Numerical Study on Flame Structure and NOx Emission Characteristics of H2-NH3/Air Counterflow Non-premixed Flames

초록

In this study, flame structure and NOx emission characteristics of H2-NH3/Air counterflow non-premixed flames were studied to improve the safety of hydrogen use numerically. For the calculation, it was considered using the detailed reaction mechanism of modified Miller and Bowman [1] and a statistical narrow-band radiation model [2] for a wide range of strain rate and various mole fractions of NH3 with various fuel temperatures. The H2-NH3/Air counterflow non-premixed flames were simulated to investigate flame structure and NOx emission characteristics using a code revised from the OPPDIF program [3]. As results, NH3 was to significantly reduce the high-stretch extinction limits that are blow-off limits, and the maximum flame temperature with increasing mole fraction of NH3 as shown in Fig. 1 (a). In addition, the temperature difference between H2/Air and H2-NH3/Air flames became smaller with increasing strain rates. In the case of NOx emission index (EINOx) as shown in Fig. 1 (b), EINOx decreased with increasing strain rates for all flames. Especially, EINOx for pure H2/Air flames was rapidly decreased. This was indicated that relatively less NOx compared with the amount of provided fuel was produced at high strain rates. However, EINOx was enhanced with increasing mole fraction of NH3, particularly at the high strain rates, even though the maximum temperature was dramatically reduced as shown in Fig. 1 (a). This was due to the chemical effects (rather than the thermal effects) of increasing mole fraction of NH3.