Numerical modeling of lean hydrogen spark-ignition engines: On the role of intrinsic instabilities

The detailed flame structure of laminar premixed cellular flames in the tubular domain is simulated in 2D using a fully-implicit primitive variable finite difference formulation that includes multicomponent transport and detailed chemical kinetics. Numerical results for H2/air flames are presented and compared against spatially resolved experimental measurements of temperature and chemical species including atomic H and OH. The experimental results compare well for flame structure and cell number, despite the numerical model under-predicting the peak temperature by 200 K. Numerical experiments were performed to assess the ability for cellular tubular flames to impact experimental and numerical investigations of practical flames. The cellular flame structure is found to provide a highly sensitive geometry that is useful for validating diffusive transport modelling approximations. This capability is exemplified through the development of a simple and accurate approximation for thermal diffusion (i.e. the Soret effect) that is suitable for practical combustion codes.

Selective diffusional demixing: Occurrence and size of cellular flames

Three-dimensional simulations of cellular non-premixed jet flames

Synergistic interactions of thermodiffusive instabilities and turbulence in lean hydrogen flames

The effect of mixture inhomogeneity and turbulence on the flame front curvature and flame surface density of turbulent planar flames of natural gas

High hydrogen content syngas fuel burning in lean premixed spherical flames at elevated pressures: Effects of preferential diffusion

5538594 Method for producing a blade coated paper from recycled, high lignin content, waste paper: Hank Mark A; Mulcahy Leo T; Peterson Ralph S; Streisel Robert C, Covington, VA, United States assigned to Westvaco Corporation

The influence of hydrodynamic instability on the structure of two-dimensional (2D) and three-dimensional (3D) cellular flames is numerically investigated. The equation used is the compressible Navier–Stokes equation including a one-step irreversible chemical reaction. We superimpose an infinitesimal disturbance on the stationary plane flame and calculate the evolution of the disturbed flame front to obtain the relation between the growth rate and the wave number, i.e., the dispersion relation. With an increase in flame temperature, the growth rate increases since hydrodynamic instability becomes stronger. The unstable range normalized by the preheat zone thickness hardly changes, even though the flame temperature increases. The critical wave number, which corresponds to the maximum growth rate, is almost constant. Therefore, the normalized spacing between cells of the cellular flame is independent of the flame temperature. Moreover, we superimpose the disturbance with the critical wave number to investigate the structure of cellular flames. The stationary cellular flame is obtained when the inlet-flow velocity is set to the flame velocity of the cellular flame. The higher the flame temperature, the deeper the cell and the broader the flame surface. In addition, the cell depth and the surface area of the 3D flame are larger than those of the 2D flame. This is caused by the difference in the disposition of cells.

The influence of hydrodynamic instability on the structure of two-dimensional (2D) and three-dimensional (3D) cellular flames is numerically investigated. The equation used is the compressible Navier–Stokes equation including a one-step irreversible chemical reaction. We superimpose an infinitesimal disturbance on the stationary plane flame and calculate the evolution of the disturbed flame front to obtain the relation between the growth rate and the wave number, i.e., the dispersion relation. With an increase in flame temperature, the growth rate increases since hydrodynamic instability becomes stronger. The unstable range normalized by the preheat zone thickness hardly changes, even though the flame temperature increases. The critical wave number, which corresponds to the maximum growth rate, is almost constant. Therefore, the normalized spacing between cells of the cellular flame is independent of the flame temperature. Moreover, we superimpose the disturbance with the critical wave number to investigate the structure of cellular flames. The stationary cellular flame is obtained when the inlet-flow velocity is set to the flame velocity of the cellular flame. The higher the flame temperature, the deeper the cell and the broader the flame surface. In addition, the cell depth and the surface area of the 3D flame are larger than those of the 2D flame. This is caused by the difference in the disposition of cells.

Cellular flame structures and thermal characteristics of axi-symmetric ceiling fires: An experimental study and scaling analysis

The two-dimensional (2-D) and three-dimensional (3-D) unsteady reactive flows are calculated to study the structure of downwards/upwards propagating cellular flames at the Lewis number unity. We superimpose an infinitesimal disturbance on the stationary plane flame to obtain the growth rate depending on the wave number, i.e., the dispersion relation. When premixed flames are propagated downwards/upwards, the growth rate decreases/increases and the unstable range becomes narrower/broader with an increase in acceleration. Since we have positive growth rates, the cellular shape of flame fronts appears owing to intrinsic instability. To study the formation of a cellular flame front, we superimpose the disturbance with the peculiar wave number which corresponds to the maximum growth rate. The disturbance on a flame is evolved, and eventually the cellular flame front is formed. When the flame is propagated downwards, the spacing between cells is almost constant and the depth of cells becomes smaller as the acceleration increases. When the flame is propagated upwards, on the other hand, the former becomes smaller and the latter becomes larger.

Hydrodynamic aspects of premixed flame stripes in two-dimensional stagnation-point flows

A consistent Artificially Thickened Flame approach for spray combustion using LES and the FGM chemistry reduction method: Validation in Lean Partially Pre-vaporized flames

Non‐premixed methane‐oxygen flame dynamics and structures confined within an alumina combustor are described. Non‐stabilized, transient flame dynamics and phenomena leading to the formation of a stable edge‐like flame and distinct cellular structures that take place within combustor channels of dimensions 35 mm long, 5 mm wide, and 0.75 mm high (combustor volume ∼ 130 mm3) are discussed. These confined flames are surveyed by measuring the external wall temperatures, high‐speed and still‐frame visual flame imaging, recordings of emitted acoustics from the combustor, and capturing visible, CH*, and OH* chemiluminescence through a sapphire window. The observed dynamic flame structure is an oscillating edge‐like flame accompanied by ignition‐extinction events that precede the formation of a stable edge‐like flame and flame cells in the reaction channel. The cellular flame structures in all cases exhibit a confined tribrachial structure with a folded or extinguished rich branch while the lean branch survives. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Structure and dynamics of kink and cellular flames stabilized on a rotating burner