Ignition and Extinction Modeling of Hydrothermal Flames

Abstract

Abstract.A modeling research is conducted for a coaxial hydrothermal combustor. The single eddy-dissipation model and finite-rate vs. eddy-dissipation model are used comparably. The latter is proved to be more precise to reflect the flow-reaction feature near the nozzle and able to predict the ignition and extinction temperatures. Large discrepancy between fuel and oxygen inlet velocities results to a recirculation zone in the reactor, which plays an important role in ignition and flame stability. Since the recirculation zone decrease with the increase in fuel concentration, the ignition temperature of 60% methanol is even higher than that of 30% methanol. The predicted extinction temperature is lower than the experimental data, which may be caused by the unsuitable of the chemical reaction model from the Fluent database.

Numerical study of a turbulent co-axial non-premixed flame for methanol hydrothermal combustion: Comparison of the EDC and FGM models

“…Taking this into account, the predicted extinction temperatures are 590 K (Case 3), 490 K (Case 4) and 450 K (Case 5), and the discrepancy with the experimental data is 33 K, 23 K and 10 K respectively. These results are significantly better than the ones obtained with the eddy dissipation / finite rate (ED/FR) model used in our previous work[17]. This is attributed mainly to the inclusion of detailed chemistry in the EDC model.…”

“…They have pointed out that at low injection temperature the chemical reaction rate is slower than the mixing rate, and therefore adopted the laminar finite-rate (FR) model with a one-step reaction mechanism. In our previous study [17], the eddy-dissipation/finite-rate (ED/FR) model was used to simulate the ETH hydrothermal flame, in which the combustion reaction rate is taken as the smaller one between the one-step chemical reaction rate and the turbulent mixing rate. By including finite-rate effects the extinction limit could be studied using the ED/FR model but was found to be underpredicted by 150 K due to the inaccurate representation of the turbulence-chemistry interaction.…”

Numerical study of the counterflow diffusion flames of methanol hydrothermal combustion: The real-fluid effects and flamelet analysis

“…For the ETH hydrothermal flame setup, the turbulent dissipation rate at the flame front is about 20 m 2 /s 3 which can be calculated by our preliminary 2-D model [19]. Then the Kolmogorov Length Scale $ can be estimated as 0.01 mm with the formula $ = ( '…”

“…Queiroz et al [18] have used a one-step finite rate reaction model to simulate the premixed hydrothermal flames in their vessel reactors. In our previous research [19], the finite-rate/eddy-dissipation model was applied to the ETH burner, by which the ignition and extinction limits were addressed. However, the extinction temperature was underpredicted by 250K, which is mainly due to the inaccurate turbulence-chemistry interaction model.…”

Effects of structural parameters on water film properties of transpiring wall reactor

“…where pre-exponential factor (A), activation energy (E a ), methanol reaction order (n), and oxygen reaction order (m) are 1 Â 10 Hence, this model is suitable for complex oxidation reactions in the TWR, and adopted for the reaction kinetics model in this research. 21 The flow velocity of transpiration water was relatively low, and its temperature was in a subcritical state. Moreover, there were also not chemical reactions in the transpiring wall.…”