Mass Burning Rate of Syngas/Air Mixtures and Gas to Liquid Fuel Auto-Ignition at High Temperatures and Pressures

2016 ◽  
Author(s):  
Mimmo Elia ◽  
Matthew Ferrari ◽  
Omid Askari ◽  
Hameed Metghalchi
Keyword(s):  
Burning Rate ◽  
High Temperatures ◽  
High Speed ◽  
Equivalence Ratio ◽  
Initial Pressure ◽  
Mass Burning Rate ◽  
System Effect ◽  
Auto Ignition ◽  
Wide Range ◽  
Gas To Liquid

Mass burning speed and onset of auto-ignition of premixed syngas/air and gas to liquid (GTL)/air mixtures respectively, have been determined at high temperatures and pressures over a wide range of fuel-air equivalence ratios. The experimental facilities consist of two spherical and cylindrical vessels. The spherical vessel was used to collect pressure data to measure the burning speed, mass burning rate and determine the onset of auto-ignition and cylindrical vessel was used to take pictures of flame propagation with a high speed CMOS camera up to 40,000 frame per second located in a Schlieren system. Effect of cellular flames on mass burning rate have been determined. Critical pressures and temperature for different fuel air equivalence ratios at which auto-ignition takes place have been measured. In this paper, mass burning rate of syngas is calculated for a wide range of equivalence ratio from 0.6 to 2, unburned temperature from 400 to 680 K and initial pressure from 2 to 25 atm. A power law correlation has been developed as a function of equivalence ratio, temperature and pressure. The onset of auto-ignition for GTL/air mixture has been identified for equivalence ratio of 0.8 to 1.2.

Auto-Ignition Characteristics Study of Gas-to-Liquid Fuel at High Pressures and Low Temperatures

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Omid Askari ◽  
Mimmo Elia ◽  
Matthew Ferrari ◽  
Hameed Metghalchi
Keyword(s):  
Chemical Kinetics ◽  
Low Temperatures ◽  
High Speed ◽  
High Pressures ◽  
Initial Temperature ◽  
Combustion Process ◽  
Pressure Rise ◽  
Auto Ignition ◽  
Wide Range ◽  
Gas To Liquid

Onset of auto-ignition of premixed gas-to-liquid (GTL)/air mixture has been determined at high pressures and low temperatures over a wide range of equivalence ratios. The GTL fuel used in this study was provided by Air Force Research Laboratory (AFRL), designated by Syntroleum S-8, which is derived from natural gas via the Fischer–Tropsch (F–T) process. A blend of 32% iso-octane, 25% n-decane, and 43% n-dodecane is employed as the surrogates of GTL fuel for chemical kinetics study. A spherical chamber, which can withstand high pressures up to 400 atm and can be heated up to 500 K, was used to collect pressure rise data, due to combustion, to determine the onset of auto-ignition. A gas chromatograph (GC) system working in conjunction with specialized heated lines was used to verify the filling process. A liquid supply manifold was used to allow the fuel to enter and evaporate in a temperature-controlled portion of the manifold using two cartridge heaters. An accurate high-temperature pressure transducer was used to measure the partial pressure of the vaporized fuel. Pressure rise due to combustion process was collected using a high-speed pressure sensor and was stored in a local desktop via a data acquisition system. Measurements for the onset of auto-ignition were done in the spherical chamber for different equivalence ratios of 0.8–1.2 and different initial pressures of 8.6, 10, and 12 atm at initial temperature of 450 K. Critical pressures and temperatures of GTL/air mixture at which auto-ignition takes place have been identified by detecting aggressive oscillation of pressure data during the spontaneous combustion process throughout the unburned gas mixture. To interpret the auto-ignition conditions effectively, several available chemical kinetics mechanisms were used in modeling auto-ignition of GTL/air mixtures. For low-temperature mixtures, it was shown that auto-ignition of GTL fuel is a strong function of unburned gas temperature, and propensity of auto-ignition was increased as initial temperature and pressure increased.

scholarly journals Prediction of Auto-Ignition Temperatures and Delays for Gas Turbine Applications

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Roda Bounaceur ◽  
Pierre-Alexandre Glaude ◽  
Baptiste Sirjean ◽  
René Fournet ◽  
Pierre Montagne ◽  
...  
Keyword(s):  
High Temperature ◽  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Process Conditions ◽  
Piping System ◽  
Gaseous Fuels ◽  
Auto Ignition ◽  
Wide Range

Gas turbines burn a large variety of gaseous fuels under elevated pressure and temperature conditions. During transient operations, variable gas/air mixtures are involved in the gas piping system. In order to predict the risk of auto-ignition events and ensure a safe operation of gas turbines, it is of the essence to know the lowest temperature at which spontaneous ignition of fuels may happen. Experimental auto-ignition data of hydrocarbon–air mixtures at elevated pressures are scarce and often not applicable in specific industrial conditions. Auto-ignition temperature (AIT) data correspond to temperature ranges in which fuels display an incipient reactivity, with timescales amounting in seconds or even in minutes instead of milliseconds in flames. In these conditions, the critical reactions are most often different from the ones governing the reactivity in a flame or in high temperature ignition. Some of the critical paths for AIT are similar to those encountered in slow oxidation. Therefore, the main available kinetic models that have been developed for fast combustion are unfortunately unable to represent properly these low temperature processes. A numerical approach addressing the influence of process conditions on the minimum AIT of different fuel/air mixtures has been developed. Several chemical models available in the literature have been tested, in order to identify the most robust ones. Based on previous works of our group, a model has been developed, which offers a fair reconciliation between experimental and calculated AIT data through a wide range of fuel compositions. This model has been validated against experimental auto-ignition delay times corresponding to high temperature in order to ensure its relevance not only for AIT aspects but also for the reactivity of gaseous fuels over the wide range of gas turbine operation conditions. In addition, the AITs of methane, of pure light alkanes, and of various blends representative of several natural gas and process-derived fuels were extensively covered. In particular, among alternative gas turbine fuels, hydrogen-rich gases are called to play an increasing part in the future so that their ignition characteristics have been addressed with particular care. Natural gas enriched with hydrogen, and different syngas fuels have been studied. AIT values have been evaluated in function of the equivalence ratio and pressure. All the results obtained have been fitted by means of a practical mathematical expression. The overall study leads to a simple correlation of AIT versus equivalence ratio/pressure.

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.

FLAME PROPAGATION AND BURNING RATES OF METHANE-AIR MIXTURES USING SCHLIEREN PHOTOGRAPHY

2016 ◽  
Vol 78 (10-2) ◽  
Author(s):  
Mohd Suardi Suhaimi ◽  
Aminuddin Saat ◽  
Mazlan A. Wahid ◽  
Mohsin Mohd Sies
Keyword(s):  
Combustion Chamber ◽  
Burning Rate ◽  
Equivalence Ratio ◽  
Burning Velocity ◽  
Initial Pressure ◽  
Markstein Length ◽  
Constant Volume Combustion Chamber ◽  
Burning Rates ◽  
Schlieren Photography

Different methodology have been shown to produce different results for Markstein length and laminar burning velocity of methane-air mixture.This study attempts to determine the aforesaid parameters using the newly developed closed vessel combustion chamber with Schlieren photography. Markstein length and burning rate of methane-air mixture was determined under the initial pressure of 1 atm, temperature range of 298-302K and equivalence ratio range of 0.7-1.3. Experiments were performed in a centrally ignited 29.16L cylindrical constant volume combustion chamber. Ignition energy was set at 25mJ for each experiment. The images of spherically expanding flame were recorded using Schlieren photography technique at a speed of 2000 frame per second. Analysis of the flame area yield flame radii from which the flame speed and stretch rate could be obtained. These parameters would allow the determination of Markstein length and burning rate of the flame. Results show that Markstein length magnitude increases proportionally with equivalence ratio with a magnitude ranging from 0.125cm to 0.245cm. Maximum burning rate occurs at equivalence ratio of 1.1 with a magnitude of 0.366 m/s. Flame of each equivalence ratio also exhibits fluctuation arising from acoustic disturbance. This disturbance becomes more apparent at higher equivalence ratio.

scholarly journals Nano-Sized and Mechanically Activated Composites: Perspectives for Enhanced Mass Burning Rate in Aluminized Solid Fuels for Hybrid Rocket Propulsion

Aerospace ◽  
2019 ◽  
Vol 6 (12) ◽  
pp. 127 ◽  
Author(s):  
Paravan
Keyword(s):  
Burning Rate ◽  
Solid Fuel ◽  
Mass Flux ◽  
High Speed ◽  
Rate Data ◽  
Mass Burning Rate ◽  
Diffusion Distance ◽  
Metal Combustion ◽  
Rate Enhancement ◽  
Regression Rate

This work provides a lab-scale investigation of the ballistics of solid fuel formulations based on hydroxyl-terminated polybutadiene and loaded with Al-based energetic additives. Tested metal-based fillers span from micron- to nano-sized powders and include oxidizer-containing fuel-rich composites. The latter are obtained by chemical and mechanical processes providing reduced diffusion distance between Al and the oxidizing species source. A thorough pre-burning characterization of the additives is performed. The combustion behaviors of the tested formulations are analyzed considering the solid fuel regression rate and the mass burning rate as the main parameters of interest. A non-metallized formulation is taken as baseline for the relative grading of the tested fuels. Instantaneous and time-average regression rate data are determined by an optical time-resolved technique. The ballistic responses of the fuels are analyzed together with high-speed visualizations of the regressing surface. The fuel formulation loaded with 10 wt.% nano-sized aluminum (ALEX-100) shows a mass burning rate enhancement over the baseline of 55% ± 11% for an oxygen mass flux of 325 ± 20 kg/(m2∙s), but this performance increase nearly disappears as combustion proceeds. Captured high-speed images of the regressing surface show the critical issue of aggregation affecting the ALEX-100-loaded formulation and hindering the metal combustion. The oxidizer-containing composite additives promote metal ignition and (partial) burning in the oxidizer-lean region of the reacting boundary layer. Fuels loaded with 10 wt.% fluoropolymer-coated nano-Al show mass burning rate enhancement over the baseline >40% for oxygen mass flux in the range 325 to 155 kg/(m2∙s). The regression rate data of the fuel composition loaded with nano-sized Al-ammonium perchlorate composite show similar results. In these formulations, the oxidizer content in the fuel grain is <2 wt.%, but it plays a key role in performance enhancement thanks to the reduced metal–oxidizer diffusion distance. Formulations loaded with mechanically activated ALEX-100–polytetrafluoroethylene composites show mass burning rate increases up to 140% ± 20% with metal mass fractions of 30%. This performance is achieved with the fluoropolymer mass fraction in the additive of 45%.

scholarly journals Development of a Model for Auto-Ignition Delays and its Use for the Prediction of Premix Combustion Reliability

2016 ◽  
Author(s):  
Roda Bounaceur ◽  
Pierre-Alexandre Glaude ◽  
Baptiste Sirjean ◽  
René Fournet ◽  
Pierre Montagne ◽  
...  
Keyword(s):  
Ignition Delay ◽  
Equivalence Ratio ◽  
Fuel Mixture ◽  
Fuel Composition ◽  
Ignition Delay Times ◽  
Auto Ignition ◽  
Wide Range ◽  
Kinetic Mechanisms ◽  
Safety And Reliability ◽  
Low Nox Combustion

Except in diesel engine applications, auto-ignition is an unwanted event from a general safety and reliability standpoint. It is especially undesirable in the premixing process involved in most low NOx combustion technologies. Therefore, in addition to auto-ignition temperature, autoignition delay (AID) is a key data for the design of modern combustors including gas turbine ones. The authors have investigated the detailed kinetic mechanisms leading to autoignition and established practical AID correlations involving the fuel composition, its temperature, pressure and equivalence ratio. The correlations brought about during this program offer a good reconciliation between calculated and experimental AID through a wide range of fuel composition, initial temperature and pressure. Validations were mainly done against data acquired with experimental setups consisting in shock tubes and rapid compression machines. The auto-ignition delay times of methane, pure light alkanes and various blends representative of several natural gas and process-derived fuels have been reviewed. For each fuel mixture, this study procures a simple equation linking the auto-ignition delay time to the temperature, pressure and equivalence ratio. As a direct application of this work, the authors have evaluated the risk of auto ignition in the premixing zone of a combustor characterized by a residence time and an associated probability density function. The results of this simulation stress the key role of larger hydrocarbon in the risk of flash-back events.

Buckling Behaviors of Metallic Columns Under Compressive Load at Extremely High Temperatures

2014 ◽  
Author(s):  
Byeongnam Jo ◽  
Wataru Sagawa ◽  
Koji Okamoto
Keyword(s):  
High Temperatures ◽  
High Speed ◽  
Nuclear Power ◽  
Power Plants ◽  
Compressive Load ◽  
Buckling Load ◽  
Severe Accident ◽  
Lateral Deflection ◽  
Wide Range ◽  
Creep Buckling

This study aims to investigate buckling behaviors of a slender stainless steel column under compressive loads in severe accident conditions, which addresses the accidents in Fukushima Daiichi nuclear power plants. Firstly, buckling load, defined a load which generates a failure of the column (plastic collapse) was experimentally measured in a wide range of temperatures from 25 °C up to 1200 °C. The buckling load values measured were compared to numerical estimations for both an ideal column and for a column initially bent. Secondly, creep buckling tests were also performed for extremely high temperatures (800 °C, 900 °C, and 1000 °C). Creep buckling was found to occur very quickly compared to general creep times under tensile stresses. Time to creep buckling was exponentially increased with decrease of loads applied. Lateral deflection of a test column was estimated using captured images by a high speed camera. It was suggested to represent creep buckling behaviors as a time-lateral deflection curve. Moreover, an empirical correlation was developed to predict creep buckling time, based on the Larson-Miller model with experimental results obtained in present study.

Auto Ignition and Knocking Phenomena in Stratified Mixture of Lean Condition

2007 ◽  
Author(s):  
Tadayoshi Ihara ◽  
Xiaojian Qin ◽  
Takafumi Tanaka ◽  
Kazunori Wakai
Keyword(s):  
Combustion Chamber ◽  
High Speed ◽  
Equivalence Ratio ◽  
Burning Velocity ◽  
Video Camera ◽  
Auto Ignition ◽  
High Speed Video Camera ◽  
The Difference ◽  
Ignition And Combustion ◽  
Bottom To Top

Experimental study has been conducted on auto ignition and knocking phenomena of stratified mixture using a rapid compression machine (RCM) in order to investigate the effects of fuel concentration gradient on the auto ignition and combustion characteristics in the condition that mean equivalence ratio is lean. N-heptane is used as a fuel and mean equivalence ratio is 0.6, 0.8 and 1.0 in the combustion chamber. In the chamber, the lower the vertical location is, the richer the concentration of the mixture is. The difference of the equivalence ratio from bottom to top in the chamber is varied from 0 to 1.4. Mixture has no gradient in horizontal direction. Initial temperature of the mixture is 290K and pressure is 0.1MPa before compression. The diameter of the combustion chamber is 65mm and the compression ratio is 10.5. High-speed video camera is set in front of chamber so that direct images of mixture from cylinder axis direction can be obtained. A pressure transducer is used to obtain pressure histories of chamber, from which ignition delay, pressure rising rate and knocking intensity are determined. The results show that: 1. Flame speed of stratified mixture obtained from direct flame images is much faster than that of calculated laminar burning velocity for corresponding mixture, thus, rapid spread of flame in the experiment is caused not by flame propagation but by consecutive auto ignition. 2. Ignition delays of stratified mixture, not depending on the gradient of mixture, are constant as far as mean equivalence ratio is same and decrease with the decrease of mean equivalence ratio. 3. Pressure rising rate of stratified mixture combustion increases with the decrease of the gradient of mixture at 0.4≤φ≤1.0. 4. In homogeneous condition, knocking intensity of smaller mean equivalence ratio is smaller. 5. With slight gradient, knocking intensities of same mean equivalence ratio are similar to that of homogeneous mixture. In excess of certain value of the gradient, knocking intensity is smaller as the gradient is larger.

Ignition and Flame Stabilization of a Premixed Jet in Hot Cross Flow

2013 ◽  
Author(s):  
Denise Schmitt ◽  
Michael Kolb ◽  
Johannes Weinzierl ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Equivalence Ratio ◽  
Large Scale ◽  
Large Diameter ◽  
Flame Temperature ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Wide Range ◽  
Cold Case

At the Institute of Thermodynamics, Technical University of Munich a large scale atmospheric combustion test rig has been designed and set up. The experimental setup is comprised of two burning zones: A first zone consists of 16 burners providing vitiated air at 1776K, into which a secondary fuel-air mixture jet is injected and ignited by the hot cross flow. The phenomenon is known in the literature as a reacting jet in hot cross flow. The hot data is compared to the cold case in order to show differences in the flow field due to flame propagation. For evaluating the flow field several experimental analyses have been applied so far (OH*, High-Speed PIV, Mixture Analysis). The focus of this paper is on the momentum ratios J = 4–10 with Jet Reynolds Numbers between 20,000 and 80,000. For the cold case the flow field is measured and compared with the reacting jet. In the injector the air and the natural gas are perfectly premixed. The equivalence ratio of the jet is varied over a wide range of mixtures (ϕ = 0.05–0.77) resulting in an adiabatic flame temperature of the jet between 800 and 2200K. As the pictures of the chemiluminescence analysis show the jet gas ignites immediately upon entering the hot cross flow. The distinct influence of the equivalence ratio on the flame length and shape can be seen in the data. The trajectory of the flame penetrates further into the channel compared to the trajectory of the cold case caused by the reaction in the flame and its resulting gas expansion. Due to the large diameter of the jet in the experiment the origins of the dominant flow patterns are obtained with high spatial resolution. Following this, flame anchoring mechanisms at different operation points are derived.

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