Moment Of Ignition Research Articles

Study on the Electronic Ignition System Bench on SCM

To enhance the power of the engine and improve the emissions performance, The Intake air temperature signal , knock signal, throttle signal and power supply voltage signal were used as the correction references for the ignition advance angle. According to the parameter characteristics, the schemes of the measurement and control were proposed. The sensors were selected and corresponding parameters were determined. And then parameters of signal processing circuits designed, so that determined the moment of ignition. The experiment proved that the electronic ignition system designed in this paper, can meet the expected demand.

Numerical modelling of unsteady heating and melting of the anode by electric arc. Part 1. Mathematical model and computed characteristics of the arc column

The two-dimensional mathematical model in the approximation of a partial local thermodynamic equilibrium of plasma and the technique for numerical computation of the unsteady electric arc characteristics, including the conjugate heat exchange of the electric-arc plasma flow with the treated product (anode) are considered. The results of overall testing of the numerical algorithm point to the correctness of the model and computational technique. The results of the computation of the arc characteristics from the conventional ignition moment until the passage to stationary regime are presented. It is found that a single thermal torus, which scatters fairly quickly in the ambient medium, forms around the arc column.

The influence of aluminum powder dispersity on composite solid propellants ignitability by laser radiation

The results of experimental study of ignition process of composite solid propellants based on ammonium nitrate and energetic binder containing aluminum powders of various particle sizes by CO 2-laser radiation in air (with ambient pressure) are presented. Partial or complete replacement of micron-sized aluminum powder on Alex ultrafine powder as part of composite solid propellants leads to the reduction of ignition time by decrease the temperature of burning surface, thickness of reaction layer and by increase of the heating rate in condensed phase. It was found that the efficiency of ultrafine aluminum powder additives in formulations increasing with decreasing of laser radiation intensity. The temperature of the formulation’s burning surface at the ignition moment was measured by usage of the thermal imager. The temperature of burning surface under ignition by radiant heat flux was 545–660 °C (formulations containing ultrafine aluminum powder) and 713–820 °C (formulations with micron-sized aluminum powder) for the radiation intensity 60 W/cm 2.

Hydrogen resistance to knock combustion in spark ignition internal combustion engines

The results of investigations focusing on knock combustion analysis of a hydrogen-fueled engine have been presented in the paper. Knock intensity was determined as the intensity of the in-cylinder combustion pressure pulsations (recorded with a sampling frequency of 100 kHz) and filtered through high-pass filtering with cut-off frequency of 3.5 kHz. The research was conducted on the CFR engine with a variable compression ratio ranging from 6 to 14. The research has shown a rapid increase in pressure pulsations amplitude was observed while the compression ratio was changed from 11 to 12. This was interpreted as a result of in-cylinder hydrogen-air mixture self-ignition at the end of the spark ignition controlled combustion. Supporting this observation the theorem of dual nature of hydrogen knock combustion was postulated. Intensity of the pressure pulsations that accompany normal combustion without hydrogen self-ignition was in an exponential correlation with the compression ratio, which directly translates into a similar correlation of the pulsations and temperature of hydrogen-air mixture at the moment of ignition.

Development of a reduced chemical kinetic mechanism for a gasoline surrogate for gasoline HCCI combustion

A reduced chemical kinetic mechanism consisting of 48 species and 67 reactions is developed and validated for a gasoline surrogate fuel. The surrogate fuel is modeled as a blend of iso-octane, n-heptane, and toluene. The mechanism reduction is performed using sensitivity analysis, investigation of species concentrations, and consideration of the main reaction path. Comparison between ignition delay times calculated using the proposed mechanism and those obtained from shock tube data show that the reduced mechanism can predict delay times with good accuracy at temperatures above 1000 K. The mechanism can also predict the two-stage ignition at the moment of ignition. A rapid compression machine (RCM) is designed to measure ignition delay times of gasoline and gasoline surrogates at temperatures between 890 and 1000 K. Our experimental results suggest that a new gasoline surrogate that has a different mixture ratio than previously defined surrogates is the most similar to gasoline. In addition, the reduced mechanism is validated for the RCM experimental conditions using CFD simulations.

Modeling diesel engine combustion using pressure dependent Flamelet Generated Manifolds

Flamelet Generated Manifolds (FGMs) are constructed and applied to simulations of a conventional compression ignition engine cycle. To study the influence of pressure and temperature variations on the ignition process after the compression stroke, FGMs with several pressure levels are created. These pressure levels, and the corresponding average temperatures are obtained from experimental curves. Auto-ignition is taken into account by tabulating igniting laminar diffusion flames, with n-heptane as a surrogate for diesel. The chemistry is parameterized as a function of the mixture fraction and a reaction progress variable, and pressure variations are accounted for by using the pressure as an extra degree of freedom. General steady combustion phase characteristics are compared to experimental observations. They show a correct phenomenological spray flame picture with a flame lift-off, fuel rich inner region and a diffusion flame at the periphery. The resolution effect of pressure discretization in the database to ignition prediction is studied by performing simulations with 1, 3, 5 and 7 pressure levels in the FGM. The results show that not more than 5 pressure levels are needed to represent the chemistry evolution during an engine cycle. All tested reaction mechanisms for n-heptane give a short burn duration, especially the reduced ones. As a result, at the moment of ignition the pressure rise rate is over-predicted.

High-throughput method for estimating the time to sustained ignition of polystyrene-clay nanocomposites based on thermogravimetric analysis

Polymer-modified clay nanocomposites were prepared by melt blending and the time to ignition was measured by cone calorimetry at various heat fluxes. Based on these experimental results, a critical mass flux and critical percentage mass loss (pmlcrit) for piloted ignition were identified and validated for both virgin polystyrene and its composites, across a wide range of heating fluxes. Based on the assumption that the polymer degradation kinetics in the heating segment of the cone calorimetry (up to the moment of ignition) and thermogravimetry experiments are similar, and using the pmlcrit, we hypothesized that the onset degradation temperature of the TGA samples (defined here as the temperature at pmlcrit) could be used to estimate the time to sustained ignition in cone calorimetry experiments. The onset degradation temperature and the time to sustained ignition showed a good correlation, regardless of the heating flux used in cone calorimetry experiments. Copyright © 2009 John Wiley & Sons, Ltd.

Ignition of single coal particles in high-temperature oxidizers with various oxygen concentrations

In this investigation, coal pellets were combusted using a high temperature oxidizer with varying oxygen concentration, using a small scale batch reactor able to preheat the oxidizer to 1273 K. In base of the experimental results, the influence of oxygen concentration on the ignition mechanism, the solid temperature inside the particle at the moment of ignition, the mass lost at the moment of the ignition and ignition time is analyzed and discussed. A theoretical basis for the division of the conditions tested into three ignition regimes is developed and a formula for the prediction of the ignition time directly from the material and oxidizer temperature and oxygen concentration is proposed.

Approximate method for solving problems of ignition theory

A method is proposed to determine the moment of ignition of a semi-infinite massif of a condensed material exposed to an external heat flux specified as an arbitrary function of time. The method uses the fractional-differentiation formalism. For large values of the heat flux, the calculation results coincide with the results obtained using well-known methods.

Numerical Study on Ignition Characteristics of Methane-air Mixture Using Detailed Chemical Kinetics

Ignition is a transient combustion phenomenon and one of the most difficult and complex problems, which include a lot of physical and chemical processes, so that it has not yet been explained suficiently. In the present study, the ignition characteristics of methane-air mixture were investigated by numerical analysis using detailed chemical kinetics. In order to clarify the effect of geometric condition of ignition source and flow field on ignition characteristics, ignition processes for 1-D plane model, 2-D plane model and axisymmetric model were examined comparatively. The following conclusions were reached : (1) Ignition characteristics are better for the case where the heat is hard to radiate to surrounding fluid, but the reaction mechanism of ignition is almost the same. (2) The elementary reactions, which are important at the moment of ignition, are as follows : CH3 + O →CH2O + H, CH3 + O → CO + H + H2, and H + O2 → O + OH. (3) The success and failure of ignition andthe ignition delay depend on the supplying manners of ignition energy, especially heating time and ignition source shape.

Critical requirements for low temperature ignition targets

The stagnation dynamics of low temperature ignition targets consisting of bare deuterium-tritium (DT) fuels is described in terms of a non-adiabatic self-similar solution, which takes the energy dissipation due to bremsstrahlung into account. Without enough optical thickness, the radiation loss, which depends non-linearly on the background temperature and density, seriously affects the compression performance, and ignition fails. This feature sets a lower limit on the peak fuel parameter rho r for a given fuel mass. Accordingly, previous gain models, in which the calculation is launched at the moment of ignition assuming a fuel assembly at rest, are limited such that the maximum compressed state at lower rho r than the threshold is not expected to be realized through virtual stagnation

Computer-controlled 40 T magnetic field regulation

A description is given of the feedback system controlling the intensity of the magnetic field for the 40-T installation. A small computer generates the voltage that controls the next ignition moment for the 6-MW thyristor rectifier supplying power to the magnet coil. Part of the data is precalculated, using the known properties of the rectifier and coil, the latter as functions of coil temperature. The actual field is measured with a pick-up coil and an electronic integrator from which the output is digitized using a 16-bit analog-to-digital converter. The computer calculates the final adjustments of the controlling voltage from the deviations of the output of this ADC from the required value. After a settling time of about 20 ms, the maximum deviation of the actual field from the desired field is about 5 mT.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A study of combustion in a divided chamber (Influences of the initial turbulence)

A divided combustion chamber is used as a tool for an elementary study of combustion of lean mixture in a speak ignition engine with an auxiliary chamber. The study in a divided chamber is usually performed under the condition of quiet mixture, through the gas in an engine has strong turbulence at the moment of ignition. This report deals with the combustion in a divided chamber with initial turbulence which preced the spark ignited combustion. The turbulence is generated in the main and sub-chambers separately. The effect of the turbulence on the combustion is influenced by the combined effects of the turbulence and jet from the sub-chamber.

Ignition and Combustion of wood in a heat flow

This paper studies the combustion in a heat flow in wood. Samples of beech wood were placed on a VLK-500 platform weigher, so that the rate of combustion could be determined. The rate of heat flow was varied by changing the distance between two radiant panels and the samples. The volatile pyrolysis products were ignited by a separate propane-butane diffusion flame set over the center of the samples. The change in the sample surface temperature with time for different rates of heat flow from the infrared panels is shown. Results show that the rate of combustion at the moment of ignition is a maximum, which decreases as the sample burns out. With increased rate of burnout from 0.5 to 4 kg.m/sup -2/ and a resulting increase in the thickness of the carbon layer from about 1 to approximately 8mm, the critical heat flow increases from 1.2 to 12.0 kW.m/sup -2/.

A critical examination of the effect of dust moisture on the rate of pressure rise in Hartmann bomb tests

The previously reported correlations between dust moisture content and the maximum rate of pressure rise in the Hartmann bomb test are challenged. A closer analysis of such correlations revealed that the delay between dust dispersion and ignition increased systematically with increasing dust moisture, indicating that part of the apparent effect of moisture on the rate of pressure rise stems from a superimposed decrease of the degree of turbulence of the dust cloud at the moment of ignition. By correlating data obtained at the same ignition delays, approximate correlations were obtained of the maximum rate of pressure rise and dust moisture, the degree of turbulence being used as parameter. It was also confirmed that care must be taken to ensure that the rate of pressure rise is related to the effective particle size distribution of the dust cloud, including stable agglomerates, rather than to a size distribution obtained in independent particle size analysis or extracted from the literature. The findings of the present investigation are likely to be applicable to all kinds of closed bomb tests in which a transient experimental dust cloud is produced by a fixed air blast.

Studies on criticality: Temperature profiles in explosive systems and criteria for criticality in thermal explosions

Measurements have been made of the time-dependent temperature profiles that are set up during the exothermic decomposition of gaseous methyl nitrate. Subcritical and supercritical conditions around 300°C have been studied and pre-ignition temperatures have been measured at different positions in a cylindrical reaction vessel. Subcritical profiles across the diameter of the vessel show peaks on either side of the vessel center, which move together to form a single, central maximum about 200 msec after the admission of the reactant. This distribution is maintained as a quasi-stationary state for a further 200 msec. Supercritical profiles near the moment of ignition also show the symmetrical double maximum and ignition was shown to originate in this annular region. Characteristic pre-explosion temperature rises there lie in the range 12° to 14°C. Annular ignition has been predicted theoretically for a reactant such as methyl nitrate under conditions not greatly dissimilar to ours, but there appear to be no other experimental data in the literature on this phenomenon. Analytical methods for determining δ (crit) for some simple shapes not treated by Frank-Kamenetskii are based on the concept of the equivalent sphere, where the term implies the sphere of such radius that it reaches criticality at the same ambient temperature as the reactant. Three methods for determining the radius of the equivalent sphere have been compared and contrasted. The form of Frank-Kamenetskii's expression for the effect of small reactant consumption on δ has been corrected and compared with Thomas' expression. More extensive reactant consumption was allowed for by Adler and Enig. However, they treated only reactants under conditions where E/RT 0 is large, i.e., where the exponential approximation is valid. We have extended their analysis to include the more general case of reactions with low activation energies. An appendix presents new results in the study of criticality in terms of the temperature gradient in the reactant at the vessel wall.

The ignition of solid explosive media by hot wires

The present paper describes an investigation of the physical factors affecting the ignition of solid explosives by heated filaments embedded in the medium. The filaments were composed of fine resistance wire and were heated electrically, the critical thermal energy required to cause ignition being measured for wires of different geometrical, thermal and electrical characteristics and for different times of heating. Systematic variation of these factors enabled the energy equation for the ignition process to be formulated and its terms analyzed, the technique involving extrapolation to zero time of heating as a means of eliminating heat losses from the ignition system, and extrapolation to zero diameter of wire in order to eliminate terms involving the heating element; the former simulates the ideal case of a heat-insulated ignition system and the latter that of a line source of heat. The energy equation for ignition in these circumstances takes a simple form which implies that, at the moment of ignition, the heat supplied to the ignition system always equals the heat gained by the system plus the heat lost, the absence of any term representing heat generated by chemical action being very significant. For a given ignition system, the amount of heat absorbed up to the moment of ignition is shown to be independent of time, so that the increase in ignition energy with increasing time of ignition is wholly attributable to the heat losses sustained by the ignition system during the heating process. Further analysis shows that the critical factor governing ignition in systems of the type considered is the temperature, and that the geometry of the heating element probably determines the amount of explosive which must be raised to the critical temperature to ensure ignition.

The electrical ignition of gaseous mixtures

The ignition of explosive gaseous mixtures for experimental purposes is generally made by an electric spark or train of sparks between fixed terminals. The temperature of inflammation cannot in this case be measured, and it is determined by that of a hot surface in contact with the gas, or by calculation from its adiabatic compression. The fact that there is a critical temperature of ignition and that the velocity of an explosion wave can be calculated from the thermal constants of the gas and air, has led to the view that the process is a thermal one throughout, with in general two stages, a period of slow combustion and rise of temperature, and the true explosion on this reaching a certain limiting value. There is, however, a more intimate possible cause of the division of the molecule of combustible gas which precedes explosive combination. Recent work on the ionisation of gases has made familiar the view that a molecule can be ionised by corpuscular radiation, and that by the gain or loss of such corpuscles the nature of the molecule can be profoundly modified. The present paper is an examination of certain typical gases and vapours for the purpose of finding evidence of the mechanism of the process by which the energy of the source is transferred to the gas at the moment of ignition. A very full report on gaseous combustion was given by Prof. W. A. Bone at the Sheffield meeting of the British Association, in the discussion upon which Sir J. J. Thomson called attention to the possible influence of electrons in preparing the way for an explosion wave by ionising the gas. Following this suggestion an important series of observations on gaseous ignitions has been recently made by my colleague, Mr. J. R. Thompson. He found that it is possible to ignite a cold explosive mixture by the incidence of X-rays on a platinum surface in it, and that when the source of ignition is a hot platinum wire an explosion is started at that temperature at which ions are discharges from the metal. These observations, if they do not decide the ionic origin of gaseous explosions in general, prove that ionisation and explosion are intimately connected.

Vibrations of rifle barrels

It has long been known that a shot fired from a rifle does not in general start from the muzzle in the direction occupied by the axis of the barrel at the first moment of ignition of the charge. The late W. E. Metford was, I believe, the first to point out the origin of this deviation, showing by experiment that it was due to the unsymmetrical position which the mass of the stock held as regards the barrel; and, further, that if the initial direction of the shot passed below the apparent direction of aim when the rifle was held in the ordinary position, the initial direction would be high if the rifle were aimed upside down, and to the right or left if the plane of the stock were horizontal and the stock itself to the left or right of the barrel.