Exhaust Waste Heat Recovery Research Articles

Coupled simulation of a thermoelectric generator applied in diesel engine exhaust waste heat recovery

This work develops a heat transfer model of a thermoelectric generator to explore the coupled relationship between high temperature exhaust flows, structure, and the external cooling air. The coupled heat transfer results showed that the fins reached a uniform high temperature, for the rated speed, the average temperature is 474 K. The coupled design scheme of the thermoelectric generator tested by installing it in a 4-cylinder turbocharged Diesel engine exhaust system. Comparison of the test and simulation results showed that as engine speed in-creased, the inlet and outlet exhaust temperatures of the thermoelectric generator exhibited a parabolic trend increase. The cooling water outlet temperature and the top, middle, and bottom fin temperatures increased linearly, and the coupled model was verified. From idle speed to rated speed, the top, middle, and bottom fin temperatures increased from 458 K to 476 K, 417 K to 463 K, and 406 K to 449 K, respectively; the cooling water outlet temperature increased from 293.6 K to approximately 303 K. Hence, the thermoelectric components installed in fins can experience temperature differences of over 100 K, the heat transfer efficiency can increase which ensures consistent output performance of the thermoelectric generator based on coupled design between the heat exchanger and thermoelectric modules array column.

Energy and Exergy Analysis of Different Exhaust Waste Heat Recovery Systems for Natural Gas Engine Based on ORC

Waste heat recovery (WHR) from exhaust gases in natural gas engines improves the overall conversion efficiency. The organic Rankine cycle (ORC) has emerged as a promising technology to convert medium and low-grade waste heat into mechanical power and electricity. This paper presents the energy and exergy analyses of three ORC–WHR configurations that use a coupling thermal oil circuit. A simple ORC (SORC), an ORC with a recuperator (RORC), and an ORC with double-pressure (DORC) configuration are considered; cyclohexane, toluene, and acetone are simulated as ORC working fluids. Energy and exergy thermodynamic balances are employed to evaluate each configuration performance, while the available exhaust thermal energy variation under different engine loads is determined through an experimentally validated mathematical model. In addition, the effect of evaporating pressure on the net power output, thermal efficiency increase, specific fuel consumption, overall energy conversion efficiency, and exergy destruction is also investigated. The comparative analysis of natural gas engine performance indicators integrated with ORC configurations present evidence that RORC with toluene improves the operational performance by achieving a net power output of 146.25 kW, an overall conversion efficiency of 11.58%, an ORC thermal efficiency of 28.4%, and a specific fuel consumption reduction of 7.67% at a 1482 rpm engine speed, a 120.2 L/min natural gas flow, 1.784 lambda, and 1758.77 kW of mechanical engine power.

Performance analysis of combined cooling heating and power (CCHP) exhaust waste heat coupled air source heat pump system

To achieve the deep recovery of exhaust waste heat, a combined cooling heating and power (CCHP) dynamic exhaust low temperature waste heat coupled air source heat pump system is proposed in this paper. Aspen Plus software was used to simulate the system and analyze the effects of the recyclable waste heat of the system, the coefficient of performance (COP) of the heat pump and the impact of the primary energy utilization rate. The results showed that under the design condition, the exhaust waste heat of CCHP system was 1.22 kW, the recyclable waste heat of heat pump system was up to 1.07 kW, the exhaust waste heat recovery rate was 87.7%. The COP was up to 4.66, increased 39.5%. The primary energy utilization efficiency was increased by 3.9%. It solves the problem of heat pump evaporator frosting and poor performance of low temperature in cold regions. This study provides an important reference for the combined and efficient application of CCHP systems and heat pump units.

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.

Performance optimization of common plate-type thermoelectric generator in vehicle exhaust power generation systems

A plate-type thermoelectric generation (TEG) system is typically used in engine exhaust waste heat recovery systems because of its appropriate structure. To obtain an effective design of these TEG systems, this study focuses primarily on optimal matching performance analysis, by building a complete numerical TEG model with the finite element method using FORTRAN. A commercial-type thermoelectric material is used in the numerical calculation. Moreover, all types of work conditions with different exhaust parameters (mf = 10–50 g s−1 and Tfin = 300–600 °C) and cooler’s heat transfer processes are included. When peak net power is achieved, all corresponding optimal features are analyzed, where both air-cooling and water-cooling methods are considered. The results indicate that, for any type of work condition, the optimal height remains the same (Bopt = 7.0 mm for the air-cooling method and Bopt = 4.0 mm for the water-cooling method) and the other optimal parameters can be expressed by fitting correlations, which can deduce the optimal length (Lopt) and width (wopt) of an exhaust heat exchanger (for example, they are Lopt = 1.55 m and wopt = 0.78 m when mf = 50 g s−1, Tfin = 500 °C, and hc = 80 W m−2 K−1 for the air-cooling method). The introduced fitting correlations are verified to have a high accuracy.

Direct vs indirect evaporation in Organic Rankine Cycle (ORC) systems: A comparison of the dynamic behavior for waste heat recovery of engine exhaust

Organic Rankine Cycle (ORC) is a prominent technology for the recovery of waste heat from internal combustion (IC) engines, in particular exhaust waste heat. An important challenge with IC engines, specially mobile, is the highly dynamic conditions and thus high variability of the waste heat thermal power which can lead to chemical decomposition of the ORC fluid or expander damage due to liquid droplets. The heat from the exhaust can be transferred to the ORC working fluid directly in one heat exchanger unit or indirectly through a heat transfer fluid. Compared to indirect evaporation, direct evaporation poses a higher risk to the integrity of the system due to a lower thermal damping capability. However, direct evaporation, is an attractive option in mobile applications due to its considerable lower footprint and potential of higher thermal efficiencies.In this paper, a methodological comparison of the dynamics of the two evaporation options in ORC is presented. The dynamic behavior of an indirect as well as two different direct evaporation options are simulated in a case study of exhaust waste heat recovery from a 240 kW Diesel Engine. The expected variability of the heat source is broken-down to relevant frequencies and amplitudes of fluctuation based on a standard engine transient cycle. The geometry of the heat exchangers for direct evaporation is chosen based on a methodology to achieve a desired thermal inertia. The results show that a non-conventional direct evaporator designed for high thermal inertia can protect the fluid from fluctuations of up to 20 kW of amplitude and not slower than 0.003 Hz even without any control measure in place. The weight and volume is reduced by 88% and 70% respectively compared to indirect evaporation structure. Such a design can enable direct evaporation by avoiding the requirement for a very fast-acting control system, while still allowing for the advantages of direct evaporation such as reduced footprint and potential for a higher thermal efficiency.

Performance investigation of an intermediate fluid thermoelectric generator for automobile exhaust waste heat recovery

In order to improve the power generation performance of automobile exhaust thermoelectric generator, an intermediate fluid thermoelectric generator system is proposed in this work. In the proposed system, the waste exhaust heat is transferred through boiling and condensation of the intermediate fluid. Consequently, the separation between the exhaust channel and thermoelectric module induces a higher heat flux on the hot side of the module. A mathematical model is also established to analyze the power generation characteristics of the proposed system. Compared with the traditional thermoelectric generator system, for the same heat exchange area on the exhaust side, not only is the peak output power increased by 32.6%, but the optimal thermoelectric module area is also reduced by 73.8%. The generation capacity per unit area is 1162 W/m2 at peak output power, which is 5.12 times that of the traditional thermoelectric generator system.

A Comparative Research on the Energy Recovery Potential of Different Vehicle Energy Regeneration Technologies

Researches on various energy regeneration technologies applied on vehicles have been conducted by many scholars. However, the comprehensive study of these technologies on a single vehicle at the same time was rarely paid attention to. This paper proposes a comprehensive vehicle energy regeneration system consists of regenerative braking, suspension vibration energy recovery and exhaust waste heat recovery. The energy recovery model is developed to explore the energy recovery potential and the ability of these three subsystems on a mild hybrid vehicle. Based on the comparative simulation results, regenerative braking and energy regenerative suspension are highly affected by the actual driving conditions. By contrast, the performance of exhaust waste heat recovery system is more stable because the exhaust temperature and mass flow rate change gently with the various driving conditions. Meanwhile, the integration of different energy recovery technologies can maximize the energy saving effect.

Innovative System for Exhaust Cooling and Waste Heat Recovery in Gasoline Engines

Innovative System for Exhaust Cooling and Waste Heat Recovery in Gasoline Engines

Thermoelectric Analysis of Automobiles Exhaust Waste Heat Recovery Material – A Simulation Study

Abstract Alongside the improvements in renewable fuel technologies, there is also a tremendous increase in research in the field of automobile exhaust waste heat recovery. This is mainly done with the help of thermoelectric generators (TEGs) which use thermoelectric materials (TEMs) as their primary elements. Thermoelectric materials have extensive application in space vehicles. This experience led to its usage for terrestrial automobile waste heat recovery. Usage of TEMs could help in producing accessory power and for fuel savings. Practically the efficiency of system level of automobile exhaust applications is 33% lower than material conversion (device) level. Further the heat exchanger’s performance plays a vital role in the outcome from TEGs. We worked on a theoretical model of heat exchanger with three different profiles of parabolic fin. The fin material which are used to transfer the heat to thermoelectric material is Bismuth Telluride/Antimony Telluride (Bi2Te3/Sb2Te3) for automobile waste heat recovery. The dimensional characteristics of fins for finding the best model were found with the simulation study using ANSYS-Steady state thermal mode. A model of the double finned profile with 8 fins, 8cm length and 1.737cm breadth was proved effective and this profile was simulated using ANSYS-CFX for temperature profiles. Based on the data collected for Bi2Te3/Sb2Te3 super lattice thermoelectric material (TEM) the TEG’s performance was calculated. Double finned parabolic fins resulted in uniformity of temperature distribution. The TEM with a figure of merit (ZT) of 2.4 is showed extraordinary theoretical efficiency, which is of better device level rather than system level.

Design and Development of Innovative Protracted-Finned Counter Flow Heat Exchanger (PFCHE) for an Engine WHR and Its Impact on Exhaust Emissions

This article describes and evaluates an Organic Rankine Cycle (ORC) for waste heat recovery system both theoretically as well as experimentally. Based on the thermodynamic analysis of the exhaust gas temperature identified at different locations of the exhaust manifold of an engine, the double-pipe, internally–externally protruded, finned counter flow heat exchanger was innovatively designed and installed in diesel engine for exhaust waste heat recovery (WHR). The tests were conducted to find the performance of heat recovery system by varying the fin geometries of the heat exchanger. The effect of heat exchanger on emission parameters is investigated and presented in this work. The experimental results demonstrated that the amount of heat transfer rate, the effectiveness of heat exchange rand the brake thermal efficiency improved with an increase in length and number of the fins. A significant reduction was observed in all major emissions after the implementation of catalytic-coated, protracted finned counter flow heat exchanger. It also demonstrated the possibility of electric power production using steam turbo-electric-generator setup driven by the recovered exhaust heat energy.

The potential of exhaust waste heat recovery (WHR) from marine diesel engines via organic rankine cycle

The rise of fuel prices due to the depletion of fossil fuel energy and unlimited carbon dioxide let-off are creating a renewed interest in techniques to increase the thermal efficiency of marine diesel engines. One promising mechanism to achieve improvement in system thermal efficiency is the conversion of engine waste heat to a more useful form of energy, either mechanical energy or electrical energy. Thus, this study investigates the potential of exhaust waste heat recovery from marine diesel engines using bioethanol production from selected microalgae as the working fluid via organic Rankine cycle (ORC). It also examines the system thermal efficiency and determines the pinch temperature of the plant. The microalgae Dunaliella tertiolecta, Chlamydomonas fasciata Ettl 437 and Synechococcus PCC 7002 are chosen as bioethanol producers based on the high yield of production. The maximum net power output and high system thermal efficiency are chosen as the evaluation criteria to select the microalgae with the best performance. The results demonstrate that among the three selected microalgae, Synechococcus PCC 7002 shows the highest efficiency of approximately 2.28% for the mass flowrate of exhaust gas of 4189 kgh−1, while the net power output was approximately 5.10 kW.

Engine Load Effects on the Energy and Exergy Performance of a Medium Cycle/Organic Rankine Cycle for Exhaust Waste Heat Recovery.

The Organic Rankine Cycle (ORC) has been proved a promising technique to exploit waste heat from Internal Combustion Engines (ICEs). Waste heat recovery systems have usually been designed based on engine rated working conditions, while engines often operate under part load conditions. Hence, it is quite important to analyze the off-design performance of ORC systems under different engine loads. This paper presents an off-design Medium Cycle/Organic Rankine Cycle (MC/ORC) system model by interconnecting the component models, which allows the prediction of system off-design behavior. The sliding pressure control method is applied to balance the variation of system parameters and evaporating pressure is chosen as the operational variable. The effect of operational variable and engine load on system performance is analyzed from the aspects of energy and exergy. The results show that with the drop of engine load, the MC/ORC system can always effectively recover waste heat, whereas the maximum net power output, thermal efficiency and exergy efficiency decrease linearly. Considering the contributions of components to total exergy destruction, the proportions of the gas-oil exchanger and turbine increase, while the proportions of the evaporator and condenser decrease with the drop of engine load.

Thermal analysis for the evaporation concentrating process with high boiling point elevation based exhaust waste heat recovery

In order to reduce energy consumption of the solution evaporation concentrating process with high boiling point elevation (BPE), a novel cogeneration system is proposed to integrate the solution evaporation concentrating and power generation processes using the exhaust waste heat as heat source. Through compared with the conventional three-effect and mechanical vapor recompression evaporation processes, influences from the key operation parameters, including the evaporation temperature and BPE of the solution on overall thermal performance of the proposed system have been investigated. The results showed the overall thermal performance of the three schemes became worse with the rise of the BPE, but the proposed cogeneration system showed prominent thermal performance when dealing solutions with high BPE compared to those of the conventional three-effect and MVR evaporating processes. Moreover, through harmonizing the vacuum evaporation concentrating process and net power output, the optimal evaporating temperatures to achieve the maximal energy saving potential are obtained under different BPE working conditions for the proposed cogeneration system.

배기폐열 회수를 위한 휴지 실린더 내 스팀분사 적용

배기폐열 회수를 위한 휴지 실린더 내 스팀분사 적용

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.

Simulation and experiments on a solid sorption combined cooling and power system driven by the exhaust waste heat

A solid sorption combined cooling and power system driven by exhaust waste heat is proposed, which consists of a MnCl2 sorption bed, a CaCl2 sorption bed, an evaporator, a condenser, an expansion valve, and a scroll expander, and ammonia is chosen as the working fluid. First, the theoretical model of the system is established, and the partitioning calculation method is proposed for sorption beds. Next, the experimental system is established, and experimental results show that the refrigerating capacity at the refrigerating temperature of–10°C and the resorption time of 30 min is 1.95 kW, and the shaft power is 109.2 W. The system can provide approximately 60% of the power for the evaporator fan and the condenser fan. Finally, the performance of the system is compared with that of the solid sorption refrigeration system. The refrigerating capacity of two systems is almost the same at the same operational condition. Therefore, the power generation process does not influence the refrigeration process. The exergy efficiency of the two systems is 0.076 and 0.047, respectively. The feasibility of the system is determined, which proves that this system is especially suitable for the exhaust waste heat recovery.

Performance enhancement of heat pipes assisted thermoelectric generator for automobile exhaust heat recovery

A new type of heat pipe assisted thermoelectric generator (HP-TEG) for automobile exhaust waste heat recovery is proposed in this paper. To confirm the optimized configurations of the thermoelectric device, an experimental prototype was constructed to obtain the best heat pipes insertion depth (Dhp), and the optimum angle between the heat pipe row and the gas flow direction (θhp). A HP-TEG device was designed, constructed after the optimization of heat pipes depth and angle. The operating parameters were further investigated to enhance the performance of thermoelectric generation (TEG). The experimental results show that the power output of HP-TEG preferred high exhaust temperature, cold water flow rate and mass flow rate. The maximum open circuit voltage of 36 thermoelectric modules (TEMs) is measured as 81.09 V. The corresponding power output and pressure drop are 13.08 W and 1657 Pa, respectively, with an optimized thermoelectric power generation efficiency of the HP-TEG as 2.58%.

Working fluid selection for a small-scale organic Rankine cycle recovering engine waste heat

This paper reports the design and evaluation of a 1 kWe Organic Rankine cycle using different working fluids for engine coolant and exhaust recovery from a 6.5 kW small ICE. Six working fluids have been selected to evaluate and compare the performance of the ORC system. The net power output, thermal efficiency, rotational speed of the scroll expander and condenser load of the ORC system have been studied. Results indicated R134a and R125a have better overall performance than other candidates when the designed inlet temperature of the expander is higher than 150 °C. The highest net power and thermal efficiency are respectively 1.2 kW and 13% when R125a is used as the working fluid. R600 and R245fa are desirable to be used when the optimal rotational speed of the scroll expander is about 3000 RPM. The proposed ORC engine coolant and exhaust waste heat recovery system has the advantages of simple system layout, low dumped heat load of condenser, high power output.

Thermoelectric performance optimization when considering engine power loss caused by back pressure applied to engine exhaust waste heat recovery

A numerical model of a thermoelectric generator (TEG) is developed using the finite element method, and the convective heat-transfer coefficient and back pressure are calculated. The effect of the back pressure on the engine power loss is analyzed at different rotating speeds using GT-POWER simulation software. The optimal thermoelectric performance is analyzed considering the maximum net power output as the optimization objective. Results show that the net power output of the TEG can be considerably higher than the engine-power loss by optimizing the dimensions of the exhaust exchanger. When the rotating speed changes, the optimal height changes slightly; however, the optimal length and width change considerably. Considering the average values of the optimal length and width, the percentage deviation in the net power (approximately 4.2%) is the lowest for the following optimal dimensions: height = 0.005 m, length = 0.68 m, and width = 0.76 m. Further, a design height of less than 0.015 m also is acceptable if the corresponding optimal length and width are chosen, as a relatively high output power can be obtained with dev<10%. In brief, a high net power can be achieved by optimizing the design of the exhaust exchanger, regardless of the change in the rotating speed of the engine.