高压密集喷雾对低过量空气系数高强化燃烧过程影响的基础研究

Nowadays highly intensity combustion has been widely adopted in the high power density diesel engines for its high power output. In the combustion chamber, massive fuel is injected at an ultra-pressure into the high density hot air where the mixing process takes places rapidly, and this is followed by an intensive combustion process. Therefore, the air fuel mixing process is dominated by the ultra-pressure high density fuel spray characteristics. The combustion process is determined by the fuel distribution and vaporization speed in the combustion chamber. Facing the key issue of the intensity combustion at a relatively low air-fuel ratio, this project will focus on the characteristics of the ultra-pressure high density fuel spray and its effects on the fuel distribution and vaporization velocity in the combustion chamber. Through the design of the injector nozzle and optimization of fuel spray in the combustion chamber, the air utilization efficiency will be improved. Hence, the combustion process will be organized more properly, resulting in the improvement of the combustion speed at the low air-fuel ratio. This work will be firstly carried out on a high pressure and temperature combustion vessel in order to emulate the environment in the combustion chamber at the start of the injection in the high power density engine. Though the laser diagnostic and optical measurement, the fuel spray characteristics of various injector nozzles and their distribution in the combustion chamber will be studied. Based on the measurement results, the spray model will be developed. The mixing of the air and fuel and the combustion process will be investigated in the 3D simulation program in order to optimize the combustion speed at low air-fuel ratio. The results will be a solution to the problem of the too high mechanical and thermal loads on high power density engines. The fundamentals of the low air-fuel ratio high intensive combustion will be utilized for the development of the combustion system for higher power density purpose.

目前高功率密度柴油机上广泛采用高强化燃烧技术实现高功率密度输出。在燃烧室内，高温、高压的气体与高压喷入的大量燃油相互混合并迅速燃烧。高压密集喷雾主导油气混合过程， 燃油分布和蒸发速率决定燃烧过程。本项目针对低过量空气系数条件下高强化燃烧技术瓶颈问题，研究高压密集喷雾特性及其对燃烧室内燃油分布和蒸发速率的影响，通过优化喷嘴设计参数制定喷雾形状的方法，提高燃烧室内空气利用率，合理地组织燃烧过程，达到提高低过量空气系数条件下的燃烧速率。本研究拟在高压定容弹内通过加温加压的方法，模拟高功率密度发动机喷油时气缸内的环境条件，采用光学测量的方法，研究不同喷嘴设计参数和喷射压力下，喷雾的形态及燃油的分布等特性。在此基础上对喷雾、混合、燃烧过程建立数值模型，研究和优化燃烧过程，为高强化柴油机的机械负荷和热负荷问题提供解决方案，为高强化燃烧系统的开发和优化提供指导。

车辆排放法规日益严格，军用装备作战对高机动性需求明显，发动机高强化技术成为军民用发动机的重要发展方向。当前车用柴油机的功率密度已达90kW/L，未来10 年还将进一步提高到120kW/L。高强化柴油机燃烧系统开发遇到高压密集燃油喷雾、快速油气混合和高效燃烧过程组织等基础科学问题，本项目围绕高强化燃烧技术中高压密集喷雾和燃烧过程组织等关键科学问题，在燃油喷雾特性、油气混合和燃烧放热三方面开展了基础研究工作，积累了基础研究数据，获得了通过高压密集喷雾组织高强化燃烧过程的基本规律，丰富了高强化燃烧系统设计和匹配方法，取得了创新研究成果。发表论文12篇，在一台高强化单缸柴油原理样机上实现了90kW/L 升功率强化指标。