For diffusers, the coefficient of pressure recovery conveys the same information as this quantity. The polytropic form of this quantity is defined as the isentropic form when the difference in pressure across a system approaches zero. This value is often measured assuming an LHV, or "lower heating value." When the second law of thermodynamics is taken into account, the "exergy" type of this quantity can be calculated. This quantity depends on both the compression ratio and the specific heat ratio in the (*) Otto Cycle. The coefficient of performance, or COP, is similar to this measure except that it can exceed 1. Both the Kelvin-Planck statement and Carnot's theorem place a fundamental upper limit on this quantity, 
For diffusers, the coefficient of pressure recovery conveys the same information as this quantity. The polytropic form of this quantity is defined as the isentropic form when the difference in pressure across a system approaches zero. This value is often measured assuming an LHV, or "lower heating value." When the second law of thermodynamics is taken into account, the "exergy" type of this quantity can be calculated. This quantity depends on both the compression ratio and the specific heat ratio in the (*) Otto Cycle. The coefficient of performance, or COP, is similar to this measure except that it can exceed 1. Both the Kelvin-Planck statement and Carnot's theorem place a fundamental upper limit on this quantity, which in its simplest formulation is equal to the heat of the hot reservoir minus the heat of the cold reservoir, over the heat of the hot reservoir. For 10 points, name this thermodynamic quantity, a measure of how little heat or energy is lost in an engine
For diffusers, the coefficient of pressure recovery conveys the same information as this quantity.