Toshitaka Fujiwara

Diode-laser tomography for arcjet plume reconstruction

Diode-laser absorption tomography is described with which the spatial temperature and the atomic number density distribution of a 3-kW class arcjet can be derived simultaneously by reconstruction of the absorption coefficient field of the arcjets argon exhaust plume. One can perform various parameter measurements by changing the arcjets mass-flow rates and discharge currents. The maximum temperature and atomic number density increase with the mass-flow rate and the discharge current. The trend for increase is not always found for a specific input power, although at a fixed mass-flow rate the power increases at that rate.

Effect of composition distribution on holographic temperature measurement of a diffuse flame

The application of phase shift holographic interferometry to non-intrusive temperature measurement of a laminar, axisymmetric, propane diffuse flame is investigated. In our previous work the effect of composition changes on the holographic temperature measurement of reacting flows was experimentally studied for cases with axisymmetric, propane, laminar premixed lean flames (PLFs) and partially premixed flames (PPFs). To further examine this effect, in this work the effect of the diffuse flame (DF) is investigated. It has been shown that for the DF, the composition distribution is the most complicated and the composition effect is more severe than that of the PLF and the PPF. In order to obtain accurate and satisfactory holographic results, it is necessary to measure the species concentration at lower flame heights, and to use linear interpolation of the molar refractivity at higher test sections.

Detonation Studies of High- Frequency- Operation Pulse Detonation Engine with Air/Hydrogen

An experimental study on pulse detonation engine (PDE) is conducted using hydrogen/air mixtures. Several key issues for PDE development, including valve operation, injection, mixing, filling, cycle repetition, ignition timing, DDT distance and propagation of detonation/quasi-detonation, are investigated. The fuel and oxidizer are injected into PDE from opposite sidewall directions to be well mixed by collision of two jets. The PDE performance is acquired to give the specific impulse about 2000 sec, which is measured from the pressure history on PDE head end. Operation at a maximum frequency 32 Hz is successfully performed. The deflagrationto-detonation transition (DDT) characteristics are measured in conjunction with operational frequency and ignition delay.

Experimental observation of oblique detonation waves around hypersonic free projectiles

We studied the oblique detonation waves around hypersonic projectiles. Projectiles (10 mm diameter, conical nose shape) were fired at hypersonic speeds (2.8 ± 0.1 km/s) into stoichiometric hydrogen-oxygen mixtures (pressure between 10 kPa and 50kPa, at room temperature T = 300.2 ± 1.4 K). The flowfields around the projectiles were visualized using a multi-frame schlieren technique. We made a comprehensive study of the oblique detonation wave phenomena around the hypersonic projectiles with variations in two parameters: the projectile nose shape and the initial gas pressure. The projectile nose cone open-angle was varied from 60° to 180°. The initial gas pressure was varied from 10 kPa to 50 kPa. Four types of combustion were observed. At the lowest initial gas pressure 10 kPa or at the smallest open angle 60°. two non-ignition types: a detached bow shock wave type and an attached bow shock wave type were observed. At the upper initial gas pressure and bigger opened-angle, an oblique detonation type was observed. The presence of an intermediate type (which we label a straw hat type, consisting of an oblique detonation + a shock induced bow combustion wave) was observed at 20 – 33 kPa and 90° – 120°. The shock shape of this type is similar to the shape of a typical straw hat. Using multi-frame schlieren pictures and comparing the pictures shot in two observation windows separated by a distance of 260 mm, we confirmed that the oblique detonation waves were steady within 92.5 μs. By detonation polar analysis, the heat release behind the detonation wave front was close to that of the theoretical Chapman-Jouguet detonation, (within 20 %, and in most cases within 10 %). It should be noted that the minimum curvature radius in the detonation wave of the straw hat type was a radius of 40 – 50 times the induction length of the detonation wave. We think this is a significant parameter in the phenomena.

A rotational temperature of oxyacetylene converging detonation

Abstract Converging cylindrical detonations are produced using a Perry-Kantrovitz-type experimental apparatus. The usual straight detonation tube is followed by the converging part, with the intermediation of the diverging part containing a cone. The converging part is 130 mm in diameter and 2.4 mm in depth. Equi-molar oxyacetylene mixtures at 28 Torr are adopted to produce the most stable detonations. It is observed that at higher pressures triple-shock intersections propagating in the in-depth directions and appearing when the detonation curves along the periphery of the converging section are not damped, whereas at lower pressures the reproducibility of the location of the collapsing center is deteriorated. In both cases the scatter of the geometrical collapsing center has exceeded the slit width adopted. The rotational temperature is measured by the multi-line method using CH 4315 A system (0,0) R branch, where the obscuring effects of continuous and other spectra are small. The measured temperature is about 20,000 ± 10,000°K, which is closer to those measured by Belokon et al. and Huni than to those by Knystautas et al. and Roberts et al. The scatter of the data is caused by the slight deviation of the collapsing point from the predicted one where the slit is located.

An absorption sensor system for arcjet multi-parameter measurements

Diode-laser absorption computerized tomography is applied to the diagnosis of the plume generated by an arcjet thruster. A protection stack is designed to carry a laser beam into the arcjet flow field at any location in the vacuum chamber. The experimental system is developed to reconstruct the maps of the temperature and the atomic number density by utilizing a small number of line-of-sight measurements. It has been demonstrated to be a convenient and useful method for the measurement of plume parameters and for monitoring the performance of the arcjet.

Radiation in a hypersonic shock layer generated around a projectile

Radiation emitted from the shock layer generated around a hypersonic flight model is experimentally investigated by using a ballistic range (two-stage light-gas gun). A polyethylene projectile of 1.2 cm in diameter is launched in this facility at the velocity of 5 km/sec (M=15), and the emission from the induced shock layer around the projectile is observed with a spectroscope. As a result, molecular band-spectra from NO and N2 are detected along with those from carboncontaining molecules. Total emission power is measured with a diode-type powermeter. In addition, dimension effect of the flight model is theoretically and numerically examined, and a scaling law on thermochemical structure of the shock layer is developed. It shows that the thickness of thermal boundary-layer formed on the model surface does not follow the conventional scaling law based on the reaction distance and on the energy relaxation distance. Finally, the radiative field around the projectile is numerically computed, and the total power emitted from the shock layer is estimated. From the comparison between computed and measured results, the validity of the calculation model is discussed.

Experimental Investigation of Plasma Thruster Parameter with Diode Laser Absorption Technique

The diode-laser absorption tomography is developed to derive the spatial temperature and atomic number density distribution by reconstructing the absorption coefficient field of argon plume exhausted by a 3-kW class arcjet plasma thruster. The simultaneous parameter measurements are performed with the various operations by changing its massflow rates and discharge currents. The maximum temperature and atomic number density increase with the massflow rate and the discharge current. The increase trend is not always found with the specific input power although at a fixed massflow rate there exists an increasing with it..

Spherical ignition of oxyhydrogen behind a reflected shock wave

Nonsteady one-dimensional hydrodynamic equations of plane and spherical symmetry are solved on the both sides of the extended second explosion limit of oxyhydrogen mixtures. Ignition is produced by the arrival and reflection of a shock wave at the shock tube end. Ignition delay, generation of pressure waves and development of subsequent reactions naturally result from the numerical integration of basic equations including twenty-two elementary reactions. It has become clear from the plane ignition model that at the wall itself the reaction is mild and produces no shock waves or shock-like discontinuity on either side of the extended second explosion limit. However, it is observed that the compression waves continue to build up and that in the meantime a detonation wave is formed at a distance of the order of centimeters from the reflection wall. The newly formed detonation soon catches up with the preceding shock wave and is merged into a single detonation wave. It is concluded from such results that the weak ignition observed by Meyer, Oppenheim and Vermeer is not the result of plane ignition. Spherical ignition from a point on the shock reflection wall is also simulated on both sides of the extended second explosion limit. It was found that for single spherical ignition of equimolar oxyhydrogen at 1000°K, mild reactions occur both below and above the second explosion limit. Although accumulation of pressure waves and acceleration of the reaction front are observed, their magnitudes are still considerably below the pressure and velocity of a self-sustaining detonation. Finally, some consideration is given to the origin of reaction centers. The possibility of statistical fluctuations of rate constants is discussed. It is shown numerically that order-unity change of the rate constant of O2+H→OH+O considerably affects the ignition delay of oxyhydrogen mixtures.