Gas Turbine Combustion Systems

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The combustion system is designed to burn the fuel as efficiently as possible over the whole range of engine operating condition.  All the energy released by the fuel is converted into heat and velocity energy. Very high temperatures exist in the combustion system, the burning temperature of the fuel being in the region of 2,000°C.  To protect the material from which the system is manufactured, about 60% of the total air flow is used for cooling and the rest is used for fuel burning.

 The combustion chamber is quite short therefore it must be efficient in completing the combustion. To achieve this fuel air mixture is made with it best ratios.

The combustion process requires 15 unit of air to 1 unit of fuel for a successful combustion.  This is known as an air/fuel ratio of 15:1 by weight

The air flow leaving the compressor is first split into two, approximately 20% - 40% being used for combustion, the other 60% - 80% is further divided for combustion support and the greater proportion for gas cooling.

These three flows are known as:-

• Primary air flow, for mixing with the fuel and to support combustion.(20% )
• Secondary air flow to shape the flame and complete combustion. ( 20%)
• Tertiary air flow, to cut off the flame and reduce gas temperature to a figure acceptable to the turbine. ( Cooling 40% & Dilution air 20%)