Two Stroke & Four Stroke Engine

First of all, let us know about the basic functioning of engines. Engines basically work on the phenomenon called combustion. It is a chemical process in which energy is released from a mixture of air and fuel. There is a piston and cylinder arrangement where the expansion of combustion gases pushes the piston which further rotates the crankshaft.

Some History:

The 4-stroke engine was patented in 1862 by Alphonse Beau de Rochas, a French engineer but based upon its principle, Nikolaus Otto, a German engineer, was the first person to invent a 4-stroke engine in 1876.

The 2-stroke engine was invented in 1879 by German inventor Karl Benz, which was later patented in 1880.

How They Work?

2-Stroke Engine: A 2-stroke engine or 2-cycle engine, as the name suggests, completes its one combustion-exhaust cycle in two strokes which are compression stroke and power stroke. During the power stroke, the air-fuel mixture is ignited and it forces the piston downwards until the exhaust port opens. As the piston moves down, the air-fuel mixture is pressurized under the piston that entered the crankcase during the previous compression stroke. The intake port allows pressurized air-fuel mixture into the cylinder. As the crankshaft turns and the piston rises, it closes off the intake and exhaust ports. Further, the air-fuel mixture is compressed. When the piston is at the top, it allows fuel to enter from the intake port into the crankcase. The compressed mixture is then ignited by the spark plug which then repeats the process.

4-Stroke Engine: A 4-stroke engine takes four strokes to complete its one engine cycle. First, the piston lowers down where the intake valve opens, drawing in the air-fuel mixture. In the second stroke, the piston rises for a compression stroke where the air-fuel mixture is compressed where the mixture is ignited for the third stroke, also called the power stroke. In the fourth stroke, the piston moves upwards where the exhaust valve opens where the piston forces out the exhaust completing one full engine cycle. This process is repeated. 

Pros & Cons

2-Stroke Engine:

• Pros: Lightweight, fewer parts as compared to a 4-stroke engine, and more powerful.

• Cons: High fuel consumption. The intake and exhaust port are open at the same time because of which un-burnt air-fuel mixture also leaves through the exhaust port and higher hydrocarbon emissions.

4-Stroke Engine:

• Pros: Good fuel efficiency, lower emissions, high low-end torque.
• Cons: Increased weights as the number of parts increased and complicated.

Will cover more about the engine in future blogs, stay tuned and comment in the section below and connect through the forum for a deep discussion on engines.

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