Midterm Exam Review: Engine Systems and Components

Comprehensive practice flashcards covering aircraft engine lubrication, fuel systems, pumps, and combustion characteristics based on midterm lecture notes.

Viscosity

The resistance to flow, where high viscosity flows slow and low viscosity flows freely.

Saybolt Universal Viscosimeter

An instrument used to measure oil viscosity for grading by heating the oil and timing its flow through a calibrated orifice.

60cc's

The volume of oil measured during a Saybolt Universal Viscosimeter test to determine viscosity based on flow time.

Flashpoint

The temperature at which a liquid begins to ignite vapors.

Cloudpoint

The temperature at which wax content in oil begins to solidify and separate into crystals.

Pour point

The lowest temperature at which oil flows or can be poured.

Firepoint

The temperature at which there are sufficient vapors to support a flame, which is higher than the flashpoint.

Straight mineral oil

Oil with no additives and a tendency to oxidize at high temperatures; used mainly in new or overhauled engines for breaking them down.

Ashless-Dispersant

The most common type of oil that does not form ash deposits and contains additives like anti-wear and anti-foam.

Wet sump

An integrated oil system where all oil is contained in the crankcase of the engine; it is simple and lightweight but difficult to cool.

Dry sump

An oil system with a separate oil tank, well suited for radial engines, but requires more components like a scavenge pump.

Scavenge pump

A component needed in dry sump systems to return oil to the separate tank, adding weight and repair cost.

Pressure lubrication

A distribution method where oil flows under pressure through passages to bearings, the camshaft, and the crankshaft main journal.

Splash lubrication

Lubrication produced by the movement of internal parts such as crankshaft gears, accessory drive gears, and cylinder walls.

Spray lubrication

A method used in large engines where oil is forced through aimed nozzles.

Oil Dilution

The process of injecting fuel into the oil pump prior to shutdown in extremely cold climates to make the oil thin for easier circulation on the next start.

Thermostatic Bypass Control Valve

A valve that allows oil to bypass the cooler on start up to help the oil warm up.

Gear type pump

The most common oil pump consisting of two mesh gears that rotate from an accessory drive providing constant displacement.

Constant displacement

A characteristic of a pump where a fixed volume of fluid is moved per revolution.

Gerotor type pump

A pump with a spur or drive gear rotating within a housing where oil is drawn in or forced out based on changing space between gear and housing.

Detonation

The uncontrolled explosion of fuel/air mixture in the cylinder causing high temperatures, high pressures, and engine knocking.

Pre-ignition

Premature ignition of the fuel/air mixture caused by hot spots in the cylinder before the spark plug fires.

Compression ratio

The ratio calculated by dividing Total Volume ($140$ cubic inches) by Combustion Chamber Volume ($20$ cubic inches), resulting in $7:1$.

Main journal

The part of the crankshaft construction that allows it to rotate freely and supports the crankcase.

Crankpins

The specific parts of the crankshaft where the connecting rods attach.

Crankcheek

The part of the crankshaft construction where the crankpins are attached.

Intake Valve

The valve through which air/fuel mixture enters the cylinder; it has a smaller shaft diameter and is made of chrome, tungsten steel, or nickel.

Exhaust Valve

The valve where exhaust gas exits; it is made of Inconel, silicon chromium, or cobalt chromium and features a metallic sodium-filled stem.

Metallic sodium

A material found in exhaust valve stems that melts to transfer heat from the valve face to the stem.

Valve lag

The condition occurring when the intake valve closes after top dead center.

Valve lead

The condition occurring when the exhaust valve opens before bottom dead center.

Valve Overlap

The period when both the intake and exhaust valves are open simultaneously.

Camshaft

The primary component used to control valve timing.

Rocker arm

The component that pushes the spring to open the valve; it can be adjusted to change valve timing.

Rich mixture

A mixture such as $11:1$ (less air, more fuel) that causes cooler running temperatures but may lead to ash deposits and fouled plugs.

Lean mixture

A mixture such as $16:1$ (more air, less fuel) that causes higher running and exhaust gas temperatures and can lead to detonation.

Absolute pressure controller

A controller consisting of bellows that sets and maintains the upper deck pressure at its maximum limit.

Variable Restrictor Valve

A valve that controls the amount of oil flowing out of the waste gate actuator.

Pressure ratio controller

A device that monitors ambient and upper deck pressure to prevent the turbo from boosting upper deck pressure more than $2.2$ times.

Pressure Relief valve

A backup valve set to open at $1-1.5$ inches of mercury above the max upper deck pressure to prevent overboost.

Rate of change controller

A device that prevents upper deck pressure from increasing more than $2.0$ to $6.5$ inches per second to prevent overboost.

Butterfly valve

A carburetor component that regulates airflow in the venturi.

Venturi

The part of the carburetor that creates low pressure used for fuel metering.

Float

A component working with a needle valve to control the amount of fuel entering the carburetor chamber.

Bending tab

The part on the float assembly used to achieve float adjustment.

Main metering jet

A jet that limits fuel flow at full throttle and incorporates an air bleed to atomize or emulsify the fuel.

Idle mixture control

A control that determines the amount of fuel/air mixture released in the intake manifold at idle only.

50 RPM rise

The targeted RPM increase observed after shutdown if the idle mixture is adjusted properly.

Idle cut off

A setting that completely cuts fuel off to the fuel metering device to stop the engine.

Variable orifice

A type of mixture control using a needle valve or rotary linkage to the pilot mixture control.

Back suction

A mixture control method using differential pressure in the float chamber to regulate airflow.

Accelerator well

A reservoir storing a small volume of fuel for smooth acceleration when the throttle is opened rapidly.

Accelerator pump

A piston-driven component that pushes fuel out of the discharge nozzle when the throttle is suddenly opened.

Discharge check valve

A valve in the accelerator system that prevents siphoning fuel from the chamber out of the discharge nozzle.

25-50 RPM rise

The range indicating the idle mixture is set correctly when the mixture control is moved to idle cut off.

Blocked air bleed hole

A condition in a fuel nozzle that results in increased fuel flow.

Blocked nozzle

A condition in a fuel nozzle that causes a lean mixture in that cylinder while the remaining nozzles run rich.

Over-advanced timing

One of the two primary causes of engine detonation, along with low grade fuel.

Hot spots

Internal cylinder issues, such as an overheated valve edge or a piece of carbon, that cause pre-ignition.

Tapered roller bearing

One of the specific types of bearings mentioned in the midterm notes along with ball and plain bearings.