pplant quiz 6

Lubricant

The primary purpose of a ________ is to reduce friction between moving parts. Lubricants allow surfaces to separate, preventing metal-to-metal contact.

Requirements for Turbine Engine Lubricants

Must have high viscosity for load-carrying ability, low viscosity for flowability, and low volatility to prevent evaporation.

Synthetic Oil Advantages

Lower tendency to deposit lacquer and coke since it does not evaporate solvents at high temperatures.

Type I- MIL-PRF-7808

military specification turbine oil.

Type II- MIL-PRF-23699F

synthetic oil with a viscosity of 5 to 5.5 centistokes at 210°F.

Wet-sump

Oil is stored in the engine.

Dry-sump

Oil is stored in an external tank.

Pressure relief system

Maintains constant pressure.

Full flow system

Pressure varies with engine speed.

Total loss system

Used for short-duration engines (drones, missiles).

Oil Tank

Stores oil, contains pressure outlet ports, scavenge and pressure inlets, and temperature gauge connections.

Oil Pump

Supplies oil under pressure, circulates it through coolers, and returns it to the tank.

Gear Pump

Common oil pump with one element for pressure and one for scavenging.

Gerotor Pump

Similar to a gear pump but allows variation in element size to control capacity.

Oil Filters

Remove contaminants from oil to prevent damage to high-speed bearings.

Oil Pressure Regulating Valve

Maintains a constant pressure within the system.

Oil Pressure Relief Valve

Prevents excessive pressure by bypassing oil when the limit is exceeded.

Oil Jets

Deliver atomized oil spray to bearings and rotor shaft couplings.

Lubrication System Instrumentation

Includes oil pressure gauge, oil quantity indicator, low oil pressure warning, oil temperature sensor, and FADEC monitoring.

Breather System

Removes excess air from bearing cavities and vents it back to the atmosphere.

Lubrication System Check Valve

Prevents oil from seeping into the engine after shutdown.

Thermostatic Bypass Valve

Maintains proper oil temperature by directing oil flow through or around the cooler.

Air Oil Cooler

Reduces oil temperature using airflow.

Fuel Oil Cooler

Uses fuel as a heat exchanger to cool oil and preheat fuel.

Deoiler

Removes oil from breather air using centrifugal force.

Magnetic Chip Detectors

Detect ferrous particles in oil to identify potential wear or damage.

Energy Transformation

A gas turbine engine converts chemical energy into heat energy, which increases gas pressure and transforms into kinetic energy. Expanding gases rotate turbine wheels, driving a compressor and accessories.

Energy Transformation Cycle

The gas turbine engine follows the Brayton cycle (constant pressure cycle). Intake, compression, combustion, and exhaust occur simultaneously and continuously.

Airflow Process

Air enters through an inlet, gets compressed, mixes with fuel and ignites in the combustor, and exits through turbines and the exhaust nozzle.

Pressure and Volume Changes

(A) Air enters the compressor.

(B) Compressed air exits the compressor with increased pressure and reduced volume.

(C) Combustion increases air volume while maintaining constant pressure.

(D) Expanding gases exit the turbine, losing pressure while increasing velocity.

Thrust

Based on Newton's Third Law—acceleration of air mass creates an equal and opposite reaction, producing _________.

Bernoulli's Principle

As air velocity increases, air pressure decreases, and vice versa. Diverging ducts increase pressure; converging ducts increase velocity.

Factors Affecting Thrust

Increasing mass flow or exhaust velocity increases thrust.

Thermal Efficiency

Ratio of actual engine power to thermal energy in fuel. Higher efficiency with increased turbine inlet temperature (TIT), compression ratio, and component efficiency.

Turbine Inlet Temperature (TIT)

Higher TIT improves efficiency but is limited by material heat resistance.

2,500-3,000°F

Typical range of turbine inlet temp

Higher

______________ compression increases thrust by forcing more air into the engine, allowing better heat energy transfer.

Temperature

Higher outside air temperature (OAT) reduces air density and engine thrust. Standard reference: 59°F (15°C).

Altitude

Higher altitude decreases air pressure and density, reducing thrust.

Airspeed

Increased airspeed reduces mass acceleration but increases ram effect, leading to ram recovery.

Engine RPM and Thrust

Turbojets have a linear thrust-to-RPM relationship, while modern turbofans use engine pressure ratio (EPR) for accurate thrust measurement.

Fan Efficiency

Higher fan efficiency improves turbofan engine performance and fuel economy compared to turbojets.