【作者】 张鹏飞；

【导师】 陈锐； 卫海桥；

【作者基本信息】 天津大学 ， 动力机械及工程， 2017， 硕士

【摘要】 随着能源危机和环境污染的日益严重,各国纷纷制定了越来越严格的汽车油耗和排放法规,因此对发动机的节能减排提出了更高的要求。合理组织缸内燃烧以提高发动机的热效率是发动机节能减排最直接、最有效的手段。SI发动机缸内燃烧为预混湍流燃烧,缸内湍流对可燃混合气的形成、着火、燃烧和火焰传播过程有着重要影响。为进一步探明湍流对火焰及燃烧的影响机理,进而通过控制湍流合理组织缸内燃烧,本文从湍流对火焰传播影响的角度出发,通过数值仿真研究了湍流脉动强度对火焰传播及火焰微观形态的影响,基于快速压缩机实验探究了湍流对点火过程及火焰传播过程的影响。首先,基于快速压缩机燃烧室建立了计算模型,在Converge软件中使用大涡模拟的方法,计算了从火花点火开始的缸内燃烧情况,通过Passot Pouquet湍动能能谱方程设置了u’=0、0.5、1.0、2.0 m/s四种不同湍流脉动,开展了不同湍流脉动强度对火焰及燃烧影响的研究。结果表明:随着湍流脉动强度增加,湍流脉动与火焰的相互作用加强,湍流脉动对燃烧的加速效果增强,燃烧相位提前;随着压力升高,湍流脉动对火焰传播的加速效果更加明显;火焰由层流火焰发展到湍流火焰时,火焰面周围湍流脉动更加强烈,由于湍流的作用火焰面也变得更加褶皱。其次,为了从实验角度研究湍流对燃烧状态的影响,进行了快速压缩机实验平台的开发及调试。通过分析各系统参数对活塞运动的影响,确定了驱动压力为1.0 MPa、排气口开启数为5、燃烧室初始压力小于1.4 bar,从而获得快速压缩、上止点前无回弹的活塞运动特性。同时,对平台其他功能进行了优化改进,加强了平台可靠性及实验效率,并提出了规范化、流程化的实验步骤。最后,基于快速压缩机实验平台,研究了热力学参数、当量比及点火时刻对燃烧的影响。在此基础上,通过使用不同结构的活塞在压缩后实现不同的缸内流动,研究了湍流强度对燃烧过程的影响。结果表明:随着初始压力的升高,活塞运动过程中产生的湍流减弱,对燃烧的促进效果减弱;在不同当量比工况下,当量比为1.0时火焰传播速度更快,此时湍流对燃烧的增强作用高于当量比为0.5和2.0工况;湍流对点火过程有抑制作用,点火时刻在上止点前5 ms到上止点后10 ms内,湍流对点火的抑制作用随着点火的延后而增强。更多还原

【Abstract】 The energy crisis and environmental pollution become more and more serious.Automobile has a lot of energy consumption and carbon emissions.So its regulations of fuel consumption and emission are also more and more stringent,which puts forward higher requirements for energy saving and emission reduction of engines.It is the most effective method for engine to realize energy saving and emission reduction that improving the thermal efficiency of the engine by appropriately organizing the combustion in the cylinder.The combustion in the cylinder of a SI engine is premixed turbulent combustion.And the turbulence in the cylinder has an important influence on the formation,ignition and combustion of combustible mixture and the propagation of flame.For further study on the influence mechanism of turbulence on flame and combustion,and then appropriately organize the combustion in the cylinder by controlling the turbulence,this paper investigated the influence of turbulence intensity on flame propagation and flame micromorphology through the numerical simulation.An experimental platform of a rapid compression machine has been build.The experiment under different turbulence intensity conditions were carried out based on that platform.The influence of turbulence on ignition and flame propagation process were explored by analyzing cylinder pressure.First of all,the calculation model of the rapid compression machine combustion chamber was established.The combustion process from the beginning of the spark ignition in cylinder was calculated by large eddy simulation in Converge software.Four different turbulence fluctuation were set up by Passot Pouquet turbulent energy spectrum equations.The effect of different turbulence intensity on the combustion and flame were researched.The results show that with the increase of turbulence intensity,the interaction of turbulent eddies and combustion flame are strengthen,the effect of turbulence on the acceleration of flame is enhanced,the combustion phase in advance.With the increasing of the pressure,the accelerate effect of turbulence on flame propagation is more obvious.When the flame propagation to the turbulent flame from the layer flame,turbulent fluctuation around flame becomes more strong,the flame surface becomes more fold because of the effects of turbulence.Secondly,the experimental platform of a rapid compression machine was developed and debugged,in order to verification the influence of turbulence on the combustion from the experiment.The influences of system parameters on the movement of the piston are analyzed.For acquire an ideal piston motion characteristics,the driving pressure has been set up as 1.0 MPa,the number of exhaust port opened has been set up as 5 and the initial pressure is less than 1.4 bar.At the same time,the other functions of the platform had been optimized,the reliability of the platform and the efficiency of the experiment were strengthened.The experimental steps were put forward for standardization.Finally,the influence of the thermodynamic parameters,the equivalent ratio and the ignition time on the combustion were studied on the experimental platform of a rapid compression machine at first.Then the effect of turbulence intensity on the combustion process was studied by using the piston of different structures for achieve different internal flow in the cylinder after compression.The results show that with the increase of initial pressure,generated weakened in the process of piston movement,and the effect of turbulence on combustion under the low initial pressure is more obvious.As the equivalent ratio was 1.0,the enhancement of turbulence on combustion was higher than that of 0.5 and 2.Turbulence has inhibitory effect on the ignition process.When the ignition time arrange from 5 ms BTDC to 10 ms ATDC,the turbulence inhibiting effect on the ignition delay increases with delay of ignition time.更多还原