Fuel systems

volatility

measurement of a liquids ability to convert to a vaporous state

flashpoint

lowest temp of a combustible substance that would ignite with a momentarily application of a flame

flash point and volatility are ____ related

inversely

increasing temperature _____ volatility

increases

JP-4 (NATO code F-40) characteristics

FP: -35 F. high volatility easier starting, slower acceleration, lower operating temperatures, higher tendency to vapor lock, shorter range

JP-5 (NATO Code F-44) characteristics

FP: 140 F. thermally stable, low volatility and high flash point

primary jet fuel of MC, navy, and cost guard

JP-5

flash point of JP-5

140 deg F

JP-8 (NATO Code F-34) characteristics

FP: 100 F. same as JP-5 but has a lower flashpoint making it not ship safe

Avgas 100

standard octane fuel with a high lead content dyed green

Avgas 100 LL

lower lead version of Avgas 100 dyed blue

the aircraft fuel system must

supply clean fuel, free from vapor, at the proper pressures and flow rates to the engine under all operating conditions

what must the designer consider when designing the fuel system

high rates of fuel flow,

low atmospheric pressure,

piping system complexity,

weight and size constraints,

vapor loss with consequent reductions in range,

cold weather starting

fuel tank

starting point for fuel

ways fuel tank can be fueled and most common

gravity, pressure, inflight

MC = pressure

boost pump

submerged and installed in the fuel tanks, they ensure an adequate supply of fuel to the engine-driven fuel pump

critical function of the boost pump

prevent aeration of the fuel supply, which may result from a rapid pressure change incurred during a climb

emergency shutoff valve

controlled electrically and mechanically and once pulled the engine cannot and will not be authorized to be put back in service during that flight

low pressure fuel filter

usually a paper cartridge type filter and located downstream of the boost pump to strain impurities from the fuel

during normal operations the bypass valve is

held closed by a spring

why does the engine driven pump provide excess fuel

ensures a sufficient supply of high-pressure fuel is available to meet engine requirements and, if available, afterburner requirements

inputs that ensure proper fuel flow within the Fuel control unit (FCU)

compressor inlet temperature

RPMs

inlet turbine temperature

PCL position

FCU Normal Operation

normal operations

FCU manual/ emergency operation

when selected the FCU is bypassed. PCL functions as a throttle and fuel flow is now regulated exclusively by its movement

fuel flow transmitter

measures fuel flow rate coming out of the FCU and converts it to electrical signals

fuel-oil cooler/ heat exchanger

preheat fuel and cool engine to remove ice crystals and increase volatility

fuel manifold

delivers fuel to the engine burner section through a series of fuel nozzles

pressurizing and dump (P&D) valve

drain the combustion manifold upon engine shutdown and to adjust fuel flow during engine starts

during engine start and shutdown the dump valve is

closed

open

afterburner FCU

meters fuel to the afterburner spray bars

fuel transfer valve

during afterburner operations, opens and permits fuel flow to the afterburner FCU

Max thrust rating is based on

allowable ITT or TIT (turbine inlet temperature)

normal rated thrust (NRT)

thrust produced at the maximum continuous turbine temperature with no time limitation

Military Rated Thrust (MRT)

thrust produced at the max turbine temp for a limited time normally 30 min

Combat Rated Thrust (CRT)

thrust produced with afterburner in operation and not based on turbine temp limitations