Construction (combustion System) Flashcards
What is the primary requirement for a combustion system in terms of operation?
The system should give efficient, stable operation over a wide range of altitudes and flight speeds, and reduce the peak temperature to an acceptable level at the turbine.
What materials can be used to build a GTE combustion chamber?
It can be built from light materials as there is no peak pressure in a GTE combustion chamber.
What should the gases at the outlet from the combustion chamber system exhibit?
The gases should have a reasonably uniform velocity and temperature distribution.
What is a key feature of the combustion system regarding engine shutdown?
It must be possible to re-light in flight after shutting down an engine.
What is the expected lifespan of the combustion system compared to the engine?
It must be reliable and have a life at least as long as the overhaul life of the complete engine.
How can the combustion chamber be maintained throughout its operational life?
With the introduction of ‘on condition maintenance’ and modular engine design, the combustion chamber can be monitored and replaced as necessary.
What is the function of the Flame Tube in a combustion chamber?
The Flame Tube contains the flame during combustion and needs to withstand very high temperatures (1800 to 2000 deg. C).
What material is typically used to manufacture the Flame Tube?
It is usually manufactured from thin heat resistant materials, usually Nimonic Alloy.
Why can the Flame Tube be made from thin materials?
There are no peak pressures during the combustion process.
What is the purpose of the holes around the circumference of the Flame Tube?
They allow air to be directed into the chamber for combustion and cooling purposes.
What material is the Outer Air Casing made from?
It is manufactured from alloy steels.
What characteristic helps identify overheating in the Outer Air Casing?
It is normally light in colour, so any overheating will show up as discolouration.
What is the Primary Zone in a combustion chamber?
The Primary Zone is a turbulent, slow-moving zone of air that stabilises the flame by mixing with atomised fuel from the burner nozzle.
What is the function of the Dilution Zone?
The Dilution Zone aids in cooling hot gases to a temperature acceptable to the turbine blades and shapes the flame to prevent it from contacting the sides of the flame tube.
What is the typical air percentage that enters the combustion chamber?
A small amount of air, typically 18%-25% depending on engine type, enters the front of the combustion chamber.
What is the typical overall air/fuel ratio in a combustion chamber?
The overall air/fuel ratio is approximately 60:1.
What are the two main types of combustion chambers in common usage?
The two main types of combustion chambers are Annular and Reverse Flow.
What is an annular combustion chamber?
An annular combustion chamber uses the whole of the annulus between the compressor and turbine for combustion.
What is the structure of an annular combustion chamber?
It is a circular flame tube that allows the compressor shaft to go through the center, surrounded by an outer casing.
What are the benefits of an annular combustion system?
- Good utilisation of area
- Structural part of the engine
- Annular gas flow
- Highly efficient
- Large total combustion area
What is a Reverse Flow combustion chamber?
A Reverse Flow combustion chamber is a circular flame tube with space for the compressor shaft to go through the center, featuring a single outer casing. It is shorter in overall length compared to other systems.
Used extensively in turbo-shaft helicopter engines and small gas turbines where length reduction is prioritized over cross-sectional area reduction.
What is the function of Combustion Chamber Drains?
Combustion Chamber Drains allow residual fuel in the chamber to be drained overboard using an Automatic Drain Valve (ADV).
The ADV consists of a spring and plate valve that opens when combustion chamber pressure falls.
How does the Automatic Drain Valve (ADV) operate?
The ADV opens to drain residual fuel when pressure falls and closes when pressure builds up during start.
The spring mechanism is key to its operation.
What is the purpose of fuel nozzles in engines?
The purpose of any nozzle is to introduce fuel into the combustion chamber in a state in which it will burn efficiently.
What are the two types of fuel nozzles?
The two types of fuel nozzles are Atomisers and Vaporisers.
What is the function of atomisers?
Atomisers are designed to produce a controlled and efficient fuel burn.
What are the three basic types of atomisers?
The three basic types of atomisers are Duplex, Single, and Multi-orifice.
What is a Duplex atomiser?
A Duplex atomiser provides two supplies of fuel depending on the quantity of fuel required.
How does the Duplex atomiser operate?
It includes a primary and main fuel manifold with two independent orifices, one smaller for lower flows and one larger for higher flows.
What happens as fuel flow and pressure increase in a Duplex atomiser?
The pressurising valve moves to admit fuel to the main manifold and thus to the main orifice, allowing flow through both orifices.
What advantages does the Duplex atomiser provide?
It provides effective atomisation over a wide flow range and efficient atomisation at lower flows required at high altitude.
What is the significance of the primary and main orifice in a Duplex atomiser?
The primary and main orifice allow for effective atomisation at varying fuel flows.
What is a key feature of the Duplex atomiser at high altitudes?
It is effective at high altitudes.
What is a Rotary Atomiser?
A device where fuel is fed through a hollow compressor shaft, and centrifugal motion ejects the fuel in an atomised spray into the combustion chamber.
What are the components of the Rotary Atomiser?
Key components include the rotor shaft, stubshaft, labyrinth, packing cone, fuel transfer tube recess, fuel ejection holes, air holes, rotating guide vanes, impeller, first stage turbine wheel, and second stage turbine wheel.
What is the function of the airspray nozzle?
It mixes a proportion of the primary combustion air with the injected fuel to aerate the spray, reducing local fuel-rich concentrations, carbon formation, and exhaust smoke.
What is an advantage of the airspray nozzle?
The low pressures required to atomise the fuel allow the use of a simpler high-pressure pump.
What are the three types of atomisers?
1) Duplex Atomiser
2) Rotary Atomiser
3) Airspray Nozzle
What is the function of the vaporiser in an engine?
The vaporiser sprays fuel into vaporising tubes, which are heated by combustion, vaporising the fuel before it enters the flame tube.
How is primary air introduced in the vaporiser?
Primary air is fed into the vaporiser and mixes with the fuel as it passes down the tube.
What role do the holes in the flame tube entry section serve?
The holes provide ‘fans’ of air to sweep the flame rearwards.
What is necessary to start an engine using a vaporising system?
A set of spray nozzles must be incorporated with the igniter plugs to initiate the combustion process.
What are the advantages of vaporisers over atomisers?
Vaporisers are effective over a wider operating range, allow easier combustion control, and produce less smoke.
How does the placement of vaporisers affect flame stabilization?
Vaporisers are located behind the flame, stabilizing it at the front of the combustion chamber and allowing for a shorter combustion section.
What is used to protect the burner in a vaporiser system?
Fine filters are used to protect the burner from debris.
