Characteristics of Hydrogen Combustion in a Rapidly Mixed Tubular Flame Burner

2018 ◽  
Author(s):  
Baolu Shi ◽  
Bo Li ◽  
Xiaoyao Zhao ◽  
Qingzhao Chu ◽  
Ningfei Wang
Keyword(s):  
Burning Velocity ◽  
Flame Structure ◽  
Hydrogen Combustion ◽  
Injection Velocity ◽  
Hydrogen Fuel ◽  
Air Flow Rate ◽  
Extinction Limit ◽  
Flame Burner ◽  
Safe Technique ◽  
Fuel Stream

Hydrogen is a carbon-free fuel expecting to be used in either combustion devices or fuel cells. However, high diffusivity and reactivity of hydrogen may result in potential hazards of flame flash back in conventional combustion systems, which greatly restricts the wide application of hydrogen fuel in engines. In this study, an inherently safe technique of rapidly mixed tubular combustion is adopted to attempt the hydrogen combustion, in which fuel and oxidizer are individually injected into the cylindrical combustor. Two methods of fuel and oxidizer feeding are tested: (1) hydrogen and air are separately injected from fuel and oxidizer inlets, respectively. Measurements are conducted by varying air flow rate and equivalence ratio (Φ), in which a steady tubular flame can only be obtained below Φ = 0.35, above which the flame becomes unsteady. (2) N2 is adopted as the diluent in both H2 and O2 streams. By adding N2 in the fuel stream to approach the same mean injection velocity as that of N2 and O2 mixture in the oxidizer inlet, fuel/oxidizer mixing is much enhanced, and a steady tubular flame has been achieved at Φ = 0.5. Then the oxygen content in the overall mixture of N2 and O2 is gradually reduced from 0.21 to investigate the combustion characteristics. Flame structure, lean extinction limit, flame stability and laminar burning velocity as well as temperature are investigated under various oxygen contents and equivalence ratios. The results provide a useful guide to the safe operation of hydrogen combustion in the rapidly mixed tubular flame burner.

CO and OH Imaging in Flames Using a Single Broadband Femtosecond Laser Pulse

2020 ◽  
Author(s):  
Pradeep Parajuli ◽  
Ayush Jain ◽  
Waruna D. Kulatilaka
Keyword(s):  
Laser Pulse ◽  
Reaction Zone ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Chemical Species ◽  
Oxidation Reactions ◽  
Simultaneous Excitation ◽  
Spatiotemporal Information ◽  
Flame Burner ◽  
Fs Laser

Abstract Carbon monoxide (CO) and hydroxyl (OH) are the two key intermediate species formed during chemical reactions inside gas turbine combustors. Spatiotemporal information and a detailed understanding of CO formation in the reaction zone are important during the combustion processes as a major part of the heat release is obtained from the oxidation of CO to CO2. Turbulent flame structures and reaction zone in different flame conditions can also be visualized through the spatial distribution profiles of OH. In the current study, both these species are excited simultaneously using a single ultrashort, broad spectral bandwidth of approximately 100-femtosecond (fs) duration laser pulse at λ = 283.8 nm. Subsequent fluorescence signals are separated through spectral filters of appropriate bandwidth and imaged using two cameras. This present study was performed in a McKenna flat-flame burner with ethylene/air as a pilot flame and non-premixed turbulent ethylene jet at the center. The partial spectral overlap of CO–X (4,0) and OH A–X (1,0) transitions are utilized for simultaneous excitation, thereby characterize the overall flame structure (via OH) and regions of oxidation reactions (via CO) in a range of flame conditions. Besides, CO and OH profiles follow the trends obtained from model predictions for a range of equivalence ratios in ethylene/air flames stabilized over the Hencken calibration burner. These results are used for obtaining quantitative calibrations of CO and OH signals. Overall, the present study extends the applicability of a single, broadband fs laser pulse for simultaneous imaging of multiple chemical species in flame.

Effects of Hydrogen Enrichment on the Reattachment and Hysteresis of Lifted Methane Flames

2013 ◽  
Author(s):  
James D. Kribs ◽  
Andrew R. Hutchins ◽  
William A. Reach ◽  
Tamir S. Hasan ◽  
Kevin M. Lyons
Keyword(s):  
Burning Velocity ◽  
Flame Structure ◽  
Flame Stabilization ◽  
Dominant Factor ◽  
Jet Flame ◽  
Lifted Flames ◽  
Methane Flames ◽  
Hydrogen Enrichment ◽  
The Stability ◽  
The Impact

The purpose of this study is to observe the effects of hydrogen enrichment on the stability of lifted, partially premixed, methane flames. Due to the relatively large burning velocity of hydrogen-air flames when compared to that of typical hydrocarbon-air flames, hydrogen enriched hydrocarbon flames are able to create stable lifted flames at higher velocities. In order to assess the impact of hydrogen enrichment, a selection of studies in lifted and attached flames were initiated. Experiments were performed that focused on the amount of hydrogen needed to reattach a stable, lifted methane jet flame above the nozzle. Although high fuel velocities strain the flame and cause it to stabilize away from the nozzle, the high burning velocity of hydrogen is clearly a dominant factor, where as the lifted position of the flame increased, the amount of hydrogen needed to reattach the flame increased at the same rate. In addition, it was observed that as the amount of hydrogen in the central jet increased, the change in flame liftoff height increased and hysteresis became more pronounced. It was found that the hysteresis regime, where the flame could either be stabilized at the nozzle or in air, shifted considerably due to the presence of a small amount of hydrogen in the fuel stream. The effects of the hydrogen enrichment, however small the amount of hydrogen compared to the overall jet velocity, was the major factor in the flame stabilization, even showing discernible effects on the flame structure.

The determination of burning velocities of slow flames

1955 ◽  
Vol 228 (1174) ◽  
pp. 297-322 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Burning Velocity ◽  
Flame Temperature ◽  
Excess Energy ◽  
Flat Flame ◽  
Straight Line ◽  
Flame Burner ◽  
Line Relationship ◽  
Propane Butane

Measurements of the burning velocities of methane, ethane, propane, butane, ethylene, carbon monoxide and cyanogen mixtures with air, in the range about 4 to 8 cm, are made by the flat-flame burner method with an accuracy of 2 to 3%. The results can be represented by a straight-line relationship between composition and burning velocity except for carbon monoxide which is sensitive to the percentage of water vapour present. Extrapolated values agree well with recent measurements of faster flames. Measurements are also made on binary mixtures with air of the gases, including hydrogen. The mixture law holds except with mixtures containing carbon monoxide. Limits of inflammability are also determined and the burning velocities at the limits average 3⋅6 cm/s. The mixtures obey the Le Chatelier rule accurately, except for carbon monoxide mixtures. The burning velocities of the hydrocarbons can be represented approximately by a straight-line relationship with the heat generated and with the maximum flame temperature, but correlation is best when thermal conductivity is introduced. At a given velocity the excess energy maintained by the flame appears to be constant for all the hydrocarbons investigated, except methane, which behaves slightly differently. The burning velocities of the hydrocarbons are controlled by a reaction which provides reasonable values of the activation energies and probably precedes the sudden development of chain branching.

Modeling of the Thermal Characteristics of an Eccentric Multi-Stage Inverse Jet Diffusion Flame Burner

2014 ◽  
Author(s):  
Sherif Amin ◽  
Ahmed Emara ◽  
Adel Hussien ◽  
Ibrahim Shabaka
Keyword(s):  
Thermal Structure ◽  
Flame Structure ◽  
Flow Characteristics ◽  
Thermal Characteristics ◽  
Maximum Temperature ◽  
Reacting Flow ◽  
Free Jet ◽  
Multi Stage ◽  
Flame Burner ◽  
Dissipation Model

The objective of this paper is to study the effect of eccentricity on the thermal characteristics and flow field of a triple-concentric free jet burner. The investigation concerns three values of eccentricity (1.25, 1.88, and 2.5 times the inner-jet diameter); and in addition to the normal centric jet (no eccentricity). Prediction of the reacting flow characteristics and the planar flow visualization for all burners’ configurations is simulated with the CFD k-ε turbulence of “ANSYS-CFX”. In addition, the finite rate and eddy dissipation model is utilized to simulate the interaction between the chemical reaction and turbulence. The temperature, velocity and turbulence intensity are investigated to simulate the thermal-structure interaction. The results are obtained at a constant momentum rate. It showed significant changes in the coherent structures shed from the annular jets. By increasing the eccentricity, the maximum temperature will be attained more rapidly than centric case. In addition, the mixing point become nearer the burner rim, which increased the flame size and shifted the flame structure.

Computation of Rotor/Stator Interaction With Hydrogen-Fuelled Combustion

2003 ◽  
Author(s):  
Masanori Sato ◽  
Takashi Nagumo ◽  
Kazuyuki Toda ◽  
Makoto Yamamoto
Keyword(s):  
Numerical Simulation ◽  
Numerical Simulations ◽  
Injection Rate ◽  
Hydrogen Combustion ◽  
Present System ◽  
Hydrogen Fuel ◽  
General Aspect ◽  
3 Dimensional ◽  
Low Emission ◽  
Rotor Stator Interaction

For the next-generation aircraft, a new propulsion system using hydrogen fuel has been proposed. In the present system, hydrogen fuel injected from a stator surface combusts in the turbine passages, accordingly, the conventional combustor can be cut out. The advantage of this system is that we can design a lighter and smaller engine with low emission. We have demonstrated the realizability of this system by using the cycle analysis and the numerical simulations. Through the previous studies, it was confirmed that the rotor/stator interaction has to be investigated, because the hydrogen combustion phenomena within the stator passage is so complex, and thus it would highly affect the rotor performance. In this paper, we focus on the rotor/stator interaction for the detailed investigation of realizability of this system. The 2- and 3-dimensional numerical simulations are performed for a single stage turbine with hydrogen-fuelled combustion. In the 2-dimensional study, the effects of the injection position and injection rate on the flow structure, the static temperature over the blades, and the blade performance are investigated. Furthermore, 3-dimensional numerical simulation is performed. The general aspect of 3-dimensional flow field is demonstrated, and the effect of hydrogen combustion on the components of turbine, for example hub, tip and blade, are investigated.

An Experimental Study on Methane/Oxygen-Air Combustion With a Rapidly Mixed Type Tubular Flame Burner

2011 ◽  
Author(s):  
Baolu Shi ◽  
Tatsuya Kowari ◽  
Daisuke Shimokuri ◽  
Satoru Ishizuka
Keyword(s):  
Experimental Study ◽  
Diffusion Flame ◽  
Turbulent Combustion ◽  
Mixed Type ◽  
Diffusion Flames ◽  
Kinetic Mechanism ◽  
Pure Oxygen ◽  
Extinction Limit ◽  
Wide Range ◽  
Flame Burner

Methane/oxygen-air combustion has been attempted by using a rapidly mixed type tubular flame burner with four slits, from two of which a fuel is injected and from another two an oxidizer is injected. The oxygen concentration (molar) in the oxygen-air oxidizer has been varied from 21% (air) to 100% (pure oxygen). Results show that uniform tubular flame combustion can be obtained for a wide range of equivalence ratios, if the oxygen molar concentration in the oxygen-air oxidizer is less than about 50%. Above 50%, however, very intense turbulent combustion occurs frequently and the circular-shaped tubular flame is deformed as oval-shaped for most equivalence ratios. The uniform tubular flame range is reduced and quite limited in the vicinity of lean condition. Detailed observations show that for pure (or near pure) oxygen oxidizer, two diffusion flames are established between the fuel and oxidizer streams at the exits of the fuel slits, which prevents fuel from mixing with oxygen, resulting in a violent turbulent combustion downstream the slits. With use of a burner with smaller slit width, however, formation of the diffusion flame is inhibited and a uniform tubular flame can be established, although still limited close to the lean extinction limit. To fully understand the flame characteristics above, the burning velocities are calculated for various equivalence ratios as well as for various oxygen concentrations in the oxygen-air oxidizer using the CHEMKIN PREMIX code with the GRI kinetic mechanism.

Sign in / Sign up

Export Citation Format

Share Document