THEORETICAL INVESTIGATION OF TURBULENT COMBUSTION IN STRATIFIED INHOMOGENOUS MIXTURES USING DIRECT NUMERICAL SIMULATION

这个项目的目的是了解湍流对碳氢燃料燃烧的影响，其中燃料和氧化剂分布在点燃时形成高度分层的混合物。对于分层装药燃烧，反应物既不均匀混合（预混），也不完全分离（非预混）。因此，与完全预混或完全非预混火焰相比，分析这种燃烧具有特殊的建模需求。分层燃料-空气混合物中的湍流燃烧与火花点火汽油发动机和压缩点火柴油发动机高度相关，并且具有降低燃料消耗的潜力，特别是在汽车应用的低速，轻负荷运行中。分层装药燃烧也可以在飞机燃气轮机的精益预混预汽化（LPP）燃烧室中发现，其中燃料和注入的二次空气在火焰前形成不均匀的燃料-空气混合物。在混合不均匀性和强烈湍流存在下准确预测火焰传播行为的能力将促进低排放、节能设备的发展，如汽车发动机和燃气轮机燃烧器。本研究计划由三部分组成。首先，将对各种混合场和湍流强度进行简化的三维（3-D）直接数值模拟（DNS），适用于实际碳氢燃料的燃烧，以提高对现有基本理解的现状，并为评估现有燃烧模型创建一个数据库，并在必要时开发新模型。在简化化学的三维DNS信息的基础上，进行具有合理精细化学程度的三维DNS。该项目的第二部分涉及在雷诺平均纳维斯托克斯（RANS）和大涡模拟（LES）的背景下开发燃烧模型。该模型的实施将着眼于未来纳入行业标准的计算流体动力学（CFD）软件包，然后可用于工程设计目的。

The aim of this project is to understand the effects of turbulence on hydrocarbon fuel combustion where the fuel and oxidizer distribution form a highly stratified mixture at the time of ignition. For stratified charge combustion the reactants are neither homogeneously mixed (premixed) nor completely separated (non- premixed). Thus the analysis of this kind of combustion has special modelling needs in comparison to fully premixed or fully non-premixed flames. Turbulent combustion in a stratified fuel-air mixture is highly relevant in the context of both spark-ignition gasoline and compression-ignition Diesel engines and has the potential for reducing fuel consumption especially at low-speed, light- load operations in automobile applications. Stratified-charge combustion can also be found in the Lean Premixed Prevaporised (LPP) combustors in aircraft gas turbines where fuel and injected secondary air form an inhomogeneous fuel-air mixture ahead of the flame front. The capability of predicting accurately the flame propagation behaviour in the presence of mixture inhomogeneities and intense turbulence would facilitate the development of low-emission, energy-efficient devices, such as automotive engines and gas-turbine combustors. The proposed research project consists of three parts. In the first, three-dimensional (3-D) Direct Numerical Simulations (DNS) with simplified chemistry, appropriate for the combustion of realistic hydrocarbon fuels, will be performed for a variety of mixing fields and turbulence intensities to enhance the present state of fundamental understanding and to create a database for the assessment of existing combustion models and to develop new models wherever necessary. Three-dimensional DNS with a reasonable degree of detailed chemistry will be carried out based on the information gained from 3-D DNS with simplified chemistry. The second part of the project involves the development of a combustion model in the context of Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulations (LES). The model will be implemented with a view to future incorporation into industry-standard Computational Fluid Dynamics (CFD) packages, which can then be used for engineering design purposes.