【作者】 杜德芳；

【导师】 解茂昭；

【作者基本信息】 大连理工大学 ， 工程热物理， 2006， 硕士

【摘要】 柴油机中的燃烧过程是典型的湍流扩散燃烧,湍流扩散燃烧是一种极其复杂的带有化学反应的流动现象。要对其工作过程进行模拟,目前使用最多的办法就是将湍流与化学反应解耦,分别进行求解,然后再将两部分结果耦合到一起。由于柴油机中在高雷诺数和高Damkoeler数的情况下,燃烧反应区厚度小于湍流耗散尺度,火焰极薄,其微元保持层流结构,因此,湍流火焰可视为嵌入湍流流场内局部具有一维结构的薄的层流小火焰的系综,这便构成了层流小火焰模型主导思想,同时也使层流小火焰模型模拟柴油机湍流燃烧过程成为可能。 层流小火焰模型在近年来得到了广泛的应用,但是,在内燃机上的应用却不多,国内关于此方面的研究基本上仍是空白。本文作为初步尝试,将层流小火焰模型应用于典型的柴油机扩散燃烧过程,以一台直喷式柴油机为对象,分别以碳十二烷与空气的单步反应和正庚烷与空气的多步反应为机理,以混和分数为自变量,以标量耗散率为参数,建立相空间中组分质量分数瞬时值及温度瞬时值的二维层流小火焰数据库。以KIVA-3程序为基础,摒弃其原有的化学反应模型,模拟内燃机缸内多维湍流流场,并补充求解混合分数的时均值及其脉动均方值的湍流输运方程,得出各曲轴转角下混合分数的时均值及其脉动均方值的缸内空间分布。将两部分结果通过Beta概率密度函数进行耦合积分,得到组分质量分数和温度等参数时均值在柴油机工作过程中的时间、空间分布。 将对这台直喷式柴油机所得到的计算结果与文献中相同类型发动机的实验及计算结果进行比较,其缸内平均温度曲线和放热率曲线在总体趋势上比较一致,表明小火焰模型应用于柴油机湍流燃烧模拟的可行性及其在预测燃烧过程细节方面所具优势。但对瞬态过程而言,为达到满意的预测精度,小火焰模型还有改进的必要和潜力。更多还原

【Abstract】 The combustion process in diesel engine is a typical turbulent diffusion combustion, which is an extremely complicated flow phenomenon coupled with chemical reactions. To simulate the diesel engine working process, the most used models decouple the turbulent flow and the chemical reaction into two parts. Firstly, the two parts are solved separately, and the results are then coupled together. Because the thickness of the combustion reaction zone at high Re and Da numbers is less than the turbulent diffusion scale in diesel engines, the flame is extremely thin, its micro-structure keeps the laminar structure, so the turbulent flame can be regard as the ensemble of locally one dimensional, thin laminar flamelet embedded within the turbulent flow field. This builds up the fundamental of the flamelet model, and makes it possible to use the laminar flamelet model to simulate the complicated turbulent combustion process in diesel engines.The laminar flamelet model has been widely used in the recent years, but its application to the internal combustion engine is still scarce. The domestic investigation in this aspect is almost blank. As the first attempt, this paper applies the laminar flamelet model to the typical diffusion combustion in diesel engines. A database of the laminar flamelet for a DI engine is built up in the phase space of the mixture fraction with the scalar dissipation rate as parameter. Based on the KIVA-3 code, deactivating its original chemical reaction module, the in-cylinder multidimensional turbulent flow field is numerically computed; to which two transport equations for the mean mixture fraction and its variance are solved additionally. By utilizing an assumed Beta function formed probability density function (PDF), the results obtained from the laminar flamelet database and the KIVA-3 code are coupled and integrated, the time history and space distribution of parameters, such as the species mass fraction and temperature through the engine working processes can be then determined.Comparing the results of the DI engine to the experimental and computational results for a similar engine from the literature, the temperature curve and the heat release rate curve are in accordance with each other in general. This indicates the feasibility of applying the laminar flamelet model to the engine simulation, and the results of this paper can be a reference for further investigation.更多还原