ABSTRACT
Objectives ◾ Introduce fuels and combustion ◾ Define A:F ratio, stoichiometry, excess air, equivalence ratio (ϕ), stoichiometric ratio (SR),
and illustrate to human engines ◾ Present wet and dry analyses and relate to A:F ◾ Introduce thermochemistry for reacting systems, define chemical enthalpy (hf), thermal
enthalpy (ht), heat of reaction, heating values-higher (gross) and lower, empirical fuels. ◾ Use of generalized energy conservation equation for reacting systems in estimation of heat
transfer and use in adiabatic flame temperature for open and closed systems ◾ Use of generalized entropy balance equation for estimation of entropy generation during
irreversible reactions ◾ Present mass conservation and mole balance equations for reacting systems
11.1 Introduction Fuels supply power to automobiles, aircraft, and ships. Œey supply power for electrical power generation and for the production of heat and steam. Fuels also supply energy to biological systems including humans. Worldwide energy consumption is currently at 420 TJ while in the U.S. consumption is about 106 TJ. By 2050, world consumption is expected to raise to 1060 TJ and the U.S. to about 275 TJ (1 TJ = 0.948 quad, 1 quad = 1015 BTU). Electric power consumption in 2000 in the U.S. is given as follows (units, BkW-h, or Billion kWhr, 1 kWhr = 3600 kJ):
Coal 2000 53% Natural Gas 600 16% Nuclear 754 20% Hydroelectric 279 7% Renewables 84 2%
Fossil fuels are those fuels dug out of ground while renewable fuels are fuels grown using sunlight and atmospheric CO2, for example, corn stover, tree leaves, rice straw, wood, and agricultural crops. Fossil fuels release CO2 on combustion. In 2000, the U.S. produced 2.1 billion tons of greenhouse gas CO2 due to coal consumption. As a result of increasing use of fossil fuels the CO2 concentration in the atmosphere keeps increasing (Figure 11.1).
