185 research outputs found
The effects of complex chemistry on triple flames
The structure, ignition, and stabilization mechanisms for a methanol (CH3OH)-air triple flame are studied using Direct Numerical Simulations (DNS). The methanol (CH3OH)-air triple flame is found to burn with an asymmetric shape due to the different chemical and transport processes characterizing the mixture. The excess fuel, methanol (CH3OH), on the rich premixed flame branch is replaced by more stable fuels CO and H2, which burn at the diffusion flame. On the lean premixed flame side, a higher concentration of O2 leaks through to the diffusion flame. The general structure of the triple point features the contribution of both differential diffusion of radicals and heat. A mixture fraction-temperature phase plane description of the triple flame structure is proposed to highlight some interesting features in partially premixed combustion. The effects of differential diffusion at the triple point add to the contribution of hydrodynamic effects in the stabilization of the triple flame. Differential diffusion effects are measured using two methods: a direct computation using diffusion velocities and an indirect computation based on the difference between the normalized mixture fractions of C and H. The mixture fraction approach does not clearly identify the effects of differential diffusion, in particular at the curved triple point, because of ambiguities in the contribution of carbon and hydrogen atoms' carrying species
Transfer learning for predicting source terms of principal component transport in chemically reactive flow
The objective of this study is to evaluate whether the number of requisite
training samples can be reduced with the use of various transfer learning
models for predicting, for example, the chemical source terms of the
data-driven reduced-order model that represents the homogeneous ignition
process of a hydrogen/air mixture. Principal component analysis is applied to
reduce the dimensionality of the hydrogen/air mixture in composition space.
Artificial neural networks (ANNs) are used to tabulate the reaction rates of
principal components, and subsequently, a system of ordinary differential
equations is solved. As the number of training samples decreases at the target
task (i.e.,for T0 > 1000 K and various phi), the reduced-order model fails to
predict the ignition evolution of a hydrogen/air mixture. Three transfer
learning strategies are then applied to the training of the ANN model with a
sparse dataset. The performance of the reduced-order model with a sparse
dataset is found to be remarkably enhanced if the training of the ANN model is
restricted by a regularization term that controls the degree of knowledge
transfer from source to target tasks. To this end, a novel transfer learning
method is introduced, parameter control via partial initialization and
regularization (PaPIR), whereby the amount of knowledge transferred is
systemically adjusted for the initialization and regularization of the ANN
model in the target task. It is found that an additional performance gain can
be achieved by changing the initialization scheme of the ANN model in the
target task when the task similarity between source and target tasks is
relatively low.Comment: 41 pages, 14 figure
Pattern of Reaction Diffusion Front in Laminar Flows
Autocatalytic reaction between reacted and unreacted species may propagate as
solitary waves, namely at a constant front velocity and with a stationary
concentration profile, resulting from a balance between molecular diffusion and
chemical reaction. The effect of advective flow on the autocatalytic reaction
between iodate and arsenous acid in cylindrical tubes and Hele-Shaw cells is
analyzed experimentally and numerically using lattice BGK simulations. We do
observe the existence of solitary waves with concentration profiles exhibiting
a cusp and we delineate the eikonal and mixing regimes recently predicted.Comment: 4 pages, 3 figures. This paper report on experiments and simulations
in different geometries which test the theory of Boyd Edwards on flow
advection of chemical reaction front which just appears in PRL (PRL Vol
89,104501, sept2002
Recommended from our members
Statistics of flame displacement speeds from computations of 2-D unsteady methane-air flames
Results of two-dimensional numerical computations of turbulent methane flames using detailed and reduced chemistry are analyzed in the context of a new theory for premixed turbulent combustion for high turbulence intensity. This theory defines the thin reaction zones regime, where the Kolmogorov scale is smaller than the preheat zone thickness, but larger than the reaction zone thickness. The two numerical computations considered in this paper fall clearly within this regime. A lean and a stoichiometric flame are considered. The former is characterized by a large ratio of the turbulence intensity to the laminar burning velocity and the latter by a smaller value of that ratio
Influence of turbulence-kernel interactions on flame development in lean methane/air mixtures under natural gas-fueled engine conditions
Harinath Reddy, John Abraha
Experimental Measurement of Local Burning Velocity Within a Rotating Flow
The final publication is
available at link.springer.com.The work presented in this paper details the implementation of a new technique for the measurement of local burning velocity using asynchronous particle image velocimetry. This technique uses the local flow velocity ahead of the flame front to measure the movement of the flame by the surrounding fluid. This information is then used to quantify the local burning velocity by taking into account the translation of the flame via convection. In this paper the developed technique is used to study the interaction between a flame front and a single toroidal vortex for the case of premixed stoichiometric methane and air combustion. This data is then used to assess the impact of vortex structure on flame propagation rates. The burning velocity data demonstrates that there is a significant enhancement to the rate of flame propagation where the flame directly interacts with the rotating vortex. The increases found were significantly higher than expected but are supported by burning velocities [22-24] found in turbulent flames of the same mixture composition. Away from this interaction with the main vortex core, the flame exhibits propagation rates around the value recorded in literature for unperturbed laminar combustion [18-21]
- …