Reciprocating Engine Theory Flashcards
Number of pounds of fuel burned per hour for each horsepower produced at the propeller shaft.
Brake specific fuel consumption.
BSFC
______ allow the engine to turn fast enough to develop the required power while keeping the prop speed slower.
Reduction gears.
Five events, in order, in the Otto cycle:
Intake stroke, Compression stroke, Ignition, Power stroke, Exhaust stroke.
_______ is the time that both the intake and exhaust valves are off their seat.
Valve overlap
Valve overlap occurs at the end of the ______ and the beginning of the ______.
Exhaust stroke,
Intake stroke.
T\F
It is not possible to directly measure the amount of indicated HP an engine is producing.
True
T/F
It is not possible to directly measure the amount of brake HP an engine is producing.
False
T\F
It is possible to directly measure the amount of indicated mean effective pressure in the cylinder of a reciprocating engine.
True
T/F
It is possible for a naturally aspirated engine to have a volumetric efficiency of 100%.
False
If both the intake and exhaust valve clearances are too great, the efficiency will _______.
Decrease.
T/F
The bore of a square engine is the same as the the stroke.
True
The ratio of the volume of a cylinder above the piston at the bottom of its stroke to the volume with the cylinder at the top of its stroke is called the _____.
Compression ratio
T/F
Increasing the compression ratio of an engine decreases its thermal efficiency.
False
The practical limit to the compression ratio an engine can tolerate is determined by the ______ of the fuel.
Detonation characteristics.
Two variables over which a pilot has control to determine the HP produced by an aircraft are:
RPM,
Brake mean effective pressure.
A measure of the number of pounds of fuel burned per hour to produce each brake horsepower is called the _____.
Brake specific fuel consumption.
BSFC
Useful work is done in a heat engine when the chemical energy is released into the air and causes it to ______.
Expand.
The energy release cycle used by a reciprocating engine is the _______.
Constant volume cycle.
The energy release cycle used by a turbine engine is the ______.
Constant pressure cycle.
Define Otto cycle.
The constant volume cycle of energy transformation used by reciprocating engines.
Valve overlap is important for these 3 reasons
Exhaust gas scavenging. Volumetric efficiency.
Proper cooling.
Define the acronym “PLANK”.
P= IMEP in PSI. L= Length of stroke in feet. A= Area of piston head. N= Number of power strokes. (RPM / 2). K= Number of cylinders.
How many watts in a horsepower?
746
Standard temp at sea level.
59 degrees F
15 degrees C
Standard pressure at sea level.
- 92” Hg.
14. 7 psi.
7 factors that affect engine power:
Mechanical efficiency. Thermal efficiency. Volumetric efficiency. Air density. (Temp/Altitude) Piston displacement. Compression ratio. Ignition timing.
Define natural aspiration in an engine
Vacuum is created in the cylinder of a reciprocating engine by the downward movement of the piston, and the opening of the intake valve causes air to be forced in due to atmospheric pressure.
For a piston to complete its 4 strokes in a reciprocating engine, the crankshaft must be turned ______ degrees during which ______ events will occur.
720.
5.
Ignition of the fuel air mixture inside the cylinders of a reciprocating engine before the normal spark occurs is called?
Preignition.
Uncontrolled explosion inside the cylinder of a reciprocating engine often caused by lower octane/improper fuel.
Detonation
Define four stroke cycle.
Constant volume cycle of energy transformation that has separate strokes for intake, compression, power and exhaust.
Define two stroke cycle.
A constant volume cycle of energy transformation that completes its operating cycle in two strokes of the piston. One up and one down.
Used to increase the pressure of the air being taken into the cylinders of a reciprocating engine.
Supercharger
Work =
Force x distance
Theoretical HP developed by a reciprocating engine’s cylinders.
Indicated horsepower
IHP
Actual horsepower delivered to the propeller shaft of a reciprocating engine.
Brake horsepower
BHP
Average pressure existing inside the cylinder of a reciprocating engine during its power stroke.
Indicated mean effective pressure.
IMEP
Theoretical average pressure inside the cylinder of a reciprocating engine during its power stroke.
Brake mean effective pressure.
BMEP
Absolute pressure, measured in inches of mercury, of the air inside the induction system of a reciprocating engine.
Manifold absolute pressure.
MAP
An engine whose bore dimensions are the same as its stroke dimensions.
Square engine.
