Flame structure and NO emissions in gas combustion of low calorific heating value

Abstract

SUMMARYNumerical study on addition effects of CO and CO 2 in fuel side (H 2 /Ar) on flame structure and NO emission behaviour in counterflow diffusion flame has been conducted with detailed chemistry to fundamentally understand gas combustion of low calorific heating value. A modified Miller-Bowman reaction scheme including a complementary C 2 -reaction subset is adopted. The radiative heat loss term, which is based on an optically thin model and it especially important at low strain rates, is included to cover the importance of the temperature dependence on NO emission. Special interest is taken to estimate the roles of added CO and CO 2 in fuel side on flame structure and NO emission characteristics. Increasing CO concentration in fuel side contributes to the enhancement of combustion due to the increase effect of the concentration of reactive species. The increase of added CO 2 concentration in fuel side suppresses overall reaction rate due to the high heat capacity. It is seen that chemical effects due to the breakdown of added CO 2 in fuel side make C 2 -branch chemical species be remarkably formed and the prevailing contribution of prompt NO is a direct outcome of these effects. It is found that in the combined forms of H 2 /CO/CO 2 /Ar fuels the effects of added CO and CO 2 concentrations in fuel side compete contrarily to each other in NO emission behaviour. Particularly the role of added CO is stressed in the side of restraining prompt NO.

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.…”

Fuel flexibility, stability and emissions in premixed hydrogen-rich gas turbine combustion: Technology, fundamentals, and numerical simulations

“…Several groups experimentally investigated NO x emissions when the fuel composition is modified in both diffusion [119,120], and premixed flames [121][122][123][124][125][126]118,125], in real gas turbine scale as well as laboratory scale configurations. Although the specific NO x emission level observed for lab-scale configurations may not be representative of a full scale device, the trends however can be considered indicative of the performance in real systems.…”

Preliminary CFD Investigation of Syngas Combustion at Different Operating Pressures

“…As CO concentration in fuel is increasing, thermal NO x increased because of higher flame temperature, but the prompt NO x was restrained. [5][6]. The results, using methane/hydrogen fuel mixtures on combustion of hydrogen-enriched methane in a lean premixed swirl burner, showed that the addition of up to 41% hydrogen significantly extended the lean burning limit.…”