Chapter 15: Fire Protection Flashcards
hot zone and cold zone section in engine
hot zone: combustor to exhaust
cold zone: from fan to compressor
why are the zones ventilated?
prevent accumulation of flammable vapours (fuel)
how can the zones be isolated?
fireproof bulkhead / firewall
purpose of engine ventilation
purge any flammable vapour from engine
why must the airflow vent be kept minimal?
1) minimise powerplant drag
2) correct proportion of air for fire extinguisher (agent wont leak out)
3) minimise intensity of fire outbreak (less air fed to fire)
what does the fire detection unit do?
uses 2 identical loops to find FIRE and FAULT to send signals to flight warning computer to EICAS
what is classified as real fire?
when both loop A and B detects fire
3 types of fire detection system
1) thermocouple
2) thermal switch
3) continuous loop
what is a thermocouple system?
2 dissimilar metal (Chromel & Alumel) makes up hot & cold junction, when difference in temp between hot and cold junction, current is created
how does a thermal switch system work?
heat present > case becomes longer causing 2 contacts inside to be drawn tgt > loop closed causing alarm to sound
3 common types of continuous loop system
1) kidde
2) fenwal
3) pneumatic pressure detector
what does a fenwal system consist of?
slender Inconel tube filled with thermally sensitive eutectic salt and nickel center wire conductor
how does fenwal system work?
eutectic salt melt from high temp > resistance drop means current flow to provide signal
how does a kidde system work?
resistance of thermistor material decreases rapidly from high temp > change of resistance is sensed by EEC
how does a pressure type sensor work?
pressure of gas inside increases with heat > actuates diaphragm switch in responder > closes circuit and send signal
