Advanced Gas Combustion Flashcards
How do you combust liquid fuel
- atomise
- vapourise
- then mix with air
What is today’s main combustor issue
- reduce pollutants!
- ICAO regulations
- military want to reduce visible emissions (smoke + NO2)
What are the 3 types of NOx
- NO formation in low T regions, fuel rich zones, staged combustion
- Thermal Nox
- Fuel Nox (not issue with kerosene but perhaps if alternative fuels used)
Describe Thermal Nox
- high temp chemical reactions
- main contributor to No production
- Exponential increase with temp
- lot’s of effort put into lowering it
Give 3 chemical equations of thermal Nox formation
O + N2 = N + NO
N + O2 = O +NO
N + OH = H + NO
Give 4 chemical equations of NO to NO2 conversion
NO + HO2 = NO2 + OH
NO + OH = NO2 + H
NO + O2 = NO2 + O
NO + O + M = NO2 + M
What is RQL combustion
Rich burn / quick-mix / lean burn combustion
Reduces oxides of nitrogen
Pros and Cons of axial staged combustor
Pros
- 50-60% NOx reduction (produces good smoke)
- Very stable
- Easily modulated
- Simple and Light
Cons
- Separate fuel injector feed arms
- Pattern factor
- Length
Pros and Cons of double annular staged combustor
Pros
- 60% reduction Nox
- length (short which impacts weight and shaft design)
Cons
- Limited smoke reduction
- Not really better than state-of-the-art conventional combustors
- complex
- costly
- Difficult diffuser design
Pros and Cons of LPP combustion
Lean Premixed Prevapourised
Pros
1. No droplet burning so low temp (reduced NOx and smoke)
Cons
- Narrow AFR operating bank
- Auto-ignition
- Weight
- Complexity
- Thermo-acoustic issues
What is auto-ignition and why is it damaging
Ignition before the combustion chamber can case damage to mixing tube and can cause flashback
What are the 2 ways to control combustion instability
- Passive damping
2. Active control damping
