Effect of fuel injection strategies on the combustion process in a PFI boosted SI engine

A low-cost solution based on fuel injection strategies was investigated to optimize the combustion process in a boosted port fuel injection spark ignition (PFI SI) engine. The goal was to reduce the fuel consumption and pollutant emissions while maintaining performance. The effect of fuel injection was analyzed for the closed and open valve conditions, and the multiple injection strategies (MIS) based on double and triple fuel injection in the open-valve condition. The tests were performed on an optical accessible single-cylinder PFI SI engine equipped with an external boost device. The engine was operated at full load and with a stoichiometric ratio equivalent to that of commercial gasolines. Optical techniques based on 2D-digital imaging were used to follow the flame propagation from the flame kernel to late combustion phase. In particular, the diffusion-controlled flames near the valves and cylinder walls, due to fuel deposition, were studied. In these conditions, the presence of soot was measured by two-color pyrometry, and correlated with engine parameters and exhaust emissions measured by conventional methods. The open valve fuel injection strategies demonstrated better combustion process efficiency than the closed ones. They provided very low soot levels in the combustion chamber and engine exhaust, and a reduction in specific fuel consumption. The multiple injection strategies proved to be the best solution in terms of performance, soot concentration, and fuel consumption.     

Experimental investigation of characteristics of pressure modulation in a fuel injection system

A piezoelectric atomization device achieves fuel pressure modulation through vibration of a piezoelectric pressure modulator. As a consequence, the fast alternating and slow moving streams collide with each other and further break up the fuel drop. In this paper, an experimental investigation was carried out to study the fluid dynamic characteristics of the spray atomization process of automotive port fuel injectors with a piezoelectric pressure modulator. The investigation mainly focuses on: (a) the coupling characteristics between the piezoelectric stack and the hydraulic as well as the transfer characteristics of pressure modulation from the piezoelectric modulator to the point above the orifice; (b) the time history of the pressure dynamic response at the point above the orifice under a typical modulation frequency, which reflects the variation of pressure modulation while the fuel injector is working; and (c) the time-variation characteristics related to mechanical structure and fluid dynamics. The experimental results expose some important dynamic characteristics of pressure modulation, which will be very significant and lead us to greatly improve the fuel injection system, optimize the control parameters and implement spray atomization with a high quality performance in the near future.     

Integrated fuzzy/optimal vehicle dynamic control

There are basically two methods to control yaw moment which is the most efficient way to improve vehicle stability and handling. The first method is indirect yaw moment control, which works based on control of the lateral tire force through steering angle control. It is mainly known as active steering control (ASC). Nowadays, the most practical approach to steering control is active front steering (AFS). The other method is direct yaw moment control (DYC), in which an unequal distribution of longitudinal tire forces (mainly braking forces) produces a compensating external yaw moment. It is well known that the AFS performance is limited in the non-linear vehicle handling region. On the other hand, in spite of a good performance of DYC in both the linear and non-linear vehicle handling regions, continued DYC activation could lead to uncomfortable driving conditions and an increase in the stopping distance in the case of emergency braking. It is recommended that DYC be used only in high-g critical maneuvers. In this paper, an integrated fuzzy/optimal AFS/DYC controller has been designed. The control system includes five individual optimal LQR control strategies; each one, has been designed for a specific driving condition. The strategies can cover low, medium, and high lateral acceleration maneuvers on high-μ or low-μ roads. A fuzzy blending logic also has been utilized to mange each LQR control strategy contribution level in the final control action. The simulation results show the advantages of the proposed control system over the individual AFS or DYC controllers.     

双绞合钢丝网加筋格宾挡土墙设计方法研究

采用六边形双绞合金属网面,经工厂化生产形成面墙,面墙与金属网面无接点整体连接形成一种新的加筋结构-加筋格宾结构,目前国内工程应用较少,相应的计算理论与设计方法滞后,难以满足工程需要.研究表明,双绞合钢丝网加筋格宾挡土墙比传统的条带式加筋、土工格栅挡土墙的稳定性好得多,适合于修筑高大及高等级公路的挡土墙.在吸收国外先进加筋技术的基础上,通过拉伸、拉拔试验合理确定了相关设计参数,采用室内大型模型试验,确定了加筋格宾结构的滑动破裂面形状,提出了一整套该新型结构的计算与设计方法.     

基于安全可靠性的多类用户交通分配模型

为探究出行安全对用户出行选择行为的影响,提出了考虑事故风险成本和旅行时间的多类用户交通分配模型。针对事故发生的随机性特征,定义了路径出行安全可靠性概念,并以此计算用户的事故风险成本预算,体现出行者的安全偏好。基于考虑事故机会和事故风险的基础事故预测模型,针对路段和交叉口的不同特征,分别定义了路段和交叉口的事故风险成本分布。构建的交叉口事故风险成本模型,体现了交叉口不同转向的事故风险成本的差异性。为了求解基于安全可靠性的多类用户交通分配模型,采用路径配流法和相继平均法设计了相应的求解算法,并通过算例分析了模型和算法的有效性。研究结果表明：安全可靠性在用户出行选择中具有重要影响。当在广义出行费用中考虑事故风险成本时,出行者会更多地选择事故风险成本较小的路径;不同风险倾向的用户会有不同的选择特征,保守型出行者倾向于选择路径事故风险成本标准差相对较小的路径,即事故风险成本波动小的路径,而中立型出行者倾向于选择事故风险成本均值相对较低的路径;考虑交叉口的事故风险成本与否会直接影响流量分配结果,即路径交叉口数量和转向的差异性同样会影响出行者的选择。所提出的模型对于客流预测和网络安全评价与管理具有潜在的应用价值。     

MMFX-2钢筋性能综述和抗腐蚀性现场实验

水泥混凝土桥面钢筋腐蚀是一普遍且复杂的问题,采用替代钢筋能有效地预防或延缓钢筋腐蚀,而近年应用的MMFX-2钢被认为具有更好的抗锈蚀性能。印第安纳州交通厅对现有的MMFX-2钢的研究成果进行了综合分析,并修建了现场试验桥面以长期评价MMFX钢筋抗腐蚀能力。同普通碳钢相比,MMFX-2钢的屈服强度和抗拉强度更高、抗腐蚀性更好,但没有明显的屈服点。试验桥面铺装的实验结果表明,施工竣工不久至竣工两年期间,MMFX-2钢筋腐蚀很少,混凝土中氯化物含量没有达到钢筋去钝化水平,但在桥面铺装上部氯离子浓度显著增加。笔者建议对于氯化物影响较大场合的混凝土桥面铺装,如果希望提供二次腐蚀保护时,可考虑使用MMFX-2钢。     

机械电子技术在未来铁道车辆中的应用与发展(待续)

全面介绍了机械电子技术在未来铁道车辆特别是悬挂系统、牵引系统和制动系统中的应用和发展。     

Predictions of porpoising inception for planing vessels

The inception of porpoising is theoretically predicted for planing vessels. Two different approaches are presented. First, a linear stability analysis is applied to find the porpoising limits while the hydrodynamic coefficients, i.e. added mass and damping coefficients, are determined by either a simplified method or a numerical method. Another approach is to seek the porpoising limits by performing nonlinear time domain simulations. Either the simplified method or the numerical method is used in the simulations. In the numerical method, a 2D+t theory together with a boundary element method is employed. The trim angle limits for porpoising are determined by changing the longitudinal position of the centre of gravity (COG) of the vessel and keeping the forward speed constant. The predicted porpoising limits are compared with Day and Haag’s (Planing boat porpoising, Thesis, Webb Institute of Naval Architecture, 1952) experimental results. The influences of parameters such as the load coefficient, the vertical position of COG and the radius of gyration of the ship are investigated by varying those parameters in the linear stability analysis. In the nonlinear time-domain simulations, by trying different longitudinal position of COG, one can find the critical trim angle when the porpoising commences. The obtained trim limits agree generally with those predicted by the linear stability analysis. Bounded oscillations for the unstable cases near the critical trim angle can be seen in the time-domain simulations due to the nonlinear effects.     

Optimal tyre usage for a Formula One car

Variations in track temperature, surface conditions and layout have led tyre manufacturers to produce a range of rubber compounds for race events. Each compound has unique friction and durability characteristics. Efficient tyre management over a full race distance is a crucial component of a competitive race strategy. A minimum lap time optimal control calculation and a thermodynamic tyre wear model are used to establish optimal tyre warming and tyre usage strategies. Lap time sensitivities demonstrate that relatively small changes in control strategy can lead to significant reductions in the associated wear metrics. The illustrated methodology shows how vehicle setup parameters can be optimised for minimum tyre usage.