Piston Engines Flashcards
The firing interval of a piston engine is found by …
dividing 720 degrees (two rotations of crankshaft per otto cycle) by the number of cylinders
What determines how far up and down the cylinder a piston will move?
the crank throw
Piston stroke is twice that of the …
crank throw
The camshaft always operates at what speed compared to crankshaft?
half
Cylinder valaves are opened by and closed by?
camshaft
spring pressure
Cylinder exhaust valve is hollowed and partially filled with … to assist …
sodium
cooling
Clearance between top of valve stem and rocker pad (connected to rocker arm) allows for …
thermal expansion
Manifold air pressure will always be higher/lower than atmospheric pressure when a normally aspirated engine is running?
lower (as the mixture gets sucked in to the cylinder)
power formula =
and using torque =
force x distance / time
torque x RPM
mechanical efficiency of a piston engine =
actual power at propellor shaft / theoretical power
thermal efficiency = …
and modern piston engines about …% thermally efficient
ratio of work done by engine to the mechanical equivalent of the heat energy released by combusting the fuel
33%
thermal efficiency independant of … but increases with increased …
altiutde
compression ratio
difference between clearance volume and total volume is called …
swept volume
compression ratio =
total volume / clearance volume
piton engine displacement =
piston area x stroke x no. of cylinders
volumetric efficiency =
modern normally aspirated piston engines achieve a volumetric efficiency of about …%
mass of mixture induced into cylinder / mass of air which would otherwise fill the swept volume
80%
Volumetric efficiency increases with altitude because …
less exhaust back pressure, allowing more mixture in to the cylinder in the given time
The primary winding of a magneto consists of … of … wire and is also called …
a few turns
thick
low tension circuit
the secondary winding of a magneto consists of … turns of … wire that acts as a … transformer.
also called the … circuit
many
thin
step up
high tension
the contact breaker in a magneto is used to …
(2)
continually open and close causing the primary winding field to collapse and build producing a surge of energy in the secondary winding.
also converts the continuous flow of ac current in to a series of pulses
why is a capacitor is fitting in parallel with the contact breaker?
prevent arcing and provide a rapid collapse of the primary current
the ignition switch must be open or closed to isolate the magneto’s ignition circuit?
why?
closed because the switch isolated the igintion circuit by connecting the primary circuit to ground
