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Engine Glossary

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A machine that converts one energy form to another form of energy
Heat engine
___ engine - An engine that converts the potential heat energy of a combustible fuel into mechanical work.
Internal Combustion Engine
___ ___ engine - A heat engine in which the combustion of fuel is contained within a cylinder. Differentiated from a steam engine
Diesel Engine
___ Engine - An IC engine in which the cylinder fuel air charge is ignited by the heat of compression.
Kinetic energy
___ energy - The energy of motion. This describes that percentage of the potential energy of the fuel that gets converted to usable mechanical energy after heat losses
Top Dead Center
The uppermost point of the piston travel in an engine cylinder.
Bottom dead center
The lowest point of piston travel in the engine cylinder.
Before top dead center
Any point of piston travel through its upstroke
After top dead center
A point of piston travel through its down stroke.
The diameter of a cylinder. ___ is expressed as the piston sectional area over which cylinder pressures act.
The distance through which a piston travels from BDC to TDC. Established by the crank throw offset; that is, the distance from the crankshaft centerline to the throw centerline multiplied by 2 equals the stroke dimension.
Swept volume
the volume displaced by the piston in the cylinder as it moves from BDC to TDC. It can be calculated if both stroke and bore are known.
Clearance volume
The remaining volume in an engine cylinder when the piston is at the top of its travel or TDC. Clearance volume influences actual compression temperatures and cylinder breathing efficiencies. Smaller on today's direct-injected engines.
Cylinder volume
The total volume in the cylinder when the piston is at BDC; swept volume plus clearance volume.
Engine displacement
The swept volume of all the engine cylinders expressed in cubic inches or cubic centimeters/liters.
Square Engine
An engine in which the cylinder bore diameter is exactly equal to the piston stroke dimension
Oversquare Engine
An engine in which the cylinder bore diameter is larger than the stroke dimension
Under-square Engine
An engine in which the cylinder bore diameter is smaller than the stroke dimension.
Compression Ratio
A measure of the cylinder volume when the piston is at BDC versus the cylinder volume when the piston is at TDC.
Compression Pressure
The actual cylinder pressure developed on the compression stroke.
Combustion Pressure
The peak pressure developed during the power stroke.
Naturally Aspirated (NA)
Describes an engine whose only means of inducing air (or air-fuel mixture) into its cylinders is the low cylinder pressure created by the down-stroke of the piston.
Manifold Boost
The extent of charge pressure above atmospheric delivered to the cylinders in a turbocharged engine.
Volumetric Efficiency
A measure of an engine's breathing efficiency.
Fire Point
The temperature at which a flammable liquid gives off sufficient vapor for continuous combustion to take place.
Otto Cycle
The engine cycle used in most SI (spark ignited) gasoline-fueled engines.
Atkinson Cycle
A variation of the Otto cycle; piston is connected to the crankshaft with a double pivot linkage.
Miller Cycle
A variation of the Otto cycle; this cycle uses a supercharger.
Ignition Lag
The time between the entry of the first droplets of fuel into the engine cylinder and the moment of ignition that begins combustion.
Mean Effective Pressure (MEP)
A way of describing the cylinder pressure that can actually be converted into torque.
Boyle's Law
States that the absolute pressure that a given quantity of gas at constant temperature exerts against the walls of a container is universally proportional to the volume occupied.
Charles's Law
States that the increase in temperature in gases produces the same increase in volume if the pressure remains constant.
The resistance to motion between two objects in contact with each other.
Static Friction
Describes the characteristic of an object at rest to attempt to stay that way.
Describes the tendency of an object in motion to stay in motion or, conversely, an object at rest to remain that way.
Established the relationship between the units of heat and work that could be done.
Calorific Value
The potential heat energy of a fuel.
British Thermal Unit
A measure of the heat energy
Thermal Efficiency
A measure of the combustion efficiency of an engine calculated by comparing the heat energy potential of the fuel (calorific value) with the amount of usable mechanical work produced.
Rejected Heat
That percentage of the heat potential of the fuel that is not converted into useful work by an engine.
Thrust bearings
In an engine, the bearings or usually shaped like a semi-circular washer which provides the proper spacing and clearances for the front to back movement of a crankshaft.
Rod bearings
Thin semi-circular aluminum or copper parts which are used in pairs. An upper “shell” and a lower shell. These fit inside the connecting rod, between the connecting rod and the rod journal on the crankshaft.
Main bearings
Thin semi-circular aluminum or copper parts used in pairs. One upper and one lower. These fit between the crankshaft and the main bearing journals.