Two Stroke Engine: Diagram, Parts, Working & Applications

In this post, we will going to learn what is two stroke engine and how it works. This article will also go over the parts, comparison, and uses.

What is a Two Stroke Engine?

A two-stroke engine is an internal combustion engine that completes one power cycle with two strokes. This involves the piston moving up and down in one revolution of the crankshaft.

A four-stroke engine completes a power cycle in two crankshaft revolutions with four piston strokes. Two-stroke engines have simultaneous combustion and compression strokes, as well as simultaneous intake and exhaust functions (or scavenging).

Scottish engineer Dugald Clerk first created and patented the two-stroke engine in 1881. These types of engines are less expensive to produce than four-stroke engines because they have fewer moving parts.

They are characterized by their durability, efficiency, and ability to produce high torque at low speeds. These are frequently found in lighter, more compact machines including mopeds, chainsaws, outboard boat engines, and certain motorbikes.

Parts of Two Stroke Engine

Following are the main parts of two stroke engine:

#1 Piston

Using a connecting rod, the piston converts the expanding force of gases into the mechanical rotation of the crankshaft.

#2 Crankshaft

It is attached to the pistons and transforms their reciprocating movement into rotating motion, thereby moving the driving gears.

#3 Connecting Rod

A connecting rod serves as a lever arm and transmits action from a piston to the crankshaft.

#4 Flywheel

A flywheel is a mechanical device that stores rotational energy effectively by utilizing the conservation of angular momentum.

#5 Spark Plug

Spark plug provides the combustion chamber with electric current, which ignites the fuel-air mixture and causes the gasses to suddenly expand.

#6 Inlet and Outlet Ports

These inlet and outlet ports provide fuel and fresh air to enter and exit the cylinder.

#7 Counter Weights

The crankshaft counterweight is intended to lessen vibrations caused by imbalances in the rotating assembly.

Working Principle of Two Stroke Engine

These engines need the following two strokes to operate:

Up Stroke

On the upstroke of the piston, the air-fuel mixture is compressed by the piston into the upper part of the piston chamber, where the spark plug ignites the mixture of fuel and air within the chamber.

It is through the ignition of the intake gases that the piston moves down to the center of the piston chamber, which opens the inlet port of the piston chamber. This causes fresh air to enter the piston chamber and force the exhaust gasses out through the exhaust port.

Down Stroke

As the piston moves to the upper part of the chamber during the down stroke, the fuel-air mixture is compressed, and a new cycle is initiated.

As the piston moves to the center of the chamber, due to the momentum gained during the upstroke, the piston will again move to the upper part of the chamber as the whole cycle continues. These two strokes work together to rotate the crankshaft one full rotation.

Difference Between Two-Stroke and Four-Stroke Engine

Two Stroke Engine	Four Stroke Engine
During a power stroke, the crankshaft makes one revolution.	During one power stroke, the crankshaft makes two revolutions.
This engine produces a lot of torque.	The torque output of this engine is lower.
It uses a port for both the input and output of fuel.	It makes use of valves for the input and exit of fuel.
Less thermal efficiency is achieved by two-stroke engines.	The thermal efficiency of four-stroke engines is higher.
When comparing power to weight, it has a higher ratio.	When comparing power to weight, it has a lower ratio.
It is less efficient and produces more smoke.	It performs better and produces less smoke.
This engine requires extra lubricating oil since some oil burns alongside the fuel.	This engine requires less lubricant oil.
There’s additional wear and tear because of inadequate lubrication.	There is less wear and tear.
These engines are easier to make and cost less to produce.	These engines are difficult to construct and cost a lot because of the lubrication and valves.
In essence, they make more noise and are lighter.	Since their flywheel is heavier and quieter, they are essentially heavier.

Advantages

Following are some of the advantages of using two stroke engine:

1. Since a two-stroke engine has no valves, it is a very basic design.
2. Operating costs for the two-stroke engine are lower.
3. In comparison to a four-stroke engine, it is less expensive to run.
4. Since it is lightweight, bikes are the primary application for it.
5. They have a high power to weight ratio and require little maintenance.

Disadvantages

Following are some of the disadvantages of using two stroke engine:

1. If the parts are not adequately lubricated, they can wear out more quickly.
2. It generates a lot of pollution because an unburned air-fuel mixture can simply flow through the exhaust port.
3. When operating, this type of engine makes a lot of noise.
4. A two-stroke engine uses expensive oil, and since most of it is wasted, a lot of it is needed.

Applications

Following are the main applications of two stroke engine:

1. When lightweight, high power-to-weight ratio, and mechanical simplicity are important design considerations, two-stroke engines are recommended.
2. Their lubrication is performed by mixing oil with fuel, they can be worked from any orientation, and gravity is not required for their reservoir. They are therefore in high demand for usage in portable instruments like chainsaws.
3. Two-stroke engines are used in small-scale propulsion systems including motorcycles, mopeds, and dirt bikes.

Wrapping It Up

That’s it. Thanks for reading. I hope I have covered everything. It would be helpful if you could let me know if there was anything I missed or if you have any doubts about anything I wrote.

Resources or External Links:

1. https://en.wikipedia.org/wiki/Two-stroke_engine
2. https://science.howstuffworks.com/transport/engines-equipment/two-stroke1.htm
3. https://www.sciencedirect.com/topics/engineering/otto-cycle

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