Difference Between SI (Spark Ignition) and CI (Compression Ignition) Engine [PDF]

HeY! today we will see the difference between Spark-Ignition Engine and Compression Ignition Engine, let’s start with the basic overview of SI and CI Engine.

And After the article, you will find the PDF downloadable link.

What is the Spark Ignition (SI) Engine?

Spark Ignition engine are those types of the engine where the combustion of the fuel occurs with the help of Spark Plug.

In this type of engine, the Air-fuel mixture comes from the carburetor and enters the engine cylinder through the valves and then fuel is compressed in the compression stroke and finally, a spark is given by the spark plug to ignite the air-fuel mixture and we get power stroke.

And what is a Compression Ignition (CI) Engine?

The engine where the rise in temperature and pressure during compression is sufficient to cause spontaneous ignition of the fuel.

In this type of engine, only air is compressed in the engine cylinder after compression the temperature and pressure of the air are rising up and sufficient enough to burn the fuel sprayed by the fuel injectors.


Four-Storke Engine
Two-Stroke Engine
Internal Combustion Engine
Difference Between SI and CI Engine
By Florian Lindner (User:SuperFloh) – Own work, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=184607 | By I, Luc Viatour, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1433279

Now Let’s See the Difference Between SI and CI Engine:

SI Engine CI Engine
It works on OTTO Cycle or constant volume heat addition.It works on DIESEL Cycle or constant pressure heat addition.
During the intake or suction process, air and fuel are used.During the intake or suction process, only air used.
The fuel used Petrol which is highly volatile. Self Ignition temperature is high.The fuel used Diesel which is low volatile. Self-ignition temperature is low.
The fuel is supplied by Carburetor.The fuel is supplied by Injector.
High speed because due to lightweight and homogeneous combustion.Comparatively low speed because due to heavyweight and heterogeneous combustion.
It is used in Small Vehicles.It is used in Heavy Vehicles.
The compression ratio is 6 to 10. The upper limit is fixed by the antiknock quality of the fuel.The compression ratio is 16 to 20. The upper limit is limited by the weight increase of the engine.
The stating of this engine is easy.Starting is a little difficult comparatively SI engine.
Due to lower peak pressure, this is having lighter weight. Due to higher peak pressure, this is having a Heavier weight.
The maintenance cost is low. The maintenance cost is high.
Engine cost is less. Engine cost is high.
Less production of hydrocarbon. In this high production of hydrocarbon.
Less noise produces. It produces high noise.
Lower thermal efficiency because of the low compression ratio. High thermal efficiency because of the high compression ratio.

These are the difference between SI Engine and CI Engine if may read the difference between the Spark plug and Fuel injector, for more clear understanding.

If you have any doubts do let me know in the comment section, till then goodbye.

P.S.: Oops I forget to mention if you like the article do share it on your favorite social media.


Print Friendly, PDF & Email

Anup Kumar Dey

A Mechanical Engineer with 19 years of working experience in various renowned MNCs.

Leave a Reply

Your email address will not be published. Required fields are marked *

Recent Posts