Combustor Exit Research Articles

Rotor Blade Heat Transfer of High Pressure Turbine Stage Under Inlet Hot-Streak and Swirl

A key consideration in high pressure (HP) turbine designs is the heat load experienced by rotor blades. Impact of turbine inlet nonuniformity of combined temperature and velocity traverses, typical for a lean-burn combustor exit, has rarely been studied. For general turbine aerothermal designs, it is also of interest to understand how the behavior of lean-burn combustor traverses (with both hot-streak and swirl) might contrast with those for a rich-burn combustor (largely hot-streak only). In the present work, a computational study has been carried out on the aerothermal performance of a HP turbine stage under nonuniform temperature and velocity inlet profiles. The analyses are primarily conducted for two combined hot-streak and swirl inlets, with opposite swirl directions. In addition, comparisons are made against a hot-streak only case and a uniform inlet. The effects of three nozzle guide vane (NGV) shape configurations are investigated: straight, compound lean (CL) and reverse CL (RCL). The present results reveal a qualitative change in the roles played by heat transfer coefficient (HTC) and fluid driving (“adiabatic wall”) temperature, Taw. It has been shown that the blade heat load for a uniform inlet is dominated by HTC, whilst a hot-streak only case is largely influenced by Taw. However, in contrast to the hot-streak only case, a combined hot-streak and swirl case shows a role reversal with the HTC being a dominant factor. Additionally, it is seen that the swirling flow redistributes radially the hot fluid within the NGV passage considerably, leading to a much ‘flatter’ rotor inlet temperature profile compared to its hot-streak only counterpart. Furthermore, the rotor heat transfer characteristics for the combined traverses are shown to be strongly dependent on the NGV shaping and the inlet swirl direction, indicating a potential for further design space exploration. The present findings underline the need to clearly define relevant combustor exit temperature and velocity profiles when designing and optimizing NGVs for HP turbine aerothermal performance.

Seeding Bias in Particle Image Velocimetry Applied to Dual-Mode Scramjet

Uniform seeding is important for particle image velocimetry due to the fact that all velocity data are derived from the movement of particles as fluid tracers. However, in some wind tunnel applications, uniform seeding is not possible due to the severe fouling of windows. One such application is in the University of Virginia Supersonic Combustion Facility. Past particle image velocimetry measurements in this facility have potential velocity bias errors due to nonuniform seeding, since particles were only introduced in the fuel stream and not the freestream of a dual-mode scramjet combustor. The present study seeks to experimentally quantify the velocity bias errors associated with introducing seed particles into a single stream of a fuel and freestream mixing and combusting region of the scramjet flowpath. The velocity bias is quantified by measuring the velocity field at the combustor exit using stereoscopic particle image velocimetry under three seeding scenarios: 1) fuel stream only seeded, 2) fuel and freestream seeded, and 3) freestream only seeded. The case of seeding both the fuel and freestream was taken as the baseline, or most ideal solution. The results indicate that the effect of the seeding bias is relatively small since seeding the fuel only results in an average seeding bias error of 3.7% in mean velocity and 2.5% for the case of freestream only seeded. For the rms velocity, the average error induced by the seeding bias was 6.6 and 4.1%, respectively.

Effect of air/fuel nozzle arrangement on the MILD combustion of syngas

The effect of air/fuel nozzle arrangement on MILD (Moderate or Intense Low-oxygen Dilution) combustion of coal-derived syngas under lean operating condition was evaluated in a parallel jet combustor. The results were presented on flow field using non-reactive numerical calculation and on OH* chemiluminescence images and exhaust emissions using experiments. The increase in equivalence ratio aids in the reduction of peak flame temperature and in the distribution of reaction volume. The critical equivalence ratios above which MILD combustion occurred were identified for four MILD configurations. The MILD configuration with both air and fuel injected from the opposite side of the combustor exit was observed to achieve MILD combustion at leaner condition than other three configurations. The MILD scheme was established for syngas fuel under highly lean condition with low NOx and CO emissions.

Thermal and emission characteristics of a CAN combustor

Experimental investigations are carried out to establish the thermal and emission characteristics of a CAN combustor. Temperature and emission levels at the combustor exit are measured for different swirler vane angles and air fuel ratios (AFR). Swirler vane angle is varied from 15° to 60° in steps of 15°. AFR is varied in the range of 41–51. Experimental analysis is carried out using methane as fuel. Measured temperature variation at combustor outlet indicates that the hot product of combustor flows near the liner wall. Gradient of temperature near the wall decreases as the swirler vane angle (and corresponding swirl number) is increased. The peak temperature reduces at higher value of AFR. Emission level of carbon monoxide decreases with increase in AFR and swirler vane orientation. A higher level of NOX emission is observed for AFR of 45. This is due to change in shape and strength of the recirculation region in the primary zone of the combustor.

항공기용 가스터빈의 고압 냉각터빈 노즐에 대한 복합열전달 해석

Conjugate heat transfer analysis was performed to investigate the flow and cooling performance of the high pressure turbine nozzle of gas turbine engine. The CHT code was verified by comparison between CFD results and experimental results of C3X vane. The combination of k-ω based SST turbulence model and transition model was used to solve the flow and thermal field of the fluid zone and the material property of CMSX-4 was applied to the solid zone. The turbine nozzle has two internal cooling channels and each channel has a complex cooling configurations, such as the film cooling, jet impingement, pedestal and rib turbulator. The parabolic temperature profile was given to the inlet condition of the nozzle to simulate the combustor exit condition. The flow characteristics were analyzed by comparing with uncooled nozzle vane. The Mach number around the vane increased due to the increase of coolant mass flow flowed in the main flow passage. The maximum cooling effectiveness (91 %) at the vane surface is located in the middle of pressure side which is effected by the film cooling and the rib turbulrator. The region of the minimum cooling effectiveness (44.8 %) was positioned at the leading edge. And the results show that the TBC layer increases the average cooling effectiveness up to 18 %.

Advanced Combustor Exit Plane Temperature Diagnostics Based on Large Eddy Simulations

The accurate description and flow calibration at the exit of a gas turbine combustor is a key point of turbine design. Indeed, the temperature field at the turbine inlet directly impacts both the work extraction by the turbine stages as well as drives the wall heat transfer occurring on the vanes and rotor surfaces. Properly simulating or measuring this critical planar interface has been an extensive topic of research. Despite such efforts, industrial exploitation of the various measures at that interface usually resumes to a quantification of the temperature heterogeneities through the Local Radial Temperature Distortion Factor (LRTDF), thereby loosing major spatial and unsteady information. As lean burn configurations become a standard for aero-engine combustors, the absence of dilution holes reduces the intensity of mixing and the use of more advanced statistical tools should propose an exhaustive representation of the temperature map and mixing quality. Current state-of-the-art numerical design of gas turbine combustor relies on Large Eddy Simulations (LES) giving access to a fully 3-D temporally dependent flow field throughout the combustion chamber. Going beyond LRTDF is therefore possible and advanced analyses of the combustor-turbine interface are accessible to better qualify proposed design changes. In this work, a simple statistical representation of the temperature distribution is introduced and applied for the analysis of a lean burn combustor simulator interface. It is shown that at the exit of this chamber, the temperature samples are distributed following a non-Gaussian shape, highlighting a most probable local temperature largely different from the conventional mean value. The use of high order moments explains such deviations and indicates the presence of strongly segregated zones governed by the technological implementation of effusion cooling systems. Based on this diagnostic, a new and complementary representation of the LRTDF is proposed, accounting for the statistical dimension of the classical (radius, temperature) formulation.

Experimental and numerical studies of pressure effects on syngas combustor liner temperature

Pressure effects on the liner temperature of a syngas model combustor are studied by experimental and numerical methods, with an attempt to analyze the influence mechanism. The model combustor, fueled with 10 MJ/Nm3 coal-derived syngas, is installed in a pressurized test-rig. Several diffusion flames with thermal powers up to 180 kw at pressures within 0.1–0.35 MPa are studied using a variety of measurement techniques. The liner temperature varies monotonically along the flow direction, and the maximum temperature appears around the dilution holes. Moreover, the liner temperature increases in the dilution zone but decreases in the primary zone with the increase of operating pressure, when the combustor exit temperature is maintained at 1073 K. Then, the combustion behaviors of the model combustor within pressure range of 0.1–2.0 MPa are simulated using CFD method, and the computed liner temperatures of testing cases agree well with the experimental data. The liner temperature varies approximately from −20 K to 150 K depending on locations when the pressure rises from 0.1 MPa to 2.0 MPa. It shows notable variation with operating pressure under low pressure conditions. However, as the operating pressure continues to increase, its impact on the liner temperature and the maximum temperature turns out to be very small. In order to explain the influence mechanism of operating pressure on the linear temperature, its effects on the flame structure, the liner heat flux, the convection and radiation are analyzed under different pressures. This study could be valuable for predicting and analyzing temperature distribution of the liner of gas turbine combustor.

Numerical Modeling of Biomass and Solid Waste-Based Syngas Fuels Combustion

The combustion of syngas fuels in gas turbine combustor is presented in this paper. The principal objective is to test the performance of the combustion process using non-conventional fuels produced from the gasification of biomass and solid waste. Three dimensional syngas combustion simulations were performed in this study. The mixture fraction/pdf and the P1 radiation models were used to model the non-premixed turbulent combustion. The syngas fuels are derived from the gasification of wood saw dust, wooden pellet and nonrecycled solid waste plastics. The effect of syngas fuel compositions and lower heating values on the combustion process was investigated. The power from the combustor was kept constant at 60 kW for all the syngas fuels tested in this study. The results show a decrease of the peak gas temperature inside the combustor for the syngas fuels compared to conventional fossil gas fuel. The peak gas temperature inside the combustor decreases by 16.1%, 19.8%, and 17.2% respectively for the syngas 1 (derived from plastic waste), syngas 2 (derived from wood saw dust) and syngas 3 (derived from wooden pellets) compared to natural gas fuel. The highest average NO mass fraction at the combustor exit was obtained with syngas 1 (plastic waste) compared to the other syngas fuels due to the high lower heating value. The highest average CO2 mass fraction at the exit of the combustor was obtained with syngas 2 (wood saw dust) compared to the other syngas due to the high amount of CO2 in the syngas fuel (15%).

Research of Flame Stabilization and Mixing Mechanisms for Turbine Inter-vane Burner Based on Jet-vortex Flow

Abstract In order to meet the requirement of flame stabilization and intensify the mixing, a new injection configuration, named double-effect injection configuration, is designed and that is the two secondary injections have been allocated with different functions to achieve the purpose of flame stabilization and intensifying mixing. The effects of the variation of secondary injections on flame stabilization, mixing and combustion performance were studied by using numerical simulation method. The conclusions are that by double-effect injection configuration, a stable recirculation zone can be formed in the cavity to stabilize the combustion flame, and the mixing effect can be intensified; and the temperature distributions at this combustor exit are more symmetric; and the influence of angle variation of secondary jet flow based on double-effect injection configuration is weaker, but it can be seen that model-1 (50° and 45° for two injection angle) has highest combustion efficiency and lowest total pressure losses.

A111 超臨界CO_2タービン向け燃焼器の開発(OS1 次世代型火力発電システム技術)

The innovative thermodynamic power cycle called "Allam Cycle" can capture 100% of carbon dioxide emission with no additional efficiency reduction by CCS, and can also get high thermal efficiency equivalent to general combined cycle. The Allam Cycle is an invention of 8 Rivers Capital, which continues to provide technology development services for the program. This unique cycle consists of a closed-loop, high-pressure, low-pressure-ratio recuperated Brayton cycle using supercritical CO_2 as the working fluid. Toshiba is developing this system with NET Power, LLC, Chicago Bridge & Iron Company and Exelon Corporation for demonstrating 25MW-class pilot plant construction. Toshiba's work scope is to design and product brand-new combustor and turbine with development. Design condition at baseload specifies combustor exit temperature as 1150 degree C and pressure as 30MPa approximately. In this paper 1st step of actual pressurized combustion testing results will be introduced and be focused on "world-first" SOMPa achievement in firing with oxyfuel combustion under supercritical CO_2 fluid using natural gas as fuel.

열 방출률에 대한 마이크로 백금 촉매 연소기의 치수 설계 기준

Design criterion for the size of micro Pt-catalytic combustor is investigated in terms of heat release rate. One-dimensional plug flow model is applied to determine the surface reaction constants using the experimental data at stoichiometric butane-air mixture. With these reaction constants, the mass fraction of butane and heat release rate predicted by the plug flow model are in good agreement with the experimental data at the combustor exit. The relationship between the size of micro catalytic combustor and mixture flowrate is introduced in the form of product of two terms-the effect of fuel conversion efficiency, and the effect of chemical reaction rate and mass transfer rate.

Studies of combustion characteristics of kerosene ethanol blends in an axi-symmetric combustor

Partial replacement of fossil fuels by biomass based alternative fuels in aviation applications is considered as a possible option toward sustainability. The present work aims to study the changes in the flame characteristics and combustor performance in a cylindrical spray combustor when operated with kerosene and kerosene–ethanol blends. A laboratory scale combustor with two concentric air entries along with a centrally fitted pressure swirl nozzle is used in the experiments. Three different fuels, viz. kerosene and two blends of ethanol (5% and 10% by volume) with kerosene have been used. Flame images are captured using a high speed camera and analyzed for characterizing the flame behavior with different fuels. Temperatures of the combustor wall and exit gas have been measured by thermocouples while, the concentrations of CO, CO2 and O2 in the exhaust gas are recorded using an online gas analyzer. The brightness of the flame and combustor wall temperature are found to decrease considerably with 5% ethanol in the blend, although a further increase of ethanol (to 10%) decreases them marginally. However, the exit gas temperature reduces consistently with the addition of ethanol with kerosene. The standard deviation of brightness data is also much lower with the ethanol blended fuels. Flicker frequency of the flames, however, remains almost unchanged with the blending of ethanol in kerosene. The concentrations of the three species are found to be radially uniform at the exhaust indicating good mixing in the combustor. The CO concentration in the exhaust reduces with blending, indicating better combustion of the fuel. The CO2 concentration simultaneously decreases with ethanol blending representing less carbon loading to the atmosphere. The reduction in carbon compounds at the combustor exit due to blending of ethanol is attributed to the lower C/H ratio of ethanol compared to kerosene.

Porous Inserts for Passive Control of Noise and Thermo-Acoustic Instabilities in LDI Combustion

In this study, ring-shaped porous inserts made from high-strength, temperature-resistant ceramic materials are utilized within the combustor to passively reduce noise and thermo-acoustic instabilities in lean direct injection (LDI) combustion. Inserts of 85% porosity; pore density of 18 pores per cm; and converging, diverging, and hyperbolic configurations are considered. Kerosene fuel atomized by an air-blast fuel injector is introduced in the swirl-stabilized combustor operated at atmospheric pressure. For a fixed equivalence ratio, emissions and acoustics measurements are obtained at different heat release rates and atomizing air to liquid mass ratios. Results show negligible effects of porous inserts on NOx and CO emissions at the combustor exit. Porous inserts are, however, very effective in suppressing both noise and thermo-acoustic instabilities for a range of operating conditions. The measured trends in acoustic absorption are predicted using a simplified thin-layer model of the porous material, and an important flow mechanism to explain the observed trends is discussed.

Non-Uniformity of the Combustor Exit Flow Temperature in Front of the Gas Turbine

Abstract Various types of damages to gas-turbine components, in particular to turbine blades, may occur in the course of gas turbine operation. The paper has been intended to discuss different forms of damages to the blades due to non-uniformity of the exit flow temperature. It has been shown that the overheating of blade material and thermal fatigue are the most common reasons for these damages. The paper presents results from numerical experiments with use of the computer model of the aero jet engine designed for simulations. The model has been purposefully modified to take account of the assumed non-homogeneity of the temperature field within the working agent at the turbine intake. It turned out that such non-homogeneity substantially affects dynamic and static properties of the engine considered as an object of control since it leads to a lag of the acceleration time and to increase in fuel consumption. The summarized simulation results demonstrate that the foregoing properties of a jet engine are subject to considerable deterioration in pace with gradual increase of the assumed non-homogeneity of the temperature field. The simulations made it possible to find out that variations of the temperature field nonhomogeneity within the working agent at the turbine intake lead to huge fluctuation of the turbine rpm for the idle run.

Film Cooling Effectiveness in a Gas Turbine Engine: A Review

This study was carried out to extend database knowledge about the function of film cooling holes at the end of combustor and the inlet of turbine. Using the well-known Brayton cycle, raising the turbine inlet temperature is the key to obtain higher engine efficiency in gas turbine engines. However, high temperature of the combustor exit flow causes non-uniformities. These non-uniformities lead to the reduction of expected life of critical components. Therefore, an appropriate cooling technique should be designed to protect these parts. Film cooling is one of the most effective external cooling methods. Various film cooling techniques presented in the literature have been investigated. Moreover, challenges and future directions of film cooling techniques have been reviewed and presented in this paper. The aim of this review is to summarize recent development in research on film cooling techniques and attempt to identify some challenging issues that need to be solved for future research.

Large-eddy/Reynolds-averaged Navier–Stokes simulation of cavity-stabilized ethylene combustion

In this study, a hybrid large-eddy/Reynolds-averaged Navier–Stokes (LES/RANS) method is used to simulate ethylene combustion inside a cavity flameholder. The cavity flameholder considered is Configuration E of University of Virginia’s Scramjet Combustion Facility, which consists of a Mach 2 inlet nozzle, a constant-area isolator, a combustor, and an extender, through which the exhaust gases are vented to the atmosphere. To increase the fuel-residence time, a cavity is fitted along the upper wall inside the combustor section of the flameholder. The configuration has the capability of injecting ethylene through a series of ports located upstream of and inside the cavity along the upper wall the combustor. In the simulations, ethylene combustion is modeled using a 22-species ethylene oxidation mechanism. Also, a synthetic eddy method is used to introduce turbulence at the inflow plane of the flameholder. For an equivalence ratio of 0.15, a cavity stabilized flame is predicted. Predictions are compared with line-of-sight temperature, water column-density, water mole-fraction, CO column-density, and CO2 column-density measurements at three stations within and downstream of the cavity. Agreement with experiment is generally good within the cavity. Downstream of the cavity, the simulations predict higher temperatures near the wall. Analysis of the flame structure predicted by the LES/RANS method indicates that the flame propagates into a stoichiometric to fuel-rich mixture near the cavity. Flame angles captured in the simulation are in close agreement with those predicted through classical premixed turbulent flame-speed estimates. Further downstream, the flame structure is non-premixed in character, and near complete conversion of CO to CO2 is observed by the time the flame reaches the combustor exit.

High-bandwidth scanned-wavelength-modulation spectroscopy sensors for temperature and H2O in a rotating detonation engine

The design and use of two-color tunable diode laser (TDL) absorption sensors for measurements of temperature and H2O in a rotating detonation engine (RDE) are presented. Both sensors used first-harmonic-normalized scanned-wavelength-modulation spectroscopy with second-harmonic detection (scanned-WMS-2f/1f) to account for non-absorbing transmission losses and emission encountered in the harsh combustion environment. One sensor used two near-infrared (NIR) TDLs near 1391.7 nm and 1469.3 nm that were modulated at 225 kHz and 285 kHz, respectively, and sinusoidally scanned across the peak of their respective H2O absorption transitions to provide a measurement rate of 50 kHz and a detection limit in the RDE of 0.2% H2O by mole. The other sensor used two mid-infrared (MIR) TDLs near 2551 nm and 2482 nm that were modulated at 90 kHz and 112 kHz, respectively, and sinusoidally scanned across the peak of their respective H2O transitions to provide a measurement rate of 10 kHz and a detection limit in the RDE of 0.02% H2O by mole. Four H2O absorption transitions with different lower-state energies were used to assess the homogeneity of temperature in the measurement plane. Experimentally derived spectroscopic parameters that enable temperature and H2O sensing to within 1.5–3.5% of known values are reported. The sensor design enabling the high-bandwidth scanned-WMS-2f/1f measurements is presented. The two sensors were deployed across two orthogonal and coplanar lines-of-sight (LOS) located in the throat of a converging-diverging nozzle at the RDE combustor exit. Measurements in the non-premixed H2-fueled RDE indicate that the temperature and H2O oscillate at the detonation frequency (≈3.25 kHz) and that production of H2O is a weak function of global equivalence ratio.

Development of an Engine Representative Combustor Simulator Dedicated to Hot Streak Generation

Nowadays, the lack of confidence in the prediction of combustor-turbine interactions and more specifically our ability to predict the migration of hot spots through this interface leads to the application of extra safety margins, which are detrimental to an optimized turbine design and efficiency. To understand the physics and flow at this interface, a full 360 deg nonreactive combustor simulator (CS) representative of a recent lean burn chamber together with a 1.5 turbine stage is instrumented at DLR in Gottingen (Germany) within the European project FACTOR. The chamber operates with axial swirlers especially designed to reproduce engine-realistic velocity and temperature distortion profiles, allowing the investigation of the hot streaks transport through the high pressure (HP) stage. First, a true scale three injector annular sector of the CS without turbine is assembled and tested at the University of Florence. To generate the hot steaks, the swirlers are fed by an air flow at 531 K, while the liners are cooled by an effusion system fed with air at ambient temperature. In addition to static pressure taps and thermocouples, the test rig will be equipped with an automatic traverse system which allows detailed measurements at the combustor exit by means of a 5-hole probe, a thermocouple, and hot wire anemometers. This paper presents the design process and instrumentation of the trisector CS, with a special focus on large Eddy simulations (LES) which were widely used to validate the design choices. It was indeed decided to take advantage of the ability and maturity of LES to properly capture turbulence and mixing within combustion chambers, despite an increased computational cost as compared to usual Reynolds averaged Navier Stokes (RANS) approaches. For preliminary design, simulations of a single periodic sector (representative of the DLR full annular rig) are compared to simulations of the trisector test rig, showing no difference on the central swirler predictions, comforting the choice for the trisector. In parallel, to allow hot wire anemometry (HWA) measurements, the selection of an isothermal operating point, representative of the nominal point, is assessed and validated by use of LES.

Combustion of straight glycerol with/without methane using a fuel-flexible, low-emissions burner

In this study, we present a fuel-flexible dual-fuel combustor to simultaneously burn methane and/or straight glycerol without preheating either glycerol or air by utilizing a novel flow-blurring (FB) liquid fuel injector. Product gas temperature, NOX and CO emissions at multiple locations inside the combustor are measured to quantitatively assess the flame structure, related to liquid atomization, droplet evaporation, and fuel–air mixing in the near field. For fixed total heat release rate, the impact of fuel mix on combustion performance is investigated by varying the methane gas and glycerol flow rates. For the same fuel mix, air to liquid mass ratio effect is evaluated by varying the atomizing air flow rate. Pure glycerol flame is also investigated to demonstrate the fuel flexibility and ease of switching between gas and liquid fuels in the present system. Results show that the methane combustion can assist glycerol vaporization to results in its rapid oxidation. In spite of the differences in the flame structure, profiles of product gas temperature and emissions at the combustor exit reveal that complete and mainly lean premixed combustion with low emissions is achieved for all of the test cases indicating excellent fuel flexibility of the present combustor using the FB injector.

Experimental study of novel passive control methods to improve combustor exit temperature uniformity

The effect of non-uniform temperature flow which comes in contact with the turbine blades is of paramount importance since the thermal damage that occur to the blade during its operation, is governed by the non-uniformities present in the oncoming flow. This thermal damage leads to increased maintenance cost and reduced life-span of the turbine blades. This paper investigates the effectiveness of some novel passive control techniques to improve the temperature uniformity of the combustor exit flow to address the need to reduce the thermal damage and hence decrease the overall maintenance cost of the gas turbine system. The novel passive control techniques tested in this study include the use of streamlined body or guide vanes in the dilution zone of the combustor. For the guide vanes four different orientations were tested—0°, 30°, 60°, 90°. Extensive experimentation was conducted under different flow conditions. The deviation of the exit temperature from the equilibrium mixing temperature was used to compare the effectiveness of different passive control techniques. It was found that the 30o guide vanes gave the most uniform temperature flow under majority of cases considered. On an average, the flow with 30o guide vanes was about 15 % more uniform in temperature as compared to the staggered holes geometry with only 1 % higher pressure loss. The possible reason for this improvement is the combination of swirl and depth to which the dilution flow can enter the dilution zone and mix with the primary hot flow. The streamlined body came second with an improvement in pressure losses. Based on these experimental findings, the use of these guide vanes and streamlined body has potential in the gas turbine industry to deal with the high maintenance cost involved in these systems.