Hot deformation behavior of an austenitic Fe–20Mn–3Si–3Al transformation induced plasticity steel

Hot deformation behavior of an austenitic Fe–20Mn–3Si–3Al transformation induced plasticity (TRIP) steel was investigated by hot compression tests on Gleeble 3500D thermo-mechanical simulator in the temperature ranges of 900–1100 °C and the strain rate ranges of 0.01–10 s⁻¹. The results show that the flow stress is sensitively dependent on deformation temperature and strain rate, and the flow stress increases with strain rate and decreases with deformation temperature. The peak stress during hot deformation can be predicted by the Zener–Hollomon (Z) parameter in the hyperbolic sine equation with the hot deformation activation energy Q of 387.84 kJ/mol. The dynamic recrystallization (DRX) is the most important softening mechanism for the experimental steel during hot compression. Furthermore, DRX procedure is strongly affected by Z parameter, and decreasing of Z value lead to more adequate proceeding of DRX.     

Sizing of a fuel cell electric vehicle: A pinch analysis-based approach

Polymer electrolyte fuel cells are considered as a promising alternative to mitigate the CO₂ emission in the transport sector. To achieve an efficient and cost-effective system, hybridisation of the energy storage system with a fuel cell is important. Efficient management of energy is the key in order to achieve an efficient and cost-effective configuration for fuel cell electric vehicle. Optimum sizing of the power source and energy storage system, which is capable of meeting the load requirement of the driving cycle is the key challenge for achieving efficient and cost-effective system. In this work, an alternative methodology based on the principles of pinch analysis is proposed, for sizing the energy storage system and the fuel cell for fuel cell-based electric vehicle, and validated for the Worldwide Harmonized Light Vehicle Test Cycle (WLTC) class-3 driving cycle.     

Hydrogen energy share enhancement in a heavy duty diesel engine under RCCI combustion fueled with natural gas and diesel oil

The aim of this study is to enhance hydrogen energy share in a RCCI engine. The engine under consideration is fueled with diesel oil and natural gas enriched with hydrogen or syngas and is set to operate at 9.4 bar gross indicated mean effective pressure (Mid- Load). The syngas used in this study consists of hydrogen and carbon monoxide which are mixed together on a volumetric ratio of 80:20. A fixed amount of diesel oil is injected per cycle into the combustion chamber of the RCCI engine. Based on two different strategies, hydrogen or syngas mixed with exhaust gas recirculation are admitted gradually along with natural gas while ensuring that always the low temperature combustion concept is fulfilled. The RCCI engine operation is simulated through commercial software coupled with chemical kinetics solver. The simulation results show that without any engine diesel knock occurrence, by adding hydrogen to natural gas, the share of hydrogen energy could be increased up to 40.43% while the engine power output is reduced only by about 1%. Also, syngas addition to natural gas causes that the share of hydrogen energy could be increased up to 27.05% while improves the engine power more than 4%. At the same time, by considering two mentioned strategies, the overall hydrocarbon fuel consumption per cycle can be reduced by up to 46.60% and 33.86%, respectively. Moreover, having the gross indicated efficiency of well over 50% and significant reduction in the engine emissions compared to RCCI combustion fueled solely with natural gas and diesel oil are achievable.     

Spontaneous emission into planar multi-dielectric microcavities: Theoretical and experimental analysis of rare earth ion radiations

Spontaneous emission control for rare earth ions implanted inside planar multidielectric microcavities is investigated theoretically and experimentally. Rigorous classical electrodynamics analyses are presented and compared in order to compute the electromagnetic power provided by sources located inside planar dielectric multilayer structures. Radiation patterns and lifetime measurements are performed in Ta₂O₅/SiO₂ microcavities implanted with erbium and praseodymium ions. Although we demonstrate a significant enhancement of the spontaneous emission in a direction normal to the layer (up to 30%), we show that a large amount of the emitted power is carried by the guided modes of the structures.     

Adaptive restricted trajectory tracking for a non-minimum phase hypersonic vehicle model

The design of a nonlinear robust controller for a non-minimum phase model of an air-breathing hypersonic vehicle is presented in this work. When flight-path angle is selected as a regulated output and the elevator is the only control surface available for the pitch dynamics, longitudinal models of the rigid-body dynamics of air-breathing hypersonic vehicles exhibit unstable zero-dynamics that prevent the applicability of standard inversion methods for control design. The approach proposed in this paper uses a combination of small-gain arguments and adaptive control techniques for the design of a state-feedback controller that achieves asymptotic tracking of a family of velocity and flight-path angle reference trajectories belonging to a given class of vehicle maneuvers, in spite of model uncertainties. The method reposes upon a suitable redefinition of the internal dynamics of a control-oriented model of the vehicle dynamics, and uses a time-scale separation between the controlled variables to manage the peaking phenomenon occurring in the system. Simulation results on a full nonlinear vehicle model that includes structural flexibility illustrate the effectiveness of the methodology.     

Grinding behavior of biomimetic fractal-branched silicon carbide ceramic inspired from leaf-vein structure

Silicon carbide ceramics are widely used in many industrial fields owing to their outstanding physical and chemical characteristics. However, their inherent hardness and brittleness make the grinding process very difficult compared to that involving ductile materials. In the present study, the effects of the biomimetic fractal-branched structure, inspired from the leaf-vein, on the grinding behavior of silicon carbide were investigated. Two biomimetic fractal-branched structures with different densities of micro-channels were designed and compared with the non-structured silicon carbide surface. The surface of the silicon carbide ceramic was textured through pulsed-laser ablation. Thereafter, the grinding experiment was conducted on the biomimetic fractal-branched and non-structured workpieces. The surface topography, subsurface damage, grinding force, grinding force ratio, surface roughness and grinding wheel wear were examined throughout the experiment. The experimental results indicated that the normal and tangential grinding forces for the fractal-branched structure surface are 7.61–18.21% and 8.34–26.13% lower than those for the non-structured surface. The grinding force ratio also increased significantly with an increase in the micro-channel density. In addition, a larger volume of coolant was transported through the grinding zone of the fractal-branched structure. The research results confirmed that the biomimetic fractal-branched structure on the silicon carbide surface enhanced the grinding performance and improved the grinding quality.     

基于视觉的四旋翼无人机自主定位与控制系统

针对GPS(global positioning system)信号缺失环境下无人机(UAV)自主飞行控制问题,设计了一种基于视觉的自主定位与控制方法.首先通过增加特征点提取数量和优化关键帧存储来对传统视觉SLAM(simultaneous localization and mapping)算法进行改进,提高了算法的鲁棒性与通用性.其次,引入光流传感器作为视觉SLAM地图丢失情况下辅助位置信息测量单元,提高无人机飞行控制的安全性,并成功地克服视觉SLAM图像丢失问题和光流法存在的位置漂移问题.然后采用EKF(extended Kalman filter)融合无人机位置和3维加速度信息,得到了较为精确的位置信息,同时提高了信号输出频率.最后,利用上述方法获取的无人机位置信息设计PID(proportion integration differentiation)和RISE(robust integral of the signum of the error)非线性控制器,增加了算法的鲁棒性.为验证该控制策略的有效性,搭建了四旋翼无人机视觉控制系统实验平台.该平台采用嵌入式控制系统架构,使用机载计算机运行所提算法,避免了图像及控制命令在无线传输过程中引起的时间延迟和信号干扰.室外飞行实验表明,此控制方案实现了自主定位与飞行控制功能.     

Experimental Study on the Performance and Emission of Chinese Small Agricultural Diesel Engine Fuelled with Methanol/Biodiesel/DTBP

中国小型农用柴油机燃用甲醇/生物柴油/DTBP的性能与排放试验研究

李瑞娜^1,2,3,张亮¹,朱佳隆¹,华琰¹,王忠¹

（1、江苏大学汽车与交通工程学院,江苏 镇江212013;

2. 汽车测控与安全四川省重点实验室,成都 610039;

3. 四川省新能源汽车智能控制与仿真测试技术工程研究中心,成都 610039）

摘 要：

为了研究甲醇和生物柴油对小型农用柴油机性能、经济性和排放的影响,分析了甲醇和生物柴油的物理化学性质（十六烷值、低热值、粘度等）。甲醇和生物柴油的性质在一定程度上表现出良好的互补性。当在生物柴油中加入大量甲醇时,甲醇/生物柴油混合物的十六烷值将大幅度降低。由于混合燃料的十六烷值对柴油机的燃烧过程有很大影响,在对甲醇/生物柴油的混合比进行试验后,分别用5%（BM5）、10%（BM10）、15%（BM15）的甲醇添加到生物柴油中制备了混合燃料。选择过氧化二叔丁基（DTBP）作为十六烷值改进剂添加到甲醇/生物柴油混合物中。在BM15中分别加入0.25%、0.50%、0.75%的DTBP。在186FA柴油机上进行台架试验,研究了甲醇和DTBP对发动机性能和排放的影响。结果表明,在额定工况下,与生物柴油相比,BM5、BM10和BM15的NOx浓度分别降低了5.02%、33.85%和21.24%,烟度分别降低了5.56%、22.22%和55.56%,发动机功率降低了5.77%、14.23%和25.41%,比能耗提高了3.31%,7.78%和6.37%。在甲醇/生物柴油中添加DTBP可以将发动机功率恢复到柴油的水平。DTBP对降低比能耗、降低NOx、CO、HC浓度有较好的效果,但排气烟度略有增加。

关键词：甲醇、生物柴油、农用柴油机、燃烧、性能、排放

     

Effect of pre-chamber geometrical parameters and operating conditions on the combustion characteristics of the hydrogen-air mixtures in a pre-chamber spark ignition system

The pre-chamber spark ignition system is a promising advanced ignition system adopted for lean burn spark ignition engines as it enables stable combustion and enhances engine efficiency. The performance of the PCSI system is governed by the turbulent flame jet ejected from the pre-chamber, which is influenced by the pre-chamber geometrical parameters and the operating conditions. Hence, the current study aims to understand the effects of pre-chamber volume, nozzle hole diameter, equivalence ratio, and initial chamber pressure on the combustion and flame jet characteristics of hydrogen-air mixture in a passive PCSI system. Pre-chamber with different nozzle hole diameters (1 mm, 2 mm, 3 mm, and 4 mm) and volumes (2%, 4%, and 6% of the engine clearance volume) were selected and manufactured in-house. The experimental investigation of these pre-chamber configurations was carried out in a constant-volume combustion chamber with optical access. The flame development process was captured using a high-speed camera at a rate of 20000 fps, and the images were processed in MATLAB to obtain quantitative data. The combustion characteristics of hydrogen-air mixtures with the PCSI system improved when compared to the conventional SI system; however, the improvement was more significant for ultra-lean mixtures. Early start of combustion and shorter combustion duration were observed for PCSI – D2 and PCSI – D3 configurations, respectively and improved combustion and flame jet characteristics were also noted for these configurations. With the increase in pre-chamber volume, ignition energy associated with the flame jet increases, which reduces the combustion duration and the ignition lag.     

Increasing RES penetration through H2 technologies on Flores island,Azores: A techno-economic analysis

On Flores island (Azores, Portugal), energy production depends up to 47% on fossil fuels, namely Diesel. To minimize CO₂ emissions, the dependency on fuel prices, and to mitigate the consequences of variability and intermittency of renewable energy sources, a new energy system, based on H₂ storage was analysed. To achieve the optimal size of the system, a computer model was developed and a multi-objective genetic algorithm function was used to minimize three objectives: the difference of levelised cost of energy (△LCOE), CO₂ emissions and the percentage of renewable energy dumped (R_{RES, dump}). From the set of solutions obtained, one that meets R_{RES, dump} ≤ 1%, lowest CO₂ emissions and lowest △LCOE is chosen and an economical and energetic analysis is performed. The newly proposed system reduces Diesel consumption by 68,7% (1057487 L/year) and CO₂ emissions by 65,9% (2455,1 CO₂ tons/year) achieving a renewable energy sources (RES) penetration of 89% (36% increase), but fails to decrease the levelised cost of energy (56,62 €/MWh increase). However, a way to make the project viable through financial support is presented and an alternative to reduce the levelised cost of energy by commercialising the products of electrolysis, hydrogen and oxygen, is proposed. Finally, it is expected that with further research and development of H₂ technologies, economic and energetic results will get more advantageous, opening up new perspectives for the future.