Organic Rankine Cycle Waste Heat Research Articles

Experimental investigation of a free piston expander-linear generator with different valve timings

In this paper, a new free piston expander-linear generator (FPE-LG) prototype for small-scale organic Rankine cycle (ORC) waste heat recovery system has been developed. Firstly, the in-cylinder pressure, motion characteristics and output performance of the FPE-LG with different valve timings are investigated. Then, the effect of external load resistance on motion characteristics and output performance with cam plate A is analyzed. Finally, the effect of external load resistance on the indicated efficiency with cam plate A is studied. The results show that the intake duration and exhaust duration have significant influence on the motion characteristics and output performance of FPE-LG. Compared with other cam plates, cam plate A (the intake exhaust duration is 60°, and the exhaust duration is 180°) can be considered as the best choice for FPE-LG. The external load resistance not only influences the motion characteristics but also effects the output performance. The displacement and velocity increase with increasing the external load resistance. The peak power output with cam plate A is up to 18.6 W. The indicated efficiency shows a downward tendency when the external load resistance increases, and the maximum indicated efficiency of 66.2% is achieved.

Artificial neural network (ANN) based prediction and optimization of an organic Rankine cycle (ORC) for diesel engine waste heat recovery

This paper presents performance prediction and optimization of an organic Rankine cycle (ORC) for diesel engine waste heat recovery based on artificial neural network (ANN). An ANN based prediction model of the ORC system is established with consideration of mean squared error and correlation coefficient. A test bench of combined diesel engine and ORC waste heat recovery system is developed, and the experimental data used to train and test the proposed ANN model are collected. A genetic algorithm (GA) is also considered in this study to increase prediction accuracy, and the ANN model is evaluated with different learning rates, train functions and parameter settings. A prediction accuracy comparison of the ANN model with and without using GA is presented. The effects of seven key operating parameters on the power output of the ORC system are investigated. Finally, a performance prediction and parametric optimization for the ORC system are conducted based on the proposed ANN model. The results show that prediction error of the ANN model with using the GA is lower than that without using GA. Therefore, it is recommended to optimize the weights of the ANN model with GA for a high prediction accuracy. The proposed ANN model shows a strong learning ability and good generalization performance. Compared to the experimental data, the maximum relative error is less than 5%. The experimental results after optimizing the operating parameters are very close to ANN’s predictions, indicating one or more operating parameters can be adjusted to obtain a higher power output during the experiment process.

Analysis and comparison of dynamic behavior of heat exchangers for direct evaporation in ORC waste heat recovery applications from fluctuating sources

Organic Rankine Cycle (ORC) is one of the most prominent technologies for power generation from waste heat sources. Due to their nature, as residual energy from an upstream process, waste heat sources typically present a fluctuating behavior that makes the recovery of the waste heat a challenging task.Direct evaporation from the waste heat carrier has gained substantial interest, especially on volume and weight sensitive applications where the introduction of an additional intermediary thermal oil heat exchanger can hinder the feasibility of the system. Because of the highly dynamic operation of direct evaporators under fluctuating waste heat sources, it is important to consider the thermal response time of the evaporator already at the design stage.In this paper, a systematic analysis and comparison of the dynamic response of two types of ORC evaporators for direct heat transfer between an exhaust gas and the organic working fluid is performed. Based on detailed dynamic models and simulations, maps are built to highlight in a generalized, compact and systematic way the dependence of the thermal response time of the evaporators on the geometric design and boundary conditions and its implications on the weight, volume and pressure drops. The analysis and application of the methodology to diesel engines long haul duty trucks, shows that fin and tube evaporators with large tube diameters and small cross-sectional areas of the exhaust side are the preferred option for high thermal inertia design, while louver fin multi-port flat tubes evaporators with large port diameters are better for fast response, despite the high pressure drops.

Experimental study of a small scale organic Rankine cycle waste heat recovery system for a heavy duty diesel engine with focus on the radial inflow turbine expander performance

The purpose of this work is to experimentally evaluate the effect on fuel efficiency of a small scale organic Rankine cycle (ORC) as a waste heat recovery system (WHRS) in a heavy duty diesel engine that operates at steady state conditions. The WHRS consists of two operating loops, namely a thermal oil loop that extracts heat from the engine exhaust gases, and the working fluid loop which is the ORC system. The expansion machine of the ORC system is a radial inflow turbine with a novel back-swept blading that was designed from scratch and manufactured specifically for this WHR application. The engine test conditions include a partial engine load and speed operating point where various operating conditions of the ORC unit were tested and the maximum thermal efficiency of the ORC was defined close to 4.3%. Simultaneously, the maximum generated power was 6.3 kW at 20,000 rpm and pressure ratio of 5.9. The isentropic efficiency reached its peak of 35.2% at 20,000 rpm and 27% at 15,000 rpm. The experimental results were compared with the CFD results using the same off-design conditions, and the results were in good agreement with a maximum deviation of 1.15% in the total efficiency. Last but not least, the engine-WHRS energy balance is also discussed and presented.

External load resistance effect on the free piston expander-linear generator for organic Rankine cycle waste heat recovery system

For this study, a test rig of free piston expander-linear generator (FPE-LG) for organic Rankine cycle (ORC) waste heat recovery system is built. Based on the free piston expander-linear generator test rig, an experiment of external load resistance effect on the motion characteristics, indicated efficiency, output performance and energy conversion efficiency of the free piston expander-linear generator is conducted. The displacement and velocity of the free piston assembly increase with the external load resistance. The indicated efficiency of the free piston expander (left cylinder) decreases with the external load resistance. As the external load resistance and intake pressure increase, the peak voltage output of the free piston expander-linear generator increases. The maximum peak voltage output is 44.4 V when the intake pressure is 3.0 bar, the operating frequency is 1.5 Hz and the external load resistance is 40 Ω. The peak power output of the free piston expander-linear generator initially shows a non-linear relation increase with external load resistance and tends to stabilize in the end. When the intake pressure is 3.0 bar, the operating frequency is 1.5 Hz and the external load resistance is 30 Ω, the maximum peak power output of 110 W can be achieved. The energy conversion efficiency of the free piston expander-linear generator increases gradually with growing of the intake pressure and external load resistance until the energy conversion efficiency reaches the maximal value, and then the energy conversion efficiency decreases with the intake pressure and external load resistance. The maximum energy conversion efficiency can reach up to 73.33%.

Computational modelling of an Organic Rankine Cycle (ORC) waste heat recovery system for an aircraft engine

Escalating fuel prices and carbon dioxide emission are causing new interest in methods to increase the thrust force of an aircraft engine with limitation of fuel consumption. One viable means is the conversion of exhaust engine waste heat to a more useful form of energy or to be used in the aircraft environmental system. A one-dimensional analysis method has been proposed for the organic Rankine cycle (ORC) waste heat recovery system for turbofan engine in this paper. The paper contains two main parts: validation of the numerical model and a performance prediction of turbofan engine integrated to an ORC system. The cycle is compared with industrial waste heat recovery system from Hangzhou Chinen Steam Turbine Power CO., Ltd. The results show that thrust specific fuel consumption (TSFC) of the turbofan engine reach lowest value at 0.91 lbm/lbf.h for 7000 lbf of thrust force. When the system installation weight is applied, the system results in a 2.0% reduction in fuel burn. Hence implementation of ORC system for waste heat recovery to an aircraft engine can bring a great potential to the aviation industry.

Technical and economic optimization of subcritical, wet expansion and transcritical Organic Rankine Cycle (ORC) systems coupled with a biogas power plant

Generally, >40% of the useful energy (cooling engine and exhaust gases) are wasted by a biogas power plant through the cooling radiator and the exhaust gases. An efficient way to convert this waste heat into work and eventually electricity is the use of an organic Rankine cycle (ORC) power system. Over the last few years, different architectures have been widely investigated (subcritical, wet expansion and trans-critical). Despite the promising performances, realistic economic and technical constraints, also related to the application, are required for a meaningful comparison between ORC technologies and architectures. Starting from the limited literature available, the aim of the present paper is to provide a methodology to compare sub-critical, trans-critical and wet expansion cycles and different types of expanders (both volumetric and turbomachinery) from both technical and economic point of view, which represent one of the main novel aspects of the present work. In particular, the paper focuses on the thermo-economic optimization of an ORC waste heat recovery unit for a 500 kWe biogas power plant located in a detailed regional market, which was not investigated yet. By means of a genetic algorithm, the adopted methodology optimizes a given economic criteria (Pay-Back Period, Net Present Value, Profitability Index and Internal Rate of Return) while respecting technical constraints (expander limitations) and thermodynamic constraints (positive pinch points in heat exchangers, etc.).The results show that optimal ORC solutions with a potential of energy savings up to 600 MWh a year and with a pay-back period lower than 3 years are achievable in the regional market analysed.

Diesel and Spark Ignition Engines Emissions and After-Treatment Control: Research and Advancements

One of the major risks mankind has encountered during recent years is, without a doubt, the anthropogenic contribution to environmental pollution [...]

Recent Advances on Organic Rankine Cycle (ORC) Waste Heat Recovery for Internal Combustion Engines

Recent Advances on Organic Rankine Cycle (ORC) Waste Heat Recovery for Internal Combustion Engines

Free piston expander-linear generator used for organic Rankine cycle waste heat recovery system

This study presents an experimental investigation of a free piston expander-linear generator (FPE-LG) used for organic Rankine cycle (ORC) waste heat recovery system. A FPE-LG test rig using compressed air as working fluid is established. The motion characteristics, dynamic characteristics and the indicated efficiency of FPE-LG are analyzed. The motion characteristics and power output performance for different valve timings are studied. The degree of symmetry is defined to evaluate the asymmetry motion characteristics of the free piston assembly. The coefficient of cycle-to-cycle variation (COV) is presented to evaluate the cycle-to-cycle variation characteristics of the FPE-LG. Experimental results show that the free piston assembly displacement profile is similar to a sinusoidal wave and the free piston assembly can operate at high and relatively constant speed at the middle portion of the stroke. The maximum power output of 19W can be achieved when the intake pressure is 2.0bar and the operation frequency is 2.5Hz. The valve timing and intake pressure demonstrate a significant influence on the asymmetric motion and the power output performance of the FPE-LG. The indicated efficiency of the FPE (left cylinder) decreases with the increase in the intake pressure. The maximum indicated efficiency reaches 92.8% when the intake pressure is 1.4bar and the operation frequency is 2.0Hz. The indicated efficiency firstly increases and then decreases with the increase in the operation frequency. The COV of the FPE-LG decreases with increasing the intake pressure. The motion stability of FPE-LG improves with the increase in the intake pressure. Valve timing and valve train should be optimized in the near future.

Modeling and optimal steady-state operating points of an ORC waste heat recovery system for diesel engines

Waste heat recovery (WHR) systems based on the Organic Rankine Cycle (ORC) are a promising method to reduce the fuel consumption of heavy-duty diesel engines. This article considers a setup with two parallel evaporators and a hydraulically closed low-pressure part. This gives additional degrees of freedom compared to a pressure balanced low-pressure part and thus allows to increase the recovering efficiency. However, these additional degrees of freedom lead to a higher system complexity, which complicates the calculation of power maximizing steady-state operating points. To determine these power maximizing steady-state operating points, this article develops a model based optimization strategy. For this task, models from the literature are extended and validated by test bench measurements. It is shown that the model has a high accuracy both in steady-state and dynamic operating situations. The optimal steady-state operating points of the considered WHR system are compared with other system topologies, utilizing, e.g., a pressure balanced low-pressure part or a single evaporator. The results of this paper can be utilized as the basis for designing optimal control strategies for the considered WHR system.

Advanced Exergoeconomic Analysis of Organic Rankine Cycle Waste Heat Recovery System of a Marine Power Plant

Advanced Exergoeconomic Analysis of Organic Rankine Cycle Waste Heat Recovery System of a Marine Power Plant

Advanced Exergoeconomic Analysis of Organic Rankine Cycle Waste Heat Recovery System of a Marine Power Plant

In this paper, superheated and saturated vapor ORCs commonly utilized as waste heat recovery systems of a marine power plant are investigated. First, a parametric study with different organic fluids has been carried out by applying conventional exergy and exergoeconomic analyses to the system considered in order to identify the best possible operating conditions and also to evaluate the findings of conventional exergy-based analyses. Then, advanced exergy and exergoeconomic analyses have been performed on ORCs by splitting exergy destruction rates, exergy destruction costs and investment costs of components and overall system to identify avoidable parts of costs and exergy destructions. Finally, decision criteria were suggested on the selection of more appropriate system depending on the results of the analysis.

Model Predictive Control of an Organic Rankine Cycle System

Organic Rankine Cycle (ORC) waste heat recovery systems offer promising engine fuel economy improvements for heavy-duty on-highway trucks. An ORC test rig with parallel evaporators to recover both tailpipe and EGR waste heat from a 13L heavy duty diesel engine was developed and used in this work to demonstrate a novel control strategy based on Model-Predictive Control (MPC). The main control objectives for the ORC system are: (i) regulation of working fluid temperature, (ii) safe turbine operation - away from 2-phase region, and (iii) maximization of waste heat recovery. The MPC uses a built-in moving boundary evaporator model to predict future system response and generate optimal actuator reference commands. Two variants of MPC were considered in this work: an adaptive linear MPC (LMPC) and a nonlinear MPC (NPMC). Compared with the traditionally used PID controller, MPC demonstrates more accurate temperature control and improved disturbance rejection in simulation. Finally, the LMPC and NMPC controllers were implemented on the ORC test rig and showing promising initial test results.

Iterative Approach for the Design of an Organic Rankine Cycle based on Thermodynamic Process Simulations and a Small-Scale Test Rig

Waste heat recovery from industrial processes may be a door opener for market penetration of Organic Rankine Cycle (ORC) systems. Within this study, an ORC for industrial waste heat recovery is designed by adopting an iterative approach. Therefore, experiments are performed in a thermal oil heated 1 kW test rig with internal recuperator and a maximum thermal efficiency of 10.6%. The results are iteratively implemented in thermodynamic process simulation. Thus, the simulation results of different stationary operating points can be compared to experimental measurements for different steps of the iterative design process. Results outline the importance of experimental results for the design of ORC systems. The simulation accuracy can be significantly improved with a single reimplementation of experimental data, which enables accurate sensitivity analysis on ORC waste heat recovery system performance. For two different representative operating points, the mean deviations between experiment and simulation decrease from 8.4% to 1.0% and 4.1% to 1.7% respectively, considering the enthalpy and pressure of all thermodynamic state points.

Radial Expander Design for an Engine Organic Rankine Cycle Waste Heat Recovery System

It is commonly accepted that waste heat recovery technologies are significant contenders in future powertrain thermal management to further minimize fuel consumption and CO2 emissions. Organic Rankine Cycle (ORC) systems are currently regarded as amongst the most potent candidates in recovering engine exhaust energy and converting it to electrical power. Crucial areas for the maximization of the efficiency of the ORC system are the appropriate selection of working fluid and the optimization of the expander design. In this study, a novel design methodology of a radial turbine expander for a heavy duty engine ORC waste heat recovery system is presented. The preliminary design of the radial turbine expander includes the development and utilization of an in-house 0/1D code that can be coupled with various organic fluids properties for the calculation of the basic expander geometry. The initial mean-line model for a 200kW-class Diesel engine application investigated produced a solution for a 20kW turbine with 73% isentropic efficiency. The preliminarily optimized expander geometry was used as an input in a detailed CFD code to further optimize rotor geometry. The rotor geometric optimization showed that by increasing exit tip radius by 10% and adopting a 54° back-swept blade design, the maximum isentropic efficiency achieved can exceed 83%.

A power dispatch model for a ferrochrome plant heat recovery cogeneration system

A Organic Rankine Cycle waste heat recovery cogeneration system for heat recovery and power generation to relieve grid pressure and save energy cost for a ferrochrome smelting plant is investigated. Through the recovery and utilization of previously wasted heat from the facility’s internal smelting process off-gases, the cogeneration system is introduced to generate electrical power to supply the on-site electricity demand and feed electricity back to the utility grid when it is necessary and beneficial to do so. In addition, the cogeneration system generates cooling power through a lithium bromide-water solution absorption refrigeration cycle to meet the cooling requirements of the plant. The heat recovery process for power generation is modeled and the optimal power dispatching between the on-site loads and the utility grid is formulated as an economic power dispatching (EPD) problem, which aims to maximize the plant’s economic benefits by means of minimizing the cost of purchasing electricity from the utility and maximizing revenue from selling the generated electricity to the grid. Application of the developed model to a ferrochrome smelting plant in South Africa is presented as a case study. It is found that, for the studied case, more than $1,290,000 annual savings can be obtained as a result of the proposed heat recovery power generation system and the associated EPD model. In addition to this, more than $920,000 annual savings is obtained as a result of the generated cooling power via the proposed absorption refrigeration system. The combined cogeneration system is able to generate up to 4.4MW electrical power and 11.3MW cooling power from the recovered thermal energy that was previously wasted.

Transient dynamic modeling and validation of an organic Rankine cycle waste heat recovery system for heavy duty diesel engine applications

This paper presents a dynamic organic Rankine cycle waste heat recovery (ORC-WHR) Simulink® model and an engine model for heavy-duty diesel applications. The dynamic, physics-based ORC-WHR system model includes parallel evaporators, flow control valves, a turbine expander, a reservoir, and pumps. The evaporator model contains an enhanced pressure drop model, which calculates pressure drop for each working fluid phase via a linear relation to the axial location inside each phase. The ORC-WHR component models parameters are identified over large range of steady state and transient experimental data, which are collected from an ORC-WHR system on a 13L heavy-duty diesel engine. The component models are integrated into an entire system model and the boundary conditions, inputs and outputs for the individual models are described. A GT-POWER® engine model and its transient validation is presented. The speed and torque profiles of a long-haul, constant speed variable-load heavy-duty cycle are processed through the engine model to produce the exhaust and recirculated exhaust gas transient conditions relevant for the ORC model. The ORC-WHR system then simulated over these highly transient engine conditions. Overall, this paper provides detailed guidelines for ORC-WHR system modeling, model calibration, and component models integration.

A Comparative Study of the Effect of Turbocompounding and ORC Waste Heat Recovery Systems on the Performance of a Turbocharged Heavy-Duty Diesel Engine

In this study the influence of utilization of two Waste Heat Recovery (WHR) strategies, namely organic Rankine cycle (ORC) and turbocompounding, have been investigated based on the performance of a heavy-duty diesel engine using 1-D simulation engine code (GT-Power) in terms of Brake Specific Fuel Consumptions (BSFC) at various engine speeds and Brake Mean Effective Pressures (BMEP). The model of a 6-cylinder turbocharged engine (Holset HDX55V) was calibrated using an experimental BSFC map to predict engine exhaust thermodynamic conditions such as exhaust mass flow rate and exhaust temperature under various operating conditions. These engine exhaust conditions were then utilized to feed the inlet conditions for both the ORC and turbocompounding models, evaluating the available exhaust energy to be recovered by each technology. Firstly the ORC system model was simulated to obtain the power that can be generated from the system. Having this additional power converted to useful work, the BSFC was observed to reduce around 2–5% depending upon engine’s speed and BMEP. The initial model of the engine was then modified by considering a second turbine representing turbocompounding heat recovery system. The BSFC was increased due to the back-pressure from the second turbine, but the energy generated from the turbine was sufficient to reduce the BSFC further. However, by application of turbocompounding no improvement in BSFC was achieved at low engine’s speeds. It is concluded that ORC heat recovery system produces a satisfactory results at low engine speeds with both low and high loads whereas at medium and high engine speeds turbocompounding heat recovery system causes higher BSFC reduction.

Dynamic model of supercritical Organic Rankine Cycle waste heat recovery system for internal combustion engine

The supercritical Organic Rankine Cycle (ORC) for the Waste Heat Recovery (WHR) from Internal Combustion (IC) engines has been a growing research area in recent years, driven by the aim to enhance the thermal efficiency of the ORC and engine. Simulation of a supercritical ORC-WHR system before a real-time application is important as high pressure in the system may lead to concerns about safety and availability of components. In the ORC-WHR system, the evaporator is the main contributor to thermal inertia of the system and is considered to be the critical component since the heat transfer of this device influences the efficiency of the system. Since the thermo-physical properties of the fluid at supercritical pressures are dependent on temperature, it is necessary to consider the variations in properties of the working fluid. The wellknown Finite Volume (FV) discretization method is generally used to take those property changes into account. However, a FV model of the evaporator in steady state condition cannot be used to predict the thermal inertia of the cycle when it is subjected to transient heat sources. In this paper, a dynamic FV model of the evaporator has been developed and integrated with other components in the ORC-WHR system. The stability and transient responses along with the performance of the ORC-WHR system for the transient heat source are investigated and are also included in this paper.