Rankine Engine Research Articles

Heat engines of the Kerr-AdS black hole

In this paper, we investigate three types of heat engines for the rotating Kerr-Anti de Sitter (Kerr-AdS) black hole. We first briefly review the thermodynamics and phase structure of the Kerr-AdS black hole and obtain the phase structure in the T–S chart. The thermal stability of Kerr-AdS black holes, along with their dependence on various parameters, is thoroughly examined. Then, by utilizing the phase diagram, we consider three types of heat engines: the maximal Carnot engine, Stirling engine, and Rankine engine. We calculate both the work and efficiency for these engines. The results indicate that angular momentum has a significant influence on these heat engines.

Scaling Performance Parameters of Reciprocating Engines for Sustainable Energy System Optimization Modelling

The increased share of variable renewable energy sources such as wind and solar power poses constraints on the stability of the grid and the security of supply due to the imbalance between electricity production and demand. Chemical storage or power-to-X technologies can provide the flexibility that is needed to overcome this issue. To quantify the needs of such storage systems, energy system optimization models (ESOMs) are used, guiding policy makers in nationwide energy planning. The key input parameters for such models are the capacity and efficiency values of the conversion devices. Gas turbines, reciprocating engines, fuel cells and Rankine engines are often mentioned here as cogeneration technologies. Their performance parameters will however need to be revised when switching from fossil to renewable fuels. This study therefore investigates the possibility of using size-based scaling laws to predict the efficiency and power values of one type of conversion technology: the reciprocating engine. The most straightforward scaling laws are the ones based on the fundamental engine performance parameters and are constructed by fitting an arithmetic function for a large set of representative engine data. Their accuracy was tested with a case study, consisting of thirty large-bore, spark-ignited gas engines. Two alternative methods were also investigated: scaling laws based on the Willans line method and scaling laws based on the similarity theory. Their use is deemed impractical for the current research problem.

Simulation of Thermosyphon Rankine Engine

The increasing global energy demand has led to other alternative ways of harvesting energy from renewable resources. This energy cause less environmental pollution and deterioration of humans' health. Thermosyphon Rankine engine (TSR) is a concept used for direct electrical power generation from low-grade heat sources. In this project, an extended investigation on previous experimental done was conducted through a simulation approach using Computational Fluid Dynamic (CFD) analysis to simulate a two-phase flow, phase change occurred during evaporation and condensation processes inside the thermosyphon under different power inputs of 245 W, 552 W, and 984 W. Also the water was used as a working fluid. The volume of fluid (VOF) technique was used to model the phase change using ANSYS FLUENT software. The simulation investigated temperature profile, water volume fraction, and velocity. Then, CFD predicted temperature profile was compared with the previous experimental data, and percentage error was calculated. Compared to the experimental one, CFD predicted temperature profile was higher than the experimental one due to mechanical losses during experimentation. Meanwhile, the model managed to simulate vapor bubbles and nucleate boiling during phase change. It showed that the VOF model with the in-built evaporation-condensation model developed by Lee only simulated nucleate boiling at the interphase between water and vapor phase during evaporation and condensation processes.

Effect of direct water injection temperature on combustion process and thermal efficiency within compression ignition internal combustion Rankine engine

Compression ignition-internal combustion Rankine cycle (CI-ICRC) concept implement oxy-fuel combustion, direct water injection (DWI) and waster heat recovery into traditional diesel cycle to realize ultra-high thermal efficiency and low emission powertrain. As indicated by ICRC concept, the DWI process show critical impact on its combustion process and thermal efficiency. This paper dedicated in investigating the effect of different DWI temperature on cycle performance and thermal efficiency within prototype CI-ICRC engine, in order to do so, independent DWI system, O2/CO2 intake system and reconfigurable electronic controller is established. Combustion characteristics including in-cylinder pressure, heat release rate, combustion stability, brake thermal efficiency are experimentally investigated. The cycle performance and thermal efficiency are proved to be optimized under elevated DWI temperature, an optimum 46.6% brake thermal efficiency is achieved, while the coefficient of variation remains around 1%. The NOX and soot emissions are both reduced under DWI utilization, the mechanism of soot reduction is highly related to thermolysis of water or carbon-water reactions which further chemical kinetic analysis is needed. The result of this study provides fundamental information for future CI-ICRC engine optimization, and can also be utilized in providing reference guidance for DWI implementation within modern internal combustion engines.

Многоцелевое конвертирование судовых дизелей при создании поршневых мотор-компрессорных агрегатов

This paper present an assessment of the energy efficiency of various combinations of piston stages of an internal combustion engine, a compressor, and a Rankine engine as part of piston motor-compressor units based on modernized marine diesel engines. An eight-cylinder single-row diesel engine 8Ch23/30-1 is chosen as the object of research, the base of which is used as a single platform for creating powertechnology units for various purposes and power. The proposed variants for converting the original engine allow, with minimal costs for the development of design and manufacturing technology, to create gas engine compressor units with reduced fuel consumption and improved weight and size characteristics in comparison with the known mobile compressor stations driven by diesel internal combustion engines. In the paper, on the basis of the developed mathematical models of working processes, the possibility of joint operation of diesel cylinders with piston expanders of the Rankine cycle and one or more stages of a piston compressor is assessed. Various possible combinations of diesel cylinders, compressor cylinders and expander cylinders are considered, as well as the dependences of engine power and compressor performance depending on the number of compressor stages and the number of diesel power cylinders used.

Application of Solar Organic Rankine System for Energy Generation in Buildings: the Case of Athens

This paper describes the performance of an ORC system driven by solar energy and R134a as working fluid. The system is predicted along the twelve months of the year. The operation of the system and the related thermodynamics are simulated by suitable computer codes and the required local climate data are determined by statistical processing over a considerable number of years. It’s found that the solar to electricity efficiency of this SORC system varies from 0.049 to 0.058 while the ambient temperature varies from 11.3oC to 29.2oC and the total solar irradiance varies from 443 W/m2 to 679 W/m2. The system’s arrangement comprises a solar thermal array which is coupled with an organic Rankine engine. The mean annual overall efficiency of the SORC system is estimated at 0.055 while the thermodynamic efficiency of Rankine is calculated at 0.107. The obvious advantage of this arrangement is that electricity can be produced in buildings by using the existing common solar thermals installed. Easy–to–find machinery is employed in order to attain a simple and practical small–scale organic Rankine cycle arrangement coupled with common solar thermals used widely in Greek buildings for DHW production and space heating assistance.

Thermal stability of n-pentane, cyclo-pentane and toluene as working fluids in organic Rankine engines

In this paper we investigate the thermal stability of three representative hydrocarbons used as working fluids in organic Rankine cycles (ORC): n-pentane, cyclo-pentane and toluene. The experimental used method is a “static” one, based on the recording of the pressure during the permanence of the fluid sample at constant temperature and on the measure of the differences in the vapour pressure in comparison with the reference values for the virgin pure fluid. The sample container and the circuit are in stainless steel.The decomposition was estimated by a parameter based on the mean value of differences in the sub-atmospheric vapour pressures at selected temperatures. The increase of the vapour pressure resulting from even a small thermal decomposition (more noticeable at sub-atmospheric pressures) is an important indicator as it may anyway have great effects on the engine in which the fluid works.The adopted procedure is relatively simple and may be applied to different fluids and to different families of fluids and the results are significant in the comparison and in the relative classification of working fluids with regards to their thermal stability.As to the three hydrocarbons considered, the cyclo-pentane results thermally very stable: at 350°C, after eighty hours, the rate of decomposition is about twenty times lower than the corresponding value for n-pentane. The toluene sample remains remarkably stable at higher temperatures, confirming its potential application in the so-called high temperature Rankine cycles: at 400°C the rate of decomposition is the same of that of n-pentane at 315°C and of that of cyclo-pentane at 375°C.

Part-Load Performance of aWet Indirectly Fired Gas Turbine Integrated with an Organic Rankine Cycle Turbogenerator

Over the last years, much attention has been paid to the development of efficient and low-cost power systems for biomass-to-electricity conversion. This paper aims at investigating the design- and part-load performance of an innovative plant based on a wet indirectly fired gas turbine (WIFGT) fueled by woodchips and an organic Rankine cycle (ORC) turbogenerator. An exergy analysis is performed to identify the sources of inefficiencies, the optimal design variables, and the most suitable working fluid for the organic Rankine process. This step enables to parametrize the part-load model of the plant and to estimate its performance at different power outputs. The novel plant has a nominal power of 250 kW and a thermal efficiency of 43%. The major irreversibilities take place in the burner, recuperator, compressor and in the condenser. Toluene is the optimal working fluid for the organic Rankine engine. The part-load investigation indicates that the plant can operate at high efficiencies over a wide range of power outputs (50%–100%), with a peak thermal efficiency of 45% at around 80% load. While the ORC turbogenerator is responsible for the efficiency drop at low capacities, the off-design performance is governed by the efficiency characteristics of the compressor and turbine serving the gas turbine unit.

Binary liquid metal–organic Rankine cycle for small power distributed high efficiency systems

There is a common interest in the distributed power generation: generally for the combined production of electrical and thermal energy and often, although not necessarily, in association with renewable energies as heat sources for the prime mover. For example, in the field of distributed concentrated solar power generation of small size, the gas engine technology now seems to be prevailing (Stirling engines operating at maximum temperatures of 600–800 ℃, with peak net efficiencies at 20–30% and power up to several kilowatts are commonly considered). Organic Rankine engines, fed by biomass, in the power range of about 1 MW are actually a standard. From a strictly thermodynamic point of view, the binary cycle technology, accomplished by alkaline metal Rankine cycle as the topping cycle and a Rankine cycle with organic fluid as the bottoming cycle, could be an advantageous alternative. By their very nature, Rankine cycles have good thermodynamic qualities and, potentially, their thermodynamic performance, for the same maximum and minimum temperatures, could be better than that of a gas cycles. This paper discusses the possibility of adopting binary cycles with a power level in the order of tens of kilowatts. Following an overview of the characteristics of alkaline metals and a look at the possible organic fluids that can be employed in Rankine engines at high temperature (400 ℃), assuming a limit condensation pressure of 0.05 bar, the thermodynamic efficiency of binary cycles was evaluated and the preliminary sizing of turbines was discussed. The results (e.g. a net cycle efficiency of around 0.46, with maximum temperature of 800–850 ℃) appear encouraging, even though setting up the systems may be far from easy. For instance, there are difficulties due to the extremely high volumetric expansion ratios of bottoming cycles (400–600, an order of magnitude larger than those of the topping cycles with alkaline metals that we considered), which are moreover associated with a very low minimum pressure and elevated number of revolutions of the turbomachinery (50,000–200,000 r/min). Without doubt, the design tends to be easier as the power levels increase and the minimum condensation pressure for the bottoming cycle rises. Although the authors know of no activity in progress on binary cycles at present, the interesting prospects suggest the topic deserves further study and research.

Assessment of a new integrated solar energy system for hydrogen production

In this paper, a novel integrated system that combines photocatalysis, photovoltaics, thermal engine and chemical energy storage for better solar energy harvesting is assessed using energy and exergy methods. The system generates hydrogen and sulfur from sulfurous waters specific to chemical and petrochemical industries. The solar light is split into three spectra using optical surfaces covered with selected dielectric coatings: (i) the high energy spectrum, consisting of photons with wavelengths shorter than ∼500nm, is used to generate hydrogen from water photolysis, (ii) the middle spectrum with wavelengths between ∼500nm and ∼800nm is used to generate electricity with photovoltaic (PV) arrays and (iii) the long wave spectrum of low energy photons with wavelengths longer than ∼800nm is used to generate electricity with a thermally driven Rankine engine (RE). The electricity generated by PV and RE is employed to generate additional hydrogen by electrolysis and to drive auxiliary devices within the system. A model is developed based on conservation equations and transport equations applied for each essential component of the system. The model allows for assessment of system performance and the comparison with other solar hydrogen production systems. A case study for an oil sands exploitation area where sulfurous aqueous wastes and hydrogen demand exist – Calgary (Alberta) – is presented. A solar tower configuration is selected as the best choice for a large scale system with 500MW light harvesting heliostat field. Hourly predictions of system output are obtained. The devised system requires 5526acres of land for the solar field and produces 41.4t hydrogen per day. If a conventional solar tower would be used instead which generates power and is coupled to a water electrolysis system the hydrogen production is lower, namely 28.7t/day. An economic scenario is considered by assuming that the co-produced sulfur and hydrogen are both valorized on the market for 25years with a levelized price of 1.65$/kg out of which 10% represents operation and maintenance costs. It is shown that the system is feasible provided that the required equity investment of capital is inferior to M$ 500.

Review of Waste Heat Recovery Mechanisms for Internal Combustion Engines

The demand for more fuel efficient vehicles has been growing steadily and will only continue to increase given the volatility in the commodities market for petroleum resources. The internal combustion (IC) engine utilizes approximately one third of the chemical energy released during combustion. The remaining two-thirds are rejected from the engine via the cooling and exhaust systems. Significant improvements in fuel conversion efficiency are possible through the capture and conversion of these waste energy streams. Promising waste heat recovery (WHR) techniques include turbocharging, turbo compounding, Rankine engine compounding, and thermoelectric (TE) generators. These techniques have shown increases in engine thermal efficiencies that range from 2% to 20%, depending on system design, quality of energy recovery, component efficiency, and implementation. The purpose of this paper is to provide a broad review of the advancements in the waste heat recovery methods; thermoelectric generators (TEG) and Rankine cycles for electricity generation, which have occurred over the past 10 yr as these two techniques have been at the forefront of current research for their untapped potential. The various mechanisms and techniques, including thermodynamic analysis, employed in the design of a waste heat recovery system are discussed.

A high-efficiency solar Rankine engine with isothermal expansion

Though the principle of the solar Rankine cycle is well known, with several examples reported in the literature, there is yet a scarcity of engines that could be efficiently applied in small-scale (<100 KW) applications. Hence, this paper presents a variant of the engine that uses an isothermal expansion to achieve a theoretical efficiency close to the Carnot limit. Generation of steam inside the power cylinder obviates the need for an external boiler. The device is suitable for slow-moving applications and is of particular interest for driving a batch-desalination process. Preliminary experiments have shown cycle efficiency of 16%, and a high work ratio of 0.997. ©The Author 2013. Published by Oxford University Press. All rights reserved.

Simulation and economic analysis of a CPV/thermal system coupled with an organic Rankine cycle for increased power generation

In concentrating photovoltaic (CPV) systems the incident solar radiation is multiplied by a factor equal to the concentration ratio, with the use of lenses or reflectors. This is implemented, in order to increase the electric power production, since this value has a linear dependence from the incident radiation. Therefore, the specific energy production of the cells (kWh/m 2) radically increases, but due to this high intensity CPVs consequently operate at elevated temperatures, because heat dissipation to the environment is not so intense and heat produced cannot naturally convected. This temperature increase not only leads to a reduction of their electric efficiency, but also it must be dissipated, since issues regarding their degradation and reduction of their lifetime might arise. There are many reported ways of removing this heat, either by adding a cooling unit on the back side of the CPV module, or by recovering with possible uses in buildings, industry, additional power production or even desalination of seawater. The current work is actually a feasibility study, concerning a concentrating photovoltaic/thermal (CPV/T) system, where the heat produced is recovered by an organic Rankine cycle (ORC) for additional power production. A pump drives the organic fluid of the cycle, which is evaporated in the tubes of the CPV/T and driven to an expander for mechanical power production. For the condensation of the organic fluid several possible alternatives can be applied. That way, the PV cells can be cooled effectively and increase their electrical efficiency, while the recovered heat is designated to produce additional electric energy through the organic Rankine process, when the expander of the Rankine engine is coupled to a generator. The scope of the present work is to investigate an alternative application of concentrating PV modules through exploiting the generated heat by the ORC process and combining both technologies into an integrated system. The design of the system is presented in details, along with an optimization of some main parameters. The performance of the system will also be examined and compared with an equivalent conventional CPV system, referring to their design points. Finally, the annual and daily performance will be studied, which is a more realistic indicator, concerning the increased efficiency this integrated system is expected to have, followed by a cost analysis, in order to examine its economic feasibility as well.

Exergy analysis of micro-organic Rankine power cycles for a small scale solar driven reverse osmosis desalination system

Exergy analysis of micro-organic Rankine heat engines is performed to identify the most suitable engine for driving a small scale reverse osmosis desalination system. Three modified engines derived from simple Rankine engine using regeneration (incorporation of regenerator or feedliquid heaters) are analyzed through a novel approach, called exergy-topological method based on the combination of exergy flow graphs, exergy loss graphs, and thermoeconomic graphs. For the investigations, three working fluids are considered: R134a, R245fa and R600. The incorporated devices produce different results with different fluids. Exergy destruction throughout the systems operating with R134a was quantified and illustrated using exergy diagrams. The sites with greater exergy destruction include turbine, evaporator and feedliquid heaters. The most critical components include evaporator, turbine and mixing units. A regenerative heat exchanger has positive effects only when the engine operates with dry fluids; feedliquid heaters improve the degree of thermodynamic perfection of the system but lead to loss in exergetic efficiency. Although, different modifications produce better energy conversion and less exergy destroyed, the improvements are not significant enough and subsequent modifications of the simple Rankine engine cannot be considered as economically profitable for heat source temperature below 100 °C. As illustration, a regenerator increases the system’s energy efficiency by 7%, the degree of thermodynamic perfection by 3.5% while the exergetic efficiency is unchanged in comparison with the simple Rankine cycle, with R600 as working fluid. The impacts of heat source temperature and pinch point temperature difference on engine’s performance are also examined. Finally, results demonstrate that energy analysis combined with the mathematical graph theory is a powerful tool in performance assessments of Rankine based power systems and permits meaningful comparison of different regenerative effects based on their contribution to systems improvements.

On site experimental evaluation of a low-temperature solar organic Rankine cycle system for RO desalination

The paper presents the on site experimental evaluation of the performance of a low-temperature solar organic Rankine cycle system (SORC) for reverse osmosis (RO) desalination. This work is a research step forward to the experimental evaluation of the SORC under laboratory conditions, where the system was tested using an electric brake as load and an electric thermal heater as heat supply. The difference is that solar collectors have been applied as heat supply and there has been a realistic investigation of the performance of the system under the conditions implied by solar energy. The thermal energy produced by the solar collectors’ array evaporates the refrigerant HFC-134a in the pre-heater–evaporator surfaces of the Rankine engine. The superheated vapour is then driven to the expander, where the generated mechanical work produced from expansion drives the high-pressure pump of the RO desalination unit. The superheated vapour at the expander’s outlet is directed to the condenser and condensates. Finally, the saturated liquid at the condenser outlet is pressurized by a positive displacement pump and the thermodynamic cycle is repeated. A special energy recovery system of Axial Pistons Pumps (APP) has been integrated into the RO unit to minimise the specific energy consumption. The results prove that the above concept is technically feasible and continuous operation is achieved under the intermittent availability of solar energy. However, considerably low efficiency has been observed, in comparison with the results taken under controlled thermal load. Nevertheless, it becomes apparent that further optimisation work is required to improve the system efficiency. The research work has been done within the framework of COOP-CT-2003-507997 contract, partly financed by EC.

Technical and economic comparison between PV-RO system and RO-Solar Rankine system. Case study: Thirasia island

This paper presents the technical characteristics as well as an economic comparison of two autonomous desalination systems. The first system concerns the laboratory experimental results of a direct coupled PV-SWRO desalination system without batteries equipped with a hydraulic energy recovery device of the Clark pump type. The PV system consists of 18 Arco-Solar monocristaline PV panels, with total peak power of 846 W. These panels are directly connected to a brushless DC motor of 510 W, powering a rotary vane pump as low pressure pump. The clark pump utilizes the high pressure brine to intensify the feed pressure to the RO desalination system. The desalination system has a capacity of 0.1 m 3/h. The specific energy recovery of this system has been experimentally found to be in the range of 3.8–6 kWh/m 3 depending on the feed water temperature and the feed water salinity. The second system is an organic solar Rankine system for RO desalination. The heat produced by the solar collectors’ field is transformed to mechanical power through an organic Rankine cycle process. The shaft power produced drives the high pressure pump of the RO unit, initiating the desalination process. The prototype system consists of vacuum tube solar collectors 90 m 2, a Rankine engine of 100 kW and an RO unit of 0.3 m 3/h. The energy recovery system of the RO unit consists of a pair of axial piston pumps (APP) manufactured by Danfoss. One of them operates reversely, as turbine, exploiting the hydraulic energy of the brine stream. The aim of the economic analysis is not only to estimate the cost of each system but also to compare them on the same basis, in order to allow a meaningful comparison. Hence, each system cost is determined having utilised the same economic assumptions like interest, operating expenses, etc. Moreover, these desalination systems can provide sufficient amounts of potable water for the local needs of a small island, like Thirasia, (Cyclades, Greece) at a cost as low as 7.77 ɛ/m 3, very close to that of water hauling.

Experimental evaluation of an autonomous low-temperature solar Rankine cycle system for reverse osmosis desalination

The present paper regards the experimental evaluation of the performance under laboratory conditions, of a low-temperature solar organic Rankine cycle system for reverse osmosis (RO) desalination. The operation principle of the system is given briefly below. Thermal energy produced by a solar collectors' array evaporates the refrigerant (HFC-134a) in the evaporator surface of Rankine engine. The super-heated vapour is driven to the expander where the generated mechanical work produced from expansion drives the RO unit high-pressure pump. The vapour at the expander's outlet is directed to the condenser and condensates. The saturated liquid at the condenser outlet is then pressurised using a piston-diaphragm pump and the thermodynamic cycle is repeated. The design of the system has already been done and presented in [1]. For manufacturing the prototype system, the design results have been used. In this paper the experimental results derived from the laboratory tests are illustrated. The next research step is the evaluation of the system performance on site, under real climatic conditions. The main difference of the above two experimental cases is that in laboratory tests the thermal energy source used is an electric heater of 100 kW, capable to operate at partial thermal load, which substitutes and simulates the behaviour of solar collectors.

A hybrid power generation system: solar-driven Rankine engine-hydrogen storage

This paper reports on the feasibility of a hybrid power generation system consisting of a solar energy-driven Rankine engine and a hydrogen storage unit. Solar energy, the power for the hybrid system, is converted into electrical power through a combination of a solar collector, a tracking device to maintain proper orientation with the sun and a Rankine cycle engine driving an electrical power generator. Excess electricity is utilized to produce hydrogen for storage through electrolysis of water. At the solar down time, the stored hydrogen can be used to produce high-quality steam in an aphodid burner to operate a turbine and with a eld modulated generator to supplement electric power. Case studies are carried out on the optimum conguration of the hybrid system satisfying the energy demand. A numerical example based on the actual measured solar input is also included to demonstrate the design potential. Copyright 2001 John Wiley & Sons, Ltd.

A hybrid power generation system: solar‐driven Rankine engine–hydrogen storage

This paper reports on the feasibility of a hybrid power generation system consisting of a solar energy-driven Rankine engine and a hydrogen storage unit. Solar energy, the power for the hybrid system, is converted into electrical power through a combination of a solar collector, a tracking device to maintain proper orientation with the sun and a Rankine cycle engine driving an electrical power generator. Excess electricity is utilized to produce hydrogen for storage through electrolysis of water. At the solar down time, the stored hydrogen can be used to produce high-quality steam in an aphodid burner to operate a turbine and with a field modulated generator to supplement electric power. Case studies are carried out on the optimum configuration of the hybrid system satisfying the energy demand. A numerical example based on the actual measured solar input is also included to demonstrate the design potential. Copyright © 2001 John Wiley & Sons, Ltd.

Formulation and analysis of the heat pipe turbine for production of power from renewable sources

The heat pipe turbine or thermosyphon Rankine engine is a new concept for power generation using solar, geothermal or other available low grade heat sources. The basis of the engine is the thermosyphon cycle, with its excellent heat and mass transfer characteristics, modified to incorporate a turbine in the adiabatic region. The basic configuration is a closed vertical cylinder functioning as an evaporator, an insulated section and a condenser. The turbine is placed in the upper end between the insulated section and condenser section, and a plate is installed to separate the high pressure region from the low pressure region in the condenser. Conversion of enthalpy to kinetic energy is achieved through the nozzles. The mechanical energy developed by the turbine can be converted to electrical energy by direct coupling to an electrical generator. This paper describes the development of the heat pipe turbine from concept to reality, a series of development steps taken to optimise the design and manufacture. Also in this paper, attempts have been made to provide relationships for the developed power in terms of the geometric and thermodynamic parameters and to discuss limitations on the efficiencies of these turbines.