부탄올 디젤 혼합연료를 적용한 디젤기관의 연소 및 배기특성에 관한 수치해석적 연구

Abstract

In this dissertation, this study investigated the numerical simulation of spray combustion and emission characteristics in a four-cylinder compression ignition engine fueled with nbutanol blended diesel fuels. In this work, numerical analysis was performed by using computational fluid dynamics (CFD) code AVL FIRE with ECFM-3Z (extended coherent flame model for 3 zones) combustion model, KH-RT (Kelvin-Helmholtz, Rayleigh – Taylor) spray break up model, and multi-component evaporation model. In addition, the Zeldovich mechanism and the kennedy/Hiroyasu/Magnussen model were employed to calculate NOx and soot formation. Based on the symmetrical of the fuel injector with seven holes, the computational 51.4􀂶 sector mesh is generated and used to calculate combustion process in the cylinder. In order to attain the effect of n-butanol blended fuel, the combustion and emissions characteristics were conducted by using three test fuels, such as diesel (D100), Bu10(diesel 80%, biodiesel 10%, butanol 10%), and Bu20 (diesel 70% biodiesel 10%, butanol 20%). In-cylinder pressure profiles of calculation results had good agreement with experimental results. The combustion characteristics and predicted results of emissions characteristics were compared to the experimental results according to various operating conditions. The results indicated that as the butanol ratio in blended fuels increase, the ignition delay was longer than that of D100 because butanol fuel has low ignition quality 􀀬􀀬􀀃 􀀃 due to the lower cetane number. Comparing the equivalence ratio of Bu20 with diesel fuel, distribution of equivalence ratio of fuel in the combustion chamber was wider than that of diesel fuel As the mixing ratio of the butanol increases, the peak of combustion pressure is decreased. because the latent heat of evaporation of butanol is higher than that of ULSD and biodiesel. The brake specific fuel consumption (BSFC) increased when the blended ratio of butanol increased. It can be explained that the injection quantity increased at all test blends because of the low LHV of butanol fuel. In emissions. NOx of Bu10 is higher than that of D100 fuel. But NOx of Bu20 is lower than diesel fuel. because the cooling effect in the cylinders due to the high heat of vaporization of bu20 exert more influence than oxidation influence of Bu10. NOx of Bu20 was reduced than that of D100. In the case of the soot, as the mixing ratio of the butanol increases, it was reduced emissions of soot emission, the soot is oxidized due to the high oxygen content of the butanol.