Dissertations / Theses on the topic 'Theory of Combustion'

Flame spread over solid samples has been studied from many points of view, as it is key for fire safety, yet it is a complex phenomenon that involves processes occurring in both the solid and the gas phases. This Ph.D. thesis studies the flame spread over thin solid samples in processes more complex than the classical cases where a flame spreads horizontally or downward over a vertical solid sample. In particular, this thesis deals with three different situations: the effects of the sides to the vertically downward flame spread over a thin solid; the effects of having various parallel samples burning simultaneously, and flame spread over horizontal and downward inclined samples. For all these situations a complete experimental study is made and a model that explains the obtained results is developed
La propagació de flames en sòlids és un fenomen complex que inclou processos que s’esdevenen tant a la fase sòlida com a la fase gasosa. Diversos autors han estudiat aquest fenomen des de diferents punts de vista ja que és un element clau en l’anàlisi del risc d’incendis i de la dinàmica de focs. En aquesta tesi doctoral estudiem la propagació de flames en sòlids prims en processos més complexos que els processos clàssics, on la flama es propaga horitzontalment o cap avall en una mostra vertical. Més concretament, aquesta tesi versa sobre tres situacions diferents: l'efecte de les vores en la propagació verticalment cap avall de la flama sobre un sòlid prim; els efectes de tenir diverses mostres paral•leles cremant alhora, i la propagació cap avall de la flama en mostres inclinades i horitzontals. Per a aquestes tres situacions es desenvolupa un estudi experimental complet i un model que descriu els resultats obtinguts

Une large gamme de problèmes physiques, des petites molécules aux étoiles géantes, contiennent des symétries de rotation et sont sujets à des oscillations azimutales ou transverses. Quand cette symétrie est rompue, le système peut devenir instable. Dans cette thèse, les brisures de symétries sont étudiées dans les chambres de combustion annulaires, sujettes à des instabilités thermo-acoustiques azimutales. En premier lieu, deux types de brisures sont obtenus analytiquement : la première en répartissant des bruleurs différents le long de la chambre et la seconde provoquée par le champ moyen lui-même. Ces ruptures de symétries entraînent une séparation des fréquences, fixe la structure du mode et peut déstabiliser le système. De plus, une approche Quantification d’Incertitudes (UQ) permet d’évaluer l’effet de la rupture de symétries provoquée par les incertitudes sur la description ou le comportement des flammes. Pour compléter cette théorie, des Simulations aux Grandes Echelles (SGE) sont réalisées sur un mono-secteur ainsi que sur une configuration complète 360° de l’expérience annulaire de Cambridge. Les résultats numériques sont comparés aux données expérimentales et montrent un bon accord. En particulier, un mode instable à 1800 Hz croît dans les deux cas. Cependant, la SGE, limitée par son coût important, ne permet pas l’étude du cycle limite s’établissant après plusieurs centaines de millisecondes. Pour pallier à ce problème, une nouvelle approche, appelée AMT, est développée : les résultats d’une théorie ou d’un solveur acoustique sont injectés dans une simulation SGE. Cette approche permet d’étudier les brisures de symétries, la nature et la dynamique des modes acoustiques, ainsi que d’évaluer l’amortissement dans des configurations réalistes
A large range of physical problems, from molecules to giant stars, contains rotating symmetry and can exhibit azimuthal waves or vibrations. When this symmetry is broken, the system can become unstable with chaotic behaviors. Symmetry breaking is investigated in annular combustors prone to azimuthal thermo-acoustic instabilities. First, theories reveal that two types of symmetry breaking exist : due to different burner types distributed along the chamber or due to the flow itself . It leads to frequency splitting, fixes the mode structure and can destabilize the configuration. A UQ analysis is also performed to quantify the symmetry breaking effect due to uncertainties of flame descriptions or behaviors. To complete theory, Large Eddy Simulations are performed on a single-sector as well as on a complete 360° configuration of the annular experiment of Cambridge. Numerical results are compared to experimental data showing a good agreement. In particular, an unstable azimuthal mode at 1800 Hz grows in both LES and experiment. However, LES cannot investigate the limit cycle because of its extreme cost. To tackle this problem, a new methodology is developed, called AMT, where theory or Helmholtz solver predictions are injected into LES or DNS. This method allows to study symmetry breaking, mode nature and dynamics as well as evaluating damping in realistic annular configurations

Finding limit cycles and their stability is one of the central problems of nonlinear thermoacoustics. However, a limit cycle is not the only type of self-excited oscillation in a nonlinear system. Nonlinear systems can have quasi-periodic and chaotic oscillations. This thesis examines the different types of oscillation in a numerical model of a ducted premixed flame, the bifurcations that lead to these oscillations and the influence of external forcing on these oscillations. Criteria for the existence and stability of limit cycles in single mode thermoacoustic systems are derived analytically. These criteria, along with the flame describing function, are used to find the types of bifurcation and minimum triggering amplitudes. The choice of model for the velocity perturbation field around the flame is shown to have a strong influence on the types of bifurcation in the system. Therefore, a reduced order model of the velocity perturbation field in a forced laminar premixed flame is obtained from Direct Numerical Simulation. It is shown that the model currently used in the literature precludes subcritical bifurcations and multi-stability. The self-excited thermoacoustic system is simulated in the time domain with many modes in the acoustics and analysed using methods from nonlinear dynamical systems theory. The transitions to the periodic, quasiperiodic and chaotic oscillations are via sub/supercritical Hopf, Neimark-Sacker and period-doubling bifurcations. Routes to chaos are established in this system. It is shown that the single mode system, which gives the same results as a describing function approach, fails to capture the period-$2$, period-$k$, quasi-periodic and chaotic oscillations or the bifurcations and multi-stability seen in the multi-modal case, and underpredicts the amplitude. Instantaneous flame images reveal that the wrinkles on the flame surface and pinch off of flame pockets are regular for periodic oscillations, while they are irregular and have multiple time and length scales for quasi-periodic and chaotic oscillations. Cusp formation, their destruction by flame propagation normal to itself, and pinch-off and rapid burning of pockets of reactants are shown to be responsible for generating a heat release rate that is a highly nonlinear function of the velocity perturbations. It is also shown that for a given acoustic model of the duct, many discretization modes are required to capture the rich dynamics and nonlinear feedback between heat release and acoustics seen in experiments. The influence of external harmonic forcing on self-excited periodic, quasi-periodic and chaotic oscillations are examined. The transition to lock-in, the forcing amplitude required for lock-in and the system response at lock-in are characterized. At certain frequencies, even low-amplitude forcing is sufficient to suppress period-$1$ oscillations to amplitudes that are 90$\%$ lower than that of the unforced state. Therefore, open-loop forcing can be an effective strategy for the suppression of thermoacoustic oscillations. This thesis shows that a ducted premixed flame behaves similarly to low-dimensional chaotic systems and that methods from nonlinear dynamical systems theory are superior to the describing function approach in the frequency domain and time domain analysis currently used in nonlinear thermoacoustics.

Les Etudes Probabilistes de Sûreté (EPS) de niveau 2 en centrale nucléaire visent à identifier les séquences d’événements pouvant correspondre à la propagation d’un accident d’un endommagement du cœur jusqu’à une perte potentielle de l’intégrité de l’enceinte, et à estimer la fréquence d’apparition des différents scénarios possibles.

Ces accidents sévères dépendent non seulement de défaillances matérielles ou d’erreurs humaines, mais également de l’occurrence de phénomènes physiques, tels que des explosions vapeur ou hydrogène. La prise en compte de tels phénomènes dans le cadre booléen des arbres d’événements s’avère difficile, et les méthodologies dynamiques de réalisation des EPS sont censées fournir une manière plus cohérente d’intégrer l’évolution du processus physique dans les changements de configuration discrète de la centrale au long d’un transitoire accidentel.

Cette thèse décrit l’application d’une des plus récentes approches dynamiques des EPS – la Théorie de la Dynamique Probabiliste basée sur les Stimuli (SDTPD) – à différents modèles de déflagration d'hydrogène ainsi que les développements qui ont permis cette applications et les diverses améliorations et techniques qui ont été mises en oeuvre.

Level-2 Probabilistic Safety Analyses (PSA) of nuclear power plants aims to identify the possible sequences of events corresponding to an accident propagation from a core damage to a potential loss of integrity of the containment, and to assess the frequency of occurrence of the different scenarios.

These so-called severe accidents depend not only on hardware failures and human errors, but also on the occurrence of physical phenomena such as e.g. steam or hydrogen explosions. Handling these phenomena in the classical Boolean framework of event trees is not convenient, and dynamic methodologies to perform PSA studies are expected to provide a more consistent way of integrating the physical process evolution with the discrete changes of plant configuration along an accidental transient.

This PhD Thesis presents the application of one of the most recently proposed dynamic PSA methodologies, i.e. the Stimulus-Driven Theory of Probabilistic Dynamics (SDTPD), to several models of hydrogen explosion in the containment of a plant, as well as the developed methods and improvements.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

Determining the characteristics of piston engines with a propeller is a complex task. Accurate calculations are based on engine and propeller characteristics from the manufacturers, which are, however, quite demanding. It is also possible to use simplified models that can predict the achievable values of propeller efficiency and fuel consumption. They are based on a simple propeller efficiency and maximum power. However, these models are often very inaccurate, which is a significant disadvantage. Therefore, it is possible to use the universal characteristics of propeller propulsion units, which offers a more accurate calculation of power and fuel consumption using a relatively simple model. The diploma thesis deals with a summary description of all characteristics of reciprocating internal combustion engines and propellers. A mathematical model was created here, which works according to a certain algorithm based on the joint work of the engine and the propeller. This model can predict the required power and fuel consumption in different flight modes much more accurately. The results were applied to the performance of ultralight aircraft, especially to the range, which was significantly increased.

Heavy-duty trucks are important links in the logistic chains of transport. Critical components in trucks include fuel injectors in which inaccuracies can lead to severe financial damage and higher emissions. Intelligent and efficient ways to detect such scenarios are thus of high importance. This thesis applies machine learning algorithms to measured or estimated engine data, focused on gas exchange signals, to detect inaccuracies in fueling quantities. The fueling inaccuracies considered were of low deviations from the nominal curve, with magnitudes not covered by the currently used fueling diagnostics. The data used for the models was generated from Scania test cell engines where different setups of injectors were deliberately set to over- or underfuel.  Seven different machine learning models were used on the data and evaluated on how well they could detect deviations from nominal fueling. The tests were mainly done with a pure data-driven approach but also improved through different data selection techniques and using domain knowledge. An investigation to connect the findings within the thesis to real customer data was initiated in order to make the results useful for e.g. predictive maintenance. The complications connected to why this was not ultimately achieved were discussed.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008.
Committee Co-Chair: Ahrens, Fred; Committee Co-Chair: Patterson, Tim; Committee Member: Aidun, Cyrus; Committee Member: Empie, Jeff; Committee Member: Frederick, Jim.

碩士
國立成功大學
航空太空工程學系
88
The rates of the interfacial exchange of the properties of energy, mass of chemical species and mass, in particular the regression rate of the propellant during the transient ignition and steady state combustion have been the central theme of modern solid and hybrid rocketry. However to this date, a satisfactory level has not known analytical laws of the propellant in side-burning configuration. By applying the method of Canonical theory developed for the analytical determination of eigen-function of the systems of the exchange of the gasification rate and the regression rate in the hybrid propellant. The numerical simulation conceives that a pipe with solid fuel surrounded. Inlet flow is oxidant with high temperature and the flow is laminar. After obtaining the information of the flow field, we can use the canonical formulations of the burning rate and regression rate to analyze all the mechanisms and parameters affecting the rates.

Emissions reduction and energy management are current and future concerns for governments and industries alike. The primary source of energy worldwide for electricity, air transport and industrial processes is combustion. Moderate or intense low oxygen dilution (MILD) combustion offers improved thermal efficiency and a significant reduction of CO and NOx pollutants, soot and thermo-acoustic instabilities compared to conventional combustion. Whilst combustion in the MILD regime offers considerable advantages over conventional combustion, neither the structure of reacting jets under MILD conditions, nor the boundaries of the MILD regime are currently well understood. This work, therefore, serves to fill this gap in the understanding of flame structure near the boundaries of the MILD regime. The MILD combustion regime has been previously investigated experimentally and numerically in premixed reactors and non-premixed flames. In this study, definitions of MILD combustion are compared and contrasted, with the phenomenological premixed description of MILD combustion extended to describe non-premixed flames. A simple criterion is derived analytically which offers excellent agreement with observations of previously studied cases and new, non-premixed MILD and autoignitive flames presented in this work. This criterion facilitates a simple, predictive approach to distinguish MILD combustion, autoignitive flames, and the transition between the two regimes. The adequacy of simplified reactors as a tool for predicting non-premixed ignition behaviour in the transition between MILD combustion and autoignition has not previously been resolved, and is addressed in this work. The visual lift-off behaviour seen in the transition between MILD combustion and conventional autoignitive flames seen experimentally is successfully replicated using simplified reactors. The location of the visible flame base in a jet-in-hot-coflow burner is shown to be highly sensitive to the relative location of the most reactive mixture fraction and the high strain-rate shear layer due to the strong coupling of between ignition chemistry and the underlying flow-field. Previous studies have demonstrated a strong dependence of ignition delay times to significant concentrations of minor species. Simulations presented in this work demonstrate that small concentrations of the hydroxyl radical (OH), similar to those expected in practical environments, significantly affect ignition delay and intensity of non-premixed MILD combustion, however have little effect on autoignitive flames. Importantly, such concentrations of OH do not result in a change in flame structure for the cases investigated. Whilst these results stress the importance of minor species in modelling the transient ignition of non-premixed MILD combustion, steady-state simulations do not demonstrate the same sensitivity to concentrations of minor species expected in hot combustion products. These results suggest that the temperature and oxygen concentration in the oxidant stream are the most important factors governing the boundaries of, the MILD combustion regime. Investigations of reaction zone structure and ignition in, and near the boundaries of, the MILD combustion regime have demonstrated the relative importance of different aspects of ambient conditions and differences in structure between non-premixed MILD and autoignitive flames. These findings build upon the understanding of this regime and provide critical insight for future studies towards both fundamental research, and the practical implementation, of MILD combustion.
Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2017

碩士
國立彰化師範大學
機電工程學系
94
The main theme of this thesis explores the fuzzy control scheme to handle the garbage incineration plant operation. The dominant role in the incineration plant plays is to burn refuse. In addition, utilisation of the reusable exhausted heat to regenerate the electricity through the power of steam evaporation is the other goal. In order to achieve complete combustion of the garbage and maintain the stability of providing electric utility, we need a steady control operation. Due to the complexity in the content of garbage, the effective heating value varies, and acts unlikely the burning coal or petroleum that is easy to be maintained in a fairly good control. The influence factors to be considered are rather complicated and need to be handled carefully. Because the entire boiler combustion system is a nonlinear system and time varying system. Therefore, using PID control, the operator must often readjust the PID controlled variables, in accordance with the change of system performance. Nevertheless, fuzzy control can obtain a good control effect. The experiment based on the estimated transfer function of plant is conducted. The time delay characteristic and lagging time related to the effective heating value are presented. In order to compare the control effort of the above problem, traditional PID controller and fuzzy controller are implemented with different lagging time. Simulation results show that the fuzzy controller can cope with the variation of garbage heating value problem with different combustion time-delay. In summary, applying fuzzy control theory in the entire boiler automatic combustion control and with expert's knowledge and operator's experience, fuzzy decision-making control exhibits a wisdom control system Therefore, a boiler combustion system with non-linear and time-delay combustion characteristics, reach more stabilized steady state, which in turn, made the cogeneration plant smooth in operation line.

碩士
國立成功大學
電機工程學系碩博士班
90
Application of Fuzzy Control Theory and Taguchi Methods to Boiler Automatic Combustion Control of Cogeneration Plant Guo-shyong Yang＊ Ming-Shing Young＊＊ Department of Electrical Engineering National Cheng Kung University , Tainan , Taiwan , R.O.C Abstract This thesis is mainly explore that the application of fuzzy control on the boiler Automatic Combustion Control (ACC) of the cogeneration plant. As the boiler combustion system is a non-linear system and the quality of system will be various with the changes of time. Hence, it is often essential for operator to adjust anew the control parameters of PID to adapt variation in the quality of system. Contrary, it is not necessary for a fuzzy control. Therefore, we can get a better control effect. This research is to take aim on the Boiler Automatic Combustion of the cogeneration plant, which in nature is a complex system of non-linear and time-delay of combustion. We employed the fuzzy control theory for the design of the fuzzy controller and for the comparison of control efficacy between PID control and fuzzy control under the transfer function model of the boiler combustion system with different combustion time-delay. Moreover, for the design of the fuzzy controller, the membership function that designer choose may not always be the best combination of membership function parameters. Therefore, in this study, we introduced the Taguchi Quality Experiment Method, which through the way of Orthogonal Array experiment, we solved for a set of best parameters combination for input variable membership function enabling higher level of fuzzy control efficiencies. In the final section of the thesis, coordinating actual Automatic Combustion Control operation with fuzzy control theory, we then proceeded with the fuzzy controller design for the cogeneration plant and calculated the operating amounts of system control and also provided related subjects for further exploration. ＊ The author ＊＊The advisor

Text in English
There are limits on performance of processes and reactions set by material balances and by thermodynamics. The interaction of these theoretical limits and how they influence the behaviour of reactions and equipment is of interest to researchers and designers. This thesis looks at the conversion of biomass to gaseous products under various conditions, including a range of temperatures from ambient to 1500 ⁰C and in the presence or absence of oxygen. The limits of performance of the material balance can be represented as an Attainable Region (AR) in composition or extent space; we call this the MB-AR. The MB-AR represents all possible material balances that can be achieved for a given a set of feeds and set of possible products. The dimension of this space depends on the number of independent material balances. The extreme points of the MB-AR are of particular interest as these define the limiting compositions and the edges of the boundary of the MB-AR represent the limiting material balances. The MB-AR does not depend on temperature. The thermodynamic limits of performance of can be represented as an AR in the space of Gibbs Free Energy (G) and Enthalpy (H); this is called the G-H AR. The G-H AR is always two dimensional, no matter what the dimension of the MB-AR. Extreme points in the G-H AR are also extreme points in the MB-AR are; however not all extreme points in the MB-AR are extreme points in the G-H AR. The extreme points in the MB-AR are transformed by calculating G and H of the points at the condition of interest (reaction temperature and pressure). It is then necessary to find the convex hull in G-H space of this set of transformed points which gives us the boundary of the G-H AR. The extreme points in the G-H AR can be associated with material balances and the extreme point with the minimum G represents the global equilibrium or equivalently the most favoured material balance for the system. The edges of G-H AR are defined by the lines between neighbouring extreme points in the boundary of the G-H AR. These edges represent the limiting material balances in terms of defining the extremes of the G and H of the system. The G-H AR depends on the feed and products through the MB-AR, but also depends on temperature (and pressure). The set of points which are extreme points of both the MB-AR and the G-H AR changes with temperature. Geometrically, the transformed set of extreme points for the MB-AR moves in the GH space as temperature is changed and they move at different rates. Hence when finding the convex hull in the G-H space of the transformed extreme points of the MB-AR, G-H points become either boundary (extreme) points or move into the convex hull at different temperatures. Thus, the material balance which corresponds to the global minimum in G may change with temperature, as do the material balances which are associated with the edges of the G-H AR. Experiments are performed on biomass anaerobically at ambient temperature using microbes as the catalyst, and the products of this process are called biogas. The experiments were performed in a nitrogen plasma system on biomass at higher temperatures (400 ⁰C to 1000 ⁰C) also in the absence of oxygen, and this process would typically be referred to as pyrolysis. Oxygen was added to the plasma system and operated at temperatures between 700 ⁰C and 900 ⁰C, and this would typically be referred to as gasification. Thus, it was able to change the MB-AR by presence or absence of oxygen. By changing operating temperatures, the G-H AR is effectively changed with either the same or different MB-AR’s. The experiments show that in all cases, the product tends towards minimum G. Although this might not be surprising at the higher temperatures, minimizing G is not thought to be the driving force in microbial systems. An important insight from this is that if one were to try and make hydrogen only in a biological system, the system would need to have organisms that make hydrogen only. This is because the material balance that produces hydrogen has a lower change in G than the material balance that make methane. Thus, if there was a consortium of organisms and some of them could make methane, the methane producing organisms would dominate as they have the higher Gibbs Free Energy driving force. If the boundary of the G-H AR around the minimum G is fairly flat, or if many of the extreme points of the MB-AR lie close to the minimum G in the boundary of the G-H AR, then there are many material balances that will give the same G and H. Thus, there are a range of compositions with similar G and H and how one approaches the minimum G will determine the chemical composition of the product. This has important implications for the design, scale up and operation of equipment if a particular product is desired rather process efficiency. The low temperature anaerobic route to gasifying waste, using microbes as catalysts, has a very simple G-H AR, and the preferred products are CH4 and CO2, known as biogas. These units should be relatively stable to operate as none of the other products have G’s that are as negative as that of the biogas. Although not part of this thesis, small-scale anaerobic digesters were installed in communities and these do run easily and stably with fairly little intervention from the operator which seems to support our conclusion. We however could ask, why then have simple technologies, such an anaerobic digestion, not been widely adopted in Africa? To this end we worked with communities and spoke to people about their knowledge about the technology, their concerns and their possible interest in using new approaches to supply energy for cooking and lighting. We found that people were not aware of the technology but would be very interested in adopting a technology that supplied energy cheaply. To our surprise however, their major concern was around hygiene and safety, in that if the gas was made from “poo” how could the gas be clean and would cooking with it not contaminate the food and make people sick? This in hindsight is a very reasonable concern, although it had never occurred to us that this would be a perception. Engineers will have to work with social scientists and psychologist, amongst others, to address the concerns and needs of communities in order for sustainable technologies to be successfully adopted by communities. In summary, this thesis presents a tool for analysing biomass conversion to gaseous products in general, whether microbial or thermal. This tool gives insight into what is achievable, what the major factors are that affect the favoured product and how this can be manipulated to improve efficiency from an overall material and energy point of view.
Physics
D. Phil. (Physics)

Includes bibliographical references.
[210] leaves : ill. ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
This thesis presents two advanced modelling studies which address some unresolved fluidized bed combustion (FBC) issues. In the first study, finite element methods are used to solve a transient continuum/percolation model of a single porous char and its surrounding boundary layer so as to generate temperature, O2,CO2, CO pressure and porosity distributions for over 100 different FBC conditions. In the second study, a new discrete approach for the determination of the diffusion coefficients of the fluid-solid system is described and used, based on moecular dynamics and percolation concepts.
Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1996

Includes bibliographical references.
[210] leaves : ill. ; 30 cm.
This thesis presents two advanced modelling studies which address some unresolved fluidized bed combustion (FBC) issues. In the first study, finite element methods are used to solve a transient continuum/percolation model of a single porous char and its surrounding boundary layer so as to generate temperature, O2,CO2, CO pressure and porosity distributions for over 100 different FBC conditions. In the second study, a new discrete approach for the determination of the diffusion coefficients of the fluid-solid system is described and used, based on moecular dynamics and percolation concepts.
Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1996

Coal is likely to remain an important energy source for the next several hundred years and hence advances in coal combustion technologies have major practical impact. Detonation combustion of coal initiated by a plasma cartridge driven detonation wave holds promise for improving both system and combustion efficiencies. Both fragmentation and chemical kinetic pathways are qualitatively different in comparison to conventional coal combustion. The present work is a theoretical investigation of fragmentation due to detonation wave. The theoretical simulation starts with simple model and progressively incorporates more realistic analysis such as combined convective and radiative boundary condition. It studies the passing of detonation wave on coal particles suspended in air. Concepts of solid mechanics are used in analysing fragmentation of coal particles. A numerical model is developed which includes stress developed due to both thermal and volatilization effects. Weibull statistical analysis is used to predict the fracture time and fracture location resulting from principal stress induced. It is observed that coal particles fragment within microseconds. Radiation does not have much effect on developed stress. Volatilization does not have much effect on fragmentation for the particle size considered in this work and stress due to thermal effect dominated the fragmentation. Coal size distribution statistics is considered to obtain real regime. Coal is used as mixture of different sized particles in real combustors. Hence it is important to analyse the effect of detonation wave on mixture of coal particles. Results presented in this work from simulation run suggest that plasma assisted detonation initiated technology can fragment coal particles faster. Average fracture time of mixture of coal particles is far less than detonation travel time for the detonation tube considered here. Simulation results suggest that almost 90% of coal particles fragment early. Average fracture time reduces as Mach number increases. Same phenomena can be observed for volatile matter generated at fracture and ow of volatile matter at fracture. Hence it can be concluded that plasma assisted detonation combustion leads to different volatilization and fragmentation pathways.

Research Doctorate - Doctor of Philosophy (PhD)
The formation of chlorobenzenes from oxidative thermal decomposition of 1,3-dichloropropene have been investigated using a combined combustion experiments and quantum chemical calculations. Experimental and computational results elucidate the chemistry of formation of toxic compounds from combustion chlorinated pesticides as could occur in bush fires or accidental fires of such chemicals in their storage facilities. Mono- to hexa-chlorobenzenes were observed between 800 – 1150 K, and the extent of chlorination was proportional to the combustion temperature. Higher chlorinated congeners of chlorobenzene (tetra-, penta-, hexa-chlorobenzene) were only observed in trace amounts between 950 – 1050 K. DFT calculations indicated that cyclisation of chlorinated hexatrienes proceeds via open-shell, radical pathways. Oxidation of phenylvinyl radical intermediates and subsequent ring closure were the key mechanistic pathways in the formation of benzofuran and chlorobenzofuran. Quantum chemical molecular dynamics (QM/MD) at 1,500 and 3,000 K revealed that the thermal oxidation of 1,3-dichloropropene was initiated by (1) abstraction of allylic H/Cl by O₂ and (2) intra-annular C-Cl bond scission and elimination of allylic Cl. A kinetic analysis showed that (2) is the more dominant initiation pathway, in agreement with QM/MD results. These QM/MD simulations revealed new routes to the formation of major products (H₂O, CO, HCl, CO₂), which were propagated primarily by the chloroperoxy (ClO₂), OH and 1,3-dichloropropene derived radicals. In particular, intra-annular C-C/C-H bond dissociation reactions of intermediate aldehydes/ketones were shown to play a dominant role in the formation of CO and CO₂. QM/MD simulations demonstrated that both combustion temperature and radical concentration can influence the product yield, however not the combustion mechanism. In order to elucidate the dehydrochlorination kinetics of 1,3-dichloropropene and related compounds, the unimolecular HCl elimination reactions of 1,3-dichloropropene and other chloroaliphatic hydrocarbons were investigated using high level computational chemistry methods. Two generic pathways for the elimination of HCl was found. The first involves a C-Cl fission at an allylic site and a C-H cleavage at a vinylic site, whereas the second entails scissions of allylic Cl and methylenic H. The latter pathway appears more favourable from thermodynamic and kinetic standpoints. The effect of the length of carbon chain on reaction and activation enthalpies was also investigated by considering analogous dehydrochlorination pathways for short chlorinated aliphatics (i.e., C₃, C₄), discovering the reaction and activation enthalpies required for HCl elimination to be independent of the length of the carbon chain. Dehydrochlorination reactions investigated exhibited a pressure-independent behaviour even under ambient pressure and results suggest that electronic factors rather than anchimeric assistance influence dehydrochlorination reactions of substituted ethyl halides.