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41.
Performance enhancement of a pulse detonation rocket engine 总被引:4,自引:0,他引:4
Jian-Ling Li Wei Fan Chuan-Jun Yan Hong-Yan Tu Kai-Cheng Xie 《Proceedings of the Combustion Institute》2011,33(2):2243-2254
Utilizing liquid kerosene as the fuel, oxygen as oxidizer and nitrogen as purge gas, a series of multi-cycle detonation experiments was conducted to improve the performance of pulse detonation rocket engine (PDRE). In order to improve the performance of the engine, it is crucial to develop an effective DDT enhancement device with less flow loss and higher survival in hostile detonation tube; therefore, three spiraling internal grooves were tested. The three spiraling internal grooves were semicircle, square and inversed-triangle grooves, respectively. The results showed that the spiraling internal groove can effectively enhance DDT and prolong the operation time of PDRE. The effect of groove shape on thrust enhancement of PDRE and the optimum length of spiraling groove were then investigated. To improve the detonability of liquid kerosene and prolong the durability of PDRE, experiments on the kerosene preheating based on active cooling were conducted. The results demonstrated that with the aid of fuel preheating, the detonation initiation time for liquid kerosene was noticeably reduced and a fully-developed detonation wave was achieved in the position away from igniter 4.67 times the diameter of the detonation tube. By adding the additive to liquid kerosene, the detonation initiation time from 0.75 ms decreased to 0.34 ms and the detonability of fuel was dramatically improved. Finally, experiments were conducted to investigate the effects of the operating frequency on the detonation parameters, the fill fraction and PDRE performance. The results indicated that detonation pressure and temperature vary with the operating frequency of PDRE, and the fill fraction has a significant influence on the specific impulse of PDRE. With the strategy of partial filling in detonation tube, the specific impulse can be remarkably enhanced. 相似文献
42.
43.
In the present study, a microwave-assisted extraction method has been investigated for the extraction of persistent organochlorine pesticides from sediment in comparison to the classical Soxhlet extraction. The extraction procedure has been screened by a complete factorial design for statistically significant parameters. Thereafter, the identified parameters, composition of extraction solvent (mixtures of n-hexane-acetone), extraction temperature and time were optimized by a Box-Behnken design. Finally, the optimized microwave-assisted procedure has been validated by extraction of two different matrix reference materials, a sediment and a mallow powder. The data obtained for both materials were in good agreement with those obtained by Soxhlet extraction and published values. Special emphasis has been given to an accurate determination of p,p′-DDT, since DDT is known as instable during GC-injection. In order to evaluate the DDT-degradation, 13C12-p,p′-DDT-solutions were analyzed and the degradation rates during GC-injection were calculated. Furthermore, 13C12-p,p′-DDT was added to the sediment samples prior to extraction and the degradation rates during the optimization experiment have been investigated. 相似文献
44.
An experimental investigation of the onset of detonation 总被引:2,自引:0,他引:2
An experimental configuration is devised in the present investigation whereby the condition at the final phase of the deflagration to detonation transition (DDT) process can be generated reproducibly by reflecting a CJ detonation from a perforated plate. The detonation products are transmitted downstream through the plate, generating a turbulent reaction front that mixes with the unburned mixture and that drives a precursor shock ahead of it at a strength of about M = 3. The gasdynamic condition that is generated downstream of the perforated plate closely corresponds to that just prior to the onset of detonation in the DDT process. The turbulence parameters can be controlled by varying the geometry of the perforated plate; thus, the condition leading to the onset of detonation can be experimentally investigated. A one-dimensional theoretical analysis of the steady wave processes was first performed, and the experimental results show good agreement, indicating that the present experimental condition can be theoretically described. Two different detonation tube geometries (one with a square cross-section of 300 mm by 300 mm and the other with a circular cross-section of 150 mm) are used to demonstrate the independence of the tube diameter at the critical condition for DDT. Perforated plates with different hole diameters (d = 8, 15, and 25 mm) were tested, and the hole spacing to hole diameter ratio was maintained at 0.5. Different hydrogen–air mixtures were tested at normal temperature and pressure. For the plate with 8 mm holes, the onset of detonation is never observed. For the plate with 15 mm holes, successful initiation of a detonation is achieved for 0.8 < < 1.75 in both detonation tubes. For the plate with 25 mm holes, detonation initiation is observed for 0.7 < < 2.1 in the square detonation tube and for 0.8 < < 1.6 in the smaller circular detonation tube. 相似文献
45.
We model interactions of a premixed flame with incident and reflected shocks in a rectangular shock tube using three-dimensional (3D) reactive Navier–Stokes numerical simulations. Shock-flame interactions occur in the presence of boundary layers that cause the reflected shock to bifurcate and form a reactive shock bifurcation (RSB), which contains a flame in the recirculation zone behind the oblique shock. The recirculation zone acts as a flame holder thus attaching the flame to the shock in the vicinity of the wall, and providing a mechanism for a detonationless supersonic flame spread. The accelerated burning induced by an RSB, and Mach stems that may result from RSB–RSB interactions, promote hot-spot formation, and eventually accelerate deflagration-to-detonation transition. Schlieren-type images generated from the simulation results show that the 3D structure of an RSB may not always be easily recognized in experiments if the RSB is attached to the surface of the observation window. The main 3D effect observed in the simulations is caused by the presence of the second no-slip wall in a 3D rectangular channel. Two RSBs that form at adjacent walls interact with each other and produce an oblique Mach stem between two oblique shocks. The oblique Mach stems then interacts with a central Mach stem that forms near symmetry plane, and this interaction creates a hot-spot that leads to a detonation initiation. 相似文献
46.
Vadim N. Kurdyumov 《Combustion Theory and Modelling》2016,20(6):1046-1067
We examine the dynamics of premixed flames in long, narrow, adiabatic channels focusing, in particular, on the effects of gas compressibility on the propagation. Recognising the importance of the boundary conditions, we examine and compare three cases: flame propagation in channels open at both ends, where the pressure must adjust to the ambient pressure at both ends and the expanding gas is allowed to leave the channel freely, and flame propagation in channels that remain closed at one of the two ends, where the burned/unburned gas remains trapped between the flame and one of the two walls. Earlier studies have shown that a flame accelerates when travelling down a narrow channel as a result of the combined effects of wall friction and thermal expansion. In the present work we show that compressibility effects enhance the transition to fast accelerating flames in channels open at both ends and in channels closed at the ignition end. In both situations, the accelerating flames could reach values that, depending on the effective Mach number, are as large as fifty times the laminar flame speed. In contrast, when the channel is closed at the far end, the acceleration is limited and the propagation speed is damped as the flame approaches the far boundary. Moreover, we show that, in channels closed at their ignition end, the flame in sufficiently long channels evolves into a steadily propagating compression-driven flame. The propagation speed of these flames depends exponentially on the constant-volume equilibrium temperature, which is higher than the (constant pressure) adiabatic flame temperature, and is therefore larger than for ordinary isobaric flames. Fast propagating compression waves cannot emerge in channels that remain open at their ignition end because of the reduced pressure forced by the open boundary. 相似文献
47.
A correlation between the electronic structure and biological activity of chosen dichlorodiphenyltrichloroethane (DDT)-type insecticides: 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane, 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene, 2,2-bis(4-chlorophenyl)ethanoic acid and 4,4'-dichlorobenzophenone (used in agriculture) has been analysed on the basis of the (35)Cl-nuclear quadrupole resonance (NQR) spectroscopy. The (35)Cl-NQR resonance frequencies measured at 77 K have been correlated with the lethal dose (LD(50)) parameter that characterises the biological activity of these insecticides. 相似文献
48.
Keisuke Aizawa Satoru Yoshino Toshio Mogi Hiroumi Shiina Yuji Ogata Yuji Wada A. Koichi Hayashi 《Shock Waves》2008,18(4):299-305
While extensive studies have been conducted concerning the formation of detonation waves in various combustible gaseous mixtures
under static conditions since the 1950s, there is very little experimental work on simple flowing systems. In this study,
experiments on the deflagration to detonation transition (DDT) of a hydrogen–air flow system were carried out to see the effects
of tube diameter, equivalence ratio, and flow types in a premixed and non-premixed flow. Tube diameters used were 25, 50,
and 100 mm. The premixed experiments show that the larger tube diameter provides a wider range in run-up distance, reduction
of L
DDT/D (ratio of the run-up distance, L
DDT to tube diameter), and expansion of the detonable concentration limit by spreading the cell width. The result of the non-premixed
experiments show that similar values of the run-up distance to the premixed experiments are obtained at an equivalence ratio
of about 1.0, however, fluctuations of DDT occur near the DDT concentration limit. Under laminar flow conditions at a Reynolds
number of less than 2,300, the difference between the two systems could not be observed. However, when the Reynolds number
increases towards turbulent conditions, the DDT run-up distance decreases compared to that of static flow conditions.
This paper is based on work that was presented at the 21st International Colloquium on the Dynamics of Explosions and Reactive
Systems, Poitiers, France, July 23–27, 2007. 相似文献
49.
研究了肉桂皮中六六六、滴滴涕农药残留量的测定方法。以丙酮-石油醚混合溶剂为提取剂,旋涡振荡提取,采用固相萃取技术对提取液净化,优化洗脱溶剂的比例和用量,用气相色谱/微电子捕获检测器(μECD)测定。在优化条件下,BHC及DDT农药在10~1 000 μg/L质量浓度范围内线性关系良好,相关系数为0.995 8~0.998 1。2种农药在肉桂皮中的加标回收率为 92.1%~112%,相对标准偏差(RSD)为2.8%~8.1%,方法的检出限(LODs)为5.0×10-3~2.4×10-2 mg?kg-1,定量下限(LOQs)为1.3×10-2~6.0×10-2 mg?kg-1。方法具有简单、灵敏、选择性高、重现性好等优点。 相似文献
50.