Advances and challenges in laminar flame experiments and implications for combustion chemistry

In recent years, advances in computational power and spatial data analysis (GIS, remote sensing, etc) have led to an increase in attempts to model the spread and behaviour of wildland fires across the landscape. This series of review papers endeavours to critically and comprehensively review all types of surface fire spread models developed since 1990. This paper reviews models of a physical or quasi-physical nature. These models are based on the fundamental chemistry and/or physics of combustion and fire spread. Other papers in the series review models of an empirical or quasi-empirical nature, and mathematical analogues and simulation models. Many models are extensions or refinements of models developed before 1990. Where this is the case, these models are also discussed but much less comprehensively.

A review of wildland fire spread modelling, 1990-present, 1: Physical and quasi-physical models

Soot formation in laminar counterflow flames

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1133&context=usdoepub

Direct numerical simulations of ignition of a lean n-heptane/air mixture with temperature inhomogeneities at constant volume: Parametric study

https://web.ics.purdue.edu/~lqiao/Publications_files/Combustion%20of%20nanofluid%20fuels%20with%20the%20addition%20of%20boron%20and%20iron%20particles%20at%20dilute%20and%20dense%20concentrations.pdf

Combustion of nanofluid fuels with the addition of boron and iron particles at dilute and dense concentrations

An experimental system was designed to stabilize steady counterflow methane diffusion flames at elevated pressures, up to 3 MPa. In contrast with the much more common coflow configuration, the counterflow one is advantageous for the following reasons: the suppression of buoyancy instabilities that typically plague coflow flames at high pressures; the one-dimensionality of the flame, that enables computational modeling with very large chemical kinetic mechanisms; and the high level of control that it provides on soot loading. Above 0.8 MPa, the replacement of nitrogen with helium as inert was found to be critical to stabilize well behaved flames with respect to steadiness, laminarity, adiabaticity, one-dimensionality and flame thickness. Scaling and experimental considerations allowed for the identification of acceptable operating conditions in terms of pressure and strain rate and yielded a synthetic representation of a domain of diffusion flames of good quality. Such a graph can inform the design of a high-pressure counterflow system with respect to the selection of burner geometry, diagnostic techniques and experimental conditions, allowing for the experimentalist to sidestep costly and time consuming trial and error. Measurements by thin-filament pyrometry and numerical simulations confirmed the proposed scaling.

Combustion and Flame

https://www.eng.yale.edu/gomez-lab/research/pdf/Figura2012.pdf

Laminar counterflow steady diffusion flames under high pressure (P ⩽ 3 MPa) conditions

Structure of incipiently sooting ethylene–nitrogen counterflow diffusion flames at high pressures

An experimental study was conducted on two C 2 H 4 /O 2 /N 2 laminar diffusion flames with identical compositions and strain rate, but operated at 0.29 MPa and 2.5 MPa, respectively, to assess pressure effects on the onset of soot formation. The low-pressure flame was permanently blue, whereas the high-pressure one was under conditions of incipient sooting. Both flames had nominally identical temperature–time history. Using gas sampling through quartz microprobes followed by GC/MS analysis and addressing potential artifacts associated with the diagnostic intrusiveness and probe-induced chemistry, we demonstrated that the flame structure was resolved even at the highest pressures, as shown by the good agreement with respect to major species between the experimental results and a one-dimensional computational model of the flame with detailed chemistry and transport. The increase in soot propensity correlates with an increase in the concentration of soot precursors like the aromatics and acetylene. Comparison with model predictions shows that the concentration of aromatics is systematically overpredicted. An ancillary computational study to estimate the sensitivity to changes in the velocity boundary conditions showed that minor species like the aromatics are sensitive to these details under certain conditions, because of changes in the temperature–time history that affects predominantly the slow chemistry.

Challenges and artifacts of probing high-pressure counterflow laminar diffusion flames

Information on the Dubrivske alkaline eluvial kaolin deposit, located in the Baranivka district of the Zhytomyr region and a part of the Dubrivksko-Khmelivsky kaolin district, is reviewed. Based on the results of generalization and analysis of materials of production reports of different years, zoning and material composition of the weathering crust within the deposit are established. Weathering crust was formed due to hypergenic changes of granites, pegmatites, migmatites, gneisses. The thickness of the eluvium varies from a few tens of centimeters to 42.7 m. The sequence and stages of weathering of crystalline rocks of the foundation were reflected in the vertical zonation of the weathering crust and the material composition of its zones. The profile of the weathering crust consists of three zones (bottom up): disintegration and leaching; initial hydrolysis (kaolinite-hydromica); final hydrolysis and oxidation of weathering products (kaolinite). Based on the coordinates and description of the wells, the relief of the bottom and surface of the kaolin deposit, as well as the lateral change in their thickness, were investigated. It was found that the kaolin deposit has a complex internal structure and morphology. The thickness of the kaolin deposit has an inverse correlation with the relief of its base, so that the increased areas of the base correspond to small thicknesses of kaolin and vice versa. Based on the results of well testing and chemical analysis of kaolins, the distribution of oxides of iron, titanium and whiteness in the vertical section of kaolins was investigated, and the lateral distribution of the contents of oxides Al2O3, Fe2O3 and TiO2 was established. It was found that in some areas of the lateral distribution of eluvial kaolins, the contents of Fe2O3 and TiO2 have a direct or inverse correlation. The whiteness indices of eluvial kaolins in the vertical section have significant variability and predominantly a direct correlation with the content of iron and titanium oxides, or with one of these indicators. In almost all wells there is a regular decrease in the whiteness index with depth. An inverse correlation was established between the Al2O3 content and the Fe2O3 content and only in some areas with the TiO2 content. Data on the average content (in %) of basic oxides within individual areas of subsoil use of the Dubrovskoye deposit are given. In general, the deposit is characterized by heterogeneity of the base, surface, and the thicknessand the content of rock-forming oxides in the vertical section and laterally.

Lorenzo Figura

Papers

Combustion and Flame

Laminar counterflow steady diffusion flames under high pressure (P ⩽ 3 MPa) conditions

Structure of incipiently sooting ethylene–nitrogen counterflow diffusion flames at high pressures

Challenges and artifacts of probing high-pressure counterflow laminar diffusion flames

Structural and lithological model of the dubrivsky deposit of alkalines eluvial kaolin