4-Stroke engine full details

 What Are the Strokes of a 4-Cycle Engine? 

In order to effectively power equipment, 4-stroke engines complete and repeat the following steps: 
 

Intake stroke:

Piston moves down the cylinder bore from top dead center (TDC) to bottom dead center (BDC) 

Intake valve is open, the exhaust valve is closed 

Downward piston motion creates a vacuum (negative air pressure) that draws that air/fuel mixture into the engine via the open intake valve 
 

Compression stroke:

Piston moves up the cylinder bore from bottom dead center to top dead center 

Both the intake and exhaust valves are closed 

Upward piston motion compresses air/fuel mixture in the combustion chamber  

Power stroke: 

At the end of the compression (previous) stroke, the spark plug fires and ignites the compressed air/fuel mixture. This ignition/explosion forces the piston back down the cylinder bore and rotates the crankshaft, propelling the vehicle forward. 

Piston moves down the cylinder bore from top dead center to bottom dead center 

Both the intake and exhaust valve are closed 
 

Exhaust stroke:

Piston moves up the cylinder bore from bottom dead center to top dead center. The momentum caused by the power stroke is what continues the crankshaft movement and the other 3 strokes consecutively. 

Intake valve is closed, the exhaust valve is open 

This final stroke forces the spent gasses/exhaust out of the cylinder. The cycle in now complete and the piston is ready to begin the intake stroke. 

Advantages of 4-Stroke engine: 

• More torque 
• More fuel economy than a 2-stroke engine 
• Less consumption of lubrication oil 
• Less pollution because of proper burning of fuel 
• More durability 

 

 

DISADVANTAGES OF 4 STROKE ENGINE  :- 

• Complicated design :- A 4 stroke engine has complex valve mechanisms operated & controlled by gears & chain. Also there are many parts to worry about which makes it harder to troubleshoot. 
• Less powerful :- As power gets delivered once every 2 rotations of crankshaft(4 strokes), hence 4 stroke is less powerful. 
• Expensive :- A four stroke engine has much more parts than 2 stroke engine. So they often require repairs which leads to greater expense. 

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The biggest difference between a two stroke and four stroke engine has to do with firing timing, which can often be noticed in terms of sound: the two engine often has a high-pitched, very loud rumble, whereas the four engine tends to have a quieter purr. In most cases this is a facet of basic operation and efficiency. Two stroke engines fire once per revolution, which gives them twice the power of a four stroke that generally fires only every other revolution. Four strokes are more efficient, but they’re heavier and more expensive, too. They’re more commonly found in cars and industrial machinery, whereas things like lawnmowers, jet skis, and most lightweight motorboats rely on the smaller two stroke model. 

 

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2-Stroke Disadvantages:

• If 2-strokes are lighter, smaller and more powerful than 4-strokes, why aren’t they more common? 2-strokes have a few distinct downsides, including: 
  
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• Less fuel efficient 
• Noisier and more prone to vibration 
• Considerably more emission pollution 
• 2-stroke oil is expensive to purchase and mixing to the correct ratio can be challenging 

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Difference between 4 stroke & 2 stroke engine

4 STROKE ENGINE	2 STROKE ENGINE
4 stroke engine completes 2 rotations of crankshaft after completing one cycle.	2 stroke engine completes 1 rotation of crankshaft after completing one cycle.
Power is produced once every 4 strokes of the piston.	Power is produced once during 2 strokes of the piston.
Engine design is a bit complicated due to valve mechanism which is operated through gear & chain mechanism.	2 stroke engine has ports which makes it's design simpler.
No need of adding oil or lubricant to fuel.	Addition of oil is required.
Top side of the piston is flat.	A bump or protuberance may be needed on top side of piston.
Mixture remains only in the combustion chamber.	Air-fuel mixture enters through inlet port & travels to combustion chamber passing through crankcase.
4 stroke engines are heavier.	2 stroke engines are lighter comparatively.
4 stroke engines make less noise.	2 stroke engines are louder comparatively.