Thermodynamics, Gas Dynamics, and Combustion (original) (raw)

Physically Based Combustion

Thermodynamics, Gas Dynamics, and Combustion, 2021

To this point, we have gathered a foundation in thermodynamics and applied thermodynamics to the area of gas dynamics to understand speed of sound, normal shocks, and critical flow. Another important application of thermodynamics is combustion. A combustion system is simply a wave which involves a chemical reaction that sustains the wave while oxidizer (usually air) and fuel are available; when the combustion is a detonation, the wave is traveling greater than Mach 1 and is a shock wave. When the combustion is deflagration, the wave is traveling much less than Mach 1. This chapter will mainly address detonation; deflagration will be addressed in Chap. 12. Various properties (states) of a detonation or deflagration are given as Table 10.1 where the subscript "1" denotes unburned gas and "2" denotes burnt gas. One representation of a detonation system is known as the Zeldovic, von Neumann, and Doren, which are commonly known as ZND models [1-4] and given as Fig. 10.1; in Chap. 13, we'll discuss ZND models and call them dynamic detonation models. In this figure the shock wave and attached reaction zone are moving from right to left and the reaction zone includes an induction zone. This chapter asks the following question "for a given initial states (1) what are the final states at either points (2) or (3)"? and assumes the heat release is instantaneous. The ZND model deals with the fact that the heat is released as a result of a chemical reaction and allows for characterization of the states within the induction/ reaction zone (2-> 3). Much of our experimental knowledge for combustion comes from shock tubes (see Fig. 10.2), which are essentially tubes divided by a diaphragm and have a

Combustion Chemistry

Thermodynamics, Gas Dynamics, and Combustion, 2021

Chapter 11 Combustion Chemistry 11.1 Preview We saw in Chap. 10 how to determine the endpoints of either the shock or combustion utilizing the Rankine-Hugoniot theory and the Chapman-Jouget theory. This theory has been shown over the last century to accurately determine the endpoint states of the reaction zone for a detonation, but doesn't work as well for deflagrations. The theory in Chap. 10 was from a purely physical basis. In Chaps. 12 (Deflagrations) and 13 (Detonation), we will incorporate chemistry and other considerations to see how states change within the control volume, but first we need to learn some chemistry. In this chapter, we will learn stoichiometry, which is the idea that for a particular set of chemistry molecules react in certain proportions and produce other molecules in other proportions. When a fuel and oxidizing run stoichiometric, there can be advantages to this situation. Other areas covered in this chapter are a more general definition of enthalpy, discussion of chemical equilibrium and kinetics, and a discussion of adiabatic temperature for a constant pressure and constant volume process. The discussion of adiabatic temperature will include complete combustion (reactions) and incomplete combustion. 11.2 Stoichiometry Stoichiometry is a branch of chemistry that asks very practical questions such as the following: if I have 10 kg of gasoline, how many kilograms of air do I need to completely combust the fuel? It's also an area of chemistry that utilizes conservation of

COMBUSTION PHYSICS

In the past several decades, combustion has evolved from a scientific discipline that was largely empirical to one that is quantitative and predictive. These advances are characterized by the canonical formulation of the theoretical foundation; the strong interplay between theory, experiment, and computation; and the unified description of the roles of fluid mechanics and chemical kinetics. This graduate-level text incorporates these advances in a comprehensive treatment of the fundamental principles of combustion physics. The presentation emphasizes analytical proficiency and physical insight, with the former achieved through complete, though abbreviated, derivations at different levels of rigor, and the latter through physical interpretations of analytical solutions, experimental observations, and computational simulations. Exercises are designed to strengthen the student's mastery of the theory. Implications of the fundamental knowledge on practical phenomena are discussed whenever appropriate. These distinguishing features provide a solid foundation for an academic program in combustion science and engineering.

A toy model for detonations and flames

2017

In the late 1970’s Fickett and Majda introduced qualitative models for supersonic combustion, in an attempt to produce simple equations describing reactive shocks [1, 2]. The rationale was to strip the compressible reactive Euler/Navier-Stokes equations of their non-essential difficulties, in order to gain a deeper mathematical (as well as physical) understanding of the dynamics of shock waves propagating in a reactive medium. Not surprisingly, both Fickett and Majda chose as the starting point Burgers’ equation (already known to represent the generic behavior of weakly non-linear hyperbolic waves), and modified it in order to account for the energy released by a chemical reaction. A few years later, Rosales and Majda [3] showed that the Burgers-like “toy” models invented in the late 1970’s were closely related to a rational asymptotic approximation, starting from the full reactive Navier-Stokes equations, of weak heat release gaseous detonations. The weak heat release limit was als...