scholarly journals Combustion of Laser-Induced Individual Magnesium Microparticles under Natural Convection

Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1276
Author(s):  
Chengyuan Lin ◽  
Minqi Zhang ◽  
Yue Wang ◽  
Shengji Li ◽  
Xuefeng Huang ◽  
...  
Keyword(s):  
Gas Phase ◽  
High Speed ◽  
Dominant Role ◽  
Combustion Process ◽  
Particle Diameter ◽  
Combustion Model ◽  
Combustion Mechanism ◽  
Rocket Propellants ◽  
High Speed Cinematography ◽  
Ignition And Combustion

Metal magnesium (Mg) fuels have been widely used in rocket propellants. The combustion study on individual Mg microparticles is crucial to the in-depth unveiling of the combustion mechanism of Mg-based propellants. In this paper, a new experimental setup was proposed to directly observe the combustion of individual micron-sized Mg particles, based on laser ignition and microscopic high-speed cinematography. The combustion process of individual Mg microparticles could be directly and clearly observed by the apparatus at high temporal and spatial resolutions. Individual Mg microparticles took gas phase combustion, and mainly underwent four stages: expansion, melting, gasification, ignition, and combustion. The ignition delay time and total combustion time had an exponential decay on the particle diameter, and they had a linear decay on the ignition power density. The melting took a dominant role in the whole burnout time. The gas-phase combustion flame seemed thick, inhomogeneous, and ring-like structure. The combustion model of individual Mg microparticles was built through combining the experimental results with the SEM, XRD, XPS, and EDS analysis of original samples and combustion residues. This study will be beneficial to understand the combustion process and reveal the combustion mechanism of metal microparticles besides Mg.

scholarly journals Laser-Induced Ignition and Combustion of Individual Aluminum Particles Below 10 μm by Microscopic High-Speed Cinematography

Processes ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 280 ◽  
Author(s):  
Fengting Hou ◽  
Shengji Li ◽  
Yue Wang ◽  
Xuefeng Huang
Keyword(s):  
Direct Observation ◽  
High Speed ◽  
Combustion Mechanism ◽  
Aluminum Particles ◽  
Experimental Apparatus ◽  
High Speed Cinematography ◽  
Metal Aluminum ◽  
Induced Ignition ◽  
Combustion Behaviors ◽  
Ignition And Combustion

Metal aluminum has been widely used as an ingredient in propellant, gunpowder and thermite, but there is less understanding of the combustion mechanism of aluminum particles from submicron to several microns in diameter. This paper proposes to experimentally investigate the ignition and combustion characteristics of individual aluminum particles below 10 μm. A specific in situ diagnostic experimental apparatus was first designed for directly observing the ignition and combustion behaviors of individual aluminum particles, with a submicrometer spatial resolution and a temporal resolution of tens of microseconds. Direct observation through microscopic high-speed cinematography demonstrated that, when heated by a continuous laser, individual aluminum particles thermally expanded, followed by shell rupture; the molten aluminum core overflowed and evaporated, leading to ignition and combustion. Further results showed that, when the laser power densities were gradually increased (5.88, 7.56 and 8.81 × 105 W/cm2), the durations of thermal expansion, melting and evaporation were shortened. The required time for the aluminum particles to expand to 150% of their initial diameter was shortened (34 s, 0.34 s and 0.0125 s, respectively). This study will be beneficial to further extend the investigation of other individual metal particles and reveal their combustion mechanism by direct observation.

Combustion in a high-speed rotary valve spark-ignition engine

2007 ◽  
Vol 221 (8) ◽  
pp. 971-990 ◽  
Author(s):  
P H P Chow ◽  
H C Watson ◽  
T Wallis
Keyword(s):  
High Speed ◽  
Combustion Process ◽  
Spark Ignition Engine ◽  
Combustion Model ◽  
Rotary Valve ◽  
Combustion Simulation ◽  
Parametric Effects ◽  
Sensitivity Studies ◽  
Valve Engine ◽  
Data Sensitivity

The current paper describes a study of combustion in the Bishop rotary valve engine by means of computation simulations. The combustion model was developed for this research at speeds up to 18 000 r/min and the results from the simulation were compared with experimental data. Sensitivity studies were performed in order to investigate the parametric effects on the combustion simulation of the engine. The major finding of this study was that convection of the flame kernels occurs and has a strong influence on the performance of the engine. The results indicated some insights as to how the combustion process of the engine can be improved.

A Methodology for Steady and Unsteady Full-Engine Simulations

2019 ◽  
Author(s):  
Luigi Romagnosi ◽  
Yingchen Li ◽  
Mohamed Mezine ◽  
Mateus Teixeira ◽  
Stephane Vilmin ◽  
...  
Keyword(s):  
High Speed ◽  
Compressible Flows ◽  
Stokes Equations ◽  
High Reliability ◽  
Combustion Process ◽  
Combustion Model ◽  
Cfd Models ◽  
Flamelet Generated Manifold ◽  
Tabulated Chemistry ◽  
Fully Coupled

Abstract With the increase of computational power, more sophisticated computational methods can be used, larger systems simulated, and complex phenomena predicted more reliably. Nevertheless, up to now, when turbomachinery systems are numerically optimized, each of the components, i.e., the compressor, combustor, and turbine, is simulated separately from the other two. While this approach allows the use of highly dedicated simulation tools, it does not account for the interactions between the different components. With the purpose to meet the future requirements in terms of low emissions, high reliability and efficiency, a novel, highly efficient, fully-coupled, approach based on the Reynolds-Averaged Navier-Stokes equations (RANS) has been developed, enabling a steady or time-accurate simulation of a full aero-engine within a single code. One of the advantages of a steady, fully coupled approach over a steady component-by-component approach, is that the boundary conditions at the interfaces do not need to be guessed. A fully coupled, time-accurate simulation has furthermore the advantage that the effect of the non-uniform temperature distribution at the outlet of the combustor is accounted for in the determination of the thermal field of the turbine. A Smart Interface methodology permits a direct coupling between the different engine components, compressor-combustor-turbine, and allows the Computational Fluid Dynamics (CFD) models to vary between each component within the same code. This allows the user to switch off, for instance, the combustion model in the turbine and compressor blocks. For the simulation of the combustion process, the Flamelet Generated Manifold (FGM) method is applied. While the approach is superior to classical tabulated chemistry approaches and reliably captures finite-rate effects, it is computationally inexpensive since it only requires the solution of a few extra scalars and the look-up of a combustion table. The model has been extended so that high-speed compressible flows can be simulated and the potential effects between the combustor and the adjacent blade rows can be accounted for. The Nonlinear Harmonic (NLH) method is used to model the unsteady interactions between the blade rows as well as the influence of the inhomogeneities at the combustor outlet on the downstream turbine blade rows. Compared to conventional time-accurate RANS simulations (URANS), this method is two to three orders of magnitude faster and makes time-accurate turbomachinery simulations affordable. With the aim of ensuring thermodynamic consistency between the different components of the engine, the same form of the energy equation is solved in all engine elements. Furthermore, the same thermodynamic coefficients, which are used to describe the reacting processes in the combustor, are used for a caloric description of the fluid in the compressor and turbine blocks. The thermodynamic data between the blocks is transferred using the OpenLabs™ module. The developed approach is described in detail and the potential of the novel full-engine methodology is exploited on the KJ66 micro-turbine gas engine case. The results of both the steady and the time-accurate, fully coupled approaches are analyzed and the interaction between the different components of the KJ66 engine discussed.

Experimental Study of Ignition and Combustion Characteristics of Mixed Rice Straw and Sewage Sludge Solid and Hollow Spherical Pellets in a Plasma Combustion System

2019 ◽  
Vol 797 ◽  
pp. 327-335 ◽  
Author(s):  
Mohamed E. Mostafa ◽  
Hao Tang ◽  
Jun Xu ◽  
Huan Ying Chi ◽  
Kai Xu ◽  
...  
Keyword(s):  
Sewage Sludge ◽  
Rice Straw ◽  
High Speed ◽  
High Surface ◽  
Combustion Process ◽  
Combustion Characteristics ◽  
Combustion System ◽  
Large Area ◽  
Char Combustion ◽  
Ignition And Combustion

In this work, the ignition and combustion characteristics of mixed rice straw and sewage sludge pellets in air atmosphere were investigated using a plasma combustion system. One common pellet shape (solid spherical pellet) and another new shape (hollow spherical) are used in this study. High-speed camera was used to record and observe ignition and combustion process of pellets. In case of hollow pellets, the shape and distribution of flame are found to be better compared to solid pellets. Also, it is clear that the values of volatile combustion times in case of hollow pellets are low compared to solid pellets. The overall heat transfer enhanced in case of hollow pellet due to the large area subjected to hot gases and the high surface to volume ratio. Hollow pellet consumed less time for internal ignition and volatiles char combustion compared to solid pellet. Volatiles and char combustion lasted for 63.05 and 61 s, respectively for hollow pellet while these values were found to be 72.8 and 83 s, respectively for solid pellet.

Deflagration Analysis of Aluminum Droplet Combustion

2012 ◽  
Author(s):  
Birce Dikici ◽  
M. L. Pantoya ◽  
B. D. Shaw
Keyword(s):  
Gas Phase ◽  
Flame Propagation ◽  
Diffusion Flame ◽  
Dominant Role ◽  
Experimental Studies ◽  
Droplet Evaporation ◽  
Combustion Model ◽  
Single Droplet ◽  
Aluminum Particles ◽  
Combustion Dynamics

The evaporation and combustion of nanometric aluminum particles with an oxidizer MoO3 is analyzed. The analysis was performed to correlate individual Al particle gasification rates to macroscopic flame propagation rates observed in flame tube experiments. Examination of various characteristic times relevant to propagation of a deflagration reveals that particles below about 1.7 nm in diameter evaporate before appreciable chemical reactions occur. Experimental studies use Al particles greater than 1.7 nm in diameter such that a diffusion flame model was developed to better understand the combustion dynamics of multiphase Al particles. The results showed that it is unlikely that droplets will fully evaporate before reacting in the gas phase. A droplet evaporation and combustion model was further applied to quantify single droplet reaction velocities in comparison to the bulk flame propagation measurements observed in the literature. The diffusion flame model predicted orders of magnitude slower propagation rates than experimentally observed. These results imply that another reaction mechanism is responsible for promoting reaction propagation or modes other than diffusion play a more dominant role in flame propagation.

Virtual High Speed Diesel Engine – A Simulated Experiment, Part I: Combustion Dynamics

2014 ◽  
Vol 659 ◽  
pp. 189-194
Author(s):  
Lidia Gaiginschi ◽  
Iulian Agape ◽  
Adrian Sachelarie ◽  
Mihai Alin Girbaci
Keyword(s):  
Diesel Engines ◽  
High Speed ◽  
Internal Combustion Engines ◽  
Combustion Process ◽  
Operating Regime ◽  
Combustion Model ◽  
Combustion Dynamics ◽  
Cycle Simulation ◽  
Simulated Experiment ◽  
High Speed Diesel

The research efforts in the direction of internal combustion engines functional cycle simulation, particularly for small capacity diesel engines, are justified by shortening the path between the new conceptual solution and its effects and also to reduce research costs. There can be adopted new organizational and management solutions for the combustion process after these, for example, confirm at the model level. This paper proposes an unizonal physico-mathematical combustion model in high speed small Diesel engines, based on a Vibe-type law and on the heat transfer through the combustion chamber walls modelated after Woschni. The complexity of the model justifies the name of „virtual engine”. This allows to determine the functional parameters as instantaneous and average values, at any engine operating regime. The simulated experiment takes place in perfectly controlled conditions and leads to good results. There are obtained, during the combustion process, dynamics of parameters concerning the vaporization characteristics, combustion characteristics and combustion kinetics, for any operating regime. The parameters are evolving in a predictable way, being experimentally confirmed.

1D Engine Simulation of a Small HSDI Diesel Engine Applying a Predictive Combustion Model

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
T. Cerri ◽  
A. Onorati ◽  
E. Mattarelli
Keyword(s):  
Diesel Engine ◽  
High Speed ◽  
Fuel Injection ◽  
Direct Injection ◽  
Combustion Process ◽  
Numerical Approach ◽  
Operating Conditions ◽  
Combustion Model ◽  
Full Load ◽  
Partial Load

The paper analyzes the operations of a small high speed direct injection (HSDI) turbocharged diesel engine by means of a parallel experimental and computational investigation. As far as the numerical approach is concerned, an in-house 1D research code for the simulation of the whole engine system has been enhanced by the introduction of a multizone quasi-dimensional combustion model, tailored for multijet direct injection diesel engines. This model takes into account the most relevant issues of the combustion process: spray development, air-fuel mixing, ignition, and formation of the main pollutant species (nitrogen oxide and particulate). The prediction of the spray basic patterns requires previous knowledge of the fuel injection rate. Since the direct measure of this quantity at each operating condition is not a very practical proceeding, an empirical model has been developed in order to provide reasonably accurate injection laws from a few experimental characteristic curves. The results of the simulation at full load are compared to experiments, showing a good agreement on brake performance and emissions. Furthermore, the combustion model tuned at full load has been applied to the analysis of some operating conditions at partial load, without any change to the calibration parameters. Still, the numerical simulation provided results that qualitatively agree with experiments.

scholarly journals The Simulation of Different Combustion Stages of Micron-sized Aluminum Particles

2021 ◽  
Vol 11 (4) ◽  
pp. 1774
Author(s):  
Zejun Hu ◽  
Tao Yang ◽  
Zhixun Xia ◽  
Likun Ma ◽  
Mingtai Li ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Gas Phase ◽  
Boiling Point ◽  
Particle Temperature ◽  
Aluminum Particle ◽  
Combustion Process ◽  
Combustion Method ◽  
Combustion Model ◽  
Phase Reaction ◽  
Calculation Results

In this study, a quasi-steady combustion model of an aluminum particle is established, which is more accurate to simulate the physical combustion process. Detailed gas-phase reaction mechanism and surface reaction mechanism are considered. Moreover, the particle temperature is not constant in this work, which is calculated in different combustion stages. The judgement standard of each combustion stage is from observational data in the experiment and the simulation results of combustion durations of each stage, and distribution of ambient temperature and gas-phase species profiles are in good agreement with experimental results. The calculation results show that in the first stage, burning rate of the particle is the fastest, and in the second stage, particle temperature can drop to more than 100 K below the boiling point for the large particles, which is slightly below the boiling point for small ones. As the combustion stage changes, Da number is going to keep going down, which will lead to the transition of combustion method from diffusion-limited control to kinetic-limited control for an aluminum particle.

Mathematical Modeling of Heat and Mass Transfer Processes During Pyrolysis and Combustion of a Single Biomass Particle

2012 ◽  
Author(s):  
Y. Haseli ◽  
J. A. van Oijen ◽  
L. P. H. de Goey
Keyword(s):  
Carbon Dioxide ◽  
Mass Transfer ◽  
Carbon Monoxide ◽  
Water Vapor ◽  
Gas Phase ◽  
Combustion Process ◽  
Combustion Model ◽  
Gas Phase Reactions ◽  
Transfer Processes ◽  
Mass Transfer Processes

A detailed mathematical model is developed for simulation of heat and mass transfer processes during the pyrolysis and combustion of a single biomass particle. The kinetic scheme of Shafizadeh and Chin is employed to describe the pyrolysis process. The light gases formed during the biomass pyrolysis is assumed to consist of methane, carbon dioxide, carbon monoxide, hydrogen and water vapor with given mass fractions relevant to those found in the experiments of high heating conditions. The combustion model takes into account the reactions of oxygen with methane, hydrogen, carbon monoxide, tar and char as well as gasification of char with water vapor and carbon dioxide. Appropriate correlations taken from past studies are used for computation of the rate of these reactions. The model allows calculation of time and space evolution of various parameters including biomass and char densities, gaseous species and temperature. Different experimental data reported in the literature are employed to validate the pyrolysis and combustion models. The reasonable agreement obtained between the predictions and measured data reveals that the presented model is capable of successfully capturing various experiments of wood particle undergoing a pyrolysis or combustion process. In particular, the role of gas phase reactions within and adjacent to particle on the combustion process is examined. The results indicate that for the case of small particles in the order of millimeter size and less, one may neglect any effects of gas phase reactions. However, for larger particles, a combustion model may need to include hydrogen oxidation and even carbon monoxide combustion reactions.

Numeberical Simulation of a New Enhanced Heat Transfer Burener

2011 ◽  
Vol 201-203 ◽  
pp. 2721-2726
Author(s):  
Xiao Feng Lu ◽  
Duo Liu ◽  
Yuan Qing Li
Keyword(s):  
Heat Transfer ◽  
Flue Gas ◽  
High Speed ◽  
Combustion Process ◽  
Flame Length ◽  
Combustion Model ◽  
Diffusion Combustion ◽  
Enhanced Heat Transfer ◽  
Local Overheating ◽  
New Type

In this paper, numerical simulation of a new type enhanced heat transfer burner was carried out by using the CFD commercial software FLUENT. Standard κ-ε turbulent model, P-1 radiation model and PDF diffusion combustion model were used to predict the influence of the combustor’s structure change on its performance in the combustion process. The results showed that: The added necking down at the outlet of the combustion chamber can significantly enhanced the jet action of the flue gas, the high speed flow flue gas formed a forced convection cyclical field, convective heat transfer rate was increased greatly and the temperature distribution in the furnace became more uniform, which guaranteed an excellent heating effect. New type of staged air distribution can promote the mixing of the fuel and air. Further more, it can improve the flame length to prevent the local overheating phenomenon during the combustion process. On the basis of the same total sectional areas, the added number of the jet orifice can also promote the mixing of the fuel and air to enhance the thermal intensity and thermal efficiency of the furnace.

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