Numerical And Experimental Study On Fuel Injection Process In Direct Injection LPG Engine

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.