Kunio Terao

Experimental Study on Cylindrical and Spherical Implosions

Cylindrically and spherically imploding detonation waves in a stoichiometric propane-oxygen mixture, produced in vessels of about 40 cm internal diameter having different convergent spaces, were experimentally investigated by applying a radially divergent detonation. The experimental results have shown that the ratio of the pressure P behind the imploding detonation waves to the initial mixture pressure P0 is related to the radial distance r from the implosion center to the detonation front approximately as follows:P/P0∝r-0.5 for the cylindrical implosion,P/P0∝r-1.0 for the spherical implosion in a conical space, andP/P0∝r-1.5 for the spherical implosion in a parabolic space. The pressure increase with the propagation of the imploding detonation is in every case higher than the theoretical one.

Temperatures in Imploding Detonation Waves

The spectroscopic and electron temperatures in spherically-imploding detonations in a stoichiometric propane-oxygen mixture were measured and the gas temperature behind the shock waves at cylindrical and spherical implosion fronts was estimated from the probability of triple shock formation. Both the spectroscopic and electron temperatures increase with the propagation of detonation as rapidly as the pressure. The temperature behind the shock waves is in agreement with the theoretical value. The results suggest that the high-pressure peak appears not behind the shock waves but in the combustion zone of the detonation. The reason for this is attributed to reactions caused by shock waves reflected at the vessel wall releasing more heat than in normal combustion, by other exothermic processes such as recombination.

Explosion Limits of Hydrogen-Oxygen Mixture as a Stochastic Phenomenon

The fluctuation in the induction period of ignition as well as the randomness of the ignition position in a hydrogen-oxygen mixture behind reflected shock waves was statistically investigated. It was proved that ignition is a stochastic phenomenon by comparing the ignition probability of the mixture obtained from a histogram of the induction period and that obtained from a histogram of the ignition position. The explosion limits of the hydrogen-oxygen mixture, the so-called explosion peninsula, was explained by the stochastic theory in which the mixture has a certain constant ignition probability.

Interaction between Combustion and Shock Waves

The pressure variations and the ionization of the gas behind a flame front propagating in a stoichionietric propane-air mixture through a plexiglass tube were measured by a piezoelectric pressure transducer and double-probe method, when shock waves produced by means of a shock tube propagated in the same plexiglass tube and collided with the flame. A remarkably high pressure increase and stimulation of ionization behind the flame front under the interaction with the shock waves were observed, and it was found that their values depended on the strength of the incident shock and the position of the shock front in relation to the flame front. These results are attributed to some exothermic reactions which follow the main normal combustion and produce detonation waves in the flame.

Experimental Study on a Propagating Flame by a Laser Light Scattering Method

The ionized state in a flame propagating in a stoichiometric propane-oxygen mixture was investigated by a laser light scattering method. The charged particles, H-ions, C-ions or O-ions and free electrons, having an anomalously high temperature from 104 to 105 K were observed on both sides of the flame front, i.e. in the front of the flame as well as behind it, where the adiabatic combustion temperature should be about 3000 K. The results suggest that the measured values of the electron and ion temperatures as well as those of the electron density fluctuate over a wide range.

Nuclear fusion reactor ignited by imploding detonation waves

In the focus of spherically imploding detonation waves propagating in a stoichiometric propane-oxygen mixture in a detonation chamber having an outer-diameter of 1 m an ion temperature of about 10/sup 8/ K is observed. The energy state is beyond the so-called Lawsons limit in which a nuclear fusion reaction can take place in deuterium-tritium mixture. Considering the experimental results, theoretical fusion reaction velocity and heat loss by radiation, the size of the detonation chamber in which a nuclear fusion can be initiated is estimated. Applying the detonation chamber, an introduction system of the fusion reaction and water as coolant and turbine driver gas, a nuclear fusion reactor much simpler than the Tokamak or laser fusion system is proposed.

Experimental Study on Suppression of Detonation Waves

In this experiment, detonation waves propagating in a stoichiometric propane-oxygen mixture through a channel containing an obstruction were investigated in order to clarify the cellular structure of the waves and also to find some methods for suppressing the detonation. The results suggest that triple shocks are formed by isochoric combustion accompanying spontaneous ignition behind the shock waves at the detonation front and that the propagation velocity must be decelerated to suppress the detonation, to the extent of keeping the temperature or the mixture so low that no spontaneous ignition takes place.

Die Wirkung des Bleitetraäthyls auf die Zündung des n-Heptan-Luft-Gemisches in Stoßwellen

The ignition delay behind reflected shock waves was measured for a pure n-heptane/air mixture and one containing tetraethyl lead. The ignition probabilities were obtained, from which the activation energies of ignition reaction were calculated. The effect of lead on ignition is discussed by considering the differences in the ignition probabilities and activation energies between these two mixtures. It is suggested that lead does not effect the ignition by its chain breaking action but its oxidation.

Die Wirkung der Kapazitäts- und Induktanzkomponente auf die Aktivierung des Gemisches bei der Funkenzündung in Gasen

The induction time to the beginning of ignition of n-hexane-air mixture by electric discharge was measured, in order to get the probabilities of ignition from its fluctuation. From these ignition probabilities the exciting energies of the spark were calculated and discussed upon the effect of two components, namely capacity component and inductance component, on the ignition.

An interpretation of the telegraph equation for animal movement near boundary wall

The telegraph equation with an additional drift term has been obtained from a one-dimensional asymmetric random walk model for an animal. If there is a boundary wall, a solution of this equation provides an exponential distribution decreasing from the boundary for the steady-state. The results suggest that the diffusion process governed by the Fokker-Planck equation can explain well the experimental position distributions of a goldfish, which decrease exponentially from the wall of the aquarium, just like the distribution of the atmospheric density on the earth under the gravity.