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

Liquid Fuel Composition Effects on Forced, Non-Premixed Ignition

2016 ◽  
Author(s):  
Brandon Sforzo ◽  
Hoang Dao ◽  
Sheng Wei ◽  
Jerry Seitzman
Keyword(s):  
High Speed ◽  
Chemical Kinetic ◽  
Optical Measurements ◽  
Liquid Fuels ◽  
Kinetic Properties ◽  
Fuel Composition ◽  
Ignition Process ◽  
Oxidation Reactions ◽  
High Speed Imaging ◽  
Ignition Probability

The effects of jet fuel composition on ignition probability have been studied in a flowfield that is relevant to turbine engine combustors, but also fundamental and conducive to modeling. In the experiments, a spark kernel is ejected from a wall and propagates transversely into a crossflow. The kernel first encounters an air-only stream before transiting into a second, flammable (premixed) stream. The two streams have matched velocities, as verified by hot-wire measurements. The liquid fuels span a range of physical and chemical kinetic properties. To focus on their chemical differences, the fuels are prevaporized in a carrier air flow before being injected into the experimental facility. Ignition probabilities at atmospheric pressure and elevated crossflow temperature were determined from optical measurements of a large number of spark events, and high speed imaging was used to characterize the kernel evolution. Eight fuel blends were tested experimentally; all exhibited increasing ignition probability as equivalence ratio increased, at least up to 1.5. Statistically significant differences between fuels were measured that have some correlation with fuel properties. To elucidate these trends, the forced ignition process was also studied with a reduced order numerical model of an entraining kernel. The simulations suggest ignition is successful if sufficient heat release occurs before entrainment of colder crossflow fluid quenches the exothermic oxidation reactions. As the kernel is initialized in air, it remains lean during the initial entrainment of the fuel-air mixture; thus richer crossflows lead to quicker and higher exothermicity.

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.

scholarly journals Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff Body Stabilised Annular Combustor

2020 ◽  
Author(s):  
Roberto Ciardiello ◽  
Rohit S. Pathania ◽  
Patton M. Allison ◽  
Pedro M. de Oliveira ◽  
Epaminondas Mastorakos
Keyword(s):  
High Speed ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Flame Kernel ◽  
Annular Combustor ◽  
Initial Flame ◽  
Limiting Condition

Abstract An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess the ignition probability and to provide insights into the mechanisms of failure and of successful propagation. The experiments are done at conditions that are close to the lean blow-off limit (LBO) and hence the ignition is difficult and close to the limiting condition when ignition is not possible. Two configurations were employed, with 12 and 18 burners, the mixture velocity was varied between 10 and 30 m/s, and the equivalence ratio (ϕ) between 0.58 and 0.68. Ignition was initiated by a sequence of sparks (2 mm gap, 10 sparks of 10 ms each) and “ignition” is defined as successful ignition of the whole annular combustor. The mechanism of success and failure of the ignition process and the flame propagation patterns were investigated via high-speed imaging (10 kHz) of OH* chemiluminescence. The lean ignition limits were evaluated and compared to the lean blow-off limits, finding the 12-burner configuration is more stable than the 18-burner. It was found that failure is linked to the trapping of the initial flame kernel inside the inner recirculation zone (IRZ) of a single burner adjacent to the spark, followed by localised quenching on the bluff body probably due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner or for a flame pocket to be convected downstream in the chamber to grow and start propagating upwards. Finally, the ignition probability (Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign ∼ 0 for most conditions, while Pign increased moving the spark away from the bluff-body or placing it between two burners and peaked to Pign ∼ 1 when the spark was located downstream in the combustion chamber, where the velocities are lower and the turbulence less intense. The results provide information on the most favourable conditions for achieving ignition in a complex multi-burner geometry and could help the design and optimisation of realistic gas turbine combustors.

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.

scholarly journals Liquid Fuel Composition Effects on Forced, Nonpremixed Ignition

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Brandon Sforzo ◽  
Hoang Dao ◽  
Sheng Wei ◽  
Jerry Seitzman
Keyword(s):  
High Speed ◽  
Chemical Kinetic ◽  
Optical Measurements ◽  
Liquid Fuels ◽  
Kinetic Properties ◽  
Fuel Composition ◽  
Ignition Process ◽  
Oxidation Reactions ◽  
High Speed Imaging ◽  
Ignition Probability

The effects of jet fuel composition on ignition probability have been studied in a flowfield that is relevant to turbine engine combustors, but also fundamental and conducive to modeling. In the experiments, a spark kernel is ejected from a wall and propagates transversely into a crossflow. The kernel first encounters an air-only stream before transiting into a second, flammable (premixed) stream. The two streams have matched velocities, as verified by hot-wire measurements. The liquid fuels span a range of physical and chemical kinetic properties. To focus on their chemical differences, the fuels are prevaporized in a carrier air flow before being injected into the experimental facility. Ignition probabilities at atmospheric pressure and elevated crossflow temperature were determined from optical measurements of a large number of spark events, and high-speed imaging was used to characterize the kernel evolution. Eight fuel blends were tested experimentally; all exhibited increasing ignition probability as equivalence ratio increased, at least up to the maximum value studied (∼0.8). Statistically significant differences between fuels were measured that have some correlation with fuel properties. To elucidate these trends, the forced ignition process was also studied with a reduced-order numerical model of an entraining kernel. The simulations suggest ignition is successful if sufficient heat release occurs before entrainment of colder crossflow fluid quenches the exothermic oxidation reactions. As the kernel is initialized in air, it remains extremely lean during the initial entrainment of the fuel–air mixture; thus, richer crossflows lead to quicker and higher exothermicity.

Simulation of the Ignition Process in an Annular Multiple-Injector Combustor and Comparison With Experiments

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Maxime Philip ◽  
Matthieu Boileau ◽  
Ronan Vicquelin ◽  
Thomas Schmitt ◽  
Daniel Durox ◽  
...  
Keyword(s):  
High Speed ◽  
Burning Velocity ◽  
Flame Structure ◽  
Combustion Model ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Flamelet Model ◽  
Swirl Injectors ◽  
Eddy Simulation ◽  
Annular Combustor

Ignition is a problem of fundamental interest with critical practical implications. While there are many studies of ignition of single injector configurations, the transient ignition of a full annular combustor has not been extensively investigated, mainly because of the added geometrical complexity. The present investigation combines simulations and experiments on a complete annular combustor. The setup, developed at EMC2 (Energétique Moléculaire et Macroscopique Combustion) Laboratory (Mesa, AZ), features sixteen swirl injectors and quartz walls allowing direct visualization of the flame. High speed imaging is used to record the space time flame structure and study the dynamics of the light-round process. On the numerical side, massively parallel computations are carried out in the large eddy simulation (LES) framework using the filtered tabulated (F-TACLES) flamelet model. Comparisons are carried out at different instants during the light-round process between experimental data and results of calculations. It is found that the simulation results are in remarkable agreement with experiments provided that the thermal effects at the walls are considered. Further analysis indicate that the flame burning velocity and flame front geometry are close to those found in the experiment. This investigation confirms that the LES framework used for these calculations and the selected combustion model are adequate for such calculations but that further work is needed to show that ignition prediction can be used reliably over a range of operating parameters.

Simulation of the Ignition Process in an Annular Multiple-Injector Combustor and Comparison With Experiments

2014 ◽  
Author(s):  
Maxime Philip ◽  
Matthieu Boileau ◽  
Ronan Vicquelin ◽  
Thomas Schmitt ◽  
Daniel Durox ◽  
...  
Keyword(s):  
High Speed ◽  
Burning Velocity ◽  
Flame Structure ◽  
Combustion Model ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Flamelet Model ◽  
Swirl Injectors ◽  
Geometrical Complexity ◽  
Annular Combustor

Ignition is a problem of fundamental interest with critical practical implications. While there are many studies of ignition of single injector configurations, the transient ignition of a full annular combustor has not been extensively investigated, mainly because of the added geometrical complexity. The present investigation combines simulations and experiments on a complete annular combustor. The setup, developed at EM2C laboratory, features sixteen swirl injectors and quartz walls allowing direct visualization of the flame. High speed imaging is used to record the space time flame structure and study the dynamics of the light-round process. On the numerical side, massively parallel computations are carried out in the LES framework using the Filtered Tabulated (F-TACLES) flamelet model. Comparisons are carried out at different instants during the light-round process between experimental data and results of calculations. It is found that the simulation results are in remarkable agreement with experiments provided that the thermal effects at the walls are considered. Further post-processings indicate that the flame burning velocity and flame front geometry are close to those found in the experiment. This analysis confirms that the LES framework used for these calculations and the selected combustion model are adequate for such calculations but that further work is needed to confirm that ignition prediction can be used reliably over a range of operating parameters.

Elastic breakdown via multi-core high frequency discharge for lean-burn ignition

2021 ◽  
pp. 095440702110622
Author(s):  
Xiaoye Han ◽  
Xiao Yu ◽  
Hua Zhu ◽  
Linyan Wang ◽  
Shui Yu ◽  
...  
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Imaging Techniques ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Lean Burn ◽  
Electric Circuits ◽  
High Frequency Discharge ◽  
Breakdown Process ◽  
Ignition Quality

An advanced ignition technique is developed to achieve multi-event breakdown and multi-site ignition using a single coil for ignition quality improvements. The igniter enables a unique elastic breakdown process embracing a series of high-frequency discharge events at the spark gap. The equivalent electric circuits and current/voltage equations are identified and verified for the first time to explain the working principle that governs such an elastic breakdown process. Benchmarking tests are first performed to compare the elastic breakdown ignition with the conventional and advanced multi-electrode ignition systems. The elastic breakdown and spark events are thereafter analyzed through current and voltage measurements and high-speed imaging techniques. Finally, ignition tests in combustion chambers are performed to examine the effects on the ignition process in comparison with conventional coil-based ignition systems. The experiments show that, the elastic breakdown ignition can distribute multiple high-frequency breakdown events at all electrode pairs of a multi-electrode sparkplug while using only one ignition coil, thereby offering significant cost saving advantage and packaging practicability.

scholarly journals Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff-Body Stabilised Annular Combustor

2020 ◽  
Author(s):  
Roberto Ciardiello ◽  
Rohit Pathania ◽  
Patton Allison ◽  
Pedro M. de Oliveira ◽  
Epaminondas Mastorakos
Keyword(s):  
High Speed ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Flame Kernel ◽  
Design And Optimization ◽  
Annular Combustor ◽  
Favorable Conditions

Abstract An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess ignition probability and provide insights into the mechanisms of failure and of successful flame propagation. Two configurations were employed, with 12 and 18 burners, mixture velocity was varied between 10 and 30 m/s, and equivalence ratio between 0.58 and 0.68. Ignition was initiated by a sequence of sparks and "ignition" is defined as successful ignition of the whole annular combustor. Mechanism of success and failure of the ignition process was investigated via high-speed imaging of OH*chemiluminescence. Lean ignition limits were evaluated and compared to the lean blow-off limits. It was found that failure is linked to the trapping of the flame kernel inside the inner recirculation zone (IRZ) of a single burner, followed by localised quenching on the bluff body due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner. Finally, the ignition probability(Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign~0 for most conditions, while Pign increased moving the spark away from the bluff body or placing it between two burners and peaked to Pign~1 when the spark was located downstream in the combustion chamber. The results provide information on the most favorable conditions for achieving ignition and could help design and optimization of realistic gas turbine combustors.

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