基于传热系数反求法的船用柴油机组合活塞热分析

建立了柴油机组合活塞的2D有限元模型,并利用传热系数反求法对该模型进行热分析。在仿真分析中,将活塞头部外表面传热系数定义为设计参数,实测温度与仿真温度的差值定义为目标函数。通过仿真计算得到了活塞头部外表面传热系数的分布,并利用反求法得到的传热系数对有限元模型进行热分析,仿真结果与实测温度吻合;传热系数反求法收敛迅速,可以有效用于活塞及其他内燃机零部件的温度分布和热负荷分析。     

活塞环-气缸套润滑摩擦研究

活塞环与气缸套间的润滑、摩擦直接影响到内燃机的动力性、经济性和可靠性。在内燃机实际运行过程中,缸内工作过程循环变动及活塞气缸套间动接触导热直接影响到润滑油膜的状态,因而活塞环在缸套中的不同位置时的摩擦、润滑状态各不相同。在传统的活塞环组稳态热混合润滑的基础上,考虑到活塞组一气缸套动接触系统瞬态传热,建立了活塞环组的非稳态热混合润滑、摩擦数理模型及数值方法。运用该方法可模拟出活塞环组润滑、摩擦特性,并可预测出不同瞬时润滑油膜的温度场、压力分布、油膜厚度、摩擦功和摩擦热等重要参数。     

高原环境重型车用柴油机热负荷性能分析

以高原修正的广安博之喷雾模型为基础,建立具有环境适应性的某特种车辆柴油机缸内燃烧与冷却系统传热耦合模型。海拔3 700m的实车试验表明:模型最大误差在4.3%以内。在不改变发动机部件的前提下,通过调整柴油机供油提前角和最大循环供油量,可改善高原运行时特种车辆柴油机的热负荷。试验结果表明:在海拔4 000m时,供油提前角提前4°CA可使涡前温度最高下降30℃,活塞表面温度最高下降15℃,且表面温度场分布稍有改善,但缸内温度峰值上升20℃;在满足任务工况功率需求的基础上,供油量调整螺钉拧入角度为255°时,热负荷参数满足发动机控制参数要求。     

高周波活塞热冲击计算与分析

本文用6150柴油机燃气温度拟合成三角形热冲击模式，作为活塞顶面的热激励源，建立了高周波三角形热冲击及集总参数导热模型，计算该活塞顶面温度响应曲线及其变化规律，以作为活塞顶面热疲劳分析和研究的基础。     

Study of the steady and transient temperature field and heat flow in the combustion chamber components of a medium speed diesel engine using finite element analyses

The present work describes the development of a model for the calculation of the temperature field and heat flow in the combustion chamber components of internal combustion piston engines, which occur both under steady and transient engine operating conditions. Two and three-dimensional finite-element analyses were implemented for the representation of the complex geometry metal components (piston, liner and cylinder head). The model is applied for the piston and liner of a medium speed diesel engine, for which relevant experimental data exist in the literature. Special care is given for accurately specifying the thermal boundary conditions (temperatures and heat transfer coefficients). Gas side boundary conditions are calculated using a thermodynamic cycle simulation code, including spatial variation of the gas side heat transfer coefficient. Coolant sides (water on the external liner surface and oil on the piston undercrown surface) boundary conditions are calculated using correlations pertaining to real engine conditions. Also an effort is made to model the piston-ring belt-liner complex thermal paths using equivalent thermal circuits. A satisfactory degree of agreement is found between theoretical predictions and experimental measurements, revealing that the finite-element methods presented are successful in formulating this kind of problem, giving accurate results with reasonable computational cost. The utilization of the model reveals very clearly the essential role of engine operating transients (sudden changes in speed and/or load) in the generation of sharp temperature excursions in the metal components until a new steady state is reached. The phenomenon should be taken into account for correct engine design and safe operation (i.e. the avoidance of high local stresses).     

基于ABAQUS软件的CB250汽油机活塞热分析

活塞作为内燃机的主要受热零部件之一,由于受热面积大,散热条件差,承受非常大的热负荷。在进行设计改进时,需考虑其热负荷问题,应对其进行热场预测及数值分析,研究其热应力和热变形。笔者运用有限元分析软件Hypermesh和Abaqus,仿真分析得到活塞三维温度场,并计算其热变形,为活塞的结构改进和优化提供了重要依据。     

ω型柴油机活塞温度特性计算机模拟

活塞作为内燃机最重要的受热零部件之一,长期处于恶劣的工作环境中,承受着很高的热负荷,容易形成热疲劳而损坏.本文在相同的稳态边界条件下,研究柴油机ω型活塞三种不同的设计方案:方案1,对活塞内腔做喷油冷却;方案2,给活塞加内冷却油道强迫冷却;方案3,给第一道环槽镶中空环槽镶圈.利用有限元ANSYS软件分别对三种方案进行模拟仿真,获得其温度特性,由此可为该型活塞的结构优化提供参考依据.     

用耦合分析法研究内燃机活塞环-气缸套传热润滑摩擦问题

在以往对活塞环-气缸套润滑摩擦性能的研究中,大都忽略了活塞组-气缸套间的导热,或者将导热过程简化,这与该摩擦副的实际润滑摩擦状况相去甚远.把柴油机缸内燃气、活塞、活塞环、润滑油膜、气缸套、冷却介质作为一个耦合体,考虑各部件间及相应物理场间的耦合关系,采用耦合分析法建立了活塞环-气缸套的三维非稳态热混合润滑摩擦模型.该模型以三维瞬态热传导模型、动压润滑模型和润滑油膜传热模型为基础,并考虑了润滑油的黏温变化、燃烧室燃气泄漏、表面粗糙度、油膜破裂位置以及气缸套圆周方向上的非轴对称性等影响因素.采用上述模型,对6110型柴油机活塞环-气缸套摩擦副进行了传热、润滑、摩擦耦合分析,得到了活塞组-气缸套的温度场,并用试验证实了耦合模型的正确性;与此同时,得出了润滑油膜的温度、黏度、最小油膜厚度和摩擦热随曲轴转角和活塞环周向高度的分布曲线.     

Experimental investigation of a molten salt thermocline storage tank

Thermal energy storage is considered as an important subsystem for solar thermal power stations. Investigations into thermocline storage tanks have mainly focused on numerical simulations because conducting high-temperature experiments is difficult. In this paper, an experimental study of the heat transfer characteristics of a molten salt thermocline storage tank was conducted by using high-temperature molten salt as the heat transfer fluid and ceramic particle as the filler material. This experimental study can verify the effectiveness of numerical simulation results and provide reference for engineering design. Temperature distribution and thermal storage capacity during the charging process were obtained. A temperature gradient was observed during the charging process. The temperature change tendency showed that thermocline thickness increased continuously with charging time. The slope of the thermal storage capacity decreased gradually with the increase in time. The low-cost filler material can replace the expensive molten salt to achieve thermal storage purposes and help to maintain the ideal gravity flow or piston flow of molten salt fluid.     

Numerical study of heat transfer of hydrogen combustion in noble gases atmosphere in compression ignition engine

The high energy content of hydrogen and zero carbon emission from hydrogen combustion is very important for compression ignition engine development. Hydrogen requires a very high auto-ignition temperature, which encourages replacing nitrogen with noble gases with higher specific heat ratio during compression process. In noble gases-hydrogen combustion, higher combustion temperature potentially leading to a higher heat loss. This paper aims to investigate the effect of hydrogen combustion in various noble gases on heat distribution and heat transfer on the cylinder wall. Converge CFD software was used to simulate a Yanmar NF19SK direct injection compression ignition engine. The local heat flux was measured at different locations of cylinder wall and piston head. The heat transfer of hydrogen combustion in various noble gases at different intake temperatures was studied using the numerical approach. As a result, hydrogen combustion in light noble gases such as helium produces faster combustion progress and higher heat temperature. The hydrogen combustion that experienced detonation, which happened in neon at 340 K and argon at 380 K, recorded a very high local heat flux at the cylinder head and piston due to the rapid combustion, which should be avoided in the engine operation. At a higher intake temperature, the rate of heat transfer on the cylinder wall is increased. In conclusion, helium was found as the best working gas for controlling combustion and heat transfer. Overall, the heat transfer data gained in this paper can be used to construct the future engine hydrogen in noble gases.     

某汽油机冷却水套三维CFD分析

鉴于冷却水的流动与传热会直接影响发动机的冷却效率,高温零件的热负荷,整机的热量分配和能量利用,使用计算流体力学(CFD)软件对某汽油机冷却水套进行三维CFD分析,得到了冷却水套内冷却液的流场、换热系数分布、压力损失以及流量分布等信息,计算结果表明:该机冷却水套中流速和换热系数均能满足设计要求;气缸盖3缸冷却效果好于其它两缸。     

柴油机活塞的热及惯性力耦合研究

采用IDEAS软件研究了某型号柴油机活塞分别在热负荷作用下、惯性力作用下、以及在惯性力和热负荷共同作用下的强度及变形变化规律,热-机械负荷耦合下应力与变形的分布规律,找出了惯性力和热负荷对活塞应力与活塞变形所作的贡献。通过对原方案和改进后的方案比较,表明改进后活塞第一环内的温度明显降低,证明了改进设计的有效性,为该型号活塞的改进设计提供了依据。     

风冷柴油机活塞温度场的三维有限元分析

建立某双缸水平对置风冷柴油机的活塞三维实体模型,利用I-DEAS软件突破传统的简化方法,并充分考虑风冷柴油机传热的特点来确定传热边界条件,对活塞温度场进行有限元计算和分析。计算结果表明:活塞头部的温度接近极限,环区温度过高造成运行受阻,并与实际运行出现的情况相符。进一步的实验表明,计算结果与实验值相差小于5%,故该计算方法的计算结果基本上可以指导设计。     

Thermal fatigue on pistons induced by shaped high power laser. Part II: Design of spatial intensity distribution via numerical simulation

In the laser induced thermal fatigue simulation test on pistons, the high power laser was transformed from the incident Gaussian beam into a concentric multi-circular pattern with specific intensity ratio. The spatial intensity distribution of the shaped beam, which determines the temperature field in the piston, must be designed before a diffractive optical element (DOE) can be manufactured. In this paper, a reverse method based on finite element model (FEM) was proposed to design the intensity distribution in order to simulate the thermal loadings on pistons. Temperature fields were obtained by solving a transient three-dimensional heat conduction equation with convective boundary conditions at the surfaces of the piston workpiece. The numerical model then was validated by approaching the computational results to the experimental data. During the process, some important parameters including laser absorptivity, convective heat transfer coefficient, thermal conductivity and Biot number were also validated. Then, optimization procedure was processed to find favorable spatial intensity distribution for the shaped beam, with the aid of the validated FEM. The analysis shows that the reverse method incorporated with numerical simulation can reduce design cycle and design expense efficiently. This method can serve as a kind of virtual experimental vehicle as well, which makes the thermal fatigue simulation test more controllable and predictable.     

活塞冷却油腔位置对活塞强度的影响

采用有限元法对某型号柴油机活塞的冷却油腔位置的两种不同的方案进行研究,分析了活塞分别在热负荷作用下、惯性力作用下、以及在惯性力和热负荷共同作用下的强度变化情况。通过对两种方案比较．表明改进后活塞第一环内的温度明显降低,证明了改进设计的有效性,为该型号活塞的改进设计提供了依据。     

基于缸内燃烧分析的发动机金属温度场计算方法

为了提高发动机缸盖、缸体金属温度场分析的准确度,提出了一种基于缸内燃烧分析的发动机金属温度场分析方法。首先,基于发动机的标定信息,进行了缸内的燃烧分析,研究了各部分边界上的对流传热量;其次,进行了水套的流动分析,对其传热系数进行了评估;再次,考虑了活塞环与缸壁的摩擦换热及活塞与缸壁的热传导;最后,基于上述的热边界条件进行了金属温度场的计算,并与试验进行了验证。结果表明:采用该算法,缸盖、缸体金属温度场分布比较合理,监测点温度与试验比较吻合。     

Performance Analysis and Optimization of a Single-Barrier Solid-State Thermionic Refrigerator With External Heat Transfer

A model of a single-barrier solid-state thermionic refrigerator with external heat transfer is established in this paper. The performance of the refrigerator is analyzed and optimized by using the combination of finite-time thermodynamics and nonequilibrium thermodynamics. The general expressions for cooling load and coefficient of performance (COP) of the refrigerator are derived. The optimum regions of cooling load and COP are obtained and the effects of the heat reservoir temperature and thermal conductance of the barrier material on the performance of the refrigerator are analyzed by detailed numerical examples. The results obtained are compared with those obtained by using traditional analysis without considering external heat transfer. For the fixed total heat transfer surface area of two heat exchangers, the ratios of the heat transfer surface area of the hot-side heat exchanger to the total heat transfer surface area of the heat exchangers are optimized for maximizing the cooling load and COP of the refrigerator, respectively. The effects of the total heat transfer surface area and the applied voltage on the optimum performance of the refrigerator are analyzed. The results obtained herein may provide some theoretical guidelines for the design and application of practical solid-state thermionic refrigerators.     

高升功率柴油机铸铁活塞的设计与计算分析

分析了内燃机升功率对活塞热负荷及机械负荷的影响,明确了活塞变形是造成活塞机械应力集中的主要影响因素的观点,提出了采用大内冷油道薄壁框架结构并配合短活塞销,以减小活塞变形并强化活塞顶部冷却,从而降低并协调活塞热负荷及机械负荷的新设计思路。将此设计思路应用于高升功率柴油机铸铁活塞的结构设计中,并对新设计活塞进行了三维接触问题的有限元计算分析。     

柴油机活塞在流域换热冷却下的温度场计算分析

活塞作为低速机中承受极高热负荷的重要部件,实现活塞的合理冷却是保证柴油机安全稳定运行的必要手段。为了丰富国内关于低速机活塞复杂冷却腔冷却问题的研究,在借鉴前人研究成果的基础上,进一步分析研究了活塞在动态流域换热冷却下的温度场分布规律。研究发现,活塞的瞬态温度场和稳态温度场分布一致,最低温度均出现在顶面中心,顶面的温度变化趋势与缸内温度场变化规律一致。同时,通过活塞流域分析可知,冷却腔壁面的温度波动主要受冷却流域与壁面对流传热系数值的影响。     

C6190ZL C-A柴油机活塞温度场有限元分析

活塞是柴油机的重要组成部件,承受着很高的热负荷,活塞的温度场可以直观的展现活塞温度及其热流分布,为活塞的设计和优化指明方向。本文利用Pro/ENGINEER4.0进行建模,结合Ansys11.0对C6190ZLC-A柴油机活塞温度场进行了分析。对柴油机活塞边界条件进行了研究。通过有限元分析,得出了活塞温度的分布情况,并与测量值进行了比较,得出计算的结果符合活塞实际温度的分布。