Module 4 Flashcards
has the difficult task of burning large quantities of fuel, supplied through the fuel spray nozzles (Part 10), with extensive volumes of air, supplied by the compressor, and releasing the heat in such a manner that the air is expanded and accelerated to give a smooth stream of uniformly heated gas at all conditions required by the turbine (Part 5).
COMBUSTION CHAMBERS
This task must be accomplished with the minimum loss in pressure and with the maximum heat release for the limited space available.
COMBUSTION CHAMBERS
Air from the engine (?) enters the combustion chamber at a velocity up to 500 feet per second, but because at this velocity the air speed is far too high for combustion, the first thing that the chamber must do is to diffuse it.
compressor
Air from the engine compressor enters the combustion chamber at a velocity up to (?) per second, but because at this velocity the air speed is far too high for combustion, the first thing that the chamber must do is to diffuse it.
500 feet
Since the speed of burning kerosine at normal mixture ratios is only a few feet per second, any fuel lit even in the diffused air stream, which now has a velocity of about (?) per second, would be blown away.
80 feet
A region of (?) has therefore to be created in the chamber, so that the flame will remain alight throughout the range of engine operating conditions.
low axial velocity
In normal operation, the overall air/fuel ratio of a combustion chamber can vary between (1) and (2), However, kerosine will only burn efficiently at, or close to, a ratio of 15:1.
1.) 45:1
2.) 130:1
In normal operation, the overall air/fuel ratio of a combustion chamber can vary between 45:1 and 130:1, However, kerosine will only burn efficiently at, or close to, a ratio of (?).
15:1
the fuel must be burned with only part of the air entering the chamber, in what is called a (?).
primary combustion zone
This is achieved by means of a flame tube (combustion liner) that has various devices for metering the airflow distribution along the chamber.
primary combustion zone
Approximately (?) per cent of the air mass flow is taken in by the snout or entry section.
20 percent
Approximately 20 per cent of the air mass flow is taken in by the (?).
snout or entry section
Immediately downstream of the snout are (1) and a (2), through which air passes into the primary combustion zone.
- swirl vanes
- perforated flare
The swirling air induces a flow upstream of the center of the flame tube and promotes the desired (?).
recirculation
The air not picked up by the snout flows into the (?) between the flame tube and the air casing.
annular space
a selected number of (?) through which a further 20 percent of the main flow of air passes into the primary zone.
secondary holes
The air from the swirl vanes and that from the secondary air holes interacts and creates a region of (?) recirculation.
low velocity
similar to a smoke ring
toroidal vortex
which has the effect of stabilizing and anchoring the flame.
toroidal vortex
is supplied to the airstream by one of two distinct methods.
Fuel
The most common is the (?) of a fine atomized spray into the recirculating airstream through spray nozzles.
injection
The second method is based on the (?) of the fuel before it enters the combustion zone.
pre-vaporization
two distinct methods of fuel
- injection
- pre-vaporization
In the (?), the fuel is sprayed from feed tubes into vaporizing tubes which are positioned inside the flame tube.
pre-vaporization
or
vaporizing method
There are three main types of combustion chamber in use for gas turbine engines.
- multiple chamber
- tubo-annular chamber
- annular chamber
This type of combustion chamber is used on centrifugal compressor
engines and the earlier types of axial flow compressor engines.
MULTIPLE COMBUSTION CHAMBER
It is a direct development of the early type of Whittle combustion chamber.
MULTIPLE COMBUSTION CHAMBER
The major difference is that the Whittle chamber had a reverse flow but, as this created a considerable pressure loss, the straight-through multiple chamber was developed by Joseph Lucas
MULTIPLE COMBUSTION CHAMBER
The major difference is that the Whittle chamber had a (?) but, as this created a considerable pressure loss.
reverse flow
the straight-through multiple chamber was developed by (?)
Joseph Lucas
bridges the evolutionary gap between the multiple and annular types.
TUBO-ANNULAR
A number of flame tubes are fitted inside a common air casing.
TUBO-ANNULAR
This arrangement combines the ease of overhaul and testing of the multiple system with the compactness of the annular system.
TUBO-ANNULAR
This type of combustion chamber consists of a single flame tube, completely annular in form, which is contained in an inner and outer casing.
ANNULAR COMBUSTION CHAMBER
The main advantage of the annular chamber is that, for the same power output, the length of the chamber is (?) of that of a tubo-annular system of the same diameter, resulting in considerable saving of weight and production cost.
only 75 percent
Another advantage is the elimination of combustion propagation problems from chamber to chamber.
ANNULAR COMBUSTION CHAMBER
advantages of the annular chamber:
- only 75 per cent of that of a tubo-annular system of the same diameter, resulting in considerable saving of weight and production cost
- elimination of combustion propagation problems from chamber to chamber.
A combustion chamber must be capable of allowing fuel to burn efficiently over a wide range of operating conditions without incurring a large (?).
pressure loss
In addition, if flame extinction occurs, then it must be possible to (?).
relight
the (1) and (2) components must be mechanically reliable
- flame tube
- spray nozzle atomizer
The gas turbine engine operates on a constant (?), therefore any loss of pressure during the process of combustion must be kept to a minimum.
pressure cycle
In providing adequate turbulence and mixing, a total pressure loss varying from about (?) percent of the air pressure at entry to the chamber is incurred.
3 to 8 percent
The heat released by a combustion chamber or any other heat generating unit is dependent on the (?) of the combustion area.
volume
