Reciprocating Engines and Thermodynamics Flashcards

Flashcards covering aircraft reciprocating engine principles, basic mechanics and thermodynamics laws, Bernoulli's theorem, Otto cycle operations, valve timing parameters, power ratings, efficiencies, and major engine components.

Force

That which, when acting on a body free to move, causes it to move, or stops or changes the direction of a moving body; calculated as $Force = Mass \times Acceleration$ ($F = M \times A$).

Work

The product of the Force and the Distance moved in the direction of the applied force, measured in Joules or Foot pounds.

Energy

The capacity of a body to do work, measured in Joules.

Law of Conservation of Energy

The principle stating that energy can be neither created nor destroyed; only its form may be changed.

Power

The rate of doing work, or work done per unit time, measured in Watts or Horsepower.

Horsepower

A unit of power measurement equal to $33{,}000\,\text{foot pounds a minute}$.

Inertia

The opposition of a body to change its motion or state of rest, corresponding to Newton's First Law of Motion, possessing no units of measurement.

Momentum

The product of mass and velocity ($Mass \times Velocity$), applying only to moving bodies, with units of measurement in $\text{kg}$ and meters per second.

Newton's Third Law of Motion

The law stating that for every action there is an equal and opposite reaction.

Thermo-Dynamics

The study of heat and pressure energy, or the behavior of gases and vapors under variations of temperature and pressure.

First Law of Thermo-Dynamics

The principle stating that heat and mechanical energy are mutually convertible and the rate of exchange is constant and can be measured.

Second Law of Thermo-Dynamics

The principle stating that heat cannot be transferred from a region at a lower temperature to one at a higher temperature without the expenditure of energy from an external source.

Bernoulli's Theorem

A principle stating that the total energy in a moving fluid or gas consists of potential energy, pressure energy, and kinetic energy, and in streamline flow of an ideal fluid, their sum is constant.

Venturi Tube

A practical application of Bernoulli's theorem consisting of a convergent-divergent duct with an inlet narrowing to a throat and a relatively longer outlet section increasing in diameter towards the rear.

Stroke

The linear distance that the piston moves in the cylinder, which is equal to twice the crank-throw.

Top Dead Centre (T.D.C.)

The position of the piston when it is at the very top of its stroke in the cylinder.

Bottom Dead Centre (B.D.C.)

The position of the piston when it is at the very bottom of its stroke in the cylinder.

Constant Volume Engine

A designation for internal combustion engines because during combustion at TDC, the volume remains unchanged while pressure and temperature rapidly rise.

Exhaust Back Pressure

The atmospheric resistance to the flow of exhaust gas as it is forced out of the cylinder by the rising piston.

Five Events

The five operational stages of the Otto cycle: Induction, Compression, Combustion, Power, and Exhaust.

Bore

The internal diameter of an engine cylinder.

Valve Lead

The condition where a valve opens before reaching TDC or BDC to improve gas flow.

Valve Lag

The condition where a valve closes after passing TDC or BDC to allow more air-fuel mixture in or more exhaust gases out.

Valve Overlap

A short period at TDC between exhaust and intake strokes when both intake and exhaust valves are open simultaneously to flush out exhaust gases and improve cylinder filling.

Indicated Horse power (IHP)

The theoretical total value of power produced within an engine.

Friction Horse power (FHP)

The power used in moving the piston and turning the crankshaft, which must be deducted from Indicated Horse Power.

Brake Horse Power (B.H.P.)

The useful power remaining to drive a propeller after Friction Horse Power is deducted from Indicated Horse Power.

Specific Fuel Consumption

The weight of fuel burnt in pounds ($\text{lbs}$) for the brake horsepower ($\text{B.H.P.}$) produced per unit time in hours ($\text{Hour}$).

Thermal Efficiency

The efficiency at which heat energy released by fuel combustion is converted to work done in the engine.

Volumetric Efficiency

The ratio of the weight of mixture induced to that which would fill the cylinder under normal temperatures and pressures.

Normally Aspirated Engine

An engine relying solely on the pressure differential between atmospheric and cylinder pressure during induction, achieving a maximum volumetric efficiency of $75\text{--}85\%$.

Supercharging

The method of increasing the force pushing the fuel-air mixture into the cylinder to improve volumetric efficiency and engine power.

Total Volume

The total volume above the piston when it is positioned at B.D.C., equal to Swept Volume plus Clearance Volume.

Swept Volume

The volume displaced by the piston during a single stroke, equal to the cross-sectional area of the cylinder multiplied by the stroke.

Clearance Volume

The volume above the piston crown when the piston is at T.D.C., forming the combustion chamber.

Compression Ratio

The ratio of the total volume enclosed in the cylinder with the piston at B.D.C. to the clearance volume at the end of the compression stroke with the piston at T.D.C.

Crankcase

An engine structure usually made of light alloy in two halves that houses main crankshaft bearings, supports cylinders, provides a sealed oil chamber, and includes an atmospheric vent to prevent gas pressure build-up.

Crankshaft

The component that converts linear reciprocating motion of the pistons into rotary motion, transmits torque to the propeller, provides drive for accessories, and determines piston stroke via crank throw.