The internal combustion engine in most cars works on the four-stroke principle. This means that to produce one pulse of power the piston must travel up and down the cylinder four times. Each stroke of the piston performs a separate function in the cycle as follows:
: the begins the process. In it, the is open and rotation of the is moving the down the cylinder, sucking in a mixture of fuel and air which travels from the along the inlet manifold and past the open .
COMPRESS withION : in this which is regarded as the next stage of operation in the chamber, both valves are shut and the rotating now raises the , compressing the mixture above it into the area.
: this is the third stage in the entire , in it; both valves remain shut and a spark from the jumping across the electrodes of the will set the compressed air-fuel mixture alight in the a very close range between the top of the and the base of the spark ,, the will lead to spontaneous explosion due to the burning of the gaseous fuels in a highly pressurized and hot condition. The whole action will lead to tremendous release of power. The power released will the to go down immediately, with such the can turn the to its half turn while the upward rising of the will prepare the chamber for .
: this is the last of the four-stroke , in this ; the burnt air-fuel mixture had formed the smoke (carbon monoxide) and will be expelled from the chamber to prepare it for the next recycle of strokes. The will open as the start going up for the last , during the period all the smoke in the chamber will be forced to enter into the exhaust channels making the ready for the next stage of which is sucking of fuel and air as the starts going done. In that stage, the will close again allowing the fuel and air to move into the chamber.
THE RATIO OF THE
The power that an develops depends on how much energy can be released above the at each . This in turn depends on the n quantity of fuel/air in the cylinder and the efficiency with which it is compressed.
The amount that the mixture is squeezed up is known as the ratio. It is the difference between volume of the mixture in the cylinder when the is at the bottom of its , and the volume when the is at its highest position. If the upward of the reduces the mixture to one-eight of its original volume, the ratio is 8:1.
In theory, the more the mixture is compressed, the more energy it releaasses when it burns. In practice, however, very high ratios result in knocking or pinking in which some of the mixture furthest away from the spark explodes or detonates causing uneven burning, overheating and loss of power. For maximum efficiency, burning of the mixture should occur rapidly but smoothly.
HOW OVERLAPPING DURING THE STROKES CAN BE RESOLVED
So far we have assumed that the incoming mixture rushes past the as soon as it opens. In practice, the mixture is slow to accelerate and in order to fill the cylinder as completely as possible, the is opened a little early, when the is near the end of the , and while the is still open. This is called overlap.
It might seem that opening the early would offer an alternative exit for the exhaust , but provided the amount of overlap is carefully chosen, the opposite happens and the last waste of exhaust leaving the cylinder will help drag the fresh mixture in the .
Once it is moving, the inlet mixture does not stop automatically when the piston reaches the bottom of the cylinder, and if the closing of the is delayed, the cylinder fills more completely even though by then the would had started to rise on for the .
In practice, in order to make the most of the momentum of fresh mixture and exhaust flowing in and out of the cylinder, the opens before the reaches the bottom of the cylinder and closes after it has reached the top. Similarly, the opens before the reaches the top of the cylinder and closes after the reaches the bottom.
CROSSFLOW CYLINDER HEAD IN THE
Crossflow have the inlet manifold on one side of the cylinder head and the exhaust system on the opposite side, so that during the four-stroke cycle, the inlet charge and the exhaust flow across the chamber an arrangement that gives efficient cylinder filling during the period of overlap.
with the inlet and exhaust manifolds on the same side of the cylinder head have a reverse flow arrangement. This is a little less efficient during the overlap period, but it means that the heat from the exhaust can be easily and cheaply used to warm the inlet manifold and so improve vaporization of the mixture inside. On a crossbow , it is necessary to pipe water from the to heat the inlet manifold.
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