고온 연소생성물 희석이 메탄연료의 점화 및 연소특성에 미치는 영향

Abstract

High-temperature combustion products are generally generated during combustion process. In this study, the dilution effects were investigated when combustion products were mixed with fuel and air stream, respectively. In case of dilution of high-temperature combustion products with the fuel stream, it could simulate the Backdraft initiation phenomenon inside a compartment. And the combustion characteristics of MILD combustor could be understood, when the air stream was diluted with these products. The ignition characteristics in a confined axisymmetric coflow CH4 jet were investigated with the Fire Dynamics Simulator (FDS) in order to understanding the fundamental physics of Backdraft. The CH4 fuel stream diluted with main combustion product gases, such as O2, N2, CO, CO2, and H2O. The mixed fuel stream was heated up to sufficient temperature where the supplying fuel stream can be ignited. The effects of boundary condition for confined wall and dilution ratio were also investigated. The ignition characteristics of CH4 stream with diluents were very sensitive to the wall temperature, composition of diluents in the fuel stream and fuel stream temperature. The characteristics of ignition and pollutant emission were also investigated numerically with supplied air temperature and dilution rate. For the chemical reactions, the GRI-v3.0 reaction mechanism was used in the simulation. Ignition temperature of CH4 by counterflowing hot air diluted with main combustion products was investigated using flame-controlling continuation method. The ignition temperature increases with the global strain rate for a fixed dilution rate. The ignition temperature also increased with the dilution rate for a fixed global strain rate. Furthermore, the MILD combustion characteristics in jet flame were computationally investigated with the ANSYS FLUENT 13.0. For a fixed air stream temperature, the maximum flame temperature gradually decreased and temperature distribution of jet became nearly uniform as dilution rate increased. In addition, as the dilution rate increased for each air stream temperature, EINO and EICO decreased. It was found that the EICO had a negative value for large dilution rates. This means that MILD combustion has advantages in low-CO emission as well as is very effect in the consumption of additionally supplied CO. Through the investigation of jet flame, a proto-type MILD combustor was applied for offering information of MILD combustor. This combustor was supplied with pure CH4 and pure heated air while the exhaust gases were exited to other nozzles on the same surface. So, the inner of combustor was automatically mixed with fuel, air, and combustion products.