Other related tidbits:
Volumetric Efficiency - Primarily related to power production. The amount of air and oxygen pumped through a given engine's physically limited size, determines the amount of fuel that can be burned, thus peak power production. However any engine design, piston or turbine, has a sweet spot (or range) of power production that has the highest thermal efficiency (converting heat to work), thus the lowest specific fuel consumption for work produced in that power range.
Turbochargers or Superchargers - Increases the amount of air and oxygen pumped through an engine, and the amount of fuel that can be burned. Superchargers NEVER add thermal efficiency only power, however a turbocharger can add thermal efficiency in 2 ways. One, it allows a smaller engine to produce the same power as a larger engine, making it possible to operate a smaller engine closer to its optimum thermal efficiency power range in a given application. Two, the recovered waste heat from the exhaust is used by the turbo to pump air through the engine, thus taking over the engine's air pumping duties and reducing or eliminating the engine's normal pumping losses.
Atkinson Cycle - A piston engine design where the power stroke is longer than the compression stroke. The purpose is to increase thermal efficiency by extracting more work from the heat of the burned air/fuel charge, at the expense of power density. True Atkinson engines used various mechanical linkages to create the dissimilar length of compression and power strokes, whereas modern Atkinson cycle engines (such as those used in hybrid autos) use clever valve timing to achieve the same result.
Lean Burning - Can increase thermal efficiency. Stoichiometric fuel burning is designed to burn just enough fuel to consume all the oxygen in an air/fuel charge, and still produce complete combustion of the hydrogen and carbon in the HC fuel, with no oxygen left over. However lean burning burns less fuel than the available oxygen can support. Less heat is added relative to the amount of air compressed in either the Otto or Brayton cycle, making it possible to convert more of a smaller heat product into mechanical work with less residual wasted heat. It can also be argued that a more open throttle for a given power output while lean burning, reduces pumping losses. Like the Atkinson cycle, lean burning produces more thermal efficiency at the expense of overall power. However clever engine design allows lean burn to be a selectable mode rather than a constant condition, to preserve an engine's high power production when needed.
Last edited by Flight Safety; 29th Nov 2011 at 10:53.