Environmental Engineering Reference
In-Depth Information
zone can be influenced by the fuel to air relationship, i.e., the Lambda number.
At lower engine speeds, the relationship is approximately k = 1.3, while cruising
the mixture has a Lambda number of around k = 1.6. The mixture of fuel and air
and the combustion process in a single combustion chamber are illustrated in
Fig. 10.2 [ 14 ].
The main combustion chamber type is the ring combustor. The compressor
pushes the air flow to the combustion chamber at a speed of approximately
150 m s -1 (335.61 mph), in which the kerosene and air mixture has a combustion
speed between 25 and 30 m s -1 (55.93 and 67.12 mph). For efficient combustion,
the fuel and air mixture must remain in the combustion zone from 0.004 to 0.008 s.
This time interval is long enough to completely burn the fuel. The fuel drops must
be gasified, mixed with air, and heated to the ignition temperature. The combustion
temperature in the burning zone is approximately 2,573C (4,663F) [ 15 ].
Higher temperature and pressure increases the damage in the combustion
chamber which requires more maintenance and repairs. Therefore, improved
cooling technology in the combustion chamber and in the exhaust gas pipe are
required which contributes to higher efficiency and to lower costs [ 16 ].
The optimal operation of the combustion chamber of a jet engine's gas turbine
must work with:
• Stable, vibration-free combustion process on the ground and in the air;
• Optimal thinning of the combustion gases at a temperature which does not lead
to overheating of the first turbine stage;
• Efficient burning fuel and efficient releasing the energy contained in the fuel;
• Low pressure loss which could be the result of increased friction;
• Simple maintenance and repair; and
• High durability of all elements [ 17 ].
These facts are the preconditions for optimal operation and must be inspected
and maintained during the whole life time of the engine.
In the future, the following goals will be more important for the further
development of combustion chamber technology:
• Improving the construction between the compressor and the turbine to save
space and weight;
• Maintaining a more uniform temperature and pressure distribution in the exhaust
cross-section; and
• Optimizing ignition [ 18 ].
10.4 Emissions from the Combustion Chamber
In aviation, the level of unburned CO and HC from engines is very low and the
amount of visible smoke is under control currently. The exhaust gases contain
more CO and HC only during idling because of the low air and fuel throughput, the
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