NIFE Engines 3-7-2 Fuel System Flashcards
Define volatility
The measurement of a liquid’s ability to convert to a vaporous state
Volatility rating
A fixed number. Similar to octane rating
Define flashpoint
The lowest temp of a combustible substance that would ignite with a momentary application of flame. An index of a fuel’s potential safety for handling and storage. Volatility rating and flashpoint are inversely related.
Describe how temperature affects flashpoint
As temperature increases, a fuel’s flashpoint will remain the same
List common military aviation fuels
- JP-4 (NATO code F-40)
- JP-5 (NATO code F-44)
- JP-8 (NATO code F-34)
JP-4 Characteristics
- Blend of kerosene, gasoline and naptha fractions
- Was the most common
- Highly volatile (flashpoint -35F)
- Easier starting
- Slow acceleration
- Lower operating temps
- High tendency to vapor lock
- Shorter range
JP-5 characteristics
- USN, USMC, USCG primary jet fuel
- A type of heavy kerosene
- Thermally stable
- High heat content per gallon
- Low volatility
- High flashpoint (140 F)
- Safe to store on ships
JP-8
- Flash point 100 F
- Does not meet ship safety standards
- Used by USAF
Describe a basic aircraft fuel system
Purpose is to supply clean fuel, free from vapor, at the proper pressures and flow rates to the engine under all operating conditions.
Describe rated thrust
Normal: A rating of a gas turbine engine that is based on the allowable ITT or TIT (turbine inlet temp), for continuous operations in order to prevent heat damage to the turbine blades
MRT: Maximum tubrine temp for 30 minutes
CRT: Thrust produced in afterburner, not based on turbine temperature
Types of rated thrust
- Normal rated thrust (NRT)
- Military rated thrust (MRT)
- Combat rated thrust (CRT)
Normal Rated Thrust
Thrust produced at the maximum continuous turbine temperature with no time limitation.
Military Rated Thrust
Thrust produced at the maximum turbine temperature for a limited time; normally 30 minutes. Temp is higher than NRT
Combat Rated Thrust
thrust produced with the afterburner in operation, and is NOT based on turbine temperature limitations
Fuel Tank
A reservoir for jet propellant. can be fueled through gravity, pressure, and/or inflight fueling
Boost Pump
A centrifugal pump and electric motor that is installed in a fuel tank to ensure an adequate supply of fuel to the engine-driven fuel pump, support startup, and the primer system. Can also transfer fuel between tanks. The pump must prevent aeration of the fuel supply, which could result in rapid pressure changes during a climb
Emergency shut off
Allows the pilot to shut off fuel to the engine in an emergency. Fuel will shut off electrically and mechanically
Fuel pressure gauge
located in the cockpit, receives signals from a pressure sensor at the boost pump outlet
Low pressure fuel filter
The low pressure fuel filter is usually a paper cartridge type filter, located downstream of the boost pump to strain impurities from the fuel.
Engine driven pump
a high pressure pump that provides fuel excess that ensures that a sufficient supply of high pressure fuel is available to meet engine requirements and, if available, afterburner requirements
Fuel control unit (FCU)
The “brain” of the engine fuel system - a hydro-mechanical or electrical device that consists of fuel computing and fuel metering systems.
FCU inputs
CRIP
- Compressor inlet temp: measures ambient air density
- RPMS: Compressor speed
- Turbine Temp (ITT): prevent turbine damage
- PCL position: aviator input
FCU modes of operation
- Normal (Automatic) operation: Monitors inputs
- Manual/Emergency operation: Lacks the acceleration limiting and RPM-governing capabilities of the normal system. PCL becomes the throttle
Fuel-flow gauge
located between the FCU and fuel-oil heat exchanger, it measures fuel flow rate from FCU in PPH (pounds per hour)
