scholarly journals Mixing and reaction in turbulent plumes: the limits of slow and instantaneous chemical kinetics

2018 ◽  
Vol 861 ◽  
pp. 1-28
Author(s):  
N. Mingotti ◽  
S. S. S. Cardoso
Keyword(s):  
Chemical Kinetics ◽  
Chemical Species ◽  
Critical Distance ◽  
Experimental Results ◽  
Chemical Concentration ◽  
Laboratory Measurements ◽  
Fast Reaction ◽  
Fast Reactions ◽  
Longitudinal Profiles ◽  
Instantaneous Chemical

We investigate the behaviour of a reactive plume in the two limiting cases of slow and instantaneous chemical reactions. New laboratory measurements show that, whereas the slow reaction between the source and entrained chemical species takes place within the whole volume of each eddy in the plume, the fast reaction develops preferentially at the periphery of the eddies. We develop a new model that quantifies the mixing of the reactive buoyant fluids at the Batchelor scale and thereby the progress of the fast reaction. We present a series of new experimental results that suggest that a critical distance from the source, $z_{crit}$, exists at which the volume of fluid that is entrained from the ambient is equal to that which is mixed within the plume at the Batchelor scale. For $z>z_{crit}$, only a fraction of the entrained fluid is rapidly mixed and reacts with the plume fluid. The results of the new experiments enable us to quantify the distance from the source at which an instantaneous reaction reaches completion, and show that it can be significantly larger than the distance $L_{s}$ at which the stoichiometric dilution of the plume fluid is achieved. In the limit of an instantaneous reaction, the longitudinal profiles of source chemical concentration in the plume depend on $(z_{crit}/L_{s})^{5/6}$. The predictions of the model are validated against the experimental results, and the profiles of source chemical concentration in the plume for slow and fast reactions are compared.

scholarly journals Description of the transformation of chemical species using a combination of chemical kinetics and chemical equilibrium

2011 ◽  
Vol 9 (3) ◽  
pp. 28-33 ◽  
Author(s):  
Jiří Hvězda
Keyword(s):  
Chemical Kinetics ◽  
Chemical Equilibrium ◽  
Chemical Species

SHRNUTÍ Tato prace prezentuje novy přistup k numericke simulaci chemicke přeměny složek v průběhu hořeni. V připadech abnormalně rychlych chemickych reakci je kineticke schema kombinovano se schematem rovnovažnym. Timto způsobem jsou řešeny važne vypočetni problemy jako je strnulost soustavy rovnic na straně jedne či numericka nestabilita na straně druhe. Navržena procedura je ověřena na připadu hořeni vodiku popsaneho reakčnim mechanismem obsahujicim 23 paralelně probihajicich obecně vratnych reakci. Funkčni sub-model chemicke transformace bude implementovan do vice-zonoveho modelu spalovani pro řešeni chemickych procesů ve frontě plamene a post-plamennych oblastech.

Computational Analysis of an Early Direct Injected HCCI Engine with Turbocharger Using Bio Ethanol and Diesel Blends

2015 ◽  
Vol 812 ◽  
pp. 70-78
Author(s):  
S. Natarajan ◽  
A.U. Meeanakshi Sundareswaran ◽  
S. Arun Kumar ◽  
N.V. Mahalakshmi
Keyword(s):  
Chemical Kinetics ◽  
Computational Analysis ◽  
Reaction Path ◽  
Chemical Species ◽  
Operating Conditions ◽  
Injection Time ◽  
Engine Operation ◽  
Hcci Engine ◽  
Hcci Combustion ◽  
Auto Ignition

In this paper the work deals with the computational analysis of early direct injected HCCI engine with turbocharger using the CHEMKIN-PRO software. The computational analysis was carried out in the base of auto ignition chemistry by means of reduced chemical kinetics. For this study the neat diesel and Bio ethanol diesel blend (E20) were used as fuel. The inlet pressure was increased to 1.2 bar to simulate the turbocharged engine operation. The injection time was advanced to 18° before top dead centre (BTDC) i.e., 5° BTDC than normal injection time of 23° BTDC. The equivalence ratio was kept at 0.6 (ɸ=0.6) and the combustion, emission characteristics and chemical kinetics of the combustion reaction were studied. Since pressure and temperature profiles plays a very important role in reaction path at certain operating conditions, an attempt had been made here to present a complete reaction path investigation on the formation/destruction of chemical species at peak temperature and pressure conditions. The result showed that main draw backs of HCCI combustion like higher levels of unburned hydrocarbon emissions and carbon monoxide emissions are reduced in the turbocharged operation of the HCCI engine when compared to normal HCCI engine operation without turbocharger.

Introduction

2006 ◽  
Author(s):  
John Ross ◽  
Igor Schreiber ◽  
Marcel O. Vlad
Keyword(s):  
Reaction Mechanism ◽  
Chemical Kinetics ◽  
Chemical Engineering ◽  
Reaction Pathway ◽  
Reaction System ◽  
Chemical Species ◽  
Pulse Method ◽  
Elementary Reaction ◽  
Elementary Reactions ◽  
Arbitrary Strength

Chemical kinetics as a science has existed for more than a century. It deals with the rates of reactions and the details of how a given reaction proceeds from reactants to products. In a chemical system with many chemical species, there are several questions to be asked: What species react with what other species? In what temporal order? With what catalysts? And with what results? The answers constitute the macroscopic reaction mechanism. The process can be described macroscopically by listing the reactants, intermediates, products, and all the elementary reactions and catalysts in the reaction system. The present book is a treatise and text on the determination of complex reaction mechanisms in chemistry and in chemical reaction systems that occur in chemical engineering, biochemistry, biology, biotechnology, and genomics. A basic knowledge of chemical kinetics is assumed. Several approaches are suggested for the deduction of information on the causal chemical connectivity of the species, on the elementary reactions among the species, and on the sequence of the elementary reactions that constitute the reaction pathway and the reaction mechanism. Chemical reactions occur by the collisions of molecules, and such an event is called an elementary reaction for specified reactant and product molecules. A balanced stoichiometric equation for an elementary reaction yields the number of each type of molecule according to conservation of atoms, mass, and charge. Figure 1.1 shows a relatively simple reaction mechanism for the decomposition of ozone by light, postulated to occur in a series of three elementary steps. (The details of collisions of molecules and bond rearrangements are not discussed.) All approaches are based on the measurements of the concentrations of chemical species in the whole reaction system, not on parts, as has been the practice. One approach is called the pulse method, in which a pulse of concentration of one or more species of arbitrary strength is applied to a reacting system and the responses of as many species as possible are measured. From these responses causal chemical connectivities may be inferred. The basic theory is explained, demonstrated on a model mechanism, and tested in an experiment on a part of glycolysis.

Excess molar volumes and isothermal vapor-liquid equilibria in the tetrahydrofuran with propan-1-ol and propan-2-ol systems at 298.15 K

1997 ◽  
Vol 75 (2) ◽  
pp. 207-211 ◽  
Author(s):  
Julio A. Salas ◽  
Eleuterio L. Arancibia ◽  
Miguel Katz
Keyword(s):  
Activity Coefficients ◽  
Chemical Species ◽  
Excess Molar Volumes ◽  
Experimental Results ◽  
Free Energies ◽  
Molar Volumes ◽  
Two Systems ◽  
Vapor Liquid Equilibria ◽  
Vapor Liquid

Densities and vapor-liquid equilibria were determined for tetrahydrofuran with propan-1-ol and propan-2-ol systems at 298.15 K. From the experimental results, excess molar volumes and excess Gibbs free energies were calculated. Information could be obtained from the possible interaction between both chemical species in the two systems. The Prigogine–Flory–Patterson method was applied to calculate excess molar volumes. Liquid activity coefficients were calculated and correlated with different expressions existing in the literature. Keywords: excess molar volumes, vapor–liquid equilibria, activity coefficients, excess Gibbs free energies, tetrahydrofuran, propan-1-ol, propan-2-ol.

Experimental study on miscible viscous fingering involving viscosity changes induced by variations in chemical species concentrations due to chemical reactions

2007 ◽  
Vol 571 ◽  
pp. 475-493 ◽  
Author(s):  
YUICHIRO NAGATSU ◽  
KENJI MATSUDA ◽  
YOSHIHITO KATO ◽  
YUTAKA TADA
Keyword(s):  
Viscous Liquid ◽  
Chemical Reaction ◽  
Chemical Species ◽  
Viscous Fingering ◽  
Shielding Effect ◽  
Species Concentration ◽  
Cell Changes ◽  
Hele Shaw Cell ◽  
Instantaneous Chemical Reaction ◽  
Instantaneous Chemical

When a reactive and miscible less-viscous liquid displaces a more-viscous liquid in a Hele-Shaw cell, reactive miscible viscous fingering takes place. We succeed in showing experimentally how a reactive miscible viscous fingering pattern in a radial Hele-Shaw cell changes when the viscosity of the more-viscous liquid is varied owing to variation in chemical species concentration induced by an instantaneous chemical reaction. This is done by making use of a polymer solution's dependence of viscosity on pH. When the viscosity is increased by the chemical reaction, the shielding effect is suppressed and the fingers are widened. As a result, the ratio of the area occupied by the fingering pattern in a circle whose radius is the length of the longest finger is larger in the reactive case than in the non-reactive case. When the viscosity is decreased by the chemical reaction, in contrast, the shielding effect is enhanced and the fingers are narrowed. These lead to the area ratio being smaller in the reactive case than in the non-reactive case. A physical model to explain this change in the fingering pattern caused by the chemical reaction is proposed.

The Problem of Predicting Rate of Heat Release in Diesel Engines

1969 ◽  
Vol 184 (10) ◽  
pp. 192-202 ◽  
Author(s):  
H. C. Grigg ◽  
M. H. Syed
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Chemical Kinetics ◽  
Diesel Engines ◽  
Turbulent Mixing ◽  
Air Entrainment ◽  
Experimental Results ◽  
Fuel Sprays ◽  
Rate Of Heat Release ◽  
Kinetics Of

Two simple models for the rate of heat release in diesel engines are described. The factors taken into account in the models are rate of entrainment of air into the fuel sprays, the rate of turbulent mixing of fuel and air within the spray, and the chemical kinetics of burning. The models differ in their treatment of the rate of air entrainment. Comparisons are made with experimental results for a diesel engine running at two speeds and a variety of turbocharging ratios. The overall agreement with experiment in respect of shape of rate of heat release diagram is good, with the exception of the naturally aspirated cases where the rate of air entrainment is too low.

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