Simple Cycle Engine Research Articles

Fluid selection and parametric analysis of organic Rankine cycle applicable to the turboshaft engine with a recuperator

With ever increasing fossil fuel price and growing demands in cutting emissions, waste heat recovery (WHR) appears as a promising pathway to improve propulsion system performance, which can be potentially achieved by incorporating a recuperator. This paper explores the advantages and potentiality of further recovering exhaust heat from recuperated turboshaft engine through the concept of organic Rankine cycle (ORC) to improve fuel economy and thermal efficiency. For the intended application, working fluid selection is conducted after systematic consideration of thermophysical properties, environmental impact, health and safety issues. Furthermore, parametric analysis is carried out from the viewpoint of thermodynamics, and the genetic algorithm is also employed to obtain the maximum net power output. Targeting the implicit coupling between recuperator effectiveness and ORC performance, the potential advantages of the combined engine-ORC system are comprehensively evaluated at different operational regimes. The influence of flight condition is also discussed through sensitivity simulations for different altitudes. Results reveal that the combination of the recuperated engine with ORC cycle operated using acetone generally offers the greatest benefits, significantly reducing specific fuel consumption by 46%–59 % relative to the baseline simple-cycle engine, depending on the availability of heat source. This analytical work contributes to provide valuable insights into WHR technologies in the aviation industry.

Maximum-efficiency architectures for steady-flow combustion engines, I: Attractor trajectory optimization approach

In this paper, we present a new systematic optimization approach to identify maximum-efficiency architectures for steady-flow combustion engines. Engine architectures are modeled as trajectories in the thermodynamic state space, and the optimal engine architecture is deduced by minimization of total irreversibility over all permissible trajectories that satisfy device constraints. In the past, both parametric and functional minimizations of engine irreversibility have been studied extensively. Our approach combines the functional optimization aspect (i.e., optimization of the process sequence or engine cycle) and the parametric optimization aspect (i.e., optimization of process lengths or parameters in the engine cycle) to identify the maximum-efficiency architecture permitted by physics. The concept central to this approach is that of chemical-equilibrium attractor states in the thermodynamic state space. It enables semi-analytical optimization for reactive engines with no need to model the detailed combustion dynamics. In this study we present the motivation and theoretical details of this method. In Part II of this study, this approach is applied to optimize the class of simple-cycle gas turbine engines. It is shown that even with modest device technology (e.g., turbine inlet temperature of 1650 K), maximum efficiency above 50% can be achieved in simple-cycle engines.

Performance assessment of simple and modified cycle turboshaft gas turbines

This paper focuses on investigations encompassing comparative assessment of gas turbine cycle options. More specifically, investigation was carried out of technical performance of turboshaft engine cycles based on existing simple cycle (SC) and its projected modified cycles for civil helicopter application. Technically, thermal efficiency, specific fuel consumption, and power output are of paramount importance to the overall performance of gas turbine engines. In course of carrying out this research, turbomatch software established at Cranfield University based on gas turbine theory was applied to conduct simulation of a simple cycle (baseline) two-spool helicopter turboshaft engine model with free power turbine. Similarly, some modified gas turbine cycle configurations incorporating unconventional components, such as engine cycle with low pressure compressor (LPC) zero-staged, recuperated engine cycle, and intercooled/recuperated (ICR) engine cycle, were also simulated. In doing so, design point (DP) and off-design point (OD) performances of the engine models were established. The percentage changes in performance parameters of the modified cycle engines over the simple cycle were evaluated and it was found that to a large extent, the modified engine cycles with unconventional components exhibit better performances in terms of thermal efficiency and specific fuel consumption than the traditional simple cycle engine. This research made use of public domain open source references.

Engine Design Strategies to Maximize Ceramic Turbine Life and Reliability

Ceramic turbines have long promised to enable higher fuel efficiencies by accommodating higher temperatures without cooling, yet no engines with ceramic rotors are in production today. Studies cite life, reliability, and cost obstacles, often concluding that further improvements in the materials are required. In this paper, we assume instead that the problems could be circumvented by adjusting the engine design. Detailed analyses are conducted for two key life-limiting processes, water vapor erosion and slow crack growth, seeking engine design strategies for mitigating their effects. We show that highly recuperated engines generate extremely low levels of water vapor erosion, enabling lives exceeding 10,000 hs, without environmental barrier coatings. Recuperated engines are highly efficient at low pressure ratios, making low blade speeds practical. Many ceramic demonstration engines have had design point mean blade speeds near 550 m/s. A CARES/Life analysis of an example rotor designed for about half this value indicates vast improvements in slow crack growth-limited life and reliability. Halving the blade speed also reduces foreign object damage particle kinetic energy by a factor of four. In applications requiring very high fuel efficiency that can accept a recuperator, or in short-life simple cycle engines, ceramic turbines are ready for application today.

The effect of firing biogas on the performance and operating characteristics of simple and recuperative cycle gas turbine combined heat and power systems

We investigated the influence of firing biogas on the performance and operating characteristics of gas turbines. Combined heat and power systems based on two different gas turbines (simple and recuperative cycle engines) in a similar power class were simulated. A full off-design analysis was performed to predict the variations in operations due to firing biogas instead of natural gas. A wide range of biogas compositions differing in CH4 content was simulated. Without consideration of operating restrictions on the compressor and turbine, using biogas was predicted to augment the power output in both engines. Power output increased as CH4 content decreased. The main reason is the increase in turbine power due to increased fuel flow. Gas turbine efficiency increased with decreasing CH4 content in the simple cycle engine, but decreased in the recuperative cycle engine. Net efficiency including the fuel compression power consumption decreased with decreasing CH4 content even in the simple cycle engine. The heat recovery also increased by firing biogas. However, the increased turbine flow was accompanied by a surge margin reduction of the compressor and overheating of the turbine blade. These two problems were more severe in simple cycle gas turbines and as the ambient temperature increased. The turbine blade temperature and the compressor surge margin could be recovered to the reference values by either under-firing or compressor air bleeding, which are effective for blade temperature control and surge margin control, respectively. However, satisfaction of both restrictions by a single modulation caused excessive power and efficiency losses. An optimal combination between under-firing and air bleeding would minimize the performance penalty.

Development of a gas turbine performance analysis program and its application

A general-purpose performance prediction program, which can simulate various types of gas turbine such as simple, recuperative, and reheat cycle engines, has been developed. A stage-stacking method has been adopted for the compressor, and a stage-by-stage model including blade cooling has been used for the turbine. The combustor model has the capability of dealing with various types of gaseous fuels. The program has been validated through simulation of various commercial gas turbines. The simulated design performance has been in good agreement with reference data for all of the gas turbines. The average deviations of the predicted performance parameters (power output, thermal efficiency, and turbine exhaust temperature) were less than 0.5% in the design simulations. The accuracy of the simulation of off-design operation was also good. The maximum root mean square deviations of the predicted off-design performance parameters from the reference data were 0.22% and 0.44% for the two simple cycle engines, 0.22% for the recuperative cycle engine, and 0.21% for the reheat cycle engine. Both the design and off-design simulations confirmed that the component models and the program structure are quite reliable for the performance prediction of various types of gas turbine cycle over a wide range of operations.

The effectiveness of using controlled power turbines in gas-turbine units and regenerative-cycle and simple-cycle engines

Results from investigating the effectiveness of using a power turbine equipped with variable guide vanes are presented. Control ranges of turbines using these guide vanes are determined in the most typical operating modes of gas-turbine engines and units for thermal power-engineering purposes and gas transportation systems. Recommendations are formulated for the expediency of using the variable guide vanes of a power turbine to improve the operational efficiency of gas-turbine engines and units during the cold period of the year under partial-load conditions and in some other cases.

Engine-fault diagnostics:an optimisation procedure

A diagnostic process capable of providing an early warning of a fault in a gas turbine is of tremendous value to the user and can result in substantial financial savings. The approach in the Genetic Algorithm based technique adopted is to treat the problem of engine diagnostics as an optimisation exercise using sensor-based and mathematical behavioural model based information. The engine performance model would simulate a range of possible combinations of potential faults (i.e the effects of model-based information) and a comparison would be made with values of the actual (sensor-based) parameters obtained from an engine. The difference between the actual and simulated values of would be converted into a suitable objective-function and the aim of the optimisation technique such as the genetic algorithm would be to minimise the objective function. The technique has given promising results for simple cycle engines.

Digital Control System Development for an Intercooled Recuperated Gas Turbine

The on-going development of a full authority digital engine control (FADEC) system for the US Navy’s Intercooled Recuperated (ICR) gas turbine requires a high level of system coordination to achieve the primary benefits of reduced specific fuel consumption and improved specific output power relative to a simple cycle engine. This paper describes the system requirements analysis and the implementation of control algorithms leading to the preliminary ICR control system design. The ICR control system is required to coordinate the actions of over 30 actuators using data taken from over 150 sensors. Primary control of the engine output power is provided by regulation of the fuel metering valve. Thermal management of the intercooler, recuperator, and variable area power turbine nozzle results in maximum cycle efficiency within safe operating limits. The new electronic engine controller (EEC) is based on a new open architecture Futurebus + backplane and is fully redundant in all operationally critical control functions. The EEC also features an operating panel and video display for local operation and maintenance of the control system. The graphic display and function keys provide access to control functions as well as assisting maintenance activities with built-in test diagnostics to trouble shoot failed circuitry.

Development of a Gas Turbine Combustor Utilizing a Catalyst

Catalytically supported thermal combustion has been successfully incorporated into a low-pressure-r atio gas turbine type system. Excellent emissions performance was obtained utilizing gaseous propane fuel. A combustor design concept has been developed that is applicable to gaseous fueled gas turbine engines. A working solution to the important questions related to the use of this type of combustor in a dynamic turbine environment has been demonstrated for low-pressure-ratio simple-cycle engines. Both straight-through flow and reverse-flow combustors have been developed for use in conjunction with the catalyst system. Fuel turndown ranges approximating 10:1 have been achieved in both systems tested, the range being limited in this instance by the machine airflow capacity. For systems of the type discussed herein, increases in combustor diameters no greater than 50% with respect to conventional combustors would be required for low-pressure-ratio engine applications. A prime goal for high-pressure-ratio applications is the development of short residence time mixing configurations.