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Using the particle-based laser scattering imaging technique, schlieren system and surface oil-flow visualization technique, the flow patterns and mixing characteristics of multiple injections with tandem multi-orifices and parallel multi-orifices in a supersonic vitiated air flow were investigated in this paper. All injectors have a declined angle of 30 degree to the freestream direction. The distance between the tandem orifices and that between the parallel orifices was varied. The experimental results showed that decreasing the distance between the tandem orifices will reduce the pressure and velocity of the stream upstream of the second jet, which results in the increase of the penetration height of the second injection and quick mixing of the whole field. For the small distance between the parallel multi-orifices, the bow shock waves upstream of the injected jets connect with each other and the air stream entered into the gap between the jets is not enough, resulting in the decrease of the mixing effect. Large distance between the parallel multi-orifices decreases the interaction between the injection jets. For the mixing enhancement, there should be a proper optimized distance between the parallel injection orifices.

Optimization structure of cladding radius and grating periods of long-period fiber grating(LPFG) was proposed,in order to achieve a high sensitivity of sensing the refractive-index of the external medium.Based on the coupled-mode theory of the LPFG,a theoretical analyzation was carried out between the cladding radius and grating period,and surrounding refractive-index,respectively.Effects of the variation of the cladding radius and grating period on the refractive-index sensing were discussed.Both of these parameters were found to be equivalently important to control the refractive-index sensing.Optimizing parameters of the grating are Λ=380 μm and rcl=17 μm in order to achieve a good apply of the LPFG with resonance wavelength in the 1.55 μm common application region.Variation of external medium refractive-index from 1.26 to 1.38 was tested and the achieved refractive-index sensing sensitivity is 0.000 12.Optimization structure of the LPFG achieves a good result.

In order to simultaneously detect the multi-solute concentrations in mixed solution,system for measuring the multi-solute concentrations in mixed solution using optical Fiber Fabry-Perot Resonator(FFPR) is proposed.The relation between FFPR interference transmission wavelength and concentrations of the mixed solution is analyzed theoretically.The measuring system consists of an InGaAs LED,fiber coupler,FFPR sensor,opto-electrical convertor,amplifier and spectrometer.The analytical equation between concentrations and interference transmission wavelengths is standardized by measuring the samples contain ethanol and glycerin.The action script 2.0 is used as the programming language according to the mathematical relation.The real-time variation of the concentration change is monitored by the PC.

A real-time solution concentration monitor based on Fabry-Perot interferometer is designed.The concentration variation measurement is realized by the F-P interferometer and optical fiber to transmit the image to the CCD.The relation between the variation of interference fringes of the F-P interferometer and the fluctuation of solution concentration is analyzed.The monitor system consists of He-Ne laser,optical fiber,planar F-P interferometer,arrayed CCD and PC is set up.Three different glycerin solution are used to verify the system design,and the experiment shows the system can provide a resolution on the order of 10-4 concentration variation.

In order to investigate the effects of fuel injection distribution on the scramjet combustor performance, there are conducted three sets of test on a hydrocarbon fueled direct-connect scramjet test facility. The results of Test A, whose fuel injection is carried out with injectors located on the top-wall and the bottom-wall, show that the fuel injection with an appropriate close-front and centralized distribution would be of much help to optimize combustor performances. The results of Test B, whose fuel injection is performed at the optimal injection locations found in Test A, with a given equivalence ratio and different injection proportions for each injector, show that this injection mode is of little benefit to improve combustor performances. The results of Test C with a circumferential fuel injection distribution displaies the possibility of ameliorating combustor performance. By analyzing the effects of injection location parameters on combustor performances on the base of the data of Test C, it is clear that the injector location has strong coupled influences on combustor performances. In addition, an inner-force synthesis specific impulse is used to reduce the errors caused by the disturbance of fuel supply and working state of air heater while assessing combustor performances.

In order to improve the performance of laser diode (LD) array pumping field in high-power solid state laser, an LD array pumping coupling system based on microlens array is used to achieve a high-uniformity pumping source with a longer transmission distance. The homogenizer has two structures based on microlens array, which are called diffracting homogenizer and imaging homogenizer. In this paper, we mainly study imaging microlens array due to its advantages of simple structure, better output homogeneity, flexibility of changing pumping field size, and insensitive to change in the input beam. First, the mathematical expression of the intensity distribution of target surface is derived based on the theory of geometrical optical. According to the geometrical optical formula, we obtain the relationship between the intensity distribution of target surface and system parameters, i.e., maximum incident angle of LD array, the distance between two microlens arrays, and the aperture and focal length of microlens. The boundary condition of microlens Fresnel number is derived based on the LD array beam parameters. Second, the influence of the number of microlens array elements on the output field homogeneity is studied theoreti-cally by the mathematical statistics method. As the input beam is considered to be divided randomly, the central limit theorem is employed to derive the mathematical expression of calculating the integrated output field non-homogeneity. The formula shows that the non-homogeneity is in inverse proportion to the root of the number of microlens array elements and the related maximum and minimum value of input field intensity distribution. And the spatial period of microlens array is designed to be unrelated to the spatial period of LD array to reduce the coherence of LD beam. According to the luminescence field parameters of an LD array consisting of 25 bars, an LD coupling imaging microlens array homogenizer test system is designed and constructed based on the theoretical analysis above. Another contrast system with a different microlens array which is not optimized is constructed at the same time. The coupling characteristics of two coupling systems with different microlens arrays are compared. The simulation and experimental test are carried out. The experimental result accords well with the simulated result, and thus proving the correctness of the theoretical studies. The coupling system with optimized microlens array shows better homogeneous effect with an output field non-homogeneity of 7.9%, and a coupling efficiency of 90.7%, proving the feasibility of the system for LD array pumping field homogenization.

The ignition transient phase in a model supersonic combustor with transverse fuel injection upstream of a cavity flame holder was experimentally investigated. Three types of ignition processes for scramjet startup were covered and compared: gaseous ethylene ignition, direct kerosene ignition by high-energy spark, and indirect ignition piloted by a preestablished ethylene flame. The flame propagation process and precombustion shock wave train dynamics were captured by using a high-speed camera and schlieren photography system. Three kinds of flame propagation failures were observed before a successful ignition result, after increasing the injection pressure to an ignitable pressure. The ignition limits of ethylene covered a much broader injection pressure range than ethylene when sparked directly in the cavity. The evolvement of the precombustion shock wave train for ethylene ignition indicated that the initiation of the ethylene flame was characterized by a subsonic flame expanding within the cavity. The enhanced mixing and evaporation process by the precombustion shock wave train provided another mechanism for piloted ignition, in addition to high-temperature heating of the ethylene flame.

A liquid nitrogen cooled dual-wavelength Tm, Ho:GdVO4 microchip laser is reported. The output dual wavelengths are at 2038.9 nm and 2050.1 nm. At each wavelength, the laser has a single longitudinal mode. The threshold power is nearly 20mW and the slope efficiency is 18.7%. The single longitudinal mode output power reaches 98 mW, and the ratio of power is about 60% (2038.9 nm) and 40% (2050.1 nm).

The ignition characteristic of the gas generator with Air/ Lf80-01 propellant combination is studied by experimental investigation in the paper. The results indicate that the ignition performance could be improved by adopting oxygen as the oxidizer instead of air or decreasing the water fraction in fuel for different propellant combination. The reason of the ignition difficulty of the gas generator is that it is difficult to stabilize the flame. Nozzle throat area, injectors’ structure, flameholders and operation parameters affect the flame stabilization of the gas generator. The capability of stabilizing the flame of the gas generator could be improved by decreasing the nozzle throat area, improving injectors’ atomization performance and fixing the V-gutter in combustion chamber, whereas it is helpless to stabilize flame by fixing the disturbing ring in combustion chamber. The capability of stabilizing the flame of the gas generator has close relation with total mass flow rate while little relation with the excess oxidizer coefficient. I. Introduction S the key subassembly of the ejector system, gas generator is widely applied in such fields as high altitude simulation experimental facility of the rocket engine, ground experimental system of the ramjet engine, pressure recovery system and vacuum simulation system1,2. The propellant of the gas generator in the paper is Air/Lf80-01 combination, where Lf80-01 is a special liquid fuel containing water. must be completed during The startup process of the gas generator includes 2 sub processes, i. e. the ignition as well as the flame propagation and flame stabilization. The torch igniter is adopted for ignition since its combustion gas has relative high temperature and energy. The research indicates that the fuel could be ignited successfully as soon as it goes into the combustion chamber when the torch works normally. However, the phenomenon often happens that gas generator extinguishes quickly after the torch is cut off during the ignition process. How to improve the ignition performance is the main problem of the gas generator.

* Doctor candidate, Department of Aerospace and Material Engineering, National Univ. of Defense Technology, E-mail:nudtliqing@gmail.com. † Associate Professor, Department of Aerospace and Material Engineering, National Univ. of Defense Technology. ‡ Professor, Department of Aerospace and Material Engineering, National Univ. of Defense Technology. Hot tests are conducted and start-up process is described and analyzed for large flux gas generator. The results suggest that:(1)In a certain extant increase of flux density does not affect the ignition delay,but it prolongs the flame spread time. (2)The time when oxygen and fuel are injected into the chamber has a great impact on the start-up; there exists an optimal interval of oxygen and fuel entering the combustion at which the rapid, smooth and safe start-up can be achieved.

Time fiducial laser is an important timing marker for different diagnostic instruments in high energy density physics experiments. The probe laser in velocity interferometer system for any reflector (VISAR) is also vital for precise shock wave diagnosis in inertial confinement fusion (ICF) research. Here, time fiducial laser and VISAR probe laser are generated from one source in SG-III laser facility. After generated from a 1064 nm DFB laser, the laser is modulated by an amplitude modulator driven by a 10 GS/s arbitrary waveform generator. Using time division multiplexing technology, the ten-pulse time fiducial laser and the 20 ns pulse width VISAR probe laser are split by a 12 multiplexer and then the time fiducial and VISAR pulses will be selected individually by acoustic-optic modulators. Using this technology, the cost for the system can be reduced. The technologies adopted in the system also include pulse polarization stabilization, high stable Nd: YAG amplification, high precision thermally controlled frequency conversion, fiber coupling, and energy transmission. The fiber laser system is connected to the Nd: YAG rod amplifier stage with polarizing (PZ) fibers to maintain the polarization state. The output laser of Nd: YAG amplification stage is coupled with different kinds of energy transfer fibers to propagate enough energy and maintain the pulse shape for the time fiducial and VISAR probe laser. The input and output fibers are all coupled to the rod amplifiers with high precision and being easy to plug and play for users. Since the time fiducial and imaging VISAR laser system is far from the front end room and located in the target area, the system also uses an arbitrary waveform generator (AWG) to generate the shaped ten-pulse time fiducial laser and 20 ns VISAR laser. This AWG and the other three AWGs used for the main laser pulse of SG-III laser facility will be all synchronized by 10 GHz clock inputs, realizing the smaller than 7 ps (RMS) jitter between the main laser pulse, time fiducial laser and VISAR pulse. After amplification and frequency conversion, the time fiducial laser finally generates 12 beam 2 and 4-beam 3 laserbeams, providing important reference marks for different detectors in the ICF experiments and making it convenient for the analysis of multiple diagnostic data. The VISAR laser pulse is also amplified by the Nd: YAG amplifiers and frequency-converted to 532 nm green light by a thermally controlled LBO crystal, with output energy larger than 20 mJ. Finally, the 532 nm VISAR probe laser beam is coupled with a 1-mm core diameter fused silica optical fiber, and then propagates 30 meters to the imaging VISAR system. The VISAR probe laser has been used in many high energy density physics experiments. The shock wave loading and slowdown processes are measured. Function for measuring velocity history of shock wave front movement in different kinds of materials can be also added to the SG-III laser facility.

*† ‡ Several kinetic models of combustion driven CO2 gas dynamic laser (GDL) are surveyed in order to provide an appropriate model in numerical simulating vibrational relaxation processes. Specially, two simpler models are analyzed detailedly for understanding vibrational energy transfer processes better. A four-vibration-five-temperature model is obtained to describe CO2-N2-H2O-CO-O2 system and its corresponding rate equations are given. The significance of vibrational relaxation time is emphasized by means of comparing calculational small signal gain (SSG) results and its effects of the rate coefficients on the calculational results are studied. Also, a mixed time model is put forward. Nomenclature g = small signal gain mn τ = the relaxation time for energy-level m relaxing to energy-level n 1 v = the symmetrical stretching mode of CO2 2 v = the doubly degenerate bending mode of CO2 3 v = the asymmetrical mode of CO2 4 v = the vibration mode of N2 M = any collision partner in the CO2 gas mixture system E1 = the energy density stored in the CO2 symmetrical stretching mode 1 v E2 = the energy density stored in the CO2 doubly degenerate bending mode 2 v E3 = the energy density stored in the CO2 asymmetrical mode 3 v E4 = the energy density stored in the N2 molecule 1