What is the Role of Decompression Lever in IC Engine?

Now there is an animal which calls itself a "single cylinder, 4-stroke, water cooled, diesel engine".

It is usually found in the thermal labs of all colleges, and i don't know of what practical use it comes to.

It is always started by hand-cranking, and while a person is cranking this, he has to lift up a small lever called the decompression lever, present near the cylinder head, rotate the crank handle really fast, and then finally release this lever.

as soon as this lever is released, the engine starts roaring to life.

now tell me , what is this decompression lever, and what is its mechanism ?

Update: Role of Decompression Lever

In an internal combustion (IC) engine, the decompression lever is a mechanical component that serves an important role in starting the engine.

It is typically found in diesel engines, although some older gasoline engines may also have a similar mechanism.

The decompression lever, also known as a compression release lever or starting aid lever, is used to alleviate the high compression pressure within the engine's cylinders, making it easier to turn over the engine during starting.

The primary function of the decompression lever is to temporarily reduce the compression ratio within the combustion chamber, which facilitates the engine's initial rotation.

This is particularly crucial in diesel engines because they rely on the heat generated by the high compression of air within the cylinder to ignite the fuel.

By reducing the compression pressure during starting, the decompression lever allows the engine to overcome the resistance caused by the high compression and enables the necessary conditions for successful ignition.

When the decompression lever is engaged or activated, it opens a valve or mechanism that allows the built-up compression pressure to escape from the cylinder before the piston reaches the top dead center (TDC) position.

This release of pressure reduces the overall resistance faced by the starter motor, making it easier to crank the engine.

Once the engine is running, the decompression lever is disengaged, and the compression release valve is closed, restoring the normal compression ratio within the cylinders.

It's important to note that the decompression lever is only used during engine starting and is typically not engaged during regular engine operation.

Once the engine is running, the high compression ratio is necessary for efficient combustion and power generation.

The decompression lever is particularly useful in situations where the engine might face difficulties starting, such as cold weather conditions or when the engine has been inactive for an extended period.

By reducing the compression pressure during starting, the lever helps prevent excessive strain on the starter motor and the entire starting system.

In summary, the decompression lever in an IC engine, specifically in diesel engines, is a mechanical device used to temporarily reduce the compression pressure within the combustion chamber during starting.

By alleviating the high compression, it facilitates the engine's rotation and helps overcome the resistance encountered during the starting process.

Once the engine is running, the decompression lever is disengaged, restoring the normal compression ratio for efficient combustion and power production.