## The concept of the 2-stroke and 4-stroke engines. 


 ![image](https://img.esteem.ws/rybyf0uihe.jpg)[image source ](https://www.pexels.com/photo/auto-auto-racing-automobile-automotive-355913/)


The 2- Stroke and 4- stroke engines has been around for centuries now and with the current speed at which technology is going this engines  have experience  tremendous improvement when it comes to their performance, and designs. yet the working principles still remains the same.
in this article am going  to try as much as I can to explain the concept, working principles, advantages and disadvantages of the 2-stroke and 4-stroke engines.

## The concept of the 2- stroke engine
 ![image](https://img.esteem.ws/6g17mpjqfl.jpg)[image source ](https://s.hswstatic.com/gif/two-stroke-parts.gif)

The term stroke is simply the movement of the piston in the cylinder of an engine. 

A 2-stroke engine is a type of engine that completes it's cycle in one revolution of the crankshaft. 
The 2-stroke cycle involved are the upward stroke (suction + compression)  and the downward stroke ( power + exhaust).
here am going to explain what happens at each stroke. 

Upward stroke : this is the process or stage at which the piston moves upward and covers the two port which are almost opposite to each other,  hence trapping the charge air fuel mixture already drawn into the cylinder.
when the piston moves further upward, it compresses the charge air fuel mixture and also open the suction port which allows entrance of fresh air fuel mixture into the crankcase.  
Towards the end of this stroke, the mixture in the cylinder is ignited by a spark plug. 

Downward stroke : The piston start moving downward due to the increased in temperature and pressure as the result of the burning of the air fuel mixture. 
when the piston moves downward the suction port is closed trapping the fresh mixture dawn into the crankcase during the upward stroke. 
further downward movement of the piston opens  the exhaust port and then the transfer port. then the fresh mixture of air and fuel in the crankcase moves into the cylinder in other to help drive out the exhaust gases. 

## Advantages of the 2-stroke engine

1. Design and  construction : 2-stroke engines do not have valves, this makes their design and construction simple. 

2. More power : 2-stroke engines fire once every revolution which gives it a significant power boost.

3. Weight and cost efficient : 2-stroke engines are lighter, and are chipper to manufacture. etc

## Disadvantages of 2-stroke engines 

1. Not durable : 2-stroke engines don't live as long because of the lack of a dedicated lubrication system, which means that the parts of a 2-stroke engine wear-out faster. 2-stroke engines require a mix of oil with the gas to lubricate the crankshaft, connecting rod and cylinder walls.

2. High operation cost : 2-stroke oil can be expensive. because  it burns  about a gallon of oil every 1,000 miles.

3. Poor efficiency : 2-stroke engines do not use fuel efficiently, yielding fewer miles per gallon.

4. high pollution : 2-stroke engines produce more pollution due to the combustion of the oil in the gas. The oil makes all 2-stroke engines smoky and can  sometimes emit more oily smoke. etc

> A 2-stroke engine made in single cylinder has no firing order.

## We will now look at the concept of the 4-stroke engine.
 ![image](https://img.esteem.ws/04ynu4pky4.jpg)[image source](https://www.makingdifferent.com/wp-content/uploads/2013/06/4-strokes-of-engine-1.gif)

4-stroke engine on like the 2-stroke engine is a type of engine that completes it's cycle in two revolution of the crankshaft. this engine uses valve  to control the opening of both the inlet and the outlet. and this process of opening and closing of valve is controlled by the cams, fitted on the camshaft. this camshaft is driven by crankshaft with the help of gears or chains. 

the event of taking place in the cylinder of a 4-stroke engine are :

(i). suction stroke 

(ii). compression stroke 

(iii). power stroke 

(iv). exhaust stroke 

we will also spend a little time to understand how each stroke works. 

1.  The suction stroke or The inlet stroke : In this stroke the inlet valve opens as the piston moves downward allowing air or a mixture of air/fuel into the cylinder. during this process the exhaust or outlet valve remind close. also for this process to be achieved the internal pressure (pressure in of cylinder ) most be less than the atmospheric pressure (external pressure ).

2. The compression stroke : during compression stroke the piston moves upward, compressing the air or the air/fuel mixture in the cylinder. both inlet and outlet valves remind close during stroke.  If only air is compressed, as in the case of a diesel engine,  the diesel is injected at the end of this stroke and ignition of fuel takes place due to the high pressure and temperature of the compressed air. but if a mixture of air/fuel is compressed in the cylinder as in the case of a petrol engine, the mixture is ignited by a spark plug. 

3. Power stroke : after the ignition of the mixture,  a very high amount of heat is generated, causing forcing the pressure in the cylinder to push the piston downward. this downward movement of the piston is called the power stroke. the power generated is transmitted from the piston to crankshaft through the connecting rod. during this process both inlet and outlet valves remind close. 

4. The exhaust stroke : after the power stroke the piston moves  back upward pushing the burnt gases in the process out through the outlet which is open at this point. during this process the inlet valve remind close. 
 it can be observed that out of this four strokes, the is only one power stroke and three idle strokes in the 4-stroke engine.

## Advantage of the 4-stroke engine

1. More torque : the 4-stroke engine produce more torque, and it is more reliable and quitter.

2. Last longer : 4-stroke engines last longer and use much, much less oil.
3. less pollution : 4-stroke engines have a dedicated oiling system that’s kept largely separate from the combustion chamber, which help to ensure that the only thing burning in the engine is gasoline. etc

## Disadvantages

1. Complicated design and construction : the 4-stroke engine valves and other parts makes its design complicated and fabrication harder. 
2. less power : the 4-stroke engine fire once every two revolutions, while two stroke engines are more powerful because every revolution of the engine includes a power stroke.

3. More expensive : the 4-stroke engine is much more expensive and complex. It has more complied with more parts so they often require repairs more often and it is usually more expensive. etc 

## Firing order of a 4-stroke engine

4-stroke engine are made in multi – cylinder so it has a firing order as per cylinder used. for example, a 6 – cylinder engine’s firing order is
## 1-5-3-6-2-4.

With this article we have seen the working principles of both 2-stroke and 4-stroke engines, their advantages and disadvantages and also the firing order of 4-stroke engine.


 Big thanks to @steemstem for giving me a platform to share this post. SteemSTEM is a community driven project which seeks to promote well written/informative Science Technology Engineering and Mathematics postings on Steemit.


## Thanks for reading