Minimum Spark Ignition Energy Research Articles

Effect of Thermal Expansion on the Minimum Energy of Gas Spark Ignition

The effect of thermal expansion on the minimum energy of gas spark ignition is studied using a mathematical model of spark ignition. It is shown that the thermodiffusion model of gas spark ignition underestimates the minimum spark energy by more than a factor of two. The dependence of the minimum spark ignition energy on the Damkohler number is studied, which characterizes the ratio of the flame propagation velocity to the speed of sound in a gas. Key words: fuel gas, spark, thermal expansion, minimum spark energy.

Effect of Radiant Heat Transfer on the Minimum Spark–Ignition Energy of Gas Suspensions

A mathematical model of spark ignition of a gas suspension is constructed on the basis of a two–temperature thermal diffusion model of gas–suspension combustion and the radiant heat transfer is modeled in a diffusion approximation. The dependences of the minimum ignition energy on the parameters which describe the disperse phase and the domain of the disperse–phase parameters in which the radiant heat transfer affects greatly the minimum spark–ignition energy is determined by solving the problem numerically. The analytical formula that was obtained for determination of the critical spark–ignition energy of the gas suspension and that takes into account the radiant heat transfer in the gas suspension gives values different from numerical results by not more than 30% in a broad range of determining parameters of the problem. The theoretically obtained values of the minimum spark–ignition energy of a gas suspension of coal dust agree satisfactorily with experimental data.

Spark ignition of near the lean limit CH 4air mixtures at low pressures

The minimum spark ignition energy in methaneair mixtures was measured for pressures between 0.1 and 0.4 atm and methane concentrations near the lean ignition limits. Spark gap sizes between 2 and 10 mm and spark durations between 70 and 120 μs and a maximum spark energy of 600 mJ were used to identify lowest ignited methane concentrations. These concentrations were found in good agreement with previous measured lower limits of flammability using similar apparatus.

Spark ignition of aerosols

An experimental investigation was carried out to determine the minimum spark ignition energy of monodisperse tetraline aerosols in a laminar gas flow. Results, presented in terms of spark ignition frequency, and for droplet sizes between 6.7 μm and 40 μm, showed: a relatively weak dependence on spark duration, an optimum spark gap width between 3 and 4 mm, an increase in minimum spark ignition energy with decreasing oxygen concentration in the gas, a decrease in spark ignition energy as the gas to fuel ratio decreased from lean to stoichiometric, a maximum ignition frequency depending on droplet size, and an optimum droplet size between 22 and 26 μm for minimum spark ignition energy. A model of droplet motion and vaporization allowed an estimation of the non-reactive fuel vapor concentration and droplet motion due to the spark discharge and was used for qualitative discussion of the experimental results.

A Computational Study of Ignition by Oxygen Dissociation

Abstract Numerical calculations have been performed on the ignition of methane-oxygen-argon mixtures due to dissociation of molecular oxygen into ground state oxygen atoms. The computations are caried out using a time and spatially dependent fluid mechanics model in one-dimension coupled with a detailed oxidation mechanism for methane. A calculation of the minimum ignition energy as a function of equivalence ratio shows that ignition by oxygen dissociation is clearly different from laboratory experimental results of spark ignition. Whereas the minimum spark ignition energy occurs at Math for methane-oxygen-argon mixtures, the computations show a steadily declining minimum ignition energy from Math. Increasing the amount of oxygen dissociation decreases the induction time and increases the flame propagation rate during tht early part of the burning. This enhanced flame propagation rate lasts only until the oxygen atom concentration relaxes to a level which is typical of a flame moving at a constant speed. ...

Minimum mass of burning aluminum particles for ignition of methane/air and propane/air mixtures

Single aluminum particles of various diameters (20 μm to 80 μm) were suspended on a glass fiber in a methane/air or propane/air combustible gas mixture at room temperature and pressure. The particle was heated and caused to burn by a pulse from a neodymium: glass laser. The minimum diameter of single burning aluminum particles that ignite methane/air mixtures was determined experimentally to be between 20 μm and 30 μm. The minimum diameter is less than 20 μm for propane/air mixtures and is presented as a function of fuel/air equivalence ratio, . The energy of combustion of aluminum particles of minimum diameter (0.3 to 1.0 mJ) is of the same order as the minimum spark ignition energy of the gas. The methane/air mixture ignitable by the smallest particles has about the same equivalence ration (≈0.9) as the mixture ignitable by the least energetic spark; and the propane/air mixture ignitable by the smallest particles has an equivalence ration (≈1.5) greater than the mixture ignitable by the least energetic spark (≈1.25). This was unexpected because the burning aluminum removes oxygen from the combustible gas making the mixture fuel-rich in the vicinity of the particle. Data from the present study and two previous studies verify that, among various metals, the minimum particle mass for ignition of the gas is inversely related to its heat of combustion.

Ignition of Combustible Gases by Converging Shock Waves

Hydrogen-oxygen and hydrogen-air mixtures were ignited by converging cylindrical shock waves using the apparatus devised by Perry and Kantrowitz [J. Appl. Phys. 22, 878–886 (1951)], and the minimum strength shock wave necessary for ignition was determined. The enthalpy increase in the wake of the shock wave within a cylinder of diameter equal to the quenching distance and of unit height was calculated and found to be comparable with the minimum spark ignition energy divided by the quenching distance. An analysis of the unsteady heat conduction problem lends support to the choice of the quenching distance as the significant dimension of the region over which heat addition is effective in causing ignition.

Effect of Initial Temperature on Minimum Spark-Ignition Energy

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Lean Flammability Limit and Minimum Spark Ignition Energy. Commercial Fluids and Pure Hydrocarbons.

Lean Flammability Limit and Minimum Spark Ignition Energy. Commercial Fluids and Pure Hydrocarbons.

Ignition and Flame Stabilization in Gases

Abstract The self-ignition of a volume of explosive gas mixture is understood to be the transition from slow to very rapid chemical reaction with approximately adiabatic heat evolution. Two known processes bring this about. They are distinguished as thermal and branched-chain explosion. In the former, the chemical reaction becomes self-accelerating owing to the temperature rise. In the latter, the self-acceleration is caused by the formation of chemically active particles at a rate that exceeds the rate of destruction of these particles. A peculiar process of the latter type plays an important contributory part in engine knock. Local ignition, as by a spark, results in the formation of a combustion wave which propagates through the explosive mixture in a manner analogous to Huyghen’s principle for the propagation of a light wave. Small sparks do not produce ignition. The minimum ignition repuirement of electric capacitance sparks in mixtures of methane or other hydrocarbons with oxygen and nitrogen is found to be only the spark energy. This is theoretically explained, and the minimum spark-ignition energy is shown to be a function of the burning velocity, the width of the combustion wave, and other variables of the gas mixture in agreement with experimental data. A combustion wave in a stream of explosive gas mixture becomes stationary, i.e., the flame becomes stable, when the burning velocity is equal to the gas velocity somewhere in the wave and is nowhere larger than the gas velocity. The mechanism is described by which the condition of equality of burning velocity and gas velocity is realized at the rim of a burner tube. It is shown that the limits for flash back and blowoff correspond to critical values of the gas-velocity gradient at the stream boundary. This applies equally to the outer boundary and any inner boundary formed by solid objects in the stream.