There are basically two types of reciprocating internal combustion engines on the basis of working
- Four stroke engines
- Two stroke engines (sometimes also referred as two cycle engine and 2 stroke engine)
If you want to understand two stroke engines completely we recommend you to also read four stroke engines.
Let us continue with our discussion of two stroke engines.
For successful operation (for generating power) an engine has to complete following steps in a cycle.
A four-stroke engine requires four steps to complete these operation
Suction of fuel air mixture
Compression of fuel air mixture
Combustion and expansion process
Remove exhaust gases from engine
But a two-stroke engine completes all the above-mentioned operations in just two steps
Intake and compression of fuel air mixture
Combustion, expansion and removal of exhaust gases from the engine
Working animation of a two-stroke engine
Attribution: By MichaelFrey – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=37919889
In the above animation we can easily see the intake of fuel air mixture, compression of it, combustion and expansion stroke.
We can also see that intake of fresh charge and removal of exhaust gases (scavenging) is simultaneous.
Scavenging is the removal of exhaust gases from an engine. This term is popularly used in the context of 2 stroke engine.
Advantages of two stroke engines
- For the same dimensions power developed is twice to that of four stroke engines
- Power required foe exhaust and suction stroke is saved
- More uniform turning moment compared to four stroke engines hence a lighter flywheel is required
- For the same power output two stroke engine occupies less space
- Two stroke engines are lighter than same power four stroke engine
- Construction and working of a two stroke is simple
- Less maintenance is required
- High power to weight ratio
Disadvantages of two stroke engines
- High speed two stroke engines are less efficient due to reduced volumetric efficiency
- In case of two stroke engine running on Otto cycle a considerable amount of fresh charge is lost due to poor volumetric efficiency
- Effective compression is less die to provision of ports for intake and exhaust
- More consumption of lubricating oil
- At high loads two stroke engine does not run smooth due to dilution of charge
Applications of two stroke engines
Due to increased regulation of air pollution the use of two stroke engines is decreased but they are still used in many low power applications. Such as
- Outboard motors
- High-performance, small-capacity motorcycles, mopeds, and dirt bikes
- Underbones, scooters, tuk-tuks, snowmobiles, karts
- Ultralight airplanes, and model airplanes and other model vehicles
- They are also common in power tools used outdoors, such as lawn mowers, chainsaws, and weed-wackers