scholarly journals Analysis of Ignition Processes at Combustors for Aero Engines at High Altitude Conditions With and Without Effusion Cooling

2020 ◽  
Author(s):  
Alexios-Dionysios Martinos ◽  
Nikolaos Zarzalis ◽  
Stefan-Raphael Harth
Keyword(s):  
High Altitude ◽  
High Speed ◽  
Fuel Injection ◽  
Spatial Information ◽  
Research Work ◽  
Low Pressure ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Ignition Process ◽  
High Speed Imaging

Abstract The ability to re-ignite at high altitude after a flameout event is critical for flight safety. One reason that makes the relight process of the engine difficult is the low temperature and pressure, which leads to poor atomization, low degree of evaporation and slow reaction rate of the vaporized fuel. For this research work a rectangular, one sector RQL combustion chamber was utilized for experimental investigations at high altitude conditions. The design of the chamber is modular so that experiments for two configurations, i.e. without and with effusion cooling holes can be conducted. The fuel injection and the ignition system are representative of the ones used in commercial aviation. The investigations were performed in the frame of the European research project SOPRANO at the ISCAR rig. The ISCAR rig is capable of generating low pressure and temperature conditions for flowing kerosene-air mixtures. The investigation focuses on the characterization of the ignition process, in terms of probability, minimum fuel to air ratio (FAR) and ignition timing for a successful ignition event. In addition, the unsteady flame kernel generation and propagation were analyzed by high-speed imaging recording. An in-house image processing code was developed in order to derive quantitative spatial information of the flame and overall trends among ignition sequences for the same or different operating conditions. In order to achieve comparability between the investigated configurations (liners without and with effusion cooling), the pressure drop across the nozzle and the liners was the same depending on the operating condition. Results show that both pressure and temperature affect the ignition process, with the former being the dominant parameter in the investigated conditions. In both configurations, the minimum FAR increased as long as the conditions in the chamber became more adverse, indicating that at high altitude low-pressure situations, the performance of the airblast atomizer deteriorated causing poor ignition. This is overcome by creating a richer fuel-air mixture in the primary zone. Finally, the air injected through the effusion cooling holes near the spark seems to create favorable conditions for the ignition process.

Simulations of flame propagation during the ignition process in an annular multiple-injector combustor

2019 ◽  
Vol 29 (6) ◽  
pp. 1947-1964 ◽  
Author(s):  
Dongmei Zhao ◽  
Yifan Xia ◽  
Haiwen Ge ◽  
Qizhao Lin ◽  
Jianfeng Zou ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Adaptive Mesh Refinement ◽  
High Speed ◽  
Early Stage ◽  
Adaptive Mesh ◽  
Critical Issue ◽  
Experimental Investigations ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Content Type

Purpose Ignition process is a critical issue in combustion systems. It is particularly important for reliability and safety prospects of aero-engine. This paper aims to numerically investigate the burner-to-burner propagation during ignition process in a full annular multiple-injector combustor and then validate it by comparing with experimental results. Design/methodology/approach The annular multiple-injector experimental setup features 16 swirling injectors and two quartz tubes providing optical accesses to high-speed imaging of flames. A Reynolds averaged Navier–Stokes model, adaptive mesh refinement (AMR) and complete San Diego chemistry are used to predict the ignition process. Findings The ignition process shows an overall agreement with experiment. The integrated heat release rate of simulation and the integrated light intensity of experiment is also within reasonable agreement. The flow structure and flame propagation dynamics are carefully analyzed. It is found that the flame fronts propagate symmetrically at an early stage and asymmetrically near merging stage. The flame speed slows down before flame merging. Overall, the numerical results show that the present numerical model can reliably predict the flame propagation during the ignition process. Originality/value The dedicated AMR method together with detailed chemistry is used for predicting the unsteady ignition procedure in a laboratory-scale annular combustor for the first time. The validation shows satisfying agreements with the experimental investigations. Some details of flow structures are revealed to explain the characteristics of unsteady flame propagations.

Experimental Inverstigations On the Pressure Fluctuations in the Sealing Gap of Dry Gas Seals with Embedded Pressure Sensors

2021 ◽  
Author(s):  
Jingjing Luo ◽  
Dieter Brillert
Keyword(s):  
High Speed ◽  
Gas Flow ◽  
Static Pressure ◽  
Pressure Sensors ◽  
Operating Conditions ◽  
Test Facility ◽  
Experimental Investigations ◽  
Mechanical Seals ◽  
Process Gas ◽  
Sealing Gap

Abstract Dry gas lubricated non-contacting mechanical seals (DGS), most commonly found in centrifugal compressors, prevent the process gas flow into the atmosphere. Especially when high speed is combined with high pressure, DGS is the preferred choice over other sealing alternatives. In order to investigate the flow field in the sealing gap and to facilitate the numerical prediction of the seal performance, a dedicated test facility is developed to carry out the measurement of key parameters in the gas film. Gas in the sealing film varies according to the seal inlet pressure, and the thickness of gas film depends on this fluctuated pressure. In this paper, the test facility, measurement methods and the first results of static pressure measurements in the sealing gap of the DGS obtained in the described test facility are presented. An industry DGS with three-dimensional grooves on the surface of the rotating ring, where experimental investigations take place, is used. The static pressure in the gas film is measured, up to 20 bar and 8,100 rpm, by several high frequency ultraminiature pressure transducers embedded into the stationary ring. The experimental results are discussed and compared with the numerical model programmed in MATLAB, the characteristic and magnitude of which have a good agreement with the numerical simulations. It suggests the feasibility of measuring pressure profiles of the standard industry DGS under pressurized dynamic operating conditions without altering the key components of the seal and thereby affecting the seal performance.

Fuel Atomization in Small Jet Engines

2002 ◽  
Author(s):  
Yeshayahou Levy ◽  
Semion Lipkin ◽  
Valery Nadvany ◽  
Valery Sherbaum
Keyword(s):  
Fuel Injection ◽  
High Energy ◽  
Operating Conditions ◽  
Fuel Vapor ◽  
Ignition Process ◽  
Jet Engines ◽  
Alternative Design ◽  
Fuel Supply ◽  
Small Engines ◽  
Supply Systems

Small and inexpensive jet engines are usually equipped with vaporizing fuel supply systems. This is in order to deliver low fuel flow-rates from relatively low-pressure fuel supply systems and the need for simple configuration. The difficulties associated with small engines are mainly during ignition or at high altitude re-lights, when the combustor is cold, air supply is poor, and fuel demand and pressure are low. Such conditions lead to poor atomization within the vaporizer resulting in very large droplets at its exit tip or even to a pool of liquid fuel within the combustor. Thus, there is no fuel vapor for ignition. Ignition is very difficult or even impossible under such conditions. Therefore, small engines are commonly equipped with dual fuel supply systems, either in the form of gaseous fuel for the ignition stage or with an additional higher-pressure supply line to the dedicated fuel nozzles for the purpose of ignition. Additional solutions involve the use of a large glow plug or high-energy pyrotechnic cartridges in the kilo-Joule range, to heat the combustor casing prior to ignition. The present work is concerned with the development of alternative and novel atomization systems, which would improve atomization at low pressures and consequently facilitate the ignition process, thus minimizing the need for supporting systems. The work refers to an alternative design for an existing vaporizer system of a small jet engine with 400 Nt of thrust. It focuses on an alternative design for the fuel injection within the vaporizer housing while maintaining all external dimensions and operating conditions unchanged. Three types of fuel nozzles were investigated: • a special impact atomizer, • a miniature pressure swirl atomizer, • a doublet atomizer involving two swirling nozzles (preliminary study only). Droplet size distribution under various nozzle pressure drops and air velocities were measured with Phase Doppler Particle Anemometry (PDPA) and global spray characteristics were obtained by photography. All modified atomization systems demonstrated improved performance and better atomization than the existing system. Initially, water was used as a liquid. At a later stage, the modified impact atomizer was tested and successful spark ignition was demonstrated.

Fuel Influence on Targeted Gas Turbine Combustion Properties: Part I — Detailed Diagnostics

2014 ◽  
Author(s):  
Thomas Mosbach ◽  
Victor Burger ◽  
Barani Gunasekaran
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Leading Edge ◽  
Operating Conditions ◽  
Optical Measurements ◽  
Test Facility ◽  
Research Centre ◽  
High Speed Imaging ◽  
Combustion Properties ◽  
First Results

The threshold combustion performance of different fuel formulations under simulated altitude relight conditions were investigated in the altitude relight test facility located at the Rolls-Royce plc. Strategic Research Centre in Derby, UK. The combustor employed was a twin-sector representation of an RQL gas turbine combustor. Eight fuels including conventional crude-derived Jet A-1 kerosene, synthetic paraffinic kerosenes (SPKs), linear paraffinic solvents, aromatic solvents and pure compounds were tested. The combustor was operated at sub-atmospheric air pressure of 41 kPa and air temperature of 265 K. The temperature of all fuels was regulated to 288 K. The combustor operating conditions corresponded to a low stratospheric flight altitude near 9 kilometres. The experimental work at the Rolls-Royce (RR) test-rig consisted of classical relight envelope ignition and extinction tests, and ancillary optical measurements: Simultaneous high-speed imaging of the OH* chemiluminescence and of the soot luminosity was used to visualize both the transient combustion phenomena and the combustion behaviour of the steady burning flames. Flame luminosity spectra were also simultaneously recorded with a spectrometer to obtain information about the different combustion intermediates and about the thermal soot radiation curve. This paper presents first results from the analysis of the weak extinction measurements. Further detailed test fuel results are the subject of a separate complementary paper [1]. It was found in general that the determined weak extinction parameters were not strongly dependent on the fuels investigated, however at the leading edge of the OH* chemiluminescence intensity development in the pre-flame region fuel-related differences were observed.

Experimental Investigation Into the High Altitude Relight of a Three-Cup Combustor Sector

2018 ◽  
Author(s):  
Michael J. Denton ◽  
Samir B. Tambe ◽  
San-Mou Jeng
Keyword(s):  
Pressure Drop ◽  
High Altitude ◽  
High Speed ◽  
Development Process ◽  
Recirculation Zone ◽  
Operating Conditions ◽  
Pressure Drops ◽  
High Speed Video ◽  
Air Jet ◽  
Flame Development

The altitude relight of a gas turbine combustor is an FAA and EASA regulation which dictates the successful re-ignition of an engine and its proper spool-up after an in-flight shutdown. Combustor pressure loss, ambient pressure, ambient temperature, and equivalence ratio were all studied on a full-scale, 3-cup, single-annular aviation combustor sector to create an ignition map. The flame development process was studied through the implementation of high-speed video. Testing was conducted by placing the sector horizontally upstream of an air jet ejector in a high altitude relight testing facility. Air was maintained at room temperature for varying pressure, and then the cryogenic heat exchanger was fed with liquid nitrogen to chill the air down to a limit of −50 deg F, corresponding with an altitude of 30,000 feet. Fuel was injected at constant equivalence ratios across multiple operating conditions, giving insight into the ignition map of the combustor sector. Results of testing indicated difficulty in achieving ignition at high altitudes for pressure drops greater than 2%, while low pressure drops show adequate performance. Introducing low temperatures to simulate the ambient conditions yielded a worse outcome, with all conditions having poor results except for 1%. High-speed video of the flame development process during the relight conditions across all altitudes yielded a substantial effect of the pressure drop on ignitability of the combustor. An increase in pressure drop was associated with a decrease in the likelihood of ignition success, especially at increasing altitudes. The introduction of the reduced temperature effect exacerbated this effect, further hurting ignition. High velocity regions in the combustor were detrimental to the ignition, and high area, low velocity regions aided greatly. The flame tended to settle into the corner recirculation zone and recirculate back into the center-toroidal recirculation zone (CTRZ), spreading downstream and likewise into adjacent swirl cups. These tests demonstrate the need for new combustor designs to consider adding large recirculation zones for combustor flame stability that will aid in relight requirements.

The Effects of Inlet Boundary Layer Condition and Periodically Incoming Wakes on Secondary Flow in a Low Pressure Turbine Cascade

2020 ◽  
Author(s):  
Tobias Schubert ◽  
Silvio Chemnitz ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
High Speed ◽  
Low Pressure ◽  
Experimental Investigations ◽  
Turbine Cascade ◽  
Flow Conditions ◽  
Low Pressure Turbine ◽  
Speed Flow ◽  
Unsteady Inflow

Abstract A particular turbine cascade design is presented with the goal of providing a basis for high quality investigations of endwall flow at high-speed flow conditions and unsteady inflow. The key feature of the design is an integrated two-part flat plate serving as a cascade endwall at part-span, which enables a variation of the inlet endwall boundary layer conditions. The new design is applied to the T106A low pressure turbine cascade for endwall flow investigations in the High-Speed Cascade Wind Tunnel of the Institute of Jet Propulsion at the Bundeswehr University Munich. Measurements are conducted at realistic flow conditions (M2th = 0.59, Re2th = 2·105) in three cases of different endwall boundary layer conditions with and without periodically incoming wakes. The endwall boundary layer is characterized by 1D-CTA measurements upstream of the blade passage. Secondary flow is evaluated by Five-hole-probe measurements in the turbine exit flow. A strong similarity is found between the time-averaged effects of unsteady inflow conditions and the effects of changing inlet endwall boundary layer conditions regarding the attenuation of secondary flow. Furthermore, the experimental investigations show, that all design goals for the improved T106A cascade are met.

Experimental study of fibre breakup and shot formation in melt blowing nozzle designs

2020 ◽  
pp. 152808372094927 ◽  
Author(s):  
Ignacio Formoso ◽  
Alejandro Rivas ◽  
Gerardo Beltrame ◽  
Gorka S Larraona ◽  
Juan Carlos Ramos ◽  
...  
Keyword(s):  
Experimental Study ◽  
High Speed ◽  
Flux Ratio ◽  
Adhesive Bond ◽  
Operating Conditions ◽  
Nozzle Geometry ◽  
Dimensionless Temperature ◽  
Melt Blowing ◽  
High Speed Imaging ◽  
Adhesive Bonds

The high demand for quality in the manufacture of absorbent hygiene products requires the adhesive bonds between layers to be as uniform as possible. An experimental study was conducted on two industrial multihole melt blowing nozzle designs used for hot-melt adhesive applications for hygiene products, in order to study two defects that influence the quality of the adhesive bond: fibre breakup, resulting in contamination, and the presence of shots, undesirable lumps that end up in the finished product. To this end, the fibre dynamics were captured at the nozzle exit region by using high-speed imaging. From the results it was observed that die drool is the main source of shot formation, while fibre breakup occurs as a result of applying a sufficiently large force in the direction perpendicular to the fibre. In addition, three dimensionless parameters were defined, the first two being the air-polymer flux ratio and the dimensionless temperature ratio, both of which represent the operating conditions, and the remaining one being the force ratio, which represents the nozzle geometry. The effect of these parameters on fibre breakup and shot formation was studied and the results indicate that both the operating conditions and the nozzle geometry were responsible for the onset of the fibre breakup and for the formation of shots. More precisely, both defects turned out to be dominated by the air-polymer flux ratio and the air tilt angle. The results that emerge from this study are useful for the enhancement of industrial melt blowing nozzles.

A Comparison of Turbulence Levels From Particle Image Velocimetry and Constant Temperature Anemometry Downstream of a Low-Pressure Turbine Cascade at High-Speed Flow Conditions

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Silvio Chemnitz ◽  
Reinhard Niehuis
Keyword(s):  
Particle Image Velocimetry ◽  
Constant Temperature ◽  
High Speed ◽  
Particle Image ◽  
Low Pressure ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Turbine Cascade ◽  
Low Pressure Turbine ◽  
Image Velocimetry

Abstract The development and verification of new turbulence models for Reynolds-averaged Navier–Stokes (RANS) equation-based numerical methods require reliable experimental data with a deep understanding of the underlying turbulence mechanisms. High accurate turbulence measurements are normally limited to simplified test cases under optimal experimental conditions. This work presents comprehensive three-dimensional data of turbulent flow quantities, comparing advanced constant temperature anemometry (CTA) and stereoscopic particle image velocimetry (PIV) methods under realistic test conditions. The experiments are conducted downstream of a linear, low-pressure turbine cascade at engine relevant high-speed operating conditions. The special combination of high subsonic Mach and low Reynolds number results in a low density test environment, challenging for all applied measurement techniques. Detailed discussions about influences affecting the measured result for each specific measuring technique are given. The presented time mean fields as well as total turbulence data demonstrate with an average deviation of ΔTu<0.4% and ΔC/Cref<0.9% an extraordinary good agreement between the results from the triple sensor hot-wire probe and the 2D3C-PIV setup. Most differences between PIV and CTA can be explained by the finite probe size and individual geometry.

Characterisation of Waves and Ligaments in Films Close to an Aeroengine Ball Bearing

2019 ◽  
Author(s):  
Jee Loong Hee ◽  
Kathy Simmons ◽  
David Hann ◽  
Michael Walsh
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Ball Bearing ◽  
Capillary Waves ◽  
Operating Conditions ◽  
Research Centre ◽  
Shaft Speed ◽  
High Speed Imaging ◽  
Liquid Phases ◽  
Mass Transfers

Abstract Surface waves are observed in many situations including natural and engineering applications. Experiments conducted at the Gas Turbine and Transmissions Research Centre (G2TRC) used high speed imaging to observe multiscale wave structures close to an aeroengine ball bearing in a test rig. The dynamic behavior and scale of the waves indicate that these are shear-driven although highly influenced by gravity at low shaft speed. To understand the interactions between gas and liquid phases including momentum and mass transfers, characterization of the observed waves and ligaments was undertaken. Waves were studied at surfaces close to the ball bearing and ligaments were assessed near the cage. Characterization was in terms of frequency and wavelength as functions of speed, flow-rate, bearing axial load and gravity. The assessments confirmed the existence of gravity-capillary waves and capillary waves. Gravity-capillary waves were measured to have a longer mean wavelength on the co-current side of the bearing (gravity and shear acting together) compared to the counter-current side (gravity and shear opposing). Using a published definition of critical wavelength (λcrit), measured wavelengths at 3,000 rpm were 2.56λcrit on the co-current side compared to 1.86λcrit at the countercurrent location. As shaft speed increases, wavelength reduces with transition to capillary waves occurring at around 0.83λcrit. At shaft speeds beyond 5000 rpm, capillary waves were fully visible and the wavelength was obtained as 0.435λcrit. Flow-rate and load did not significantly influence wavelength. Wave frequency was found to be proportional to shaft speed. The gravity-capillary waves had frequencies within the range 13–25 Hz while capillary waves exhibited a frequency well beyond 100 Hz. The frequencies are highly fluctuating with no effect of load and flow rate observed. Ligaments were characterized using Weber number and Stability number. The number of ligaments increased with shaft speed. A correlation for ligament number based on operating conditions is proposed.

Visualizing an ignition process of hydrogen jets containing sodium mist by high-speed imaging

2019 ◽  
Vol 56 (6) ◽  
pp. 521-532
Author(s):  
Daisuke Doi ◽  
Hiroshi Seino ◽  
Shinya Miyahara ◽  
Masayoshi Uno
Keyword(s):  
High Speed ◽  
Ignition Process ◽  
High Speed Imaging
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