ABSTRACT
Solid and liquid fuels, along with their general thermochemical properties and combustion characteristics, were treated separately in Chapters 6 and 7. In this chapter, the remaining fuel category by phase, i.e., gaseous fuels, will be discussed. Depending on temperature and pressure, every pure compound can exist as a gas, liquid, and/or a vapor, and, obviously, gases can be liquefied. Many fuel gases, in fact, can be condensed simply by compression. Some, such as liquefied natural gas (LNG) and liquid hydrogen, require a supercold, or cryogenic, state in order to exist and will not remain in this condition without extreme refrigeration and insulation. For the sake of this discussion, therefore, a fuel will be considered to be a gas if it is noncondensable over normal temperatures and pressures. Examples of gaseous fuels include hydrogen gas, methane, and natural and synthetic natural gas (SNG). Vapors such as propane, butane, and liquefied petroleum gas (LPG) are fuels that are condensable over normal temperatures and pressures. Organizations such as the American Gas Association (AGA) are involved in supporting many aspects of fuel gas technology, including research and development within the natural gas industry, production of synthetic gas via coal gasification, and development of biomass-generated methane systems. Gaseous fuel science will continue to play an important role in combustion engineering in part because of the clean-burning nature of these energy resources, the fact that most fuels actually burn in the gas phase, and insights into the complex nature of general combustion processes that studies of simple gas-phase molecular reactions provide.
