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Introduction |
External
Combustion Engines |
Internal
Combustion Engines |
Electric Motors Where does burning take place in an internal combustion engine? Did you know that there's a fire inside the engine of your family car? It's what makes the engine operate. You can't see the flames because they're deep inside. This internal (inner) fire means that your family's car is powered by an internal combustion engine. Gasoline, diesel, gas turbine, and rocket engines are all internal combustion engines. Although you can see the flames in some jet engines and all rocket engines, the combustion still takes place inside the engine.
Engine Cycles Are engine cycles like other type of cycles? When a set of events happens over and over again, we say that the events go in cycles. The seasons of the year follow a cycle. There are also life cycles, food cycles, and business cycles, just to name a few. A
What is involved in a four-stroke cycle? Much like your legs pedaling a bicycle, the pistons inside an engine move up and down. The most popular type of engine is the four-stroke cycle engine. The pistons make four strokes before they repeat themselves. These strokes are the intake, compression, power, and exhaust strokes. The four stroke engine was first demonstrated by Nikolaus Otto in 1876, hence it is also known as the Otto cycle. The technically correct term is actually four-stroke cycle. The four-stroke engine is probably the most common engine type nowadays. It powers almost all cars and trucks. The strokes are illustrated in the four drawings below:
There you have it. The four stroke cycles of a four-stroke engine - Intake, Compression, Power, and Exhaust.
The pistons are connected to the
crankshaft by
connecting rods. The main purpose of the camshaft (the oblong rotating wheel on the drawing above) and valve lifter system is to open the valves. Notice how the camshaft is "timed" by gears to open the valve at just the right time. The larger camshaft gear has twice as many teeth as the smaller gear on the crankshaft. So, the crankshaft must make two turns for the camshaft to make one. That way, the valve will only open on the exhaust stroke, or every other turn of the crankshaft. Most modern engines use this system to open both the intake and exhaust valves. The flywheel is a heavy wheel
connected to the end of the crankshaft. The momentum of the turning
flywheel is used to keep the crankshaft turning smoothly. This turning motion can then be directed to the wheels of the car
to make the
car go. Most cars have four-stroke cycle engines. Also, most cars have either four, six, or eight cylinders, all connected to one crankshaft and working together to provide a smooth source of power. When oil is added to the engine for lubrication, it is put in separately. Oil is not mixed with the fuel in a four-stroke cycle engine.
How does a two-stroke cycle work? Some small gasoline engines operate with
only two strokes. The intake and compression strokes are combined.
The power and exhaust strokes are also combined. Such engines
operate on a two-stroke cycle. The piston makes two strokes before
it begins to repeat itself.
A two-stroke cycle engine is illustrated in the animated picture on the right. Stroke 1 Notice how at the start of the com-pression stroke, the intake opening on the left side of the piston allows the air and gas mixture to be drawn up and into the cylinder. As the piston moves up it closes this port and the mixture is compressed. This effectively combines the intake stroke and compression stroke into one stroke. Stroke 2 After the spark plug ignites the mixture, the piston is driven down. Notice how the exhaust port on the right side of the piston is now open to allow the exhaust gases to escape. This effectively combines the power stroke and the exhaust stroke into one stroke. As the crankshaft begins to push the piston back up again, the next cycle begins. There you have it again. The two-stroke cycles of a two-stroke engine.
Two-stroke cycle engines are less efficient and emit more pollutants into the environment. In them, the fuel and oil are mixed together. To read more about how the two stroke cycle engine works, click the picture of the flying cycles on the left.
Introduction | External Combustion Engines | Internal Combustion Engines | Electric Motors Copyright (c) 2006 Harley D. Brown All rights reserved. |
Most engines that we use in our daily lives create power
from a piston sliding inside a cylinder. Fuel and air are placed
inside the cylinder. An electric spark causes this mixture to ignite
(catch fire) and build up high pressure in a very short time. The
pressure pushes the piston down with great force. Another device,
such as a crankshaft, changes the downward motion to circular motion.
This process produces enough power to cause automobiles to travel on land,
boats to move through water, and small airplanes to fly in the air.
bicycle has
cycle as part of its name. In
pedaling a bicycle, your legs go up and down, repeating the motions over
and over again. One motion of your leg makes a downward stroke.
Lifting your leg creates an upward stroke. (A stroke is movement in one
direction.) Your legs make two strokes before repeating the same motions.
We could say that your bicycle is operated by a two-stroke human power
plant. Your legs deliver power to the rear wheel, which is called
the driving wheel. Wheels under power are called driving wheels.
Other wheels are called trailing wheels.
An actual piston and connecting rod is shown on the left. The
crankshaft is the part of an engine
that changes the reciprocating
(up and down) motion of the pistons to a
rotary (circular) motion.
