Spray combustion modeling

Continello, G., and W. A. Sirignano. 1990. Counterflow spray combustion modeling. Combustion Flame 81 325-40. 

S. Z. Burstein, S. S. Hammer, and V. D. Agosta, Spray Combustion Model with Droplet Breakup Analytical and Experimental Results, in Detonation and Two-Phase Flow, vol. 6 of Progress in Astronautics and Rocketry, S. S. Penner and F. A. Williams, eds.. New York Academic Press, 1962, 243-267. 

Sirignano WA (1986) The Formulation of Spray Combustion Models Resolution Compared to Droplet Spacing. Journal of Heat Transfer 108 633-639... 

As discussed in the context of the conceptual spray combustion model of Dec [12], illustrated in Fig. 13.3, soot tends to form in fuel-rich regions at relatively low temperatures. The exact soot formation process is a rather complex topic more details can be found in the texts of Refs. [4, 23,44]. In the following, a relatively simple production-oxidation soot model, used in the prediction of particle emissions in diesel engines, is outlined. 

In this subsection, a brief exposition of chemical reactions related to spray combustion modeling is presented. More details, together with additional references, can be found in Chap. 10. 

Ghaffarpour, M., and B. Chehroudi. 1993. Experiments on spray combustion in gas turbine model combustor. Combustion Flame 92 173-200. 

Peters, J.E., and Mellor, A.M., An ignition model for quiescent fuel sprays, Combustion and Flame, 38, 65-74, 1980. 

The current status of prediction and modelling in the area of fuel spray combustion requires, among other parameters, the measurement of droplet or solid particle size distribution and the relative velocity between the fuel and the surrounding gas. Many optical techniques, based on laser light scattering, have been investigated to this purpose (Refs.1,2,2,]+,, 6 and j), but the only system able to simultaneously determine the size and the velocity is the dual-beam laser Doppler velocimeter shown in Figure 1. 

Of major interest concerning these problems are influences of turbulence in spray combustion [5]. The turbulent flows that are present in the vast majority of applications cause a number of types of complexities that we are ill-equipped to handle for two-phase systems (as we saw in Section 10.2.1). For nonpremixed combustion in two-phase systems that can reasonably be treated as a single fluid through the introduction of approximations of full dynamic (no-slip), chemical and interphase equilibria, termed a locally homogeneous flow model by Faeth [5], the methods of Section 10.2 can be introduced reasonably successfully [5], but for most sprays these approximations are poor. Because of the absence of suitable theoretical methods that are well founded, we shall not discuss the effects of turbulence in spray combustion here. Instead, attention will be restricted to formulations of conservation equations and to laminar examples. If desired, the conservation equations to be developed can be considered to describe the underlying dynamics on which turbulence theories may be erected—a highly ambitious task. 

Oince the earliest theoretical models by Spalding (I) and Godsave (2) describing the quasi-steady, spherically symmetric combustion of individual fuel droplets in quiescent atmospheres, numerous more elaborate theories have been proposed to provide a better understanding of droplet spray combustion. These theories are based on the premise that the physical and chemical processes involved dmmg single-droplet combustion are fundamental to complex spray combustion processes. 

De Chaisemarttn, S., Freret, L Kah, D. et al. 2009 Eulerian models for turbulent spray combustion with polydispersity and droplet crossing. Comptes Rendus Mecanique 337, 438 48. 

C. Chryssakis, D.N. Assanis, A unified fuel spray breakup model for internal combustion engine applications. Atomization and Sprays, 18(5) 375-426, 2008. 

B. Abramzon and Sirignano. Droplet vaporization model for spray combustion calculations. International Journal of Heat and Mass Tranter, 32(9) 1605-1618,1989. 

Sprays are an important means of supplying fuel to a combustion process, for example in engines, turbines, rocket motors, furnaces, and boilers. The central issues associated with spray combustion include fuel economy and pollution formation, both of which have been major driving forces in the past and the current spray combustion research. The vast amount of literature on the subject is a reflection of its complexity. There are many texts on combustion at various levels of difficulty and with different applications in mind (cf. [9, 17, 20, 23, 28, 29, 30, 37, 52, 56]). In addition, various modeling approaches are discussed in the articles of Pope [41], Borghi [6] and, more recently, in Veynante and Vervisch [51]. 

Fig. 13.3 Conceptual model of diesel spray combustion according to Dec [12]...

This implies that the spray tends to approach a saturation state unless additional heat and oxygen are supplied from the outside of the spray stream. It also implies that the behavior of the outer diffusion flame dominates the subsequent evolution of spray combustion from the spray boundary side. In real spray combustion, this boundary-layer type of change occurs dynamically because the boundary of the spray stream is located in the coherent vertical structure of the shear layer. In addition, turbulent effects are inevitable. However, such fluid dynamic effects have not yet been well characterized. Therefore, we focus on the behavior of the outer diffusion flame based on a quasi-steady continuum spray model. Chiu s theory is developed on this basis to classify the combustion modes excited by the penetration of the outer diffusion flame into the spray region. 

Boysan F, Ayers WH, Swithenbank J, Pan Z (1982) Three-Dimensional model of spray combustion in gas turbine combustors. J Energy 6 368-375... 

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