Influence of Ambient Conditions on Laminar Burning Velocity, Ignition and Flame Extinction for Ethanol-Air Mixtures

2012 ◽  
Author(s):  
Daniel de la Rosa ◽  
Andrew P. Crayford ◽  
Philip J. Bowen ◽  
Agustin Valera-Medina
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Initial Conditions ◽  
Burning Velocity ◽  
Experimental Studies ◽  
Initial Pressure ◽  
Ambient Conditions ◽  
Discharge System ◽  
Stretch Rate ◽  
Nonlinear Trends

Experimental studies of laminar ethanol - air gaseous flames have been undertaken in a large (34 l) cylindrical constant volume combustion bomb to investigate combustion fundamentals at varying ambient conditions. This vessel has been designed to minimise the influence of boundary walls, hence extending the quasi steady pressure region over which meaningful data may be obtained. Gaseous homogeneous mixtures are achieved by injecting liquid ethanol into the bomb which pre-vaporises prior to ignition. Initial pressure and equivalence ratio are predetermined using partial pressure methodology. Flame propagation is recorded utilising high-speed Schlieren photography, and low ignition energies were achieved via a variable discharge system enabling the sensitive early stages of flame propagation and extinction limits to be studied. Data is presented in terms of flame speed against stretch rate from which Markstein lengths and laminar burning velocities are derived for a variety of different initial conditions. The effect of ignition energy, initial pressure (from sub-atmospheric to elevated pressure) along with the effect of increasing initial temperature is studied. Results are discussed in terms of those of previous workers, and compared with predictions from detailed chemical kinetic schemes. Nonlinear trends witnessed during early stage flame propagation are further investigated as a suitable method for deriving extinction stretch rate.

Experimental Study of Flame Stretch Under Engine-Like Conditions

2017 ◽  
Author(s):  
Behdad Afkhami ◽  
Yanyu Wang ◽  
Scott A. Miers ◽  
Jeffrey D. Naber
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
High Speed ◽  
Combustion Engine ◽  
Turbulent Flame ◽  
Experimental Studies ◽  
Flame Velocity ◽  
Turbulent Flame Speed ◽  
Stretch Rate ◽  
Flame Stretch

Since fossil fuels will remain the main source of energy for power generation and transportation in next decades, their combustion processes remain an important concern for the foreseeable future. For liquid or gaseous fuels, flame velocity that propagates normal to itself and relative to the flow into the unburned mixture is one of the most important quantities to study. In a non-uniform flow, a curved flame front area changes continually which is known as flame stretch. The concept becomes more important when it is realized that the stretch affects the turbulent flame speed. The current research empirically studies flame stretch under engine-like conditions since there has not been enough experimental studies in this area. For this reason, a one-cylinder, direct-injection, spark-ignition, naturally-aspirated optical engine was utilized to image the flame propagation process inside an internal combustion engine cylinder on the tumble plane. The flame front was found by processing high speed images which were taken from the flame inside the cylinder. Flame front propagation analysis showed that after the flame kernel was developed, during flame propagation period, the stretch rate decreased until the flame front touches the piston surface. This trend was common among stoichiometric, lean, and rich mixtures. In addition, the fuel-air mixture with λ = 0.85 showed lower stretch rate compared to stoichiometric or lean mixture with λ = 1.2. However, based on previous studies, further enrichment may result in the flame stretch rate become greater than that of the stretch rates for stoichiometric or lean mixtures. Also, comparing the stretch rate at two different engine speeds revealed that as the speed increased the stretch rate also increased; especially during the early flame development period. Therefore, according to previous studies which discussed flame stretch as a mechanism for flame extinguishment, the probability of the flame extinction is higher when the engine speed is higher.

Experimental Investigation on Rapid Evaporation of High-Pressure Liquids due to Depressurization

2012 ◽  
Author(s):  
Qiaoling Zhang ◽  
Qincheng Bi ◽  
Zesen Nie ◽  
Jun Liang ◽  
Yajun Guo ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
High Pressure ◽  
High Speed ◽  
Initial Conditions ◽  
Initial Pressure ◽  
Fluid Temperature ◽  
Shape Variation ◽  
Nitrogen Gas ◽  
Test Vessel ◽  
Variation Characteristics

This paper reports an experimental investigation of rapid evaporation process of high-pressure ethanol liquid during depressurization. The study focused on pressure and temperature transients with the influence of different initial conditions, and the shape variation was recorded via a high speed camera. During an experiment, the ethanol liquid was contained in a small round tube with a diameter 10mm in the test vessel, and a thermocouple was put within the fluid which was used to measure the fluid temperature during the depressurization. The predetermined pressure was provided by the high-pressure nitrogen gas, and the process of quick depressurization was started by opening the magnetic valve, which was connected with the test vessel. The transitions of the pressure and the fluid temperature were recorded by the NI data collection system. According to the experimental results, during the fast pressure drop, with the same initial temperature and other test conditions, the higher the initial pressure is, the faster the liquid temperature decreases, and the lower the minimum temperature reaches. In addition, the effect of initial fluid conditions, initial environmental pressure on temperature transition and so on are summed up and are experimentally analyzed on the fluid temperature change under the same test equipment. Also, the variation characteristics of kerosene fluid were compared with ethanol liquid under the same experiment conditions.

The Critical Pressure at the Onset of Flame Instability of Syngas/Air/Diluent Outwardly Expanding Flame at Different Initial Temperatures and Pressures

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Ziyu Wang ◽  
Ziwei Bai ◽  
Guangying Yu ◽  
Sai Yelishala ◽  
Hameed Metghalchi
Keyword(s):  
High Speed ◽  
Critical Pressure ◽  
Hydrodynamic Instability ◽  
Experimental Studies ◽  
Initial Pressure ◽  
High Energy ◽  
Oxide Semiconductor ◽  
High Energy Density ◽  
Flame Instability ◽  
Wide Range

Syngas has gained attention recently due to its high energy density and environmentally friendly characteristics. Flame stability plays an important role in flame propagation in energy conversion devices. Experimental studies were performed in a cylindrical chamber to investigate flame instability of syngas/air/diluent mixture. A Z-shape Schlieren system coupled with a high-speed complementary metal–oxide–semiconductor camera was used to record flame pictures up to 40,000 frames per second. In this research, syngas is a mixture of hydrogen and carbon monoxide and diluent is a blend of 14% CO2 and 86% N2 with the same specific heat as the burned gases. Three main flame instabilities namely Rayleigh–Taylor (body force) instability, hydrodynamic instability, and thermal-diffusive instability have been studied. For the onset of flame instability, a power law correlation for the ratio of critical pressure to initial pressure of syngas/air/diluent flames over a wide range of initial temperatures (298–450 K), initial pressures (1.0–2.0 atm), equivalence ratios (0.6–3.0), diluent concentrations (0–10%), and hydrogen percentages (5–25%) in the fuel has been developed.

The Effect of Spark Electrode Geometry on Flame Kernel of Premixed Methane-Air Mixtures

2008 ◽  
Author(s):  
Kian Eisazadeh Far ◽  
Farzan Parsinejad ◽  
Matt Gautreau ◽  
Hameed Metghalchi
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Initial Pressure ◽  
Experimental System ◽  
Cylindrical Vessel ◽  
Spark Ignition Engines ◽  
Electrode Geometry ◽  
Electrode Thickness ◽  
Flame Kernel ◽  
Fundamental Factor

Flame kernel formation and structure is a fundamental factor of spark ignition engines’ performance. An experimental study about the effect of spark electrode geometry on premixed flame propagation has been done with methane-air premixed mixtures. The experimental system consists of a constant volume cylindrical vessel and a shadowgraph optical system. Experiments were performed at atmospheric initial pressure with various equivalence ratios and spark electrode geometries. Flame propagation pictures and movies were taken by a CMOS high speed camera at 10,000 frames per second. Flame radii were measured by MIDAS software and parameters affecting flame location and formation were investigated. Experimental results show that the spark electrode thickness and its tip impact flame location and structure propagation.

Interaction of Flame Flashback Mechanisms in Premixed Hydrogen-Air Swirl Flames

2014 ◽  
Author(s):  
Thomas Sattelmayer ◽  
Christoph Mayer ◽  
Janine Sangl
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Burning Velocity ◽  
Ambient Pressure ◽  
Turbulent Flame ◽  
Quantitative Information ◽  
Flow Speed ◽  
Flame Stabilization ◽  
Bulk Flow ◽  
Wall Region

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen-air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed PIV/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approx. 1/3 of the typical flow velocities in gas turbine burners. In that range the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approx. 0.45 and delivers NOx-emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.

Flashback in a Swirl Burner With Cylindrical Premixing Zone

2001 ◽  
Author(s):  
Jassin Fritz ◽  
Martin Kröner ◽  
Thomas Sattelmayer
Keyword(s):  
Flame Propagation ◽  
Gas Turbines ◽  
High Speed ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Measurement Techniques ◽  
Mean Flow

Flame flashback from the combustion chamber into the mixing zone is one of the inherent problems of lean premixed combustion and essentially determines the reliability of low NOx burners. Generally, flashback can be initiated by one of the following four phenomena: flashback due to the conditions in the boundary layer, flashback due to turbulent flame propagation in the core flow, flashback induced by combustion instabilities and flashback caused by combustion induced vortex breakdown. In this study, flashback in a swirling tubular flow was investigated. In order to draw maximum benefit from the tests with respect to the application in gas turbines, the radial distribution of the axial and circumferential momentum in the tube was selected such that the typical character of a flow in mixing zones of premix burners without centerbody was obtained. A single burner test rig has been designed to provoke flashback with the preheating temperature, the equivalence ratio and the mean flow rate being the influencing parameters. The flame position within the mixing section is detected by a special optical flame sensor array, which allows the control of the experiment and furthermore the triggering of the measurement techniques. The burning velocity of the fuel has been varied by using natural gas or hydrogen. The characteristics of the flashback, the unsteady swirling flow during the flame propagation, the flame dynamics and the reaction zones have been investigated by applying High Speed Video recordings, the Laser Doppler Anemometry and the Laser Induced Fluorescence. The presented results show that a combustion induced vortex breakdown is the dominating mechansim of the observed flashback. This mechanism is very sensitive to the momentum distribution in the vortex core. By adding axial momentum around the mixing tube axis, the circumferential velocity gradient is reduced and flashback can be prevented.

scholarly journals The Effect of Initial Conditions on the Laminar Burning Characteristics of Natural Gas Diluted by CO2

Energies ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2892 ◽  
Author(s):  
Zhiqiang Han ◽  
Zhennan Zhu ◽  
Peng Wang ◽  
Kun Liang ◽  
Zinong Zuo ◽  
...  
Keyword(s):  
Natural Gas ◽  
Dilution Rate ◽  
Initial Temperature ◽  
Initial Conditions ◽  
Burning Velocity ◽  
Initial Pressure ◽  
Chemical Kinetic ◽  
Laminar Burning Velocity ◽  
Flame Instability ◽  
Highly Correlated

The initial conditions such as temperature, pressure and dilution rate can have an effect on the laminar burning velocity of natural gas. It is acknowledged that there is an equivalent effect on the laminar burning velocity between any two initial conditions. The effects of initial temperatures (323 K–423 K), initial pressures (0.1 MPa–0.3 MPa) and dilution rate (0–16%, CO2 as diluent gas) on the laminar burning velocity and the flame instability were investigated at a series of equivalence ratios (0.7–1.2) in a constant volume chamber. A chemical kinetic simulation was also conducted to calculate the laminar burning velocity and essential radicals’ concentrations under the same initial conditions. The results show that the laminar burning velocity of natural gas increases with initial temperature but decreases with initial pressure and dilution rate. The maximum concentrations of H, O and OH increase with initial temperature but decrease with initial pressure and dilution rate. Laminar burning velocity is highly correlated with the sum of the maximum concentration of H and OH.

Ignition and Flame Propagation in Oxy-Methane Mixtures Diluted With CO2

2015 ◽  
Author(s):  
Bader Almansour ◽  
Luke Thompson ◽  
Joseph Lopez ◽  
Ghazal Barari ◽  
Subith S. Vasu
Keyword(s):  
Flame Propagation ◽  
Atmospheric Pressure ◽  
High Speed ◽  
Dynamic Pressure ◽  
Burning Velocity ◽  
Reaction Rates ◽  
Current Data ◽  
Initiation And Propagation ◽  
Experimental Values ◽  
Good Agreement

Ignition and flame propagation in methane/O2 mixtures diluted with CO2 are studied. A laser ignition system and dynamic pressure data are utilized to ignite the mixture and to record the combustion pressure, respectively. The laminar burning velocities (LBV) are obtained at room temperature and atmospheric pressure in a spherical combustion chamber. Flame initiation and propagation is recorded by using a high-speed camera in select experiments to visualize the effect of CO2 proportionality on the combustion behavior. The laminar burning velocity is studied for a range of equivalence ratios (ϕ =0.8–1.3, in steps of 0.1), and oxygen ratios, D=O2/(O2+CO2) (26–38% by volume). It was found that the LBV decreases by increasing the CO2 proportionality. It was observed that the flame propagates toward the laser at a faster rate as the CO2 proportionality increases. Current experiments are in very good agreement with existing literature data. The premixed flame model from CHEMKIN PRO [1] software and two mechanisms (GRI-Mech 3.0 [2] and ARAMCO Mech 1.3 [3]) are used to simulate the current data. In general, simulations are in reasonable agreement with current data though the mechanisms predict slower flame speeds. The LBV values obtained by the ARAMCO 1.3 mechanism are closer to the experimental values. Additionally, sensitivity analysis is carried out to understand the important reactions that influence the predicted flame speeds. Improvements to the GRI predictions are suggested after incorporating latest reaction rates from literature for key reactions.

Interaction of Flame Flashback Mechanisms in Premixed Hydrogen–Air Swirl Flames

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Thomas Sattelmayer ◽  
Christoph Mayer ◽  
Janine Sangl
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Burning Velocity ◽  
Ambient Pressure ◽  
Turbulent Flame ◽  
Quantitative Information ◽  
Flow Speed ◽  
Flame Stabilization ◽  
Bulk Flow ◽  
Wall Region

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen–air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed (HS) particle image velocimetry (PIV)/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures, the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approximately 1/3 of the typical flow velocities in gas turbine burners. In that range, the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approximately 0.45 and delivers NOx emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.

scholarly journals Experimental Study of Premixed Gasoline Surrogates Burning Velocities in a Spherical Combustion Bomb at Engine Like Conditions

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3430
Author(s):  
Miriam Reyes ◽  
Francisco V. Tinaut ◽  
Alexandra Camaño
Keyword(s):  
Equivalence Ratio ◽  
Internal Combustion Engines ◽  
Initial Conditions ◽  
Burning Velocity ◽  
Initial Pressure ◽  
Power Laws ◽  
Liquid Fuels ◽  
Diagnostic Model ◽  
Positive Dependence ◽  
Thermodynamic Variables

In this work are presented experimental values of the burning velocity of iso-octane/air, n-heptane/air and n-heptane/toluene/air mixtures, gasoline surrogates valid over a range of pressures and temperatures similar to those obtained in internal combustion engines. The present work is based on a method to determine the burning velocities of liquid fuels in a spherical constant volume combustion bomb, in which the initial conditions of pressure, temperature and fuel/air equivalence ratios can be accurately established. A two-zone thermodynamic diagnostic model was used to analyze the combustion pressure trace and calculate thermodynamic variables that cannot be directly measured: the burning velocity and mass burning rate. This experimental facility has been used and validated before for the determination of the burning velocity of gaseous fuels and it is validated in this work for liquid fuels. The values obtained for the burning velocity are expressed as power laws of the pressure, temperature and equivalence ratio. Iso-octane, n-heptane and mixtures of n-heptane/toluene have been used as surrogates, with toluene accounting for the aromatic part of the fuel. Initially, the method is validated for liquid fuels by determining the burning velocity of iso-octane and then comparing the results with those corresponding in the literature. Following, the burning velocity of n-heptane and a blend of 50% n-heptane and 50% toluene are determined. Results of the burning velocities of iso-octane have been obtained for pressures between 0.1 and 0.5 MPa and temperatures between 360 and 450 K, for n-heptane 0.1–1.2 MPa and 370–650 K, and for the mixture of 50% n-heptane/50% toluene 0.2–1.0 MPa and 360–700 K. The power law correlations obtained with the results for the three different fuels show a positive dependence with the initial temperature and the equivalence ratio, and an inverse dependence with the initial pressure. Finally, the comparison of the burning velocity results of iso-octane and n-heptane with those obtained in the literature show a good agreement, validating the method used. Analytical expressions of burning velocity as power laws of pressure and unburned temperature are presented for each fuel and equivalence ratio.

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