【作者】 杨峰；

【导师】 陈征； 王健；

【作者基本信息】 湖南大学 ， 动力工程（专业学位）， 2016， 硕士

【摘要】 双对置柴油机拥有对置活塞发动机与对置气缸发动机的结构优势与工作特点,同转速下比传统柴油机多一倍输出功率。由于采用对置进排气活塞形式使得其进排气活塞运动速度是传统柴油机活塞运动速度的一半,因此双对置柴油机只能依靠较弱的进气涡流以及缸内湍流动能实现燃油与空气的混合,易导致喷雾燃烧过程中油气混合和燃烧效果不佳、碳烟和NOx排放高等问题。本文拟使用计算流体力学(CFD)软件开展双对置柴油机喷油雾化燃烧过程的分析研究,通过优化双对置柴油机喷雾与燃烧过程中的关键参数,实现改善其排放性能的目的。主要研究工作与研究成果包括:(1)根据双对置柴油机进排气活塞运动规律与活塞特殊的结构形式,利用三维建模软件提取进排气活塞顶面形状和气缸套共同构建成燃烧室模型,并在此基础上创建双对置柴油机侧向组合喷雾燃烧系统的三维CFD网格模型。(2)开展双对置柴油机非对称喷孔喷油器的定容弹喷雾试验,结果表明喷油压力和燃烧室背压是影响喷雾形态及喷雾贯穿距离的主要因素。在试验结果基础上进行CFD网格模型适应性和模型适应性研究,确定了双对置柴油机侧向组合喷雾的计算网格尺寸、湍流与喷雾模型。(3)基于喷雾试验拟定非对称喷孔布置方案与预喷-主喷方案,并进行了双对置柴油机燃油雾化燃烧过程的模拟计算。结果表明:恰当的喷孔布置方式可实现燃烧室内喷射的燃油油束的均匀分布,并易与缸内压缩空气迅速混合成可燃混合气;采用燃油预喷方案可缩短滞燃期使得缸内可燃混合气分布范围更大,缸内燃烧放热更快;随着预喷-主喷间隔角度增大,一氧化氮生成量曲线呈现先减小后增多的趋势;预喷燃油量增多,一氧化氮生成量越高,碳烟排放峰值依次减小。(4)后喷方案在减少一氧化氮排放量方面影响效果不明显,仅能实现小幅削减作用;但后喷方案对降低碳烟排放有着较显著的作用,主喷-后喷间隔角越大,碳烟排放量下降趋势与幅度越大;当后喷油量限定为主喷油量5%时,适当大的主喷-后喷间隔角更利于降低碳烟排放量。(5)开展双对置柴油机侧向组合喷雾和燃烧系统参数优化匹配的仿真计算。结果表明:通过合理的喷孔布置与合适的预喷与后喷方案可以同时降低氮氧化物与碳烟污染物排放水平。本文的研究对实现双对置柴油机缸内低排放燃烧具有一定的理论指导意义。更多还原

【Abstract】 Dual opposed diesel engine have both the structure advantages of opposed piston engine and opposed cylinder engine. Due to the special opposite intake and outlet piston form which makes traditional engine piston relative velocity is twice faster than dual opposed diesel engine. At the same time, the special arrangement of the inlet and exhaust port determines that the mixture can only rely on weak swirl, which easily lead to non-ideal mixing effect, high soot and NOx emissions during fuel injection and combustion, etc.In order to improve the emission performance, this paper intended to study the fuel injection and combustion process of dual opposed diesel engines by optimizing the key parameters of its spray and combustion. the main research content and results include:(1) According to the motion law of dual opposed diesel engine inlet and exhaust piston and its special structure, the intake and exhaust piston top surface shape and the cylinder sleeve which were extracted by using three-dimensional model software were joint to build combustion chamber physical model, and then lateral combined spray and combustion progress mesh model of dual opposed diesel engine were established.(2)The asymmetric injector volume bomb experiment showed that the injection pressure and combustion chamber pressure is the main factor which affected the shape of spray. Based on the test results, mesh adaptation and model study on the adaptability were carried out to determine the size of the grid and turbulence model for dual opposed diesel engine spray and combustion calculation.(3) Aimed at different injector hole arrangement mode and pre injection scheme of duel opposed diesel engine, the dual opposed diesel fuel spray progress and combustion were simulated. It could be concluded that the uniform distribution of fuel oil in the combustion chamber can be realized by the proper arrangement of injector holes, and the pre injection method can shorten the ignition delay period, which enlarge the distribution range of the combustible mixture in the cylinder. With the increase of pre injection fuel quantity, the production of nitric oxide increased, while the peak of the emission of carbon smoke decreased.(4)Pre injection and post injection scheme has a weak effect on reducing nitricoxide emissions, while post injection scheme has a more significant effect on reducing the soot emissions, and the bigger the interval angle between main-injection and post injection is, the more soot emissions decreased. When the volume of the rear spray amount is 5% of the main injection, the proper large main injection and post injection interval angle will help to reduce the soot emission.(5) Simulated the calculation of dual opposed diesel engine lateral combined spray and combustion, the results show that: under different conditions, through reasonable hole layout and appropriate pre injection and post injection scheme can be a certain way to reduce nitric oxide and carbon smoke emissions.The results of this study have certain guiding significance for low emission combustion of dual opposed diesel engine.更多还原