【作者】 郑瑞；

【导师】 张煜盛；

【作者基本信息】 华中科技大学 ， 动力机械及工程， 2006， 硕士

【摘要】 本文以直喷式LPG发动机的燃油喷射过程为研究对象,通过开展数值模拟与试验研究,探讨了低沸点、低粘度和高可压缩性燃料在高压燃油系统内的流动特性、变化规律、油泵内漏及其对燃油喷射过程的影响。本文的研究内容和创新点主要有以下几个方面:在广泛阅读国内外文献的基础上,对LPG代用燃料的特点、LPG在内燃机上的应用,以及压燃式发动机燃油喷射系统数值模拟研究的国内外现状进行了综述,全面分析了LPG直喷式发动机燃油喷射系统的关键技术问题。针对采用普通泵-管-嘴常规喷油系统的液化石油气直喷式发动机,建立了考虑高压油泵柱塞偶件、针阀偶件间隙燃油泄漏量影响的燃油喷射过程的数学模型,并且结合实验发动机供油系统的实际情况,对其燃油喷射过程进行了数值模拟计算及其计算结果的试验验证,判明了高压燃油泵内出现较严重燃油泄漏对发动机燃油喷射过程的影响。开展了LPG与柴油供油特性的对比分析,研究结果表明,由于LPG具有较高的饱和蒸汽压和可压缩性,致使其油管压力上升和下降都比较缓慢,供油持续期加长,油管内燃油残余压力较高,压力波动较大,容易发生二次喷射现象。通过适当增大出油阀卸载容积,可有效解决二次燃油喷射现象的发生。应用先进的流体分析软件,对LPG在高压燃油泵柱塞偶件环形缝隙中的流动问题,进行了三维瞬态液固耦合计算分析,揭示了低粘度燃料在高压燃油泵中产生泄漏的机理,并且提出了定量分析其燃油泄漏量的数学模型与计算方法,为直喷式LPG发动机燃油系统的改进与优化设计提供了理论依据。开展了油泵泄漏试验研究,测量了LPG在高压油泵内的泄漏量,并将实测值与模拟计算值进行了对比分析,二者吻合较好。在此基础上,提出了解决低粘度燃油泄漏问题的技术措施。此外,还对喷油器针阀偶件的燃油泄漏问题进行了类似的分析,得出了一些有益的结论。更多还原

【Abstract】 Among the alternative gaseous fuels, liquefied petroleum gas (LPG) is widely used as a clean fuel for SI engines because of its low cetane number. LPG SI engine has some drawbacks. However, LPG in-cylinder direct-injection (DI) combustion has a potential to achieve less pollutants and more efficient combustion characteristics. In this thesis both experimental and numerical studies are employed to clarify the performance characteristics of fuel injection process in a direct injection diesel engine fuelled with LPG and ignition improving additive. The research works and new findings are as follows:The research of LPG as a clean fuel for internal combustion engines and its applications are generally analyzed and the technology issues of IC engines running on LPG are described in this thesis. Experimental and numerical studies on the performance characteristics of fuel injection process are reviewed and the technological trends as well as wide potential application of LPG are discussed.This thesis also presents an experimental and computational study on the hydraulic phenomena and the dynamics of conventional pump-pipe-injector fuel system in an engine fuelled with LPG. It also describes in detail the characteristics and variations of the LPG fuel injection system parameters during the fuel injection process. Based on the results of computer simulation and experiments it is shown that in comparison with the diesel fuel larger line oscillations, higher residual pressure, retarded start of fuel injection and secondary injection phenomena for LPG have been observed as a result of its higher compressibility. The computed parameters such as line pressure waves and needle lift of the injector operated on LPG and diesel fuel are compared with the experimental results and good agreements between them are obtained.In view of LPG having much lower viscosities compared to diesel fuel and serious fuel leak from high pressure fuel pump, a methodology is presented in this thesis to analyze the effect of low viscosity liquefied fuel on the fuel leak from the clearance between plunger and plunger sleeve. Based on the FEA software named ANSYS, a fluid-solid coupling FEA model is developed to investigate the deformation of plunger pinion and fuel leak from the tolerance clearance of the fuel pump. Results are presented of computational investigations into the fuel leak and some suggestions are also made to solve fuel leak problem of diesel engine operated with much lower viscosity fuels, such as LPG. The computational data are compared with the leak testing results and good agreements between them are obtained.更多还原