【作者】 夏怀成；

【导师】 安子军；

【作者基本信息】 燕山大学 ， 机械设计及理论， 2014， 博士

【摘要】 变冲程发动机升功率和比质量功率大，经常工作的四冲程模式负荷率较高，排量小，具有良好的动力性、经济性和排放性。因此，开展变冲程发动机的研究具有理论意义和实际意义。在本文的前期研究工作中，对变冲程发动机的配气相位、热力性能等进行了初步的仿真分析。研究中发现，变冲程发动机在二冲程模式下，其换气方式、换气压力、配气定时和凸轮廓线等均对变冲程发动机的性能有重要影响。为分析这些影响因素及其确定方法，为变冲程发动机的实现奠定理论基础，开展主要研究工作如下：在充分论证国内外变冲程发动机研究现状的基础上，根据传统的内燃机结构及原理，分析了变冲程发动机的工作原理，明确了其两种工作模式——动力模式和经济模式，建立了变冲程发动机动力模式顶进顶排换气方式的配气定时原理图，阐述了四冲程和二冲程发动机主要换气理论，为变冲程发动机换气系统的研究奠定了理论基础。基于发动机热力学理论，运用AVL-BOOST的建模方法，建立了变冲程发动机顶进顶排模式热力学性能仿真数学模型和BOOST仿真模型，按照实验与经验相结合的方法，设置了仿真模型的边界条件和初始条件，经仿真得到了坎贝尔图，以动力性为目标，优化了变冲程发动机动力模式的配气定时，并对仿真结果进行了实验验证。基于流体力学理论，运用AVL-FIRE流场分析软件，分别建立了变冲程发动机动力模式顶进顶排和变冲程发动机动力模式顶进侧排两种换气方式的流场仿真模型，得到了两种换气方式的网格划分方法，对顶进侧排式仿真模型，建立了用固定网格与移动网格相结合划分其体网格的模型，研究了传统网格划分中交界面速度不连续的问题。根据发动机性能仿真分析和实验，设置了两种换气方式下缸内流场分析的边界条件、初始条件和合理的点火提前角，定义了观测缸内工质流动情况的截面。按照定性分析与定量分析相结合的方法，根据换气系统速度矢量场、燃烧温度场和湍动能场，定性分析了变冲程发动机动力模式顶进顶排和定进侧排两种换气方式的换气品质，根据仿真和实验，定量分析了两种换气方式的优缺点，比较研究了两种换气方式的缸内残余废气系数、气缸压缩压力、发动机功率、转矩、油耗率和排放物量等参量，定性分析和定量分析结果表明，顶进顶排换气是变冲程发动机动力模式的合理换气方式。对比分析了不同换气压力时各换气关键时刻的缸内流场纵向截面、不同位置横向截面的速度场和压力场，得出即无气流反喷又能减小换气短路损失的换气压力。在此基础上，基于ADAMS系统动力学和热机耦合理论，建立了曲柄连杆机构动力学模型，仿真得出热机耦合分析所需的压力、温度等边界条件，研究了变冲程发动机的活塞和活塞环等关键件的温度场和热应力场，得出其强度可以满足实验要求。基于ADAMS系统动力学理论，建立了变冲程发动机配气切换机构多柔体系统动力学仿真模型并对各种凸轮片体进行了模态处理；仿真得出该模型下的气门升程曲线并与TYCON刚性弹性体模型的气门升程曲线进行了对比，运用热力学仿真模型分析了这两种气门升程曲线对发动机动力性的影响；分析了多柔性体系统动力学的凸轮廓线的动力学特性，结果表明柔性体凸轮廓线能够更好地满足配气切换机构动力学要求。在此基础上，设计了变冲程发动机经济模式和动力模式的凸轮廓线。根据WH125-6原型机结构及参数，研制了变冲程发动机配气切换机构，确定了试验工况下的点火提前角、喷油脉宽和喷油时刻，搭建了变冲程发动机样机试验平台的，通过发动机台架试验，分析了WH125-6原型机、变冲程发动机经济模式、动力模式顶进侧排和动力模式顶进顶排等机型的性能，试验结果表明变冲程发动机经济模式具有较好的经济性，顶进顶排动力模式则具有较好的动力性。更多还原

【Abstract】 Variable stroke engines possess large output per litre and high ratio of mass toproduced power, in which the four stroke mode can allow higher load ratio and smallerdisplacement as compared to two stroke mode, thus it is a main working mode in variablestroke engine and has excellent power, fuel economy and emission performances.Therefore, it is meaningful to carry on the theory study and corresponding tests forvariable stroke engine. On the basis of the preliminary study about timing phase andthermodynamic performance, it is concluded that gas exchange type and pressure andvalve timing at the two stroke mode are three most import factors to decide the variablestroke engine performances. In order to further study the related factors, this papercompleted the following research works.The working principle of variable stroke engine was first analyzed according topervious study results as well as structure and working principle of traditional engine. Ithas two working modes, i.e. power mode and economy mode. In power mode, valvetiming principle was established for gas exchange way of top-in and top-exhaust (TITE).Furthermore, the theories of gas exchange both for the four stroke and the two strokeengines were analyzed respectively to prepare for studying gas exchange theory ofvariable stroke engine.Both the thermodynamic mathematic model and simulation model for TITE way ofvariable stroke engine were then established by means of engine thermodynamic theoryand AVL-BOOST software platform. Through setting boundary conditions and initialconditions of simulation model based on test and empirical data in AVL-BOOST software,Campbell chart was achieved as well as valve timing of power mode was optimizedconsidering power performance as optimization goal. The simulation results were alsochecked with a set of experiments.In power mode of variable stroke engine, the simulation models of two gas exchangeways of TITE and TISE (top-in and side-exhaust) were founded separately according tohydromechanics theory and AVL-FIRE software platform, in which the corresponding meshing method was studied. The volume mesh in TISE mode was meshed by combiningfixed mesh and moving mesh. There is a problem in traditional meshing, i.e., thediscontinuous velocity at interface which was solved in the simulation model. Accordingto engine performance results simulated in AVL-BOOST and experimental data, theboundary conditions, initial conditions and ignition advance angle were confirmed foreach gas exchange way, and then the flowing process of working medium in cylinders canbe simulated and observed directly.Through observing velocity vector field, temperature of combustion field andturbulent kinetic energy field on lateral and longitudinal section of gas exchange system,the features of two gas exchange ways were analyzed qualitatively. In addition, test resultswere also used to quantitatively analyze advantages and disadvantages of every gasexchange way besides simulation results. The features were compared with residual burntgas ratio and compression pressure in cylinders, effective power, torque, specific fuelconsumption and the amount of emission. In conclusion, TISE way in power mode canmake the performances of variable stroke engine more excellent than TITE way.Both velocity field and pressure field on longitudinal section and lateral sectionwithin cylinder were analyzed at every critical moment of gas exchange process withdifferent pressure. To eliminate reverse jet and decrease the loss caused by short out in gasexchange, a best gas exchange pressure was gained. On the basis of ADAMS andthermo-mechanical coupling theory, dynamics model of piston-crank mechanism wasestablished, and then the boundary condition including the parameters of temperature andpressure was simulated. Successively, in the case of different gas exchange pressure forvariable stroke engine, both thermal stress field and temperature field were studied aimingat some important parts consisting of piston and rings. The results indicate that most partsof engine can meet the experiment demand.The flexible multibody dynamic model was built for switching mechanism of valvetiming in ADAMS software and model analysis was carried out to various cams. Next,valve lift curve was gained through simulating and was contrasted with the curve achievedby TYCON software. BOOST thermodynamic model was also used to analyze power andtorque difference in two kinds of valve lift curve. The dynamic features of cam profile were then studied with the flexible multibody dynamic simulation. Results show flexiblecam profile is better to meet the dynamic demand of switching mechanism of valve timing.Additionally, cam profiles both for power mode and economy mode were designed in thispaper.The switching mechanism of valve timing for variable stroke engine was developedby referring to the structure and parameters of WH125-6engine. Then, the engine testplatform was set up after determining the spark advance angle, plus width and certainmoments of fuel injection. With the help of engine rig test, the performances of economymode of variable stroke engine, as well as TITE way and TISE way of power mode wereanalyzed besides WH125-6engine. To sum up, the economy mode of variable strokeengine has excellent fuel economy, while TITE way has better power performance thanTISE way in power mode of variable stroke engine.更多还原