Flame Characteristics of CH₄/H₂ on a Jet-in-Hot-Coflow Burner Diluted by N₂, CO₂, and H₂O

Abstract

To enhance the knowledge to the combination of oxy-fuel combustion and MILD (moderate or intense low-oxygen dilution) combustion, namely oxy-MILD combustion, the present article examines the effects of different diluents (i.e., N2, CO2, and H2O) on the flame characteristics of CH4/H2 blended fuel in a JHC (jet-in-hot-coflow) burner, which can produce MILD combustion regime in the upstream and conventional combustion regime in the downstream. CFD modeling method considering RANS equations and detailed reaction mechanism (GRI-Mech 2.11) are used for such purpose. Results show that, in MILD combustion regime, peak temperature under oxy-fuel condition (diluted by CO2 and H2O) is reduced as compared to air-fuel condition (diluted by N2) from both physical and chemical effects of the diluents. However, in the conventional combustion regime, chemical effect of the diluents on suppressing the peak temperature is weakened, resulting in the predominance of its physical effect. As for the flame ignition behavior, the dilution with CO2 or H2O causes flame liftoff according to OH appearance. More noticeably, the liftoff distance is even larger in H2O diluted case than CO2 diluted case. On the other hand, by calculating the Damköhler number in the computational domain, MILD combustion region is found well under reaction-controlled status. However, as compared to CO2, H2O plays a weakened role on the reaction-controlled status, suggesting that CO2 might be preferable to H2O in realizing oxy-MILD combustion.

Review on MILD Combustion of Gaseous Fuel: Its Definition, Ignition, Evolution, and Emissions

“…This simple definition has apparently built up a base for a great deal of research into MILD combustion in either premixed cases ,, or nonpremixed cases − ,,,,,,,− since 2004. Both experimental ,,,− ,,,− ,− , and numerical − ,,,− ,− ,− investigations have been conducted for understanding of the MILD combustion characteristics, including its occurrence and development, as well as its ignition and stability.…”

“…To improve our understanding of this combustion, a great deal of research work on its definition, ignition, evolution, and emissions has been conducted experimentally ,,− ,− ,,,− ,,,− ,− , and numerically. ,,,− ,− ,,,− ,− ,− In particular, the ch...…”

Experimental and Numerical Study on the Combustion Characteristics of a Laminar Non-Premixed Methane Jet Flame in Oxygen/Carbon Dioxide Coflow

“…Recently, the influences of CO 2 on the combustion characteristics of multidimensional flames has been studied in detail. The physical and chemical effects of CO 2 dilution on a CH 4 /H 2 jet flame in the MILD oxy-combustion regime have been investigated using two-dimensional numerical computations with a detailed kinetic mechanism (Tu et al, 2016;Tu et al, 2017). It was found that the chemical effects of CO 2 play a comparable role in the suppression of temperature rise to the physical effects (Tu et al, 2016).…”

“…The influences of CO 2 dilution on the shape and structure of laminar CO/H 2 diffusion flames in an O 2 /N 2 /CO 2 coflow was examined (Xu et al, 2017), and the chemical effects of the thermal and transport properties of CO 2 on the flames were discussed in detail. The previous numerical studies provide important information on the effects of CO 2 under MILD (Tu et al, 2016;Tu et al, 2017) and syngas (Xu et al, 2017) combustion regimes. However, the effects of CO 2 on the flame shape and temperature distribution of gaseous-fuel-fired flames in an O 2 /CO 2 environment with a high O 2 concentration needs special attention and was not clarified.…”

Experimental and Numerical Study on Moderate or Intense Low-Oxygen Dilution Oxy-Combustion of Methane in a Laboratory-Scale Furnace under N2, CO2, and H2O Dilutions

“…Although the previous studies have revealed some significant features of MILD oxy-combustion, they were almost all conducted by numerical simulation using ideal physical models, ,,− such as WSR, , counterflow flame, TFR, and open jet flame. ,, There has been some lack of experimental work for the MILD oxy-combustion, especially for H 2 O dilution. Moreover, to our best knowledge, the previous studies have never compared the in-furnace flame characteristics of MILD oxy-combustion under N 2 , CO 2 , and H 2 O dilutions over a relatively wide range of oxygen concentrations (from lean to rich oxygen) by experimental measurements and numerical simulations together.…”