Hysteretic behavior induced by an electroacoustic feedback loop in a thermo-acousto-electric generator

An active control method of the spatial distribution of the acoustic field is applied in a thermo-acousto-electric generator. An auxiliary acoustic source is used to force the self-sustained thermoacoustic oscillation in order to control the thermoacoustic amplification. The auxiliary source consists of a loudspeaker, located inside the loop-tube close to the main ambient heat exchanger, and supplied with a delayed signal through an electric feedback loop, comprising a phase-shifter and an amplifier, connected to a reference microphone. Experiments are performed on a prototype engine working with air at a static gauge pressure of 5 bars. Experimental results demonstrate how it is possible to tune the acoustic oscillations in order to increase the global performance of the generator, compared to the case without control, as well as the existence of a hysteretic behavior induced by the electroacoustic feedback loop itself, which leads to a discrepancy between the onset heat input and the offset one.     

A new green system of HPW@MOFs catalyzed desulfurization using O2 as oxidant

A series of crystalline compounds were obtained from simple one-step hydrothermal reaction of copper nitrate, benzentricaboxylate and different Keggin polyoxometalates. Phosphotungstic acid immobilized in host matrix was selected for the first time as a recyclable and efficient catalyst in oxidative desulfurization process, under eco-sustainable conditions supported by the green oxidant O₂ and the green extracting agent distilled water. The efficiency of desulfurization with air was studied and it is possible to use air as green oxidant in desulfurization. Moreover, the catalyst is effective for the desulfurization of real diesel.     

Deep desulfurization of diesel by selective oxidation using amphiphilic paradodecatungstate catalyst

An amphiphilic paradodecatungstate catalyst, [(C₁₈H₃₇)₂N(CH₃)₂]₉[NaH₂W₁₂O₄₂] was prepared and characterized by Fourier transform infrared spectroscopy, UV–visible spectrum, differential thermal analysis, and thermogravimetric analysis. The amphiphilic catalyst exhibits very high catalytic activity that dibenzothiophene (DBT) in model diesel can be oxidized into dibenzothiophene sulfones using hydrogen peroxide as an oxidant. The reactivity of sulfur compounds decreased in the order of DBT > 4,6-DMDBT > BT > 5-MBT. The reaction rates of these sulfur compounds are sensitive to the electron density on sulfur atoms and the steric hindrance of the substituted groups of sulfur compounds. The sulfur level of a commercial diesel after desulfurization can drop from 200 ppm to about 12 ppm.     

关于教材中热力学第二定律的若干逻辑问题

指出了一些物理化学教材在叙述热力学第二定律时存在的若干逻辑问题,表明它们违反了逻辑学中的同一律、不矛盾律和充足理由律。并从历史的角度简述了Carnot循环和Carnot机效率公式的由来。     

基于STAF自动化测试框架的研究与应用

随着软件功能实现技术越来越复杂,软件测试领域迫切需要具有自动化、多平台、开销小的自动化测试框架,STAF的出现很好地解决了这个问题。提出一种基于STAF的自动化测试框架,并进行模拟实践,采用ATT工具设计自动测试引擎,通过模拟实验测试,构建基于STAF的自动化测试框架。测试结果显示：在不同环境下,该框架均具有软件测试自动化程度高、测试效率高,易于管理、维护和可扩展等优点。     

相对主元分析在船舶机舱监控系统的应用

目前船员对于船舶状况、航行状态等的判断主要还是依靠经验,难免会出现不恰当的决策,造成不必要的人力、财力的损失;针对这一问题提出并开发了一套融入相对主元分析船舶机舱监控系统;该系统除了具有常规机舱监控系统功能外,还能实现故障监测功能;协助管理人员进行系统故障的分析,从而更好地保证船舶航行的安全与效率,减少人为误操作带来的事故问题;增强了船舶监控系统的功能,大大提高了人员的工作效率减轻了人员的劳动强度;其设计满足船级社的定期无人机舱值守操作,为机舱监控系统的设计提供了一种新的思路。     

Understanding in-cylinder soot reduction in the use of high pressure fuel injection in a small-bore diesel engine

This study shows how soot particles inside the cylinder of the engine are reduced due to high pressure fuel injection used in a light-duty single-cylinder optical diesel engine fuelled with methyl decanoate, a selected surrogate fuel for the diagnostics. For various injection pressures, planar laser induced incandescence (PLII) imaging and planar laser-induced fluorescence of hydroxyl (OH-PLIF) imaging were performed to understand the temporal and spatial development of soot and high-temperature flames. In addition, a thermophoresis-based particle sampling technique was used to obtain transmission electron microscope (TEM) images of soot aggregates and primary particles for detailed morphology analysis. The OH-PLIF images suggest that an increase in the injection pressure leads to wider distribution of high-temperature flames likely due to better mixing. The enhanced high-temperature reaction can promote soot formation evidenced by both a faster increase of LII signals and larger soot aggregates on the TEM images. However, the increased OH radicals at higher injection pressure accelerates the soot oxidation as shown in a higher decreasing rate of LII signals as well as dramatic reduction of the sampled soot aggregates at later crank angles. The analysis of nanoscale carbon layer fringe structures also shows a consistent trend that, at higher injection pressure, the soot particles are more oxidized to form more graphitic carbon layer structures. Therefore, it is concluded that the in-cylinder soot reduction at higher injection pressure conditions is due to enhanced soot oxidation despite increased soot formation.     

In-flame soot particle structure on the up- and down-swirl side of a wall-interacting jet in a small-bore diesel engine

This study shows how the structure of soot particles within the flame changes due to the relative direction of the swirl flow in a small-bore diesel engine in which significant flame–wall interactions cause about half of the flame travelling against the swirl flow while the other half penetrating in the same direction. The thermophoresis-based particle sampling method was used to collect soot from three different in-flame locations including the flame–wall impingement point near the jet axis and the two 60° off-axis locations on the up-swirl and down-swirl side of the wall-interacting jet. The sampled soot particle images were obtained using transmission electron microscopes and the image post-processing was conducted for statistical analysis of size distribution of soot primary particles and aggregates, fractal dimension, and sub-nanoscale parameters such as the carbon layer fringe length, tortuosity, and spacing. The results show that the jet-wall impingement region is dominated by many small immature particles with amorphous internal structure, which is very different to large, fractal-like soot aggregates sampled from 60° downstream location on the down-swirl side. This structure variation suggests that the small immature particles underwent surface growth, coagulation and aggregation as they travelled along the piston-bowl wall. During this soot growth, the particle internal structure exhibits the transformation from amorphous carbon segments to a typical core–shell structure. Compared to those on the down-swirl side, the soot particles sampled on the up-swirl side show much lower number counts and more compact aggregates composed of highly concentrated primary particles. This soot aggregate structure, together with much narrower carbon layer gap, indicates higher level of soot oxidation on the up-swirl side of the jet.     

Differences between PREMIER combustion in a natural gas spark-ignition engine and knocking with pressure oscillations

PREMIER (PREmixed Mixture Ignition in the End-gas Region) combustion occurs with auto-ignition in the end-gas region when the main combustion flame propagation is nearly finished. Auto-ignition is triggered by the increases in pressure and temperature induced by the main combustion flame. Similarly to engine knocking, heat is released in two stages when engines undergo this type of combustion. This pattern of heat release does not occur during normal combustion. However, engine knocking induces pressure oscillations that cause fatal damage to engines, whereas PREMIER combustion does not. The purpose of this study was to elucidate PREMIER combustion in natural gas spark-ignition engines, and differentiate the causes of knocking and PREMIER combustion. We applied combustion visualization and in-cylinder pressure analysis using a compression–expansion machine (CEM) to investigate the auto-ignition characteristics in the end-gas region of a natural gas spark-ignition engine. We occasionally observed knocking accompanied by pressure oscillations under the spark timings and initial gas conditions used to generate PREMIER combustion. No pressure oscillations were observed during normal and PREMIER combustion. Auto-ignition in the end-gas region was found to induce a secondary increase in pressure before the combustion flame reached the cylinder wall, during both knocking and PREMIER combustion. The auto-ignited flame area spread faster during knocking than during PREMIER combustion. This caused a sudden pressure difference and imbalance between the flame propagation region and the end-gas region, followed by a pressure oscillation.     

Infrared radiation characteristics of liquid oxygen/kerosene rocket engine plume with different number of nozzles

A method for calculating the liquid oxygen (LOX)/kerosene rocket engine plume infrared radiation characteristics was proposed, infrared radiation characteristics of the gas oxygen/kerosene model engine were studied by simulation and experiment, and the accuracy of the method was proved. On this basis, studies on infrared spectral radiation characteristics and infrared imaging characteristics of single- and double-nozzle 120?ton thrust LOX/kerosene engine plume were carried out. It is found that, the engine nozzle number can be determined according to infrared imaging characteristics of the engine plume at the appropriate detection angle. Compared to using 2–5?µm band, the infrared radiation imager with clearer plume structure can be obtained using the spectral band such as 2.7 and 4.3?µm bands. The change in the detection angle and the increase in the engine number will have a significant effect on the infrared radiation intensity of the LOX/kerosene engine plume, but they will not change the infrared spectral radiation characteristics.