内燃机光学诊断试验平台和测试方法综述

活塞式内燃发动机是现代工业中应用最为广泛的动力机械装置。由于其内部燃料喷射、蒸发、燃烧等复杂的工作过程会对发动机的结构可靠性、能量利用效率和污染物生成产生极大影响，研究内部过程的物理机理并确定控制策略对于发动机的设计和改进具有重要的科学意义和实用价值。近年来，为更加深入理解发动机内部工作过程，研究人员广泛采用光学诊断试验技术来测量发动机缸内流动和燃烧特性。本文首先介绍了各类用于模拟发动机工作过程的试验台架（如定容燃烧弹、快速压缩机、光学发动机等）。在此基础上，分析了各类光学诊断技术的基本原理及其在发动机研究中的应用。光学诊断技术分为两类进行讨论，分别是基于传统光学的传统诊断技术（如纹影法、双色法等）和基于激光的先进诊断技术（如粒子图像测速法、激光诱导荧光法等）。光学诊断技术可在多尺度下测量缸内温度、物质浓度、液滴粒径等参数，为准确评估发动机喷油、蒸发、燃烧过程提供试验依据。更重要的是，光学诊断技术为更加深入理解高温高压环境下流动、燃烧的物理/化学机理提供了可能性，为开发高功率、高能效、低排放的先进发动机提供可靠的试验手段，同时为研究人员未来开展基础试验研究、更加深入地理解发动机工作过程提供指导。

A review of optical diagnostic platforms and techniques applied in internal combustion engines

The Internal Combustion engine (IC engine) is one of the most widely applied power machines in modern industry. Investigating the mechanisms of and developing control strategies for IC engines are of practical importance and give rise to interesting scientific issues, as the fuel penetration, evaporation and ignition inside the engine can tremendously affect the structure reliability, power efficiency and pollutant generation. In recent years, lots of efforts have been performed to achieve deeper understanding of the working processes of IC engines by applying experimental optical diagnostic techniques in engine-like laboratory platforms. This review starts with introducing the engine-like platforms (e.g. Constant Volume Combustion Bomb(CVCB), Rapid Compression Machine(RCM), optical engine, etc.) developed to experimentally simulate the practical working processes of practical IC engines. Moreover, multiple advanced optical diagnostic techniques are discussed, including their basic principles and particular applications for the study of detailed processes in IC engines. Specifically, two categories of optical diagnostic techniques are respectively discussed, including the traditional diagnostic techniques based on conventional optics (e.g. schlieren, Two Color Method, etc), and the laser-based diagnostic techniques (e.g. Particle Image Velocimetry, Laser Induced Fluorescence, etc). These techniques offer advantages to examine the spraying, evaporation and combustion processes of the IC engines by measuring the temperature, concentrations, droplet sizes and other valuable characteristics with multi-scale resolution. Furthermore, the diagnostic techniques enable deeper insights into the nature of the flow/combustion under high ambient pressure and temperature, which benefits us from understanding the physical and chemical mechanisms of engine processes in both macro and micro scales. This brief review is intended to be beneficial for both researchers and engineers to analyze the current shortcomings and limitations of the IC engines, and to design the state-of-the-art IC engines with better power performance, energy efficiency and pollutant reduction. Besides, the review paper is also intended to provide a guideline for researchers to conduct further fundamental experiments in IC engines to investigate the flow and combustion mechanisms.