Fatigue behavior and damage evolution of SiC/SiC composites under high-temperature anaerobic cyclic loading

In the present study, the fatigue behavior and damage evolution of SiC/SiC minicomposites at elevated temperatures in oxygen-free environment are investigated which are important for their application and are still unclear. The high-temperature fatigue test platform is developed and the fatigue stress-life curve and the stress-strain response are obtained. The test result shows that the life of the material at elevated temperature is shorter than that at room temperature under the same stress level. Moreover, the hysteresis loop width and the residual strain increase with the increasing of the cycles while the hysteresis modulus decreases during the fatigue cycling. The evolution process of matrix cracks is observed using the real-time remote detection system. It is found that matrix cracking is insensitive to the cyclic loading which is similar to room temperature and is due to that the degeneration of the interfacial shear stress reduces the area of high stress in matrix. The fiber/matrix interfacial shear stress under different cycles is determined based on the fatigue modulus of each hysteresis loop. The result shows a fatigue enhancement phenomenon for the interface which is not observed at room temperature.     

Performance indices of a common rail-system CI engine powered by diesel oil and biofuel blends

Conventional fuels used for supplying internal combustion piston engines include petrols and diesel oils produced from petroleum. These are a non-renewable energy source. The environmental policy of the European Union is geared towards increasing the share of renewable fuels in the overall energy consumption. An alternative fuel originating from a renewable source, which could be used for feeding self-ignition internal combustion engines are the fatty acid methyl esters (FAME) of plant oils. The paper reports selected results of testing a 1.3 MULTIJET SDE 90 PS self-ignition engine with the Common Rail reservoir feed system supplied with mixtures of diesel oil and rape oil fatty acid methyl esters (FAME). Tests were carried out on an engine test bed equipped with an eddy-current brake. The purpose of the tests was to determine the economic–energy and ecological indices of engine operation. The concentrations of exhaust gas gaseous components were measured using a MEXA-1600DEGR analyzer, while the particulate concentrations, with a MEXA-1230PM analyzer. In addition, the variations of working medium pressures in the engine chamber and of fuel pressure upstream the injector were recorded as a function of crankshaft rotation angle using the AVL IndiSmart 612 indication system for this purpose. The physicochemical properties of fuels used in the tests were determined using a fuel analyzer. The obtained testing results made it possible to determine and assess the operation indices of the engine fed with mixtures of diesel oil and rape oil fatty acid methyl esters (FAME) with slightly higher ester contents than the requirements of the currently applicable diesel oil standard.     

Experimental investigations on the effect of fuel injection parameters on diesel engine fuelled with biodiesel blend in diesel with hydrogen enrichment

Fuel injection pressure and injection timing are two extensive injection parameters that affect engine performance, combustion, and emissions. This study aims to improve the performance, combustion, and emissions characteristics of a diesel engine by using karanja biodiesel with a flow rate of 10 L per minute (lpm) of enriched hydrogen. In addition, the research mainly focused on the use of biodiesel with hydrogen as an alternative to diesel fuel, which is in rapidly declining demand. The experiments were carried out at a constant speed of 1500 rpm on a single-cylinder, four-stroke, direct injection diesel engine. The experiments are carried out with variable fuel injection pressure of 220, 240, and 260 bar, and injection timings of 21, 23, and 25 °CA before top dead center (bTDC). Results show that karanja biodiesel with enriched hydrogen (KB20H10) increases BTE by 4% than diesel fuel at 240 bar injection pressure and 23° CA bTDC injection timing. For blend KB20H10, the emissions of UHC, CO, and smoke opacity are 33%, 16%, and 28.7% lower than for diesel. On the other hand NOx emissions, rises by 10.3%. The optimal injection parameters for blend KB20H10 were found to be 240 bar injection pressure and 23 °CA bTDC injection timing based on the significant improvement in performance, combustion, and reduction in exhaust emissions.     

YZC12Ⅱ型振动压路机的降噪技术浅析

YZC12Ⅱ型振动压路机为双频双幅串联式振动压路机,该机为全液压传动,采用全电液控制技术,具有两挡无级调速、双频双幅振动、三级减振、三级制动、铰接式转向和无级喷雾洒水等功能.投放市场后,用户反应该机机外噪声大,并存在非常刺耳的周期性啸叫声的问题.对压路机的动力系统进行分析,认为柴油机风扇在高速转动过程中,风扇叶片和高速通过发动机机罩的冷却风流所发生的周期性相互作用是产生高频噪声的主要原因.运用阻尼降噪和拍振现象的原理,对发动机机罩进风口的结构形式进行改进,将原平板式网状进风口改成百叶窗式的进风口,并在百叶窗叶片下侧粘贴海绵,同时在机罩内侧封闭部分粘贴吸音海绵.改进后测得机外噪声为95.7 dB(A),降噪效果明显.同时,在发动机罩顶部的左右方向增加两条加强筋,以使发动机机罩的固有频率远离噪声的激振频率,试验证明,经过改进后,发动机高速运转时产生的周期性啸叫声被消除.     

发动机缸体轴承盖专用机床设计

发动机缸体轴承盖是支撑曲轴的关键零件,其螺栓孔尺寸精度对发动机产品的工作性能有着重要影响。通过对所加工轴承盖加工工艺分析研究,并结合用户实际需求,设计了一种用于加工多品种多工件的发动机缸体轴承盖螺栓孔专用组合机床,并对其关键技术作了介绍和研究。该机床的成功研制和应用,实现了轴承盖螺栓孔加工精度和效率的进一步提高。     

Modeling and optimization of biodiesel engine performance using kernel-based extreme learning machine and cuckoo search

This study presents the optimization of biodiesel engine performance that can achieve the goal of fewer emissions, low fuel cost and wide engine operating range. A new biodiesel engine modeling and optimization framework based on extreme learning machine (ELM) is proposed. As an accurate model is required for effective optimization result, kernel-based ELM (K-ELM) is used instead of basic ELM because K-ELM can provide better generalization performance, and the randomness of basic ELM does not occur in K-ELM. By using K-ELM, a biodiesel engine model is first created based on experimental data. Logarithmic transformation of dependent variables is used to alleviate the problems of data scarcity and data exponentiality simultaneously. With the K-ELM engine model, cuckoo search (CS) is then employed to determine the optimal biodiesel ratio. A flexible objective function is designed so that various user-defined constraints can be applied. As an illustrative study, the fuel price in Macau is used to perform the optimization. To verify the modeling and optimization framework, the K-ELM model is compared with a least-squares support vector machine (LS-SVM) model, and the CS optimization result is compared with particle swarm optimization and experimental results. The evaluation result shows that K-ELM can achieve comparable performance to LS-SVM, resulting in a reliable prediction result for optimization. It also shows that the optimization results based on CS is effective.     

基于MongoDB的HIAF Archive Engine设计与实现

强流重离子加速器装置（HIAF）的控制系统采用实验物理和工业控制系统（EPICS）架构，运行数据存储系统为HIAF运行中的运行数据、历史数据和静态参数提供稳定可靠的存储。针对当前EPICS架构下的数据存储工具仅支持关系型数据库的不足，开发非关系型数据库MongoDB接口，并利用MongoDB嵌套对象和多层级存储结构的特点优化存储表结构，实现波形、图像等非关系型数据的高效存储；为调束人员提供基于标志位PV（Flag PV）方式的加速器运行数据手动存储方案以提升历史数据检索效率及数据可用性；同时针对海量历史数据的存储需要，利用MongoDB Sharding搭建MongoDB分布式集群。     

新型空气动力发动机进气门的研究

为实现气动发动机利用外界较高压力空气推动气缸内活塞并对外输出动力,本文设计一种利用电磁装置的新型进气门结构,它结构简单,能够实现对大流量高压气体的流量调节,使其能很好的满足气体发动机的工作要求。     

Evaluation of fuel consumption and vibration characteristic of a compression ignition engine fuelled with high viscosity biodiesel and hydrogen addition

Viscosity property of a fuel is a crucial point for internal combustion engine characteristics. Performance and emission parameters as well as injector's life of an engine is primarily effected by viscosity of the fuels. In present study, effect of high viscosity biodiesel fuels with hydrogen addition was investigated in a compression ignition engine. Biodiesels that are produced from Pongamia Pinnata and Tung oils were used as pure biodiesels as well as blended with low sulphur diesel fuel at the volume ratios of 50% and 75%. Furthermore, hydrogen gas was injected into intake manifold in order to evaluate its effect with the usage of high viscous liquid fuels. The results revealed that brake specific fuel consumption was increased with biodiesel fuels, whereas hydrogen addition into intake manifold improved the consumption. Total vibration acceleration of the engine reduced with biodiesel and hydrogen additions. Frequency spectrum indicated that this decrement was primarily lowered due to less energy transmitted through engine pistons that converted from chemical energy of fuels.     

Numerical model to analyze Nox reduction by ammonia injection in diesel-hydrogen engines

Nowadays, the even increasing stringent environmental legislations have promoted interest in alternative fuels for internal combustion engines. Particularly, hydrogen is becoming a promising fuel due to its high specific energy and low emissions production. Environmentally, the main disadvantage of hydrogen is the high level of nitrogen oxides (NO_x) which produces. In this regard, this work proposes a NO_x reduction method which consists on direct injection of ammonia (NH₃) into the combustion chamber. A numerical model validated with experimental measurements was carried out to analyze emissions and brake specific consumption in a commercial engine operating with diesel-hydrogen blends. Comparing to diesel operation, a 10% hydrogen content increases a 5.3% the peak pressure and 5.7% the maximum temperature. The CO₂, CO and HC emissions are reduced but NO_x emissions increase up to 18.3%. Several injection instants and ammonia flow rates were analyzed, obtaining more than 70% NO_x reductions with a negligible effect on other emissions and brake specific consumption. It was found that the start of ammonia injection is too critical since the maximum NO_x reduction takes place when the temperature is around 1200 K. The NO_x reduction increases with the ammonia flow rate but an excessive quantity of ammonia can lead to un-reacted ammonia slip to the exhaust.