Environmental assessment of a hybrid system composed of solid oxide fuel cell, gas turbine and multiple effect evaporation desalination system

This study deals with a solid oxide fuel cell- gas turbine (SOFC-GT) hybrid system coupled with a multi-effect evaporation desalination plant with steam condensation. The environmental evaluation is also done due to the importance of waste energy recovery especially waste heat in power generation systems. The evaporation desalination plant is studied for using the excess heat to produce freshwater. The thermodynamic relationships governing different components of the system are first provided, including fuel cells, heat exchangers, gas turbine, and desalination plant. Next, given the absence of previous research on the environmental effects of cogeneration systems, despite its necessity, the study system is analyzed from an environmental point of view. Accordingly, the impacts of the system performance parameters, including the fuel consumption coefficients, compressor pressure ratio, fuel pre-reforming percentage, and the steam to carbon ratio are investigated on the CO2, CO, and NOx emission rates. Based on the findings, it is concluded that of different species, the impacts of CO, CO2, and NOx emission rates are significant on the environment. Thus, the impacts of pressure ratio and pre-reforming percentage on their emission rates have been studied. The results revealed with increasing the compressor pressure ratio, increasing the fuel consumption coefficients, and decreasing the fuel cell's exhaust temperature, the CO and NOx emission rates and corresponding social costs diminished. On the other hand, with elevation of the ratio of steam to carbon, the recovery rate, the fuel cell's exhaust temperature, the concerned gas emission rates, and corresponding social costs increased.

Off-Design Performance Comparison Between Single and Two-Shaft Engines: Part 1 — Fixed Geometry

This paper describes an investigation into the off-design performance comparison of single and two-shaft gas turbine engines. A question that has been asked for a long time which gas turbine delivers a better thermal efficiency at part load. The authors, notwithstanding their intensive searches, were unable to find a comprehensive answer to this question. A detailed investigation was carried out using a state of the art performance evaluation method and the answer was found to be: It depends! In this work, the performance of two engine configurations is assessed. In the first one, the single-shaft gas turbine operates at constant shaft rotational speed. Thus, the shape of the compressor map rotational speed line will have an important influence on the performance of the engine. To explore the implications of the shape of the speed line, two single-shaft cases are examined. The first case is when the speed line is curved and as the compressor pressure ratio falls, the non-dimensional mass flow increases. The second case is when the speed line is vertical and as the compressor pressure ratio falls, the non-dimensional mass flow remains constant. In the second configuration, the two-shaft engine, the two-shafts can be controlled to operate at different rotational speeds and also varying relationships between the rotational speeds. The part-load operation is characterized by a reduction in the gas generator rotational speed. The tool, which was used in this study, is a 0-D whole engine simulation tool, named Turbomatch. It was developed at Cranfield and it is based on mass and energy balance, carried out through an iterative method, which is based on component maps. These generic, experimentally derived maps are scaled to match the design point of a particular engine before an off-design calculation is performed. The code has been validated against experimental data elsewhere, it has been used extensively for academic purposes and the research activities that have taken place at Cranfield University. For an ideal cycle, the single-shaft engine was found to be a clear winner in terms of part-load thermal efficiency. However, this picture changed when realistic component maps were utilized. The basic cycle and the shape of component maps had a profound influence on the outcome. The authors explored the influence of speed line shapes, levels of component efficiencies and the variation of these component efficiencies within the operating range. This paper describes how each one of these factors, individually, influences the outcome.

Variance in Compressor Turndown When Implementing Surge Control Fallback Strategies

A centrifugal compressor surge prevention system is used to protect a compressor from surging while in operation. When using an invariant coordinate system for the compressor performance map within the surge protection system, reduced head versus reduced flow, surge control fallback strategies can be implemented within the control system to maintain operation of the compressor when instrumentation fails without placing the unit into a surge event, increasing unit availability. This paper reviews the different fallback strategies that can be implemented based on the function of the instrumentation that faulted and determine the variance between the calculated and actual turndown when different fallback strategies are active. Depending on the fallback strategy implemented, additional turndown margin may be required to ensure compressor surge is prevented by the surge prevention control system. This paper also reviews how the specific gravity, compressor pressure ratio, and compressor flow impact the variance between actual and calculated turndown when a given fallback strategy is active. Knowing the variance in the turndown allows the operator of the compressor to correctly select the desired fallback strategies and determine the needed control margin to safety operate the compressor without process disruptions. Several recommendations are outlined in the paper.

Theoretical Assessment of Turbocharged Pulse Detonation Engine Performance at Various Flight Conditions

A typical Pulse Detonation Engine (PDE) cycle of operation includes three basic processes: initiation and propagation of detonation wave in the Detonation Chamber (DC); a quasi-steady exhaust of detonation products from the DC at varying pressure through the supersonic nozzle; and a steady exhaust of remained detonation products at constant pressure through the nozzle while filling the DC with fresh air. In the present work, a novel method of Turbo-charging is proposed to increase the inlet pressure/density of fresh air fed into the DC in each cycle so as to increase the thrust developed per unit area of DC. The thermodynamic cycle of operation of Turbocharged Pulse Detonation Engine (TPDE) is analyzed based on quasi-steady state one dimensional formulation, and a computer code is developed in MATLAB to simulate the cycle performance at different compressor pressure ratios. Thrust per unit area of DC, the specific thrust and the fuel-based specific impulse are estimated at various flight conditions at different pressure ratios by considering C2H4/air as the fuel-oxidizer. The net thrust developed per unit area of DC increases with an increase in compressor pressure ratio, up to the pressure ratio of 4.0, at all flight conditions. The compressor pressure ratio of about 2.0 is observed to be optimum pressure ratio as TPDE develops nearly the same air-based specific thrust at this pressure ratio irrespective of flight operating conditions.

Comprehensive Performance Analysis for the Rotating Detonation-Based Turboshaft Engine

The potential advantages of rotating detonation combustion are gradually approved, and it is becoming a stable and controllable energy conversion way adopted to the propulsion devices or ground-engines. This study focuses on the rotating detonation-based turboshaft engine, and the architecture is presented for this form of engine with compatibility between the turbomachinery and rotating detonation combustor being realized. The parametric performance simulation model for the rotating detonation-based turboshaft engine are developed. Further, the potential performance benefits as well as their generation mechanism are revealed, based on the comprehensive performance analysis of the rotating detonation-based turboshaft engine. Comparisons between the rotating detonation turboshaft engine and the conventional one reveal that the former holds significant improvements in specific power, thermal efficiency, and specific fuel consumption at lower compressor pressure ratios, and these improvements decrease with the increase of compressor pressure ratio and increase as turbine inlet temperature increases. The critical compressor pressure ratio corresponding to the disappearance of specific power improvement is higher than that corresponding to the disappearance of thermal efficiency and specific fuel consumption. These critical compressor pressure ratios are positively correlated with flight altitude and negatively correlated with flight velocity. The conductive research conclusion is guidable for the design and engineering application of rotating detonation-based engines.

USE OF VACUUM MICROGAS TURBINE PLANTS FOR HEATPOWER SUPPLY OF LOCAL OBJECTS

Consideration subject in article are vacuum cycles of microgas turbine plants (MGTP) for the purpose of studying of their profitability and perspectives of use for heatpower supply of local objects. Vacuum MGTP of a simple cycle and with warmth regeneration is investigated. Optimum parameters of cycles – ratio of turbine expansion and regeneration ratio are found. It is established that profitability of MGTP with regeneration of warmth is higher in comparison with MGTP of a simple cycle almost twice, specific power decreases approximately by 1,35 times. By virtue of profitability and smaller values of compressor pressure ratio increase of the microturbine it is reasonable to apply in MGTP of a vacuum cycle with warmth regeneration.

Investigation of the Pressure Gain Characteristics and Cycle Performance in Gas Turbines Based on Interstage Bleeding Rotating Detonation Combustion

To further improve the cycle performance of gas turbines, a gas turbine cycle model based on interstage bleeding rotating detonation combustion was established using methane as fuel. Combined with a series of two-dimensional numerical simulations of a rotating detonation combustor (RDC) and calculations of cycle parameters, the pressure gain characteristics and cycle performance were investigated at different compressor pressure ratios in the study. The results showed that pressure gain characteristic of interstage bleeding RDC contributed to an obvious performance improvement in the rotating detonation gas turbine cycle compared with the conventional gas turbine cycle. The decrease of compressor pressure ratio had a positive influence on the performance improvement in the rotating detonation gas turbine cycle. With the decrease of compressor pressure ratio, the pressurization ratio of the RDC increased and finally made the power generation and cycle efficiency enhancement rates display uptrends. Under the calculated conditions, the pressurization ratios of RDC were all higher than 1.77, the decreases of turbine inlet total temperature were all more than 19 K, the power generation enhancements were all beyond 400 kW and the cycle efficiency enhancement rates were all greater than 6.72%.

Optimization of turbojet engine cycle with dual-purpose PSO algorithm

In this article, the J85-GE-21 turbojet engine for an altitude of 1000–8000 m, with the speed of 200 m/s and at 10, 20, and 40 °C, was provided, and then, based on the objective functions, the above system was optimized using particle swarm optimization method. For the purpose of optimization, the Mach number, compressor efficiency, turbine efficiency, nozzle efficiency, and compressor pressure ratio were assumed to be in the range of 0.6–1.4, 0.8–0.95, 0.8–0.95, 0.8–0.95, and 7–10, respectively. The highest exergy efficiency of 73.1% for different components of the engine at sea level and speed of 200 m/s belonged to the diffuser. Second and third to it were nozzle and combustion chamber with 68.6 and 51.5%, respectively. The lowest exergy efficiency of 4% belonged to the compressor, and the second to it was the afterburner with 11.6%. Also, the values of entropy production and efficiency of the second law of thermodynamics were 1176.99 and 479 K/W, respectively, prior to optimization, which were respectively changed to 1129 and 51.4 K/W postoptimization. Obviously, the entropy production is reduced, while the efficiency of the second law of thermodynamics is increased.

Numerical Evaluation of the Effects of Low Pressure EGR Mixer Configuration on Turbocharger Compressor Performance

Low-pressure exhaust gas recirculation (LP-EGR) is an EGR configuration in which clean exhaust gas is taken downstream of the turbine and aftertreatment, and then reintroduced upstream of the compressor (1). Employing LP-EGR on Diesel engines can improve fuel economy by reducing pumping losses, lowering intake manifold temperature and facilitating advanced combustion phasing (2, 3). The LP-EGR can also improve compressor and turbine performance by moving their operating points towards higher flow rate and higher efficiency points, which is reflected as a net reduction in pumping losses of the engine. In this study, we focus on effects of introducing LP-EGR on the compressor pressure ratio, and isentropic total-to-total efficiency. The flow field of LP-EGR and air mixing upstream of the compressor as well as the entire compressor stage were studied using a CFD RANS model. The model was validated against turbocharger gas stand measurements. A T-junction mixer was chosen as the design baseline, and various configurations of this mixer were evaluated. The impact of the geometric configuration of the mixer was studied by varying mixing length, EGR jet introduction angle, and EGR-to-air cross section area ratio over a wide range of relevant engine operating conditions. The flow field upstream of the compressor is strongly affected by the dimensionless quantity EGR-to-air momentum ratio. At intermediate momentum ratios, stream-wise counter-rotating vortex pairs (4) are induced in the flow. These vortices can reach the impeller inlet, and depending on vorticity and length scale, perturb the local velocity triangle. At low and high momentum ratios, creeping or impinging jets respectively are formed. In addition prewhirl can be induced by eccentric introduction of EGR. The EGR-induced prewhirl acts similar to an inlet guide vane and can alter the incidence angle at the impeller inlet. The performance of the compressor is altered by the EGR-induced flow field. Compressor pressure ratio is either increased or decreased depending on the direction of EGR-induced prewhirl with eccentric EGR introduction. The compressor efficiency decreases at low flow rates by introduction of concentric EGR due to perturbation of the velocity triangle at the impeller inlet. On the other hand, at low flow rates compressor efficiency can be improved by eccentric EGR introduction, which generates prewhirl in the direction of rotation of the impeller leading to improved incidence angle. The extent to which the compressor is influenced by the EGR-induced flow field is generally reduced by increasing the EGR mixing length, due to viscous damping and breakdown of large-scale EGR-induced vortices. The LP-EGR configuration provides a potential pathway towards improvement of compressor performance, not only by increasing compressor flow rate, but also by manipulation of the flow field. Given that the engine pumping losses are strongly dependent on compressor performance, specifically the compressor efficiency, this study indicates that LP-EGR provides an important path towards reducing pumping loss and improving fuel conversion efficiency.