Effect of Recirculated Exhaust Gas on Flame Structure and Pollutant Emission of Oxygen Enhanced Flame

초록

Recently, many nations are putting intensive restrictions on greenhouse gases including CO2, which contribute to the increase of earth average temperature. Because CO2 is the inevitable byproducts generated from fossil fuel combustion, one of the best strategies for reducing the amount of CO2 is to increase thermal efficiency of combustion systems. In accordance with the cost reduction of the oxygen production, the oxygen-enriched combustion (OEC) is recommended as another promising technique for a high efficient combustion system. OEC is the combustion method that uses oxygen as an oxidizer partly or entirely. In OEC system, many benefits are expected such as increased thermal efficiency, increased processing rates, reduced flue gas volumes and etc.. But in spite of such benefits, the industrial fields utilizing OEC are limited because of shortcomings such as refractory damage by a high temperature, increased pollutant emission by oxidizer contamination and the risk of flashback. Among the above shortcomings, problems concerned with high temperature are expected to be solved by controlling oxidizer with exhaust gas recirculation (EGR). However, fundamental and systematic researches on these oxidizer-controlled flames are few. In this study, numerical calculations on the counter diffusion flames have been done so as to investigate the flame structure and pollutant (such as NO and CO) formation characteristics of two kinds of oxygen-enhanced flame. One is CH4/O2-CO2 EGR flame and the other is CH4/O2-CO2-H2O EGR flame. The OPPDIF code modified to incorporate the radiative heat loss is used. Radiative heat loss caused by CO2, H2O, CO, and CH4 is calculated using an optically thin model [1]. The nozzle separation distance is 2cm and the strain rate is defined by the formulation proposed by Seshadri et al. [2]. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. Emission Index is utilized in order