Group Ignition of a Cloud of Coal Particles

1991 ◽  
Vol 113 (3) ◽  
pp. 677-687 ◽  
Author(s):  
W. Ryan ◽  
K. Annamalai
Keyword(s):  
Initial Conditions ◽  
Numerical Study ◽  
Ignition Time ◽  
Volatile Matter ◽  
Combustion Model ◽  
Ambient Conditions ◽  
Experimental Conditions ◽  
Coal Particles ◽  
Group Combustion ◽  
Ignition Characteristics

Ignition of an isolated single coal particle is known to occur either heterogeneously or homogeneously. While single-particle studies may be useful for dilute coal sprays, their application to burners is limited since ignition occurs in the vicinity of the burners where the spray is dense. Rather than considering an isolated particle, one must consider a collection of particles in order to determine the change in ignition characteristics resulting from particle interactions. Thus, group combustion models have been developed essentially to predict the ignition and combustion characteristics of a larger number of interacting drops/particles. This paper presents results of the ignition characteristics of a spherical cloud of uniformly distributed coal particles in quiescent surroundings using a simple group combustion model. For the conditions studied, the results are as follows: (1) Ignition is heterogeneous if the cloud is dilute and homogeneous if the cloud is dense under the same ambient conditions; (2) there is a minimum ignition time for a given set of initial conditions corresponding to a certain cloud denseness; (3) ignition time is less sensitive to the denseness of the cloud at higher ambient temperatures; and (4) decreased proximate volatile matter can result in either increased or decreased ignition time depending on the cloud denseness (ignition mode). Qualitative comparisons to experimental data are given; however, these comparisons should be approached with caution since the experimental conditions and geometries may be vastly different than those used in the numerical study presented here.

Numerical studies of a thermokinetic model for oscillatory cool flame and complex ignition phenomena in ethanal oxidation under well-stirred flowing conditions

1989 ◽  
Vol 422 (1863) ◽  
pp. 289-310 ◽  
Keyword(s):  
Numerical Study ◽  
Thermal Characteristics ◽  
Kinetic Scheme ◽  
Ambient Conditions ◽  
Two Stage ◽  
Experimental Conditions ◽  
Cool Flame ◽  
Cool Flames ◽  
Spatial Uniformity ◽  
Acetyl Radical

A numerical study has been undertaken to predict quantitatively each of the non-isothermal reaction modes (stationary-state reaction, oscillatory cool flames and oscillatory two-stage and multiple-stage ignitions) associated with the oxidation of ethanal in a non-adiabatic well-stirred flow system (0.5 dm 3 ) at a mean residence time of 3 s. The kinetic scheme comprises 28 species involved in 60 reactions and it is coupled to the thermal characteristics through enthalpy change in each step, heat capacities of the major components and a heat transfer coefficient appropriate to heat loss through the reaction vessel wall. Spatial uniformity of temperature and concentrations is assumed, matching the experimental conditions. Very satisfactory accord is obtained between the experimentally measured and predicted location of the different reaction modes in the ( p - T a ) ignition diagram (where p is pressure and T a is temperature at ambient conditions), and the time-dependent patterns for oscillatory reaction agree with experimental measurements. The competition between degenerate branching and non-branching reaction modes is governed ultimately by the equilibrium CH 3 +O 2 ⇌CH 3 O 2 . The predicted behaviour is found also to be especially sensitive to the rate of decomposition of the acetyl radical CH 3 CO + M → CH 3 + CO + M. Corrections for its pressure dependence are essential if the predicted form of the oscillatory cool flame region in the ( p - T a ) diagram is to match the experimental results. Variations of the rate of this reaction also give new kinetic insight into the origins of complex oscillatory wave-forms for cool flames that have been observed experimentally. Relationships between the results of the detailed kinetic computations and the predictions from a three-variable, thermokinetic model are examined. This model is the simplest of all reduced schemes that makes successful predictions of two-stage ignition phenomena.

Group Combustion of a Cylindrical Cloud of Char/Carbon Particles

1988 ◽  
Vol 110 (1) ◽  
pp. 190-200 ◽  
Author(s):  
K. Annamalai ◽  
S. Ramalingam ◽  
T. Dahdah ◽  
D. Chi
Keyword(s):  
Experimental Data ◽  
Collective Behavior ◽  
A Priori ◽  
Individual Particle ◽  
Combustion Model ◽  
Carbon Particles ◽  
Particle Combustion ◽  
Combustion Models ◽  
Coal Particles ◽  
Group Combustion

Extensive experiments were carried out in the past in order to obtain kinetics data on the pyrolysis of coal particles and the char reactions. The literature survey distinctively reveals two kinds of studies: (i) Individual Particle Combustion (IPC) and (ii) Combustion of Particle Streams or Clouds. The experimental data obtained with particle streams are normally interpreted using IPC models with the a priori assumption that the cloud is dilute. But the term “dilute” is rarely quantified and justified considering the collective behavior of a cloud of particles. The group combustion model accounts for the reduction in burning rate due to the collective behavior of a large number of particles. While the spherical group combustion model may be employed for coal/char spray combustion modeling, the cylindrical group combustion model is more useful in interpreting the experimental data obtained with a monosized stream of particles. Hence a cylindrical group combustion model is presented here. As in the case of spherical group combustion models, there exist three modes of combustion: (i) Individual Particle Combustion (IPC), (ii) Group Combustion (GC), and (iii) Sheath Combustion (SC). Within the range of parameters studied, it appears that the cylindrical and spherical cloud combustion models yield similar results on nondimensional cloud burning rates and on the combustion modes of a cloud of particles. The results from group theory are then used to identify the mode of combustion (IPC, GC, or SC) and to interpret the experimental data.

scholarly journals Experimental Study on Ignition Characteristics of RP-3 Jet Fuel Using Nanosecond Pulsed Plasma Discharge

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6463
Author(s):  
Xiaoyang Guo ◽  
Erjiang Hu ◽  
Xiaotian Li ◽  
Geyuan Yin ◽  
Zuohua Huang
Keyword(s):  
Initial Conditions ◽  
Plasma Discharge ◽  
Jet Fuel ◽  
Pulsed Plasma ◽  
Ignition Energy ◽  
Minimum Ignition Energy ◽  
Experimental Conditions ◽  
Ignition Probability ◽  
Ignition Characteristics ◽  
The Impact

A study on forced ignition characteristics of RP-3 jet fuel-air mixture was conducted around a constant volume combustion vessel and a nanosecond pulsed plasma discharge power supply. Experiments were carried out at different initial pressures (pu = 0.2, 0.3, 0.5 atm), equivalence ratios (ϕ = 0.7, 0.8, 1.1), steam concentrations (ZH2O = 0%, 10%, 15%) and oxygen concentrations (ZO2 = 13.5%, 16%, 21%). The relationship between ignition probability and ignition energy is investigated. The experimental results show that the decrease in pressure, equivalence ratio, oxygen concentration and the increase in steam concentration all lead to an increase in minimum ignition energy (MIE). In order to further analyze the experimental data, one existing fitting equation is reformed with the initial conditions taken into account. Multivariate fitting is carried out for different conditions, and the fitting results of ignition probability are in good agreement with the experiments. The MIE results under different experimental conditions are figured out with the new fitting equation. The impact indexes, which stand for the effects of different factors, are also calculated and compared in present work.

Coal Particles Combustion Model and Micro Feeding Technology in Drop Tube Furnace

2011 ◽  
Vol 236-238 ◽  
pp. 680-683 ◽  
Author(s):  
Zheng Zhong Ma ◽  
Xiang Xu ◽  
Yun Han Xiao
Keyword(s):  
Design Principle ◽  
Tube Furnace ◽  
Combustion Model ◽  
Drop Tube ◽  
Test Results ◽  
Drop Tube Furnace ◽  
Coal Particles ◽  
Group Combustion ◽  
Feeding Technology

For investigation of wide use of drop tube furnace (DTF), the design and characterization of DTF and shaftless screw microfeeder are presented. With a developed group combustion model, a introduced non-dimensional number is to characterize the combustion zone of coal particles in DTF. Calculated relation is proposed to be operation criteria of DTF and design principle of feeder. It is found that the test results of coal feeder show good performance for micro feeding.

Pyrolysis and Ignition Characteristics of Pulverized Coal Particles

2000 ◽  
Vol 123 (1) ◽  
pp. 32-38 ◽  
Author(s):  
Masayuki Taniguchi ◽  
Hirofumi Okazaki ◽  
Hironobu Kobayashi ◽  
Shigeru Azuhata ◽  
Hiroshi Miyadera ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fine Particles ◽  
Early Stage ◽  
Radiant Heat ◽  
Volatile Matter ◽  
Combustible Mixture ◽  
Radiant Heat Transfer ◽  
Coal Particles ◽  
Intermediate Size ◽  
Ignition Characteristics

Pyrolysis and ignition characteristics of pulverized coals were examined under similar burning conditions to those of industrial burners. In the early stage, fine particles (less than 37 μm) were mainly pyrolyzed by convective heat transfer from surrounding gas. The coals ignited when pyrolyzed volatile matter mixed with surrounding air and formed a combustible mixture. Pyrolysis of large particles was delayed, but accelerated after ignition by radiant heat transfer from coal flames. The effects of radiant heat transfer were strong for intermediate-size particles (37–74 μm). Ignition temperature was examined analytically by using a modified distributed activation energy model for pyrolysis. The calculated results agreed with experimental ones obtained from both laboratory-scale and semi-industrial-scale burners.

scholarly journals Linking gas and particle ejection dynamics to boundary conditions in scaled shock-tube experiments

2021 ◽  
Vol 83 (8) ◽  
Author(s):  
Valeria Cigala ◽  
Ulrich Kueppers ◽  
Juan José Peña Fernández ◽  
Donald B. Dingwell
Keyword(s):  
Particle Size ◽  
Shock Tube ◽  
Initial Conditions ◽  
Volcanic Eruptions ◽  
Tube Length ◽  
Experimental Investigations ◽  
Clear Correlation ◽  
Angular Deviation ◽  
Dynamic Nature ◽  
Experimental Conditions

AbstractPredicting the onset, style and duration of explosive volcanic eruptions remains a great challenge. While the fundamental underlying processes are thought to be known, a clear correlation between eruptive features observable above Earth’s surface and conditions and properties in the immediate subsurface is far from complete. Furthermore, the highly dynamic nature and inaccessibility of explosive events means that progress in the field investigation of such events remains slow. Scaled experimental investigations represent an opportunity to study individual volcanic processes separately and, despite their highly dynamic nature, to quantify them systematically. Here, impulsively generated vertical gas-particle jets were generated using rapid decompression shock-tube experiments. The angular deviation from the vertical, defined as the “spreading angle”, has been quantified for gas and particles on both sides of the jets at different time steps using high-speed video analysis. The experimental variables investigated are 1) vent geometry, 2) tube length, 3) particle load, 4) particle size, and 5) temperature. Immediately prior to the first above-vent observations, gas expansion accommodates the initial gas overpressure. All experimental jets inevitably start with a particle-free gas phase (gas-only), which is typically clearly visible due to expansion-induced cooling and condensation. We record that the gas spreading angle is directly influenced by 1) vent geometry and 2) the duration of the initial gas-only phase. After some delay, whose length depends on the experimental conditions, the jet incorporates particles becoming a gas-particle jet. Below we quantify how our experimental conditions affect the temporal evolution of these two phases (gas-only and gas-particle) of each jet. As expected, the gas spreading angle is always at least as large as the particle spreading angle. The latter is positively correlated with particle load and negatively correlated with particle size. Such empirical experimentally derived relationships between the observable features of the gas-particle jets and known initial conditions can serve as input for the parameterisation of equivalent observations at active volcanoes, alleviating the circumstances where an a priori knowledge of magma textures and ascent rate, temperature and gas overpressure and/or the geometry of the shallow plumbing system is typically chronically lacking. The generation of experimental parameterisations raises the possibility that detailed field investigations on gas-particle jets at frequently erupting volcanoes might be used for elucidating subsurface parameters and their temporal variability, with all the implications that may have for better defining hazard assessment.

scholarly journals Numerical Study of Engine Performance and Emissions for Port Injection of Ammonia into a Gasoline\Ethanol Dual-Fuel Spark Ignition Engine

2021 ◽  
Vol 11 (4) ◽  
pp. 1441
Author(s):  
Farhad Salek ◽  
Meisam Babaie ◽  
Amin Shakeri ◽  
Seyed Vahid Hosseini ◽  
Timothy Bodisco ◽  
...  
Keyword(s):  
Numerical Study ◽  
Combustion Process ◽  
Engine Performance ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Combustion Model ◽  
Dual Fuel ◽  
Spark Ignition Engines ◽  
Performance And Emissions ◽  
Hc Emissions

This study aims to investigate the effect of the port injection of ammonia on performance, knock and NOx emission across a range of engine speeds in a gasoline/ethanol dual-fuel engine. An experimentally validated numerical model of a naturally aspirated spark-ignition (SI) engine was developed in AVL BOOST for the purpose of this investigation. The vibe two zone combustion model, which is widely used for the mathematical modeling of spark-ignition engines is employed for the numerical analysis of the combustion process. A significant reduction of ~50% in NOx emissions was observed across the engine speed range. However, the port injection of ammonia imposed some negative impacts on engine equivalent BSFC, CO and HC emissions, increasing these parameters by 3%, 30% and 21%, respectively, at the 10% ammonia injection ratio. Additionally, the minimum octane number of primary fuel required to prevent knock was reduced by up to 3.6% by adding ammonia between 5 and 10%. All in all, the injection of ammonia inside a bio-fueled engine could make it robust and produce less NOx, while having some undesirable effects on BSFC, CO and HC emissions.

Numerical Study of an Impact Oscillator

1995 ◽  
Author(s):  
Kannan Marudachalam ◽  
Faruk H. Bursal
Keyword(s):  
Dynamical Systems ◽  
Numerical Algorithm ◽  
Initial Conditions ◽  
Numerical Study ◽  
Harmonic Excitation ◽  
General Purpose ◽  
Constrained Systems ◽  
Global Dynamics ◽  
Impact Oscillator ◽  
Stick Slip

Abstract Systems with discontinuous dynamics can be found in diverse disciplines. Meshing gears with backlash, impact dampers, relative motion of components that exhibit stick-slip phenomena axe but a few examples from mechanical systems. These form a class of dynamical systems where the nonlinearity is so severe that analysis becomes formidable, especially when global behavior needs to be known. Only recently have researchers attempted to investigate such systems in terms of modern dynamical systems theory. In this work, an impact oscillator with two-sided rigid constraints is used as a paradigm for studying the characteristics of discontinuous dynamical systems. The oscillator has zero stiffness and is subjected to harmonic excitation. The system is linear without impacts. However, the impacts introduce nonlinearity and dissipation (assuming inelastic impacts). A numerical algorithm is developed for studying the global dynamics of the system. A peculiar type of solution in which the trajectories in phase space from a certain set of initial conditions merge in finite time, making the dynamics non-invertible, is investigated. Also, the effect of “grazing,” a behavior common to constrained systems, on the dynamics of the system is studied. Based on the experience gained in studying this system, the need for an efficient general-purpose numerical algorithm for solving discontinuous dynamical systems is motivated. Investigation of stress, vibration, wear, noise, etc. that are associated with impact phenomena can benefit greatly from such an algorithm.

scholarly journals Laminar Burning Velocities of Hydrogen-Blended Methane–Air and Natural Gas–Air Mixtures, Calculated from the Early Stage of p(t) Records in a Spherical Vessel

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7556
Author(s):  
Maria Mitu ◽  
Domnina Razus ◽  
Volkmar Schroeder
Keyword(s):  
Natural Gas ◽  
Initial Conditions ◽  
Numerical Study ◽  
Early Stage ◽  
Linear Trend ◽  
Burning Velocity ◽  
Pressure Rise ◽  
Spherical Vessel ◽  
Practical Applications ◽  
Hydrogen Addition

The flammable hydrogen-blended methane–air and natural gas–air mixtures raise specific safety and environmental issues in the industry and transportation; therefore, their explosion characteristics such as the explosion limits, explosion pressures, and rates of pressure rise have significant importance from a safety point of view. At the same time, the laminar burning velocities are the most useful parameters for practical applications and in basic studies for the validation of reaction mechanisms and modeling turbulent combustion. In the present study, an experimental and numerical study of the effect of hydrogen addition on the laminar burning velocity (LBV) of methane–air and natural gas–air mixtures was conducted, using mixtures with equivalence ratios within 0.90 and 1.30 and various hydrogen fractions rH within 0.0 and 0.5. The experiments were performed in a 14 L spherical vessel with central ignition at ambient initial conditions. The LBVs were calculated from p(t) data, determined in accordance with EN 15967, by using only the early stage of flame propagation. The results show that hydrogen addition determines an increase in LBV for all examined binary flammable mixtures. The LBV variation versus the fraction of added hydrogen, rH, follows a linear trend only at moderate hydrogen fractions. The further increase in rH results in a stronger variation in LBV, as shown by both experimental and computed LBVs. Hydrogen addition significantly changes the thermal diffusivity of flammable CH4–air or NG–air mixtures, the rate of heat release, and the concentration of active radical species in the flame front and contribute, thus, to LBV variation.

scholarly journals Computational Design of Sensitized Combustion Chemistry Experiments

2021 ◽  
Vol 7 ◽  
Author(s):  
Cody Ising ◽  
Pedro Rodriguez ◽  
Daniel Lopez ◽  
Jeffrey Santner
Keyword(s):  
Shock Tube ◽  
Initial Conditions ◽  
Computational Design ◽  
Reaction Rates ◽  
Oxidation Reactions ◽  
Combustion Chemistry ◽  
Experimental Conditions ◽  
As Species ◽  
User Friendly

In combustion chemistry experiments, reaction rates are often extracted from complex experiments using detailed models. To aid in this process, experiments are performed such that measurable quantities, such as species concentrations, flame speed, and ignition delay, are sensitive to reaction rates of interest. In this work, a systematic method for determining such sensitized experimental conditions is demonstrated. An open-source python script was created using the Cantera module to simulate thousands of 0D and hundreds of 1D combustion chemistry experiments in parallel across a broad, user-defined range of mixture conditions. The results of the simulation are post-processed to normalize and compare sensitivity values among reactions and across initial conditions for time-varying and steady-state simulations, in order to determine the “most useful” experimental conditions. This software can be utilized by researchers as a fast, user-friendly screening tool to determine the thermodynamic and mixture parameters for an experimental campaign. We demonstrate this software through two case studies comparing results of the 0D script against a shock tube experiment and results of the 1D script against a spherical flame experiment. In the shock tube case study we present mixture conditions compared to those used in the literature to study H + O2 (+M)→HO2(+M). In the flame case study, we present mixture conditions compared to those in the literature to study formyl radical (HCO) decomposition and oxidation reactions. The systematically determined experimental conditions identified in the present work are similar to the conditions chosen in the literature.

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