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

该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火时形成高度分层的混合物。对于分层进气燃烧，反应物既不是均匀混合的（预混合），也不是完全分离的（非预混合）。因此，与完全预混或完全非预混火焰相比，这种燃烧的分析具有特殊的建模需求。分层燃料-空气混合物中的湍流燃烧在火花点火汽油和压缩点火柴油发动机的情况下都是高度相关的，并且具有降低燃料消耗的潜力，特别是在汽车应用中的低速、轻负载操作下。分层充气燃烧也可以在飞机燃气涡轮机中的贫预混合预蒸发（LPP）燃烧室中找到，其中燃料和喷射的二次空气在火焰前缘之前形成不均匀的燃料-空气混合物。准确预测混合物不均匀性和强烈湍流情况下火焰传播行为的能力将促进低排放、高能效设备的开发，如汽车发动机和燃气轮机燃烧室。拟议的研究项目包括三个部分。在第一，三维（3-D）直接数值模拟（DNS）与简化的化学，适用于现实的碳氢燃料的燃烧，将进行各种混合场和湍流强度，以提高目前的基本理解状态，并创建一个数据库，用于评估现有的燃烧模型，并在必要时开发新的模型。将根据从具有简化化学的3-D DNS获得的信息进行具有合理程度的详细化学的三维DNS。该项目的第二部分涉及在雷诺平均纳维尔-斯托克斯（RANS）和大涡模拟（LES）的背景下的燃烧模型的发展。该模型将被实施，以期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.