Exhaust Waste Heat Recovery Research Articles

Development and tri-objective optimization of a novel biomass to power and hydrogen plant: A comparison of fueling with biomass gasification or biomass digestion

Regarding the low energy density of solid biomass, it usually is converted to gaseous bio-fuels to be utilized in power generation systems. In this regard, the biomass gasification and digestion are of two major conversion routes. The main goal of this research is to make a comparison between biomass gasification and digestion to fuel a power and hydrogen cogeneration plant. The proposed plant is composed of a micro-scale gas turbine and an absorption power cycle for exhaust waste heat recovery of the gas turbine. The generated power by the absorption cycle is utilized in an alkaline electrolyzer for hydrogen production. Thermodynamic, economic and electrochemical models are developed to simulate and investigate the systems performances from exergy, economic and environmental standpoints. Also to determine the best operating conditions, tri-objective optimization is conducted based on maximizing the exergy efficiency and minimizing CO2 emission and product cost. The results indicate that the digester-based system yields higher values of power and hydrogen production, and exergy efficiency as well as lower value of CO2 emission compared to gasifier-based system. It implies that selection of the better system between the two considered ones depends on the user/designer special criteria.

Performance investigation of a thermoelectric generator system applied in automobile exhaust waste heat recovery

In this paper, a novel fluid-thermal-electric multiphysics numerical model is presented to predict the performance of a thermoelectric generator system applied in automobile waste heat recovery. The model considers the complete geometry, temperature-dependent material properties, topological connection among thermoelectric modules, and impedance matching, which can simulate the actual working conditions. Numerical simulations are carried out on the COMSOL platform combined with the exhaust temperature and exhaust mass flow rate under different vehicle speeds. In addition, the detailed physical field distribution characteristics of the automobile thermoelectric generator system, as well as the variations of output power, conversion efficiency, power losses, and net power with vehicle speed, are obtained. The position of thermoelectric modules on the hot side heat exchanger plays an important role in output uniformity, and the higher the vehicle speed is, the more uniform the output will be. At the vehicle speed of 120 km h−1, the output power and conversion efficiency of the automobile thermoelectric generator system are 38.07 W and 1.53% respectively. Considering the weight power loss and coolant pumping power loss, the net power is 23.66 W. This work fills the gap in evaluating the performance of automobile thermoelectric generator systems at different vehicle speeds comprehensively.

Exhaust waste heat recovery from a heavy-duty truck engine: Experiments and simulations

Waste heat recovery using an (organic) Rankine cycle is an important and promising technology for improving engine efficiency and thereby reducing the CO2 emissions due to heavy-duty transport. Experiments were performed using a Rankine cycle with water for waste heat recovery from the exhaust gases of a heavy-duty Diesel engine. The experimental results were used to calibrate and validate steady-state models of the main components in the cycle: the pump, pump bypass valve, evaporator, expander, and condenser. Simulations were performed to evaluate the cycle performance over a wide range of engine operating conditions using three working fluids: water, cyclopentane, and ethanol. Additionally, cycle simulations were performed for these working fluids over a typical long haul truck driving cycle. The predicted net power output with water as the working fluid varied between 0.5 and 5.7 kW, where the optimal expander speed was dependent on the engine operating point. The net power output for simulations with cyclopentane was between 1.8 and 9.6 kW and that for ethanol was between 1.0 and 7.8 kW. Over the driving cycle, the total recovered energy was 11.2, 8.2, and 5.2 MJ for cyclopentane, ethanol, and water, respectively. These values correspond to energy recoveries of 3.4, 2.5, and 1.6%, respectively, relative to the total energy requirement of the engine. The main contribution of this paper is the presentation of experimental data on a complete Rankine cycle-based WHR system coupled to a heavy-duty engine. These results were used to validate component models for simulations, allowing for a realistic estimation of the steady-state performance under a wide range of operating conditions for this type of system.

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.

Synergies between aliphatic bio-alcohols and thermo-chemical waste heat recovery for reduced CO2 emissions in vehicles

The impact of aliphatic (C1–C5) bio-alcohols for on-board thermo-chemical exhaust waste heat recovery, H2 production and hence fuel savings for a gasoline direct injection (GDI) engine has been investigated with iso-octane as reference. Gibbs free energy analysis was conducted to establish which reaction pathways for fuel reforming were dominant and how these reactions are influencing H2 and CO yield. To obtain engine exhaust temperature and mass flow maps for several steady-state engine operation conditions, an engine model was created in AVL CRUISE M and validated with real GDI engine data. A methodology was developed to couple the thermodynamic reactor results and engine model results to compute waste exhaust heat recovery by accounting limited available exergy in exhaust and optimising reforming reactor’s operational parameters to maximise exergy recovery and reforming efficiency in the reformer. Under steady state engine operation, iso-pentanol was more effective overall due to its high hydrogen content by weight (8.3% and 4.3% higher than methanol and ethanol respectively), high energy density of 34.6 MJ/kg (42.2%, 22.3% 13.2% and 4.3% higher than C1-C4 alcohols respectively), high reforming endothermicity and the versatility for heat recovery under all engine operation conditions with heat recovery of at-least 2% of engine power even under low-load conditions.Subsequently, the engine model was evolved into a full AVL CRUISE M vehicle model and was studied over a duty-cycle to evaluate the fuels further. Iso-pentanol and iso-propanol were most effective concerning average heat recovery over the duty cycle. For the high-speed regions of the cycle, up-to 9% of waste heat recovery is observed for C4 and C5 bio-alcohols. In terms of vehicle’s carbon emissions, iso-pentanol, n-butanol, and ethanol exhibited maximum CO2 reduction of 8.4%, 7.7% and 7.1% respectively. The results presented herein indicates versatility of bio-alcohols for cleaner and more efficient powertrains.

Thermoeconomic analysis of improved exhaust waste heat recovery system for natural gas engine based on Vortex Tube heat booster and supercritical CO2 Brayton cycle

Polygeneration has gained increased attention since it embraces efficient energy utilization while contributing to alleviate environmental pollution. The fossil-fuel dependence of trigeneration/cogeneration systems presses for maximizing energy conversion rates. Waste Heat Recovery (WHR) from natural gas engine exhaust represents a significant opportunity to improve fuel utilization. This study presents a thermoeconomic analysis of a novel WHR system consisting of a Vortex Tube heat booster coupled to the exhaust stream of a 2000 kW natural gas engine that drives a Supercritical CO2 Brayton Cycle (SCBC). SCBC operates under two different configurations, namely Regenerative and Recompression. Results indicate that implementing the Vortex Tube (or Ranque-Hilsch tube) increases energy and exergy efficiencies up to around 1.85% and reduces exergy destruction by approximately 4–8%. The Recompression SCBC features higher thermal and exergy efficiencies, while the Regenerative SCBC results in higher power output. Economic indicators reveal that the energy production cost of the Recompression configuration is significantly lower than that of the Regenerative. The turbine features the highest share of total equipment cost, with around 40–50%, followed by the heater and regenerators. The proposed WHR system can potentially recover up to around 7.8% of the total engine power output and provide an electricity price lower than 0.3 $·kWh−1 with a payback period in the range of 8–12 years. Heat exchangers represent an opportunity to improve thermoeconomic performance since they significantly increase exergy costing and limit overall efficiency. Incorporating high thermal conductivity materials that fulfill safety requirements is vital for improving heat exchanger's performance and developing a cost-effective WHR system.

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

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

Energy Saving and Economic Evaluations of Exhaust Waste Heat Recovery Hot Water Supply System for Resort

The objective of this study is to investigate the energy savings and economics of the hot water supply system for the luxury resort. The hot water was generated using the waste heat from the exhaust gas heat (EGH) of internal combustion engine (ICE) installed at the luxury resort. The capacity and characteristics of waste heat source, flow demand and supply system of hot water were surveyed, and data is collected from the real system. The new heat exchanger system which utilizes the EGH to produce the hot water is designed considering the dew point temperature and the back pressure of exhaust gas system. The results show that the proposed system could supply hot water at a temperature of 55 °C corresponding to the present resort demand of 6 m3/h using EGH of ICE at 20% load. The proposed system could achieve the saving of 400 L/day in diesel oil (DO) fuel consumption and the payback time of new system could be evaluated as 9 months. The proposed system could produce hot water of 14 m3/h at 25% of engine load and 29 m3/h at full engine load which are sufficient to satisfy the regular and maximum hot water demand of resort. The presented results show the capability of the proposed system to satisfy the current hot water demand of resort and suggest the larger potential to save energy by recovering EGH of ICE. The novelty of the present work involves detailed methodology to design heat exchangers and evaluate system economics for hot water supply system based on EGH of ICE.

Experimental study on exergy and sustainability analysis of the thermoelectric based exhaust waste heat recovery system

Experimental study on exergy and sustainability analysis of the thermoelectric based exhaust waste heat recovery system

Thermodynamic analysis of exhaust waste heat recovery from turbocharged HCCI engine fueled by wet-ethanol using an absorption refrigeration cycle (ARC)

This paperpresents a thermodynamicstudy of the exhaust waste heat recovery from turbochargedHomogenous Charge Compression Ignition (HCCI) enginepowered by wet-ethanol for a combined output of engine power and cooling system by using a LiBr-H2O absorption refrigerationcycle (ARC). For power production, an HCCI engine has been used, and an ARC driven by engine exhaust heat has been used as a bottoming cycle for refrigeration. While varying the compressor pressor ratio, compressor efficiency, and ARC generator temperature, the thermal and exergetic performance of the combined power and coolingcycle was investigated. The results showed that increasing the compressor ratio (2.25–3.75), and efficiency of the compressor (0.725–0.875), increases HCCI engine power and increases the cooling of the bottoming cycle. As a result, both thermal and exergeticefficienciesof the HCCI engineandcombined cycle increase. In addition, as the temperature of the generator (361–385 K) rises, the ARC's thermal and exergetic COPs decreases.

A numerical study on processes of charge and discharge of latent heat energy storage system using RT27 paraffin wax for exhaust waste heat recovery in a SI engine

In the present paper, the numerical analyses of the heat charge and discharge processes of the latent heat energy storage (LHTES) system designed for the recovery of the exhaust waste heat energy of the SI engine presented. In the LHTES system as phase change material (PCM), the charge and discharge ability of paraffin wax commercially identified with code RT27 were analyzed depending on time. Two closed-loop fluid circulation system consisting of two heat exchangers (HESs) was designed, someone connected to the exhaust path of SI engine for waste heat recovery, and the other used for the charging and discharging of waste heat energy in the PCM. To transfer the waste heat from the hot exhaust gases to the PC, cold water was used as the heat carrier fluid. In the numerical analysis, the exhaust gas temperature and flow rate values of a single-cylinder, air-cooled having a stroke volume of 476.5 cm3 SI engine operated with gasoline at 1600 rpm engine speed and 1/2 throttle position were used. As a result, at designed LHTES system and numerical analysis performed for RT27 paraffin wax under boundary conditions, the process of heat charge (melting) completed at 8000.sec with 93% liquid-fraction, while the process of heat discharge (solidification) completed at 55000.sec with 15% liquid-fraction.

Thermoelectric performance of an exhaust waste heat recovery system based on intermediate fluid under different cooling methods

Thermoelectric generators (TEGs) can effectively recover waste heat from the exhaust of automobiles and generate electricity. An intermediate-fluid TEG system is based on the vaporization and condensation of an intermediate medium, exhibiting high-efficiency thermoelectric conversion. In this study, a mathematical model of an intermediate-fluid TEG system is established, and the influences of cooling methods and condensed-boiling heat transfer performance in the cavity on the thermoelectric performance are analyzed. The results show that the new generator exhibits better characteristics than the traditional TEG system under both water-cooling and air-cooling methods. We not only improved the power output, but also reduced the optimal thermoelectric module area under the water-cooling method. Moreover, the condensation heat transfer coefficient in the cavity had a significant effect on the power performance of the proposed system. The boiling and condensation heat transfer coefficients should both remain greater than 5000 W/m2K for a high efficiency of the TEG. This work provides guidance for the design of new TEGs and high-efficiency utilization of exhaust.

Experimental study on exergy and sustainability analysis of the thermoelectric based exhaust waste heat recovery system

In the present study, the energy and exergy analysis of a thermoelectric based waste heat recovery system of a passenger automobile is performed at different loads. Further, an exergetic sustainability assessment is performed by incorporating parameters like exergy destruction factor, environmental impact factor and exergetic sustainability index. Results revealed that by employing waste heat recovery, the exergetic efficiency can be improved by up to 5.78%. The study showed that the exhaust gas is more suitable for heat recovery as it has 81.8% more exergy than the cooling water.

Waste heat recovery in commercial gas-fired tumble dryers

Thermal drying is energy intensive due to the unavoidable thermodynamic constraint of supplying sufficient energy to evaporate the water (hfg > 2000 kJ kg−1). Textile dryers only use about half (∼55%) of the total input energy for drying. To reduce the wasted energy, exhaust gas recirculation and waste heat recovery using a recuperative heat exchanger are investigated numerically and experimentally. The two methods aim to recover energy from the exhaust stream typically at T < 55 °C for most of the drying period. Experiments are conducted on a commercial gas-fired tumble dryer. A theoretical model is developed to simulate and optimize the drying process. Recirculating the hot humid exhaust gases improves heat and mass transfer in the drum; however, the high humidity ratio of the recirculated air is not amenable to enhancing evaporation. An optimal recirculation ratio of 51% is found to reduce the specific moisture extraction ratio and drying time by 9% and 164 s, respectively. To avoid the rise in humidity associated with recirculation, a compact plate-fin heat exchanger is used to recuperatively preheat the air entering the combustor. Energy savings of ∼15% and reduction in drying time by 216 s over the baseline case are estimated. The predicted data demonstrate good agreement with experiments.

Optimization of the integrated power and desalination plant with algal cultivation system compromising the energy-water-environment nexus

This article examines the exhaust waste heat recovery potential of a microturbine (MT) for seawater desalination using an organic Rankine cycle (ORC). Waste heat from microturbine is exploited using organic Rankine cycle (ORC) and the power generated is delivered to the reverse osmosis (RO) plant. The brine of the reverse osmosis plant is sent to a membrane distillation (MD) plant for further treatment after preheating using the excess heat from the turbine. Also, biological capture of CO2 through cultivation of microalgae has been considered by using flue gases from the microturbine. Plant integration is performed on the basis of the energy-water-environment nexus concept. In this regard, a multi-objective optimization approach is implemented in this work considering economic and environmental points of views. The first objective function is to maximize the annual profit of the system. The second objective function is an environmental index which is defined as the CO2 emission per desalinated water production. Minimization of this index is considered as the second objective function. The results showed that the proposed integrated ORC-RO-MD-CO2 capture plant can considerably improve the system both economically and environmentally.

Further Development of Exhaust Waste Heat Recovery

Further Development of Exhaust Waste Heat Recovery

A comparative study on the energy flow of a conventional gasoline-powered vehicle and a new dual clutch parallel-series plug-in hybrid electric vehicle under NEDC

Energy flow analysis is an effective tool for refined development of vehicle to improve its energy efficiency. To reveal the energy-saving principles of hybrid vehicle, a plug-in hybrid electric vehicle (PHEV) which is in charge sustenance phase and a conventional vehicle with the same internal combustion engine (ICE) are selected to conduct energy flow test under New European Driving Cycle (NEDC) of cold start and warm start. Various energy distributions are quantified, the differences are compared, and the influencing factors are analyzed. Research results show that the conventional vehicle with turbocharged engine overcharges in non-supercharging conditions, and this phenomenon could be alleviated in hybrid vehicle. Tested PHEV could reduce the working range of engine to a certain extent through the electrification of powertrain, but the tank-to-wheel efficiency increases little. This indicates that the design purpose of powertrain topology is to ensure that the benefits of improved engine thermal efficiency outweigh the losses caused by longer energy transmission paths. Brake energy regeneration could reduce the demand for effective engine output, which contributes the most to energy saving, so the braking energy should be recovered as much as possible on the premise of safety and driving comfort. The proportion of exhaust gas enthalpy-increase for the tested PHEV is relatively high, and the use of exhaust waste heat recovery technology can further improve its energy efficiency. Compared with tested conventional vehicle, the energy-saving contribution rates of tested PHEV under NEDC are 5% for idling condition, 20% for braking condition, and −5% for driving condition, respectively. These provide guidance for further tapping the potential of hybrid vehicles.

Automobile Waste Heat Recovery System Using Thermoelectric Generator

Energy crisis is major problem in this era. Thermoelectric generator is a promising solution for this problem. This research aims to recover waste heat energy from automobile by converting it into electrical energy using thermoelectric generator. Thermoelectric generator is applied at automobile exhaust system to produce electrical energy from heat energy directly with a phenomenon called see-beck effect. This work develops a heat exchanger model with thermoelectric generator for automobile waste heat recovery in which heat source and cold sink are actually modeled. Main emphasis is put on effective temperature difference across the TEGs to get better performance of the exhaust waste heat recovery system. This research shows that the model is able to produce up to 2.67 W energy using 3 Numbers of TEGs in this design.

Electric power conversion of exhaust waste heat recovery from gas turbine power plant using organic Rankine cycle

In this study, an examination of a bottoming organic Rankine cycle for power conversion of the flue gases from a 5.75 MW gas turbine power plant was carried out. First law of thermodynamics was applied to the four major components of the system and simulated using developed MATLAB codes, while the thermo-physical properties at each state were supplied by engineering equation solver database. Five organic working fluids were compared based on selected performance indices. Toluene exhibited the best performance at full and partial electric generator load conditions with net power outputs of 532.70 kW at full load and 412.95 kW at partial load of 75%, while at 50% partial load, R245fa has the highest net power output of 469.09 kW. The cycle efficiency of the organic Rankine cycle system was improved from 34.67% at full load to 40.51% with exhaust gases from the power plant considered as sources of low-grade heat. R245fa showed the best adaptability at 50% partial load but at excessively high mass flow rate of 13.62 kg/s. It is evidently shown from this study that, waste heat recovery technologies can effectively generate about 16.8% of the nominal power of a gas turbine power plant and hence, reduce emissions per kW generated, suitable for sustainable environment as well as promoting energy security.

Thermodynamic analysis of a compression ignition engine with latent heat storage unit

This study deals with the thermodynamic analysis of a compression ignition (CI) engine coupled with a longitudinal triangular finned tube construction in a shell and tube heat exchanger which has segmental baffle cut of 50% at 20° slope and a latent heat thermal storage (LHTS) unit, using nano-enhanced organic phase change material (NeOPCM) for improved exhaust waste heat recovery process. The exergy is an effective method to estimate the quantity and quality of energy recovered from the CI engine and stored in the LHTS unit. The results show that nearly 82% of the energy from the engine exhaust is successfully recovered and stored in a heat exchanger with NeOPCM based LHTS unit. The thermodynamic balance of the exergy and energy for the complete system is calibrated and represented by applying the respective data from the Sankey heat flow balance diagrams. The maximum percentages of the energy and exergy saved from the diesel fuel by the LHTS unit using NeOPCM combined with heat exchanger are nearly 24% and 41% more than those of the virgin paraffin wax.