某轮主机缸套异常磨粒磨损原因探讨

根据某轮主机缸套异常磨粒磨损的故障现象及故障发展过程,结合柴油机磨粒磨损机理,对该轮主机缸套异常磨粒磨损故障的原因进行了探讨与分析。分析表明：燃油中催化剂粉末含量偏高、燃油在贮存环节受到污染及燃油净化处理不当是造成此次故障的根本原因。据此提出了加强柴油机日常维护管理的措施。     

膨胀聚苯乙烯泡沫热氧化分解动力学研究

用非等温热重分析方法对膨胀聚苯乙烯泡沫的热氧化分解特性进行了研究.样品在空气气氛下由10,℃/min、20,℃/min、40,℃/min和50,℃/min共4个升温速率从室温加热至800,℃.分别使用积分等转化率方法中的Flynn-Wall-Ozawa(FWO)和Kissinger-Akahir-Sunose(KAS)方法以及基于动力学补偿效应的恒定动力学参数方法(invariant kinetic parameter method,IKP)计算膨胀聚苯乙烯非等温热氧化分解的动力学参数.由等转化率方法得到的结果可认为膨胀聚苯乙烯泡沫在空气气氛下主要为一步反应.FWO方法和KAS方法得到的平均活化能与IKP方法得到的活化能具有较好的一致性.由IKP方法和常用固相反应机理函数在不同升温速率下动力学参数的对应准则可确定膨胀聚苯乙烯泡沫热氧化分解过程可由成核和核生长控制的机理函数(Avrami Eroféev方程)A1.7描述.     

白背三七多糖的分离纯化

采用D315弱碱性阴离子交换树脂和Sephadex G-25凝胶柱层析,从白背三七叶粗多糖中分离纯化得到中性多糖GDPs-1、GDPs-2及酸性多糖GDPs-3 3个多糖组分。经高效凝胶色谱测定,重均分子质量分别为：1.06×104、4.17×103D和3.74×103D;纯度分别为94.08%、92.3%和99.8%。红外光谱证明3种多糖均含有多糖类特征吸收峰,初步推测GDPs-1中α和β构型并存,GDPs-2和GDPs-3为α构型;核磁共振结果进一步证实3种多糖中均只含有α构型。     

Numerical predictions on thermal characteristic and performance of methanol steam reforming with microwave-assisted heating

Microwave irradiation is an effective route to trigger methanol steam reforming (MSR) for hydrogen production because of the double absorption of microwaves by both the reagents and the catalyst. To recognize the thermal characteristic and performance of MSR in an environment with microwave irradiation, a numerical method is employed to predict the coupling phenomena of electromagnetic field, flow field and chemical reactions. Methanol decomposition (MD) is also regarded while MSR proceeds. Two sets of complex relative permittivity are established to account for the transmission of electromagnetic waves to heat reactants in the non-porous zone and the porous zone. Moreover, the effects of heat loss, microwave power and reagent flow rate on MSR are taken into account. The predictions suggest that heat loss is an important factor when the appropriate models with microwave-assisted heating are developed. A higher power is conducive to the performance of MSR, resulting from more heat generated in the reaction tube. At a given microwave power, heat generation due to microwave irradiation is independent of Reynolds number. As a result, increasing Reynolds number lessens methanol conversion and H₂ yield, as a consequence of more reagents passing through the catalyst bed. However, it is of interest that there exists an optimal Reynolds number for MSR to consume heat stemming from microwave irradiation.     

Experimental and modeling study of the thermal decomposition of methyl decanoate

The experimental study of the thermal decomposition of methyl decanoate was performed in a jet-stirred reactor at temperatures ranging from 773 to 1123 K, at residence times between 1 and 4 s, at a pressure of 800 Torr (106.6 kPa) and at high dilution in helium (fuel inlet mole fraction of 0.0218). Species leaving the reactor were analyzed by gas chromatography. Main reaction products were hydrogen, carbon oxides, small hydrocarbons from C₁ to C₃, large 1-olefins from 1-butene to 1-nonene, and unsaturated esters with one double bond at the end of the alkyl chain from methyl-2-propenoate to methyl-8-nonenoate. At the highest temperatures, the formation of polyunsaturated species was observed: 1,3-butadiene, 1,3-cyclopentadiene, benzene, toluene, indene, and naphthalene. These results were compared with previous ones about the pyrolysis of n-dodecane, an n-alkane of similar size. The reactivity of both molecules was found to be very close. The alkane produces more olefins while the ester yields unsaturated oxygenated compounds.A detailed kinetic model for the thermal decomposition of methyl decanoate has been generated using the version of software EXGAS which was updated to take into account the specific chemistry involved in the oxidation of methyl esters. This model contains 324 species and 3231 reactions. It provided a very good prediction of the experimental data obtained in jet-stirred reactor. The formation of the major products was analyzed. The kinetic analysis showed that the retro-ene reactions of intermediate unsaturated methyl esters are of importance in low reactivity systems.     

Combustion of polymer pellets in a bubbling fluidised bed

Single pellets (≈3 mm diameter) of high density polyethylene (HDPE) have been burned in an electrically heated bed of silica sand, fluidised by air or mixtures of N₂ and O₂ at atmospheric pressure. During the combustion of single pellets, measurements were made of the concentrations of CO and CO₂ in the off-gas, enabling burnout-times to be derived. This was done for different temperatures (400–900 °C) in a bubbling fluidised bed and a range of masses for the HDPE pellets. In addition, the size of the sand, the fluidising velocity and the concentration of O₂ in the fluidising gas were all varied. In a bed above 400 °C, a polymer pellet melted on entering the hot sand, which was wetted to form a small aggregate (or “blob” ∼5 mm in diameter) of sand particles held together by molten polymer. Next, the blob sank and volatilisation and thermal decomposition of the polymer produced hydrocarbon vapours, which burned mainly above the sand. It was deduced that there are actually three ranges of temperature, each with a different mechanism of combustion. With the bed in the high temperature regime at 640–900 °C, burnout was controlled by mass transfer of hydrocarbon vapour (deduced to have a mean composition of approximately (C₂H₄)₅) away from such a blob of sand and molten polymer. When the bed was between 485 and 640 °C (the medium temperature regime), radiative heat transfer to a blob of polymer controlled burnout. At 400–485 °C (the low temperature region) the burnout-time was controlled by the volatilisation (gasification) of a polymer pellet to produce a combustible hydrocarbon vapour. The activation energy for this gasification was ∼58 kJ/mol. This is the same as that characterising the ignition delay, which was also measured. The measured rates of burning indicate an enthalpy of gasification of ≈450 J/g. The total yield of CO and CO₂ was found to depend on the bed’s temperature and was low enough to indicate that soot, together with unburned hydrocarbons, can be important products from such a bed.     

重卡柴油机轴系扭振性能研究

发动机轴系扭振是产品开发过程中必须认真研究的一个课题,扭振计算和实机测试相结合是一种有效的扭振分析方法。笔者以研制开发的某柴油机为例,运用AVLEXCITE软件建立轴系模型,分析其轴系扭振特点,并通过实际测试进行验证,取得预期效果。曲轴系自由端共振振幅和减振器消耗功是校核重卡柴油机曲轴系扭振性能的两项重要指标。     

一种面向复杂系统的多学科设计优化方法

目前复杂系统多学科设计优化的工作主要集中在结构设计或设计过程的某个阶段,较少从整体角度对多学科设计优化过程进行研究。文中在前人系统分解研究的基础上,提出了一种基于学科分解的多学科设计优化方法,并建立了具体实现该方法的框架和应用流程。借助多学科设计优化领域主流分析软件Isight为优化平台,通过批处理命令调用各学科专业软件循环运行实现多学科综合设计,利用数据挖掘寻找整体最优解在应用层面实现了复杂系统整体优化设计。最后以某T形波导连接器隔板位置和形状优化设计为例,展示了该优化方法的应用过程和实效性。     

阵列双稳随机共振在微弱信号检测中的应用研究

阵列双稳随机共振(stochastic resonance, SR)系统可利用噪声在单个双稳SR系统基础上进一步增强微弱信号检测的能力,为强噪声背景下微弱信号的检测开创了新方法。本文应用阵列双稳SR原理进行微弱信号检测的研究,采用理论和数值仿真相结合,通过稳态自协方差函数,分析了阵列双稳SR系统输出信噪比（signal-to-noise ratio, SNR）增益。在此基础上,分别讨论了阵列噪声、外部噪声及阵列单元数对检测性能的影响。并与单个双稳SR检测弱信号进行性能比较,分析和仿真结果都表明,在相同条件下,采用阵列双稳SR比采用单个双稳SR检测微弱信号性能有较大改善。这些研究结果对于阵列双稳SR的进一步发展及应用具有重要意义。      

基于分解的二维指数交叉熵图像阈值分割

尽管用对数定义的Shannon熵是测度信息不确定性的有效方法,但存在无定义值和零值的问题,且现有的二维Shannon交叉熵法其运行速度仍有提升空间。为此,提出了一维和二维指数交叉熵阈值分割算法。首先给出了指数交叉熵的定义,并导出了一维指数交叉熵阈值选取方法;然后将其推广提出了基于分解的二维指数交叉熵阈值分割算法。通过分别求原像素灰度级图像和邻域平均灰度级图像的一维指数交叉熵最佳阈值,并将其组合求解二维指数交叉熵最佳阈值,从而将二维运算转换到两个一维空间上,大大缩小了搜索空间,使计算复杂度由O(L4)降为O(L)。实验结果表明,与最近提出的二维Shannon交叉熵法及二维Tsallis交叉熵法相比,所提出的方法能够得到更为优越的分割效果,且运行时间大幅减少。