HISTORY
The first commercial two-stroke engine involving in-cylinder compression is attributed to Scottish engineer Dugald Clerk, who in 1881 patented his design, his engine having a separate charging cylinder. The crankcase-scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day.
The two-stroke engine was very popular throughout the 20th century in motorcycles and small-engined devices, such as chainsaws and outboard motors, and was also used in some cars, a few tractors and many ships. Part of their appeal was their simple design (and resulting low cost) and often high power-to-weight ratio. Because of the lower cost to rebuild and maintain, the two stroke engine was incredibly popular in the dirt bike and motocross industry for many years, until recently when the EPA required the industry to switch to four-stroke engines because they emit less pollution than two stroke engines
WORKING OF TWO STROKE PETROL ENGINE
Two stroke cycle are very widely employed where small power required for motor cycle,auto rickshaw,scooters.This type of engines are compact in size,easy for manufacturing and simple in operations.One drawback is there,Specific Fuel Consumption (S.F.C) is more.(means fuel per Break Horse Power (b.h.p.) per hour is more).
There are no inlet and exhaust valves as in four stroke engine but we have inlet and exhaust ports only,due to which suction and exhaust stroke are eliminated in two stroke cycle engine.Here the burnt exhaust gases are forced out through the exhaust port by a fresh charge of fuel which enters the cylinder nearly at the end of working stroke through inlet port.This process is called as "Scavenging".
As I told above,it has no valves but consists of the inlet port(IP),exhaust port(EP) and transfer port(TP).The ignition starts due to the spark given by spark plug when the piston be nearing the completion of its compression stroke.As a result,piston is pushed down performing the working stroke and in doing so,the air-fuel mixture already drawn from the inlet port in the previous stroke is compressed to a pressure of about 1.4 kilogram/centimeter square.
When 80% of this stroke is completed the exhaust port is uncovered slightly and some of the charge of burnt gases escape to the atmosphere.As the exhaust port is uncovered by the further downward movement of the piston,the transfer port,which is slightly lower than exhaust port,is also uncovered and a charge of compressed air-fuel mixture enters the cylinder and further pushes out the burnt gases out of the exhaust port.
To facilitate the deflection of the fresh charge upward and to avoid its escape along with exhaust gases,the top of the piston is made of a particular shape. From bottom dead centre,when the piston moves up,it first closes the transfer port and then exhaust port.The charge of fuel which previously entered in the cylinder is now compressed.When the piston is nearing the upward movement the inlet port opens and afresh charge of air-fuel mixture from the carburettor enters the crankcase.After the ignition of charge takes place the piston moves down for the power stroke and thus the cycle is repeated.
It can be fairly assumed that the crankcase and the bottom of the piston form a compressor assembly.In which the work used up in compressing the charge is negative.The top of the piston is considered as positive and crankcase is as negative.The difference between the positive and negative loop gives us the net work available from engine.
The principle of the way the 2-stroke engine works:
1st stroke:
The compressed fuel-air mixture ignites and thereby the piston is pressed down. At the same time the intake port I is covered by the piston. Now the new mixture in the crankcase becomes precompressed. Shortly before the piston approaches the lower dead centre, the exhaust port and the overflow conduit are uncovered. Being pressurized in the crankcase the mixture rushes into the cylinder displacing the consumed mixture (exhaust now).
2nd stroke
The piston is moving up. The overflow conduit and the exhaust port are covered, the mixture in the cylinder is compressed. At the same time new fuel-air mixture is sucked into the crankcase.
By means of a crank shaft the up and down motion is converted into a rotational motion.
The first commercial two-stroke engine involving in-cylinder compression is attributed to Scottish engineer Dugald Clerk, who in 1881 patented his design, his engine having a separate charging cylinder. The crankcase-scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day.
The two-stroke engine was very popular throughout the 20th century in motorcycles and small-engined devices, such as chainsaws and outboard motors, and was also used in some cars, a few tractors and many ships. Part of their appeal was their simple design (and resulting low cost) and often high power-to-weight ratio. Because of the lower cost to rebuild and maintain, the two stroke engine was incredibly popular in the dirt bike and motocross industry for many years, until recently when the EPA required the industry to switch to four-stroke engines because they emit less pollution than two stroke engines
WORKING OF TWO STROKE PETROL ENGINE Two stroke cycle are very widely employed where small power required for motor cycle,auto rickshaw,scooters.This type of engines are compact in size,easy for manufacturing and simple in operations.One drawback is there,Specific Fuel Consumption (S.F.C) is more.(means fuel per Break Horse Power (b.h.p.) per hour is more).
There are no inlet and exhaust valves as in four stroke engine but we have inlet and exhaust ports only,due to which suction and exhaust stroke are eliminated in two stroke cycle engine.Here the burnt exhaust gases are forced out through the exhaust port by a fresh charge of fuel which enters the cylinder nearly at the end of working stroke through inlet port.This process is called as "Scavenging".
As I told above,it has no valves but consists of the inlet port(IP),exhaust port(EP) and transfer port(TP).The ignition starts due to the spark given by spark plug when the piston be nearing the completion of its compression stroke.As a result,piston is pushed down performing the working stroke and in doing so,the air-fuel mixture already drawn from the inlet port in the previous stroke is compressed to a pressure of about 1.4 kilogram/centimeter square.
When 80% of this stroke is completed the exhaust port is uncovered slightly and some of the charge of burnt gases escape to the atmosphere.As the exhaust port is uncovered by the further downward movement of the piston,the transfer port,which is slightly lower than exhaust port,is also uncovered and a charge of compressed air-fuel mixture enters the cylinder and further pushes out the burnt gases out of the exhaust port.
To facilitate the deflection of the fresh charge upward and to avoid its escape along with exhaust gases,the top of the piston is made of a particular shape. From bottom dead centre,when the piston moves up,it first closes the transfer port and then exhaust port.The charge of fuel which previously entered in the cylinder is now compressed.When the piston is nearing the upward movement the inlet port opens and afresh charge of air-fuel mixture from the carburettor enters the crankcase.After the ignition of charge takes place the piston moves down for the power stroke and thus the cycle is repeated.
It can be fairly assumed that the crankcase and the bottom of the piston form a compressor assembly.In which the work used up in compressing the charge is negative.The top of the piston is considered as positive and crankcase is as negative.The difference between the positive and negative loop gives us the net work available from engine.
FOR BETTER UNDERSTANDING REFER VIDEO ATTACHED
The principle of the way the 2-stroke engine works:
1st stroke:
The compressed fuel-air mixture ignites and thereby the piston is pressed down. At the same time the intake port I is covered by the piston. Now the new mixture in the crankcase becomes precompressed. Shortly before the piston approaches the lower dead centre, the exhaust port and the overflow conduit are uncovered. Being pressurized in the crankcase the mixture rushes into the cylinder displacing the consumed mixture (exhaust now).
2nd stroke
The piston is moving up. The overflow conduit and the exhaust port are covered, the mixture in the cylinder is compressed. At the same time new fuel-air mixture is sucked into the crankcase.
By means of a crank shaft the up and down motion is converted into a rotational motion.
Categories:
automobile,
engines,
mechanical
Wonderful post.Looking forward to seek more of your fantastic post.
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information
sohailshaiks087@gmail.com
Nicely explained. Inlet port 'I' as said in the explanation is not marked in the sketch.
Ma Shaa Allah keep it up :)