https://hal.archives-ouvertes.fr/hal-00803230/document

Large Eddy Simulations of gaseous flames in gas turbine combustion chambers

Soot formation in laminar counterflow flames

https://hal.archives-ouvertes.fr/hal-00811961/document

Large Eddy Simulation of combustion instabilities in a lean partially premixed swirled flame

This paper reviews basic results and recent developments in the field of small-scale gaseous hydrodynamics which has received significant attention in connection with small-scale science and technology. We focus on the modeling challenges arising from the breakdown of the Navier-Stokes description, observed when characteristic lengthscales become of the order of, or smaller than, the molecular mean free path. We discuss both theoretical results and numerical methods development. Examples of the former include the limit of applicability of the Navier-Stokes constitutive laws, the concept of second-order slip and the appropriate form of such a model, and how to reconcile experimental measurements of slipping flows with theory. We also review a number of recently developed theoretical descriptions of canonical nanoscale flows of engineering interest. On the simulation front, we review recent progress in characterizing the accuracy of the prevalent Boltzmann simulation method known as direct simulation Monte Carlo. We also present recent variance reduction ideas which address the prohibitive cost associated with the statistical sampling of macroscopic properties in low-speed flows.

http://absimage.aps.org/image/DFD05/MWS_DFD05-2005-020061.pdf

The limits of Navier-Stokes theory and kinetic extensions for describing small-scale gaseous hydrodynamics

A compact skeletal mechanism for n-dodecane with optimized semi-global low-temperature chemistry for diesel engine simulations

https://hal.archives-ouvertes.fr/hal-01272968/document

A two-step chemical scheme for kerosene–air premixed flames

Tabulated chemistry is a popular technique to account for detailed chemical effects with an affordable computational cost in gaseous combustion systems. However its performances for spray combustion have not completely been identified. The present article discusses the chemical structure modeling of spray flames using tabulated chemistry methods under the hypothesis that the chemical subspace accessed by a two-phase reactive flow can be mapped by a collection of gaseous flamelets. It is shown that tabulated chemistry methods based either on pure premixed flamelets or on pure non-premixed flamelets fail to capture the structure of spray combustion. The reason is the complexity of the chemical structure of spray flames which exhibits both premixed-like and non-premixed-like reaction zones. To overcome this issue, a new multi-regime flamelet combustion model (called Partially-Premixed Flamelet Tabulation 2PFT) is presented in this paper. Information from premixed, partially-premixed and diffusion flames are stored in a 3-D look-up table parametrized as a function of the progress variable Y c , describing the progress of the reaction, the mixture fraction Y z , denoting the local equivalence ratio, and the scalar dissipation χ ∗ , which identifies the combustion regime. The performances of the 2PFT method are evaluated on counterflow laminar spray flames for different injection conditions of droplet diameter, liquid volume fraction and velocity. The 2PFT tabulation method better describes the chemical structure of spray flames compared to the classical techniques based on single archetypal flamelets. These results also confirm that the chemical structure of laminar spray flame can be modeled by a multi-regime flamelet combustion model based on gaseous flamelets.

/pdf/a-tabulated-chemistry-method-for-spray-combustion-29yv087o97.pdf

A tabulated chemistry method for spray combustion

The understanding of spray combustion processes is of primary importance, as it is encountered in a wide range of industrial applications In the present work, mesoscale-resolved simulations of a 3D turbulent counterflow spray configuration are conducted Primary focus is on examining the effect of the coupling between turbulence, evaporation, mixing, and combustion By considering different initial droplet diameters and through comparisons with turbulent and laminar configurations at the same operating condition, it is shown that preferential concentration can lead to conditions of locally high mixture-fraction composition In addition, local variability in strain rate and droplet diameter introduces a bifurcation of the spray flame This bifurcation consists of spray flame structures exhibiting single-reaction or double-reaction structures It is shown that this bimodal behavior is linked to the existence of a hysteresis in the laminar spray flame structure for droplet diameter variations, as well as the occurrence of a bifurcation for strain rate variations These results have direct implications for flamelet-based tabulation methods, since identifying the appropriate flamelet structure in turbulent spray flames would require informations about boundary conditions and the flamelet history

/pdf/analysis-of-segregation-and-bifurcation-in-turbulent-spray-d88bj4narf.pdf

Benedetta Franzelli

Papers

Large Eddy Simulation of combustion instabilities in a lean partially premixed swirled flame

A two-step chemical scheme for kerosene–air premixed flames

A tabulated chemistry method for spray combustion

Analysis of segregation and bifurcation in turbulent spray flames: A 3D counterflow configuration

Coupling an LES approach and a soot sectional model for the study of sooting turbulent non-premixed flames