i) Definition of the Systems
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion.
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion apply direct force to some component of the engine. This force is applied typically to pistons, turbine blades, or a nozzle. This force moves the component over a distance, transforming chemical energy into 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 six-stroke piston engine and the Wankel rotary engine.
Operation of Four Stroke Engine
Four-stroke internal combustion engines have four basic steps that repeat with every two revolutions of the engine:
(1) Intake stroke
(2) Compression stroke
(3) Power stroke and
(4) Exhaust stroke
1. Intake stroke: The first stroke of the internal combustion engine is also known as the suction stroke because the piston moves to the maximum volume position (downward direction in the cylinder). The inlet valve opens as a result of the cam lobe pressing down on the valve stem, and the vaporized fuel mixture enters the combustion chamber. The inlet valve closes at the end of this stroke.
2. Compression stroke: In this stroke, both valves are closed and the piston starts its movement to the minimum volume position (upward direction in the cylinder) and compresses the fuel mixture. During the compression process, pressure, temperature and the density of the fuel mixture increases.
3. A Power stroke: When the piston reaches a point just before top dead center, the spark plug ignites the fuel mixture. The point at which the fuel ignites varies by engine; typically it is about 10 degrees before top dead center. This expansion of gases caused by ignition of the fuel produces the power that is transmitted to the crank shaft mechanism.
4. Exhaust stroke: In the end of the power stroke, the exhaust valve opens. During this stroke, the piston starts its movement in the maximum volume position. The open exhaust valve allows the exhaust gases to escape the cylinder. At the end of this stroke, the exhaust valve closes, the inlet valve opens, and the sequence repeats in the next cycle.
Operation of Wankel Engine
The Wankel engine (rotary engine) does not have piston strokes. It operates with the same separation of phases as the four-stroke engine with the phases taking place in separate locations in the engine. In thermodynamic terms it follows the Otto engine cycle, so may be thought of as a "four-phase" engine. While it is true that three power strokes typically occur per rotor revolution due to the 3:1 revolution ratio of the rotor to the eccentric shaft, only one power stroke per shaft revolution actually occurs; this engine provides three power 'strokes' per revolution per rotor giving it a greater power-to-weight ratio than piston engines. This type of engine was most notably used in the Mazda RX-8, the earlier RX-7, and other models.
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| Mazda RX-8 Wankel Engine |
source : wikipedia
Common Types of Engine
- Singles : typically used in motorbikes, snowblowers, chainsaws etc.
- V-twins : found in motorbikes.
- The triple : almost unique to Triumph motorbikes where they call it the
Speed Triple, or the 675.
- Straight 4/Inline-fours : the mainstay of car engines, as well as being found in
some motorbikes too such as the BMW K1200S.
- Straight 5/Inline fives : used a lot in Audi but have found a new home in
current Volvo.
- The V5 : find in some Volkswagen.
- The V6 : has the benefits of being smoother than an inline-four but without
the fuel economy issues of a V8.
- Boxer engines : found in BMW motorbikes (twins), Porsche and
Subaru (fours and sixes).
source : http://www.carbibles.com/fuel_engine_bible.html
(...will continue on Location of the system in vehicle in the next post...)
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