Why are there holes on Combustion Chamber?

If you have got to see combustion chamber of jet engine, you may have wondered that why holes are there? Are not they leaking the gas building up there in combustion chamber?

There is very good reason for that. To understand, I consider you already know the working of jet engine.

When air flow comes from high pressure compressor of the the engine, the flow is highly pressurized and temperature is around 450 degree Celsius.

Construction of Combustion Chamber:-
There is Flame Tube in which the air fuel mixture is burnt and it is divided in to three section described below. Then, a number of holes are made on flame tube known as Dilution Holes. The flame tube is covered by Air Case.

Basically Flame Tube has three sections
1. Primary Section
2. Secondary Section
3. Tertiary Section

When air enters the combustion chamber, 20% air go in the flame tube and rest 80% go in the air case. That 20% air is mixed with the fuel in primary section and burnt and to make the combustion stable, some air also enters in the combustion chamber from the dilution holes of secondary zone.
After making the combustion totally stable, the remaining air in the air casing cools down the combustion chamber as the combustion temperature reaches up-to 2000 degree Celsius. Air also enters from the dilution holes in tertiary zone to mix with the high temperature air fuel burnt mixture to cool it down and to reduce the temperature to 1700 degree Celsius.