Experimental Investigation of Dual-Swirl Spray Flame in a Fuel Staged Optical Model Combustor With Laser Diagnostics

2021 ◽  
Author(s):  
Siheng Yang ◽  
Jianchen Wang ◽  
Zhichao Wang ◽  
Meng Han ◽  
Yuzhen Lin ◽  
...  
Keyword(s):  
Heat Release ◽  
Shear Layer ◽  
Optical Model ◽  
Flame Structure ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Main Stage ◽  
Staged Combustion ◽  
Swirl Number ◽  
Fuel Distribution

Abstract Lean premixed prevaporized combustors often feature staged combustion with a premixed main flame anchored by the nonpremixed pilot flame to obtain a wide operating range. Interaction between pilot flame and main flame is complex. The present article investigates the flame topologies and flame-fuel interactions in separated stratified swirl flames under various operating conditions (fuel to air ratio FAR and fuel stage ratio α) and injector designs (main stage swirl number Sm and fuel injection angle JA). Experiments are carried out in the centrally staged optical model combustor at inlet pressure P3 = 0.49–0.7 MPa and inlet temperature T3 = 539 K. At first, the flame structures obtained from OH-PLIF are investigated and discussed for the baseline injector (Sm = 0.9, JA = −50°). The V-shaped flame is stabilized in the inner shear layer (ISL) with the flame attachment point located at the lip for the pilot flame mode (α = 1). Dual flame is observed in the combustor for the fuel staged combustion (α < 1): the main flame stabilized in the outer shear layer (OSL) and the pilot flame stabilized in the inner shear layer (ISL). For increasing α from 0.15 to 0.25, gaps between the main flame and pilot flame are decreased, indicating a stronger interaction between the two flames. The flame structure for different injector geometries is then investigated. It is found that the higher main stage swirl number induces a larger flame opening angle, decreasing the interaction between two flames. Fuel injected into crossflow (JA = −50°) is found to generated a more separated flame, decreasing the flame interactions. Finally, fuel distribution measured by kerosene-PLIF is analyzed with the correlation to flame structure. Results show that the existence of a good mixing of fuel and fresh air in ISL and OSL provide favorable conditions for chemical reaction with high heat release. The OH distribution is highly correlated to fuel distribution. The fuel zone is located at the inner side of high OH region, indicating the reaction and heat release take place after the mixing of preheating of fuel-air mixture.

The Effects of Fuel Composition on Flame Structure and Combustion Dynamics in a Lean Premixed Combustor

2007 ◽  
Author(s):  
Lorenzo Figura ◽  
Jong Guen Lee ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca
Keyword(s):  
Heat Release ◽  
Equivalence Ratio ◽  
Flame Structure ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Fuel Composition ◽  
Two Dimensional ◽  
Inlet Velocity ◽  
Unstable Combustion ◽  
Fuel Mixtures

The stability characteristics of a laboratory-scale lean premixed combustor operating on natural gas - hydrogen fuel mixtures have been studied in a variable length combustor facility. The fuel and air were mixed upstream of the choked inlet to the combustor to eliminate equivalence ratio fluctuations and thereby ensure that the dominant instability driving mechanism was flame-vortex interaction. The inlet velocity, inlet temperature, equivalence ratio and percent hydrogen in the fuel were systematically varied, and at each operating condition the combustor pressure fluctuations were measured as a function of the combustor length. The results are presented in the form of two-dimensional stability maps, which are plots of the normalized rms pressure fluctuation versus the equivalence ratio and the combustor length, for a given inlet temperature, inlet velocity, and fuel mixture. In order to understand the effects of operating conditions and fuel composition on the observed stability characteristics, two-dimensional chemiluminescence images of the flame structure were recorded at all operating conditions and for all fuel mixtures under stable conditions. Changes in the stable flame structure, as characterized by the location of the flame’s “center of heat release”, were found to be consistent with the observed instability characteristics. The location of the flame’s “center of heat release” was found to lie along a single path for all operating conditions and fuel mixtures. It was also observed that there were regions of stable and unstable combustion as one moved along this path. Furthermore it was found that flames having the same “center of heat release” location, but different operating conditions and fuel composition, have very nearly the same flame shape. These results will be useful for developing phenomenological models for predicting unstable combustion.

Influence of Main Swirler Vane Angle on the Ignition Performance of TeLESS-II Combustor

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Bo Wang ◽  
Chi Zhang ◽  
Yuzhen Lin ◽  
Xin Hui ◽  
Jibao Li
Keyword(s):  
High Speed ◽  
Inlet Temperature ◽  
Main Stage ◽  
Ignition Process ◽  
High Speed Camera ◽  
Fuel Distribution ◽  
Fuel Droplets ◽  
Planar Laser ◽  
Cfd Method ◽  
Vane Angle

In order to balance the low emission and wide stabilization for lean premixed prevaporized (LPP) combustion, the centrally staged layout is preferred in advanced aero-engine combustors. However, compared with the conventional combustor, it is more difficult for the centrally staged combustor to light up as the main stage air layer will prevent the pilot fuel droplets arriving at igniter tip. The goal of the present paper is to study the effect of the main stage air on the ignition of the centrally staged combustor. Two cases of the main swirler vane angle of the TeLESS-II combustor, 20 deg and 30 deg are researched. The ignition results at room inlet temperature and pressure show that the ignition performance of the 30 deg vane angle case is better than that of the 20 deg vane angle case. High-speed camera, planar laser induced fluorescence (PLIF), and computational fluids dynamics (CFD) are used to better understand the ignition results. The high-speed camera has recorded the ignition process, indicated that an initial kernel forms just adjacent the liner wall after the igniter is turned on, the kernel propagates along the radial direction to the combustor center and begins to grow into a big flame, and then it spreads to the exit of the pilot stage, and eventually stabilizes the flame. CFD of the cold flow field coupled with spray field is conducted. A verification of the CFD method has been applied with PLIF measurement, and the simulation results can qualitatively represent the experimental data in terms of fuel distribution. The CFD results show that the radial dimensions of the primary recirculation zone of the two cases are very similar, and the dominant cause of the different ignition results is the vapor distribution of the fuel. The concentration of kerosene vapor of the 30 deg vane angle case is much larger than that of the 20 deg vane angle case close to the igniter tip and along the propagation route of the kernel, therefore, the 30 deg vane angle case has a better ignition performance. For the consideration of the ignition performance, a larger main swirler vane angle of 30 deg is suggested for the better fuel distribution when designing a centrally staged combustor.

Response of Spray and Heat Release to Forced Air Flow Fluctuations in a Gas Turbine Combustor at Elevated Pressure

2007 ◽  
Author(s):  
U. Meier ◽  
J. Heinze ◽  
C. Hassa
Keyword(s):  
Heat Release ◽  
Modulation Depth ◽  
Air Flow ◽  
Mie Scattering ◽  
Operating Conditions ◽  
Diffusion Type ◽  
Spray Cone ◽  
Low Frequencies ◽  
Fuel Distribution ◽  
Fuel Feed

The objective of this work was to investigate the response of the heat release and liquid fuel distribution to forced periodic modulations of the primary air flow through diffusion type burners with different exit geometries. The spatial distribution of spray density and heat release at different modulation frequencies was studied using phase-resolved OH chemiluminescence for heat release visualization, and planar Mie scattering of kerosene. Experiments were performed for a variety of operating conditions. It was observed that the exit geometry of the nozzle has a considerable effect on the flame shape and fuel distribution, but also on the amplitude of the response to forcing of the air flow. The expanding and contracting fuel spray cone drives the region of the heat release during a period of the air flow modulation, by establishing favourable flammability conditions at varying locations during the oscillation. The temporal shape of the response of the fuel mass in the combustor, as well as the large modulation depth at low frequencies compared to the changes of air flow velocity, suggest that the fuel feed rate into the combustor is affected by a storage mechanism.

Influence of Main Stage Air Splits on the Ignition Performance of TeLESS-II Combustor

2017 ◽  
Author(s):  
Xiaotong Mi ◽  
Chi Zhang ◽  
Bo Wang ◽  
Yuzhen Lin
Keyword(s):  
Flow Field ◽  
Air Flow ◽  
Pollutant Emissions ◽  
Recirculation Region ◽  
Stable Operation ◽  
Inlet Temperature ◽  
Main Stage ◽  
Fuel Distribution ◽  
Baseline Case ◽  
The Impact

The centrally staged layout is preferred in the advanced aero-engine combustor to achieve low pollutant emissions as well as stable operation in lean premixed prevaporized combustion. However, because the high-speed main stage airflow prevents the pilot fuel droplets arriving at igniter tip and has a strong convection effect on the initial flame kernel, the application of centrally staged combustor is restricted by its poor ignition and lean blow-out performance. In the centrally staged combustor, the main stage and pilot stage have strong coupled influences on the flow field and fuel distribution. The aim of this paper is to research the impact of the main stage air split on the ignition performance for the baseline case and the comparison case of the main swirler in the TeLESS-II combustor. The main stage air flow rate of the comparison case is about 8 percent less than that of the baseline case. The results of the ignition test at room inlet temperature and pressure indicate that the ignition performance of the comparison case is significantly better than that of the baseline case. The results of the lean blow-out tests show that the main stage air splits do not make the lean blow-out performance worse. To achieve a better understanding of the test results, PLIF technology and CFD analysis were used to measure the fuel distribution and non-reacting flow field. The PLIF and CFD results demonstrate that the most of the fuel spray disperse outward into the main stage cold airflow in the baseline case so that the pilot flame is hard to be established, which leads to poor ignition performance. On the other hand, in the comparison case, the most of the fuel is confined in the recirculation region, which gives a better ignition performance. Compared with the baseline case, the main stage airflow velocity decays faster in the comparison case. It changes the direction of the instantaneous velocity in the spark vicinity, which makes it more likely for the ignition kernel to be captured by the recirculation stream in the comparison case. Therefore, the different fuel distribution and flow field characteristics cause the ignition performance improvement in the comparison case. The improvement is due to the different main stage air flow rates, which is the consequence of the main stage air split.

Comparison of Crankangle Based Ignition Timing Methods on an HCCI Engine

2010 ◽  
Author(s):  
Ahmad Ghazimirsaied ◽  
Mahdi Shahbakhti ◽  
Charles Robert Koch
Keyword(s):  
Heat Release ◽  
Operating Conditions ◽  
Main Stage ◽  
Cyclic Variation ◽  
Ignition Timing ◽  
Crank Angle ◽  
Pressure Trace ◽  
Engine Operating Condition ◽  
Start Of Combustion ◽  
Third Derivative

Autoignition timing of a mixture in Homogeneous Charge Compression Ignition (HCCI) is very dependant and sensitive to the engine operating condition. To characterize combustion timing, different crank angle dependant methods are used but these methods can exhibit inaccurate results at some operating conditions. In this paper, a criterion that divides the engine operating condition into two regions, low and high cyclic variations (unstable operation) is defined. Then, different crankangle based methods for determining the start of combustion inside the cylinder for each of the two regions are compared. The start and duration of combustion are compared for wide range of operating conditions and the relative merits of each method discussed. The methods for characterizing the start of combustion are: CA50 based on the total heat release; the start of combustion from the third derivative of the pressure trace with respect to crank angle; the start of combustion from the third derivative of the pressure trace with respect to crank angle with two limits; CA10 based on total heat release; CA10 based on peak of main stage of combustion. The last method is introduced in this paper and has advantages in terms of accuracy of ignition timing detection and correlation with the start of combustion particularly for high cyclic variation engine operation. A new criterion, defined as the ratio between peak of main stage and the sum of peak of main stage and cool flame stage of heat release, is introduced to more accurately identify the operating region of the engine. This criterion is used to understand the performance of each of those crank angle based methods. The performance of each of those methods is investigated for both the low cyclic variation and the high cyclic variation (unstable) region of the engine.

Design of an optically accessible turbulent combustion system

2018 ◽  
Vol 233 (1) ◽  
pp. 336-349
Author(s):  
Mohammad A Hossain ◽  
Ahsan Choudhuri ◽  
Norman Love
Keyword(s):  
Gas Turbine ◽  
Turbulent Combustion ◽  
High Intensity ◽  
Flame Structure ◽  
Experimental Studies ◽  
Deep Understanding ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Operating Pressure ◽  
Combustion System

In order to design the next generation of gas turbine combustors and rocket engines, understanding the flame structure at high-intensity turbulent flows is necessary. Many experimental studies have focused on flame structures at relatively low Reynolds and Damköhler numbers, which are useful but do not help to provide a deep understanding of flame behavior at gas turbine and rocket engine operating conditions. The current work is focused on the presentation of the design and development of a high-intensity (Tu = 15–30%) turbulent combustion system, which is operated at compressible flow regime from Mach numbers of 0.3 to 0.5, preheated temperatures up to 500 K, and premixed conditions in order to investigate the flame structure at high Reynolds and Damköhler numbers in the so-called thickened flame regime. The design of an optically accessible backward-facing step stabilized combustor was designed for a maximum operating pressure of 0.6 MPa. Turbulence generator grid was introduced with different blockage ratios from 54 to 67% to generate turbulence inside the combustor. Optical access was provided via quartz windows on three sides of the combustion chamber. Extensive finite element analysis was performed to verify the structural integrity of the combustor at rated conditions. In order to increase the inlet temperature of the air, a heating section is designed and presented in this paper. Separate cooling subsystem designs are also presented. A 10 kHz time-resolved particle image velocimetry system and a 3 kHz planer laser-induced fluorescence system are integrated with the system to diagnose the flow field and the flame, respectively. The combustor utilizes a UNS 316 stainless steel with a minimum wall thickness of 12.5 mm. Quartz windows were designed with a maximum thickness of 25.4 mm resulting in an overall factor of safety of 3.5.

Influence of Main Swirler Vane Angle on the Ignition Performance of TeLESS-II Combustor

2016 ◽  
Author(s):  
Bo Wang ◽  
Chi Zhang ◽  
Yuzhen Lin ◽  
Xin Hui ◽  
Jibao Li
Keyword(s):  
High Speed ◽  
Inlet Temperature ◽  
Main Stage ◽  
Ignition Process ◽  
High Speed Camera ◽  
Fuel Distribution ◽  
Fuel Droplets ◽  
Pilot Fuel ◽  
Cfd Method ◽  
Vane Angle

In order to balance the low emission and wide stabilization for lean premixed prevaporized combustion, the centrally staged layout is preferred in advanced aero-engine combustors. However, compared with the conventional combustor, it is more difficult for the centrally staged combustor to light up as the main stage air layer will prevent the pilot fuel droplets arriving at igniter tip. The goal of the present paper is to study the effect of the main stage air on the ignition of the centrally staged combustor. Two cases of the main swirler vane angle of the TeLESS-II combustor, 20° and 30° are researched. The ignition results at room inlet temperature and pressure show that the ignition performance of the 30° vane angle case is better than that of the 20° vane angle case. High speed camera, PLIF and CFD are used to better understand the ignition results. The high-speed camera has recorded the ignition process, indicated that an initial kernel forms just adjacent the liner wall after the igniter is turned on, the kernel propagates along the radial direction to the combustor center and begins to grow into a big flame, and then it spreads to the exit of the pilot stage, and eventually stabilizes the flame. CFD of the cold flow field coupled with spray field is conducted. A verification of the CFD method has been applied with PLIF measurement, and the simulation results can qualitatively represent the experimental data in terms of fuel distribution. The CFD results show that the radial dimensions of the primary recirculation zone of the two cases are very similar, and the dominant cause of the different ignition results is the vapor distribution of the fuel. The concentration of kerosene vapor of the 30° vane angle case is much larger than that of the 20° vane angle case close to the igniter tip and along the propagation route of the kernel, therefore, the 30° vane angle case has a better ignition performance. For the consideration of the ignition performance, a larger main swirler vane angle of 30° is suggested for the better fuel distribution when designing a centrally staged combustor.

CFD Predictions of Low NOx Radial Swirlers With Vane Passage Fuel Injection With Comparison With Internal Gas Analysis Flame Composition

2008 ◽  
Author(s):  
Phil T. King ◽  
Nick H. Escott ◽  
Gordon E. Andrews ◽  
Mohammed M. Pourkashanian ◽  
Andrew C. McIntosh
Keyword(s):  
Heat Release ◽  
Shear Layer ◽  
Gas Turbines ◽  
Fuel Injection ◽  
Flame Structure ◽  
Gas Analysis ◽  
Experimental Results ◽  
Combustion Model ◽  
Nox Emissions ◽  
Flamelet Model

Radial swirlers with vane passage natural gas injection, similar to those used in some industrial low NOx gas turbines, were investigated for their flame structure both experimentally and using CFD. The radial swirler NOx emissions at 600K and 1 atmosphere pressure were shown to be 3–4 ppm at 15% oxygen at 1800K and 1–2 ppm at 1700K. These levels were similar to the best published low NOx emissions using any flame stabilizer design. A flame at O̸ = 0.5 and 600K air temperature was investigated for its structure using a 10mm OD water cooled gas sample probe with a 1mm gas sample inlet on the upstream side of the probe. This showed that the mixing in the vane passage and outlet duct was very good. The maximum unmixedness at the first traverse location, 10mm downstream of the dump expansion zone, was 20% of the mean and the unmixedness was less than 5% within 30mm from the dump expansion. The flame structure was shown to involve a thick turbulence reaction zone of about 100mm thickness to the 90% heat release point. The CFD predictions were made using the RSM and k-ε turbulence models and the flamelet combustion model with a strain rate library. The isothermal aerodynamics predictions were in good agreement with others for similar geometries. There was an inner and outer recirculation zone with a swirling shear layer between. The peak turbulent kinetic energy was predicted to be on the inside of the shear layer. The experimental results showed that the flame developed in this region of high turbulence and low axial velocities. The flamelet model was less successful at predicting the flame development. The NOx results were predicted to be 2ppm less than the experimental results, due to the shorter predicted heat release region with associated lower prompt NOx.

Unsteady simulations of migration and deposition of fly-ash particles in the first-stage turbine of an aero-engine

2021 ◽  
pp. 1-21
Author(s):  
Z. Hao ◽  
X. Yang ◽  
Z. Feng
Keyword(s):  
Fly Ash ◽  
Film Cooling ◽  
Particle Deposition ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Velocity Model ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Aero Engine

Abstract Particulate deposits in aero-engine turbines change the profile of blades, increase the blade surface roughness and block internal cooling channels and film cooling holes, which generally leads to the degradation of aerodynamic and cooling performance. To reveal particle deposition effects in the turbine, unsteady simulations were performed by investigating the migration patterns and deposition characteristics of the particle contaminant in a one-stage, high-pressure turbine of an aero-engine. Two typical operating conditions of the aero-engine, i.e. high-temperature take-off and economic cruise, were discussed, and the effects of particle size on the migration and deposition of fly-ash particles were demonstrated. A critical velocity model was applied to predict particle deposition. Comparisons between the stator and rotor were made by presenting the concentration and trajectory of the particles and the resulting deposition patterns on the aerofoil surfaces. Results show that the migration and deposition of the particles in the stator passage is dominated by the flow characteristics of fluid and the property of particles. In the subsequential rotor passage, in addition to these factors, particles are also affected by the stator–rotor interaction and the interference between rotors. With higher inlet temperature and larger diameter of the particle, the quantity of deposits increases and the deposition is distributed mainly on the Pressure Side (PS) and the Leading Edge (LE) of the aerofoil.

scholarly journals Experimental Study on Dynamic Combustion Characteristics in Swirl-Stabilized Combustors

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1609
Author(s):  
Donghyun Hwang ◽  
Kyubok Ahn
Keyword(s):  
Experimental Study ◽  
Heat Release ◽  
Dynamic Pressure ◽  
Combustion Instability ◽  
Flame Structure ◽  
Pressure Sensors ◽  
Necessary Condition ◽  
Rayleigh Criterion ◽  
Pressure Oscillations ◽  
Geometric Conditions

An experimental study was performed to investigate the combustion instability characteristics of swirl-stabilized combustors. A premixed gas composed of ethylene and air was burned under various flow and geometric conditions. Experiments were conducted by changing the inlet mean velocity, equivalence ratio, swirler vane angle, and combustor length. Two dynamic pressure sensors, a hot-wire anemometer, and a photomultiplier tube were installed to detect the pressure oscillations, velocity perturbations, and heat release fluctuations in the inlet and combustion chambers, respectively. An ICCD camera was used to capture the time-averaged flame structure. The objective was to understand the relationship between combustion instability and the Rayleigh criterion/the flame structure. When combustion instability occurred, the pressure oscillations were in-phase with the heat release oscillations. Even if the Rayleigh criterion between the pressure and heat release oscillations was satisfied, stable combustion with low pressure fluctuations was possible. This was explained by analyzing the dynamic flow and combustion data. The root-mean-square value of the heat release fluctuations was observed to predict the combustion instability region better than that of the inlet velocity fluctuations. The bifurcation of the flame structure was a necessary condition for combustion instability in this combustor. The results shed new insight into combustion instability in swirl-stabilized combustors.

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