LPG发动机行车无力原因分析与故障诊断维修

针对用于大型公交车的LPG发动机行车无力故障,从LPG发动机类型、LPG特性、LPG发动机工作原理及LPG公交车的维修情况入手,系统分析了导致行车无力的主要原因,通过典型维修案例,归纳总结了LPG公交车行车无力故障诊断维修方法与技巧。     

LPG发动机系统及其应用

概述LPG燃料的特性及使用LPG作燃料的发动机的优点，重点介绍了1—3t叉车上采用的尼桑H系列汽油机与美国IMPCO LPG转换装置配套的汽油／LPG双燃料系统。     

发动机工作原理模拟机构的设计与仿真

对单缸四冲程汽车发动机工作原理进行了分析,确定了汽车发动机工作原理模拟机构的简化设计方案,基于Pro/E自顶向下的设计方法,建立了汽车发动机工作原理模拟机构的缸体模型。在缸体模型里设计了曲轴滑块机构、正时与配气系统,并在Pro/E的Mechanism模块中进行了运动学仿真分析,实现了发动机工作原理模拟机构的四冲程模拟运动仿真。该模拟机构能够演示汽车发动机四个冲程的工程过程,具有操作简单、携带方便、原理易懂、成本低廉等特点。     

基于数值模拟的便携式机箱热仿真分析和设计

随着便携式机箱应用越来越广泛,其小型化和高集成度成为趋势,结构设计问题也随之而来,尤其是散热问题成为其能否可靠工作的关键因素。文中首先介绍了热仿真分析在当今电子设备设计中的重要性,利用数值模拟软件对某便携式机箱进行热仿真分析,采用强迫风冷的散热形式,对仿真分析模型进行合理的参数设置及网格划分,通过改变进风口的结构布局,使其主要功耗器件的温度低于85 ℃,满足了机箱的热设计要求,为其他类似电子设备机箱热仿真分析和设计提供了参考。     

发动机冷却系统中流动与传热问题数值模拟进展

着重论述利用数值模拟技术研究发动机冷却系统中流动与传热问题的发展现状,包括水套单相流及气液两相流流动、流－固耦合传热、一维与三维联合模拟等该研究领域的热点内容。耦合系统之间联合分析的方法准确反映了发动机各部件之间的影响关系,这种分析方法是目前研究的重点,但其中仍存在一些问题。基于此状况提出改进办法：针对不同工况选用循环平均参数作为燃气侧传热边界条件;水套进出口的流动边界条件,在稳态工况下设为定值,在过渡工况下通过循环一维仿真计算确定;应采用整体耦合方法进行计算,计算模型应尽量完整,但可以进行适当的简化,并总结出模型简化的原则。     

LPG公交客车发动机舱散热特性的CFD分析

针对液化石油气公交客车在高温环境下低速行驶时发动机舱温度过高的问题,利用计算流体动力学和传热学,研究公交客车发动机舱内空气对流传热基本规律.为了定量分析在恶劣工况下的发动机舱内空气流动速度场和温度场特性,在UG中建立了发动机舱的几何模型,并利用FLUENT软件对发动机舱的散热特性进行了数值仿真,通过仿真与分析,获取了在选定工况下的发动机舱内空气气流速度场和温度场,可知发动机舱内的不合理布局是引起发动机舱温过高的主要因素之一,同时对发动机舱的合理布局提出了建议.     

LNG发动机最佳点火提前角的模拟优化仿真

在某系列天然气发动机点火控制系统基础上,提出利用神经网络在线优化点火提前角,从而解决天然气发动机在使用过程中因磨损、老化等造成最佳点火提前角发生变化的问题,达到提高天然气发动机的动力性和燃气经济性的目的。首先通过Matlab/simulink建立的LNG发动机模型,编写标定程序,得出初始点火提前角,然后设计神经网络。优化策略为在稳定工况时,利用自适应神经网络在线修正,得出实时最佳点火提前角;在工况变化较快时直接读取MAP图,得到点火提前角。最后利用GT-POWER搭建天然气发动机模型进行仿真并与实测数据进行比较。     

脉冲爆震火箭发动机数值模拟研究

脉冲爆震火箭发动机是一种利用脉冲式爆震波产生高温、高压燃气发出的冲量来产生推力的新型推进系统。与常规液体火箭发动机相比,脉冲爆震火箭发动机具有更高的性能,并且结构更简单。本文应用特征线法给出一维爆震波在爆震管内的传播过程的解析解。对爆震波到达爆震管口后发动机的非定常排气流动过程进行了二维数值模拟,并对比了无喷管和带3种不同形式喷管(收敛喷管、收敛扩张喷管和扩张喷管)对发动机推力等性能参数的影响。     

产品喷涂装置Fluent仿真内部流场数值分析

现代工业设计智能分析机械喷涂的实际操作过程中,存在喷涂不均、喷幅上重或下重等问题。针对此类问题,利用数值仿真方法,通过Fluent软件中气-液两相流模型,对颗粒介质在喷枪内的流动状况进行数值模拟,分析喷幅分裂、喷涂不均、喷幅中央过厚等问题的原因,提出调整喷涂压强、喷嘴口径渐扩的变化率等解决措施。     

发动机燃烧性能的仿真分析

主要分析了过量空气系数对CNG发动机燃烧及排放物生成的影响，简要分析了点火提前角对燃烧的影响。     

Model-based optimization of injection strategies for SI engine gas injectors

A mathematical model for the prediction of the mass injected by a gaseous fuel solenoid injector for spark ignition (SI) engines has been realized and validated through experimental data by the authors in a recent work [1]. The gas injector has been studied with particular reference to the complex needle motion during the opening and closing phases. Such motion may significantly affect the amount of injected fuel. When the injector nozzle is fully open, the mass flow depends only on the upstream fluid pressure and temperature. This phenomenon creates a linear relationship between the injected fuel mass and the injection time (i.e. the duration of the injection pulse), thus enabling efficient control of the injected fuel mass by simply acting on the injection time. However, a part of the injector flow chart characterized by strong nonlinearities has been experimentally observed by the authors [1]. Such nonlinearities may seriously compromise the air-fuel mixture quality control and thus increase both fuel consumption and pollutant emissions (SI engine catalytic conversion systems have very low efficiency for non-stoichiometric mixtures). These nonlinearities arise by the injector outflow area variation caused by needle impacts and bounces during the transient phenomena, which occur in the opening and closing phases of the injector. In this work, the mathematical model previously developed by the authors has been employed to study and optimize two appropriate injection strategies to linearize the injector flow chart to the greatest extent. The first strategy relies on injection pulse interruption and has been originally developed by the authors, whereas the second strategy is known in the automotive engine industry as the peak and hold injection. Both injection strategies have been optimized through minimum injection energy considerations and have been compared in terms of linearization effectiveness. Efficient linearization of the injector flow chart has been achieved with both injection strategies, and a similar increase in injector operating range has been observed. The main advantage of the pulse interruption strategy lies on its ease of implementation on existing injection systems because it only requires a simple engine electronic control unit software update. Meanwhile, the peak and hold strategy reveals a substantial lack of robustness and requires expressly designed injectors and electronic components to perform the necessary voltage commutation.     

Numeric simulation for structure''s damage identification of space truss

Damage detection by using the changes of dynamic parameters is a conventional damage diagnosis method, however, some indices are not sensitive enough to the most structural damages. In this study, the analytical data of displacement modes of truss structure are obtained by using the finite element analysis soft—ANSYS. The mode analysis technique for the axial strain change of any stick is used to detect the steel trusses with different damages. The analytical results show that the damage location and degree of the truss stick can be effectively diagnosed by means of the axial strain change. __________ Translated from Journal of Wuhan University of Technology, 2006, 30(2): 285–288 [译自: 武汉理工大学学报]     

基于CFD的发动机冷却风扇性能仿真分析

基于CFD(Computational Fluid Dynamics)计算流体动力学方法,通过建模和数值模拟计算,对风扇进行流场分析,研究风扇结构对风扇性能的影响,得出不同风扇叶片倾角、轮毂比和叶片数下风扇的流量和效率值,分析探讨风扇结构参数对风扇性能的影响规律,为风扇改进设计提供参考.     

基于Pro/E的发动机曲柄滑块机构的运动仿真分析

阐述了单活塞发动机的工作原理,研究了在Pro/E软件环境中建立曲柄滑块机构模型,并可动态地进行曲柄滑块机构的运动仿真分析.以实例验证了参数化设计的曲柄滑块机构在计算机中虚拟装配完成之后的运动学仿真结果,可以快速完成机构设计的同时还能对所设计结果进行初步检验,节省了传统样机试验所需的时间、人力和财力.     

一种描述铝合金发动机活塞安定状态的非线性材料模型算法解析及其仿真验证

本文基于金属材料非线性本构理论,分析其连续函数构成方法,对一种适用于发动机活塞铸铝材料的非线性本构模型的算法进行数值化解析。利用ABAQUS接口开发相应的户材料子程序,并对铝合金活塞在高温环境下循环热载荷工况下安定性响应进行仿真计算。研究结果表明:这种本构模型对热荷载安定状态响应的描述合理可信,可以应用于发动机活塞低周热疲劳分析的仿真计算。     

发动机配气系统运动学仿真分析

配气机构是内燃机的重要组成部分,虚拟样机技术是研究配气机构的重要方法。本文基于多刚体系统运动学原理,并利用ADAMS中的专用模块ADAMS/Engine对某高速汽油机的配气机构进行了运动学建模及仿真研究,获得了气门在不同转速下的位移、速度和加速度曲线。通过分析仿真结果,得出了气门的运动规律,指出了气门冲击、振动随速度变化的趋势。这对发动机配气机构的结构设计、动力学分析、性能预测、故障诊断起到积极的作用。     

Piston crevice hydrocarbon oxidation during expansion process in an SI engine

Combustion chamber crevices in SI engines are identified as the largest contributors to the engine-out hydrocarbon emissions. The largest crevice is the piston ring-pack crevice. A numerical simulation method was developed, which would allow to predict and understand the oxidation process of piston crevice hydrocarbons. A computational mesh with a moving grid to represent the piston motion was built and a 4-step oxidation model involving seven species was used. The sixteen coefficients in the rate expressions of 4-step oxidation model are optimized based on the results from a study on the detailed chemical kinetic mechanism of oxidation in the engine combustion chamber. Propane was used as the fuel in order to eliminate oil layer absorption and the liquid fuel effect. Initial conditions of the burned gas temperature and in-cylinder pressure were obtained from the 2-zone cycle simulation model. And the simulation was carried out from the end of combustion to the exhaust valve opening for various engine speeds, loads, equivalence ratios and crevice volumes. The total hydrocarbon (THC) oxidation in the crevice during the expansion stroke was 54.9% at 1500 rpm and 0.4 bar (warmed-up condition). The oxidation rate increased at high loads, high swirl ratios, and near stoichiometric conditions. As the crevice volume increased, the amount of unburned HC left at EVO (Exhaust Valve Opening) increased slightly.     

Artificial neural network based on genetic algorithm for emissions prediction of a SI gasoline engine

This paper proposes a hybrid learning of artificial neural network (ANN) with the nondominated sorting genetic algorithm-II (NSGAII) to improve accuracy in order to predict the exhaust emissions of a four stroke spark ignition (SI) engine. In the proposed approach, the genetic algorithm (GA) determines initial weights of local linear model tree (LOLIMOT) neural networks. A multi-objective optimization problem is determined. A sensitivity analysis is performed on NSGA-II parameters in order to provide better solutions along the optimal Pareto front. Then, a fuzzy decision maker and the technique for order preference by similarity to ideal solution (TOPSIS) are employed to select compromised solutions among the obtained Pareto solutions. The LOLIMOT-GA responses are compared with the provided by radial basis function (RBF) and multilayer perceptron (MLP) neural networks in terms of correlation coefficient R ².