柴油微引燃天然气（HPDI）发动机缸内直喷射流诱导湍流场和燃烧相互作用机制研究

For the advanced internal combustion engine, the formation of the air-fuel mixture in the engine cylinder determines the quality of the combustion. The process of the air-fuel mixture due to fuel injection induces the turbulence in the cylinder. The interaction mechanism between combustion and turbulence is a decisive factor for the engine performance. The study object of this project is a diesel engine fueled with pilot-ignited high-pressure direct injection (HPDI) compressed nature gas (CNG). This project is to study the formation mechanism of the air-fuel mixture induced by high-pressure direct injection of two-phase fuels in the HPDI cylinder, and also the effects on the turbulence combustion. Optical experiments is carried out based on a constant volume bomb (CVB) and a rapid compression machine (RCM) to gain the basic experimental data of both the gaseous CNG & liquid diesel fuel jet injection and mixing as well as the stratified combustion. This project will investigate the synergy interaction mechanism of gaseous CNG and liquid diesel fuel under conditions of varied air turbulence. Further, the project is to illustrate the influences of both the large- and the small-scale turbulences on CNG and diesel fuel jet injection, and reveal the interaction mechanism of the turbulence on the combustion in the engine cylinder. The research of the project may provide the basic experimental data for realizing the stratified combustion of directly injected two-phase fuels in the engine cylinder.

高压直喷发动机的燃料在高速射流到气缸内时将通过卷吸空气，在缸内形成非均匀可燃混合物浓度场，该过程诱发的缸内湍流场特征及其与燃烧相互作用机制是决定发动机缸内燃烧质量的关键因素。项目以柴油微引燃天然气缸内高压直喷（HPDI）发动机为对象，研究HPDI发动机缸内高压直喷气液两相双燃料射流诱导的混合气形成机理及其对湍流燃烧的作用机制，具体包括在定容弹、快速压缩机上开展光学测试， 获得发动机气缸有限空间内气态天然气和液态柴油射流混合和分层扩散燃烧的基础实验数据，探索发动机不同空气湍流度背景下气态天然气、液态柴油射流协同作用机制；阐明缸内空气大尺度和小尺度湍流对气态天然气、液态柴油射流的影响规律，掌握缸内湍流场的形成机制及其对燃烧的作用机制。申请项目将完善“有限空间多物理、多参数耦合的湍流与燃烧相互作用过程”的研究领域的基础试验数据，符合计划中“受限空间内复杂湍流和燃烧的相互作用”的研究范畴。

本项目基于柴油微引燃天然气缸内高压直喷（HPDI）发动机工作原理为基础，研究高压甲烷直喷射流着火特性。通过在定容弹上开展光学测试，获得气态天然气（甲烷）和液态柴油射流、混合和燃烧的基础实验数据，探索不同空气压力背景下气态甲烷、液态柴油射流协同作用机理；在此基础上结合三维甲烷直喷射流、柴油喷雾仿真计算，研究缸内高压甲烷直喷、柴油喷雾的动态特性及高压直喷气液两相混合气对湍流分层燃烧的作用机制。通过本项目的研究，探索了高压柴油射流喷雾贯穿特性的两段发展规律，并提出了贯穿距两段式的修改公式；建立了三维柴油喷雾的模型，提出了基于动态识别柴油喷雾破碎特征的ELSA改进方法；分析了高压甲烷直喷射流，发现了甲烷射流是脉动射流，具有动态特性，射流受喷孔内流动影响存在一定延时性；研究了甲烷射流对预混火焰的作用规律，发现甲烷射流对层流火焰有增强作用，促进层流火焰发展为湍流火焰。本项目的研究的理论成果可以为HPDI发动机燃烧提供理论支撑。