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This paper presents experimental results from a model rocket combustor that uses a gas-centered swirl-coaxial injector element injecting warm oxygen and ambient temperature RP-2 fuel with 900 psia ...

The present study is a thermodynamic analysis of a Regenerative Air-Bottoming combined (RABC) cycle /Steam bottoming combined (RABC) cycle operated by the exhaust gases the topping gas turbine cycle. The fractional mass of exhaust gases passes through the first heat exchanger where it exchanges heat with the compressed air from the air compressor of topping cycle and remaining amount of exhaust gasses passes through a second heat exchanger where it uses to supply heat to RABC cycle or third heat exchanger where it uses to supply heat to RSBC cycle. The energetic and exergetic performance of RABC cycle and RSBC cycle is investigated using turbine inlet temperature (1000 K⩽ TIT⩽1500 K) and mass fraction of exhaust gas (0⩽x⩽1) of the topping cycle as the input variables. The work net output attained its peak value at x=0 which is 22.1 % to 27.3 % for RABC cycle and 22.7 % to 21.5 % for RSBC cycle whereas the maximum thermal efficiency and minimum specific fuel consumption is observed at x=1. Also exergy loss by exhaust gases is minimum at x=0 for both RABC cycle and RSBC cycle. Finally, it is concluded that for the maximum work net output and minimum exergy loss by exhaust gases, RABC cycle is the best option followed by RSBC cycle but for optimum thermal efficiency and minimum specific fuel consumption purely regenerative gas turbine cycle have no comparison with RABC cycle and RSBC cycle.

In this work an intercooled reheat gas/steam combined power cycle with CO2 capture and methanation is studied. CO2 capture and methanation unit is integrated to capture CO2 from the exhaust of gas/steam combined cycle plant and converted it into methane (CH4) so that this methane can be used as additional fuel and hence reduces the amount of carbon emission into the atmosphere. An organic Rankine cycle is integrated between the high-pressure compressor and low-pressure compressor to utilize the heat extraction during the intercooling process. Suitable working fluids for the Organic Rankine cycle have been chosen taking thermophysical properties into consideration such as lower boiling point, critical temperature & pressure and global warming potential. The energy and the mass balance equations have been developed to analyse thermodynamic performance of the proposed combined cycle system. Parametric analysis of the cycle has been performed to evaluate the impact of several cycle variables such as cycle pressure ratio, turbine inlet temperature, condenser temperature, vapor turbine inlet pressure, etc. on the system performance. The study reveals that higher cycle pressure ratio of topping cycle results in less formation of steam in HRSG which further advocates that cycle pressure ratio might be kept low to achieve the high rate of steam generation which again results in increased work output of the cycle. The study reveals that the overall work output of combined system is increased from 220.9 MW to 370 MW by including carbon capture unit at a turbine inlet temperature (TIT) of 1475 K and a cycle pressure ratio of 20.

The present study proposed the water generating system through humidification-dehumidification desalination unit and RO powered by organic Rankine cycle to generate both power and drinking water from the waste heat of Naval Ship by using a low-temperature organic Rankine cycle. Waste heat from the naval ship is used in order to run the topping cycle namely the organic Rankine cycle for power generation which operates the RO system for drinking water. A water-heated humidification dehumidification (HDH) desalination unit is also integrated with the organic Rankine cycle system to produce additional freshwater. The mass and energy balance equations are designed to analyze the thermodynamic performance of the cogeneration of the power-water system at the designed conditions. Suitable working fluids for the organic Rankine cycle are chosen on the basis of thermophysical properties i.e. lower boiling point, critical temperature & pressure and global warming potential. Furthermore, the impact of various vital parameters like extraction pressure, vapor extraction ratio, condenser temperature, turbine inlet pressure, etc. on the performance. It was founded that the impact of extraction parameters on the cycle, the net power, total efficiency and water production is 16.74 kW, 42.10% and 75.18 kg h−1 respectively. The extraction ratio variation causes the improvement in the water production and power generation and lower extraction ratio has better results. The RO System used is direct mechanical coupling which uses the power to run the system and produces the water, 2.4L of drinking water is produced using 16.74 kW power, respectively.

The paper presents 3E (energy, exergy and economic) analysis of a modified Kalina power-cooling vapour absorption cycles (KLPCCs) for better thermo-economic figures of merit to drive affordable energy access and climate change mitigation. The analysis presents a balanced technical and economic conclusion in view of resource management and sustainability. The system utilized a Kalina power-cooling system at the topping cycle and an embedded vapour absorption system (VAB) at the bottoming cycle, which is a novelty. In the modified KLPCC, a supplementary evaporator and heat exchangers are integrated with the bottoming cycle. The considered performance indicators include energy efficiency, exergy efficiency, cooling rate, turbine net output, COP, and cost rate. From the results, about 1077 kW cooling rate was produced, while the energy efficiency, exergy efficiency, COP, and turbine output were estimated at 16.97 %, 8.15 %, 0.706, and 291 kW, respectively. The LCC of $ 1.573 million was achieved, with the break-even point and unit energy cost calculated at five years and 0.0134 $/ kWh, respectively. The outcomes are holistic and adequate for policymakers in the field of energy access and environmental sustainability.

Hybrid solid oxide fuel cells (SOFC) cycles of varying complexity are widely studied for their potential efficiency, carbon recovery and co-production of chemicals. This study introduces an alternative de-coupled fuel cell-gas turbine hybrid arrangement that retains the high efficiency thermal integration of a topping cycle without the high temperature heat exchanger of a bottoming cycle. The system utilizes a solid-state oxygen transport membrane to divert 30%–50% of the oxygen from the turbine working fluid to the intermediate temperature SOFC. Thermodynamic modeling delineates design trade-offs and identifies a flexible operating regime with peak fuel-to-electric efficiency of 75%. Co-production of electricity and high purity hydrogen result in net energy conversion efficiencies greater than 80%. The potential to retrofit existing turbine systems, particularly micro-turbines and stand-by ‘peaker’ plants, with minimal impact to compressor stability or transient response is a promising pathway to hybrid fuel cell/turbine development that does not require turbomachinery modification.

According to the new characteristics of the solid–liquid strap-on launch vehicle and the liquid oxygen/kerosene staged combustion cycle engines, a finite element model of the launch vehicle propuls...

The current paper presents a thermodynamic analysis of an air-bottoming cycle (ABC) operated by the exhaust gasses of a regenerative gas turbine cycle. The partial exhaust heat of a topping gas turbine cycle is utilized to heat the compressed air of the ABC by passing it through a heat exchanger (H.E.2), whereas remaining heat is used to heat the compressed air of the topping cycle before entering a combustion chamber by passing it through a heat exchanger (H.E.1). The effects of the turbine inlet temperature of the topping cycle (1000 K ⩽ $${\text{TIT}}$$ ⩽ 1500 K) and fraction of mass flow rate of the exhaust gas (0 ⩽ $$x$$ ⩽ 1) on the net output, combined thermal efficiency, exergy destruction, exergy loss by exhaust gasses, and specific fuel consumption (SFC) are investigated parametrically for a particular value of the pressure ratio of the topping and bottoming cycles. At $$x = 0$$ , the net output and thermal efficiency of the combined cycle increase by 15.1% and 31.3%, respectively, whereas the SFC decreases by 13.1% and 15.5% at $${\text{TIT}} = 1000\;{\text{K}}$$ and $${\text{TIT}} = 1500\;{\text{K}}$$ , respectively. The exergy destruction of the heat exchanger of the topping cycle increases, whereas that of the bottoming cycle decreases with an increase in x. Overall, in terms of the net output and thermal efficiency, a simple gas turbine cycle with an air-bottoming combined cycle performs better than a simple regenerative gas turbine cycle; however, in view of the exergy loss by exhaust gasses, a simple regenerative gas turbine cycle is better than the combined cycle.

The present investigation is the comparative energy and exergy analysis of a proposed gas turbine (PGT) cycle with a simple gas turbine (SGT) cycle while maintaining the same mass flow rate of fuel in both cycles. In the PGT cycle, a bypass valve (BVP) connects the topping regenerative gas turbine cycle with the air bottoming cycle. It is found that with increase in pressure ratio (rp), turbine inlet temperature (TIT) of topping cycle of PGT cycle decreases continuously in the absence of the BPV, whereas in the PGT cycle with the BVP, the net output and thermal efficiency increased by 20% at rp = 12 and TIT = 900 K to 81% at rp = 4 and TIT = 1000 K. SFC of PGT cycle is reduced by 43–45% for TIT = 900 K and 1000 K, respectively, at rp = 4 as compared to SGT cycle. Also the total exergy destruction and exergetic efficiency of SGT cycle are 62.1–55% less and 26.5–49.7% more, respectively, in contrast to PGT cycle. In addition to this, the exhaust gas exergy losses decrease by 75.5% at the maximum output as compared to the SGT cycle.

The U.S. Department of Energy has a renewed interest in direct power extraction (DPE) technologies, such as a magnetohydrodynamic (MHD) generator, in conjunction with oxy-fuel combustion. As a topping cycle, this configuration can enable efficient CO2 capture, while offsetting oxygen separation penalties. In order to appropriately evaluate these cycles in the context of modern plant configurations, validated modeling tools are needed. In a prior publication (Bedick et al., 2016), an electrical conductivity model was presented for oxy-fuel MHD applications. However, rigorous validation of the model could not be performed due to a lack of high-quality experimental data at relevant conditions. In this publication, validation experiments were performed and relevant parameters quantified using spectroscopic and electrostatic probe diagnostics. Oxygen-methane flames were generated using a Hencken burner and seeded with K2CO3 to increase ionization and electrical conductivity. The electrical conductivity model from Bedick et al. (2016) was integrated into a 3D CFD simulation of a single burner quadrant and a reaction mechanism including potassium kinetics and ionization was utilized. Lineshape fitting techniques were implemented to determine atomic potassium concentration and gas temperature, while appropriate electrostatic probe theory was applied to derive potassium ion concentrations from experimental current-voltage characteristics. Measured quantities are compared to CFD predictions as a function of seed rate and spatial location within the flame, showing good overall agreement. Indirect validation of electrical conductivity predictions is performed using measured quantities, with results falling well within the bounds of measurement uncertainty.

This work stems from the idea of demonstrating the feasibility of using micro combined plants for the simultaneous generation of electrical and thermal energy, by external combustion of low quality fuels. In particular, this study is aimed at acquiring the knowledge necessary for the development of a small power plant consisting of a micro gas turbine and an innovative steam micro-turbine. The topping cycle is carried out with a micro gas turbine coupled with a heat exchanger and an external combustor, in which biomass is burned. For the bottoming cycle an impulse turbine has been adopted, characterized by a variable section nozzle, capable of expanding widely variable steam flow rates, with small efficiency losses. For the purpose of an immediate display of proportions, dimensions and assembly possibilities, 3D printing of a turbine scale model was also made.

High-Temperature Gas-cooled Reactors (HTGRs) have excellent development prospects because of their inherent safety and multiple application areas, such as hydrogen production. The combined cycle coupled with HTGR is a type of cycle for cascade utilization of energy that can efficiently convert heat from HTGR. In this paper, an off-design control strategy, called integral mass flow control, is proposed. The calculation model is discussed, and the performance at partial load is analyzed. When the load changes, the topping cycle is controlled by the inventory, and the bottoming cycle is adjusted by sliding pressure (the temperature of the main steam remains unchanged, and the pressure changes with the load), while the mass flow of the topping cycle and that of bottoming cycle changes synchronously. With this control strategy, the combined cycle coupled with the HTGR can be operated safely and efficiently within a load range of 100% to 30%.

The present study focuses upon the solar powered triple combined cycle consisting of Brayton cycle running on air, Rankine cycle running on steam and organic Rankine cycle on R245fa as working fluid. The absence of combustion in the topping cycle yields zero emission and carbon free power. Topping cycle receives the heat from the molten salt heat exchanger run on Concentrating Solar Power (CSP) technology employing heliostat field solar collectors for providing high temperature to compressed air for being expanded in gas turbine. Discharge from topping cycle is used for providing working fluid for Rankine cycle, and organic Rankine cycle through respective heat recovery systems. This theoretical study includes thermodynamic analysis based on the first and second law of thermodynamics and aims at the evaluation of performance parameters along with identification of optimal operating conditions and estimation of second law efficiency of major constituent components of triple combined cycle configuration. Results obtained from the study can be used for creating a prototype for field trial and future improvements in it. The total power of 331.59 kW per kg of air entering in the topping cycle is produced by the triple combined cycle having gas turbine, steam turbine and organic Rankine cycle turbine along with the thermal efficiency up to 33.15% at cycle pressure ratio of 24 in Indian context. Second law analysis of the considered triple combined cycle helps in identifying the sources of inefficiencies in the cycle and the second law efficiency of the major constituent components is found to be 97.07% for gas turbine followed by 96.05% for the compressor, 81.33% for ORC turbine, 80.31% for LPST and 79.5% for HPST.

Gas-centered swirl-coaxial injectors are typically adopted for staged combustion-cycle engines. The dynamic characteristics of gas-centered swirl-coaxial injectors were investigated in this study b...

The objective of the current research is to analyze the steady state performance of staged combustion cycle liquid propellant rocket engines (SCCLPREs) and to provide a comprehensive case study with all the required technical input data. For this purpose, using the modular concept, engine components are classified into 14 modules and a modeling and simulation platform for SCCLPRE integrated system simulation has been developed in MATLAB Simulink. Space shuttle main engine (SSME) has been selected as a case study, and its static performance has been studied. A total of 34 elements has been taken into account, and using 110 linear/non-linear equations the engine's system modular model has been established. Most of the equations are solved by direct substitution of the initial guesses and iteration through eleven nested iterative loops and a few nonlinear complex equations are solved by Newton–Raphson method. The SSME's throttled performance at four different throttling levels has been simulated, and the effect of throttling has been studied on engine major elements. It is found that by throttling, the pressure of preburners, combustion chamber and high-pressure turbopumps are influenced more than other elements. The simulation mean error at 109% rated thrust level (RTL), 100% RTL, 60% RTL and 50% RTL is 1.63%, 5.76%, 12.91% and 15.28% respectively. Comparing to the previous studies, the simulation accuracy has been enhanced 3% to 7%. The developed model is a basis for further research over SSME and other SCCLPRE.

In this paper, a method for improving the efficiency of the cascade mechanical compression–ejector cooling cycle is described. The considered cooling cycle is the combination of the electrically driven carbon dioxide (CO2) subcritical mechanical compression cooling cycle as a bottoming cycle, and the heat driven ejector cooling cycle as a topping cycle. This cooling cycle is proposed to use superheated CO2 vapor to preheat the working fluid supplied to the vapor generator, thus improving the whole system's efficiency. This paper provides thermodynamic analysis results for the cascade cooling system in a wide range of evaporating temperatures. Refrigerants R245ca, R600, and R601b were investigated as the working fluids for the ejector cooling cycle, and the results show that the proposed cooling cycle is the most effective at low evaporating temperatures.

This study investigates the hybridization scenario of a single-flash geothermal power plant with a biomass-driven sCO2-steam Rankine combined cycle, where a solid local biomass source, olive residue, is used as a fuel. The hybrid power plant is modeled using the simulation software EBSILON®Professional. A topping sCO2 cycle is chosen due to its potential for flexible electricity generation. A synergy between the topping sCO2 and bottoming steam Rankine cycles is achieved by a good temperature match between the coupling heat exchanger, where the waste heat from the topping cycle is utilized in the bottoming cycle. The high-temperature heat addition problem, common in sCO2 cycles, is also eliminated by utilizing the heat in the flue gas in the bottoming cycle. Combined cycle thermal efficiency and a biomass-to-electricity conversion efficiency of 24.9% and 22.4% are achieved, respectively. The corresponding fuel consumption of the hybridized plant is found to be 2.2 kg/s.

The improvement of gas turbines flexibility has been driven by more use of renewable sources of power due to environmental concerns. There are different approaches to improving gas turbine flexibility, and they have performance implications for the bottoming cycle in the combined cycle gas turbine (CCGT) operation. The CCGT configuration is favourable in generating more power output, due to the higher thermal efficiency that is key to the economic viability of electric utility companies. However, the flexibility benefits obtained in the gas turbine is often not translated to the overall CCGT operation. In this study, the flexibility improvements are the minimum environmental load (MEL) and ramp-up rates, that are facilitated by gas turbine compressor air extraction and injection, respectively. The bottoming cycle has been modelled in this study, based on the detailed cascade approach, also using the exhaust gas conditions of the topping cycle model from recent studies of gas turbine flexibility by the authors. At the design full load, the CCGT performance is verified and subsequent off-design cases from the gas turbine air extraction and injection simulations are replicated for the bottoming cycle. The MEL extension on the gas turbine that brings about a reduction in the engine power output results in a higher steam turbine power output due to higher exhaust gas temperature of the former. This curtails the extended MEL of the CCGT to 19% improvement, as opposed to 34% for the stand-alone gas turbine. For the CCGT ramp-up rate improvement with air injection, a 51% increase was attained. This is 3% points lower than the stand-alone gas turbine, arising from the lower steam turbine ramp-up rate. The study has shown that the flexibility improvements in the topping cycle also apply to the overall CCGT, despite constraints from the bottoming cycle.

Improving the overall efficiency of a present power system has significant importance as much as developing renewable energy systems. Because, there are many constructed power systems, which damages the environment by releasing a considerable amount of heat to the environment without use. Therefore, in the present paper, probable single, dual and triple system configurations were assessed in terms of energy, exergy and environment. In the concept of the study, a present gas turbine (GT) cycle was used as topping cycle, while the Rankine cycle (RC) and Kalina cycle (KC) were used as the bottoming cycle. For each single, dual and triple systems, the parametric optimisation of the cycles was made to find best performing system working parameters, in addition to finding probable maximum overall performances. After comprehensive analyses, recoverable heat was found as 30.74% for using single RC and 24.99% for using single KC. By designing a dual system using GT as a topping and RC as a bottoming cycle, the thermal efficiency was calculated as 41.72%. Moreover, it was concluded that 46.39% of total heat input could be recovered by the triple GT-RC-KC. By recovering the heat with these power system configurations, the maximum net power production amounts were found as 1746.80 kW with single RC, 890.14 kW with single KC, 7946.82 kW with dual GT-RC and 8836.96 kW with triple GT-RC-KC. With dual RC-KC configuration integrated to the GT, nearly 1687 tones-CO2/h reduction in CO2 emission amount was achieved. Payback periods of the RC, KC and RC-KC subsystems integrated to the GT were determined as 3.48, 3.22 and 3.39 years, respectively.

A novel cascade refrigeration system with half effect absorption system as the topping cycle and vapor compression system as bottoming cycle has been proposed. Parametric analysis has been performed, and the result of changing different input parameters on the performance of the system has been quantitatively studied. First law and second law analyses have been applied to each component of the system proposed. Total exergy destruction by entire system has been evaluated using second law of thermodynamics and exergy equations. Effect of change in working fluid in bottoming VCR cycle has been done and observed that R507A has least exergy destruction out of chosen working fluids. In addition to this, optimization using minimization of total exergy destruction principle has also been done with proposed system giving less exergy destruction as compared to conventional VCRS system.

The design of single-stage organic Rankine cycle (ORC) systems can be challenging owing to large volumetric expansion ratios and sub-atmospheric condensation pressures. Cascaded systems could lead to more efficient expansion processes, higher condensation pressures, whilst introducing the possibility of two-phase expansion to enhance performance. The aim of this paper is to compare single-stage ORC systems to a novel two-phase cascaded system that combines a two-phase expansion topping cycle and a single-phase bottoming cycle for waste-heat recovery applications. Thermodynamic cycle models are integrated with variable efficiency expander models and discretised heat-exchanger sizing models, and single- and multi-objective optimisation studies are completed for three heat-source temperatures (473, 523 and 573 K). The results indicate the relative performance improvement of cascaded systems increases as the heat-source temperature and relative heat-sink size increase, and could increase power output and first-law thermal efficiency by up to 11.1% and 9.5% respectively. The multi-objective optimisation reveals that for a fixed total heat-transfer area the cascaded systems produce approximately 3.6% and 10.5% more power than the single-stage systems for the 523 and 573 K cases respectively with a heat-sink mass-flow rate of 1 kg/s. This increases to 11.7% and 14.5% for heat-sink mass-flow rate of 4 kg/s.

Gas/steam combined cycles have been increasingly used in power plants due to better energy utilization for getting better performance from them as compared to Brayton cycle based gas turbine plant or the Rankine cycle based steam turbine plant individually. However, there exists ample scope for further improvement in the performance of combined cycles through variations in their arrangements. The present study deals with the thermodynamic analysis of different combined cycle power plant configurations having the simple gas turbine with closed loop cooling of gas turbine blades and varying arrangements in the bottoming cycle. The variation in the bottoming cycle relies upon the effective utilization of energy available in the topping cycle. The bottoming cycle considered uses steam cycle or ammonia water cycle or its combination. The comparison of eight different combined cycle configurations considered in this study reveals that, the work output is maximum for simple gas turbine with bottoming cycle having reheat ammonia water turbine and steam turbine, with an output of 638 kJ/kg of air, first and second law efficiency of 54.95% and 57.87% respectively for ammonia mass fraction of 0.7. The exergy loss is found to be maximum for the combustion chamber followed by heat recovery vapor generator.

A combined Brayton/Brayton power cycle has been investigated using the advanced exergy analysis. The combustion chamber was shown to be the component with the largest exergy destruction. However, the analysis revealed that most of the irreversibility generation at the combustion chamber was endogenous and unavoidable. In contrast, the irreversibility generation at both turbines and both compressors was largely endogenous and avoidable. The total exergy destruction, endogenous unavoidable and exogenous avoidable exergy destruction at the combustion chamber monotonically decreased, while the endogenous avoidable and exogenous unavoidable exergy destruction at the same component initially decreased, reached a minimum, and then increased when the topping cycle pressure ratio was increased. On the other hand, when the bottoming cycle pressure ratio was increased, the endogenous and exogenous unavoidable exergy destruction at the combustion chamber decreased, reached a minimum, and then increased. All four terms of the exergy destruction of the topping cycle turbine and compressor consistently increased with the topping cycle pressure ratio, while their sensitivity to the bottoming cycle pressure ratio was relatively small. Finally, varying the combustion temperature from 1000 K to 1600 K has resulted in a reduction of the total exergy destruction, as well as the endogenous unavoidable, endogenous avoidable, exogenous unavoidable and exogenous avoidable exergy destruction at the least efficient components of the power plant.

Maisotsenko Humid Air Bottoming Cycle (MHABC) is a viable option for the waste heat recovery of gas turbine topping cycle to attain a higher efficiency point of the combined cycle power plant; thus, having a potential of lower CO2 emissions towards environment. In this work, instead of the typically proposed counter flow configuration of the air saturator, a novel mixed flow configuration is proposed. The proposed configuration uses a hybrid cross-flow and a regenerative counter-flow heat and mass exchanger (HMX). This hybrid HMX is numerically simulated to estimate optimal amount of saturated air which can lead to maximum efficiency and power output. The mathematical model of the mixed flow configuration HMX based air saturator is developed by applying mass and energy balance laws on a selected control volume. The results of the air saturator are initially validated using previously published experimental data for air cooling applications. Furthermore, simulations for high-pressure operations suitable for power generation are performed and a parametric analysis shows that optimal mass flow rate ratio between the working air in the dry channel and incoming air for cross-flow part is 0.65. Optimal mass flow ratio between the working air wet channel and working air dry channel for the counter-flow part is 0.5. The integration of hybrid air saturator in MHABC can yield a maximum of ~57 MW of output work and ~42% of thermal efficiency. The proposed system can achieve a 7% increment in total output work, and 9% increment in thermal efficiency as compared to the counter-flow configuration as an air saturator in the bottoming cycle. Furthermore, the proposed system has ~55% fewer carbon footprint as compared to counter-flow configuration alone as an air saturator.

The present work deals with the thermodynamic analysis of a solar-powered triple combined power cycle to generate emission-free power. The triple combined cycle comprises one topping cycle as Brayt...

The combustion characteristics of gas-centered, liquid-swirl coaxial injectors typically used in oxidizer-rich staged combustion cycle engines are numerically investigated at supercritical conditions. Turbulence closure is achieved using large-eddy-simulation techniques, and turbulence/chemistry interaction is modeled by a steady laminar flamelet approach. Gaseous oxygen (GOX) at 687.7 K is injected into the center post while kerosene at 492.2 K is delivered tangentially into the outer coaxial annulus. The operating pressure is 25.3 MPa. Detailed flow structures and flame dynamics are explored. The entire flowfield can be divided into four regimes: propellant injection, flame initialization, flame development, and intensive combustion. The diffusion-dominated flame is anchored in the wake of the GOX post and further enhanced in the downstream taper region. The surface of the coaxial annulus and taper is covered by fuel-rich mixtures and thus protected from thermal flux in the flame zone. Effects of the recess length (from the end of GOX post to the entrance of taper region) on the flow and flame evolution are investigated in depth. The efficiency of propellant mixing and subsequent combustion is found to increase with increasing recess length. The kerosene film is nearly depleted before the exit of the recess region for cases with long recess length, and the flame spreads upwards in the taper region for cases with reduced recess length due to insufficient mixing between GOX and kerosene. In a fully recessed injector without fuel shielding, the injected kerosene behaves like a liquid jet in a crossflow. Two recirculating zones containing fuel-rich mixtures are formed between the injection slit and the headend. A broad flame region is established at the exit of the recess region. In a non-recessed injector, the occurrence of combustion is delayed to the taper region. The flame resides along the taper surface and the injector faceplate, with most of GOX convecting downstream unburned. Results obtained from the present study can also be used to characterize combustion responses to local flow oscillations.

Combustion instability is caused by the coupling of acoustics, hydrodynamics, and flame dynamics. Therefore, understanding the dynamic characteristics of the injector ejecting fuel and oxidizer into the combustion chamber is very important in understanding the combustion instability. This study measures the injector transfer function (ITF) to investigate the dynamics of a gas–gas coaxial jet–swirl injector capable of simulating a full-flow staged combustion cycle. The ITF peaks were generated at the frequency corresponding to the resonant frequency of the tube through which the excited fluid flows. The Kelvin–Helmholtz (K–H) instability was strong when the velocity difference between two flows (ΔV) was large; hence, the ITF was large. The K–H instability weakened and the ITF was small when ΔV ≈ 0, but the Holmboe instability corresponding to the second mode of the K–H instability occurred, such that the perturbation corresponding to twice the excitation frequency became bigger. The results of the dynamic characteristics of the gas–gas coaxial jet–swirl injector in this study will be helpful in understanding the injector dynamics and in solving the combustion instability, which applies to the full-flow staged combustion cycle.

With gradual increase in reactor outlet temperature, the efficient power conversion technology has become one of developing trends of (very) high temperature gas-cooled reactors (HTGRs/VHTRs). In this paper, physical and mathematical models of two combined cycle schemes coupled with the VHTR, Reheated Combined Cycle (RCC) and Regenerative-Reheated Combined Cycle (RRCC), are established. Their topping cycle is a no precooling and no intercooling Brayton cycle, and their bottoming cycle is a supercritical Rankine cycle. The effects and mechanism of key parameters were analyzed. Based on parameter analysis, two schemes were compared within the temperature range of the VHTRs (ROT 950–1200 °C). The analysis shows that, for the combined cycle of the VHTR, by adding a recuperator, can further utilize the helium turbine exhaust heat, then to improve the cycle efficiency. When the ROT is 1050 °C, the cycle efficiency of the RRCC (recuperator's effectiveness 0.4）is 56.4%, which is 2.18% higher than that of the RCC. But because of the regenerative process, the reactor inlet temperature (RIT) of the RRCC is higher than 490 °C, additional reactor pressure vessel (RPV) cooling system is necessary, and it increases the system complexity and reduce the cycle's efficiency. The RIT of the RCC can be controlled below 490 °C, no RPV cooling system is required. Amongst the main parameters, the recuperator's effectiveness and compression ratio are the most important factor affecting the cycle efficiency of the VHTR. The cycle efficiency can be increased by 0.61% when the recuperator's effectiveness is increased by 0.1. The main factors that limit the increase of the recuperator's effectiveness are the RIT and the system flow resistance. When the average compression ratio increases by 0.1, the combined cycle efficiency increases by 0.33% (RCC) and 0.373% (RRCC). The main factors that limit the increase of compression ratio are the manufacturing capacity of magnetic bearings, turbines and compressors. These results provide insights on the combined cycle of the VHTRs, and reveal the effects of key parameters on performance of these cycles. It could be helpful to understand and develop a combined cycle coupled with a VHTR in the future.

Adopting finite-time thermodynamics and building a model of closed endoreversible binary Brayton cycle with two isothermal processes, this paper derives analytical expressions of power output and thermal efficiency of the cycle. The influences of characteristic parameters of compressor pressure ratio, effectivenesses of the hot- and cold-side heat exchangers and effectivenesses of the ordinary regenerator and isothermal regenerator on the cycle performances are analyzed through detailed calculations. The results indicate that the maximum power output is achieved when the optimal pressure ratios of the topping and bottoming cycles are chosen, and the power output increases first and then decreases with the increase of pressure ratio of the topping cycle. The thermal efficiency of cycle gradually increases with the increase of pressure ratio of the topping cycle. It is also discovered that the power output and thermal efficiency of cycle increase by increasing effectivenesses of hot- and cold-side heat exchangers, ordinary regenerator, isothermal regenerator as well as heat reservoir temperature ratio of the cycle. The effects of effectivenesses of regenerators on power output obtained herein differ from those obtained based on classical thermodynamics. The results of this paper can provide some guidelines for the designs of new-type gas turbine plants.

A great amount of energy gets lost through the exhaust of simple, reheat and inter-cooling cycle. Sometimes, this energy is enough to run another cycle or can be used to heat the compressed air from the compressor to the combustion chamber which leads to an increase in the overall efficiency of the plant. Combined cycle is an alternative to utilize the lost energy. In this way, not only the efficiency of the plant increases but it also helps to reduce air pollution and global warming. This paper is a parametric analysis conducted in order to optimize the performance of combined cycle which involves the bypass valve. The result shows that gain in network output is about 45% when the temperature at the inlet of the turbine of topping cycle increases from 1000 K to 1400 K. The gain in net efficiency of the cycle is from 15% to 31% when the temperature at the inlet of the turbine of topping cycle increases from 1000 K to 1400 K. The bypass valve should be opened for small compression ratio and closed for high value of compression ratio. Keywords: Turbine inlet temperature, Compression ratio, Topping cycle, Combined cycle, Bypass valve

The purpose of the present study is to investigate the effect of connecting bypass valve between topping and bottoming cycles in a combined cycle system consisting of a regenerative topping gas turbine and bottoming air turbine cycles, the system explored using first and second laws of thermodynamics. The bypass valve placed between two heat exchangers and when this bypass valve opens the exhaust gasses of the turbine of topping cycle leave to the environment through both heat exchangers and when it is close the exhaust gasses of the turbine of topping cycle leave to the environment through the second heat exchanger only. The effects of the bypass hot gases on the work output, efficiency and the exergy destruction of the combined cycle plant are investigated parametrically and all pertinent parameters and function (compressor pressure ratio and turbine inlet temperature) are simulated and implemented to reports their effect on the overall performance. The result shows that gain in net work output is from 13.5% to 45% when the temperature at the inlet of turbine of topping cycle is 1400 K and 14%–19%, at turbine inlet temperature of 1000 K. And the gain in net efficiency of the cycle is from 15% to 31% when the temperature at the inlet of turbine of topping cycle is 1400 K and 4%–15%, at turbine inlet temperature of 1000 K.

The aim of this study is to perform an exergetic evaluation of a gas-steam combined cycle power utility that is integrated with vapor absorption inlet air cooling system. Effect of several thermodynamic parameters on component-level and total exergy destruction are discussed. A detailed breakdown of exergy destruction in the cycle has been presented along with useful recommendations to improve exergy based cycle performance. The integration of inlet air cooling has been observed to increase exergy efficiency of combined cycle beyond a turbine inlet temperature of 1650 K. The combustor has been identified as the greatest source of irreversibility with highest exergetic improvement potential. The total exergy destruction for the cycle has been observed to reduce with increase in turbine inlet temperature (TIT) and decrease in compressor inlet temperature (TIC). At higher compressor pressure ratio (βcomp), except combustor all other components of topping cycle has been observed to suffer an increase in exergy destruction where as exergy destruction has been observed to reduce for all bottoming cycle components except the stack. The summation of exergy destruction of all cycle components is observed to be reduced at lower ambient relative humidity and lower ambient temperature.

Combined cycle power plants have a combination of gas based topping cycle and steam based bottoming cycle through the use of Heat Recovery Steam Generator (HRSG). These HRSG may be either of single pressure (SP) or dual pressure (DP) or multiple pressure type. Here in this study thermodynamic analysis is carried out for optimal performance of HRSG using different types of HRSG layout for combined cycle efficiency improvement. Performance of single pressure HRSG and dual pressure HRSG, utilized in gas/steam combined cycle is analyzed and presented here. In comparison to single pressure, dual pressure HRSG offers 10 to 15% higher reduction in stack temperature due to greater heat recovery and thus improved plant efficiency.

Thermo-economic performance analyses of an externally fired biomass gasification based combined cogeneration plant (EF-BGCCP) is reported in the present paper. The plant is capable of producing 700-800 kW electrical power, the gas turbine (GT) providing a fixed output of 500 kWe and the bottoming steam turbine (ST) providing the rest. Utility heat of 100 kW or more is also available from the plant. Saw dust is considered as fuel feed to the plant which undergoes gasification in a downdraft gasifier. A combustor-heat exchanger (CHX) duplex unit is used in the topping GT cycle to heat up the working fluid. Effects of plant design parameters, such as, topping cycle pressure ratio (rp=4-12), gas turbine inlet temperature (TIT=900-1100 oC), cold end temperature difference (CETD=230-280 oC) of the heat exchanger of CHX unit and outlet temperature of the economizer (EOUT=130-180 oC) on the energetic and techno-economic performance is reported in the study. Energetic performance of the EF-BGCCP reveals that, plant efficiency along with fuel energy savings ratio (FESR) is maximized at a particular value of rp, for a given GT TIT. Higher TIT results in higher efficiency and FESR value. However increased CETD value results in decreased overall area (UAHX) of the exchanger. Also, increased value of EOUT results in decrease in plant efficiency and increase in FESR of the plant. Techno-economic analysis of the plant suggest that levelized unit cost of electricity (LUCE) and levelized unit cost of heat (LUCH) change with changes in operating conditions of the plant. LUCE value is minimized at a particular value of pressure ratio, for a fixed GT TIT. Also, higher TIT results in higher LUCE and LUCH delivered to the consumers. Again, higher CETD value of the heat exchanger results in decreased LUCE value as the size of the heat exchanger decreases with increase in CETD. Delivered LUCH value as well as heat to power ratio of the plant is found to be decreased at higher economizer outlet temperature.

Supercritical carbon dioxide (S-CO2) cycle is proven to be one promising alternative to provide high efficiency and has been developed for a wide range of energy conversion applications. Thermal efficiency of the S-CO2 cycle can be further improved by incorporating an appropriate bottoming cycle utilizing the residual heat. In this paper, an Organic Rankine Cycle (ORC) is added to the S-CO2 cycle for heat recovery. Different recuperative ratios of the topping S-CO2 cycle are considered and the influence of heat source initial temperature and total heat load on the bottoming ORC is evaluated. Two configurations of the S-CO2-ORC combined cycle system are presented, one without a pre-cooler and the other still with a pre-cooler, corresponding to total and partial residual heat recovery respectively. Though the entire residual heat recovery by the bottoming cycle could definitely increase the system thermal efficiency, the low ORC evaporation temperature and mediocre ORC performance leads to a limited improvement. While in the combined cycle system with a pre-cooler, higher ORC evaporation temperature could be attained and it has a remarkable effect on the ORC performance, even though part of the topping cycle residual heat is discharged to the ambient. The simulation results reveal that the S-CO2-ORC combined cycle system performance could be significantly improved through this parametric optimization. The recompression S-CO2 cycle with bottoming ORC is then analyzed and thermal performance is improved based on the previous optimization results. The bottoming ORC could effectively recover the residual heat of the topping S-CO2 cycle and increase the system thermal efficiency, thus it can be considered and applied in similar practical cases.

The supercritical CO2 (sCO2) power cycle has emerged as a promising technology for the use of nuclear energy. However, a large amount of cooling heat is wasted in the sCO2 gas cooler. In this paper, two typical sCO2 Brayton cycles including simple sCO2 cycle (SSC) and recompression sCO2 cycle (RSC) are integrated with Kalina power cycles to provide a higher energy conversion efficiency for nuclear power plants. A comparison study of the SSC-Kalina cycle and the RSC-Kalina cycle is conducted from the viewpoints of thermodynamics and economics, and multi-objective optimization using genetic algorithms is carried out to gain maximum exergetic efficiency (ηex) and minimum levelized cost of electricity (LCOE) at the design stage. To meet the requirement of wide-range load adjustment, the valve control strategy and variable-speed compressor control strategy are proposed for the topping sCO2 cycle, while the sliding pressure control strategy is adopted for the bottoming Kalina cycle. The part-load performance of the combined cycle under different control strategies is analyzed and compared based on the preliminary design parameters for the main system components. Results show that the RSC-Kalina cycle always has better performance than the SSC-Kalina cycle, and they can gain an improvement by 6.37% and 7.53% for the ηex, and 3.51% and 5.84% for the LCOE compared with the stand-alone RSC and SSC, respectively. Compared with the valve control strategy, the variable-speed compressor control strategy enables the RSC-Kalina cycle to obtain higher efficiency under partial plant loads, and the ηex ranges from 29.67% to 58.24% under 10–100% relative plant load. The bottoming Kalina cycle can be well adapted to the parameter variations of the topping cycle by using the sliding pressure control strategy no matter which sCO2 control strategy is adopted.

During the last few decades, low-grade heat sources such as solar energy and wind energy have enhanced the efficiency of advanced renewable technologies such as the combined Rankine cycle, with a significant reduction in CO2 emissions. To address the problem of the intermittent nature of such renewable sources, energy storage technologies have been used to balance the power demand and smooth out energy production. In this study, a detailed thermodynamic analysis of a hybrid open Rankine cycle was conducted by using engineering equation solver (EES) software in order to investigate the performance of such a cycle using a liquid nitrogen energy storage system. In this cycle configuration, the conventional closed loop Rankine cycle (topping cycle) is combined with a direct open Rankine cycle (bottoming cycle) for a more efficient system which can solve the problem of discontinuous renewable sources. In the direct open-Rankine cycle, the small expander is the main component that can improve the cycle’s performance and as a result, this small expander needs to be optimized for maximum efficiency to achieve high system performance levels. In this work a small-scale nitrogen axial expander has been optimized and modeled to be incorporated into a hybrid open-Rankine cycle, using a one-dimensional preliminary design and CFD three-dimensional ANSYS design exploration and a novel camber line control point parametrization technique, which is outlined in detail. The design optimization approach has been proven as an effective tool that could enhance turbine efficiency from 72% to 76.3% and output power from 2076 W to 2597.6 W. The optimized turbine using the control points’ approach could also improve the cycle’s thermal efficiency by 3.38% compared with the baseline design. Such results underline the potential of full simulation optimization by using a blade camber line control point’s parametrization technique for a small-scale expander with low flow rate and rotational speed.

A humidified combined gas power cycle has been theoretically investigated in this paper. The topping cycle is a conventional air Brayton cycle, whereas the bottoming cycle has an air humidifier installed between the compressor and the recovery heat exchanger. Using mass and energy balance equations, the performance of the combined power plant has been calculated and its sensitivity to various operation parameters has been discussed. The energy efficiency and specific power generation varied linearly when the air mass flowrate in the bottoming cycle increased. The performance of the plant initially improved, reached a maximum, and then degraded when the topping cycle pressure ratio was increased. The same qualitative behavior was observed upon increasing the bottoming cycle pressure ratio while maintaining the topping cycle pressure ratio constant. The power output increased in a quasi linear fashion and the energy efficiency increased in a logarithmic fashion when the combustion chamber temperature was increased. In all these cases, humidification of the air after the bottoming cycle compressor proved to be a good means of improving the performance of the power plant, especially when the combustion temperature is low or the bottoming cycle pressure ratio is high.