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Chang J.,Harbin Institute of Technology | Chang J.,Academy of Fundamental and Interdisciplinary science | Wang L.,Harbin Institute of Technology | Bao W.,Harbin Institute of Technology | And 3 more authors.
AIAA Journal | Year: 2014

Scramjet and ramjet propulsion are developing technologies for a future generation of hypersonic atmospheric and space vehicles. Unfortunately, scramjet engines are susceptible to a highly detrimental operation mode called unstart, which would cause an abrupt drop of both engine thrust and specific impulse and unsteady aerodynamic and thermal loads. The direct-connected experiment system runs in a blowdown mode. The high-pressure air was supplied by a big enough chamber, which can ensure that the effective run time reaches about 1 min. An air heating system, in which compressed air was heated by the combustion of alcohol, was located upstream of the supersonic nozzle. In the air heating system, additional oxygen was supplied to keep the oxygen content equal to that in the atmosphere. It is installed at the center of the combustor upper wall next to the downstream of the strut. The plasma torch is turned off as long as the ignition is successful, and so it works for less than 1 s in the ignition period of every experiment.

Chang J.,Harbin Institute of Technology | Chang J.,Academy of Fundamental and Interdisciplinary science | Wang L.,Harbin Institute of Technology | Bao W.,Harbin Institute of Technology
49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference | Year: 2013

Hysteresis phenomenon in ramjet/scramjet was studied seldom although it has frequently been observed in aerodynamic experiments. The current works aim to investigate experimentally the hysteresis phenomenon in a scramjet engine that is caused by excessive heat release from combustion. The experiments were conducted in a direct-connect scramjet engine in Mach 3.0 flow. To determine the hysteresis characteristics, many runs under different changes in fuel equivalence ratio were carried out. The experimental results show that there exists an obvious hysteresis phenomenon in mode transition between inlet start and unstart, and the changes in fuel equivalence ratio have a little effect on hysteresis phenomenon. Thus, a prior knowledge of hysteresis effects will benefit the restart control. Moreover, the hysteresis effect has a great effect on unstart control, which demands a far reduction in fuel for inlet restarting.

Chang J.,Harbin Institute of Technology | Chang J.,Academy of Fundamental and Interdisciplinary science | Wang L.,Harbin Institute of Technology | Bao W.,Harbin Institute of Technology | And 4 more authors.
Journal of Propulsion and Power | Year: 2012

Unstart flows of a hypersonic inlet were experimentally studied at freestream Mach number of 4.5-6.0. With the aid of high-speed schlieren and time-accurate pressure measurements, the unsteady flow processes of the entire inlet, including the shock system motions and the surface pressure fluctuations, were recorded and discussed. The started flowfield analysis was conducted first, and then the unstarted flowfield was analyzed by using the unsteady pressure signals and schlieren pictures. Results indicate that two novel oscillatory patterns were observed in comparison with the past reported inlet buzz patterns. One is a mixed oscillatory pattern that mixes the "big buzz" with "little buzz," and the other is a nonoscillatory violent pattern. These novel findings on oscillatory patterns of hypersonic inlet can provide more insight on inlet buzz mechanism, prediction, and control. Copyright © 2012 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc.

Wei X.Q.,Harbin Institute of Technology | Zhang X.J.,Academy of Fundamental and Interdisciplinary science | Yu H.,Harbin Institute of Technology | Song S.M.,Harbin Institute of Technology
Proceedings of the 2nd International Conference on Intelligent Control and Information Processing, ICICIP 2011 | Year: 2011

The particle filter is a Monte Carlo method that allows us to treat any probability distribution, nonlinear and non-Gaussian. However the choice of the proposal distribution is the most critical problem. Unscented particle filter (UPF) uses UKF to generate and propagate the Gaussian distribution which provides a better approximation to the optimal conditional proposal distribution. It is not practical to fulfill the requirement for large-scale problems that the number of the sigma points will be larger than twice the degree-of-freedom of the system model. To overcome this difficulty, a new particle filter equipped with ensemble unscented Kalman filter (EnUKF) is proposed with the name EnUPF. The analyses indicate that EnUPF needs less computational cost and simulation validate the similar performance to UPF. © 2011 IEEE.

Jiao X.,Harbin Institute of Technology | Chang J.,Academy of Fundamental and Interdisciplinary science | Wang Z.,Harbin Institute of Technology | Yu D.,Harbin Institute of Technology
AIAA Journal | Year: 2015

A viscous numerical simulation was performed to study the forebody shock reflection at the cowl under the condition of inflow Mach number higher than the design value for different forebody/cowl configurations. With the help of shock reflection theory and numerical simulation, it was found that the shock reflection changed from overall regular reflection wave configuration to overallMachreflection wave configuration as the cowl angle decreased or the ramp angle increased. Mach reflection in this situation would be harmful; it could result in the shock propagating forward to cause a shock detachment at the cowl lip (the so-called local unstart of inlet in this paper). And the local unstart of inlet essentially resulted from the transition of forebody shock reflection from overall regular reflection to overall Mach reflection at the cowl. It was also found through comparison with inviscid analysis that the viscous effect had to be considered in the local unstart of inlet for practical applications. The obtained results would be useful for the design of hypersonic forebody/cowl configurations.

Qiao J.S.,Beijing Institute of Technology | Zhang C.Y.,Beijing Institute of Technology | Yin X.J.,Academy of Fundamental and Interdisciplinary science | Sun K.N.,Academy of Fundamental and Interdisciplinary science
Advanced Materials Research | Year: 2014

Mn-Ce based catalysts doped with transition metal were synthesized via a sol-gel method for low-temperature Selective catalytic reduction DeNOx. NOx conversion of these catalysts was evaluated under 100 °C -300 °C. H2-Temperature Programmed Reduction was used to investigate the reduction capability effect on NOx conversion. On this basis, sulfur resistance of catalysts was analyzed and Fourier Transform Infrared (FI-IR) spectra were used to discuss sulfur poisoning mechanism of catalysts. The results indicated that NOx conversion of catalysts was Mn-Ce-W0.03 ≈ Mn-Ce-Y0.03 > Mn-Ce-Zr0.03 > Mn-Ce >Mn-Ce-La0.03 > Mn-Ce-Pr0.03.W, Zr, Y elements was doped to improve catalytic activity at low-temperature and enhance anti-sulfur ability of catalysts. Especially, W element can restrain sulfate formation and reduce the channel blocking of the catalyst and Mn-Ce-W0.03 catalyst displays optimal performance of resistance to sulfur poisoning. © (2014) Trans Tech Publications, Switzerland.

Shen Y.,Tianjin University | Shen Y.,CAS National Center for Nanoscience and Technology | Zeng L.,CAS National Center for Nanoscience and Technology | Lei D.,Tianjin University | And 9 more authors.
Journal of Materials Chemistry | Year: 2011

The nanoporous network formed by 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) was used as the host nanoporous network. It has been identified that a variety of guest molecules (such as triphenylene, 1-phenyloctane and copper(ii) phthalocyanine (CuPc)) can be dispersed in this template to form binary supramolecular architectures, which were studied by scanning tunneling microscopy (STM). It is interesting to observe that the host network can adjust itself in response to the molecular size and shape of the guest, and the guest molecules can be excluded by some other guest molecules. The dynamics of CuPc molecules entrapped in TCDB is reported. The STM images as well as the density-functional theory (DFT) calculations reveal that the guest selectivity depends not only on geometry of guest molecules, but also on their adsorption energy in host networks. © 2011 The Royal Society of Chemistry.

Li Y.,CAS National Center for Nanoscience and Technology | Wan J.,Hangzhou Normal University | Deng K.,CAS National Center for Nanoscience and Technology | Han X.,CAS Beijing National Laboratory for Molecular | And 5 more authors.
Journal of Physical Chemistry C | Year: 2011

We have designed and synthesized one molecular building block, an aromatic trialdehyde derivative with three aldehyde groups, to form a potentially active structure. The scanning tunneling microscopy (STM) images show that the trialdehyde derivative forms lamellar structures. By the addition of active reactant, 5-aminoisophthalic acid, it is found that the structure of the adlayer can be transformed from lamellar to hexagonal structure as was expected. The structural formation of molecular networks is attributed to the condensation reaction between aldehyde and amine. Density functional theory (DFT) calculations reveal the observation of structural transformation at the solid/liquid interface due to the more stable adsorption of the triimine product than that of the trialdehyde derivative. © 2011 American Chemical Society.

Lei S.,Catholic University of Leuven | Lei S.,Academy of Fundamental and Interdisciplinary Science | Tahara K.,Osaka University | Adisoejoso J.,Catholic University of Leuven | And 3 more authors.
CrystEngComm | Year: 2010

Surface-confined porous molecular networks can be formed by self-assembly at the liquid-solid interface by controlling the subtle interplay between molecules, solvent and substrate. Typically, directional interactions such as hydrogen bonding or metal-ligand interactions are at play in defining the topology of the networks. However, porous molecular networks maintained only by van der Waals interactions are at the focus in this Highlight. The liquid-solid interface at atomically flat conductive substrates such as graphite is an excellent medium to support the self-assembly of alkylated molecules. Molecular symmetry defines the shape of the pores, ranging from diamond to honeycomb and Kagomé. Solvent often plays an important role and sometimes several porous and non-porous structures are formed. The solute concentration is a key factor too, the formation of porous patterns is favoured at low concentrations. These pores, with diameters ranging from about three nanometres to more than seven nanometres, can be filled with guest molecules. In some cases, these porous topologies can only be formed upon addition of template molecules, which direct the structural transformation from a high-density to a low-density, i.e. porous, phase. The template molecules stabilize the pores. Following appropriate design principles, multicomponent networks can be formed, containing up to four different organic molecules. © 2010 The Royal Society of Chemistry.

Lei S.,Academy of Fundamental and Interdisciplinary Science | Yang Y.,CAS National Center for Nanoscience and Technology | Zeng Q.,CAS National Center for Nanoscience and Technology | Wang C.,CAS National Center for Nanoscience and Technology
Langmuir | Year: 2011

The morphology of the composite film of organic semiconductors determines the properties and performances of devices to a large extent. In this work, we present a combined AFM and STM study on the interfacial structures of CuPcOC8 and CuPcOC8/PmPV composite films on graphite surface. For CuPcOC8 thin films, the face-on epitaxial growth of CuPcOC8 could persist within 3 to 5 monolayers and the formation of π-π stacked columns will occur with edge-on configuration when the film thickness further increases. For the CuPcOC8/PmPV composite film with 1:1 weight ratio, STM results reveal a preferential adsorption of PmPV on graphite surface, while AFM results indicate the phase segregation in the upper layer. STM also reveals in the molecular scale good compatibility of CuPcOC8 with PmPV. © 2011 American Chemical Society.

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