Concept design of a novel reformer producing hydrogen for internal combustion engines using fuel decomposition method: Performance evaluation of coated monolith suitable for on-board applications

Hydrogen addition effectively reduces the fuel consumption of spark ignition engines. We propose a new on-board reformer that produces hydrogen at high concentrations and enables multi-mode operations. For the proposed reformer, we employ a catalytic fuel decomposition reaction via a commercial NiO–CaAl₂O₄ catalyst. We explore the physical and chemical aspects of the reforming process using a fixed bed micro-reactor operating at temperatures of 550–700 °C. During reduction, methane is decomposed to form hydrogen and carbon. Carbon formation is critical to hydrogen production, and free space for carbon growth is essential at low temperatures (≤600 °C). We define a new accumulated conversion ratio that quantitatively measures highly transient catalytic decomposition. The free space of the coated monolith clearly aided low-temperature decomposition with negligible pressure drop. The coated substrate is therefore suitable for on-board applications considering that our reformer concept also utilizes the catalytic fuel decomposition reaction.     

Modeling of material removal rate in electric discharge grinding process

The mechanism of material removal in electric discharge grinding (EDG) is very complex due to interdependence of mechanical and thermal energies responsible for material removal. Therefore, on the basis of conceived process physics for material removal, an attempt has been made to predict the material removal rate (MRR). The proposed mathematical model is based on the fundamental principles of material removal in electric discharge machining (EDM) and conventional grinding processes. The inter-dependence of the thermal and mechanical phenomena has been realized by scanning electron microscopy (SEM) characterization of the samples machined at different processing conditions. The key input process parameters like pulse on time, pulse current, gap voltage, duty cycle, pulse off time, frequency, depth of cut, wheel speed and table speed are co-related with MRR for three distinct idealized processing conditions. The constant showing the extent of interdependence of two phenomena were evaluated by experimental data. The obtained expressions of MRR have been validated for processing conditions other than those used for obtaining constants. It was found that the discharge energy plays prominent role in material removal. The percentage difference in experimental findings and theoretical predictions was found to be less than 3%.     

The influence of grain geometry and wear conditions on the material removal mechanism in silicon carbide grinding with single grain

High efficiency and precision grinding of brittle materials is challenging due to material physical and chemical properties. To understand the effect of grain geometry and wear conditions on the material removal mechanism in brittle material precision grinding, a single diamond grain grinding experiment was conducted on Silicon Carbide (SiC). The cutting edge radius and deflection angle were measured by confocal scanning. Under six different cutting edge radius and three maximum undeformed chip thickness, grinding force and ground surface were measured. Diamond grain wear was investigated by observing the grain morphology, wear rate, grinding force, and ground surface change over accumulative material removal volume. The result showed the existence of a critical cutting edge radius for improving SiC ground surface quality.. Normal grinding force increased with the cutting edge radius increase. Tangential grinding force increased with the cutting edge radius increase and reached the peak value at the critical cutting edge radius. Flank wear was the major wear mode in precision SiC grinding. The grain wear was associated with the grinding force and ground surface.     

选区激光熔化GH3536合金的热处理工艺

采用OM、SEM和力学性能测试等分析研究了不同热处理工艺对选区激光熔化成形GH3536合金组织及力学性能的影响规律。结果表明,随着固溶温度越高,晶粒尺寸越大,且抗拉强度在高温条件下逐渐增加而室温条件则下降。当固溶温度达到1120 ℃时,室温条件下横向试棒与纵向试棒的抗拉强度分别达到816和731 MPa;900 ℃高温条件下则分别达到189和204 MPa。800 ℃时效处理后合金基体组织析出细小碳化物,产生第二相强化作用,强度得以提升。随着时效时间的增加,碳化物变的密集,但晶粒尺寸几乎没有发生变化,表现为室温抗拉强度与断后伸长率得到提升。当时效时间达到20 h时,室温条件下横向试棒与纵向试棒的抗拉强度分别达到832和747 MPa;900 ℃高温条件下横向试棒与纵向试棒的断后伸长率分别达到8.5%和21.5%。最后得出选区激光熔化成形GH3536合金最优的热处理工艺为:固溶(1120 ℃×1 h)+时效(800 ℃×20 h)。     

Performance evaluation of Ti–6Al–4V grinding using chip formation and coefficient of friction under the influence of nanofluids

Nanofluid, fluid suspensions of nanometer sized particles are revolutionizing the field of heat transfer area. Addition of nano-particles to the base fluid also alters the lubricating properties by reducing the friction. In grinding process, friction between the abrasive grains and the workpiece is a key issue governing the main grinding output. It has a direct influence on grinding force, power, specific energy and wheel wear. Moreover, high friction force increases the heat generation and lead to thermal damage in the surface layer of the ground work. Hence, any effort towards the friction control will enhance the component quality significantly. In this study, nanofluid as metal working fluid (MWF) is made by adding 0.05, 0.1, 0.5 and 1% volume concentration of Al₂O₃ and CuO nano-particles to the water during the surface grinding of Ti–6Al–4V in minimum quantity lubrication (MQL) mode. Surface integrity of ground surface, morphology of the wheel, and chip formation characteristics are studied using surface profilometer, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and stereo zoom microscopy (SZM). Coefficient of friction was estimated On-Machine using the measured forces. The results showed that the type of nanoparticle and its concentration in base fluid and the MQL flow rate play a significant role in reducing friction. Application of nanofluid leads to the reduction of tangential forces and grinding zone temperature. The cooling effect is also evident from the short C-type chip formation. MQL application with Al₂O₃ nanofluid helps in effective flushing of chip material from the grinding zone, thereby solving the main problem during the grinding of Ti–6Al–4V.     

六西格玛管理在O形橡胶密封圈内径控制中的应用

通过六西格玛管理DMAIC(定义、测量、分析、改善、控制)流程并结合Minitab软件,对O形橡胶(氟硅橡胶)密封圈(简称O形密封圈)内径控制进行研究。通过试验数据分析得出O形密封圈影响因子最优组合,通过回归分析确定O形密封圈内径的关键影响因子,通过流程控制使O形密封圈内径合格率得到提高。     

机载冷源参数对蒸发循环系统性能的影响

为了深入研究机载蒸发循环系统的工作特性及为搭建仿真计算模型做准备，基于试验室已有设备和条件，以一台新型微通道换热器作为研究对象，以R134a为工质，通过控制压缩机转速和电子膨胀阀开度一定，分别调节冷源温度和流量，考察冷源温度和流量对压缩机入口过热度、热源出口温度和制冷量的影响，并基于试验数据搭建了针对该蒸发器的仿真计算模型。试验结果表明在试验工况下，冷源防冻液入口温度对系统性能的影响明显，随冷源入口温度升高，压缩机入口过热度逐渐降低、热源出口温度明显升高，但冷源流量对系统性能的影响不显著。基于试验数据，建立了蒸发器仿真计算模型，将该模型应用于蒸发循环系统模型中，对比试验数据和仿真计算数据，可知，该蒸发器仿真计算模型准确可靠，可用于针对该蒸发器的性能仿真计算。     

丁腈橡胶和氢化丁腈橡胶与金属的粘合性能研究

采用不同的开姆洛克(Chemlok)双涂体系胶粘剂,对比研究航空燃油系统常用丁腈橡胶(NBR)和氢化丁腈橡胶(HNBR)与金属(钢30CrMnSiA和铝合金2A12)的粘合性能。结果表明:Chemlok双涂体系对NBR的粘合效果较好,NBR-金属粘合的破坏形式主要为橡胶破坏;橡胶-钢30CrMnSiA的粘合强度大于橡胶-铝合金2A12;面涂型胶粘剂的粘合效果与金属种类有关。     

单边固支板结构弯矩光纤光栅监测方法

在飞行过程中,机翼结构会受到不同外力作用而产生变形。作为内力矩的一种,弯矩大小与结构受力和变形量有关。因此,针对变形状态下的弯矩测量对于飞行器状态监测具有重要意义。该文以等宽、等厚、等截面的单边固支板结构作为机翼的简化模型,提出一种基于光纤光栅传感器的结构弯矩测量方法,推导得到板结构在弯曲变形情况下的应变-弯矩转换方程。通过构建单边固支板结构光纤监测系统,实现对不同载荷下板结构关键位置的弯矩测量,单点加载、多点加载与均布加载方式下均方根误差分别约为0.883、0.825、0.689。     

Stress and failure analysis of woven composite plates with adhesive patch-reinforced circular hole

The application of a single-sided patch reinforcement to a woven E-glass fiber/epoxy composite panel with a central circular fastener hole is studied using three-dimensional finite element analysis. The width of the panel is 25.4 mm, while three hole diameters (3, 6 and 9 mm) are used in the study. The reinforcement patch is square in shape and is made of either E-glass fiber/epoxy or carbon fiber/epoxy laminae, with the patch-to-panel-thickness varying from 0.1 to 0.7. To simulate the ‘fastened’ condition, the patch-reinforced panel is bolted to a mild steel bar, which is fixed in the direction normal to the panel. One end of the panel is subject to unidirectional tensile load while the other end is under clamped boundary conditions. The through-thickness stress distributions and the failure loads of the patch-reinforced panels are evaluated by finite element analysis. Contact elements are used to account for interaction between contact surfaces. Experiments are also performed to verify the model.The relationships between the patch-to-panel-thickness and the strength of the panel and the material of patch reinforcement are considered and discussed.