An engine is a machine designed to convert energy into useful mechanical motion. In common usage, an engine burns or otherwise consumes fuel, and is differentiated from an electric machine (i.e., electric motor) that derives power without changing the composition of matter. An engine may also serve as a "prime mover", a component that transforms the flow or changes in pressure of afluid into mechanical energy; An automobile powered by an internal combustion engine may make use of various motors and pumps, but ultimately all such devices derive their power from the engine. The term "motor" was originally used to distinguish the new internal combustion engine-powered vehicles from earlier vehicles powered by steam engines, such as the steam roller and motor roller, but may beused to refer to any engine.
Internal Combustion Engine
The internal combustion engine is an engine in which the combustion of a fuel (generally, fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable componentof the engine, such as the pistons or turbine blades and by moving it over a distance, generate useful mechanical energy.
The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines, along with variants, such as the Wankel rotary engine. A second class of internal combustionengines use continuous combustion: gas turbines, jet engines and most rocket engines, each of which are internal combustion engines on the same principle as previously described.
The internal combustion engine (or ICE) is quite different from external combustion engines, such as steam or Stirling engines, in which the energy is delivered to a working fluid not consisting of, mixedwith, or contaminated by combustion products. Working fluids can be air, hot water, pressurized water or even liquid sodium, heated in some kind of boiler.
Four-stroke cycle (or Otto cycle)
o Combustible mixtures are emplaced in the combustion chamber
o The mixtures areplaced under pressure
o The mixture is burnt, almost invariably a deflagration, although a few systems involve detonation. The hot mixture is expanded, pressing on and moving parts of the engine and performing useful work.
o The cooled combustion products are exhausted into the atmosphere
Many engines overlap these steps in time; jet engines doall steps simultaneously at different parts of the engines.
Two stroke configuration
Engines based on the two-stroke cycle use two strokes (one up, one down) for every power stroke. Since there are no dedicated intake or exhaust strokes, alternative methods must be used to scavenge the cylinders. The most common method in spark-ignition two-strokes is to use the downward motion of the pistonto pressurize fresh charge in the crankcase, which is then blown through the cylinder through ports in the cylinder walls.
Spark-ignition two-strokes are small and light for their power output and mechanically very simple; however, they are also generally less efficient and more polluting than their four-stroke counterparts. In terms of power per cubic centimetre, a single-cylinder small motorapplication like a two-stroke engine produces much more power than an equivalent four-stroke engine due to the enormous advantage of having one power stroke for every 360 degrees of crankshaft rotation (compared to 720 degrees in a 4 stroke motor).
Small displacement, crankcase-scavenged two-stroke engines have been less fuel-efficient than other types of engines when the fuel is mixed with...
Leer documento completo
Regístrate para leer el documento completo.