用于发动机虚拟开发的3D-CFD-CHT方法

An Effective 3D-CFD Methodology for the Complementary Virtual Development of Alternative Fuels and Engine Concepts

摘要:

为降低开发成本，需要在开发过程中明确几何结构、总成布置及不同燃料对内燃机性能的影响，这其中一种有效的创新性融和分析方法——三维计算流体动力学-热-结构耦合（3D-CFD-CHT）方法已然成为内燃机开发过程中必不可少的工具。该类工具正在被越来越多的制造商用于发动机开发方案筛选及样机原型确定。本文主要介绍一种由斯图加特汽车工程与车辆发动机研究所（FKFS）开发的针对内燃机虚拟开发的3D-CFD仿真工具—QuickSim。该工具通过将较为粗糙的计算网格与自行开发的内燃机模型有效结合，有效减少计算时间，能以较高精度模拟整个发动机的运行。本文以尽可能实现高燃烧效率及低污染排放为目标，展示该工具在不同替代燃料发动机方面的设计优化能力，探讨不同燃料如氢气、甲醇、各类合成燃料及生物燃料对不同发动机几何结构的影响，探讨燃油喷射系统以及点火系统（包括主动和被动预燃室）对发动机的影响。同时，针对甲烷和氢气发动机，讨论稀薄燃烧对减少节流和爆震的影响；总结如何根据任一选定燃料，通过合理的几何结构设计，提高发动机的指示功率。

Abstract:

With the aim of reducing the cost of developing internal combustion engines， while at the same time investigating different geometries， layouts and fuels， 3D-CFD-CHT simulations represent an indispensable part for the development of new technologies. These tools are increasingly used by manufacturers， as a screening process before building the first prototype. This paper presents an innovative methodology for virtual engine development. The 3D-CFD tool QuickSim， developed at FKFS， allows both a significant reduction in computation time and an extension of the simulated domain for complete engine systems. This is possible thanks to a combination of coarse meshes and self-developed internal combustion engine models， which simultaneously ensure high predictability. The present work demonstrates the capabilities of this innovative methodology for the design and optimization of different engines and fuels with the goal of achieving the highest possible combustion efficiencies and pollutant reductions. The analysis focuses on the influence of different fuels such as hydrogen， methanol， synthetic gasolines and methane on different engine geometries， in combination with suitable injection and ignition systems， including passive and active pre-chambers. Lean operations as well as knock reduction are discussed， particularly for methane and hydrogen injection. Finally， it is shown how depending on the chosen fuel， an appropriate ad-hoc engine layout can be designed to increase the indicated efficiency of the respective engines.