis can help identify irreversible losses that occur during the transfer of exhaust energy, which is essential for comprehending and developing exhaust thermoelectric generator systems. In this study, we proposed a model based on thermodynamic of the exhaust thermoelectric generator and conducted energy and exergy analyses. The results indicate that convective heat transfer exergy loss and PN junction thermal conductivity exergy loss are the primary exergy losses of the exhaust thermoelectric generator, accounting for more than 52.0 % of the total. Increasing the temperature of exhaust can boost the performance of systems, but it may also reduce the proportion of available energy obtained by the cooling water. When the exhaust heat transfer coefficient is increased to 300, the convective exergy losses of the exhaust can be reduced to 17.6 %, resulting in an overall exergy efficiency of 38.8 %. Furthermore, by increasing the exhaust flow rate from 10 g/s to 50 g/s, the power generation capacity has increased by a factor of 6.87, with little change in exergy losses. These findings are valuable for developing high-efficiency exhaust power generators.

Experimental examination of the effect of thermal barrier coating in a 2-stroke gasoline engine on recovery performance in exhaust waste heat recovery system with thermoelectric generator and engine performance

In internal combustion engines, while the decrease in in-cylinder wall temperature increases the amount of energy passing towards the cooling system, it decreases temperature and pressure at the end of compression and accordingly reduces thermal efficiency of the engine. Moreover; combustion chamber elements are exposed to chemical corrosion and deformation as a result of uncompleted combustion in the cylinder. With thermal barrier coating application, the energy lost in cooling system will decrease and exhaust temperatures will increase in 2-stroke engines. Placement of a waste heat recover system with thermoelectric generator into the exhaust system can provide exhaust waste heat recovery and increase thermal efficiency of the engine. There is no study in the literature, which examines waste heavy recovery systems with thermal barrier and thermoelectric generator altogether. In this article, yttria stabilized zirconia coating has been applied by means of plasma spraying method in the combustion chamber of a 2-stroke gasoline engine, and effect of thermal barrier coating application on engine performance and exhaust waste heat recovery system has been examined experimentally. According the results of the experiment, maximum engine power has increased by 6.23%, maximum engine torque has increased by 6.02%, and specific fuel consumption decreased by 5.56%. While the exhaust temperatures have increased by 78.5 °C at maximum by means of thermal barrier coating application; by means of thermal barrier coating application with waste heat recovery system with thermoelectric generator, a higher waste heat recovery has been obtained by 64.8%.

Performance Optimization and Exergy Analysis of Thermoelectric Heat Recovery System for Gas Turbine Power Plants.

Thermoelectric (TE) waste heat recovery has attracted significant attention over the past decades, owing to its direct heat-to-electricity conversion capability and reliable operation. However, methods for application-specific, system-level TE design have not been thoroughly investigated. This work provides detailed design optimization strategies and exergy analysis for TE waste heat recovery systems. To this end, we propose the use of TE system equipped on the exhaust of a gas turbine power plant for exhaust waste heat recovery and use it as a case study. A numerical tool has been developed to solve the coupled charge and heat current equations with temperature-dependent material properties and convective heat transfer at the interfaces with the exhaust gases at the hot side and with the ambient air at the heat sink side. Our calculations show that at the optimum design with 50% fill factor and 6 mm leg thickness made of state-of-the-art Bi2Te3 alloys, the proposed system can reach power output of 10.5 kW for the TE system attached on a 2 m-long, 0.5 × 0.5 m2-area exhaust duct with system efficiency of 5% and material cost per power of 0.23 $/W. Our extensive exergy analysis reveals that only 1% of the exergy content of the exhaust gas is exploited in this heat recovery process and the exergy efficiency of the TE system can reach 8% with improvement potential of 85%.

Optimization design and performance analysis of methanol reforming reactor for exhaust waste heat recovery of marine engine

In order to improve the heat utilization of exhaust from the small or medium-sized ships without exhaust boilers, four types of methanol reforming reactors were designed and optimized via the field synergy principle. The effect of the operating parameters on the performance of optimized reactor under typical loads was also investigated. The analysis based on the field synergy principle shows that the R(S,1) reactor has higher heat transfer synergy performance, better evaporation performance, and more uniform vapour distribution at the inlet of the reaction section, which is more beneficial to the reforming reaction. The effect of the operating parameters on reactor performance shows that the reactor performs better at 75% load with hydro-alcohol molar fraction ratios (S/C) of 1.2 or 1.3. The engine load affects the reactor performance by influencing the temperature of the evaporation and reaction sections. The S/C of the mixed solution at the inlet of the reactor were set at 1.2 and 1.3 to explore the effect of engine loads on the reforming performance under E3 test cycle. The results show that the reactor performs better at S/C = 1.3 under the loads of 100, 75, and 25%; at S/C = 1.2, the reactor performed better under 50% load.

Optimization Design of an Intermediate Fluid Thermoelectric Generator for Exhaust Waste Heat Recovery

The intermediate fluid thermoelectric generator (IFTEG) represents a novel approach to power generation, predicated upon the principles of gravity heat pipe technology. Its key advantages include high-power output and a compact module area. The generator’s performance, however, is influenced by the variable exhaust parameters typical of automobile operation, which presents a significant challenge in the design process. The present study establishes a mathematical model to optimize the design of the IFTEG. Our findings suggest that the optimal module area sees substantial growth with an increase in both the exhaust heat exchanger area and the exhaust flow rate. Interestingly, the optimal module area appears to demonstrate a low sensitivity to changes in exhaust temperature. To address the challenge of determining the optimal module area, this study introduces the concept of peak power deviation. This method posits that any deviation from the optimal module area results in an equivalent power deviation. For instance, with an exhaust heat exchanger area of 1.6 m2, the minimum peak power deviation is 27.5%, corresponding to a design module area of 0.124 m2. As such, the actual output power’s deviation from the maximum achievable output power will not exceed 27.5% for any given set of exhaust parameters. This study extends its findings to delineate the relationship between the optimal design module area and the exhaust heat exchanger area. These insights could serve as a useful guide for the design of future power generators.

Comparative Assessment of sCO2 Cycles, Optimal ORC, and Thermoelectric Generators for Exhaust Waste Heat Recovery Applications from Heavy-Duty Diesel Engines

This study aimed to investigate the potential of supercritical carbon dioxide (sCO2), organic Rankine cycle (ORC), and thermoelectric generator (TEG) systems for application in automotive exhaust waste heat recovery (WHR) applications. More specifically, this paper focuses on heavy-duty diesel engines applications such as marine, trucks, and locomotives. The results of the simulations show that sCO2 systems are capable of recovering the highest amount of power from exhaust gases, followed by ORC systems. The sCO2 system recovered 19.5 kW at the point of maximum brake power and 10.1 kW at the point of maximum torque. Similarly, the ORC system recovered 14.7 kW at the point of maximum brake power and 7.9 kW at the point of maximum torque. Furthermore, at a point of low power and torque, the sCO2 system recovered 4.2 kW of power and the ORC system recovered 3.3 kW. The TEG system produced significantly less power (533 W at maximum brake power, 126 W at maximum torque, and 7 W at low power and torque) at all three points of interest due to the low system efficiency in comparison to sCO2 and ORC systems. From the results, it can be concluded that sCO2 and ORC systems have the biggest potential impact in exhaust WHR applications provided the availability of heat and that their level of complexity does not become prohibitive.

GA−BP Prediction Model for Automobile Exhaust Waste Heat Recovery Using Thermoelectric Generator

Thermoelectric generator (TEG) has important applications in automotive exhaust waste heat recovery. The Back propagation neural network (BP) can predict the electrical generating performance of TEG efficiently and accurately due to its advantage of being good at handing nonlinear data. However, BP algorithm is easy to fall into local optimum, and its training data usually have deviation since the data are obtained through the simulation software. Both of the problems will reduce the prediction accuracy. In order to further improve the prediction accuracy of BP algorithm, we use the genetic algorithm (GA) to optimize BP neural network by selection, crossover, and mutation operation. Meanwhile, we create a TEG for the heat waste recovery of automotive exhaust and test 84 groups of experimental data set to train the GA−BP prediction model to avoid the deviation caused by the simulation software. The results show that the prediction accuracy of the GA−BP model is better than that of the BP model. For the predicted values of output power and output voltage, the mean absolute percentage error (MAPE) increased to 2.83% and 2.28%, respectively, and the mean square error (MSE) is much smaller than the value before optimization, and the correlation coefficient (R2) of the network model is greater than 0.99.

Performance analysis of a dual-loop organic Rankine cycle system for waste heat recovery from engine coolant and exhaust of a heavy-duty truck

• Heat exchanger employed influences the system efficiency. • Significant heat loss observed from engine block at part-load. • Variable expander-to-engine speed gear ratio gives a small gain in power. • Performance comparison for unique Scandinavian motorway data. Strict legislations over emissions from heavy-duty trucks are pushing the manufacturers towards improving their brake thermal efficiency, thereby mitigating fuel consumption and reducing CO 2 emissions. Organic Rankine cycle-based waste heat recovery system has proven to be an inevitable technology in boosting the engine performance besides the other methods and approaches. In addition to recovering the exhaust heat from the engine, recovering heat from the engine coolant is also beneficial, provided its nominal temperature is raised. Thus, this work investigates the scope of improvement in performance of a heavy-duty truck engine when integrated with a dual-loop organic Rankine cycle system for recovering heat from its exhaust and coolant, simultaneously. The analysis has been performed as a simulation study on GT-SUITE using the one-dimensional model of the engine with its organic Rankine cycle heat recovery setup. The model was developed based on the components of a real commercial truck engine connected with a simple exhaust waste heat recovery system. For the work described in this paper, model of the single-loop exhaust waste heat recovery system was modified to a dual-loop circuit comprising of two scroll expanders and R1233zd(E) as the working fluid. Notably, performance investigation was carried out using a unique Scandinavian motorway road data retrieved from the truck. This paper addresses the challenges associated with simultaneous heat recovery from engine exhaust and coolant. Performance comparison at four steady-state engine operating points reveal that the low temperature radiator installed for the indirect condensation of the working fluid is the major influencing component on system efficiency. At higher engine loads, the overall system efficiency considerably decreased due to limited heat rejection capacity of this radiator. Moreover, on assessing the scope of improving the system’s performance by having variable gear ratio between the engine and the expanders, 1.6% points (0.12 kW) gain in power was observed by having the high-pressure expander’s speed fixed and the low-pressure expander’s speed varied. Furthermore, elevating the engine coolant temperature from 120 °C to 140 °C, significant heat loss from the coolant to the engine surroundings resulted in a substantial drop in net power at lower part loads although it had improved at higher engine operating points.

Experimental investigation of a novel thermoelectric generator design for exhaust waste heat recovery in a gas-fueled SI engine

In this paper, a series of tests are performed on the exhaust waste heat recovery using a thermoelectric generator (TEG) in a propane-fueled spark-ignition (SI) engine. A three-layer TEG is designed, consisting of two engine coolant exchangers (Ec_hex) positioned on both surfaces of the rectangle exhaust heat exchanger (Ex_hex). Unlike the literature papers, a novel design is created by placing copper serpentine pipes in each Ec_hex to allow propane to pass through the TEG. The reason for this is both to ensure the evaporation of propane and to increase the ΔT temperature differences by increasing the cold surface activity of TEG. A total of 12 pieces of thermoelectric modules (TEMs), 56x56 mm in size, are positioned between the rectangular Ex_hex and each Ec_hex, and a total of 24 pieces of TEMs are used in TEG. Experimental studies were performed for eight different engine speeds in the range of 1500–5000 rpm for TEGs with and without a propane inlet. In addition, computational fluid dynamic (CFD) analyses are performed to visualize both the cold and hot surface temperature contours of the TEMs. The results of the paper illustrate that the DC electrical power of the TEG with propane is higher in the range of 11.5–12.1% compared to the TEG without propane in the 1500–5000 rpm range of the engine. At 4500 rpm engine speed, the propane input TEG produced a maximum of 90.2 W of DC electrical power and a 3.02% energy conversion efficiency. In addition, there is a good correlation between the experimental and numerical findings, varying between 3% and 15% with the engine speed.

Improvement of volume controlled thermal energy storage system using phase change material for exhaust waste heat recovery in a SI engine

In this paper, the effect of volume control on the melting process of phase change material (PCM) in a latent heat storage (LHTS) system used for storing the exhaust waste heat energy of a typical SI engine is explored experimentally. In the LHTS system, paraffin wax, commercially known by the code RT55, is used. A closed-loop liquid circulation system with two heat exchangers is designed with one (exhaust heat exchanger-Ex_hex) mounted to the exhaust tailpipe of the SI engine and the other (PCM heat exchanger-PCM_hex) used in the storing and melting of the RT55. The PCM_hex is designed to have a cylindrical geometry and variable internal volume and is fabricated of optical material to monitor the melting process of the RT55. The cylindrical side surface of the PCM_hex is designed as two layers for vacuum insulation application. For volume control, the movable top surface of the cylindrical PCM_hex is controlled by a linear actuator with a 1000 N capacity. Experimental studies are performed under 1/2 throttle opening and 2800 rpm constant engine speed of a propane fueled SI engine for three different PCM_hex arrangements (i.e., free volume, constant volume, and volume controlled) during 7200 s (120 min). As a result, the melting process of the RT55 with the volume controlled PCM_hex is improved, and the energy storage capacity is increased by approximately 4.57%. At the end of 7200 s for 9.136 kg solid RT55, 85.2%, 85.7%, and 87.4% liquid fractions are obtained with the free volume, constant volume, and volume controlled PCM_hex, respectively. With free volume, constant volume, and volume controlled PCM_hex, 2339.9 kJ, 2355.9 kJ, and 2446.8 kJ of energy are stored as sensible and latent heat, respectively, while 37.2%, 38%, and 39.5% PCM_hex efficiency are obtained. In addition, the rate of fuel energy stored in PCM_hex is 3.97%, 4.01%, and 4.17%, respectively.

Analysis of printed circuit heat exchanger (PCHE) potential in exhaust waste heat recovery

Exhaust waste heat recovery technology based on power cycles requires high efficiency, low flow resistance, and a compact structure for exhaust gas heat exchangers. It is a huge challenge for traditional heat exchangers, such as double tube or shell and tube heat exchangers. A printed circuit heat exchanger (PCHE), which is a compact heat exchanger, has not been used in the heat exchange process between the exhaust gas and supercritical CO2. Focusing on this application, a novel design concept of PCHE based on a comprehensive performance index is proposed, which fully considers the differences in physical properties and working conditions between the exhaust gas side and the CO2 side. A series of experiments were carried out in a CO2-based transcritical power cycle system. The experimental test results show that the PCHE with a novel structure is stable and feasible. To further optimise the PCHE, a numerical analysis of different structures was conducted. The calculation results show that the comprehensive performance of the PCHE with an optimised structure was improved by 11.92%. This research shows that PCHE has great potential for achieving a compact design with excellent performance, especially for use in engine waste heat recovery.

Performance assessment of annular thermoelectric generators for automobile exhaust waste heat recovery

Annular thermoelectric generators (ATEGs), matched well with the exhaust pipe in geometry, are proposed to recover the heat from automobiles. A theoretical model was constructed to assess the performance of automotive exhaust ATEGs (AEATEGs), where a finite element method was used to incorporate the temperature variation and temperature-dependent properties. The local pressure drop as to the change of cross-section area and shape was considered. Performance comparison with commonly used automotive exhaust flat-plate thermoelectric generators (AEFTEGs) was conducted. Also, the effects of flow arrangement and operating parameters were clarified. Results show that the performance of AEATEGs outperforms AEFTEGs, with the net power on average 1.1% higher. With increasing cooling medium flow rate, the net power increases until attaining a maximum and decreases afterwards. A flow rate of 0.05 kg/s is preferred for the compromise of coolant temperature rise and tank volume. In light of a large temperature drop from exhaust to generators, a simple strategy, inserting a hollow cylinder into heat exchanger, was developed and its effectiveness was evaluated. The maximum enhancement in net power of 214.0% is exhibited, but which reduces notably with increasing exhaust flow rate. For gasoline automobiles, a cylinder with dimensionless diameter of 0.8 is recommended.

Energy harvesting in diesel engines to avoid cold start-up using phase change materials

In diesel engines, a significant amount of energy is wasted to the environment by the exhaust gases and coolants. In this study, a new design of the exhaust waste heat recovery (WHR) heat exchanger is proposed to preheat the intake air before supplying it into a diesel engine at the cold start-up conditions. The heat exchanger is designed of ribbed plates containing paraffin wax phase change material (PCM). This PCM is used to store the thermal energy coming out from the engine during the operation for later use in cold start-up conditions. A numerical model is developed and validated with the experimental results in the literature. The effect of different design conditions along with various operating conditions is evaluated. The influences of ribs height and spacing, engine rotational speed, and intake air temperature on the thermal energy storage were evaluated. Based on the results, it can be concluded that the highest thermal performance was obtained at a rib gap of 90 mm and a rib height of 7.5 mm. Through the warming-up process, in less than 1 min, the cold intake air temperature can be increased from 273 to 302.2 and from 283 K to 300.7 K. This results in overcoming the cold start-up difficulties, specifically in icy weather, and delivers preheated air to the engine after 1 min.

Compression-assisted decomposition thermochemical sorption energy storage system for deep engine exhaust waste heat recovery

In the context of the stringent automobile emission legislations, this paper proposes a novel compression-assisted decomposition thermochemical sorption energy storage system for recovering engine exhaust waste heat, which is utilized to produce cooling capacity for a refrigerated vehicle. In this system, the desorption pressure of sorbent can be flexibly adjusted by changing the suction pressure of compressor embedded between the sorption bed and condenser, which ensures the stable operation of system even at relatively low exhaust temperatures. Simultaneously, the decomposition reaction increases suction pressure of compressor, so the coefficient of performance (COP) is thus greatly improved. Furthermore, the sorption bed can output cooling capacity for refrigerated compartment when the vehicle is parked. Currently, vehicle emission standards generally adopt World Harmonized Stationary Cycle test, and 13 engine operating points are selected. At an operating point 3 (a low engine load), i.e. 55% speed and 25% torque, the COP of the novel system at an evaporating temperature of −25 °C and a condensing temperature of 45 °C is 1.65, 1.5 times higher than that of conventional one. The weighted average COP under 13 operating points is still up to 1.48. Eventually, the novel system promotes the realization of low-carbon and low-cost refrigerated transportation.

Car exhaust waste heat recovery using hexagon shaped thermoelectric generator

Heat recovery technology using thermoelectric has attracted many research intentions mainly for its ability to generate power passively. The automotive engine usually produces waste heat ranging from 30-40% due to the thermodynamic limit. The use of thermoelectric generator (TEG) for waste heat recovery and power generation could increase the efficiency of the internal combustion engine system. This research developed and investigated a heat recovery system using a thermoelectric generator (TEG) for power generation. A thermoelectric generator (TEG) consisted of thermoelectric modules, hexagonal pipe connector and heat sinks was built and connected to an exhaust pipeline. A theoretical model was developed to access the thermal and electrical performance of the TEG system. The theoretical model consisted of the heat transfer mechanism including the thermal resistance networks from the flue gas to TEG and the heat sink. The electrical power output was determined using the Seebeck principle. The early stage of finding reveals that the system was able to produce an open circuit voltage of 0.13 V for a small temperature gradient of 3ᵒC between the cold and hot surface of the TEG. The further improvement of the system is currently under investigation for producing higher power. In the future, this system hopefully could replace the car battery for charging the alternator as well as increasing the overall efficiency of the engine system.