TWO-STROKE ENGINE
Hello guys, in this post we are going to see about the two-stroke engines with its classifications, parts of a two-stroke engine, working and applications of two-stroke engines.
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What is a Two-stroke engine?
It is also one of the categories of internal combustion(IC) engines which completes the combustion process with just two-strokes i.e.,
1. Up-stroke
2. Down-stroke
at one revolution of the crankshaft.
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| (Two-stroke engine - Yamaha RX100 model) |
Types of Two-stroke engine
The two-stroke engine is also categorized into two types. They are
1. Two-stroke Petrol engine
2. Two-stroke Diesel engine
Two-stroke- petrol engine
It is the type of two-stroke engine which operates with the principle of OTTO CYCLE.
Two-stroke- diesel engine
The type of two-stroke engine which operates with the principle of diesel cycle.
The practical applications of this two-stroke diesel engine are very low because it doesn't have enough compression ratio or pressure required to burn the fuel. So under these circumstances and drawbacks these types of engines are neither available in the market nor in use.
Also, there are some more limitations that are there for these engines those criteria sets were mentioned below as limitations of the two-stroke engine.
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Basic Terminologies
There are some basic terminologies that one must learn before knowing about the two-stroke engine they are
It is the uppermost end position of the piston at the head of the cylinder.
At TDC the angle of the crank is supposed to be at 0'.
The lower end position of the piston at the end of the crank is called the bottom dead center. At BDC, the angle of the crank is supposed to be at 180'
The inner diameter of the cylinder is called the cylinder bore.
The distance through which the piston moves within the cylinder of the engine during one stroke is known as stroke length.
Parts of a Two-stroke engine
The two-stroke is comprised of the following parts. They are:
- Cylinder
- Cylinder head
- Piston
- Connecting rod
- Crank
- Crankcase
- Crankshaft
- Ports
- Spark plug (For Petrol engine)
- Fuel Injector (For Diesel engine)
It is also referred to as the heart of the engine. The piston of the engine moves within the cylinder.
2. Cylinder head:
It is the topmost portion of the cylinder nearer to Top dead center(TDC), and it is called as cylinder head.
3. Piston:
The reciprocating member of the engine which moves within the cylinder is called the Piston.
The piston is provided with some ring-like structures in it. So, it is called Piston rings. And it is sealed between the gap cylinder lines and the piston. It is responsible for carrying the lubricants between those parts, i.e. Piston and Cylinder.
The rotating member of the engine which makes circular motion inside the crankcase is known as a crank.
It is one of the parts of the engine which provides shelter for the crank and other engine parts. It also acts as the sump for storing lubricants in it.
The part of the engine which converts the reciprocating motion of the piston into rotary motion of the crankshaft is called the connecting rod.
The rotating member of the that connects the crank and connecting rod is known as the crankshaft.
It is provided for operating the function of opening and closing of both Inlet and Exhaust valves and it also operates the fuel injection pump in case of a Diesel engine.
In two engine valves are replaced by ports. They were generally used in Two-stroke engines like two-stroke petrol engines. These are the openings for inlet charge and exhaust gases. There are 3 ports are present in a two-stroke engine:
- Inlet port
- Transfer port
- Exhaust port
It is the small part of a Petrol engine or SI engine which is used to produce a spark to burn the fuel.
12. Fuel injector:
The part which is only used in a Diesel engine or CI engine for spraying the fuel inside the engine cylinder is called the fuel injector.
It is a part that mounted over the crankshaft and made up of cast iron. It is responsible for storing energy in the form of inertia and also for converting it into mechanical work.
Two-stroke engine working animation
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| Source: Wikimedia commons Creative commons file Attribution-Share Alike-3.0 |
Working Principle of Two-Stroke engine
As we said earlier, In a two-stroke engine, there will be one power stroke for every single revolution of the flywheel. The two-stroke engine is comprised of the following two strokes.
- First stroke ( Suction and Compression stroke)
- Second stroke (Power and Exhaust stroke)
Suction and Compression stroke
- During the suction and compression stroke, the piston starts reciprocating from the BDC to the TDC.
- At the same time, it will close all ports such as the inlet port, transfer port, and exhaust port. Then the fuel filled above the piston is adiabatically compressed.
- At the same, while the spark plug produces the spark, and the fuel gets ignited and the power stroke will follow after it.
- The power from the crankshaft is transferred by means of a connecting rod. During this stroke, the piston reciprocates downward as it uncovers the inlet port.
- Due to the production of partial pressure in the crankcase, the inlet port opens and the air-fuel mixture enters the crankcase.
Second stroke or Power and Exhaust stroke
- During the second stroke, the piston reciprocates down from TDC and at that time the inlet port is kept closed.
- Due to the downward motion of the piston air-fuel mixture is pushed by the bottom end of the piston so that the fuel from the crankcase passes out through the transfer port.
- Since the exhaust port opens, the output exhaust gas leaves the cylinder through the exhaust port but after this stroke also there are some exhaust gas remains inside the cylinder.
- The unique shape of the two-stroke piston head deflects the fresh charge inside the cylinder.
- So, the air-fuel mixture moves downward and pushes the exhaust gas out by means of the exhaust port.
- The process at which the exhaust burnt gas is pushed out by the fresh air-fuel mixture is called SCAVENGING.
- After the completion of one revolution by the crankshaft.
- This cyclic process is repeated once again for the next cycle.
The difference of Two-stroke engine
Generally, both the two-stroke petrol and diesel engine functions under the same principle but the only difference is the usage of the spark plug in the case of a petrol engine whereas the fuel injectors in the case of diesel engines.
Lubrication system in the Two-stroke engine
In a two-stroke petrol engine,
A petrol lubrication system was used.
In this kind of lubrication, a small quantity of lubricant is mixed with petrol itself. The normal mixing ratio is of this type is near equals to 3% that of the oil. If it less than it creates damage to the engine or if it added more there will be excess deposition of carbon elements in the cylinder head and the engine will also produce grey smoke.
When the air-fuel mixture enters the cylinder due to the production of the high temperature it evolves and passes out through a thin film of lubricant over the cylinder wall, crankcase, and shaft.
Two-stroke engine Port timings
Two-stroke- petrol engine
- The Inlet port opens at an angle of - 40' before TDC.
- The Inlet port closes at an angle of - 40' after TDC.
- The exhaust port opens at an angle of - 60' before BDC.
- The exhaust port closes at an angle of - 60' after BDC.
- The transfer port opens at an angle of - 50' before BDC.
- The Transfer port closes at an angle of - 50' after BDC.
- Ignition takes place between 15 and 20' before TDC.
Benefits and limitations of Two-stroke engine
Benefits
- More power production.
- Simple in design and less weight when compared to a Four-stroke engine in which the design is complex and also carries more weight.
- The two-stroke engine has a low weight compared to a four-stroke engine because of its small flywheel size.
- Only less friction is produced when compared to a Four-stroke engine. So mechanical efficiency is a little bit high in the case of a two-stroke engine.
- Low maintenance cost.
Limitations
- Consumption of lubricants is more than that of a four-stroke engine.
- The power stroke is created at every stroke, so more amount of heat will be produced, therefore we have to lubricate the engine often and cool it properly.
- In the two-stroke engine, some quantity of fresh fuel mixes with the exhaust gas and passes out from the cylinder. Therefore, the engine has less output efficiency.
- The absence of a well developed lubricating system is the main limitation. It lacks the Lubrication system which is present in the four-stroke engine.
- It produces more air and noise pollution than the four-stroke engine.
Two-stroke Engine's applications
- There many olden motorcycle models that operate with two-stroke engines but those are not available nowadays.
- In the early stages, two-stroke engines are also used in Racing cars. But now almost all the countries banned two-stroke racing cars.
- Two-stroke engines are used in boats.
Why we are not using Two-Stroke engines nowadays?
The two-stroke engine is not in use nowadays because it creates more air pollution and noise pollution. This is the main reason behind the prohibition of using two-stroke engines in many countries. Not all countries banned these types of engines but almost many countries banned.
This type of engine for keeping an idea of making pollution a free atmosphere in the future.
Conclusion
That's all about TWO-STROKE ENGINE.
I hope that you understand the Two-Stroke engine types, working, principle, lubrication and etc...
If you have any doubts or any queries about this or anything that you want to include here.
Put that in the comments section. Also, Comment your thoughts in the comments section below.
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