Turbulent Spray Combustion

Document Type

Book Chapter

Publication Date

12-13-2017

Department

Department of Mechanical Engineering-Engineering Mechanics

Abstract

Understanding turbulence is one of the most difficult topics in science and engineering. This is because turbulent spray combustion involves many areas of physics and chemistry which accompany a variety of mathematical challenges. Defining the various length and timescales existing in turbulent flow provides a better way to understand and characterize this chaotic phenomenon. However, the degree of complexity increases when there is a strong interaction between turbulence flow and chemistry. Here, characteristic times of chemical reaction in a molecular level (chemical) and fluid-mechanic level (physical) determine which of these are more dominant. This interaction remains as one of the most important and challenging aspects of turbulent reacting spray. In the present chapter, we begin with a general discussion on turbulence. The following section covers description of key features involved in a spray combustion scenario. Concepts involving higher fidelity in description of turbulent combustion are covered by discussion of interaction of turbulence and combustion. In most actual spray combustion applications, the combustion is dominantly non-premixed. There is a minor aspect of premixed combustion too which are discussed in this chapter. New advanced combustion modes such as partially premixed combustion (PPC) and multiple injections, topics with growing interests, are introduced and discussed later. Finally, numerically simulating these aspects is a key area of combustion research. It is of utmost important to optimize the combustion system using computer-based simulations to avoid higher cost for experimentally parametric study. Reynolds-averaged Navier–Stokes (RANS) models are mostly used in commercial sector for computationally tractable simulation time. Large-eddy simulation (LES) offers a higher fidelity approach. With the advent of higher computational resources, LES approaches are becoming more popular for obtaining solutions of turbulent combustion. Aspects of both RANS and LES relevant to spray combustion scenarios are discussed. Although usually requiring very high computational power, direct numerical simulation (DNS) can provide an actual representative of many chemical and physical aspects of spray combustion such as evaporation and auto-ignition, which are discussed at the end of this chapter.

Publication Title

Energy, Environment, and Sustainability

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