Related Research Articles
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion does not always result in fire, because a flame is only visible when substances undergoing combustion vapourise, but when it does, a flame is a characteristic indicator of the reaction. While the activation energy must be overcome to initiate combustion, the heat from a flame may provide enough energy to make the reaction self-sustaining. Combustion is often a complicated sequence of elementary radical reactions. Solid fuels, such as wood and coal, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that incandescent light in the form of either glowing or a flame is produced. A simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. This reaction releases 242 kJ/mol of heat and reduces the enthalpy accordingly :
Kenneth Joseph Arrow was an American economist, mathematician, writer, and political theorist. He was the joint winner of the Nobel Memorial Prize in Economic Sciences with John Hicks in 1972.
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between those layers.
A flame is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. Very hot flames are hot enough to have ionized gaseous components of sufficient density to be considered plasma.
In combustion, a diffusion flame is a flame in which the oxidizer and fuel are separated before burning. Contrary to its name, a diffusion flame involves both diffusion and convection processes. The name diffusion flame was first suggested by S.P. Burke and T.E.W. Schumann in 1928, to differentiate from premixed flame where fuel and oxidizer are premixed prior to burning. The diffusion flame is also referred to as nonpremixed flame. The burning rate is however still limited by the rate of diffusion. Diffusion flames tend to burn slower and to produce more soot than premixed flames because there may not be sufficient oxidizer for the reaction to go to completion, although there are some exceptions to the rule. The soot typically produced in a diffusion flame becomes incandescent from the heat of the flame and lends the flame its readily identifiable orange-yellow color. Diffusion flames tend to have a less-localized flame front than premixed flames.
A premixed flame is a flame formed under certain conditions during the combustion of a premixed charge of fuel and oxidiser. Since the fuel and oxidiser—the key chemical reactants of combustion—are available throughout a homogeneous stoichiometric premixed charge, the combustion process once initiated sustains itself by way of its own heat release. The majority of the chemical transformation in such a combustion process occurs primarily in a thin interfacial region which separates the unburned and the burned gases. The premixed flame interface propagates through the mixture until the entire charge is depleted. The propagation speed of a premixed flame is known as the flame speed which depends on the convection-diffusion-reaction balance within the flame, i.e. on its inner chemical structure. The premixed flame is characterised as laminar or turbulent depending on the velocity distribution in the unburned pre-mixture.
In combustion engineering and explosion studies, the Markstein number characterizes the effect of local heat release of a propagating flame on variations in the surface topology along the flame and the associated local flame front curvature. The dimensionless Markstein number is defined as:
The Sugden Award is an annual award for contributions to combustion research. The prize is awarded by the British Section of The Combustion Institute for the published paper with at least one British Section member as author, which makes the most significant contribution to combustion research. The prize is named after Sir Morris Sugden.
Brian Edward Launder, FRS, FREng is a Professor of Mechanical Engineering at the University of Manchester, United Kingdom. He is known for his work in the field of turbulent flows in general and turbulence modelling in particular. In 1994, he became a Fellow of the Royal Society.
Chemical reaction models transform physical knowledge into a mathematical formulation that can be utilized in computational simulation of practical problems in chemical engineering. Computer simulation provides the flexibility to study chemical processes under a wide range of conditions. Modeling of a chemical reaction involves solving conservation equations describing convection, diffusion, and reaction source for each component species.
The laminar flamelet model is one of the methods of modelling turbulent combustions apart from SCRS, eddy flamelet model and others. Combustion is a very important thermochemical process with significant material and aerodynamic implications and thus CFD modeling of combustion has become indispensable. The laminar flamelet model is basically for non pre-mixed fuel.
Multiscale turbulence is a class of turbulent flows in which the chaotic motion of the fluid is forced at different length and/or time scales. This is usually achieved by immersing in a moving fluid a body with a multiscale, often fractal-like, arrangement of length scales. This arrangement of scales can be either passive or active
The Darrieus–Landau instability is an intrinsic flame instability that occurs in premixed flames due to the thermal expansion of the gas produced by the combustion process. It was predicted independently by Georges Jean Marie Darrieus and Lev Landau.
In combustion, the Karlovitz number is defined as the ratio of chemical time scale to Kolmogorov time scale , named after Béla Karlovitz. The number reads as
Forman Arthur Williams is an American academic in the field of combustion and aerospace engineering who is Emeritus Professor of Mechanical and Aerospace Engineering at the University of California San Diego.
Paul Andrews Libby is an Emeritus Professor of Mechanical and Aerospace Engineering at the University of California, San Diego, a specialist in the field of Combustion and Aerospace Engineering.
In Combustion, G equation is a scalar field equation which describes the instantaneous flame position, introduced by Forman A. Williams in 1985 in the study of premixed turbulent combustion. The equation is derived based on the Level-set method. The equation was studied by George H. Markstein earlier, in a restrictive form.
In premixed turbulent combustion, Bray–Moss–Libby (BML) model is a closure model for a scalar field, built on the assumption that the reaction sheet is infinitely thin compared with the turbulent scales, so that the scalar can be found either at the state of burnt gas or unburnt gas. The model is named after Kenneth Bray, J. B. Moss and Paul A. Libby.
Thierry Poinsot, born 22 March 1958, is a French researcher, research director at the CNRS, researcher at the Institute of Fluid Mechanics in Toulouse, scientific advisor at CERFACS and senior research fellow at Stanford University. He has been a member of the French Academy of sciences since 2019.
David S-K Ting is a Canadian academic, author and researcher. He is a Professor of Mechanical, Automotive & Materials Engineering at the University of Windsor. He is the founder of the Turbulence & Energy Laboratory.
References
- ↑ Bray, K. N. C.; Riley, N. (2014). "John Frederick Clarke 1 May 1927 -- 11 June 2013". Biographical Memoirs of Fellows of the Royal Society . doi: 10.1098/rsbm.2014.0012 .
- ↑ "Cambridge University Engineering Department: Annual Reports". Archived from the original on 6 April 2012. Retrieved 10 April 2015.
- ↑ Swaminathan, N.; Bray, K.N.C. (2011). Turbulent Premixed Flames. Cambridge University Press. ISBN 9781139498586 . Retrieved 10 April 2015.
