Question

Describe the design criteria for the next combustor sections.

1.-Diffuser

2.-Primary zone

3.-Intermediate Zone

4.-Dilution Zone

5.-Swirler

6.-Primary zone holes

7.-Cooling slot

Answer 1

A combustor is the area where combustion is take place in the gas turbine,ramjet or scramjet engine.

Combustor play a main role in order to determine the engine operating characteristics like fuel efficiency.

Now we will discuss its parts and designing paramters of its parts-

1. Diffuser- The work of the diffuser is to slow down or decrease speed of high speed,highly compressed air coming from compressor. So in order to decrease the velocity there will be losses in pressure too so when we are disigning diffuser to overcome this pressure loss is the bigger challenge.

It should be designed to be short and light as possible and slo it should be designed in a way that it will avoid the flow effect like boundry layer separation.

2.Primary zone - In this zone the mixing process is occur.
The air coming from the compressor is split into two parts The smaller stream enter into primary combustion zone along with the fuel. Due to the high T and and convective and radiative heat transfer the rate of vaparasation of droplets is very rapid.For the flame stbalization we keep the primary combustion zone to near the stoichiometry.And due to swirling flow mixing between gas and fuel vapour is rapid in the primary zone .

3.Intermediate zone -
In this zone the second part(bigger stream) of the air that has been splited into two parts come into this and injected into the combustor via the second set of liner holes.
In this part air comletes the reaction process and cool the air and dercease it temprature and also dilute the concentration of carbon mono oxide and hydrogen .

Approximately 30% air flows through the intermediate zone

4.Dilutaion zone-
In this zone the splitted air from compressor is come into this part after intermediate zone and. In this zone the air is injected through the linear holes so that it cools the air before it recahes to the turbine. Approximately 50 % air flows through the dilution zone

5. Swirler I

It Is the part of primary zone as it enters the combustor. Its role is to generate the turbulance so that mixing process would be rapid.It establishes a local low pressure zone which forces to recirculation and higher turbulance.

The drawback for the designing the swirler is that the higher the turbulance the higher the presuure loss so we have to maintain the balance .

6. Primary zone holes - In the combustor air is feeded by the larger holes known as primary holes .The air coming from the multiple cooling holess and from the vaporiser tubes is sufficient for the air feeding of the primary zone.

7.Cooling slot - they are the small holes with these slots cooling air is supplied ti generate a layer of cool air in order to protect the liner from the high combustion temprature. These should be perfectly design so that it does not directly Interact with the air coming from conbustion chamber. In most of the processe approx 40-60 % of inlet air is used as cooling air.