# difference between two stroke and four stroke

## Difference Between Two-Stroke and Four-Stroke Engines

### Introduction

The engine is the heart of any machine and it can be broadly classified into two types – two-stroke and four-stroke engines. While both of them are used in a variety of machines, there are significant differences between the two. Let’s take a closer look at these engines and find out what makes them unique.

### The Basic Difference

The most significant difference between two-stroke and four-stroke engines is the number of strokes required to complete a full cycle. In a two-stroke engine, the combustion cycle is completed in two strokes, while in a four-stroke engine, the same is completed in four strokes. It’s as simple as that.

### Four-Stroke Engine – The Working Cycle

In a four-stroke engine, the working cycle is divided into four strokes – intake, compression, combustion, and exhaust. During the intake stroke, the piston moves down and the air-fuel mixture is drawn into the cylinder. In the compression stroke, the piston moves up and compresses the air-fuel mixture, which gets ignited during the third stroke or the combustion stroke. Finally, the fourth stroke or the exhaust stroke expels the burnt gases from the cylinder.

### Two-Stroke Engine – The Working Cycle

A two-stroke engine, on the other hand, does not have separate strokes for intake and exhaust. The working cycle is divided into two strokes – compression and combustion/exhaust. During the compression stroke, the piston moves up, compressing the air-fuel mixture. In the next stroke, which is a combination of combustion and exhaust, the compressed mixture is ignited, and the piston moves down, expelling the burnt gases and drawing in fresh air-fuel mixture for the next cycle.

### Fuel Efficiency

One of the major differences between the two engines is their fuel efficiency. Four stroke engines are more fuel-efficient than two-stroke engines. The reason is simple – in a four-stroke engine, the combustion cycle is completed in four strokes, which means more time for fuel and air to mix, resulting in better combustion and better fuel efficiency.

### Power Output

Two-stroke engines are known for their high power output, which is why they are mostly used in applications that require high power such as racing and off-road vehicles, and chainsaws. In comparison, four-stroke engines deliver consistent power and are more suited for applications that require sustained use.

### The Bottom Line

Both two-stroke and four-stroke engines have their unique set of advantages and disadvantages, and each engine type is suited for specific applications. While two-stroke engines are known for their high power output, they are less fuel-efficient and produce more pollution. In contrast, four-stroke engines are more fuel-efficient, produce less pollution, and offer consistent power output. Ultimately, the choice between the two depends on the intended use and specific requirements of the machine.