Development Of Detonation Research Articles

On the development of detonation with pre-ignition

Importance of pre-ignition to the development of detonation is examined on the basis of a wavedynamic analysis of schlieren photographs obtained by Schmidt, Steinicke and Neubert. Present results complement those published at the Seventh Combustion Symposium for the case without pre-ignition. Although a definite stimulating effect of pre-ignition has been noticed, characteristic features of both solutions being the same, it is concluded that progress of the process, expressed in terms of intermediate states that must be attained in the course of its development, is essentially the same in both cases.

Statistical Study of Accelerating Flames

Study of velocity fluctuations observed by means of ionization probes during the development of detonation reveals its significance as an indicator of physical characteristics of the flame. The scatter in time of arrival (the reciprocal of the velocity) was found normally distributed at an 85% probability level. The means and standard deviation were determined within 5% and 20%, respectively, at a confidence level of 90%. The intensity of scatter is interpreted consequently as indicative of the combustion front fluctuation that can be considered to delineate the ``effective flame thickness.'' It is found then that, as the flame accelerates, its effective thickness first increases, reaching a maximum in the vicinity of velocity overshoot, and then decreases, attaining finally a minimum, constant value when the steady detonation wave is established. An interesting bimodal distribution of scatter for the 2H2–02 mixture has been observed, indicating a possible existence of two alternative, independent modes for the development of the process.

Detonation overpressure in saturated knallagas-steam mixtures

Reflected pressures corresponding to the development of detonation in saturated mixtures of knallgas and steam at 100°C were measured. The maximum pressure observed was about three times that predicted for theoretical reflected detonation by solution of the Chapman-Jouguet detonation equations and equations for normal shock reflection. Composition limits defining non-reactive and detonatable regions for the particular experimental system employed were also determined. Some considerations applicable to the study of detonation in gaseous mixtures having long detonation stabilization distances are noted, and pressure/time records of different stages of the transition from flame to detonation are shown.

On the development of gaseous detonation—Analysisof wave phenomena

On the development of gaseous detonation—Analysisof wave phenomena

Water-Channel Analog to High-Velocity Combustion

Abstract This paper is a sequel to one presented in 1951, by the author (1). It was shown that during the development of detonation, the combustion zone which appears first in a unidimensional flow field as a single discontinuity, is later transformed into an unsteady, double discontinuity system, and it was demonstrated that such a transformation is necessary because of the restrictions imposed on the system by the dynamic boundary conditions. In the water channel the combustion-front discontinuity is simulated by a unidimensional source formed by admitting water from the bottom. By a proper selection of state parameters analogous relationships are derived to those between pressure and specific volume in a gaseous combustion system. Thus the consequences of restrictions imposed by dynamic boundary conditions on the propagation of combustion are illustrated in an analogous system which, being simpler in nature, is easier to understand. Moreover, the water-channel analog is utilized as an illustrative model of a system where controlled, stationary detonation could be achieved.

Gasdynamic analysis of the development of gaseous detonation and its hydraulic analogy

This research quantifies the evolution of pressure for fast burning regimes characterized by various degrees of compressibility and involving turbulent flames and shocks. The experimental exploration is conducted in a Turbulent Shock Tube facility, where the level of flame compressibility is controlled by varying the equivalence ratio of the hydrogen-air mixture. High-speed particle image velocimetry, chemiluminescence, schlieren, and pressure measurements are simultaneously acquired to capture the rise in stagnation pressure for various regimes from fast flames to shock-flame complexes. The pressure and velocity measurements are used to analyze combustion regimes on the Rankine-Hugoniot diagram that shows the flame-driven compression for a range of fast flame conditions evolving toward detonation onset. Various levels of compression are dependent on the level of shock-flame coupling and flame velocities. Lower degrees of compressibility show 52% efficiency of an ideal ZND cycle with 40% thermal efficiency, while shock-flame complexes are shown to produce 81% of the work produced by an ideal ZND cycle with 53% thermal efficiency.

Discussion: “A Contribution to the Theory of the Development and Stability of Detonation in Gases” (Oppenheim, A. K., 1952, ASME J. Appl. Mech., 19, pp. 63–71)

Discussion: “A Contribution to the Theory of the Development and Stability of Detonation in Gases” (Oppenheim, A. K., 1952, ASME J. Appl. Mech., 19, pp. 63–71)

A Contribution to the Theory of the Development and Stability of Detonation in Gases

Abstract The development of detonation of an explosive gas mixture contained in a constant-cross-section duct is analyzed on the basis of a unidimensional, gasdynamic treatment of a double-discontinuity combustion system. A steady and an unsteady system are considered, and it is shown that the latter yields an adequate explanation of the effect of coalition of the two discontinuities on the establishment and subsequent stability of the detonation wave. The locus of states behind the detonating combustion zone during the development of the process is determined and analyzed.

Gaseous Detonation. I. Initiation of Detonation

By means of piezoelectric gauges, a study has been made of the development of detonation from a shock wave propagated into a mixture. With a sufficiently strong shock, detonation above the stable velocity is immediately established which decays smoothly to the steady state. When the shock is weaker than required for detonation the phenomena which ensue depend upon the strength of the shock wave and the nature of the medium. A zone of combustion, accompanied by a build-up of the pressure, develops in the wake of the shock front. This may lead to a smooth acceleration of the latter until detonation is established; shock waves may be formed which overtake the front and cause detonation; or the initial shock may decay without detonation. The hydrodynamic properties of the medium are particularly important in determining the sequence of events. Composition and pressure limits are observed beyond which detonation cannot be initiated in any case. Near these limits there is always ``spin'' in the detonation, which appears on the pressure records as a periodic oscillation of the pressure for some distance behind the wave front. In these experiments the initiating shock wave was produced by a detonating mixture such as 2H2–O2 contained behind a Cellophane diaphragm. The strength of the shock wave was very much increased when this mixture was diluted with hydrogen.

Photographic investigation of flame movements in gaseous explosions. Parts IV, V and VI

In Part III of our previous memoir* upon “ Flame Movements in Carbonic Oxide-Oxygen Explosions ” experiments were described showing certain effects of superimposed “ shock waves ” upon flame-velocities up to the development of detonation in such explosions. Also the phenomenon of “ spin ” in the detonation of carbonic oxide-oxygen mixtures, first observed in 1926 by C. CAMPBELL and D. W. WOODHEAD, was illustrated, but its further discussion deferred pending the accumulation of more experimental evidence. In reviewing the experiments in ‘Nature’ the late Professor H. B. DIXON said they had revealed how shock waves catching up an accelerating flame, and vice versa , may impose a succession of “ uniform movements ” upon it, and how such waves ahead of the flame may set up “ detonation ” in explosions, a point of which, though formerly he had doubted, he had now been quite convinced.

X. Contributions to the history of explosive agents. —Second memoir

Since the publication of the experiments on the explosion of gun-cotton and other compounds and mixtures by detonation, which are detailed in a memoir submitted by me to the Royal Society in March 1869, this matter has received considerable practical development, and has also been made the subject of further scientific investigation, both in England and on the Continent. In continuing my researches into the conditions to be fulfilled for accomplishing the detonation of explosive substances, I have arrived at further results confirmatory of, and additional to, those described in my former memoir. I have also been led to pursue experiments bearing upon this subject in somewhat new directions; and I venture to believe that an account of the results arrived at may possess some value as tending to throw further light upon the behaviour and properties of explosive agents. The exceptional behaviour which I have described as being exhibited by certain explosive compounds when applied to the development of detonation, in comparison with other substances, to which they were not inferior as regards the force and heat developed by their explosion, has been confirmed by further experiment. It was stated by me that 0·32 grm. (5 grains) of mercuric fulminate, if applied under favourable conditions, suffice to develop the detonation of compressed gun-cotton, that 3·25 grms. (50 grains) of chloride of nitrogen appeared to be the minimum amount by which detonation of gun-cotton could be developed, that 6·5 grms. (100 grains) of iodide of nitrogen failed to produce this result, and that repeated trials with different quantities of nitroglycerine ranging up to 31·2 grms. (1 ounce) did not in any one instance result in the detonation of gun-cotton by that substance, although the mechanical force and heat developed by its explosion were at least fully equal to those brought into operation by corresponding quantities of the most violent of the above explosive agents.