Aspects Of Combustion Research Articles

Effect of combustion duration on the performance and emission characteristics of a spark ignition engine using hydrogen as a fuel

The deteriorating quality of air due to exhaust emissions and the increasing number of motor vehicles in the world, is sending alarming waves throughout the world to try to do something to cut off or significantly reduce these emissions in order to save our planet. Scientists have found that hydrogen presents the best and unprecedented solution to this problem, for its superior combustion qualities and availability. This paper discusses analytically one aspect of combustion i.e. combustion duration and how it is affected by an engine’s operating parameters like compression ratio, equivalence ratio, spark plug location, spark timing and engine speed, and how it affects an engine’s performance parameters like brake specific fuel consumption, brake mean effective pressure, thermal efficiency, as well as emission characteristics.

Physical and Chemical Aspects of Combustion: a Tribute to Irvin Glassman. Edited by F.L. Dryer and R.F. Sawyer. Gordon and Breach Science Publishers, Amsteldijk 166, 1st Floor, 1079 LH Amsterdam, The Netherlands. 1997. 505pp. Illustrated. £69.

Physical and Chemical Aspects of Combustion: a Tribute to Irvin Glassman. Edited by F.L. Dryer and R.F. Sawyer. Gordon and Breach Science Publishers, Amsteldijk 166, 1st Floor, 1079 LH Amsterdam, The Netherlands. 1997. 505pp. Illustrated. £69.

SOLID FUEL RAMJET COMBUSTOR DESIGN

Combustion aspects of solid fuel ramjet (SFRJ) are reviewed. On the point of view of the ability of an SFRJ to operate satisfactorily at all off-design conditions the areas of concern to propulsion system designer are (1) selection of a fuel type, (2) flame holding requirements that limit maximum fuel loading, (3) understanding the fuel regression rate behaviour as a function of flight speed and altitude, (4) diffusion-controlled combustion process and its efficiency enhancement, and (5) inlet/combustor matching. Considering these areas, the following aspects are reviewed from the information available in open literature: (1) different experimental set-up conditions adopted in combustor research, (2) various suitable fuel types, (3) flammability limits, (4) fuel regression rate behaviour, (5) methods of achieving high efficiency in metallized fuel, and (6) various modelling efforts. Detailed discussion is presented on two different types of regression rate mechanism in SFRJ: one that is controlled by the heat transfer processes downstream of the reattachment region and the other by that in the region itself. With a view to demonstrate the use of the information collected through this review, a preliminary design procedure is presented for an SFRJ-assisted gun launched projectile of pseudo-vacuum trajectory.

Lasers in combustion: From basic theory to practical devices

In recent years, a large number of linear and nonlinear laser-based diagnostic techniques for nonintrusive measurements of species concentrations, temperatures, and gas velocities in a wide pressure and temperature range with high temporal and spatial resolution were developed and have become extremely valuable tools to study many aspects of combustion. Modern “pump-probe” laser spectroscopic methods give direct insight into the microscopic dynamics, product channel distributions, and reaction rates of elementary combustion reactions over a wide range of temperatures and pressures. Nonlinear laser spectroscopic techniques using infrared-visible sum-frequency generation can now bridge the pressure and materials gap to provide kinetic data for catalytic combustion. Laminar flames are ideal objects to develop the application of laser spectroscopic methods for practical combustion systems and to test and improve gas-phase reaction mechanism in combustion models. Besides diagnostics, lasers can also provide well-defined starting conditions for detailed experimental and theoretical studies of ignition processes. Non-intrusive laser point and field measurements, especially joint velocity-scalar data at the same point in space and time, are of basic importance in the validation and further development of turbulent combustion models. As an are for the application of quanitative laser spectroscopy to practical combustion devices, investigations in internal combustion engines are described. Finally, the potential of laser techniques for active combustion control in various devices from laboratory burners to full-scale jet engines, municipal waste incinerators, and pressurized fluidized-bed reactors are illustrated.

A group combustion model for treating reactive sprays in I.C. engines

A model is presented and discussed treating the complex interactions between the fluid dynamics, the size, space, and time distributions of droplets as well as the combustion chemistry in a Diesel spray. The three-dimensional droplet characteristics are modeled with an overset gridding scheme, CHIMERA, and time dependent solutions of the Navier-Stokes equations have been carried out with the digital computer. The chemistry is treated with global and detailed reaction kinetics in a two-stage model. The global kinetics were used with the detailed Navier-Stokes equations, and the detailed kinetics were employed with a time dependent one-dimensional model that used information from the detailed model. The typical thermodynamic conditions of a modern truck engine have been used to provide insight into the details of ignition, combustion, and pollutant formation in spray commbustion. The study has considered droplet groups that have both uniform and different size droplets, and different groupings of the droplets have been investigated. The present model allows the droplets to move and vaporize in time, and the time development of ignition has been studied. The results indicate that group combustion effects have a dominant influence on all aspects of spray combustion.

Surface and coatings effects in catalytic combustion in internal combustion engines

Various aspects of catalytic combustion relating to engines have been investigated. MoO 3 and coatings of transition metal oxides (prepared by flame pyrolysis) were confirmed to have combustion catalytic activity commencing at ~325–430 °C. Evidence from experiments and the literature indicates that in-cylinder catalysts can aid in fuel ignition (beneficial), but may also cause early quenching of the flame-front (detrimental) at combustion chamber surfaces. Catalytic combustion, when it occurs on thermocouple or heat probe surfaces, will cause surface temperature measurements in furnaces or engines to be erroneously high. This may explain the Woschni effect, a controversial finding wherein thermal insulation (which raises combustion chamber wall temperatures) appears to increase heat rejection from the combustion chamber.

97/03999 Ecological and economic aspects of coal combustion

97/03999 Ecological and economic aspects of coal combustion

96/06690 Releases of natural radionuclides from oil-shale-fired power plants in Estonia

It is becoming widely recognized that our society must transition to low-carbon energy systems to combat global climate change, and renewable energy sources are needed to provide energy security in a world with limited fossil-fuel resources. While many clean power-generation solutions have been proposed and are being developed, our ability to transition to a low-carbon society is prevented by the present lack of clean and renewable energy carriers that can replace the crucial roles that fossil fuels play, due to their abundance, convenience and performance, in global energy trade and transportation. Any future low-carbon energy carriers that aim to displace or supplement fossil fuels must have high energy densities for convenient trade and storage, and should be consumable within efficient high-power-density engines for transportation, heavy machinery, and other off-grid energy applications.Hydrogen and batteries have been widely studied but they are not suitable for use as international energy-trading commodities and they cannot provide the energy density and safety demanded by society. Metal fuels, produced using low-carbon recycling systems powered by clean primary energy, such as solar and wind, promise energy densities that are competitive to fossil fuels with low, or even negative, net carbon dioxide emissions. To date, however, few practical high-power-density end-use devices for generating heat or power from metal fuels have been proposed.This paper proposes a novel concept for power generation in which metal fuels are burned with air in a combustor to provide clean, high-grade heat. The metal-fuel combustion heat can be used directly for industrial or residential heating and can also power external-combustion engines, operating on the Rankine or Stirling cycles, or thermo-electric generators over a wide range of power levels. A design concept is proposed for a metal-fuelled combustor that is based upon extensive experimental and theoretical studies of stabilized and propagating metal flames performed at McGill University. This paper also reviews the fundamental and applied aspects of metal-fuel combustion in order to provide the framework needed to assess any potential metal engine technologies. The energy and power densities of the proposed metal-fuelled zero-carbon heat engines are predicted to be close to current fossil-fuelled internal-combustion engines, making them an attractive technology for a future low-carbon society.

96/02038 Ecological and economical aspects of coal combustion as a function of its quality parameters

96/02038 Ecological and economical aspects of coal combustion as a function of its quality parameters

Some issues in modelling bubbling and circulating fluidized-bed coal combustors

Fundamental aspects of coal combustion in the two types of atmospheric fluidized combustors, i.e. those based on bubbling and on circulating technologies, have been studied in order to determine those variables which play a dominant role in the reactor performance. The analysis is based on two relatively simple models, which take into account carbon surface reaction, intraparticle and external diffusion as well as phenomena of comminution of coal and its char. Performances of the two types of fluidized-bed combustors are discussed with reference to coal combustion only, without taking into consideration the emission issues. Sensitivities of main output variables to changes in fuel properties, design and operating variables are evaluated.

Some critical combustion aspects of reformulated heating fuels

The combustion characteristics of six middle distillate oil blends were examined using the controlled combustion testing facilities at the Energy Research Laboratories of the Canada Centre for Minerals and Energy Technologies (CANMET). Test fuels were specifically prepared for a research project to study the impact of changes in commercial heating fuel composition on the combustion performance of a residential heating appliance. Compositional formulation was modified in such a way that the fuel properties still met Canadian national heating fuel specifications. The experimental combustion conditions were set to reflect possible poor operating situations found in the field and to accelerate the emissions data acquisition process. The results from this combustion study indicate that performance deteriorated with a decrease in the fuel hydrogen-carbon ratio, which relates to the decreasing ratio of aliphatic, saturated hydrocarbon to aromatic hydrocarbon concentrations. When concentrations of high boiling, high molecular weight aromatic hydrocarbons are increased, while simultaneously reducing those of low molecular weight hydrocarbons, other fuel properties, such as flash point, distillation range, density and viscosity are altered. These compositional changes resulted in poorer burner performance characteristics and higher pollution emissions. Video recordings of the combustion experiments revealed progressive degradation of transient flame characteristics as the fuel reformulation changed from moderate to severe. Performance degradation was more pronounced at 7°C, significantly colder than the normal operating temperature range of a residential heating appliance. The effects of hydrocarbon compositional changes in distillate heating fuels on combustion performance, especially in terms of increased aromatics concentrations, were discussed.

Some critical combustion aspects of reformulated heating fuels

Some critical combustion aspects of reformulated heating fuels

On flame propagation along vortex tubes

Analyses of the influence of vortical structures on a two-density fluid indicate a possible motion of the light fluid into the heavy one and vice versa. Various simplifying assumptions including that of an inviscid theory have been made in this report, but the results provide an insight into the fast burning observed along vortex tubes. The analysis is a contribution to our understanding of the hydrodynamics aspect of turbulent combustion; it could also be useful in modeling turbulent premixed combustion. No limits have been placed on the scales of the vortical structures. Our estimates of the induced axial velocities (the burst) are valid for any combination of two fluids (i.e. for any thermal expansion ratio) thereby making them more acceptable than previous estimates by Chomiak [1] and by Daneshyar and Hill [2].

Electrical perturbation of cellular premixed propane / air flames

The phenomenon originally called polyhedral flame structure was first reported 100 years ago. Subsequent investigations showed that polyhedral structure was only one example of a more general phenomenon known now as cellular flame structure, and the range of combustion mixtures that produce them has been broadened to include lean mixtures of H[sub 2]/air, lean H[sub 2]/Br[sub 2], and rich mixtures of hydrocarbons from ethylene to octane with air. Of particular interest to the authors is the role of charged species in flames, and especially in flames that exhibit cellular structure. The electrical aspects of combustion has a long and distinguished history and this subject has been the subject of a classic monograph by Lawton and Weinberg. Electrical perturbation has been reported to affect the temperature of flames, to stabilize them at high flow rates and, in the absence of gravity, to change the speed of flame propagation, and to affect the amount of soot produced. The authors report here that premixed propane/air flames exhibiting cellular structure are quite susceptible to perturbation by electric fields. Since only charged species in the flame would be affected by the potential, and a small current would not modify transport properties of neutral species appreciably,more » this observation suggests that studies of this type may be useful in helping to further elucidate the role of charged species in flames.« less

Effect of an external electrical field on ignition and combustion processes

Published results of experimental studies on the effect of an external sub-breakdown electrical field on and combustion characteristics are reviewed. Analysis of the material presented reveals general princip features of the electrophysical aspects of combustion of various fuel compositions as a function of co practical application conditions.

Some Specific Aspects of Combustion in Supersonic H2-Air Laminar Mixing Layers

Development of Scramjet engines requires a detailed knowledge of the coupling between supersonic flow and chemical kinetics of combustion. In this paper we consider a stationary uniform, laminar supersonic mixing layer of hydrogen and air and investigate some conditions under which ignition occurs. More specifically, the influences of viscous dissipation effects, initial temperature and/or velocity gradients are investigated. This problem, where detailed chemistry for H2-air is used, is solved numerically. The structure of the reactive mixing layer is shown to consist of an induction region, a thermal runawayregion, a region where both premixed and diffusion flames coexist, and a pure diffusion flame region. The exact length of the induction zone is found to depend sharply on the upstream boundary conditions and more precisely on the intensity of viscous dissipation together with amplitude and direction of transverse temperature and velocity gradients.

Interrelationship Between Solid Propellant Combustion and Materials Behavior

AbstractThermochemical and physical processes which occur in various aspects of solid-propellant combustion including steady-state burning, ignition, transient burning, cook-off and crack propagation are presented in this paper. For each case, the various thermochemical and physical properties involved are summarized. In addition, the current direction of solidpropellant research is highlighted. The intent of this paper is to stimulate the interest of materials scientists and engineers in the field of solid propellants so that they will contribute their unique expertise to the advancement of current research. It is also the hope of the authors that the paper will serve as a useful summary of important relationships and parameters for scientists and engineers currently involved in solid-propellant research.

Combustion Aspects of Sodium Azide and its mixtures with potassium perchlorate and burning catalysts

Linear burning rate, thermal aualysis, temperature profile, flame structure and cryogenic burnability for the mixtures of sodium azide (SA) of different particle sizes (3.5 μm, 22 μm, and 67 μm), potassium perchlorate (KP) and with or without three kinds of burning catalysts (GeO2, Er2O3, and Y2O3) have been investigated. The linear burning rates increase with the KP content up to 33Wt% for similar SA particle size. The temperature-time histories in the vicinity of burning surface were obtained with 20 μm Type K thermocouple embedded in a Strand. The burning surface temperaturres of neat SA and of the SA/KP mixtures are nearly 350°C and 350°C ∼ 550°C, respectively, while the existence of the decomposition surface at 250 °C and condensed layer was suggested with SA/KP mixtures. In visual observation for the flame structure, the front of luminous flame zone appers to be in contact with the condensed phase surface. For example, however, the temperature profile suggests that there exists finitc distance from decomposition surface to flame front in the order of 0.05 mm ∼ 0.1 mm at 1 MPa for SA/KP = 80/20. The differential thermal analysis indicates that the tested catalysts have retarding effect on SA combustion, but a positive effect on neat KP decomposition in spite of being impotent for the burning rate increase of the SA/KP mixture. It was also found that SA strands containing appropatiae fractions of KP can hurn even in liquid nitrogen.

Model for airblast atomization

The objective of fuel injection modeling activities is generally to give support to the atomizer design effort to achieve improved spray quality. In gas turbine combustors, enhanced atomization is essential for satisfactory performance because droplet sizes can have direct impact on almost all key aspects of combustion. A model that includes the integration of the submodels of airflow, fuel injection and atomization, and droplets turbulent dispersion has been formulated. The model was applied to an airblast atomizer that incorporated a short prefilming device. The predictions were validated against two-component phase Doppler interferometry data of that atomizer. The results of the present investigation demonstrate the capability of the developed model to predict satisfactorily the airflow field and spray characteristics. The results also indicate the need for detailed measurements in the near field of the atomizer in order to quantitatively verify the modeling of the initial atomization processes in this region. CD d FN g P t U u V P a Nomenclature = drag coefficient = droplet diameter, m = atomizer flow number, m2 = gravitational acceleration, m/s2 = kinetic energy of turbulence, m2/s2 = static pressure, Pa = film thickness, m = velocity of carrier phase, m/s = fluctuation velocity of carrier phase, m/s = velocity of droplets, m/s = axial distance, m = dynamic viscosity, kg/ms = density, kg/m3 = surface tension, N/m I. Introduction T HE development of gas turbine combustors depends largely upon understanding the flow and combustion processes within the combustor. In order to accurately simulate the combustor flowfield, analytical approaches are required to account for various flow processes in addition to the details of the combustor configuration. It is equally important to establish a wide base of benchmark quality data needed for model validation. Most of the combustor performance parameters are directly related to the quality of the spray produced by the fuel injector.l The initial drop sizes formed at the injector exit and their trajectories coupled with the combustor primary zone aerodynamics significantly influence the evaporation and combustion characteristics of the spray. Fuel injection calculation concepts currently in use include empirical methods that readily provide a global picture of the whole spray as well as more complex models that account for the detailed spray dynamics.2'3 Spray correlations provide a convenient means of calculating such parameters as mean drop size and spray angle. However, it is difficult to develop a design method based only on empirical data because each correlation was derived for a certain application and may not

Combustion: a study in theory, fact and application

Part 1 Combustion of gases: fundamentals of chemical kinetics - reaction rates, chemical equilibrium, chemical kinetic rate equations flame propagation in laminar flows - aerodynamics, dynamic stability, flammability limits flame propagation in turbulent flows - vortex stretching, combustion models, wrinkled laminar flame and local reaction models ignition and flame stabilization explosion and detonation diffusion flames. Part 2 Combustion of liquids and solids: combustion of droplets and sprays combustion of coal, combustion of char, transformations of ash, fixed-bed and fluidized-bed combustion free-burning fires - cellulosic materials, fire suppression combustion of condensed systems - the SHS process, combustion of solid propellants environmental aspects of combustion - major pollutants, clean systems. Part 3 Combustion design and research fundamentals: application of chemical reactor theory to combustor design physical modeling of combustion processes - similarity theory basic diagnostic techniques in combustion - measurements, visualization, diagnostics combustion in practical systems - gas-turbibes, boilers, LCVG. Appendices: The earliest scientific definition of combustion and flame data for thermochemical calculations.