Thermodynamic Cycle Performance Research Articles

Performance Analysis of Wave Rotor Combustor Integration into Baseline Engines: A Comparative Study of Pressure-Gain and Work Cycles

This study presents two concepts for integrating a wave rotor combustor (WRC) into a baseline engine: the wave rotor pressure-gain cycle (WRPGC) and the wave rotor work cycle (WRWC). Performance parameters were calculated under different thermodynamic cycles, and a comparative analysis of the thermodynamic cycles was conducted, considering both the ideal- and actual-loss conditions. Furthermore, the impact of the WRC precompression ratio, turbine inlet temperature, and fixed peak cycle temperature on the thermodynamic-cycle performance was investigated. The results indicate that embedding a WRC into a baseline engine with a compressor pressure ratio higher than 24.0 does not lead to an improvement in the thermal efficiency. However, under a baseline engine pressure ratio of 3.6, the actual-loss WRC cycle achieves efficiency improvements of 40.5% and 49.5% in the WRPGC and WRWC, respectively, compared to the baseline engine cycle. Increasing the wave rotor precompression ratio or the turbine inlet temperature ratio results in greater performance improvements for the WRWC compared to the WRPGC. When the peak cycle temperature of the wave rotor is fixed, there exists a narrow pressure ratio range wherein the WRPGC outperforms the WRWC. Therefore, the WRPGC is more suitable for embedment in baseline engines with lower pressure ratios.

Enhancing Thermal Performance of Thermodynamic Cycle through Zeotropic Mixture Composition Regulation: An Overview

Composition regulation of zeotropic mixture working fluid for a thermodynamic cycle is an effective way to improve energy conversion efficiency, which offers the potential to construct efficient, flexible and intelligent cycles. Current research on cycle construction of zeotropic mixture composition regulation still heavily relies on construction methods using pure working fluids, where the characteristics of flexible composition variations fail to be utilized. In this paper, the research progress of cycle construction methods and composition regulated structures are comprehensively reviewed, aiming to clarify the potential for enhancing a thermodynamic cycle based on composition regulation. The characteristics of different cycle construction methods are firstly summarized and compared. Then, the composition-regulated structures of a physical-based method and chemical-based method are introduced, and the composition regulation performance are also concluded. Finally, a future outlook on the cycle design and structure design is provided. The review results show that the combination of 3D construction method and superstructure/intelligences construction method has the potential to maximize the cycle performance, where the improvement of each thermal process and the optimization of complex cycles can be considered simultaneously. The composition regulation based on a passive physical method has the advantage of being readily applicable; however, the composition regulation range is limited. In addition, the distillation and hydrate method have a wider regulation range through extra energy input, where the trade-off between energy consumption and cycle performance improvement should be considered in the future. This study greatly assists in the design of thermodynamic cycles involving zeotropic mixture composition regulation and the corresponding composition regulation structures.

Preparation and Analysis of Experimental Findings on the Thermal and Mechanical Characteristics of Pulsating Gas Flows in the Intake System of a Piston Engine for Modelling and Machine Learning

Today, reciprocating internal combustion engines are used in many branches of the economy (power engineering, machine engineering, transportation, and others). In order for piston engines to meet stringent environmental and economic regulations, it is necessary to develop complex and accurate control systems for the physical processes in engine elements based on digital twins, machine learning, and artificial intelligence algorithms. This article is aimed at preparing and analysing experimental data on the gas dynamics and heat transfer of pulsating air flows in a piston engine’s intake system for modelling and machine learning. The key studies were carried out on a full-scale model of a single-cylinder piston engine under dynamic conditions. Some experimental findings on the gas-dynamic and heat-exchange characteristics of the flows were obtained with the thermal anemometry method and a corresponding measuring system. The effects of the inlet channel diameter on the air flow, the intensity of turbulence, and the heat transfer coefficient of pulsating air flows in a piston engine’s inlet system are shown. A mathematical description of the dependences of the turbulence intensity, heat transfer coefficient, and Nusselt number on operation factors (crankshaft speed, air flow velocity, Reynolds number) and the inlet channel’s geometric dimensions are proposed. Based on the mathematical modelling of the thermodynamic cycle, the operational and environmental performance of a piston engine with intake systems containing channels with different diameters were assessed. The presented data could be useful for refining engineering calculations and mathematical models, as well as for developing digital twins and engine control systems.

Combining cubic equations with group contribution methods to predict cycle performances and design working fluids for four different organic Rankine cycles

• The property deviations are obtained and analyzed by PR, VTPR, GCM-PR and GCM-VTPR. • The prediction deviations of models are investigated for four different ORCs. • Novel working fluids are designed for subcritical and transcritical cycles. Selecting high-efficient and environmentally friendly working fluids has always been the research focus of Organic Rankine cycle (ORC). Thus, in this work, based on the group contribution method (GCM) and cubic equation of state (CEOS), relationships between molecular structures and cycle performances are established to design working fluids for subcritical and transcritical cycles. In order to determine the calculation deviation, Peng-Robinson (PR) and volume translated Peng-Robinson (VTPR) models are firstly employed to predict the entropy, enthalpy and density. Meanwhile, the two equations are combined with GCMs to estimate these properties. Thereafter, cycle performances are predicted for four different ORCs, namely subcritical basic/regenerative cycles, transcritical basic/regenerative cycles. The obtained results show that PR and VTPR have satisfied and equivalent accuracy for the calculation of thermodynamic properties and cycle performances. Meanwhile, although the calculation deviations of GCM-CEOS are higher than those of CEOS, the deviations caused by GCM-CEOS are still within acceptable limits. For the subcritical cycle, average absolute relative deviations (AARDs) of net work and cycle efficiency are respectively less than 2.251% and 2.528%. As for the transcritical cycle, the corresponding AARDs are smaller than 9.168% and 8.364%. Based on the GCM-CEOS, working fluid can be designed for the four ORCs. Thus, a design case of working fluid is provided under a given heat source and PR is employed for simplicity. In the design process, when a working fluid is generated by combining groups, the corresponding cycle parameters are optimized with the target of maximizing output work. Thereafter, environmental and safety properties are furtherly considered to determine the optimum fluid. It is discovered that the optimum fluid for subcritical basic and regenerative cycles is R245cb, while R272fa and 1,1,2-trifluoropropane are respectively selected for transcritical basic and regenerative cycles.

Energy, exergy, and exergoeconomic analysis of a polygeneration system driven by solar energy with a thermal energy storage tank for power, heating, and freshwater production

A trigeneration system based on parabolic trough solar collectors and thermal energy storage tank is devised for simultaneous power, heating, and freshwater production. The proposed system is analyzed from energy, exergy, and exergoeconomic viewpoints. Moreover, a parametric analysis was applied to evaluate the effects of some basic thermodynamic parameters cycle performance. Also, the optimum performance of the system in two optimization scenarios is found by applying the multi-objective genetic algorithm and using LINMAP decision-making method. The results revealed that the system could yield net output power, heating capacity, and freshwater rate of370.1kW,2423kW, and1.34kg/s, respectively. The energy and exergy efficiencies, coefficient of performance, and the total cost rate of the product are obtained as34.78%,13.42%,0.49, and176.73$/h. Also, it is revealed that the solar section is responsible for56% of the overall exergy destruction rate. The parametric study showed that increment of pinch point temperature of RORC evaporator results in lower energy and exergy efficiencies and higher total cost rate of products. Also, the final optimal solution selected by the LINMAP method is a maximum exergy efficiency of19.87% and the minimum cost rate of157.73$/h for the second optimization scenario.

Sensitivity of transcritical cycle and turbine design to dopant fraction in CO2-based working fluids

Abstract Supercritical CO2 (sCO2) power cycles have gained prominence for their expected excellent performance and compactness. Among their benefits, they may potentially reduce the cost of Concentrated Solar Power (CSP) plants. Because the critical temperature of CO2 is close to ambient temperatures in areas with good solar irradiation, dry cooling may penalise the efficiency of sCO2 power cycles in CSP plants. Recent research has investigated doping CO2 with different materials to increase its critical temperature, enhance its thermodynamic cycle performance, and adapt it to dry cooling in arid climates. This paper investigates the use of CO2/TiCl4, CO2/NOD (an unnamed Non-Organic Dopant), and CO2/C6F6 mixtures as working fluids in a transcritical Rankine cycle implemented in a 100 MWe power plant. Specific focus is given to the effect of dopant type and fraction on optimal cycle operating conditions and on key parameters that influence the expansion process. Thermodynamic modelling of a simple recuperated cycle is employed to identify the optimal turbine pressure ratio and recuperator effectiveness that achieve the highest cycle efficiency for each assumed dopant molar fraction. A turbine design model is then used to define the turbine geometry based on optimal cycle conditions. It was found that doping CO2 with any of the three dopants (TiCl4, NOD, or C6F6) increases the cycle’s thermal efficiency. The greatest increase in efficiency is achieved with TiCl4 (up to 49.5%). The specific work, on the other hand, decreases with TiCl4 and C6F6, but increases with NOD. Moreover, unlike the other two dopants, NOD does not alleviate recuperator irreversibility. In terms of turbine design sensitivity, the addition of any of the three dopants increases the pressure ratio, temperature ratio, and expansion ratios across the turbine. The fluid’s density at turbine inlet increases with all dopants as well. Conversely, the speed of sound at turbine inlet decreases with all dopants, yet higher Mach numbers are expected in CO2/C6F6 turbines.

Feasibility of using near‐azeotropic refrigerant mixture R290/R1234ze(E) as substitute for R22

AbstractThe flammability and explosiveness are the disadvantages of the application of R290 practically as an alternative refrigerant of R22. However, adding flame‐retardant R1234ze(E) to R290 can make up for those shortcomings. The refrigerant mixture R290/R1234ze(E) with mass ratio 55%:45% (coded RC01) was proposed to replace R22. The data of RC01 were obtained by calculating using the refrigerant software REFPROP9.1. The environmental impact indexes, temperature glide characteristics, thermodynamic and thermophysical properties, theoretical thermodynamic cycle performances, safety, and lubrication properties of RC01 were analyzed and compared with that of R22, R410A, R407C, R290, R1234ze(E), respectively. The results show that the RC01, with the ozone depletion potential of 0 and global warming potential of 12, is a near‐azeotropic refrigerant whose glide temperature is approximately 0, and it has better thermodynamic and thermophysical properties as well as theoretical thermodynamic cycle performances. The RC01 also has good lubrication characteristics and low flammability. So it is technically feasible to replace R22.

Understanding the 3D construction method of thermodynamic cycle: Insights from limiting performance of pure working fluid

The 2D temperature-entropy diagram, which is commonly applied to construct and analyze conventional thermodynamic cycles, cannot clearly express novel thermodynamic cycles with multi-working fluids. The 3D construction method provides a methodological guidance to the construction and analysis of novel thermodynamic cycles. In order to understand the mechanism of the 3D construction method, in this study, the limiting performance of 3D thermodynamic cycle with pure working fluid is analyzed and compared with the limiting performance of organic Rankine cycle. Based on the diagram of the 3D coordinates in terms of temperature, entropy, and mass flow rate, the 3D limiting thermodynamic cycle is defined and decoupled into two limiting organic Rankine cycle first. Then, equations of limiting thermal efficiency and thermodynamic perfection are derived based on pure working fluid. Three parameters affecting limiting performance are revealed, namely the latent heat, the slope of the saturated liquid line in the temperature-entropy diagram, and the separation quality. Lastly, effects of key operating parameters on the limiting efficiency of the 3D cycle are analyzed. With the increase of high temperature or middle temperature, the limiting thermal efficiency increases, and thermodynamic perfection increases first and then declines. With the increase of separation quality, the limiting thermal efficiency shows a downward trend. However, the trend of thermodynamic perfection with separation quality depends on values of high temperature and middle temperature. Besides, the limiting performance between the 3D cycle and conventional organic Rankine cycle is compared. The limiting thermodynamic perfection of 3D cycle using R245fa is 7.3%-16.42% higher than that of conventional organic Rankine cycle.

Thermodynamic and exergy analysis of 2 MW S-CO2 Brayton cycle under full/partial load operating conditions

Supercritical carbon dioxide (S-CO2) Brayton cycle with high efficiency and compact structure merits is proposed as an ideal candidate power cycle driven by new energy. Considering the characteristic curves of compressor and heat exchangers, a 2 MW shunt type S-CO2 Brayton cycle based on waste heat recovery is designed to match the thermodynamic parameters of experimental prototype. Then the thermodynamic parameters of the cycle and each component are calculated adopting Ebsilon code. From both the thermal and exergy efficiency viewpoints, the changing laws of thermodynamic parameters and cycle performance with the electricity production are studied under partial load conditions. Results show the highest exergy loss ratio in cycle comes from the furnace, followed by the regenerator and cooler, which are 58.72%, 10.81% and 5.06%, respectively. The exergy efficiency changing law of regenerator with the electricity production greatly affects the exergy loss ratio distribution of all the components. Both the thermal and exergy efficiencies decrease as the electricity production decreases, and the electricity generation efficiency, electricity supply efficiency, and exergy efficiency are 41.57%, 27.20% and 33.59% respectively under full load condition. The present research may lay a foundation for the components’ optimization design, system integration and operation regulation program development during the demonstration unit construction.

Vapor–Liquid Equilibrium Prediction of Refrigerant Mixtures with Peng–Robinson Equation of State and Binary Interaction Parameters Calculated Through Group Contribution Model

Vapor–liquid equilibrium (VLE) properties of refrigerant mixtures are essential to the analysis of thermodynamic cycle performance. The accurate value of binary interaction parameter (kij) for classical Van der Waals (VDW) mixing rules is highly significant for the VLE prediction of mixtures. Therefore, in this contribution, a theoretical correlation for kij is derived as a function of the activity coefficients, which are obtained from the group contribution model UNIFAC. So that, the widely applied Peng–Robinson equation of state with the VDW mixing rule can be predictable for any refrigerant mixtures, according to the existing group contribution values. 18 alternative refrigerant mixtures and two GE models, namely MHV1 and WS are used to exhibit the capacities and limitations of the proposed VDW. The calculated results show that the developed VDW can correlate the VLE experimental data well in most cases. Compared with the MHV1 and WS, the proposed model has better VLE prediction, especially for HFCs + HFCs/HFOs mixtures. Thereafter, VLE of 6 refrigerant mixtures are obtained by GC-VTPR. The comparison shows that the accuracy of VDW model is comparable with that of GC-VTPR. Furthermore, mixture densities at different temperatures and pressures are predicted by the developed VDW and GC-VTPR. Results show that GC-VTPR has better density prediction than VDW and the largest deviation of VDW between predicted results and experimental data is 7.04% for R125 + R143a.

Thermodynamic Analysis on the Performance of a Low-Enthalpy Geothermal Field Using a CO 2 Supercritical Binary Cycle

The exploitation of geothermal energy can play a significant role for providing clean and renewable energy, especially when environmentally-friendly working fluids are used for power production. Along these lines, in the present work a thorough analysis is attempted on the thermodynamic performance and the power production potential of a binary cycle, using supercritical carbon dioxide (sCO2) as working fluid, for the exploitation of a low-enthalpy geothermal field, located in Sidirokastron, Greece. As regards the associated analysis, simplified thermodynamic models of the sCO2 cycle were developed, attempting to incorporate the binary-cycle main components performance characteristics, based on the literature-available data of similar applications. For further improvement of the thermodynamic cycle performance, the use of preheating of the working fluid after the condenser, with the use of solar power, was also considered. The effect of cycle heat-addition pressure and heat-rejection temperature conditions were assessed through parametric studies, taking into consideration the annual regional variations. Furthermore, the effect of the technology level of the critical cycle components, such as the heat exchangers, on the thermodynamic cycle performance was considered. The results were compared to similar, low-enthalpy configurations described in literature. The aforementioned analysis clearly reveals the effect of cycle-operating conditions on the thermodynamic performance of the binary cycle and the high potential of using sCO2 as working fluid, for the exploitation of low-enthalpy geothermal fields, in the pursue of an environmentally-friendly power production.

Entransy analysis of reversible thermodynamic cycles based on the conservation of entransy equation and its application

Entropy analyses and entropy generation analyses have been widely used to analyze and optimize thermal processes. For instance, the entropy generation minimization principle has been used to optimize heat transfer processes, heat transfer systems and thermodynamic cycles. However, some studies have reported that the entropy generation minimization principle cannot derive the optimal results for pure heat transfer processes and heat transfer systems without heat-work conversion processes. The concept of entransy and the principle of the least entransy dissipation-based thermal resistance were proposed for these problems, and they have been widely applied to optimize pure heat transfer processes and systems. Besides, the concept of work entransy was developed for irreversible thermodynamic cycles involving heat-work conversion processes, and it is defined as the product of the work and the temperature. This concept was then used as the entransy analysis approach to optimize thermodynamic cycles. However, previous studies applying the work entransy concept mainly focused on (1) the relation between the work entransy loss and the endoreversible thermodynamic cycle efficiency, and (2) the optimization of practical thermodynamic cycles involving irreversible processes. There have been few such studies of reversible thermodynamic cycles or combined cycles. This article analyzes reversible thermodynamic cycles and combined thermodynamic cycles using the entransy analysis method with a derivation of the conservation of entransy equation. First, the entransy conservation equation for a reversible thermodynamic process is derived, which introduces the concept of heat entransy and heat-work entransy flow. They are both process dependent physical quantities. The corresponding entransy conservation equation is then derived for a reversible thermodynamic cycle. The equation shows that there are two different conservation equations for reversible thermodynamic cycles, i.e. the energy conservation equation (1st law of thermodynamics) and the entransy conservation equation. Meanwhile, according to thermomass theory, the entransy is nothing else but the relative energy. The entransy conservation equation can be used to analyze the performance of reversible thermodynamic cycles. On the other hand, since the entropy returns to the initial value in a reversible thermodynamic cycle, an entropy analysis cannot evaluate the performance of reversible thermodynamic cycles. Second, a combined heat engine-heat pump cycle is taken as an example application of entransy analysis. In the philosophy of entransy analyses, the performance indicator of the combined cycle is its net heat entransy flow. For the properly chosen parameters, the combined cycle can be regarded as an ideal voltage transformer. Therefore, this kind of combined cycle can be referred to as a temperature transformer, which is different from the absorption temperature transformer. A diagram is introduced to show the total effect of the combined cycle to help understand the combined cycle. Finally, two practical cases, i.e. combined cycles for heating and refrigeration, are chosen to show applications of this entransy analysis approach. The concept of entransy efficiency of combined cycles is introduced to evaluate the performance of the combined cycles.

Working fluid selection for a combined system based on coupling of organic Rankine cycle and air source heat pump cycle

Abstract The performance of thermodynamic cycle strongly depends on the properties of working fluids. A gas-fuelled hot water system based on coupling of an organic Rankine cycle and an air source heat pump cycle (ORC-ASHP) was investigated in this paper. This system is integrated with a gas burner to provide heat for ORC. The power generated in ORC is used to drive the air source heat pump cycle. Comparisons on the system performance are presented for seven different organic working fluids, with emphasis on the effect of thermodynamic properties of the working fluids. In terms of fuel-to-heat efficiency, benzene, toluene and cyclohexane have better performance for the high temperature heat source. The results indicate that working fluids presenting higher decomposition temperatures shows a higher fuel-to-heat-efficiency. When benzene is used as working fluids, the fuel-to-heat efficiency reaches 161.7% and 139.47% to provide 50 °C and 65 °C hot water respectively.

Use of Ce to Reinforce the Interface of Ni-Rich LiNi0.8 Co0.1 Mn0.1 O2 Cathode Materials for Lithium-Ion Batteries under High Operating Voltage.

Nickel-rich cathode materials are among the most promising cathode materials for high-energy lithium-ion batteries. However, their structural and thermodynamic stability, cycle and rate performances still need to be further improved. In this study, the rare earth element Ce is employed to reinforce the interface of Ni-rich cathode materials both internally and externally. High-valence Ce4+ can easily cause the oxidization of Ni2+ to Ni3+ when doped into the material owing to its strong oxidation performance, thus reducing Li+ /Ni2+ mixing. In addition, the inert Ce3+ ions in transition metal slabs with strong Ce-O bonds can maintain the layered structure at high delithiation state. Furthermore, when the calcination temperature during synthesis is above 500 °C, a CeO2 coating layer will form, which can protect the electrode from erosion by the electrolyte and alleviate the increasing resistance during cycling. The modified Ni-rich materials fabricated with an erosion-resistant CeO2 layer outside and stronger Ce-O bonds inside with reduced Li+ /Ni2+ mixing exhibit excellent electrochemical properties, especially at high operating voltages, for example, the 50th capacity retention at 0.2 C within 2.75-4.5 V is improved from 89.8 % to 99.2 % after the modification.

Thermodynamic performance prediction of rhombic-drive beta-configuration Stirling engine

A single-cylinder rhombic drive beta-configuration Stirling engine, heated and cooled at designated temperature, and fuelled with a fixed amount of Helium gas is used to predict and analyse the thermodynamic cycle performance. A general zero-dimensional numerical model is adapted throughout the prediction of Stirling engine performance. The numerical model is determined based on overall geometrical parameters, working fluid properties, swept and un-swept volume. Schmidt and ideal adiabatic analysis based on methodology presented by Berchowitz and Urieli are carried out to predict the cycle pressure, volumetric displacement, work and energy produced during the expansion and compression processes in the cylinder. Based on the designated working condition, the engine is predicted to generate 500 W of power at engine speed of 300 rpm. The indicated thermal efficiency is found to be 66% based on 90° phase angle setting, 4.5 bar of Helium cylinder mean pressure, 893 K of expansion space temperature and 303 K of cooler space temperature.

A preliminary approach to the 3D construction of thermodynamic cycle based on zeotropic working fluids

Thermodynamic cycle is one of the important ways to convert energy. Improving the efficiency of thermodynamic cycle is still an important way to promote the efficient use of energy at the present stage, and it is also the efficient way to solve the energy crisis. Organic Rankine cycle (ORC), with advantages of simple structure, less maintenance and possibility of small scales, has been widely applied for various types of source in recent years. In exiting researches, the working fluid, as the blood of ORC, is commonly considered to play a vital role in the cycle: (1) relative to ideal cycle, the actual power cycles in the engineering field cannot operate without working fluid; (2) energy efficiency, considering the analysis of second-law efficiency, of actual cycle has a significant decrease due to the introduction of working fluid. The thermos-physical properties parameters, transport parameters and other parameters of working fluid could directly affect the efficiency, safety, stability and economy of ORC. With the increasing requirements on working fluids, it is difficult to find a pure working fluid not only with satisfied thermodynamic performance but also permissible environmental protection and safety. In contrast, zeotropic working fluid, which is mixed with two or more pure working fluids, is easier to meet the requirements of thermos-physical properties, environmental and safety. But at the present stage, the application of zeotropic working fluids in ORC still adapts or employs the methodology originated from what we learn from pure working fluids, which leads to the fact that the efficiency of the ORC using zeotropic working fluids is still low. This paper takes the working fluid as the starting point and uses the characteristics of the component shift to break the limitation of the thermodynamic cycle performance of the single circulating working fluids by adding the mixing and separation processes of zeotropic working fluids. Firstly, the 3D construction method of ORC is proposed by adding the dimensionality of the zeotropic component on the basis of the transmission temperature entropy analysis. Subsequently, the 3D ORC is compared with the traditional 2D ORC, and the advantages of 3D construction of thermodynamic cycle are clearly defined: (a) analysis of variable mass system; (b) reveal the thermodynamic process of composition regulation; (c) explore new ways to reduce the loss of exergy. At last, in view of the utilization of waste heat of internal combustion engine, a component adjustable ORC is proposed, and the application and function of the 3D construction method are expounded. The preliminary exploration results are given for the advantages of the thermodynamic cycle in 3D space relative to the traditional 2D construction method.

Comparative study on different water/steam injection layouts for fuel reduction in a turbocompound diesel engine

Waste heat recovery is considered to be promising way to reduce fuel consumption of the internal combustion engines. Turbocompounding and water/steam injections are two kinds of methods to recover waste heat from the exhaust. This paper focuses on the impacts of different water/steam injection layouts on the fuel saving potentials of a turbocompound engine. Firstly, the simulation model for an 11-L diesel turbocompound engine is established and validated against experimental data. It is shown that the model obtains high accuracy on predicting the engine BSFC, power, in-cylinder peak pressure, exhaust temperature, etc. Based on the simulation model, the impacts of intake port water injection, in-cylinder water/steam injection and turbocharger turbine (CT) inlet steam injection on the engine BSFC are investigated. The influences of injection parameters including injection mass ratio, temperature and timing on the engine performance are studied in detail. The influence mechanisms of the water/steam injection on the thermodynamic cycle performance are also discussed thoroughly. The results show that merely liquid water injection at intake port or in cylinder cannot obtain fuel reduction. It is mainly due to the fact that water evaporating lowers the in-cylinder temperature, resulting in larger ignition delay and lower in-cylinder pressure. Steam injections in cylinder or at CT inlet can both achieve significant fuel reductions. At engine 1300 rpm condition, the steam injection in cylinder or at CT inlet can reduce the BSFC by 10% and 3.5%, respectively.

Modeling of natural gas fueled quadruple cycle for power applications

Performance improvement being a major need of the power sector aims at increasing efficiency, lowering air pollutants and ultimately cost. This paper explores a quadruple cycle, a hybrid of solid oxide fuel cell integrated with gas turbine, steam turbine and organic Rankine cycle totaling four cycles (SOFC-GT-ST-ORC), fueled primarily by natural gas for stationary power generation. A mathematical model of the configuration of the quadruple cycle is developed and the performance investigated through a parametric study of the thermodynamic components. The power output, efficiency and other results were validated with those found in literature. The quadruple cycle produced an efficiency of 66.1% with 1,1,1,2-tetrafluoroethane, R134a as the organic working fluid. This efficiency exceeded the performance of traditional thermodynamic cycles like single steam cycle, combined and triple cycle at similar operating conditions. Lastly, the quadruple cycle presents a potential for optimization with waste heat recovery.

Numerical investigation of MIL-101(Cr)/GrO composite performance in adsorption cooling systems

MIL-101(Cr)/graphene oxide composites were investigated for the application of adsorption cooling. Two composites with two different synthesis techniques were chosen, 2%GrO_syn and 5%GrO_phys, owing to the superior water adsorption uptake of the first and the high thermal conductivity of the latter. The thermodynamic cycle performance of a two-bed adsorption system was evaluated using Simulink software to assess the performance of each composite. Under the operating conditions investigated, the 2%GrO_synthesis composite showed a similar specific cooling power (SCP) and coefficient of performance (COP) to the MIL-101(Cr) system with no change in cycle time and with a lower desorption temperature of 90°C. The 5%GrO_phys composite showed a decreased SCP and an increased COP at the same cycle time. Nevertheless, the desorption temperature of such system decreased from 100°C for the neat material to only 80°C. This highlights the potential of such composites in more efficient adsorption heat pump systems.

The performance of thermodynamic cycles based on the properties of working fluids

With the increase of global energy demand, themodynamic cycles, such as Rankine cycle, refrigeration or heat pump, have been widely employed to generate work or transfer heat. Since these cycles generally consist of a linked sequence of state points with physical properties variables, the physical properties of working fluid are essential to the cycle analysis. They directly determine the design of components, the cycle performance, the cycle stability and safety. However, in the thermodynamic analysis, the determination of cycle performance and the calculation of required physical properties are usually seperated. The thermodynamic peroperties of working fluids are often obtained from the complex experimental equations, so that the relationship between the cycle performance and the working fluids has not been established yet. What′s more, due to the fact that Carnot efficiency doesn′t contain detailed information on the properties of working fluids, a nature idea emerges how to derive the efficiency limit under the constraint of working fluids. Thus, in this work, the influences of thermodynamic properties on power cycles are investigated and the limiting efficiencys are proposed. In order to derive the cycle performances from the physical properties of working fluids, a general cubic equation of state is employed to obtain the residual properties, such as residual enthalpy, residual entropy and residual internal energy. Thereafter, on the basis of the properties of ideal gas, thermodynamic parameters of working fluids at any state are determined. According to the thermodynamic general relationships, the required heat is obtained for four classical processes, namely isochoric, isobaric, isothermal and isentropic processes. Based on the derived expressions, the output work and cycle efficiency are obtained for power cycles including Carnot cycle, Rankine cycle, Brayton cycle and Sterling cycle. The relationship between the cycle performance and the temperature, the properties of working fluids is developed. As a theoretical upper bound of cycle efficiency, Carnot efficiency is only determined by temperatures of heat source and sink. While the output work of Carnot cycle is a function of temperatures and the properties of working fluids. For other power cycles, it can be concluded that the thermodynamic performances are related with temperatures and working fluids, based on the derived expressions from cubic equation of state. Furthermore, compared with the Carnot efficiency under the same heat source and sink, the thermodynamic perfections of cycles are very low in practical engineering. Therefore, performance limits of thermodynamic cycles are investigated on the basis of the characteristics of working fluids in this paper. Limiting performance is derived from the equation of state and the temperature-entropy diagram of working fluids. For Rankine cycle and Brayton cycle, a maximum isobaric slope in the temperature-entropy diagram is employed to cut out the unexploited area from the enclosed area of Carnot cycle, so that the limiting work and efficiency can be obtained from the cycle areas. For Sterling cycle, when the used working fluid is ideal gas, the cycle efficiency is equal to Carnot efficiency. Although the proposed limiting performance can not be achieved by practical cycles, it can provide some theoretical guidance for the operating condition and the optimal design of thermodynamic cycles.