Showing papers in "Journal of Engineering for Gas Turbines and Power-transactions of The Asme in 1995"

The Role of Fuel Preparation in Low-Emission Combustion

Abstract: The attainment of very low pollutant emissions, in particular oxides of nitrogen (NO{sub x}), from gas turbines is not only of considerable environmental concern but has also become an area of increasing competitiveness between the different engine manufacturers. For stationary engines, the attainment of ultralow NO{sub x} has become the foremost marketing issue. This paper is devoted primarily to current and emerging technologies in the development of ultralow emissions combustors for application to aircraft and stationary engines. Short descriptions of the basic design features of conventional gas turbine combustors and the methods of fuel injection now in widespread use are followed by a review of fuel spray characteristics and recent developments in the measurement and modeling of these characteristics. The main gas-turbine-generated pollutants and their mechanisms of formation are described, along with related environmental risk and various issues concerning emissions regulations and recently enacted legislation for limiting the pollutant levels emitted by both aircraft and stationary engines. The impact so these emissions regulations on combustor and engine design are discussed first in relation to conventional combustors and then in the context of variable-geometry and staged combustors. Both these concepts are founded on emissions reduction by control of flame temperature. Basicmore » approaches to the design of dry low-NO{sub x} and ultralow-NO{sub x} combustors are reviewed.« less

A Review of Droplet Dynamics and Vaporization Modeling for Engineering Calculations

Abstract: The present paper reviews the methodologies for representing the droplet motion and vaporization history in two-phase flow computations. The focus is on the use of droplet models that are realistic in terms of their efficient implementation in comprehensive spray simulations, representation of important physical processes, and applicability under a broad range of conditions. The methodologies available at present to simulate droplet motion in complex two-phase flows may be broadly classified into two categories. First one is based on the modified BBO equation. This approach is more comprehensive, but requires modifications and/or correlations at higher droplet Reynolds number. The second approach aims at developing correlations, using detailed numerical simulations or laboratory experiments, for the effects of flow nonuniformity and droplet relative acceleration on the instantaneous drag and lift coefficients. Recent advances made in the droplet vaporization models are also discussed. The advanced vaporization models include the effects of transient liquid heating, gas-phase convection, and variable thermophysical properties. All of these models are discussed, and recommendations are made for their inclusion in comprehensive two-phase computations.

Comparative Evaluation of Combined Cycles and Gas Turbine Systems With Water Injection, Steam Injection, and Recuperation

Abstract: Combined cycles have gained widespread acceptance as the most efficient utilization of the gas turbine for power generation, particularly for large plants. A variety of alternatives to the combined cycle that recover exhaust gas heat for re-use within the gas turbine engine have been proposed and some have been commercially successful in small to medium plants. Post notable have been the steam-injected, high-pressure aeroderivatives in sizes up to about 50 MW. Many permutations and combinations of water injection, steam injection, and recuperation, with or without intercooling, have been shown to offer the potential for efficient improvements in certain ranges of gas turbine cycle design parameters. A detailed, general model that represents the gas turbine with turbine cooling has been developed. The model is intended for use in cycle analysis applications. Suitable choice of a few technology description parameters enables the model to represent accurately the performance of actual gas turbine engines of different technology classes. The model is applied to compute the performance of combined cycles as well as that of three alternatives. These include the simple cycle, the steam-injected cycle, and the dual-recuperated intercooled aftercooled steam-injected cycle (DRIASI cycle). The comparisons are based on state-of-the-art gas turbine technology and cycle parameters in four classes: large industrial (123-158 MW), medium industrial (38-60 MW), aeroderivatives (21-41 MW), and small industrial (4-6 MW). The combined cycle's main design parameters for each size range are in the present work selected for computational purposes to conform with practical constraints. For the small posterns, the proposed development of the gas turbine cycle, the DRIASI cycle, are found to provide efficiencies comparable or superior to combined cycles, and superior to steam-injected cycles. For the medium posterns, combined cycles provide the highest efficiencies but can be challenged by the DRIASI cycle. For the largest posterns, the combined cycle was found to be superior to all of the alternative gas turbine based cycles considered in this study

An assessment of the thermodynamic performance of mixed gas-steam cycles. Part A: Intercooled and steam-injected cycles

Abstract: This paper discusses the thermodynamics of power cycles where steam or water are mixed with air (or combustion gases) to improve the performance of stationary gas turbine cycles fired on clean fuels. In particular, we consider cycles based on modified versions of modem, high-performance, high-efficiency aeroderivative engines. The paper is divided into two parts. After a brief description of the calculation method, in Part A we review the implications of intercooling and analyze cycles with steam injection (STIG and ISTIG). In Part B we examine cycles with water injection (RWI and HAT). Due to lower coolant temperatures, intercooling enables us to reduce turbine cooling flows and/or to increase the turbine inlet temperature. Results show that this can provide significant power and efficiency improvements for both simple cycle and combined cycle systems based on aero-engines ; systems based on heavy-duty machines also experience power output augmentation, but almost no efficiency improvement. Mainly due to the irreversibilities of steam/air mixing, intercooled steam injected cycles cannot achieve efficiencies beyond the 52-53 percent range even at turbine inlet temperatures of 1500°C. On the other hand, by accomplishing more reversible water-air mixing, the cycles analyzed in Part B can reach efficiencies comparable (RWI cycles) or even superior (HAT cycles) to those of conventional unmixed combined cycles.

An Assessment of the Thermodynamic Performance of Mixed Gas-Steam Cycles: Part B—Water-Injected and HAT Cycles

Abstract: Part B of this paper 1 focuses on intercooled recuperated cycles where water is injected to improve both efficiency and power output. This concept is investigated for two basic cycle configurations : a Recuperated Water Injected (RWI) cycle, where water is simply injected downstream of the HP compressor, and a Humid Air Turbine (HAT) cycle, where air/water mixing is accomplished in a countercurrent heat/mass transfer column called saturator. For both configurations we discuss the selection and the optimization of the main cycle parameters, and track the variations of efficiency and specific work with overall gas turbine pressure ratio and turbine inlet temperature (TIT). TIT can vary to take advantage of lower gas turbine coolant temperatures, but only within the capabilities of current technology. For HAT cycles we also address the modelization of the saturator and the sensitivity to the most crucial characteristics of novel components (temperature differences and pressure drops in heat/mass transfer equipment). The efficiency penalties associated with each process are evaluated by a second-law analysis, which also includes the cycles considered in Part A. For any given TIT in the range considered (1250 to 1500°C), the more reversible air/water mixing mechanism realized in the saturator allows HAT cycles to achieve efficiencies about 2 percentage points higher than those of RWI cycles : At the TIT of 1500°C made possible by intercooling, state-of-the-art aero-engines embodying the above-mentioned cycle modifications can reach net electrical efficiencies of about 57 and 55 percent, respectively. This compares to efficiencies slightly below 56 percent achievable by combined cycles based upon large-scale heavy-duty machines with TIT = 1280°C.

Combined Power Plants—Past, Present, and Future

Abstract: The early history of combined power plants is described, together with the birth of the CCGT plant (the combined cycle gas turbine). Sustained CCGT development in the 1970s and 1980s, based on sound thermodynamic considerations, is outlined. Finally more recent developments and future prospects for the combined gas turbine/steam turbine combined plant are discussed.

The Importance of the Nitrous Oxide Pathway to NOx in Lean-Premixed Combustion

Abstract: This study addresses the importance of the different chemical pathways responible for NO x formation in lean-premixed combustion, and especially the role of the nitrous oxide pathway relative to the traditional Zeldovich pathway. NO x formation is modeled and computed over a range of operating conditions for the lean-premixed primary zone of gas turbine engine combustors. The primary zone, of uniform fuel-air ratio, is modeled as a micromixed well-stirred reactor, representing the flame zone, followed by a series of plug flow reactors, representing the postflame zone. The fuel is methane. The fuel-air equivalence ratio is varied from 0.5 to 0.7. The chemical reactor model permits study of the three pathways by which NO x forms, which are the Zeldovich, nitrous oxide, and prompt pathways. Modeling is also performed for the well-stirred reactor alone. Three recently published, complete chemical kinetic mechanisms for the C1−C2 hydrocarbon oxidation and the NO x formation are applied and compared. Verification of the model is based on the comparison of its NO x output to experimental results published for atmospheric pressure jet-stirred reactors and for a 10 atm. porous-plate burner. Good agreement between the modeled results and the measurements is obtained for most of the jet-stirred reactor operating range. For the porous-plate burner, the model shows agreement to the NO x measurements within a factor of two, with close agreement occurring at the leanest and coolest cases examined. For lean-premixed combustion at gas turbine engine conditions, the nitrous oxide pathway is found to be important, though the Zeldovich pathway cannot be neglected. The prompt pathway, however, contributes small-to-negligible NO x . Whenever the NO x emission is in the 15 to 30 ppmv (15 percent O 2 , dry) range, the nitrous oxide pathway is predicted to contribute 40 to 45 percent of the NO x for high-pressure engines (30 atm), and 20 to 35 percent of the NO x for intermediate pressure engines (10 atm). For conditions producing NO x of less than 10 ppmv (15 percent O 2 , dry), the nitrous oxide contribution increases steeply and approaches 100 percent. For lean-premixed combustion in the atmospheric pressure jet-stirred reactors, different behavior is found. All three pathways contribute; none can be dismissed. No universal behavior is found for the pressure dependence of the NO x . It does appear, however, that lean-premixed combustors operated in the vicinity of 10 atm have a relatively weak pressure dependence, whereas combustors operated in the vicinity of 30 atm have an approximately square root pressure dependence of the NO x

A Design Procedure for Effervescent Atomizers

Abstract: A methodology for the design of effervescent atomizers is described The objective is to achieve sprays of minimum mean drop size for any stipulated values of liquid flow rate, air supply pressure, and air/liquid ratio Application of the method leads to optimum values for all the key atomizer dimensions, including the number and size of the air injection holes, and the diameters of the mixing chamber and discharge orifice It also enables optimum dimensions to be determined for a convergent-divergent nozzle should such a device be fitted to the nozzle exit to improve atomization performance Examples are provided to demonstrate the application of the recommended design procedure and to illustrate the relative importance of various flow and geometric parameters in regard to their effects on atomization quality

Arbitrary Surface Flank Milling of Fan, Compressor, and Impeller Blades

Abstract: It is generally conceived that a blade surface is flank millable if it can be closely approximated by a ruled surface ; otherwise the slow machining process of point milling has to be employed. However, we have now demonstrated that the ruled surface criterion for flank milling is neither necessary nor sufficient. Furthermore, many complex arbitrary surfaces typical of our blades in fans, axial compressors, and centrifugal impellers in aviation gas turbines are actually closely flank millable and can be rendered exactly flank millable with one or more passes per surface often without sacrificing, indeed usually with gain, in performance.

Steam-Injected Gas Turbine Analysis: Steam Rates

Abstract: This paper presents an analysis of steam rates in steam-injected gas turbines (simple and reheat). In considering a gas turbine of this type, the steam-injection flow is separated from the main gas stream for analysis. Dalton`s and Avogadro`s laws of partial pressure and gas mixtures are applied. Results obtained provide for the accurate determination of heat input, gas expansion based on partial pressures, and heat-rejection steam-enthalpy points.

A combined cycle designed to achieve greater than 60 percent efficiency

Abstract: In cooperation with the US Department of Energy`s Morgantown Energy Technology Center, Westinghouse is working on Phase 2 of an 8-year Advanced Turbine Systems Program to develop the technologies required to provide a significant increase in natural gas-fired combined cycle power generation plant efficiency In this paper, the technologies required to yield an energy conversion efficiency greater than the Advanced Turbine Systems Program target value of 60% are discussed The goal of 60% efficiency is achievable through an improvement in operating process parameters for both the combustion turbine and steam turbine, raising the rotor inlet temperature to 2,600 F (1,427 C), incorporation of advanced cooling techniques in the combustion turbine expander, and utilization of other cycle enhancements obtainable through greater integration between the combustion turbine and steam turbine

A new approach to the challenge of machinery prognostics

Abstract: Current generation mechanical diagnostic equipment is designed to identify individual events or trends in the output of sensors mounted on a mechanical component, subsystem, or system. Such equipment can provide a useful indication that a failure condition may be developing, but it cannot provide reliable prediction of the remaining safe or operational life. Typically, these diagnostic systems simply compare the output of individual sensors against a priori thresholds to establish a measure of the system's health. Two problems result from this approach: (1) There is no advantage taken of possible synergy among the sensors, i.e., the determination of health is one dimensional; and (2) the diagnosis provides only a statement regarding the current equipment health, but does not provide a prediction of the time remaining to failure. This often leads to an operational environment in which diagnostic equipment outputs are either ignored because of frequent false alarms or frequent (and costly) time-based preventive maintenance is performed to avoid hazardous failures. This paper describes a new approach to the development of a more robuts diagnosis and prognostic capability. It is based on the fusion of sensor-based and model-based information. Sensor-based information is the essence of current diagnostic systems. Model-based information combines dynamic models of individual components with micromechanical models of relevant failure mechanisms, such as fracture and crack propagation. These micromechanical models must account for initial flaw size ditribution and other microstructural parameters describing initial component condition. A specific application of this approach is addressed, the diagnosis of mechanical failure in meshing gears. Four specific issues are considered: (a) how to couple a validated numerical simulation of gear transmission error (due to tooth spacing irregularity, or material inhomogeneity) with physically and empirically based descriptions of fatigue crack grawth to predict a failure precursor signature at the component level; (b) how to predict the manifestation of this signature at the subsystem or system level where sensors are located; (c) how to fuse this model-based information with the corresponding sensor-based information to predict remaining safe or operational life of a gear; and (d) issues associated with extending this methodology to bearings and other rotating machinery components

Gas turbine bottoming cycles: Triple-pressure steam versus Kalina

Abstract: The performance of a triple-pressure steam cycle has been compared with a single-stage Kalina cycle and an optimized three-stage Kalina cycle as the bottoming sections of a gas turbine combined cycle power plant. A Monte Carlo direct search was used to find the optimum separator temperature and ammonia mass fraction for the three-stage Kalina cycle for a specific plant configuration. Both Kalina cycles were more efficient than the triple pressure steam cycle. Optimization of the three-stage Kalina cycle resulted in almost a two percentage point improvement.

Influence of Hardware Design on the Flow Field Structures and the Patterns of Droplet Dispersion: Part I—Mean Quantities

Abstract: In a gas turbine engine combustor, performance is likely tied to the spatial distribution of the fuel injected into the dome. The GE/SNECMA CFM56 combustor swirl cup is one example of a design established to provide a uniform presentation of droplets to the dome. The present study is part of a series to detail the dispersion of droplets in practical hardware, and to assess the effect of isolated parameters on the continuous and dispersed-phase distributions. In this study, the influence of the swirling sir outlet geometry is evaluated relative to the effect on the flow field structures and the patterns of droplet dispersion. This is accomplished by comparing the continuous-phase (air in the presence of a spray) and dispersed-phase (droplets) behavior downstream of the swirl cup assembly outfitted with two different conical expansions (``flares``). One features a narrow expansion angle, the other possesses a wide expansion angle. Two-component phase-Doppler interferometry was employed to provide the information of droplet size and velocity components as well as continuous-phase velocity components. Photographs of light scattered by droplets from laser sheet were used for the study of flow field structures. This study reveals that (1) the air stream issued from the narrow flare remainsmore » close to the centerline and expands gradually downstream while the air stream issued from the wide flare expands immediately downstream of the swirl cup, and (2) the narrow flare provides weaker droplet dispersion, slower decay of droplet velocities, and finer droplet size compared to the wide flare. The results demonstrate that a relatively modest change in flare geometry can create a significant change in the structure of both the continuous and dispersed phases.« less

Computation of turbulent evaporating sprays: Eulerian versus Lagrangian approach

Abstract: A new Eulerian model for turbulent evaporating sprays is presented. It comprises droplet heating and evaporation processes by solving separate transport equations for the droplet's temperature and diameter. A Lagrangian approach, which we have discussed in detail on other occasions, is used in comparing the results of the new method. A comparison with experimental data shows that both approaches are successful in predicting the main features of turbulent evaporating sprays

Design and Development of a Direct Injected, Glow Plug Ignition-Assisted, Natural Gas Engine

Abstract: Conventional (Otto cycle) natural gas engines are limited in power and thermal efficiency relative to a diesel engine due to detonation and the need to run a nearly stoichiometric air/fuel ratio. Technology is under development to burn natural gas in a direct-injected diesel cycle that is not prone to detonation or air/fuel ratio control limitations. Direct-injected gas (DIG) technology will allow natural gas engines to match the power and thermal efficiency of the equivalent diesel-fueled engine. Laboratory development now under way is targeted for field experimental evaluation of a DIG 3516 engine in a 1500 kW road switcher locomotive. This paper will describe DIG 3516 engine component design and single and multicylinder performance development.

Nonlinear Behavior of a Magnetic Bearing System

Abstract: This paper describes the result of a study into the dynamic behavior of a magnetic bearing system. The research focuses attention on the influence of nonlinearities on the forced response of a two-degree-of-freedom rotating mass suspended by magnetic bearings and subject to rotating unbalance and feedback control. Geometric coupling between the degrees of freedom leads to a pair of nonlinear ordinary differential equations, which are then solve using both numerical simulation and approximate analytical techniques. The system exhibits a variety of interesting and somewhat unexpected phenomena including various amplitude driven bifurcational events, sensitivity to initial conditions, and the complete loss of stability associated with the escape from the potential well in which the system can be thought to be oscillating. An approximate criterion to avoid this last possibility is developed based on concepts of limiting the response of the system. The present paper may be considered as an extension to an earlier study by the same authors, which described the practical context of the work, free vibration, control aspects, and derivation of the mathematical model.

Variables Affecting NOx Formation in Lean-Premixed Combustion

Abstract: The formation of NO x in lean-premixed, high-intensity combustion is examined as a function of several of the relevant variables. The variables are the combustion temperature and pressure, fuel type, combustion zone residence time, mixture inlet temperature, reactor surface-to-volume ratio, and inlet jet size. The effects of these variables are examined by using jet-stirred reactors and chemical reactor modeling. The atmospheric pressure experiments have been completed and are fully reported. The results cover the combustion temperature range (measured) of 1500 to 1850 K, and include the following four fuels: methane, ethylene, propane, and carbon monoxide/hydrogen mixtures. The reactor residence time is varied from 1.7 to 7.4 ms, with most of the work done at 3.5 ms. The mixture inlet temperature is taken as 300 and 600 K, and two inlet jet sizes are used. Elevated pressure experiments are reported for pressures up to 7.1 atm for methane combustion at 4.0 ms with a mixture inlet temperature of 300 K. Experimental results are compared to chemical reactor modeling. This is accomplished by using a detailed chemical kinetic mechanism in a chemical reactor model, consisting of a perfectly stirred reactor (PSR) followed by a plug flow reactor (PFR). The methane results are also compared to several laboratory-scale and industrial-scale burners operated at simulated gas turbine engine conditions.

Development Requirements for an Advanced Gas Turbine System

Abstract: In cooperation with US Department of Energy`s Morgantown Energy Technology Center, a Westinghouse-led team is working on the second part of an 8-year, Advanced Turbine Systems Program to develop the technology required to provide a significant increase in natural gas-fired combined cycle power generation plant efficiency. This paper reports on the Westinghouse program to develop an innovative natural gas-fired advanced turbine cycle, which, in combination with increased firing temperature, use of advanced materials, increased component efficiencies, and reduced cooling air usage, has the potential of achieving a lower heating value plant efficiency in excess of 60%.

Laser vibrometry measurements of rotating blade vibrations

Abstract: One of the most important design factors in modern turbomachinery is the vibration of turbomachinery blading. There is a need for developing an in-service, noncontacting, noninterfering method for the measurement and monitoring of gas turbine, jet engine, and steam turbine blade vibrations and stresses. Such a technique would also be useful for monitoring rotating helicopter blades. In the power generation industry, blade failures can result in millions of dollars of downtime. The measurement of blade vibrations and dynamic stresses is an important guide for preventive maintenance, which can be a major contributor to the availability of steam turbine, gas turbine, and helicopter operations. An experiment is designed to verify the feasibility of such a vibration monitoring system using the reference beam on-axis laser-Doppler technique. The experimental setup consists of two flat, cantilever blades mounted on a hub attached to the shaft of a dc motor. The motor rests on a linear bearing permitting motion only in the direction of the motor shaft. The motor and blade assembly is then excited via an electrodynamic shaker at the first natural frequency of the blades. The resulting blade vibration is then detected using a laser vibrometer. The vibration frequencies and amplitudes of the two rotating blades are successfully measured.

A Methane-Steam Reformer for a Basic Chemically Recuperated Gas Turbine

Abstract: Several illustrative designs are presented for a methane-steam reformer (MSR) that is used as a chemical recuperator in a Basic Chemically Recuperated Gas Turbine power cycle (a «Basic» CRGT is defined as one without intercooling or reheat). In this cycle, an MSR, heated by the turbine exhaust flow, converts a methane-steam mixture into a hydrogen-rich fuel that powers the gas turbine. A computer code was developed to calculate the size and performance characteristics of counterflow reformers. The code consists of a one-dimensional marching scheme that integrates the chemical, thermodynamic, and geometric variables along the heat exchanger/reformer tubes. The calculated designs were selected to give near-minimum catalyst volumes. These designs show that maintaining a high reformer gas temperature, using combustion-side heat transfer augmentation techniques, and using a catalyst of high reactivity are critical to obtaining a compact reformer design

Improved Method for Flame Detection in Combustion Turbines

Abstract: A fast response chemiluminescent flame detection approach is presented along with field test results from a fiber optic based flame detector device. Chemiluminescence, the light given off by molecules formed in their excited states, has long been recognized as a diagnostics method for use in combustion. The recent advent of higher quality optical fibers with improved transmission properties in the UV, as well as UV optical detectors, has made the use of chemiluminescence for gas turbine diagnostics and monitoring practical. Advances in combustor designs on a new low-emissions machines as well as reliability issues with some existing machines are creating the need for improved flame dynamics measurements as well as improvements in reliability for existing measurements such as combustor flame detection. This paper discusses the technology, principle of operation, and detectors that operate on the chemiluminescence principle.

Calculation of Two-Phase Flow in Gas Turbine Combustors

Abstract: A method is presented for computing steady two-phase turbulent combusting flow in a gas turbine combustor. The gas phase equations are solved in an Eulerian frame of reference. The two-phase calculations are performed by using a liquid droplet spray combustion a model and treating the motion of the evaporating fuel droplets in a Lagrangian frame of reference. The numerical algorithm employs nonorthogonal curvilinear coordinates, a multigrid iterative solution procedure, the standard k-{epsilon} turbulence model, and a combustion model comprising an assumed shape probability density function and the conserved scalar formulation. The trajectory computation of the fuel provides the source terms for all the gas phase equations. This two-phase model was applied to a real piece of combustion hardware in the form of a modern GE/SNECMA single annular CFM56 turbofan engine combustor. For the purposes of comparison, calculations were also performed by treating the fuel as a single gaseous phase. The effect on the solution of two extreme situations of the fuel as a gas and initially as a liquid was examined. The distribution of the velocity field and the conserved scalar within the combustor, as well as the distribution of the temperature field in the reaction zone and in themore » exhaust, were all predicted with the combustor operating both at high-power and low-power (ground idle) conditions. The calculated exit gas temperature was compared with test rig measurements. Under both low and high-power conditions, the temperature appeared to show an improved agreement with the measured data when the calculations were performed with the spray model as compared to a single-phase calculation.« less

The Performance Optimization of a Gas Turbine Cogeneration / Heat Pump Facility with Thermal Storage.

Abstract: With the push for greater energy conservation, the need for heating and/or power production is being filled by cogeneration facilities. Thus, the search for the best performance at the least cost for such multipurpose plants is made much more difficult by the fact that such facilities must meet differing goals or demands. Such a facility exists at the Ecole Polytechnique Federale de Lausanne (EPFL) and has been studied in order to find the optimum modes of operation as a function of time for variations in both the heating and electrical demands this facility must meet. The results of this study are presented here. The plant itself provides heat and electricity for both the EPFL and the University of Lausanne and is projected to supply electricity to the exterior utility grid provided it can be shown to be economically viable. The plant’s primary components include two gas turbines, a heat recovery system, two heat pumps, a set of heat storage tanks, and both medium and low-temperature district heating networks. In order to find the optimum mode of operation, a mixed-integer linear programming approach was used, which balances the competing costs of operation and minimizes these costs subject to the operational constraints placed on the system. The effects of both the cost of the fuel and the costs of electricity sold and bought on the best performance of the system are evaluated. In addition, the important features of the modeling process are discussed, in particular the heat storage tanks, which complicate the optimization of the series of steady-state models used to model the overall quasi-steady-state behavior of the system.

Degradation of a Jet A Fuel in a Single-Pass Heat Exchanger

Abstract: The formation of bulk and surface insolubles in a Jet A fuel during a single pass through heated stainless-steel tubes has been studied. Low temperature and low flow rates were utilized to produce near-isothermal conditions. In a second series of experiments, depletion of oxygen in the fuel saturated with respect to room-temperature air was measured under identical isothermal conditions. At a wall/bulk-fuel temperature of 185°C, rates of surface deposition and oxygen depletion were correlated; the maximum in the surface-deposition rate was found to occur after the Jet A fuel was stressed sufficiently that the dissolved oxygen was totally consumed. Results are discussed in terms of the autoxidation of the Jet A fuel and the concurrent production of deleterious bulk and surface insolubles

Detailed Measurements on a Modern Combustor Dump Diffuser System

Abstract: An experimental investigation has been carried out to determine the flow characteristics and aerodynamic performance ofa modern gas turbine combustor dump diffuser The system comprised a straight walled prediffuser, of area ratio 135, which projected into a dump cavity where the flow divided to pass either into the flame tube or surrounding feed annuli In addition, a limited amount of air was removed to simulate flow used for turbine cooling The flame tube was relatively deep, having a radial depth 55 times that of the passage height at prediffuser inlet, and incorporated burner feed arms, cowl head porosity, cooling rings, and primary ports Representative inlet conditions to the diffuser system were generated by a single-stage axial flow compressor Results are presented for the datum configuration, and for a further three geometries in which the distance between prediffuser exit and the head of the flame tube (ie, dump gap ) was reduced Relatively high values of stagnation pressure loss were indicated, with further significant increases occurring at smaller dump gaps These high losses, which suggest a correlation with other published data, are due to the relatively deep flame tube and short diffuser length Furthermore, the results also focus attention on how the presence of a small degree of diffuser inlet swirl, typical of that which may be found within a gas turbine engine, can result in large swirl angles being generated farther downstream around the flame tube This is particularly true for flow passing to the inner annulus

Blade erosion in automotive gas turbine engine

Abstract: In this work, a study has been conducted to predict blade erosion and surface deterioration of the free power turbine of an automotive gas turbine engine. The blade material erosion model is based on three-dimensional particle trajectory simulations in the three-dimensional turbine flow field. The particle rebound characteristics after surface impacts were determined from experimental measurements of restitution ratios for blade material samples in a particulate flow tunnel. The trajectories provide the spatial distribution of the particle impact parameters over the blade surfaces. A semi-empirical erosion model, derived from erosion tests of material samples at different particulate flow conditions, is used in the prediction of blade surface erosion based on the trajectory impact data. The results are presented for the three-dimensional particle trajectories through the turbine blade passages, the particle impact locations, blade surface erosion pattern, and the associated erosion parameters. These parameters include impact velocity, impact angle, and impact frequency. The data can be used for life prediction and performance deterioration of the automotive engine under investigation

Effects of Oxygen and Additives on the Thermal Stability of Jet Fuels

Abstract: A previously developed flowing single-pass heat-exchanger test rig (Phoenix rig) has been used to evaluate the effectiveness of various additives and the kinetic mechanism of both deposit formation and oxygen consumption. The Phoenix rig has been modified to include not just a heated single tube, but also a cooling test section and both hot and cold filters. The effects of flow conditions, antioxidants, and metal deactivator additives on the location and amount of the deposit are discussed. In general antioxidants were effective at reducing the deposits on the hot test section, but almost invariably caused increased plugging of cool downstream filters. Downstream plugging of cool filters also increased with decreased temperatures in the heated section or with increased flow. Tests with both oxygen-saturated and oxygen-depleted fuels have shown that the solubility of oxygen is linearly related to the fraction of oxygen in a sparge gas, and that the amount of deposit is linearly related to the total quantity of dissolved oxygen passed. Finally, in contrast to initial modeling efforts, the consumption of oxygen is shown to be significantly more complex than a simple bimolecular, pseudo-first-order in oxygen, process. It is found to be much closer to pseudo-zero-order in the early stages, decaying to pseudo-firt-order when the oxygen nears depletion

Reduction of Combustion Irreversibility in a Gas Turbine Power Plant Through Off-Gas Recycling

Abstract: Combustion in conventional fossil-fueled power plants is highly irreversible, resulting in poor overall energy conversion efficiency values (less than 40 percent in many cases). The objective of this paper is to discuss means by which this combustion irreversibility might be reduced in gas turbine power cycles, and the conversion efficiency thus improved upon. One such means is thermochemical recuperation of exhaust heat. The proposed cycle recycles part of the exhaust gases, then mixes them with fuel prior to injection into a reformer. The heat required for the endothermic reforming reactions is provided by the hot turbine exhaust gases. Assuming state-of-the-art technology, and making a number of simplifying assumptions, an overall efficiency of 65.4 percent was attained for the cycle, based on the lower heating value (LHV) of the methane fuel. The proposed cycle is compared to a Humid Air Turbine (HAT) cycle with similar features that achieves an overall efficiency of 64.0 percent. The gain in cycle efficiency that can be attributed to the improved fuel oxidation process is 1.4 percentage points. Compared to current high-efficiency gas turbine cycles, the high efficiency of both cycles studied therefore results mainly from the use of staged compression and expansion with intermediate coolingmore » and reheating, respectively.« less

Part-load operation of combined cycle plants with and without supplementary firing

Abstract: The design point performance of combined cycle power plants has been steadily increasing, because of improvements both in the gas turbine technology and in the heat recovery technology, with multiple pressure heat recovery steam generators. The concern remains, however, that combined cycle power plants, like all installations based on gas turbines, have a rapid performance degradation when the load is reduced. In particular, it is well known that the efficiency degradation of a combined cycle is more rapid than that of a classical steam plant. This paper describes a methodology that can be used to evaluate the part-load performances of combined cycle units. Some examples are presented and discussed, covering multiple pressure arrangements, incorporating supplemental firing and possibly reheat. Some emphasis is put on the additional flexibility offered by the use of supplemental firing, in conjunction with schemes comprising more than one gas turbine per steam turbine. The influence of the gas turbine controls, like the use of variable inlet guide vanes in the compressor control, is also discussed.