An approximate thermal analysis of Stirling engine regenerators

This paper approximates the transport phenomena in a Stirling engine regenerator to aid its practical design. The mass flow rates are simplified by a square-wave function and the pressure variations, by a saw-tooth function with a phase difference. Approximate analytical solutions obtained in this study agree well with the available numerical solutions. Using the approximate solutions of the transport phenomena the entropy generation rates in a regenerator are analytically formulated and calculated, which come from axial conduction loss, imperfect heat regeneration, and pressure drop due to fluid friction. The geometry of the minimum entropy generation rate can represent the optimal design parameters of the regenerator     

Design of a transverse-flux permanent-magnet linear generator and controller for use with a free-piston stirling engine

Transverse-flux with high efficiency has been applied in Stirling engine and permanent magnet synchronous linear generator system, however it is restricted for large application because of low and complex process. A novel type of cylindrical, non-overlapping, transverse-flux, and permanent-magnet linear motor(TFPLM) is investigated, furthermore, a high power factor and less process complexity structure research is developed. The impact of magnetic leakage factor on power factor is discussed, by using the Finite Element Analysis(FEA) model of stirling engine and TFPLM, an optimization method for electro-magnetic design of TFPLM is proposed based on magnetic leakage factor. The relation between power factor and structure parameter is investigated, and a structure parameter optimization method is proposed taking power factor maximum as a goal. At last, the test bench is founded, starting experimental and generating experimental are performed, and a good agreement of simulation and experimental is achieved. The power factor is improved and the process complexity is decreased. This research provides the instruction to design high-power factor permanent-magnet linear generator.     

自由活塞斯特林发动机运行频率

自由活塞斯特林发动机运行频率是发动机的关键参数。区别于传统的曲柄连杆斯特林发动机,自由活塞斯特林发动机的运行频率由系统充气压力、动质量、弹簧刚度、阻力系数等热动力学参数耦合确定,因此确定自由活塞斯特林发动机的运行频率较为复杂。为了能够定量计算自由活塞斯特林发动机的运行频率,笔者建立了耦合发动机热动力学参数的数值模型。首先,在模型中对压力波进行线性化处理,得到了自由活塞斯特林发动机运行频率的计算公式;然后,运用模型分析了主要参数对发动机运行频率的影响规律,并与实验结果相对比,发现模型计算结果较为准确;最后,分析了当板弹簧刚度大幅度增加时,发动机的运行频率却变化较小,主要原因在于原有板弹簧的最高自然频率较低。结果表明：优化设计了新的板弹簧,使发动机运行频率大幅度升高,在采用新的板弹簧之后发动机的运行频率从原来的35 Hz提高到60 Hz。     

自由活塞斯特林发动机动力活塞气体作用效应

为了能够深入认识自由活塞斯特林发动机动力活塞的运行特性,找到提高自由活塞斯特林发动机效率的方法,对配气活塞固定不动时的动力活塞的气体作用效应进行了理论分析,并设计了动力活塞的单独运动实验,在此基础上提出了动力活塞自然频率的计算公式。研究了压缩腔压力波超前与滞后动力活塞位移两种情况下动力活塞受到的气体力的作用情况,采用旋转矢量法阐述了气体力的作用机理。当压力波超前或滞后活塞位移小于90°时,一部分气体力发挥了气体弹簧的作用,使系统自然频率增大;当压力波超前或滞后活塞位移大于90°但小于180°时,一部分气体力发挥了惯性力的作用,使系统自然频率减小,且热源温度越高,系统的自然频率越大。利用本实验室的一台自由活塞斯特林发动机进行实验,验证了上述气体力作用的效应与规律,利用此理论计算系统自然频率和实验相差不超过2%,使得斯特林发动机成功启动。     

活塞轴向综合误差对斯特林热机循环影响分析

基于施密特循环理论分析方法,以功率25 kW、转速1500 r/min的斜盘式太阳能斯特林热机为例,考虑各个工质循环单元中最小循环压力不变及各种热损失的情况下,利用Matlab软件计算分析了斜盘传动机构中活塞轴向综合误差对斯特林热机循环性能的影响.分析结果表明：该误差对斯特林热机的最大循环压力、基本功率、输出轴扭矩和示功循环效率等性能产生了一定的影响,对斯特林整机运行造成不同程度的不平衡性.     

生物质直燃斯特林发电机组实验分析

对斯特林发动机的工作原理与生物质燃料的热能转换过程进行了分析,在此基础上进行了1kW生物质直燃微型斯特林发电机组设计。对该设计样机进行了热、电联产实验,通过对实验数据与仿真曲线的分析,得出了该机在工作过程中充电电压、充电电流随发动机转速与压力的变化规律,以及热、电关系,发电效率和热电总效率。生物质直燃斯特林发电机组的设计为生物质能源的充分利用拓展了市场。     

斯特林发动机活塞环密封摩擦副法向力研究

针对一种斯特林发动机组合式活塞环动密封结构,根据系统运行及气体密封泄漏机理,考虑密封结构的各个设计参数及密封材料的物理特性,结合密封摩擦副的工况条件,再基于一定的假设及近似等值取代,构建了一套活塞环密封摩擦副正压力的计算公式。     

The effect of exhaust gas recirculation (EGR) on combustion stability, engine performance and exhaust emissions in a gasoline engine

The EGR system has been widely used to reduce nitrogen oxides (NOx) emission, to improve fuel economy and suppress knock by using the characteristics of charge dilution. However, as the EGR rate at a given engine operating condition increases, the combustion instability increases. The combustion instability increases cyclic variations resulting in the deterioration of engine performance and emissions. Therefore, the optimum EGR rate should be carefully determined in order to obtain the better engine performance and emissions. An experimental study has been performed to investigate the effects of EGR on combustion stability, engine performance, NOx and the other exhaust emissions from 1. 5 liter gasoline engine. Operating conditions are selected from the test result of the high speed and high acceleration region of SFTP mode which generates more NOx and needs higher engine speed compared to FTP-75 (Federal Test Procedure) mode. Engine power, fuel consumption and exhaust emissions are measured with various EGR rate. Combustion stability is analyzed by examining the variation of indicated mean effective pressure (COV_imep) and the timings of maximum pressure (P_max) location using pressure sensor. Engine performance is analyzed by investigating engine power and maximum cylinder pressure and brake specific fuel consumption (BSFC).     

环状与蜂窝蓄热体传热与阻力特性试验研究

蓄热换热器具有结构简单、造价低、效率高等优点,在余热回收方面有着广阔的应用前景。蓄热体作为蓄热换热器的关键部分,其形状、大小及材质等各项性能参数都会对蓄热系统的余热回收效果产生重要的影响。对环状和蜂窝这两种蓄热体的传热与阻力特性进行了试验研究,通过对试验结果分析,得出了热空气进口温度和速度对蓄热体冷热空气出口温度、传热速率、温度效率、热效率及阻力损失的影响规律,并从温度效率、热效率和阻力损失几方面比较了两蓄热体的传热与阻力性能,发现在低进口速度时环状蓄热体的综合性能更好。     

微型斯特林制冷机用线性压缩机研究

通过建立活塞运动方程、电机驱动方程,对线性压缩机的运行参数进行推导,进而结合实验数据对新研制的线性压缩机进行了动力学分析;实验给出了频率、充气压力等对制冷机运行特性的影响,得出影响压缩机性能的重要参数及其相互关系,从而为微型斯特林制冷机的优化设计提供了研究依据。     

双火花塞发动机性能的仿真分析

应用发动机三维性能模拟分析软件,计算出单火花塞点火发动机缸内循环工作压力,将其与实验值进行对比并修正,确定了合理的仿真参数。在此基础上,分别对单火花塞和双火花塞点火发动机的缸内燃烧状态和缸内循环工作压力变化趋势进行瞬态仿真对比,分析了双火花塞点火对发动机性能的影响。研究结果表明,双火花塞的火焰传播距离短、缸内燃烧迅速、最高爆发压力大,其最高爆发压力可提高4%以上。     

大型催化裂化装置再生器大孔分布板结构优化设计

由于催化裂化装置中再生器大孔分布板承受高温载荷作用，大孔分布板的热变形量很大，因此大孔分布板裙座根部的应力很大。本文通过调整大孔分布板的结构型式和不同材质的结构尺寸，采用有限元方法对大尺寸的大孔分布板在高温载荷作用下的十九个不同结构模型进行了计算和分析，从而确定了较为优化的结构设计方案。优化后的结构模型的最大应力比传统的设计方案下降77％。     

Numerical simulation of fully developed flow and heat transfer characteristics in a curved tube with pulsating pressure gradient

Characteristics of fluid flow and convective heat transfer of a pulsating flow in a curved tube have been investigated numerically. The tube wall is assumed to be maintained at a uniform temperature peripherally in a fully developed pulsating flow region. The temperature and flow distributions over a cross-section of a curved tube with the associated velocity field need to be studied in detail. This problem is of particular interest in the design of Stirling engine heat exchangers and in understanding the blood flow in the aorta. The time-dependent, elliptic governing equations are solved, employing finite volume technique. The periodic steady state results are obtained for various governing dimensionless parameters, such as Womersley number, pulsation amplitude ration, curvature ratio and Reynolds number. The numerical results indicate that the phase difference between the pressure gradient and averaged axial velocity increases gradually up to π/2 as Womersley number increases. However, this phase difference is almost independent of the amplitude ratio of pulsation. It is also found that the secondary flow patterns are strongly affected by the curvature ratio and Reynolds number. These, in turn, give a strong influence on the convective heat transfer from the pipe wall to the pulsating flow. The results obtained lead to a better understanding of the underlying physical process and also provide input that may be used to design the relevant system. The numerical approach is discussed in detail, and the aspects that must be included for an accurate simulation are discussed.     

Wear behavior of polymeric compositions in dry reciprocating sliding

The development of Stirling engines as high efficiency motors for automobiles is critically dependent on the ability of sliding seals to operate for long periods (up to 3500 h) without excessive leakage or wear. Piston rings must run completely dry while sealing against hydrogen leakage under a pressure drop of 5–20 MPa. Main seals, cooled by oil, must seal against similar pressures without admitting any oil which could contaminate the high temperature sections of the engine.The results of an initial search for materials with lower wear rates than the polytetrafluoroethylene (PTFE) polymer compositions currently used in test engines are described in this paper. On the basis of a literature review, the results of engine development tests and experience with solid lubricants, several commercially available formulations were selected for a screening test program. In addition, some custom formulations were prepared by commercial vendors.A reciprocating screening tester, operating at 1200 cycles min^?1 with a stroke of 40 mm, was used to determine material wear rates at a PV factor below the first PV limit of the reference PTFE material. Materials with wear rates in the range of 0.13 × 10^?6–0.16 × 10^?6 mm³ N^?1 m^?1 (the reference material wear rate was 0.40 × 10^?6 mm³ N^?1 were found.Friction coefficients were also measured since friction power loss in the seals represents a significant portion of the total mechanical engine losses. Compositions which significantly reduced the friction coefficient while retaining a low wear rate were found.     

Supercharging performance of a gasoline engine with a supercharger

Supercharging of intake air can improve the engine power and combustion characteristics by boosting the intake pressure above atmospheric pressure. In this work, the supercharging performance of a supercharged gasoline engine was discussed on the basis of experimental investigation. The investigation results showed that the output and torque performance of a supercharged engine were improved in comparison with the naturally aspirated engine. In the engine system with a supercharger, owing to supercharging of intake air into the cylinder, the combustion pressure, the rate of heat release, and the burning rate of fuel-air mixture were found to be higher than those of the naturally aspirated engine. In this paper, the effect of the drive pulley ratio and the pressure ratio of supercharger, and the other factors on the supercharging performance were also investigated.     

Dynamic deformation of hot temperature degraded POM and PP using a modified SHPB with pulse shaper technique

The conventional split Hopkinson pressure bar (C-SHPB) technique with a special experimental apparatus is used to obtain a dynamic deformation material behavior under a high strain rate loading condition. An experimental modification is introduced to reduce the non-equilibrium on the dynamic material response during a short test period for two polymeric materials. The proposed method uses aluminum pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials such as hot temperature degraded POM (Poly Oxy Methylene) and PP (Poly Propylene) to obtain more distinguishable experimental signals. In addition, a pulse shaper technique is used for increasing the rise time of the incident pulse to ensure the dynamic stress equilibrium and the homogeneous deformation in the specimen under dynamic compression loading condition. The details on the dynamic stress equilibrium and the duration of uniform strain rate during the dynamic deformation of the specimen are experimentally investigated. The effects of degradation at a few different hot temperatures on the maximum compressive stresses are also experimentally studied under varying impulsive loading conditions.     

A dynamic model of a V-shaped free-piston engine

A model of one of the classes of a free-piston Stirling engine, namely a two-piston engine with V-shaped positioning of cylinders, is considered. The differential equations describing the dynamics of the engine as a self-oscillating system are derived taking sluggishness of the moving engine elements (pistons) and redistribution of the actuating medium volumes in the cylinders into account.     

基于大小气缸与大小活塞的新型发动机系统性能预测分析

为提高现有内燃发动机的热效率,在分析斯特林发动机以及常规发动机特点的基础上提出基于大小气缸与大小活塞的带回热器的新型发动机系统.气体在该新型发动机系统的小气缸中受到压缩,压缩的过程中喷入水雾以便降低压缩功耗.压缩后的气体在回热器中受到初步加热后进入大气缸,与喷入大气缸中的燃料混合、燃烧并做功,做功后的气体在回热器中放热后被排入大气.在对系统深入分析的基础上,建立新型发动机系统的性能计算模型.利用数学模型,计算该新型发动机系统热效率在不同压缩比、不同的最高工作温度以及不同的活塞效率条件下的变化规律,并与相同条件下的常规奥托循环与狄塞尔循环的热效率进行对比.结果表明,这种新型发动机系统比常规发动机具有更高的热效率,最多可以提高20%以上.而且新型发动机系统的效率还随着回热器的效率增加而增加,增幅可以接近10%.     

Network analysis of an engine lubrication system

A computer program for the analysis of engine lubrication systems has been developed. A case study of a four-cylinder gasoline engine is illustrated. This paper gives the mathematical models for oil flow through a hydraulic tappet as well as those of an oil jet and plain journal bearings. The flow from an oil pump and the flow resistance through an oil filter is considered at various temperatures. In the analysis, various design guidelines are applied. The distribution of flow and pressure of an engine lubrication system is calculated, and the pressure data compared with the experimental data at a few points in the engine lubrication system. This method is helpful to design an engine lubrication system efficiently.     

The effect of combustion parameters on the nitric oxide emission in direct injection type diesel engine

This paper presents the investigation of influence factors on the output performance and the reduction of exhaust emission in the direct injection type diesel engine. In this work, the analysis of combustion products and combustion characteristics are investigated by numerical method and experiment under the various engine operating conditions. The combusion performance and exhaust emissions are analyzed in terms of the heat release, cylinder pressure and major exhaust emissions of engine. The accuracy of the prediction versus experimental data and the capability of the heat release, cylinder pressure and all the major exhaust emissions are demonstrated. The results of this study show that the combustion parameters have influence on the combustion processes and the nitric oxide emission in the direct injection type diesel engine. The nitric oxide concentration decreases with the increase of engine speed and the advance of injection timing.