Combustion modeling

Ideally, one would numerically model these equations using computational fluid dynamic (CFD) modeling, which we will discuss later. 

---

M. W. Beckstead and co-workers, "Convective Combustion Modelling AppHed to Deflagation Detonation Transition," in Proceedings of the 12th JANNAF Combustion Meeting, Pub. No. 273, Chemical Propulsion Information Agency (CPIA), Johns Hopkins University, Laurel, Md., 1975. 

R. Borghi, Turbulent Combustion Modeling Progress in Energy and Combustion Science, Vol. 14, No. 4, Pergamon Press, Ehnsford, N.Y., 1988, pp. 

Combustion modeling capability. Combustion/ chemical reaction. Combustion/ chemical reaction Combustion/ chemical reaction Combustion/ chemical reaction Simple combustion/ Chemical reaction... 

Although the status of many 3D codes makes it possible to carry out detailed scenario calculations, further work is needed. This is particularly so for 1) development and verification of the porosity/distributed resistance model for explosion propagation in high density obstacle fields 2) improvement of the turbulent combustion model, and 3) development of a model for deflagration to detonation transition. More data are needed to enable verification of the model in high density geometries. This is particularly needed for onshore process plant geometries. 

Bakke, J. R., and B. H. Hjertager. 1986a. Quasi-laminar/turbulent combustion modeling, real cloud generation and boundary conditions in the FLACS-ICE code. CMI No. 865402-2. Chr. Michelsen Institute, 1986. Also in Bakke s Ph.D. thesis Numerical simulation of gas explosions in two-dimensional geometries. University of Bergen, Bergen, 1986. 

With these goals in mind, several investigators have undertaken to set down quantitative expressions which will predict propellant burning rates in terms of the chemical and physical properties of the individual propellant constituents and the characteristics of the ingredient interactions. As in the case of ignition, the basic approach taken in these studies must consider the different types of propellants currently in use and must make allowances for their differences. In the initial combustion studies, the effort was primarily concerned with the development of combustion models for double-base propellants. With the advent of the heterogeneous composite propellants, these studies were redirected to the consideration of the additional mixing effects. 

These studies have indicated that the independent parameters controlling the postulated solid-phase reactions significantly affect the resulting acoustic admittance of the combustion zone, even though these reactions were assumed to be independent of the pressure in the combustion zone. In this combustion model, the pressure oscillations cause the flame zone to move with respect to the solid surface. This effect, in turn, causes oscillations in the rate of heat transfer from the gaseous-combustion zone back to the solid surface, and hence produces oscillations in the temperature of the solid surface. The solid-phase reactions respond to these temperature oscillations, producing significant contributions to the acoustical response of the combustion zone. 

In an effort to determine the processes responsible for this type of behavior, Akiba and Tanno (A3), Sehgal and Strand (S2), and Beckstead (B6) have studied the coupling between the dynamics of the combustion process and the dynamic ballistics of the combustion chamber as described by Eq. (7). Each of these investigators has postulated admittedly simplified but slightly different combustion models to couple with the transient ballistic equations. Each has examined the combined equations for regions of instability. The results of these studies suggest a correlation between the L of the motor (the ratio of combustion-chamber volume to nozzle throat area) and the frequency of the oscillations. 

The combustion processes which control the critical depressurization rate are not understood. Landers (LI) and Von Elbe (VI) have tired to derive an expression for the critical depressurization rate, but the transient combustion model they used is far too simplified to predict the effects shown in Figs. 24 and 25. One possible explanation for these large variations would be that heat-release processes within the solid phase are important. From light-emission measurements during depressurization, Ciepluch observed that it was much easier to eliminate light emission than to terminate combustion (i.e., approximately 12,000 psi/sec produced light emission, compared with 100,000 psi/sec for termination). 

R. Borghi 1988, Turbulent combustion modelling. Prog. Energy Combust. Sci. 14(4) 245-292. 

The ability to resolve the dissipation structures allows a more detailed understanding of the interactions between turbulent flows and flame chemistry. This information on spectra, length scales, and the structure of small-scale turbulence in flames is also relevant to computational combustion models. For example, information on the locally measured values of the Batchelor scale and the dissipation-layer thickness can be used to design grids for large-eddy simulation (LES) or evaluate the relative resolution of LES resulfs. There is also the potential to use high-resolution dissipation measurements to evaluate subgrid-scale models for LES. 

RANS codes were not unsuccessful for the study of piston engines [25-27]. However, it is only with LES [30], for example, that the study of cycle-to-cycle variations becomes possible. For such studies, the solver must have moving-grid capabilities for the piston and the valves, while retaining all the required properties for LES, such as a high-order numerical method. From the point of view of modeling, the combustion model must handle... 

Vervisch, L., R. Hauguel, R. Domingo, and M. Rullaud, Three facets of turbulent combustion modelling DNS of premixed V-flame, LES of lifted nonpremixed flame and RANS of jet flame. /. Turbulence, 2004. 5(4) 004. 

The fact that the fuel/air ratio is spatially constant in HCSI engines, at least within a reasonably close approximation, allows substantial simplifications in combustion models. The burn rate or fuel consumption rate dm /dt is expressed as a function of flame surface area the density of the unburnt fuel/air mixture Pu, the laminar burning velocity Sl, and the fluctuations of velocities, i.e., E as a measure of turbulence, u. ... 

Some characteristics of edge-flames are identified by S.H. Chung in Chapter 4.3. Flames with edges occur in many forms. A thorough understanding of this subject is essential for turbulent combustion modeling. 

Excellent treatments of modem approaches to combustion modeling are available elsewhere (Kuznetsov and Sabel nikov 1990 Wamatz et al. 1996 Peters 2000 Poinsot and Veynante 2001). 

In particular, premixed combustion models based on the flame surface density (Veynante and Vervisch 2002). 

Anand, M. S., S. James, and M. K. Razdan (1998). A scalar PDF combustion model for the national combustion code. Paper 98-3856, AIAA. 

Turbulent combustion modelling. Progress in Energy and Combustion Science 14, 245-292. 

Large eddy simulation of a nonpremixed reacting jet Application and assessment of subgrid-scale combustion models. Physics of Fluids 10, 2298-2314. 

Haworth, D. C. (2001). Application of turbulent combustion modeling. In J. P. A. J. van Beeck, L. Vervisch, and D. Veynante (eds.), Turbulence and Combustion, Lecture Series 2001-03. Rhode-Saint-Genese, Belgium Von Karman Institute for Fluid Dynamics. 

Veynante, D. and L. Vervisch (2002). Turbulent combustion modeling. Progress in Energy and Combustion Science 28, 193-266. 

A fuel cell vehicle requires only 1/10 the parts needed for internal combustion models. A change to fuel cell power could end overcapacity problems for GM. It would no longer have to consider different state or country environmental regulations. Fuel cells also free designers and allow them to be more creative with styles and body designs. 

---