Shiro Taki

Homogeneous-dilution model of partially fueled simplified pulse detonation engines

A model for estimating the propulsive performance of a partially fueled simplified pulse detonation engine is proposed. The model has two significant advantages: no empirical parameter is required, and the model enables estimation of both the impulse and the duration during which the pressure at the thrust wall remains higher than its initial value. In the model, an objective partially fueled pulse detonation engine is replaced with the equivalent fully fueled pulse detonation engine. The equivalent pulse detonation engine is fully filled with a homogeneous mixture of the detonable and inert gases that separately fill the objective partially fueled pulse detonation engine. The performances of the equivalent fully fueled pulse detonation engine are instead estimated by a previously developed performance-estimation model for a fully fueled pulse detonation engine. The applicability of the model is examined by comparing the results of the model with numerical and experimental results in the cases where hydrogen or ethylene was used as fuel. Further, the applicability limits, which arose from replacement of the objective partially fueled pulse detonation engine with the equivalent fully fueled pulse detonation engine, are described.

Homogeneous-dilution model of partially-fueled pulse detonation engines

A model requiring no empirical parameter for estimating the propulsive performances of a partially-fueled (P-F) pulse detonation engine (PDE) was proposed. The model was developed based on a hypothesis that every performance parameters obtained by integrating phenomena in one cycle are predominantly determined by energetics only. In the model, an objective P-F PDE is replaced with the equivalent fully-fueled (F-F) PDE which is a hypothetical PDE fully filled with the homogeneous mixture of the detonable and inert gases filling the objective P-F PDE. And the propulsive performances of the equivalent F-F PDE are estimated by using a previously-developed performance-estimation model for a F-F PDE. By comparing the results of the model with those of numerical simulations and experiments, the applicability of the model was verified. As results, the model reproduced the numerical and experimental results within about 25%.

Numerical simulation of the unsteady processes in starting period of ram accelerator

The ram accelerator is a device to accelerate projectile up to hypervelocity in a tube filled with combustible gaseous mixtures. One of the most troublesome problems in operating facility is the difficulty to start. In order to improve the ram accelerator system in Hiroshima University, direct numerical simulations are carried using finite difference methods. A projectile and an igniter move at speed of 1200 m/s from an evacuated chamber into a ram acceleration tube, where hydrogen-oxygen-nitrogen gas mixtures are filled as combustible gases. When the ram acceleration tube is filled by nitrogen as a non-reactive gas, we got a numerical solution that the projectile fly without choking. When combustible gas mixtures are filled in the ram acceleration tube, we could not get a solution without detonation or quenching. Then, we introduce an ignition tube between the evacuated chamber and the ram acceleration tube. In the ram acceleration tube, undetonable but combustible gas mixtures are filled, while in the ignition tube, detonable gas mixtures are filled. The ignition tube works well in getting a very close solution to choking mode combustion.

Development of PDTE for CHP System Using Hydrocarbon Gas

Fundamental studies to develop pulse detonation turbine engines, ie. PDTEs powered by hydrocarbon gas, as high-emciency power generators for combined heat and power system CHP are curried out. A novel device, i.e. shock wave diffuser which converts a strong shock wave into a series of weaker shock waves to prevent the turbine blade damage is introduced, its performance being evaluated by experiments. The experimental results seem to promise successful application of the shock difiser for PDTEs. In addition, the detonability of blended fuel containmg low detonability gas like methane is examined, focusing upon the detonation cell sizes as an indicator of detonability.

EXPERIMENTS ON FLAME HOLDING POSITION OF THE FIN-LESS PROJECITLE IN RAM ACCELERATOR

Supersonic combustion flow around a projectile in a ram accelerator has been visualized and investigated by using the rectangular bore ram accelerator in Hiroshima University. The velocity range of the experiment is 1100 to 1350m/s, that is 0.77 to 0.93 of the velocity ratio to the C-J detonation velocity of the CH4-O?-CO2 mixture. In the present paper, the effects of the projectile velocity on the supersonic combustion flow around the projectile are discussed. In the present study, it becomes clear that the flame propagates quickly forward up to the front of the projectile when the projectile comes into the ignition tube, where easily ignitable gas mixture is filled. If the projectile velocity is enough high, the remained flame in boundary layer on the leading wedge of the projectile will be blew out and goes back to the rear part of the projectile. On the other hand, the flame front remains at the leading wedge, if the velocity is not so high. In the present experimental conditions, we can divide into three cases. When the projectile velocity is smaller than 1200m/s, ram acceleration occurs even through the leading flame front exists at the leading wedge. But the stronger leading shock wave, caused by the leading flame front, reduces the thrust. When the projectile velocity is 1200-1300m/s, the leading flame exits around the projectile shoulder. But because the thermal choking point is a little bit far from the projectile, the

Detonation drive pellet injector

A detonation drive pellet injector has been developed and tested. By this method the free piston is not necessary because the pellet accelerated the high pressure shock directly. In the experiment, the Teflon pellet (5 mm dia., 5 mm length) was accelerated by hydrogen, oxygen and dilution gas mixture detonation. When the gas pressure was only 500 kPa and the mixture rates of hydrogen, oxygen and helium were 3:6:1 or 3:6:0, the Teflon pellet speed was up to 747 m/s. Typical experimental results for 300 kPa of the initial gas pressure range are 78-92% of the one-dimensional calculational values. It showed that the pellet could be accelerated by a relative low pressure gas. When the helium dilution rate is larger than 20%, it was often found that the strong detonation speed is more than the Chapman-Jouguet speed. Then a pellet speed above 1100 m/s was obtained.