1. Copyright © 2011 by Oxford University Press, Inc. Energy and the Environment James A. Fay / Dan S. Golomb FIGURE 3.4 The Otto cycle comprises two isentropic compression and expansion strokes of a piston in a cylinder (1  2, 3  4) interspersed with two constant-volume heating and cooling processes (2  3, 4  1). It is a model for the spark ignition engine.

2. Copyright © 2011 by Oxford University Press, Inc. Energy and the Environment James A. Fay / Dan S. Golomb FIGURE 3.5 The Brayton cycle models the gas turbine cycle, where air is compressed from the inlet pressure p i in a compressor to the outlet pressure p c (1  2), then burned with fuel to a higher temperature at the constant pressure p c (2  3), and subsequently expanded in the turbine (3  4), producing net work w.

3. Copyright © 2011 by Oxford University Press, Inc. Energy and the Environment James A. Fay / Dan S. Golomb FIGURE 3.6 The vapor compression cycle for refrigeration begins with an isentropic compression (1  2) of the vaporized fluid leaving the evaporator, followed by constant-pressure cooling in the condenser (2  4) to form a saturated liquid (4).The liquid leaving the condenser undergoes an adiabatic pressure decline (4  5), entering the evaporator as a cold liquid.vapor mixture (5), whereupon it absorbs heat from the refrigerated space (5  1). (In the T, s diagram on the left, the area beneath the dashed line delineates the conditions where both vapor and liquid refrigerant coexist, in contrast to vapor only to the right and liquid to the left.)

4. Copyright © 2011 by Oxford University Press, Inc. Energy and the Environment James A. Fay / Dan S. Golomb FIGURE 3.7 Steady flow of reacting material through an energy processing device, with heat input q from, and work output w to, the environment.

5. Copyright © 2011 by Oxford University Press, Inc. Energy and the Environment James A. Fay / Dan S. Golomb FIGURE 3.8 The enthalpy h of the reactants (upper curve) and the products (lower curve) of a combustion process, as functions of the temperature T, are related by the fuel heating value. For adiabatic, constant-pressure combustion, the products temperature T p is greater than the reactant temperature T r.