Engine Waste Heat Research Articles

Study on the Control Strategy of Free Piston Expander-Linear Generator Used for Organic Rankine Cycle Waste Heat Recovery

This study presents a free piston expander-linear generator (FPE-LG) for engine waste heat recovery. The control strategies based on displacement (control strategy A) and valve timings (control strategy B) are proposed. The operation and output characteristics with different control strategies are conducted. The results show that control strategy has significant effect on the FPE-LG performance. When FPE-LG operates with control strategy A, the operation frequency is determined by the intake pressure, advanced exhaust duration, fixed position point and external load resistance, whereas it is only related with the intake/exhaust time and advanced exhaust duration (ta) for control strategy B. The external load resistance has slight influence on the stroke length for these two control strategies. For control strategy A, when advanced exhaust duration is more than 40 ms, the stroke length rises with the intake pressure, whereas it first rises and then reduces when advanced exhaust duration is less than 40 ms. There exist the optimal external load resistance and advanced exhaust duration to achieve the maximum power output with control strategy A, whereas the average power output reduces with the increasing advanced exhaust duration when using control strategy B. Stable operation and high power output can be obtained by using different control strategies and adjusting relevant operation parameters.

Design and optimization of hydrogen production by solid oxide electrolyzer with marine engine waste heat recovery and ORC cycle

Hydrogen is considered as a promising alternative to future energy systems. Water or steam electrolysis at elevated temperature consumes less electricity due to the highly efficient utilization of thermal energy. In this paper, a solid oxide electrolyzer cell (SOEC) is integrated with a marine diesel engine to use both electricity and waste heat for hydrogen production. An Organic Rankine Cycle (ORC) is applied to produce electricity from SOEC production streams. A comprehensive thermodynamic analysis model of SOEC, ORC and marine diesel engine waste heat recovery is conducted. The results indicated that the system could produce hydrogen at a rate of 0.431 kg/s and power output of 32386.45 kW with a power reduction of 60%. An efficiency of 104.41%, 12.12% and 53.56% could be achieved for the electrolyzer cell, ORC and integration system, respectively. The waste heat available efficiency could reach only 44.13% under the design conditions. To study the impact of some key parameters on the system performance, sensitivity analysis of current density, H2O inlet flow rate and total SOEC area were performed. It was found that an optimal current density and H2O flow rate can be obtained. Moreover, higher total cell area benefits the integration system thermodynamically.

A Thermoelectric Coupling Control Strategy Based on FDP for REEVs Under Low-temperature Environment

Abstract Efficient energy management strategy (EMS) and thermal management strategy (TMS) are important to improve the energy efficiency of the range extender electric vehicles (REEVs). This paper aims to develop a thermaoelectric coupling control strategy for REEVs in low-temperature environment with the comprehensive consideration of the coupling relationship between energy management system and thermal management system of REEVs. First, a coupled thermal management system (CTMS) is designed in order to efficiently use the engine waste heat to preheat the power battery in low-temperature. Sequentially, a forward dynamic programming (FDP) method is employed to solve the optimal problem considering the impact of the thermal system dynamics on energy consumption. Finally, simulation results show that the proposed strategy efficiently reduces the warm-up time of the battery and improves the energy utilization efficiency.

Monitoring the efficiency of cooling air at the inlet of gas engine in integrated energy system

The fuel efficiency of gas engines is effected by the temperature of intake air at the suction of turbocharger. The data on dependence of fuel consumption and engine electric power on the intake air temperature were monitored for Jenbacher gas engine JMS 420 GS-N.LC to evaluate its influence. A waste heat of engine is rejected for heating water to the temperature of about 90??. The heat received is used in absorption lithium-bromide chiller to produce a cold in the form of chilled water. A cooling capacity of absorption chiller firstly is spent for technological needs and then for feeding the central air conditioner for cooling the ambient air incoming the engine room, from where the air is sucked by the engine turbocharger. The monitoring data revealed the reserves to enhance the efficiency of traditional cooling system of intake air by absorption chiller through deeper cooling. This concept can be realized in two ways: by addition cooling a chilled water from absorption chiller to about 5-7?? for feeding engine intake air cooler or by two-stage cooling with precooling ambient air by chilled water from adsorption chiller, in the first stage and subsequent deep cooling air to the temperatures 7-10?? in the second stage of intake air cooler by using a refrigerant as a coolant. In both cases the ejector chiller could be applied as the most simple in design.

Applications and technological challenges for heat recovery, storage and utilisation with latent thermal energy storage

Thermal energy storage (TES) technology is considered to have the greatest potential to balance the demand and supply overcoming the intermittency and fluctuation nature of real-world heat sources, making a more flexible, highly efficient and reliable thermal energy system. This article provides a comprehensive state-of-the-art review of latent thermal energy storage (LTES) technology with a particular focus on medium-high temperature phase change materials for heat recovery, storage and utilisation. This review aims to identify potential methods to design and optimise LTES heat exchangers for heat recovery and storage, bridging the knowledge gap between the present studies and future technological developments. The key focuses of current work can be described as follows: (1) Insight into moderate-high temperature phase change materials and thermal conductivity enhancement methods. (2) Various configurations of latent thermal energy storage heat exchangers and relevant heat transfer enhancement techniques (3) Applications of latent thermal energy storage heat exchangers with different thermal sources, including solar energy, industrial waste heat and engine waste heat, are discussed in detail.

Design and Blade Number Ratio Analysis of Organic Rankine Cycle Radial-Inflow Turbine on Vehicle

The organic Rankine cycle is widely used in industrial waste heat, engine waste heat and other waste heat recovery applications, and as a key component of the system, it affects the efficiency and output power of the system. In this paper, a centripetal turbine is designed for the organic Rankine cycle, using vehicle exhaust gas as the heat source. Numerical simulations are performed to analyze the effect of the ratio of the number of guide vane blades to the number of impeller blades (vane number ratio) on the turbine performance and flow field. The results show that the effect of the number of impeller blades on the turbine entropy efficiency, the average exit velocity and the temperature of the guiding grate becomes less and less as the ratio of the number of blades increases. The optimum turbine performance is obtained when the number of impeller blades and the ratio of the number of blades are 17 and 1.5882, respectively, and the expansion performance of the guide impeller is improved and the isentropic efficiency of the turbine is improved by 3.84% compared with the preliminary number of blades.

Energy, exergy, and economic (3E) analysis of an organic Rankine cycle using zeotropic mixtures based on marine engine waste heat and LNG cold energy

In this paper, thermo-economic performance comparisons between zeotropic mixtures and pure fluids are conducted via simulation for a parallel two-stage organic Rankine cycle (PTORC) driven by waste heat from LNG-fueled ship. The exhaust gas and jacket water of the marine engine work as heat sources, and the LNG fuel is considered as heat sink. R1150/R170 and R170/R1270 are employed as the working fluids in the first stage while R600a/R601a and R600/R601 are used in the second stage. The effects of working fluids and pinch point temperature difference (PPTD) on the PTORC performances are studied from the viewpoint of the first and the second law of thermodynamics. It concludes that the zeotropic mixtures do not always exhibit an advantage over the pure fluids. The highest net power of the PTORC is 146.9 kW obtained with R1150-R600a. The results of PPTD indicate that LNG regasification should occur in the first-stage condenser. The maximum energy efficiency and exergy efficiency of the PTORC are 22.09% and 23.28%, respectively. The best economic performances of the PTORC are achieved with R170/R1270 (0.9/0.1, mass fraction)-R600. The total cost, payback period, and levelized energy cost vary in the range of 5.98–8.08 × 105 $, 4.58–5.18 years, and 0.065–0.074 $/kWh, respectively.

Comparison of Conventional and Advanced Exergy Analysis for Dual-Loop Organic Rankine Cycle used in Engine Waste Heat Recovery

At present, the dual-loop organic Rankine cycle (DORC) is regarded as an important solution to engine waste heat recovery (WHR). Compared with the conventional exergy analysis, the advanced exergy analysis can better describe the interactions between system components and the irreversibility caused by economic or technical limitations. In order to systematically study the thermodynamic performance of DORC, the conventional and advanced exergy analyses are compared using an inline 6-cylinder 4-stroke turbocharged diesel engine. Meanwhile, the sensitivity analysis is implemented to further investigate the influence of operating parameters on avoidable-endogenous exergy destruction. The analysis result of conventional exergy analysis demonstrates that the priorities for the components that should be improved are in order of the high-temperature evaporator, the low-temperature turbine, the first low-temperature evaporator and the high-temperature condenser. The advanced exergy analysis result suggests that the avoidable exergy destruction values are the highest in the low-temperature turbine, the high-temperature evaporator and the high-temperature turbine because they have considerable endogenous-avoidable exergy destruction. The sensitivity analysis indicates that reducing the evaporation pinch point and raising the turbine efficiency can decrease the avoidable exergy destruction.

Extended state observer assisted Coulomb counting method for battery state of charge estimation

The state of charge (SOC) estimation method for power batteries in engine waste heat recovery system is studied in this article. The nonmodel-based Coulomb counting (CC) method is among the most popular techniques. However, challenges imposed by inaccurate estimation of initial SOC, current measurement error as well as uncertain system dynamics caused by temperature, and thermal effects will produce an accumulated error. To overcome this error and improve the CC method's disturbance rejection capability, a linear second-order extended state observer (ESO) is designed to address this problem. A comparative simulation study is carried out to study the estimation performance of the proposed ESO-assisted CC method and the conventional CC method. Study results of the proposed approach exhibit better estimation performance and adaptability for inaccurate estimation of initial SOC, current measurement error, and uncertain system dynamics. There is only one parameter ωo to tune. The adaptability of estimation performance can be maintained without parameters resetting, which proves the effectiveness and disturbance rejection capability of the proposed ESO-assisted CC method for SOC estimation.

Exchange Rate Analysis for Ultra High Bypass Ratio Geared Turbofan Engines

This paper investigates the impact of thermal management methods on the design point and synthesis exchange rates of an ultra-high bypass ratio geared turbofan engine. In a typical thermal management system, where heat is managed by means of heat exchangers that transfer engine waste heat into oil, air, or fuel. However, the utilization of air–oil and fuel–oil heat exchangers has an adverse impact on engine performance. This paper investigates the impact on and engine’s specific fuel consumption and summarizes it into common exchange rates for different thermal management configurations. The results show that any pressure loss in the bypass duct results in a severe specific fuel consumption penalty (an increase of 1% pressure loss in the bypass duct causes a 2% specific fuel consumption increase at cruise conditions). In addition, quite severe is the impact of extracting air from the gas path, particularly when the bleed location is in the bypass duct or the high-pressure compressor. It is also found that the utilization of a fuel–oil heat exchanger improves the specific fuel consumption at a higher rate than an air–oil heat exchanger. For the performance characteristics of the examined engine, the specific fuel consumption benefit with the former is 1.33%, while for the latter it is 0.38%.

Development of a Hybrid Cooling, Heating, and Power System for Distributed Energy Applications

Abstract A unique hybrid cooling, heating, and power (HCHP) concept has been recently developed as an alternative to environmental control units. It combines a small-scale organic Rankine cycle (ORC) with a vapor compression cycle. The unique drive-train design flexibly and efficiently converts engine waste heat into useful energy in the form of cooling, heating, and power depending upon the energy needs. Compared to a standard military environmental control unit which puts an electric load on a diesel generator, the HCHP system uses engine exhaust heat as the primary energy input. Utilizing the exhaust heat can potentially provide 27% reduction on fuel consumption when operating in the cooling mode. When cooling is not needed, it is able to provide power and/or heating output using engine waste heat—a significant advantage over other heat activated cooling technologies. The prototype unit based on the HCHP design has been developed to demonstrate the concept. It leveraged the microchannel heat exchanger and scroll expander technologies to achieve high-performance, small-size, and low-cost design in order to meet the growing distributed energy applications.

Research on waste heat recovery from gas engine for auxiliary heating: An emerging operation strategy to gas engine-driven heat pump

Abstract Gas engine-driven heat pump (GEHP) is attracting increasing interest owing to the high heating efficiency and energy-saving. However, the waste heat from engine is mostly used to directly heat domestic hot water. In this study, a new type of waste heat utilization mode of GEHP was proposed: auxiliary heating. The heating capacity, gas consumption, waste heat recovery and compression ratio of water-source GEHP system with waste heat auxiliary heating mode was studied. In addition, the effects of two utilization modes of engine waste heat domestic hot water (mode Ⅰ) and auxiliary heating (mode Ⅱ) on the thermodynamic parameters were compared. The results indicated that the system efficiency was decrease with engine speed. Even in high speed operation, the primary energy efficiency (PER) of the system was more than 1.55. Under the same range of condenser water inlet temperature, the COP of mode Ⅰ was in the range of 4.71–4.95, and that of mode Ⅱ was in the range of 5.17–5.67. The energy saving and emission saving were also researched. Compared with mode Ⅰ, mode Ⅱ had higher efficiency and less pollution to the environment.

Cylinder steam injection (CSI) for internal combustion (IC) engine waste heat recovery (WHR) and its application on natural gas (NG) engine

In this study, the approach of CSI for IC engine WHR was discussed based on a heavy-duty NG engine. The thermodynamic processes of IC engine cycle coupling with CSI cycle were investigated under three typical speeds of full load based on the calibrated model, and then the effects of steam injection parameters on engine performance especially thermal efficiency were studied. Results show that, the improvement of engine thermal efficiency is determined by both steam injection parameters and engine operating conditions. The earlier steam injection timing, higher steam temperature and larger steam amount are beneficial for improving the WHR efficiency. Although the higher steam temperature leads to lower steam amount generated by waste heat, the maximum improvement of engine thermal efficiency still appears at the highest steam temperature. Compared with original engine, the thermal efficiency of this NG engine can be improved by at least 6% points through steam injection, and the maximum improvement comes up to 6.6% points at 2000 rpm. Accordingly, the engine indicated power is increased by 38.6 kW at the expense of 0.29 kW pumping power. All these demonstrate that this WHR approach has great energy-saving potential for IC engine.

Exergoeconomic analysis and optimization of a hybrid Kalina and humidification-dehumidification system for waste heat recovery of low-temperature Diesel engine

Internal combustion engines are of the important systems with extensive applications in power generation and agricultural/industrial machines and vehicles due to their promising features such as high thermal efficiency, and reliability. The reuse of the exhaust gas and jacket water waste heat is an effective method to improve engine performance and decrease fuel consumption and environmental pollution. In this paper, to recover the waste heat of a diesel engine, cogeneration of electrical power and freshwater is proposed. The Kalina cycle is used for power generation through the utilization of exhaust gas energy, and for freshwater production, the HDH system is employed using jacket water energy. Thermodynamic and exergoeconomic analysis and optimization are applied to the proposed system. The effect of several parameters on net output power, exergy efficiency, HDH unit performance, and the sum unit cost of the system's product is studied. The comparison of the Multi-objective optimization results with the base case outcomes betokens that the thermal efficiency and exergy efficiency are improved by 1.88% and 1.52%, respectively. Moreover, the SUCP value is reduced by 0.94 $/GJ. For the electricity sale price of 0.09 $/kWh, the payback period is estimated 7.2 years, and the NPV at the end of the plant's life obtained 165,814 $.

Prediction and optimization of power output of single screw expander in organic Rankine cycle (ORC) for diesel engine waste heat recovery

The output characteristics of single screw expander has a direct and crucial influence on the performance of organic Rankine cycle (ORC) system. In this paper, a machine learning prediction model driven by experimental data is developed and applied to predict the power output of single screw expander. After screening different structural parameters of the model, genetic algorithm (GA) is used to optimize the initial weights and thresholds of the model, so as to further improve the generalization ability of the model. In addition, the generalization ability of the model is compared with that of the model not optimized by GA. Furthermore, the influence of operating parameters on the power output of single screw expander is analyzed by fitting algorithm in three-dimensional space. The optimization boundary value needed for prediction and optimization is determined by fitting algorithm in four-dimensional space. Finally, a prediction and optimization model is created by coupling the machine learning prediction model with GA, and the maximum power output and corresponding operating parameters of the single screw expander under full operating conditions are predicted and optimized. The results show that with the application of machine learning and GA, the maximum power output of single screw expander can be predicted and optimized precisely under full operating conditions. So as to directly guide the selection of relevant parameters in the process of theoretical analysis and experimental research.

Thermodynamic analysis of a combined supercritical CO2 and ejector expansion refrigeration cycle for engine waste heat recovery

An engine waste heat driven combined power and refrigeration system, comprised of a regenerative supercritical CO2 Brayton cycle (RSCBC) and an ejector expansion refrigeration cycle (EERC), is proposed. In this system, the RSCBC is adopted as the topping cycle to generate power by recovering the high-temperature waste heat of engine. Meanwhile, the power is utilized by the compressor in the EERC. Such a waste heat recovery system can not only decrease the specific fuel consumption, but also provide refrigeration for refrigerated trucks to realize food preservation. Energy and exergy analysis are conducted on the RSCBC/EERC. The performance of four zeotropic mixtures used in EERC and different mixture compositions are compared. Moreover, the effects of several significant operating parameters are discussed in detail, including turbine inlet pressure and temperature, compressor inlet pressure and temperature, pressure drop in the ejector, evaporating temperature, and condensing temperature. To investigate the influence of the installation of the RSCBC/EERC system, weight estimation analysis is conducted. The results show that the refrigerating capacity and COPcomb of the system with R32/CO2 (0.9/0.1) are up to 225.5 kW and 2.05, respectively. And the equivalent power loss due to the additional weight is estimated to be 5.21 kW. In general, the RSCBC/EERC has proven its application potential in recovering waste heat to provide refrigeration through thermodynamic analysis.

Performance analysis and optimization of engine waste heat recovery with an improved transcritical-subcritical parallel organic Rankine cycle based on zeotropic mixtures

Effective recovery of engine waste heat is a key strategy to alleviate energy and environmental issues. In this study, an improved transcritical-subcritical parallel organic Rankine cycle based on zeotropic mixtures is proposed to recover engine waste heat. Firstly, the proposed system is compared with other systems and shows the best performance. Then energy and exergy analyses are conducted, and three design parameters are analyzed. According to the results, for each turbine inlet temperature of high-pressure branch, the system performance initially increases then decreases with turbine inlet pressure of high-pressure branch, and the net power output firstly increases then decreases with evaporation temperature of low-pressure branch. Furthermore, the effect of composition of zeotropic mixtures on system performance is investigated, and zeotropic mixtures R600a/R601a and R600/R601 are compared. The results indicate that adopting zeotropic mixture can improve system performance significantly, and system based on R600/R601 performs better than based on R600a/R601a. Finally, performance optimization of system is conducted. The results show that system based on R600/R601 (0.5/0.5) achieves the maximum net power output of 114.47 kW which is higher 10.68% and 6.42% than based on pure R600 and R601 respectively, and the engine power output is improved by 11.49%.

Control of superheat of organic Rankine cycle under transient heat source based on deep reinforcement learning

The organic Rankine cycle (ORC) is a promising technology for engine waste heat recovery. During real-world operation, the engine working condition varies frequently to satisfy the power demand; thus, the transient nature of engine waste heat presents significant control challenges for the ORC. To control the superheat of the ORC precisely under a transient heat source, several optimal control methods have been used such as model predictive control and dynamic programing. However, most of them depend strongly on the accurate prediction of future disturbances. Deep reinforcement learning (DRL) is an artificial-intelligence algorithm that can overcome the aforementioned disadvantage, but the potential of DRL in control of thermodynamic systems has not yet been investigated. Thus, this paper proposes two DRL-based control methods for controlling the superheat of ORC under a transient heat source. One directly uses the DRL agent to learn the control strategy (DRL control), and the other uses the DRL agent to optimize the parameters of the proportional–integral–derivative (PID) controller (DRL-based PID control). Additionally, a switching mechanism between different DRL controllers is proposed for improving the training efficiency and enlarging the operation range of the controller. The results of this study indicate that the DRL agent can satisfactorily perform the control task and optimize the traditional controller under the trained and untrained transient heat source. Specifically, the DRL control can track the reference superheat with an average error of only 0.19 K, whereas that of the traditional PID control is 2.16 K. Furthermore, the proposed switching DRL control exhibits excellent tracking performance with an average error of only 0.21 K and robustness over a wide range of operation conditions. The successful application of DRL demonstrates its considerable potential for the control of thermodynamic systems, providing a useful reference and motivation for the application to other thermodynamic systems.

A Study on Performance Characteristics of a Heat Pump System with High-Pressure Side Chiller for Light-Duty Commercial Electric Vehicles

One of barriers for the present heat pump system’s application in an electric vehicle was decreased performance under cold ambient conditions due to the lack of evaporating heat source. In order to improve the heat pump’s performance, a high-pressure side chiller was additionally installed, and the tested heat pump system was modified with respect to refrigerant flow direction along with operating modes. In the present work, the performance characteristics of the heat pump system with a high-pressure side chiller for light-duty commercial electric vehicles were studied experimentally under hot and cold ambient conditions, reflecting real road driving. The high-pressure side chiller was located after the electric compressor so that the highest refrigerant temperature transferred the heat to the coolant. The controlled coolant with discharged refrigerant from the electric compressor was used to heat up the cabin, transferring heat to the inlet air like the internal combustion engine vehicle’s heating system, except with unused engine waste heat. In the cooling mode, for the exterior air temperature of 35 °C and interior air temperature of 25 °C, cooling performance along with the compressor speed showed that the system efficiency decreased by 16.4% on average, the cooling capacity increased by 8.0% on average and the compressor work increased by 27% on average. In heating mode, at the exterior and interior air temperature of −6.7 °C, compressor speed and coolant temperature variation with steady conditions were tested with respect to heating performance. In transient mode, to increase coolant temperature with a closed loop from −6.7 °C, tested system characteristics were studied along the compressor speed with respect to heating up the cabin. As the inlet air of the HVAC was maintained at −6.7 °C, even though the heat-up rate of the cabin room was a little slow, the cabin temperature reached 20 °C within 50 min and the temperature difference with the ambient air attained 28.7 °C.

Experiment on waste heat recovery‐assisted heat pump drying of food chips: Performance, economic, and exergoeconomic analyses

Novel waste heat recovery-assisted heat pump dryer is designed, developed, and experimented in different operating modes. Energy, exergy, economic, and exergoeconomic parameters of the dryer with and without waste heat recovery are experimentally compared. Radish chips are dried to remove moisture from 93.5% to 10.5% at fixed dryer inlet air velocity. Both energy and exergy efficiencies are found highest for the waste heat recovery-assisted (hybrid) system (56.26% and 35.9%, respectively). Specific moisture extraction rate (2.4 kg/kWh) and coefficient of performance (6.72) are highest for the hybrid system. The payback period for the hybrid system over the simple system is 33 months. The lowest exergoeconomic factor is for expansion devices in both simple and hybrid systems (0.0918 and 0.1348, respectively). Total exergy destruction costs for simple and hybrid systems are 0.10148 and 0.1266 $/h, respectively. The most important component that needs to improve based on the exergoeconomic factor is the drying chamber. Practical applications In the present study, a novel heat pump dryer assisted with waste heat recovery from the diesel engine is designed and developed. Various energy, exergy, economic, and exergoeconomic performance parameters with and without waste heat recovery are experimentally compared. To check the applicability, the radish chips have been dried to remove moisture from 93.5% to 10.5% at fixed dryer inlet air velocity. The testing shows that the proposed system is superior as compared to the simple heat pump dryer in terms of both energy and exergy efficiencies, specific moisture extraction rate, and overall heating coefficient of performance. The payback period for the proposed system over a simple one is found 3 years approximately. The proposed system can be a futuristic and promising solution for the drying applications, which satisfies two purposes: An effective way to utilize the engine waste heat and superior system performance.