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The study of the ignition of a combustible mixture induced by means of an unsteady gas jet, at an initial temperature ranging from 700 to 3000 K, requires the construction of an original test facility which consists of a shock tube connected to a combustion chamber via an injector. With this new experimental setup, the ignition conditions of hydrogen-air ( + carbondioxide) mixtures, induced by a hot hydrogen-argon mixture, have been extensively studied, resulting in the determination of the ignition limits of these combustible mixtures, at an initial pressure and temperature of 100 kPa and 403 K respectively.

An original facility has been built, which consists of a shock tube connected to a combustion chambervia an injector, in order to analyze the ignition of a combustible mixture by a subsonic hot gas jet. Using this technique, it is shown that the stagnation temperature, just prior to ejection, of an H2−Ar mixture heated behind a reflected shock wave between 750 and 3000 K is the main parameter for igniting H2-air-diluent (CO2 or H2O) mixtures. The minimum stagnation temperature to ignite an H2-air mixture is approximately equal to the self-ignition temperature of this mixture. If CO2 or H2O is added to the combustible mixture, the minimum stagnation temperature must be increased. Beyond the critical diluent concentration, the mixture cannot be ignited whatever the initial jet temperature is. The temperature corresponding to the critical composition is called the minimum critical temperature. Under these conditions, the ignition limits by a hot jet constituted of a shock-heated H2−Ar mixture have been determined for H2-air-CO2 and H2-air-H2O mixtures. The conditions for which ignition is no longer observed for an H2-air-H2O mixture are the following: equivalence ratio φ=0.55, initial temperature and pressure, respectively, of 403 K and 100 kPa, and mol% H2O=48. The ignition limits are compared with the classical flammability limits. The influence of the composition of the hot gas jet on the ignition limits of H2-air-H2O mixtures has been analyzed and discussed. The present results provide a new assessment, particularly important for nuclear reactor safety.

The ignition limits of hydrogen-air mixtures diluted with steam or carbon dioxide have been studied in function of the mixture composition. Ignition was produced by a hot transient jet emerging from the downstream end of a shock tube and entering a combustion chamber. The spurted gas was heated by a reflected shock wave between 750 and 2800 K. The ejection velocity was subsonic. It was noticed that, with an initial jet at 2600 K, the ignition area of H2-Air-CO2 mixtures was larger than that of H2-Air-H2O mixtures. The ignition area was located inside the flammability range of these systems for rich mixtures. On the contrary, ignition limits and flammability limits were almost similar for lean mixtures. The chemical effect of steam on the ignition of these combustible systems are discussed.

The values of the detonation velocity of HN/sub 3/ in narrow tubes was measured and the time dependence of the heat flow into the tube walls and pressure profiles at three points along the tube length were obtained. A comparison of the results of the experiments with the theoretical calculations made on the assumption of various values of heat losses to the tube walls allows the authors to make conclusions about the location of the Chapman-Jouguet plane in which complete heat liberation occurs. On the basis of the experimental detonation velocity as a function of the heat release the heat losses at which the total value of heat release h=H-Q is determined. Additional information about the state of the gas behind the detonation wave was obtained by means of oscillograms of the pressure.

The detonation of gaseous HN 3 was studied in tubes of 1, 2, 5 and 10 mm i.d. in 1–25 Torr pressure range. Detonation velocities were measured by different techniques and wall heat fluxes were deduced from the temperature recordings given by thin-film platinum resistance gauges. The propagation and stability of the wave were studied down to the critical conditions of detonation quenching. For the lowest pressures and smallest diameters, the detonation velocity D ф is about 30% lower than D ∞ , the wave velocity independant of wall effect. D ∞ is some percents higher than D CJ , the Chapman-Jouguet velocity. The velocity deficit D ∞ − D ф is discussed in relation to the classical Fay's theory. The features of the temperature-time curves are analyzed in the whole range of pressure and diameter and especially near detonation limits. The heat transfer rates behind the detonation wave are computed from wall temperature recordings and compared to theoretical predictions provided by Mirels' theory. For the largest diameter and the highest pressures, experimental and theoretical values are in good agreement if a laminar regime in the boundary layer is assumed. In the narrowest tubes, near limit pressures, the temperature gradients behind the detonation wave are too large to use the ZND model and the Mirels' theory.

A pressure relief valve has been constructed which improves the ability to study fast reactions behind reflected shock waves, using a shock tube coupled with a time-of-flight mass spectrometer. This possibility is interesting, especially in order to study different reaction mechanisms depending on the pressure range. The valve, installed on the shock tube, allows a fast pressure decrease in the shock tube and, consequently, in the mass spectrometer ion source, after the observation of the concentration changes of the reacting mixture. A study has been made with this apparatus of the oxidation reaction of the stoichiometric mixture of methane and oxygen diluted in argon over a wide temperature range. Some results of this preliminary study are reported, in order to confirm the reliability of this original apparatus.

The detonation of gaseous HN3 was studied in tubes of 1, 2, 5 and 10 mm i.d. in 1–25 Torr pressure range. Detonation velocities were measured by different techniques and wall heat fluxes were deduced from the temperature recordings given by thin-film platinum resistance gauges. The propagation and stability of the wave were studied down to the critical conditions of detonation quenching. For the lowest pressures and smallest diameters, the detonation velocity Dφ is about 30% lower than D∞, the wave velocity independant of wall effect. D∞ is some percents higher than DCJ, the Chapman–Jouguet velocity. The velocity deficit D∞ – Dφ is discussed in relation to the classical Fay's theory. The features of the temperature-time curves are analyzed in the whole range of pressure and diameter and especially near detonation limits. The heat transfer rates behind the detonation wave are computed from wall temperature recordings and compared to theoretical predictions provided by Mirels' theory. For the largest diameter and the highest pressures, experimental and theoretical values are in good agreement if a laminar regime in the boundary layer is assumed. In the narrowest tubes, near limit pressures, the temperature gradients behind the detonation wave are too large to use the ZND model and the Mirels' theory.