Numerical study on flame structure and NO formation in CH4-O2-N2 counterflow diffusion flame diluted with H2O

Choi

Kim

et al. 2004

Int. J. Energy Res.

Self Cite

SUMMARYNumerical study on flame structure and NO emission is conducted covering a wide range of atmospheric temperature, high temperature, and mild combustion regimes in H 2 -Air laminar flames diluted with steam. Special concern is focused on the difference of flame structure and NO emission behaviour between hightemperature combustion and mild combustion modes. The important role of chemical effects of added steam in flame structure and NO emission behaviour is also discussed. It is seen that there exists an oxidizer-side temperature limit which the combustion mode changes from high temperature combustion to mild combustion. In high temperature combustion modes the OH production via the reaction step, (-R23) is suppressed while in mild combustion modes is enhanced by the increase of oxidizer-side temperature. It is also found that chemical effects of added steam are influenced by the competition between both the reaction steps, (R21) and (-R23).NO emission index increases with increasing oxidizer-side temperature and decreases with mole fraction of added steam. The remarkably produced OH due to chemical effects of added steam does not contribute to the increase of NO but plays a role of holdback on NO in thermal mechanism. It is also seen that in both the high temperature combustion and mild combustion modes NO emission indicates a consistently similar tendency, and is consequently recognized that in the whole ranges steam addition suppresses NO emission.

Section: Resultsmentioning

confidence: 98%

Numerical study on steam-added mild combustion

Choi

Kim

et al. 2004

Int. J. Energy Res.

Self Cite

“…HYDROGEN UTILIZATION AS A FUEL 483 HNO-related reaction steps in prompt NO formation has been already stressed in the previous study (Hwang et al, 2004). As shown in Figure 7(b), for the CH 4 -H 2 flame of X CH 4 =0.5, the HNO-related reaction steps of (ÀR212) and (R214) become much more prevailing and the reaction steps of (ÀR244) and (ÀR245) become important.…”

mentioning

confidence: 71%

Hydrogen utilization as a fuel: hydrogen-blending effects in flame structure and NO emission behaviour of CH4–air flame

Hwang

et al. 2007

Int. J. Energy Res.

Self Cite

SUMMARYHydrogen-blending effects in flame structure and NO emission behaviour are numerically studied with detailed chemistry in methane-air counterflow diffusion flames. The composition of fuel is systematically changed from pure methane to the blending fuel of methane-hydrogen through H 2 molar addition up to 30%. Flame structure, which can be described representatively as a fuel consumption layer and a H 2 -CO consumption layer, is shown to be changed considerably in hydrogen-blending methane flames, compared to pure methane flames. The differences are displayed through maximum flame temperature, the overlap of fuel and oxygen, and the behaviours of the production rates of major species. Hydrogen-blending into hydrocarbon fuel can be a promising technology to reduce both the CO and CO 2 emissions supposing that NO x emission should be reduced through some technologies in industrial burners. These drastic changes of flame structure affect NO emission behaviour considerably. The changes of thermal NO and prompt NO are also provided according to hydrogen-blending. Importantly contributing reaction steps to prompt NO are addressed in pure methane and hydrogen-blending methane flames.

“…According to the OH concentration profile across the reaction zone, it was observed that the H 2 O and N 2 vitiation gas had almost the same peak concentration, although the adiabatic flame temperature with H 2 O vitiation gas was lower. This can be explained by the results of the previous research work, which indicated that more OH radicals were produced based on the chemical reaction step O + H 2 O → OH + OH [8,9]. At high flame temperature, the steam dissociation could also contribute to OH production [10].…”

Section: Reaction Zone Characteristicsmentioning

confidence: 84%

Impact of Vitiation on a Swirl-Stabilized and Premixed Methane Flame

Tong

Klingmann

et al. 2017

Energies

Vitiation refers to the condition where the oxygen concentration in the air is reduced due to the mix of dilution gas. The vitiation effects on a premixed methane flame were investigated on a swirl-stabilized gas turbine model combustor under atmospheric pressure. The main purpose is to analyze the combustion stability and CO emission performance in vitiated air and compare the results with the flame without vitiation. The N 2 , CO 2 , and H 2 O (steam) were used as the dilution gas. Measurements were conducted in a combustor inlet temperature of 384 K and 484 K. The equivalence ratio was varied from stoichiometric conditions to the LBO (Lean Blowout) limits where the flame was physically blown out from the combustor. The chemical kinetics calculation was performed with Chemkin software to analyze the vitiation effects on the flame reaction zone. Based on the calculation results, the changes in the temperature gradient, CO concentration, and active radicals across the flame reaction zone were identified. The time-averaged CH chemiluminescence images were recorded and the results indicated the features of the flame shape and location. The CH signal intensity provided the information about the heat-release zone in the combustor. The combustion LBO limits were measured and the vitiation of CO 2 and H 2 O were found to have a stronger impact to elevate the LBO limits than N 2 . Near the LBO limits, the instability of the flame reaction was revealed by the high-speed chemiluminescence imaging and the results were analyzed by FFT (Fast Fourier Transfer). CO emission was measured with a water-cooled probe which is located at the exit of the combustor. The combustion vitiation has been found to have the compression effect on the operation range for low CO emission. However, this compression effect could be compensated by improving the combustor inlet temperature.