초록
For the development of high efficiency and low emission combustion systems, high temperature air combustion technology has been tested by utilizing preheated air over 1100 K and exhaust gas recirculation. In this system, combustion air is diluted with large amount of exhaust gases ($N_2$, $CO_2$), such that the oxygen concentration is relatively low in the reaction zone, leading to low flame temperature. Since, the temperature fluctuations and sound emissions form the flame are small and flame luminosity is low, the combustion mode is expected to be flameless or mild combustion. Experiment was performed to investigate the turbulent flame structure and $NO_X$ emission characteristics in the high temperature air combustion focused on coflowing jet diffusion flames which has a fundamental structure of many practical combustion systems. The effect of turbulence has also been evaluated by installing perforated plate in the oxidizer inlet nozzle. LPG was used as a fuel. Results showed that even though $NO_X$ emission is sensitive to the combustion air temperature, the present high temperature air combustion system produce low $NO_X$ emission because it is operated in low oxygen concentration condition in excess of dilution.