Flame non-premixed

Raman, V. and Pitsch, H., Large-eddy simulation of a bluff-body-stabilized non-premixed flame using a recursive filter-refinement procedure. Combust. Flame, 142, 329, 2005. 

In Chapfer 7.2, J.H. Frank and R.S. Barlow describe the basic characteristics of non-premixed flames wifh an emphasis on fundamenfal phenomena relevant to predictive modeling. They show how the development of predictive models for complex combustion systems can be accelerated by combining closely coupled experiments and numerical simulations. 

Branley, N. and W. P. Jones (2001). Large eddy simulation of a turbulent non-premixed flame. Combustion and Flame 127, 1914-1934. 

Bilger, R.W. On reduced mechanisms for methane-air combustion in non-premixed flames, Combustion Flame, 80, 135-149, (1990). 

The relative importance of these three mechanisms in NO formation and the total amount of prompt NO formed depend on conditions in the combustor. Acceleration of NO formation by nonequilibrium radical concentrations appears to be more important in non-premixed flames, in stirred reactors for lean conditions, and in low-pressure premixed flames, accounting for up to 80% of the total NO formation. Prompt NO formation by the hydrocarbon radical-molecular nitrogen mechanism is dominant in fuel-rich premixed hydrocarbon combustion and in hydrocarbon diffusion flames, accounting for greater than 50% of the total NO formation. Nitric oxide formation by the N20 mechanism increases in importance as the fuel-air ratio decreases, as the burned gas temperature decreases, or as pressure increases. The N20 mechanism is most important under conditions where the total NO formation rate is relatively low [1],... 

The conclusion at which we arrive above, that the temperature of a non-premixed flame is equal to the combustion temperature of the stoichiometric mixture, is in contradiction with experiment it is well known from daily laboratory experience that in the combustion of a given luminescent gas in a Bunsen burner when the apertures for air suction are closed the temperature of the flame is lower than when the same gas burns with open apertures so... 

DISCUSSION By using a mixture of hydrogen and methane as the fuel, a case 2 (see above) experiment has been contrived, i.e., the effective Rayleigh scattering cross section of the fuel, air, and products are nearly ( < 2%) equal. It was then possible to make the first application of laser Rayleigh thermometry to non-premixed flames. 

H. El-Asrag and S. Menon. Large eddy simulation of bluff-body stabilized swirling non-premixed flames. Proc. Combust. /nsL, 31 1747-1754, 2007. 

In the context of combustion in non-premixed flames, this is called the Burke-Schumann solution. If the initial condition is such that T(x, t = 0) is not homogeneous in space, solving its advection-diffusion equation to obtain T(x, t) is needed in addition to solving the one for (x, t) before using (5.8)-(5.9) to obtain C(x, t). 

Experimental and computational aeroacoustics and emissions of modern swirl combustor flows are underway. Preliminary measurements of turbulent non-premixed flame sound highlight the influence of combustion as a sound source. Particle Image Velocimetry measurements in swirl combustors reveal the influence of heat release and its effect on the complex spatial structures that are present. Acoustic measurements in confined turbulent jets are used to better understand sound sources in such flows. Computational aeroacoustics studies of unconfined and confined flows and flames have allowed acoustic source identification. Preliminary LES of diffuser and swirl combustor flowfields serve as benchmarks for future combustion simulations. 

Garman, J. D., and Dunn-Rankin, D. "Spatial Averaging Effects in CARS Thermometry of a Non-Premixed Flame." Combustion and Flame 115 (1998) 481. 

With these identifications, according to Borghi [6], one obtains a diagram with almost identical regions as for premixed combustion. In Fig. 13.1, the non-premixed regions are identified with the letter N. Note that the basic turbulence-chemistry interactions which define these regions, that is Ret =, Da = 1, and Ka = I, also define the different regions for the non-premixed flame structures. 

For a non-premixed flame, the relatively thin reaction zone is viewed as a collection of laminar flamelets subject to turbulence fluctuations. The chemical reactions within a flamelet can be treated as a locally one-dimensional phenomenon that depends on the fuel-oxidizer mixture. This mixture is expressed in terms of the mixture fraction... 

Fig. 42.13 Extinction mass concentration with respect to strain rate for different powder particle sizes in a propane/air, counterflow, non-premixed flame [1]...

W. Grosshandler, A. Hamins, K. McGrattan, S. R. Charagundla, C. Presser Suppression of a non-premixed flame behind a step. Proceedings of the Combustion Institute, Vol. 28, pp. 2957-2964, Combustion Institute, Pittsburgh (2000). 

In the 1980s reduced mechanisms for premixed and non-premixed flames of methane were described and, shortly after, these mechanisms were used in the asymptotic and numerical analysis [11]. In the 1980s, some research groups focused their attention on methane flames and developed useful techniques for the systematic reduction of the detailed kinetic mechanism. It was found that kinetic models for hydrocarbons have a logical hierarchical stractuie, where the kinetic mechanism of any fuel contains, as a subset, the mechanism of smaller molecules [12]. 

Non-premixed flames can be generated in a variety of ways, as detailed in [PRU 13]. Here, we examine the influence of an acceleration fleld, followed by that of an electrical field, on a candle flame. Finally, we look at the effect of a magnetic field on a diffusion flame from a burner formed of two coaxial cylindrical tubes, with the central tube providing the fuel and the outer tube the oxidant. 

Shmakov, A. Korobeinichev, O. Shvartsberg, V. Knyazkov, D. Bolshova, T. Rybitskaya, I. (2004). Inhibition of Premixed and Non-Premixed Flames with Phosphorus-Containing Compounds, Proc. Combust Inst, Vol. 30, No. 2, pp. 2342-2352, ISSN... 

Maas, U., Thevertirt, D. Correlation analysis of direct numerical simulation data of turbulent non-premixed flames. Proc. Combust Inst. 27, 1183-1189 (1998)... 

Tabulation was successfully used for the description of the oxidation of n-heptane, iso-octane, -decane and -dodecane. The agreement was good compared with the results of detailed chemical calculations for all alkanes when only 20 progress variable light species were used (Kourdis and Bellan 2014). Tabulation was applied by Xuan and Blanquart (2014) for the calculation of the concentrations of polycyclic aromatic hydrocarbons (PAHs) in non-premixed flames. 

The above approaches to tabulation, whilst mostly applied in the simulation of combustion problems, have a general foundation that would be relevant to many kinetic systems. However, a special class of tabulation methods has been developed for flame simulations. If a fast exothermic reaction takes place between two components (e.g. a fuel and an oxidiser) of a gaseous system, then flames are observed. In premixed flames the fuel and the oxidiser are premixed before combustion takes place, whilst in non-premixed (diffusion) flames, the fuel and the oxidiser diffuse into each other, and the flame occurs at the boundary or flame front. Premixed and non-premixed flames are two extreme cases, but in many practical flames, continuous states between these two extremes will exist. Flames can be classified as laminar or turbulent according to the characteristics of the flow. Flames are special types of reaction—diffusion systems, characterised by high spatial gradients in temperature and species concentrations, and consequently reaction rates will have a high spatial variability. 

Xuan, Y., Blanquart, G. A flamelet-based a priori analysis rai the chemistoy tabnlatimi of polycyclic aromatic hydrocarbons in non-premixed flames. Cranbust. Flame 161, 1516-1525 (2014)... 

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