This chapter presents the main jet engine components: inlet diffuser, compressor, combustor, turbine, and exit nozzle. Typical configurations are presented for each component, followed by a description of the main processes and parameters. The performance of each component is then related to the engine real cycle, which establishes a tight connection between this chapter and . The section describing the combustors is also connected toand .

Rocket propulsion is a form of jet propulsion where mass (or matter) is accelerated from storage to high exit velocities. Rockets differ from typical air-breathing jet propulsion in that the rocket vehicle itself supplies all the propellant for the rocket motor. The exception to this is the mixed-mode (or multi-mode) engine that will be discussed later in this chapter.

An important challenge of compressor design is flow separation. A significant challenge of turbine design is heat transfer from the hot gases to the metal blades. To understand the physics of these two challenges, this chapter will introduce the viscous boundary layer and thermal boundary layer concepts.

Adiabatic combustion raises the temperature of the working fluid in a power cycle and provides the source of “high-temperature heat” to the heat engine. Analysis in the previous chapter showed that adiabatic combustion reactions are irreversible, and lead to entropy generation and hence loss of availability. Isothermal reactions that operate at equilibrium with the environment avoid this loss mechanism. If carefully executed, these can lead to more efficient use of the chemical energy. One practical way to directly convert chemical energy to electricity under nearly isothermal conditions is in a fuel cell, where reactions occur in the form of an electrochemical pair, or a redox pair.

Energy is one of the most important needs of humanity. Mobility, lighting, communications, heating, and air conditioning are all energy-intensive functions that are indispensable in modern life. Industrial production, food production, and clean water require energy.

In Chapter 5 we covered gas turbine cycles and discussed conditions under which they are expected to achieve high efficiency or high specific work. With high-temperature energy sources, such as combustion of clean fuels, gas turbines offer many advantages in electricity generation, as well as high-speed propulsion. They are not, however, compatible with intermediate-temperature sources, such as lower-temperature nuclear reactors and concentrated solar thermal energy, or low-temperature sources such as concentrated solar power or geothermal energy. Two-phase Rankine cycles can be designed to operate at high efficiency while utilizing these sources. This is the subject of this chapter.

Thermomechanical energy conversion is concerned with the conversion of heat and thermal energy to mechanical work or mechanical energy. The latter may be used directly (e.g., for propulsion) or to generate electricity. Currently, the major source of thermal energy is the combustion of fossil fuels and biomass, followed by thermonuclear reactions, with geothermal energy and solar energy at much smaller scales. The conversion efficiency is directly related to the temperature of the heat source or the “quality” of the thermal energy. The temperature of the source and that of the environment determine the maximum efficiency of energy conversion cycles.

Renewable sources of thermal energy have been used to generate electricity in power plants using power cycles similar to those described in Chapters 5 and 6, although with some modifications to make them compatible for the intermediate- and lower-temperature heat sources. These renewable sources include geothermal energy and concentrated solar thermal energy. The power cycles used for these two types will be discussed in this chapter, starting with general guidelines regarding how to maintain the cycle efficiency as high as possible while using lower-temperature heat sources. For instance, using different working fluids in Rankine cycles can improve the efficiency by operating the cycle as a supercritical cycle even though the source temperature is relatively low.

Energy conversion systems, in which the energy source is a fuel or a chemical energy carrier such as hydrogen, very often involve reacting mixtures. Reactions among species in these mixtures result in the conversion of their chemical bond energy into other forms, such as thermal energy or electrical energy. In exothermic reactions, of which combustion reactions are an important subset, the stored chemical energy is converted into thermal energy, which raises the temperature of the mixture. In jet engines and rockets, the thermal energy is converted into kinetic energy in the nozzle, which produces thrust. Exothermic chemical reactions are also used in industrial operations – where thermal energy delivered at fast rates is required – and domestic and commercial heating systems. Endothermic reactions, which absorb energy, are also important. Examples of practical applications of endothermic reactions include some fuel reforming processes, the production of synthetic fuels and other chemicals, chemical storage of hydrogen, and the formation of nitric oxides in combustion. In endothermic reactions, thermal energy is supplied through heat transfer to energize the reactions. Reactions involving the conversion between chemical and thermal energies are generally called thermochemical reactions. Such reactions are the principal scope of this chapter.

In this chapter, some proposed power cycles for CO2 capture in coal power plants are presented. These, as discussed in Chapter 11, include post-combustion capture, pre-combustion capture, and oxy-combustion capture cycles. The objective of the coverage is, besides describing the processes in some of these cycles, to evaluate their efficiency and contribution of the capture process toward derating the power production. While similar in principle to those designed for use with natural gas, coal (and other solid fuels) differs in fundamental ways from natural gas because it is consumed in the solid phase and it is often contaminated with sulfur, nitrogen, and ash, among other undesirable substances. Both the nature of the fuel and the contaminants make coal more challenging to use in energy production, and more so when carbon capture is implemented. However, and given its wide availability, lower cost, and higher CO2 emission per unit of useful energy produced, it is imperative to develop this technology.

Carbon dioxide production in electric power plants depends strongly on the fuel and power cycle efficiency. Coal and natural gas generate approximately one mole of CO2 for each mole of fuel burned, but they differ in their plant conversion efficiency. Table 10.1 shows average data for CO2 production when using either fuel for electricity generation. The absolute majority of pulverized coal plants operate on steam Rankine cycles. The most efficient natural gas plants operate on combined cycles, although some operate on simple cycles.

Coal is a widely available cheap fuel that has been used extensively in heating, electricity generation, and industrial processes. Coal reserves and resources are the largest among other known fossil fuel reserves and resources. Besides carbon, hydrogen, and some oxygen, raw coal contains, among other things, sulfur, metallic compounds, mercury, and nitrogen. Technologies have been developed to utilize coal while limiting the emissions of “criteria” pollutants, including sulfur compounds, nitric oxides, mercury, and fine particulates. While increasing the cost of electricity by raising the plant capital cost and lowering its efficiency, these technologies made it possible to continue to expand the use of coal without negatively affecting air quality. More recently, coal use has accelerated significantly in developing economies. This and the fact that coal produces the largest amount of CO2 per unit of useful energy has intensified the effort to improve the overall efficiency of coal power plant and to develop technologies for CO2 capture from these plants.