Preferential Diffusion Effects on NO Formation in Methane/Hydrogen-Air Diffusion Flames

Abstract

A numerical study in methane/hydrogen diffusion flames has been conducted to clarify the preferential diffusion effects of H2 and H with detailed chemistry. The composition of fuel is systematically changed from pure methane to pure hydrogen through the molar addition of H2 to methane. A comparison was made by employing three species diffusion models, i.e., mixture-averaged species diffusion and the suppression of the diffusivities of H and H2. The behavior of maximum flame temperatures with the three species diffusion models is not explained by the scalar dissipation rate but the nature of chemical kinetics such as the behaviors of chain carrier radicals of H, O, and OH. It is found that the preferential diffusion of H radical into the reaction zone curbs the populations of the chain carrier radicals and then flame temperature while that of H2 into the reaction zone produces the reduction of the scalar dissipation rate and the population of chain carrier radicals and these force the flame temperature to decrease. These preferential diffusion effects of H2 and H are also compared among NO emission behaviors through the three species diffusion models. Under all flame conditions, Fenimore NO is much more remarkable compared to thermal NO. It is also seen that the preferential diffusion of H radical into the reaction zone suppresses the thermal and Fenimore NO while that of H2 into the reaction zone increases them. To facilitate the details of those NO behaviors through preferential diffusion effects of H2 and H, importantly contributing reaction steps to the production and destruction of Fenimore NO are addressed.

The characteristics and mechanism of the NO formation during oxy-steam combustion

“…Moreover, the GRI 3.0 has successfully predicted the flame structure [40][41][42][43], ignition [29] and extinction [44] during oxy-combustion combustion. Some computational studies [10,[25][26][27][28][29][30][31][32][45][46][47][48][49] using the OPPDIF model with GRI V3.0 are conducted to reveal the characteristics and mechanism of some novel combustion, such as MILD combustion [25][26][27][28]49], oxy-fuel combustion [30,32], oxy-steam combustion [10] and oxy-steam MILD combustion [49], in which the mole fraction of H 2 O is up to 95% [49]. Therefore, it was adopted in this study.…”

Effects of Reaction Mechanisms and Differential Diffusion in Oxy-Fuel Combustion Including Liquid Water Dilution

“…Considering the different modeling descriptions applied to each analyzed approach (see Section 2.1) and analyses presented in preceding studies [3,9,39,40], deviations among s l values were expected. By changing the way that diffusion transport is modeled, impacts on the full set of differential equations given by Equations ( 1)-( 4) would be noticed.…”

“…The effects of diffusion transport in oxy-fuel combustion for different fuels, fuel mixtures, and dilution agents are comprehensively addressed in the literature [3,9,39,40]. In contrast with [3,9,39,40], in which focus is predominantly given on the phenomenological evaluation of the diffusion transport, typical strategies applied to model the chemical reactions in general combustion applications are evaluated here in single-and two-phase flows. To reach this objective, both unitary Lewis and mixture averaged approaches, as described in Section 2.1, are compared with results achieved with complex transport modeling.…”

Numerical Study on H₂ Preferential Diffusion Effect in Downstream Interactions between Premixed H₂-air and CO-air Flames

“…앞서 언급했듯이, 낮은 발열량을 가진 H2, CO로 인해 합성가스를 사용하는 버너를 설계할 시에 심각 한 화염 안정성 문제가 생기게 되며, 산업 및 발전 소 등에서 현재의 버너 시설 개조를 통해 탄화수소-합성가스(또는 H2) 혼합 가스의 연소 특성에 대해 연 구가 진행되고 있다 [8][9][10].…”