Adjoint-based optimisation of detonation initiation by a focusing shock wave

An optimisation study of a shock-wave-focusing geometry is presented in this work. The configuration serves as a reliable and deterministic detonation initiator in a pulsed detonation engine. The combustion chamber consists of a circular pipe with one convergent–divergent axisymmetric nozzle, acting as a focusing device for an incoming shock wave. Geometrical changes are proposed to reduce the minimum shock wave strength necessary for a successful detonation initiation. For that purpose, the adjoint approach is applied. The sensitivity of the initiation to flow variations delivered by this method is used to reshape the obstacle’s form. The thermodynamics is described by a higher-order temperature-dependent polynomial, avoiding the large errors of the constant adiabatic exponent assumption. The chemical reaction of stoichiometric premixed hydrogen-air is modelled by means of a one-step kinetics with a variable pre-exponential factor. This factor is adapted to reproduce the induction time of a complex kinetics model. The optimisation results in a 5% decrease of the incident shock wave threshold for the successful detonation initiation.

Estimation of the energy of detonation initiation in a hydrogen-oxygen mixture by a high-velocity projectile

The paper presents the results of a numerical study of the initiation of oblique detonation modes by a high-velocity projectile moving in an argon-diluted hydrogen?oxygen mixture. The simulation of oblique detonation wave modes showed that calculated and experimental flow patterns agree. The calculated detonation cell size agreed with experimental data. For the initial pressure Pst = 121 kPa and Pst = 141 a series of calculations were carried out for a different projectile diameters. The detonation initiation energy was estimated, and the results were compared with theoretical models.

COMPARISON OF SPARK CHANNEL EXPANSION IN HYDROGEN, OXYGEN AND NITROGEN

The results of the spark channel expansion simulation in various gases such as hydrogen, oxygen and nitrogen have been presented. Difference in thermodynamic properties of the various gases has been taken into account. Influence of a type of gas on the discharge current, the spark resistance, the energy deposited in the spark and the spark gas-dynamic expansion has been found out. Influence of initial species concentration in mixture of nitrogen, hydrogen and oxygen on detonation initiation by spark discharge has been discussed.