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Coal, Biomass and Alternative Fuels

1991;():V003T05A001. doi:10.1115/91-GT-132.
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Synthesis gas produced in coal gasification processes contains hydrogen, along with carbon monoxide, carbon dioxide, hydrogen sulfide, water, nitrogen, and other gases, depending on the particular gasification process. Development of membrane technology to separate the hydrogen from the raw gas at the high operating temperatures and pressures near exit gas conditions would improve the efficiency of the process.

Tubular porous alumina membranes with mean pore radii ranging from about 9 to 22 A have been fabricated and characterized. Based on the results of hydrostatic tests, the burst strength of the membranes ranged from 800 to 1600 psig, with a mean value of about 1300 psig. These membranes were evaluated for separating hydrogen and other gases.

Tests of membrane permeabilities were made with helium, nitrogen, and carbon dioxide. Measurements were made at room temperature in the pressure range of 15 to 589 psi. In general, the relative gas permeabilities correlated qualitatively with a Knudsen flow mechanism; however, other gas transport mechanisms such as surface adsorption may also be involved.

Efforts are under way to fabricate membranes having still smaller pores. At smaller pore sizes, higher separation factors are expected from molecular sieving effects.

Commentary by Dr. Valentin Fuster
1991;():V003T05A002. doi:10.1115/91-GT-184.
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In the eight-year, multicontractor program to develop a 220-MW coal-fired combustion turbine combined cycle plant, the team is now into its third year of subscale slagging combustor testing. Because of an ability to accept unbeneficiated, utility-grade coal, the slagging combustor is the key to the direct coal-fired combustion turbine. The projected plant will contain two 80-MW combustion turbines equipped with slagging combustors, two heat recovery steam generators, and a 65-MW steam turbine.

In testing to date, the concept has demonstrated its ability to handle high- and low-sulfur bituminous coals, and low-sulfur subbituminous coal. Feeding the fuel in the form of pulverized coal has proven to be superior to coal-water mixture type feed. The program objectives relative to combustion efficiency, combustor exit temperature, NOx emissions, carbon burnout, and slag rejection have been met. Work continues to reduce alkali, particulate, and SOx levels leaving the combustor. Parametric studies have been made that focus on the latter two problems. They indicate that faster, more thorough slag removal between the rich and lean stages is the path toward achieving lower emission of SOx, alkali, and particulates. New components have been added to the subscale combustor for this purpose.

Commentary by Dr. Valentin Fuster
1991;():V003T05A003. doi:10.1115/91-GT-187.
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Solar Turbines is developing a coal fueled version of its 3.8 MW Centaur H gas turbine for cogeneration applications. To protect gas turbine components from erosion and corrosion due to impacting particulates, and to meet New Source Performance Standards for particulate emissions, ceramic barrier filters are being employed. The test program includes evaluation of silicon carbide candle filters. Fourteen candles are being tested for 50 h at design temperature and face velocity using the particulate-laden gas stream from a two-stage slagging combustor system. The testing includes determining collection efficiency and obtaining pressure drop versus time profiles. Additionally, exposure testing is being used to determine whether loss in strength, or changes in the chemical or mineralogical structure have occurred. This includes four-point bend testing, X-ray diffraction and scanning electron microscopy with energy dispersive X-rays.

Commentary by Dr. Valentin Fuster
1991;():V003T05A004. doi:10.1115/91-GT-188.
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A new hot gas filter for removal of particulates upstream of gas turbines is described and compared with a device called a candle. Candle filters are made in the shape of a large test tube from ceramic materials bonded with a glassy phase. The filtering membrane is fairly thick making candles relatively heavy. A thinner filter would be easier to support, more tolerant of thermal shock, and would offer less resistance to flow. A filter of a ceramic/ceramic composite may achieve these goals and specimens are being fabricated by depositing a ceramic material on a ceramic fiber preform by chemical vapor infiltration. The ceramic matrix is silicon carbide and the ceramic fiber reinforcement is alumina-boria-silica. Progress toward filter development is described.

Commentary by Dr. Valentin Fuster
1991;():V003T05A005. doi:10.1115/91-GT-206.
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This paper summarizes 1/10 scale combustor test results and design parameters that have lead to the fabrication, assembly and test of a full-scale, 22 MW thermal-input (76 mmbtu/hr) combustor and engine system. The engine is a production Allison 501-K industrial turbine that has been modified to accept an external combustor designed for burning coal-water-slurry (CWS) fuel. The combustor utilizes rich-quench-lean (RQL) staging to control emissions of both thermal NOx and NOx formed from nitrogenous compounds contained in the coal-water slurry. Water is injected into the quench zone to freeze molten ash that is formed in the rich zone. The dry ash is removed from the system and collected in storage vessels by passing the hot combustion products through parallel cyclone separators. The cleaned fuel-rich gases pass to the lean zone where the addition of compressor-discharge air results in auto-ignition of the gas mixture and provides sufficient oxygen for completion of the combustion reactions.

Measurements made of emissions from the bench-scale combustor at simulated power conditions show that NOx and CO concentrations of less than 50 ppmvd corrected to 15% oxygen can be expected. Check out testing of the full-scale combustor on CWS and the combined combustor/engine assembly on distillate fuel are now in progress. It is anticipated that engine testing on CWS will commence in early 1991.

Commentary by Dr. Valentin Fuster
1991;():V003T05A006. doi:10.1115/91-GT-212.
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A full size combustor for a coal-fueled industrial gas turbine engine has been designed and fabricated. The design is based on extensive work completed through one-tenth scale combustion tests. Testing of the combustion hardware will be completed with a high pressure air supply in a combustion test facility before the components are integrated with the gas turbine engine. The combustor is a two-staged, rich-lean design. Fuel and air are introduced in the primary combustion zone where the combustion process is initiated. The primary zone operates in a slagging mode inertially removing coal ash from the gas stream. Four injectors designed for coal-water mixture (CWM) atomization are used to introduce the fuel and primary air. In the secondary combustion zone additional air is injected to complete the combustion process at fuel lean conditions. The secondary zone also serves to reduce the gas temperatures exiting the combustor. Between the primary and secondary zones is a Particulate Rejection Impact Separator (PRIS). In this device much of the coal ash that passes from the primary zone is inertially separated from the gas stream. The two-staged combustor along with the PRIS have been designated as the combustor island. All of the combustor island components are refractory lined to minimize heat loss. Fabrication of the combustor has been completed. The PRIS is still under construction. The combustor hardware is being installed at the Caterpillar Technical Center for high pressure test evaluation. The design, test installation, and test plan of the full size combustor island are discussed.

Commentary by Dr. Valentin Fuster
1991;():V003T05A007. doi:10.1115/91-GT-213.
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An experimental investigation was conducted to study the ash particle rebound characteristics and the associated erosion behavior of superalloys and aluminide coatings subjected to gas-particle flows at elevated temperatures. A three-component LDV system was used to measure the restitution parameters of 15 micron mean diameter coal ash particles impacting some widely used superalloys and coatings at different angles. The presented results show the variation of the particle restitution ratios with the impingement angle for the coated and uncoated superalloys. The erosion behaviors of INCO-738, MAR 246 and X40 superalloys and protective coatings C, N, RT22 and RT22B have also been investigated experimentally at high temperatures using a specially designed erosion tunnel. The erosion results show the effect of velocity, temperature and the impact angle on the erosion rate (weight loss per unit weight of particles). Based on the experimental results of the particle mass effect on both weight losses and erosion rates, the coating lives have been estimated for different particle concentrations.

Commentary by Dr. Valentin Fuster
1991;():V003T05A008. doi:10.1115/91-GT-214.
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An approach for estimating deposition in gas turbines is described. This approach extrapolates deposition data from lower cost experiments than turbine engine or cascade tests. The purpose is a method to screen candidate fuels and turbine protection methods so that only the most promising need be evaluated in turbine tests. The deposition approach is applied to estimate deposition maintenance intervals for a tested fuel, evaluate benefits of hot gas cleanup, and provide fuel screening criteria.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1991;():V003T05A009. doi:10.1115/91-GT-215.
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This paper describes a procedure used to model the performance of gas turbines designed to fire natural gas (or distillate oil) when fired on medium-BTU fuel, such as coal-derived syngas. Results from such performance studies can be used in the design or analysis of Gasification Combined-Cycle (GCC) power plants. The primary difficulty when firing syngas in a gas turbine designed for natural gas is the tendency to drive the compressor toward surge. If the gas turbine has sufficient surge margin and mechanical durability, Gas Turbine Evaluation code (GATE) simulations indicate that net output power can be increased on the order of 15% when firing syngas due to the advantageous increase in the ratio of the expander-to-compressor mass flow rates. Three classes of single-spool utility gas turbines are investigated spanning firing temperatures from 1985 F to 2500 F (1358 K to 1644 K). Performance simulations at a variety of part-load and ambient temperature conditions are described; the resulting performance curves are useful in GCC power plant studies.

Commentary by Dr. Valentin Fuster
1991;():V003T05A010. doi:10.1115/91-GT-288.
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This paper discusses the performance benefits available from compressor discharge water injection in an indirect-fired gas turbine. The results of parametric performance studies are the main technical focus. The performance studies are part of the U.S. Department of Energy (DOE) Morgantown Energy Technology Center (METC) indirect-fired gas turbine program. The key technical approach is to develop a high-pressure, coal-fired ceramic heat exchanger to serve as the air heater.

A high-pressure coal-fired ceramic air heater is now under development in a DOE-sponsored program at Hague International. The goal of this program is to develop a heat exchanger suitable for turbine inlet temperatures from 1,100 to 1,260 °C. With a turbine inlet temperature in this range, coal-fired indirect systems have performance superior to direct-fired gas-fueled simple cycle systems. Using conservative assumptions, the coal-fired indirect cycle has calculated net plant efficiencies in the 32 to 37 percent range, on a higher heating value (HHV) basis, at typical pressure ratios and 1,260 °C (2,300 °F) turbine inlet temperature. Adding a steam bottoming cycle raises the net plant efficiency (NPE) to 44–48 percent HHV. Adding water injection raises the simple cycle efficiency to 41–43 percent HHV and the combined cycle efficiency to 47–54 percent HHV. These NPE’s compare favorably to the most advanced industrial direct-fired systems. For example, a natural gas-fired GE MS7001-F has published HHV efficiencies of 31.1 percent simple cycle and 46.1 percent combined cycle (Gas Turbine World, 1990).

Commentary by Dr. Valentin Fuster
1991;():V003T05A011. doi:10.1115/91-GT-289.
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Effects of the exhaust of a coal fueled gas turbine combustion system on turbine hot section materials and coatings are being determined. A system has been developed to evaluate currently used turbine materials and coatings exposed to coal combustion exhaust. Using an engine to test these materials is not feasible due to the inordinately expensive fuel costs associated with running the engine. Therefore, a scaled-down Hot End Simulation Rig (HESR) was designed and built to economically evaluate turbine components operating with a coal-water mixture (CWM) flow rate of 3.8–7.6 liters/hour (1–2 gallons/hour). The rig incorporates primary and secondary combustion zones, a ceramic barrier filter, and a housing for the material samples. Cooling air is metered to the samples to simulate the material temperatures of subsequent turbine stages. Because of the small scale of the rig, much development focused on the design of an adequate fuel injector that would operate reliably for long periods without plugging. Long-term testing is planned to subject the test specimens to coal exhaust using the alkali level in the fuel as the principle variable. An initial level of 300 ppm is used for a 1000 hour preliminary test. The design, development, and test procedure of the HESR are discussed.

Commentary by Dr. Valentin Fuster
1991;():V003T05A012. doi:10.1115/91-GT-292.
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An analytic study was conducted to determine the effects of turbine design, airfoil shape and material on particulate erosion of turbine airfoils in coal-fueled, direct-fired gas turbines used for electric power generation. First-stage, mean-line airfoil sections were designed for 80 MW output turbines with 3 and 4 stages. Two-dimensional particle trajectory calculations and erosion rate analyses were performed for a range of particle diameters and densities and for ductile and ceramic airfoil materials. Results indicate that the surface erosion rates can vary by a factor of 5 and that erosion on rotating blades is not well correlated with particle diameter. The results quantify the cause/effect turbine design relationships expected and assist in the selection of turbine design characteristics for use downstream of a coal-fueled combustion process.

Commentary by Dr. Valentin Fuster
1991;():V003T05A013. doi:10.1115/91-GT-293.
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Imatran Voima Oy (IVO) is developing an advanced gas turbine power plant process for wet fuels as peat, biomass, and lignite. The process consists of a steam injected gas turbine, an air blown gasifier and a pressurized fuel dryer. The dryer operates at steam atmosphere and is integrated to the process to produce injection steam for the gas turbine. The heat needed for drying is taken from the exhaust gases of the gas turbine. The process is patented and called IVOSDIG.

Topics: Fuels , Power stations
Commentary by Dr. Valentin Fuster
1991;():V003T05A014. doi:10.1115/91-GT-342.
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A preliminary design study of four coal-burning gas-turbine engines using the exhaust-heated cycle and state-of-the-art components has been completed. In the exhaust-heated cycle the combustor takes air from the turbine exhaust and delivers hot combustion products to a heat exchanger. In the program reported here a rotary ceramic-matrix regenerator is used; in it the temperature of the compressor-delivery air is raised to that required at the turbine inlet. Some initial experiments on the flow of hot coal-combustion products through ceramic passages and of cold ash-laden air through a rotary ceramic-matrix regenerator have been conducted. Highly favorable results have been obtained on all aspects on which definite conclusions could be drawn.

Commentary by Dr. Valentin Fuster
1991;():V003T05A015. doi:10.1115/91-GT-380.
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This work presents the results of a study conducted to investigate particle surface interaction characteristics and their effects on the particle dynamics and blade erosion in axial flow gas turbines. The particle restitution velocities measured experimentally using Laser Doppler Velocimetry in a special tunnel are analyzed using statistical methods. The resulting distribution functions of the rebounding particle velocities after surface impacts are introduced in the particle trajectory simulations through the turbine blade passages, using a methodology that combines particle dynamics computations in a probabilistic model. The presented results for the simulated ash particle dynamics demonstrate the effect of the experimentally measured variance in the particle restitution characteristics on the particle surface impacts, and the associated blade erosion in an axial flow turbine.

Commentary by Dr. Valentin Fuster
1991;():V003T05A016. doi:10.1115/91-GT-381.
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A pilot hot gas particulate removal system based on positive porous ceramic filters has been tested on the Grimethorpe Pressurized Fluidized Bed Combustor facility. The filters are in the form of closed ended tubes, 1.5 m long: these are generally called ‘candles’. The dust accumulates on the outside of the candles, and is periodically removed by a pulse of air into the candle interior, which then flows outwards through the candle wall in the reverse direction to the normal flow of the combustion gas. The EPRI system contained a maximum of 130 candles, which is approximately equivalent to the requirement for 7 MW(e) capacity, depending on the filter operating parameters. The filter unit operated for a total of 860 hours under PFBC conditions, of which 790 hours were at defined process conditions, typically 850°C and 10 bar.

The amount of gas flowing through each filter element was varied, and the time between cleaning pulses was also varied. The pressure drop through each filter element rose as the dust accumulated on the outer wall, and recovered after the cleaning pulse. However, the post-cleaning pressure drop does not recover to the original clean candle value, but increases with time. It is believed that a steady-state value is attained, but the exposure in the Grimethorpe test series was insufficient to establish this unequivocally.

During the test, five candles failed. This appears to have been due to mechanical shock, as a result of candles lifting because of excessive pressure differentials across their support plate, and dropping back. The failures are not believed to be intrinsic to the technology. However, in addition a reduction in the strength of the candles with time of exposure was observed. This might also attain a steady state value, but this too could not be established on the basis of the tests reported in this paper. This is clearly a matter of importance, and further work will be required to determine the suitability of the clay-bonded silicon carbide medium used in these tests for this application.

A number of deficiencies in the design of the unit emerged with the operating experience, and suggestions have been made for improvements. However, it is clear that further work on design optimization is required.

The pulse cleaning air usage in the tests was greater than would be economically acceptable in a practical system. Further work needs to be done to optimize the cleaning cycle.

Overall, the test was very successful, and when operating properly the filters removed essentially all of the dust in the gas exiting from the combustor. Apart from the issues with the candle strength and the pulse cleaning air usage, the other problems were not believed to be of major importance in the further development of the technology.

This paper will summarize the test results, emphasizing the problems of candle durability and the pulse cleaning system.

Commentary by Dr. Valentin Fuster
1991;():V003T05A017. doi:10.1115/91-GT-383.
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Secondary erosion caused by particulate flow is a new research direction. On the basis of numerical analysis of the trajectory of particle motion in rotating gas flow, its equilibrium condition and causes of aggregation, a physical flow model of secondary erosion is suggested. By this model the mechanism of secondary erosion caused by particulate gas flow could be primarily explained. The vortex chamber experiment verifies the particle aggregation tendency in vortex flow and the experiment of particle deposition in bending tube proves in certain extent the correctness of the suggested model.

Commentary by Dr. Valentin Fuster
1991;():V003T05A018. doi:10.1115/91-GT-384.
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Advanced coal based power generation systems such as the British Coal Topping Cycle offer the potential for high efficiency electricity generation with minimum environmental impact. An important component of the Topping Cycle programme is the development of a gas turbine combustion system to burn low calorific value (3.5–4.0 MJ/m3 wet gross) coal derived fuel gas, at a turbine inlet temperature of 1260°C, with minimum pollutant emissions.

The paper gives an overview of the British Coal approach to the provision of a gas turbine combustion system for the British Coal Topping Cycle, which includes both experimental and modelling aspects. The first phase of this programme is described, including the design and operation of a low-NOx turbine combustor, operating at an outlet temperature of 1360°C and burning a synthetic low calorific value (LCV) fuel gas, containing 0 to 1000 ppmv of ammonia. Test results up to a pressure of 8 bar are presented and the requirements for further combustor development outlined.

Commentary by Dr. Valentin Fuster

Combustion and Fuels

1991;():V003T06A001. doi:10.1115/91-GT-036.
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The objective of the Innovative High-Temperature Fuel Nozzle Program was to design, fabricate, and test propulsion engine fuel nozzles capable of performance despite extreme fuel and air inlet temperatures. Although a variety of both passive and active methods for reducing fuel wetted-surface temperatures were studied, simple thermal barriers were found to offer the best combination of operability, cycle flexibility, and performance. A separate nozzle material study examined several nonmetallics and coating schemes for evidence of passivating or catalytic tendencies. Two pilotless airblast nozzles were developed by employing finite-element modeling to optimize thermal barriers in the stem and tip. Operability of these prototypes was compared to a current state-of-the-art piloted, prefilming airblast nozzle, both on the spray bench and through testing in a can-type combustor. The three nozzles were then equipped with internal thermocouples and operated at 1600F air inlet temperature while injecting marine diesel fuel heated to 350F. Measured and predicted internal temperatures as a function of fuel flow rate were compared. Results show that the thermal barrier systems dramatically reduced wetted-surface temperatures and the potential for coke fouling, even in an extreme environment.

Commentary by Dr. Valentin Fuster
1991;():V003T06A002. doi:10.1115/91-GT-037.
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A propane-fueled research combustor has been designed and developed to investigate lean blowouts in a simulated primary zone of the combustors for aircraft gas turbine engines. To better understand the flow development and to ensure that the special provisions in the combustor for optical access did not introduce undue influence, measurements of the velocity fields inside the combustor were made using laser Döppler anemometry. These measurements were made in isothermal, constant density flow to relate the combustor flow field development to known jet behavior and to backward-facing step experimental data in the literature. The major features of the flow field appear to be consistent with the expected behavior, and there is no evidence that the provision of optical access adversely affected the flows measured.

Commentary by Dr. Valentin Fuster
1991;():V003T06A003. doi:10.1115/91-GT-042.
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A numerical model for turbulent reacting flow is described and applied for predictions in an industrial gas turbine combustor operating on low-Btu coal gas. The model, based on fast-reaction limit, used Favre averaged conservation equations with the standard k-ε model of turbulence. Effects of turbulent fluctuations on chemistry are described statistically in terms of the mean, variance and probability density function (assumed to be β-distribution) of the mixture fraction. Two types of geometric approximations, namely axisymmetric and three-dimensional, were used to model the combustor. Computations were performed with (a) no swirl (b) weak swirl and (c) strong swirl at the fuel and primary air inlets. Essentially, the same bulk mean temperature distributions were obtained for axisymmetric and three-dimensional calculations while the computed pattern factors and the liner wall temperatures for the two differed significantly. Complete combustion was predicted with strong swirl, a result supported by the available test data. The maximum liner wall temperature predicted for three-dimensional calculations compared favorably with the experimental data while the predicted maximum exhaust gas temperature differed by ≈120 K. The difference was attributed to measurement uncertainties, model assumptions and lack of accurate data at the inlets. The maximum flame temperature was below 1,850 K indicating that thermal NOx may be insignificant.

Commentary by Dr. Valentin Fuster
1991;():V003T06A004. doi:10.1115/91-GT-043.
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A pressure-swirl fuel nozzle generating a hollow-cone spray with nominal cone angle of 30 degrees is used in a swirl-stabilized combustor. The combustor is circular in cross section with swirl plate and fuel nozzle axes aligned and coinciding with the axis of the chamber. Kerosene is injected upward inside the chamber from the fuel nozzle. Separate swirl and dilution air flows are uniformly distributed into the chamber that pass through the honey comb flow straighteners and screens. Calculated swirl number of 1.5 is generated with the design swirl plate exit air velocity of 30 degrees with respect to the chamber axis. Effects of swirl and dilution air flow rates on the shape and stability of the flame are investigated. Stable and classical liquid fuel sheet disintegration zone exists close to the nozzle with no visible light followed by a luminous blue region and a mixed blue/yellow region that subsequently turns into yellow for most of the part in the flame. A Phase Doppler Particle Analyzer (PDPA) is used to measure drop size, mean and rms axial velocity for two cases of with and without combustion at six different axial locations from the nozzle. For the no-combustion case all air and fuel flow rates were kept at the same values as the combusting spray condition. Results for mean axial drop velocity profiles indicate widening of the spray due to combustion while the magnitudes of the peak velocities are slightly increased. No measurements inside the hollow-cone spray are possible due to burning of fuel droplets. Drop turbulence decreases due to combination of increase in gas kinematic viscosity and elimination of small drops at high temperatures. Sauter Mean Diameter (SMD) radial profiles at all axial locations increase with combustion due to preferential burning of small drops.

Commentary by Dr. Valentin Fuster
1991;():V003T06A005. doi:10.1115/91-GT-062.
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A computational procedure based on the solution of fully elliptic Navier-Stokes equations on a body-fitted non-orthogonal grid was used to obtain flow fields in annular diffusers with a suction slot at the inner and outer walls. The turbulence effects were simulated by high Reynolds number form of the k-ε model. The calculation method was used to modify an industrial gas turbine (GE MS · 7001F) compressor/combustor annular diffuser to allow extraction of compressed airflow for coal gasification in simplified IGCC Systems. The air for gasification was extracted through a suction slot on the outer wall of the diffuser which was curved to improve the overall performance and to avoid flow separation; both of these insured by providing accelerated flow through the suction slot and nearly constant wall pressure downstream of the slot. Suction slot and outer wall geometries to result in the above conditions were determined by a trial and error procedure. The diffuser’s performance was further improved by extracting 6% of the compressed air through a slot at the inner wall, kept straight due to structural constraints. The resulting diffuser arrangement was relatively insensitive to the upstream disturbances.

Commentary by Dr. Valentin Fuster
1991;():V003T06A006. doi:10.1115/91-GT-097.
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The thermal stability characteristics of four kerosine-type fuels are examined using a heated-tube apparatus which allows independent control of fuel pressure, fuel temperature, tube-wall temperature, and fuel flow rate. It is a closed loop system, and fuet flows through the heated tube for periods ranging from 6 to 22 hrs. The deposition rates of carbon on the tube walls are measured by weighing the tube before and after each test.

The results obtained show that tube-wall and fuel temperatures both have a marked influence on deposition rates, the impact of fuel temperature being stronger than that of wall temperature. It is also found that deposition rates increase continuously with increases in tube-wall temperature. This finding contradicts the results of previous studies which had led to the conclusion that deposition rates increase with increase in wall temperature up to a certain value beyond which any further increase in wall temperature causes the deposition rate to decline.

Commentary by Dr. Valentin Fuster
1991;():V003T06A007. doi:10.1115/91-GT-098.
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The Transfer Number (B) assumes considerable importance in the evaporation and diffusion of fuels prior to their combustion. Quite often the Transfer Number is assumed to be a constant for a given fuel. These notes examine the feasibility of this assumption New correlations have been derived for the specific heats of the liquid fuels and their latent heats, over a wide range of temperatures and pressures, as also the effects of pressure upon the boiling characteristics. New prediction techniques are also proposed for critical temperatures and pressures.

Taking note of the above correlations, it becomes possible to assess the values of B for a wide range of combustor operating conditions for any given fuel. The significance of these variations upon the probable combustion behaviour of the fuels is then commented upon. The results show that the assumption of a constant value for B could lead to a significant mis-interpretation of combustion behaviour due to operating conditions and/or the use of different fuels.

Commentary by Dr. Valentin Fuster
1991;():V003T06A008. doi:10.1115/91-GT-106.
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In this paper research is focused on the inner operation of prefilming airblast atomizers and its effect on liquid atomization. Liquid wavy film thickness and wavelength-frequency spectra, which characterize the liquid motion inside the atomizers, are measured with specifical techniques. The motion and separation of liquid wavy film are picturized by means of laser pulse micrography technique. The spray is measured with the Malvern Particle Sizer. The experiments show the liquid atomization is initiated by separation of the liquid film waves from their main film. The atomization characteristics are dominated by the extent of air/liquid interaction inside the atomizers. In addition, liquid flow rate effect on atomization is comfirmed. No liquid collection near the atomizer edges is found.

Commentary by Dr. Valentin Fuster
1991;():V003T06A009. doi:10.1115/91-GT-107.
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In the present paper, anatomization model for a prefilming airblast atomizer is constructed and put into numerical computation. A separation criterion is suggested to judge the liquid wavy film disintegration. Quantitative relationships between the spray and the wavelength-frequency spectrum of the liquid wavy film are analysed. A computational method called Trace-Statistics is developed to trace the liquid wavy film separation and droplet motion. Through statistical computation of the droplets, desired parameters of spray distributed in the calculated plane can be obtained. A computation example of the model is demonstrated. Its results agree with the experiments.

Topics: Computation
Commentary by Dr. Valentin Fuster
1991;():V003T06A010. doi:10.1115/91-GT-108.
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Combustion of a single fuel droplet has long been studied because it establishes the background of understanding the behavior of spray combustion. Ignition is the most critical process during its life time. According to a practical ignition criterion, many parametric studies are performed to examine the effects on ignition under different droplet conditions and different ambient conditions. In addition, two liquid-phase models, infinite conductivity model and conduction limit model, are discussed to demonstrate the heating effect of droplet itself. Dual-period concept is introduced to clarify the dominant factor that governs the ignition process. A special hybrid numerical scheme, ICED-ALE, is used to resolve the difficulties arising from the rapid transition of ignition and regression behavior of a fuel droplet. The numerical predictions show good agreement with the experimental data.

Topics: Fuels , Drops , Ignition
Commentary by Dr. Valentin Fuster
1991;():V003T06A011. doi:10.1115/91-GT-109.
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This paper describes a theoretical study of combustion in mixtures of fuel vapour, droplets and air under conditions representative of cold starting in gas turbines. It combines two previously developed models — one for heterogeneous flame propagation and the other for describing the complex evaporative behaviour of real fuel blends. Both models have been validated against experimental data, and the combined model is used to investigate the effect of fuel properties and injection system performance on minimum ignition energy, blowout velocity, lean extinction limits and related aspects significant for cold starting. Conditions are identified when fuel volatility is important and single component approximations are unrepresentative of real fuel behaviour. Explicit equations are given which predict the vapour pressures of JP-4, Jet A1 and diesel fuel.

Commentary by Dr. Valentin Fuster
1991;():V003T06A012. doi:10.1115/91-GT-110.
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Four computer codes (PHOENICS, PCGC, FLUENT and INTERN) representing a spectrum of existing combustion modeling capabilities were evaluated for low-Btu gas applications. In particular, the objective was to identify computer code(s) that can be used effectively for predictions of (a) the flow field to yield efficient combustion, (b) the temperature field to ensure structural integrity and (c) species concentrations to meet environmental emission standards in a gas turbine combustor operating on low-Btu coal gas. Detailed information on physical models, assumptions, limitations and operational features of various codes was obtained through a series of computational runs of increasing complexity and grouped as (a) experimental validation, (b) code comparison and (c) application to coal gas combustion.

INTERN is not suitable for the present application since it has been tailored to model combustion process of premixed hydrocarbon fuels. FLUENT is easy to use and has detailed combustion models (in Version 3), however, it is not favored here because the user is unable to alter, modify or change the existing model(s). While PCGC-2 has the most comprehensive models for combustion, it is not user friendly and is inherently limited to axisymmetric geometry. PCGC-3 is expected to overcome these drawbacks. Built in combustion models in PHOENICS are similar to those in FLUENT. However, the user can implement advanced models on PHOENICS leading to a flexible and powerful combustion code.

Topics: Combustion
Commentary by Dr. Valentin Fuster
1991;():V003T06A013. doi:10.1115/91-GT-111.
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Computations are reported on the detailed structures of unconfined turbulent combusting sprays. Favre-averaged gas-phase equations are used and a k-ε-g turbulence closure model is utilized. Using a conserved scalar approach and assuming the form of probability density function to be a clipped Gaussian, the thermodynamic scalar variables are calculated from a partial equilibrium model. The major features of the liquid-phase model are that a stochastic random-walk approach is used to represent the effect of gas-phase turbulence on droplet trajectory and vaporization, the variable-property effects are considered in a comprehensive manner, and a conduction-limit mode is employed to represent the transient liquid-phase processes. This two-phase model is used to study the structure of an unconfined methanol spray flame. Important observation is that the turbulent spray flame structure is significantly different, both quantitatively and qualitatively, from that of the corresponding gaseous diffusion flame. In addition, the spray flame exhibits a strong sensitively to the transient liquid-phase processes. The latter result is interesting since, in an earlier computational study for an evaporating spray, the vaporization behavior for the same liquid fuel indicated only a weak sensitivity to these processes.

Topics: Turbulence , Sprays
Commentary by Dr. Valentin Fuster
1991;():V003T06A014. doi:10.1115/91-GT-112.
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The purpose of this paper is to describe a new approach in which one uses different kinds of post processing to obtain, from 2D or 3D computation codes, the representation of internal flow inside a combustion chamber as an association of elementary reactors (well stirred, plug flow…)

To reach this goal and, in order to test this method, different computation codes are used for the gas phase description: mean flow computation or unsteady codes like “R.V.M.” (Random Vortex Method) or “F.C.T.” (Flux corrected transport) - For the liquid phase behaviour, we use to kinds of Lagrangian transport schemes: one purely deterministic is linked to the mean gas flow computation, the second one provides individual instantaneous trajectories.

These various approaches are used for two kinds of 2D geometries: the backward facing step and a simplified afterburner geometry. Examples of residence time computations are presented for the liquid and gas phases and the effect of unsteady flow and drop sizes are demonstrated by experimental comparisons.

Commentary by Dr. Valentin Fuster
1991;():V003T06A015. doi:10.1115/91-GT-113.
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Second Generation Pressurized Fluidized Bed Combustion Combined Cycles utilize topping combustion to raise the combustion turbine inlet temperature to the state of the art. Principally for this reason, cycle efficiency is improved over first generation PFB systems. Topping combustor design requirements differ from conventional gas turbine combustors since hot, vitiated air from the PFB is used for both cooling and combustion. In addition, the topping combustor fuel, a hot, low-heating value gas produced from coal pyrolysis, contains ammonia. This NOx-forming constituent adds to the combustor’s unique design challenges.

The candidate combustor is the multi-annular swirl burner (MASB) based on the design described by J.M. Beér. This concept embodies rich-burn, quick quench, and lean-burn zones formed aerodynamically. The initial test sponsored by the Department of Energy, Morgantown, West Virginia, has been completed and the results of that test are presented.

Commentary by Dr. Valentin Fuster
1991;():V003T06A016. doi:10.1115/91-GT-177.
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The dispersion quotient method, an optical measuring technique for particles, has been applied to in situ measurements of the soot particle size and density in the secondary zone of a KHD GT-216 gas turbine combustor under operating engine conditions. The optical technique, which has been developed at the Institut of Thermische Strömungsmaschinen, is based on the light extinction at different wavelength by a particle cloud due to absorption and scattering. It is of particular advantage in applications, where particles of small size (d ≤ 1.0μ) and high density are to be investigated.

In the present investigation, two idling running conditions of the turbine have been studied: 30.000 rpm and 47.000 rpm. The results show, that the dispersion quotient method is well suited for soot measurements in pressurized flames. In particular, it was found, that the soot particle diameter is not effected by the rotating speed of the turbine. The size of the soot particles was always in the range from 0.1 to 0.3 mircon. The soot volume fraction, however, was found to be strongly influenced by different rotating speeds, with higher rotating speed causing higher volume fraction of soot.

Commentary by Dr. Valentin Fuster
1991;():V003T06A017. doi:10.1115/91-GT-207.
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Detailed measurements of wavy liquid films driven by the shear stress of turbulent air flow are obtained for different air temperatures, air velocities and flow rates of the liquid. The experimental conditions are chosen from characteristic data of liquid film flow in prefilming airblast atomizers and film vaporization employing combustors.

For the measurement of the local film thickness and film velocity a new optical instrument — based on the light absorption of the liquid — has been developed, which can be used at high temperatures with evaporation.

The measured data of the gas phase and the liquid film are compared with the results of a numerical code using a laminar as well as a turbulent model for the film flow and a standard numerical finite volume code for the gas phase.

The results utilizing the two models for the liquid film show that the film exhibits laminar rather then turbulent characteristics under a wide range of flow conditions. This is of considerable interest when heat is transferred across the film by heating or cooling of the wall. With this information the optical instrument can also be used to determine the local shear stress of the gas phase at the phase interface.

Using time averaged values for the thickness, the velocity and the roughness of the film the code leads to relatively accurate predictions of the interaction of the liquid film with the gas phase.

Commentary by Dr. Valentin Fuster
1991;():V003T06A018. doi:10.1115/91-GT-217.
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The Rich-burn/Quick-mix/Lean-burn (RQL) combustor has been identified as a potential gas turbine combustor concept to reduce NOx emissions in High Speed Civil Transport (HSCT) aircraft. To demonstrate reduced NOx levels, cylindrical flametube versions of RQL combustors are being tested at NASA Lewis Research Center. A critical technology needed for the RQL combustor is a method of quickly mixing by-pass combustion air with rich-burn gases.

In this study, jet mixing in a cylindrical quick-mix section was numerically analyzed. The quick-mix configuration was five inches in diameter and employed twelve radial-inflow slots. The numerical analyses were performed with an advanced, validated 3-D Computational Fluid Dynamics (CFD) code named REFLEQS. Parametric variation of jet-to-mainstream momentum flux ratio (J) and slot aspect ratio was investigated. Both non-reacting and reacting analyses were performed.

Results showed mixing and NOx emissions to be highly sensitive to J and slot aspect ratio. Lowest NOx emissions occurred when the dilution jet penetrated to approximately mid-radius. The viability of using 3-D CFD analyses for optimizing jet mixing was demonstrated.

Commentary by Dr. Valentin Fuster
1991;():V003T06A019. doi:10.1115/91-GT-218.
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Detailed information on the influence of geometric and flow parameters on the structure and properties of recirculation zone in confined combusting flows is not available. In this paper, recirculation zone structure and turbulence properties of methane-air mixtures downstream of several conical flameholders were measured using LDA. These tests employed different blockage ratios (13% and 25%), cone angles (30, 45, 60, and 90 degrees), equivalence ratios (0.56, 0.65, 0.8, and 0.9), mean annular velocities (10, 15, and 20 m/s), and approach turbulence levels (2%, 17%, and 22%).

It was found that increasing the blockage ratio and cone angle affected the recirculation zone size and shape only slightly. Also, these parameters increased the shear stress and turbulent kinetic energy (TKE) moderately. Increasing the equivalence ratio or approach turbulence intensity produced a recirculation zone shape very similar to that found in the cold flow. TKE decreased due to turbulent dilatation produced by increased heat release. These observations are discussed from the viewpoint of their importance to practical design and combustion modeling.

Commentary by Dr. Valentin Fuster
1991;():V003T06A020. doi:10.1115/91-GT-234.
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Weak extinction data obtained from an experimental apparatus designed to simulate the characteristics of practical afterburner combustion systems are presented. The apparatus supplies mixtures of varied composition (equivalence ratio and degree of vitiation), temperature and velocity to Vee-gutter flame holders of various widths and shapes similar to those found in jet engine systems. The fuel employed is a liquid hydrocarbon whose chemical composition and physical properties correspond to those of aviation kerosine, JP5. An equation for predicting weak extinction limits which accounts for upstream vitiation and the chemical characteristics of the fuel is derived from stirred reactor theory. The correlation between the predictions and experimental results indicates that the stirred reactor approach can provide a framework for predicting the lean blowout limits of practical flameholders over wide ranges of engine operating conditions.

Commentary by Dr. Valentin Fuster
1991;():V003T06A021. doi:10.1115/91-GT-235.
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Novel direct measurements of the entrainment coefficient in the initial zone of a pulsating air jet have been successfully accomplished. A series of pulsating air jets flowing from different nozzle orifice sizes into surrounding air were investigated for the effects of jet axial length, excitation power and Strouhal number. The entrainment coefficient of the excited jet varied strongly with axial distance downstream of the orifice exit plane and with pulsation strength. The acoustic drive considerably increased the entrainment coefficient by up to 4.6 times at 10 diameters downstream of the nozzle. There was only a tendency for the entrainment coefficient to increase with the Strouhal number and hence an optimum Strouhal number for jet response was not found.

Topics: Acoustics , Air jets
Commentary by Dr. Valentin Fuster
1991;():V003T06A022. doi:10.1115/91-GT-257.
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The formation of the oxides of nitrogen, NOx, is examined through experiments and chemical kinetic modeling for lean, premixed combustion in a laboratory, atmospheric pressure, jet-stirred reactor. The experimental conditions are as follows: fuel-air equivalence ratio (ϕ) of 0.6, temperatures of 1460 to 1730 K, and reactor loadings of 20 to 150 kg/sec-m3-atm2, which correspond to reactor mean residence times of 11.4 to 1.8 milliseconds. Two fuels are examined: ethylene, because of its importance as a combustion intermediate, and methane, because of its importance as a component of natural gas. Besides the premixed operation, the reactor is also operated non-premixed. For both modes, the NOx increases with decreasing loading, from about 3–4 ppmv at the highest loading to about 11–21 ppmv at the lowest loading for the ethylene fuel. This increase in NOx occurs because a hot spot develops on centerline when the reactor is lightly loaded. Also for the lowest loading, the non-premixed mode produces about twice as much NOx as the premixed mode, i.e., about 21 versus 11 ppmv. At the other reactor loadings, however, because of the intense mixing, the NOx levels are only slightly elevated for the non-premixed mode compared to the premixed mode. Upon switching to methane fuel, the NOx decreases by about 25%.

The major finding of this study is that prompt NO is the predominant mechanism for the NOx formed. The other mechanisms considered are the Zeldovich and nitrous oxide mechanisms. Furthermore, the amount of NOx measured and modeled agrees almost exactly with the extrapolation of Fenimore’s (1971) original prompt NO data to the present conditions of ϕ = 0.6. Although Fenimore conducted his experiments with porous plate and Meker-type burners for 0.8 ≤ ϕ ≤ 1.7, our findings show that his results apply well to high-intensity, lean combustion. In the gas turbine literature, e.g. see Shaw (1974) and Toof (1985), Fenimore’s results are expressed as:Display Formula

(1)
NO/(NO)equil=P1/2func(ϕ)
It is func (ϕ) that extrapolates well to our conditions. This finding indicates that func (ϕ) applies to laboratory burners of widely different mixing intensity, i.e., from Fenimore’s burners with structured flame fronts to our high-intensity burner with dispersed reaction. In our opinion this finding strengthens the justification of using func (ϕ) for the prediction of NOx formation in practical combustors, including lean, premixed combustors.

Commentary by Dr. Valentin Fuster
1991;():V003T06A023. doi:10.1115/91-GT-302.
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Measurements of mean and rms temperature fluctuations were performed in confined turbulent premixed methane-air flames, stabilized on a conical flameholder. A CARS system was used for these measurements. These tests employed flameholders of different blockage ratios (13% and 25%), and mixtures with different equivalence ratios (0.56, 0.65, 0.8, and 0.9) and approach turbulence intensity (2%, 17%, and 22%).

It was found that the recirculation zone closely resembles a perfectly well-stirred reactor. Blockage ratio, equivalence ratio, or approach turbulence intensity did not alter the scalar field. The turbulent flame structure enveloping the recirculation zone comprises: (i) an ignition/thin flame region in the vicinity of the flameholder base, (ii) a reacting shear layer region of large-scale coherent structures, and (iii) a thick flame region where entrainment is the dominant mechanism. Finally, analysis suggests that the scalar gradient-diffusion relationship is valid and areas of non-gradient diffusion, if any, are probably small.

Topics: Scalars , Automobiles , Flames
Commentary by Dr. Valentin Fuster
1991;():V003T06A024. doi:10.1115/91-GT-303.
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The experimental results from the rig testing of an ultra-low NOx, natural gas-fired combustor for an 800 to 1000 kw gas turbine are presented. The combustor employed lean-premixed combustion to reduce NOx emissions and variable geometry to extend the range over which low emissions were obtained.

Testing was conducted using natural gas and methanol. Testing at combustor pressures up to 6 atmospheres showed that ultra-low NOx emissions could be achieved from full load down to approximately 70% load through the combination of lean-premixed combustion and variable primary zone airflow.

Commentary by Dr. Valentin Fuster
1991;():V003T06A025. doi:10.1115/91-GT-304.
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Prior tests showed that a maximum increase of stagnation pressure equal to 4% of the compressor absolute delivery pressure was obtained on a very small gas turbine equipped with a prototype, valveless, pulse, pressure-gain, combustor. Accordingly, a new core pulse-combustor has been developed for a proposed pulse, pressure-gain, combustor for larger, more representative, gas turbines. The new core pulse-combustor differs from the earlier prototype design in that the single inlet passage has been replaced with four parallel inlet passages. It is shown that this concept reduces the time required for pre-combustion mixing of the air, fuel and products in the combustion zone. This results in the overall length of the combustor being reduced to about 60% of that required for a single inlet design. It was concluded, on the basis of tests, that a pulse, pressure-gain, combustor incorporating the new core unit should be capable of generating a maximum stagnation pressure-rise of about 10% of the compressor delivery pressure with a volumetric loading 3 to 4 times that of the original prototype.

Commentary by Dr. Valentin Fuster
1991;():V003T06A026. doi:10.1115/91-GT-305.
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In order to formulate a common approach that could provide the spray parameters of airblast atomizers, various processes of liquid preparation, breakup and secondary atomization have been included in a semi-analytical calculation procedure. The air velocity components in the atomizer flow field are provided by mathematical expressions, and the spray droplets are considered to form at ligament breakup through a disturbance wave growth concept. The validation of the developed approach included the application to six atomizers that significantly varied in concept, design, and size. They represented both prefilming and plain-jet types, and their data utilized in the present effort were obtained with six different liquids. Satisfactory agreement between the measurements and the predictions has been achieved under wide ranges of air/fuel ratio and air pressure drop for various test liquids. The results of this investigation indicate the potential of using such an approach in the early phases of airblast atomizer design, and may be followed by more detailed calculations using analytical tools.

Commentary by Dr. Valentin Fuster
1991;():V003T06A027. doi:10.1115/91-GT-306.
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There is great interest in an alternative to the current rather expensive, high maintenance, weather sensitive, Continuous Emission Monitoring Systems (CEMS) or Continuous Emission Rate Monitoring Systems (CERMS) for stationary power sources. This is particularly relevant for smaller sources (<10 MW), as well as sites in remote areas and sites subject to extreme ambient conditions.

This paper describes the development of a predictive NOx monitoring system for industrial gas turbines. This type of system is currently being used as an alternative to in-stack CEMS or CERMS. This Predictive Emission Monitoring System (PEMS) utilizes a time-tested, proven mathematical model for NOx to verify the accuracy of a proven performance/emissions computer program which predicts NOx emissions from gas turbines based on measured ambient and turbine control parameters.

The technical background of this predictive NOx monitoring system and relevant experience are reviewed. The system design, including input and output, is described. A comparison of some technical issues between this predictive monitoring system and an actual typical in-stack NOx emission monitoring systems is also presented. A manual verification of the principle of this predictive system is reported.

Commentary by Dr. Valentin Fuster
1991;():V003T06A028. doi:10.1115/91-GT-307.
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The influence of large scale structures on the flow in a lobed mixer (a device utilized to enhance streamwise vorticity for increased mixing) is examined by a pseudo flow visualization method (v. Delville et al. 1988), and the Proper Orthogonal Decomposition (POD) (v. Lumley 1967). The pseudo flow visualization method utilizes specially designed hot wire rakes with high spatial resolution to provide the capability of plotting instantaneous velocity profiles. In this work, a rake of 15 hot wires is used to provide these profiles for a velocity ratio of 2:1, at several positions downstream of the lobed mixer. From these profiles a detailed description of the flow field is achieved. In particular, from this information, an idea of the spatial extent and shedding frequency of the large scale structures is determined. The shedding frequencies found are consistent with those found from spectral measurements. A one-dimensional version of the POD is then applied, which utilizes the measured streamwise velocity two-point correlation tensor. The pseudo flow visualization technique is then used to view the contribution from each proper orthogonal mode to the instantaneous signal and comparisons made to the full signal.

Commentary by Dr. Valentin Fuster
1991;():V003T06A029. doi:10.1115/91-GT-359.
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A propane-fueled research combustor has been designed to represent the essential features of primary zones of combustors for aircraft gas turbine engines in an investigation of lean blowouts. The atmospheric pressure test facility being used for the investigation made it difficult to directly approach the maximum heat release condition of the research combustor. High combustor loadings were achieved through simulating the effects on chemical reaction rates of sub-atmospheric pressures by means of a nitrogen diluent technique. A calibration procedure is described, and correlated experimental lean blowout results are compared with well-stirred reactor calculations for the research combustor to confirm the efficacy of the calibration.

Commentary by Dr. Valentin Fuster
1991;():V003T06A030. doi:10.1115/91-GT-360.
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To improve the performance of gas turbine combustors (i.e. stability and emissions), the process of fuel-air mixing, within the dome region, must be better understood and enhanced. This paper takes a preliminary step by evaluating the influences of nozzle air/fuel ratio, swirl angle, and dome geometry on fuel-air mixing. A model combustor, fabricated from quartz and designed to utilize flow visualization as the primary diagnostic, was operated at atmospheric pressure with JP-4 injected through a twin-fluid (air-assist) atomizer. Photographs of the dome region were acquired for a variation in (1) nozzle air/fuel mass flow ratio from 2.0 to 4.0, (2) swirl angle from 45° to 60°, and (3) the shape of the dome from a dump to a 45° conical expansion configuration. The results show trends of improved mixing for higher nozzle air/fuel ratios as manifested by the improved homogeneity and reduced intermittency of the reaction structure. The effects of dome geometry and swirl strength also affect mixing, with the degree and direction of effect depending on the atomizer operating conditions.

Commentary by Dr. Valentin Fuster
1991;():V003T06A031. doi:10.1115/91-GT-361.
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PCGC-2, a two-dimensional combustion code for pulverized coal gasification and combustion, and PHOENICS, a general purpose fluid dynamics code, were adapted for use in simulating the conversion of fuel nitrogen to nitric oxide, NO, in a gas turbine combustor using low-Btu fuel. A two-reaction global mechanism was used to describe the oxidation of fuel nitrogen. PCGC-2 is limited to two-dimensional, axisymmetric calculations. Both two- and three-dimensional simulations were made with PHOENICS. A parametric study was conducted to determine the variation of fuel nitrogen conversion with changes in the input variables including the inlet fuel nitrogen concentration and swirl numbers. The fuel nitrogen conversion predicted with both codes is similar to those reported in experimental studies on gaseous fuels. The conversion decreased with increasing fuel nitrogen inputs as shown in experimental data. The fuel conversion predicted in three-dimensional simulations for an industrial gas turbine was slightly higher than those in simplified two-dimensional simulations.

Commentary by Dr. Valentin Fuster
1991;():V003T06A032. doi:10.1115/91-GT-363.
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The influence of vane angle and hence swirl number of a radial swirler on the weak extinction, combustion inefficiency and NOx emissions was investigated at lean gas turbine combustor primary zone conditions. A 140mm diameter atmospheric pressure low NOx combustor primary zone was developed with a Mach number simulation of 30% and 43% of the combustor air flow into the primary zone through a curved blade radial swirler. The range of radial swirler vane angles was 0–60 degrees and central radially outward fuel injection was used throughout with a 600K inlet temperature. For zero vane angle radially inward jets were formed that impinged and generated a strong outer recirculation. This was found to have much lower NOx characteristics compared with a 45 degree swirler at the same pressure loss. However, the lean stability and combustion efficiency in the near weak extinction region was not as good. With swirl the central recirculation zone enhanced the combustion efficiency. For all the swirl vane angles there was little difference in combustion inefficiency between the swirlers. However, the NOx emissions were reduced at the lowest swirl angles and vane angles in the range 20–30 degrees were considered to be the optimum for central injection. NOx emissions for central injection as low as 5ppm at 15% oxygen and 1 bar were demonstrated for zero swirl and 20 degree swirler vane angle. This would scale to well under 25 ppm at pressure for all current industrial gas turbines.

Commentary by Dr. Valentin Fuster
1991;():V003T06A033. doi:10.1115/91-GT-364.
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Two instantaneous chemistry descriptions (full chemical equilibrium and laminar flamelet) were applid to the prediction of gaseous reaction in a small-scale combustor. The chemical state relationships were combined with a single conserved scalar/β-function pdf/k-ε turbulence model closure. Encouraging results were obtained for the flowfield and conserved scalar distributions, although only when the jet entry boundary conditions were altered to accord closely with several expected experimental features. These predictions imply that any acceptable approach to combustor modelling must extend calculations to include the outer annulus. Exit temperature levels were predicted fairly well, but the quality of internal distributions deteriorated due to errors in predicted fuel/air mixing. Differences between the two chemistry models were small except for CO and H2 species concentrations where the flamelet model gave better agreement with experiments.

Commentary by Dr. Valentin Fuster

Oil and Gas Applications

1991;():V003T07A001. doi:10.1115/91-GT-034.
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A full range mathematical model of the LM-1600 gas turbine has been developed, for future use in EHM studies. No data was available from the manufacturer other than sales brochures giving some design and off-design performance. The model was developed using generalized component characteristics and shows excellent agreement with field data from a pipeline operator.

A new method has been developed for doing the matching calculations, starting from the turbine (hot) end rather than from the compressor operating point. This method permits solution on a PC, and can be used for studying the full range of operating conditions and the development of fault matrices.

Commentary by Dr. Valentin Fuster
1991;():V003T07A002. doi:10.1115/91-GT-047.
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With the advent of computerized monitoring techniques, it is becoming evident that more automated methods of trend analysis and other diagnostic techniques are both possible and necessary. The implementation of a computerized health monitoring system has led to research into techniques for identifying trend behavior which can be used to detect equipment deterioration. The result has been the development of statistical techniques to characterize generic trend behavior and of an expert system to translate these into a diagnosis of equipment deterioration.

Commentary by Dr. Valentin Fuster
1991;():V003T07A003. doi:10.1115/91-GT-048.
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A Dresser Rand compressor and a General Electric Frame 5 turbine were uprated from 26,950 to 37,960 horsepower to increase injection capacity at Prudhoe Bay, Alaska. This paper discusses the user’s experience in field performance testing the machinery train to verify the operation and reliability of the uprate. Aerothermal performance was verified on both the gas turbine and compressor. Emissions testing conducted on the gas turbine demonstrated the equipment would be in compliance with Alaska regulations. To assess reliability, optical alignment, transient vibration checks and lubrication system heat balance analysis were also undertaken. Results from the testing verified the performance and reliability of the conversion, providing confidence to continue with the thirteen-machine, multi-year project.

Commentary by Dr. Valentin Fuster
1991;():V003T07A004. doi:10.1115/91-GT-049.
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A turbine-compressor train consisting of a General Electric MS5001 Model R single-shaft gas turbine, a Philadelphia Gear speed-increasing gearbox, and a Dresser-Clark centrifugal compressor was uprated for 30% increased gas throughput. This train is one of thirteen units operated by ARCO Alaska, Inc. for high pressure natural gas injection service in Alaska’s Prudhoe Bay Oil Field. The uprate included an in-place conversion of the gas turbine from a Model R to a Model P configuration. This paper describes the engineering, planning, and implementation activities that led up to the successful uprate of this train with only a 24 day equipment outage.

Commentary by Dr. Valentin Fuster
1991;():V003T07A005. doi:10.1115/91-GT-066.
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A deterministic approach for troubleshooting in axial multistage flow compressors, that is to say, the solution of the diagnostic or inverse problem is presented.

The approach utilizes a model which is capable of predicting the compressor performance with and without faults — solution of analysis or direct problems — previously developed and tested in several applications. The diagnostic problem solution, where the actual compressor performance is known, allows the type, level and position of a fault to be determined.

The novel method is presented and described in detail. The possibility to integrate this deterministic approach with heuristic diagnostic procedures, to take into account more complex fault configurations, is also discussed.

Commentary by Dr. Valentin Fuster
1991;():V003T07A006. doi:10.1115/91-GT-067.
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This paper discusses gas turbine engine health monitoring with a fleet of 3 MW units operating at ambient temperatures up to 45 °C. The engines operate continuously near the topping temperature and cannot tolerate a significant performance loss due to compressor fouling. Various parameters indicating engine health condition were investigated and the single best parameter was found to be compressor delivery pressure. A simple predictive monitoring scheme was developed for assessing the degree of compressor fouling to help in optimizing the time between compressor washes.

Commentary by Dr. Valentin Fuster
1991;():V003T07A007. doi:10.1115/91-GT-237.
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For the conveyance and storage of natural gas, compressor stations are required where the installed power output varies mostly between 1 MW and 20 MW.

The noise control measures involved to meet the environmental noise immission regulations in Europe will be presented.

The most economical methods of noise control techniques are described particularly for the intake system and the exhaust system of gas turbines, the housing of such engines and for peripheral sound sources like gas coolers, oil coolers and the above ground piping.

Commentary by Dr. Valentin Fuster
1991;():V003T07A008. doi:10.1115/91-GT-238.
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This paper presents design stage methods to acoustically analyze centrifugal compressor station piping. The methods have been successfully applied to the design of 26 stations since 1988. Full details of the calculation procedures are given, as well as guidelines for interpreting predicted results. Finally, the relationships between acoustical and mechanical response are described.

Commentary by Dr. Valentin Fuster
1991;():V003T07A009. doi:10.1115/91-GT-239.
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Stringent environmental constraints are usually associated with or applied to the siting and installation of new pipeline facilities. This has resulted in a significant portion of the design effort and ultimate cost of the facility to be dedicated to the mitigation of these environmental concerns. This paper describes how a compressor station can be designed and built such that stringent silencing requirements can be satisfied. The paper also references specific aspects of design which were successfully applied to the Parkway Compressor Station, Canada.

Commentary by Dr. Valentin Fuster

Cycle Innovations

1991;():V003T08A001. doi:10.1115/91-GT-139.
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Future space power requirements will vary from the subkilowatt range for deep space probes, to the hundreds of kilowatts range for a lunar base, to the multimegawatt range for interplanetary propulsion systems. Closed Brayton cycle (CBC) power conversion has the flexibility to be used in all these power ranges and with a variety of heat source options such as isotope, solar, and nuclear. Each of these types of heat sources has different characteristics that make it more appropriate for particular mission profiles and power output ranges. Heat source characteristics can also be major design drivers in the closed Brayton cycle design optimization process.

This paper explores heat source selection, the resulting CBC system designs, and discusses optimization methods as a function of the main design drivers. Such power system requirements as power level, man-rated radiation shielding, fuel costs, eclipse/darkness duration, system mass, radiator area, reliability/mission duration, and insolation level are evaluated through several CBC parametric case studies. These cases include:

(1) A 500 We power system for deep space probes,

(2) A 50 kWe solar dynamic system for earth orbit and other applications,

(3) A 100 kWe man-rated lunar/Mars stationary/rover power system,

(4) A 200 to 825 kWe power system for the lunar outpost, and

(5) 3300 kWe modules for interplanetary propulsion.

Commentary by Dr. Valentin Fuster
1991;():V003T08A002. doi:10.1115/91-GT-199.
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A multi-component (NH3/H2O) Kalina type cycle that utilizes the exhaust from a gas turbine is investigated in this paper. The turbine inlet pressure, 5.96106 N/m2 (850 psig), and temperature, 755.372 K (900 F), were kept constant as well as the working fluid temperature at the condenser outlet, 290 K (62.3 F). The NH3 mass fraction at the turbine inlet was varied along with the separator temperature, and the effects on the cycle efficiency were studied. The relationship between turbine inlet flow and separator inlet flow is shown in this paper in addition to the upper and lower NH3 mass fraction bounds. The multi-component working fluid cycle investigated is 10% to 20% more efficient than a Rankine cycle at the same border conditions.

Commentary by Dr. Valentin Fuster
1991;():V003T08A003. doi:10.1115/91-GT-200.
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In long–term U.S. energy planning three major factors are paramount, (1) environmental considerations will play a major role in power plant design, (2) alternate (and cleaner burning) transportation fuels must be introduced to wean the country from dependence on imported oil, and (3) increasing reliance will be placed on indigenous resources, namely uranium and coal. It will likely take several decades for the above goals to be implemented on a large scale, and will surely necessitate the utilization of advanced technologies. A proposed advanced version of the modular helium reactor (MHR) has bi–modal operating capability in that it can be used for power generation, and the emission–free production of clean–burning fuels to meet transportation needs. The advanced hybrid MHR plant concept utilizes a direct cycle helium nuclear gas turbine for electrical power generation (with an efficiency potential of 50%), and in addition embodies an intermediate heat transport loop for high temperature process heat needed for the emission–free conversion of coal into future cleaner burning transportation fuels, namely methanol, synthetic natural gas, or hydrogen. The high grade sensible reject heat from both the prime–mover and process heat loop is ideally suited for desalination, and thus gives the plant capability for generating three revenue streams. This paper highlights an advanced very high temperature hybrid plant concept, and discusses the enabling technologies necessary to make such an energy complex a reality, perhaps in the first decade of the 21st century. Such a power generating and fuel production facility would be in concert with improved clean air goals, and the national security and economic advantages of making U.S. power and fuel supplies dependent only on indigenous resources.

Commentary by Dr. Valentin Fuster
1991;():V003T08A004. doi:10.1115/91-GT-202.
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A number of studies have shown that the Kalina cycle, using an ammonia-water mixture, can reach higher efficiencies than the normal steam Rankine cycle. In this paper, the Kalina cycle, with a gas turbine topping cycle is applied to cogeneration for district heating. Since the district heating temperatures vary with the heat demand over the year, this application may prove to be especially suitable for the Kalina cycle with its many degrees of freedom in the condensation system.

A theoretical comparison between different bottoming cycles producing heat for a typical Scandinavian district heating network has been carried out. The Kalina cycle, the Rankine cycle with a mixture of ammonia and water as the working fluid and the normal single pressure steam Rankine cycle are compared. It is shown that a simple Rankine cycle with an ammonia-water mixture as the working fluid produces more heat and power than the steam Rankine cycle. The best results, however, are obtained for the Kalina cycle, which generates considerably higher heat and power output than the steam Rankine cycle.

Commentary by Dr. Valentin Fuster

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