Piston Engines

Question 1

The firing interval of a piston engine is found by …

Answer 1

dividing 720 degrees (two rotations of crankshaft per otto cycle) by the number of cylinders

Question 2

What determines how far up and down the cylinder a piston will move?

Answer 2

the crank throw

Question 3

Piston stroke is twice that of the …

Answer 3

crank throw

Question 4

The camshaft always operates at what speed compared to crankshaft?

Answer 4

half

Question 5

Cylinder valaves are opened by and closed by?

Answer 5

camshaft

spring pressure

Question 6

Cylinder exhaust valve is hollowed and partially filled with … to assist …

Answer 6

sodium

cooling

Question 7

Clearance between top of valve stem and rocker pad (connected to rocker arm) allows for …

Answer 7

thermal expansion

Question 8

Manifold air pressure will always be higher/lower than atmospheric pressure when a normally aspirated engine is running?

Answer 8

lower (as the mixture gets sucked in to the cylinder)

Question 9

power formula =

and using torque =

Answer 9

force x distance / time

torque x RPM

Question 10

mechanical efficiency of a piston engine =

Answer 10

actual power at propellor shaft / theoretical power

Question 11

thermal efficiency = …

and modern piston engines about …% thermally efficient

Answer 11

ratio of work done by engine to the mechanical equivalent of the heat energy released by combusting the fuel

33%

Question 12

thermal efficiency independant of … but increases with increased …

Answer 12

altiutde

compression ratio

Question 13

difference between clearance volume and total volume is called …

Answer 13

swept volume

Question 14

compression ratio =

Answer 14

total volume / clearance volume

Question 15

piton engine displacement =

Answer 15

piston area x stroke x no. of cylinders

Question 16

volumetric efficiency =

modern normally aspirated piston engines achieve a volumetric efficiency of about …%

Answer 16

mass of mixture induced into cylinder / mass of air which would otherwise fill the swept volume

80%

Question 17

Volumetric efficiency increases with altitude because …

Answer 17

less exhaust back pressure, allowing more mixture in to the cylinder in the given time

Question 18

The primary winding of a magneto consists of … of … wire and is also called …

Answer 18

a few turns

thick

low tension circuit

Question 19

the secondary winding of a magneto consists of … turns of … wire that acts as a … transformer.

also called the … circuit

Answer 19

many

thin

step up

high tension

Question 20

the contact breaker in a magneto is used to …

(2)

Answer 20

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

Question 21

why is a capacitor is fitting in parallel with the contact breaker?

Answer 21

prevent arcing and provide a rapid collapse of the primary current

Question 22

the ignition switch must be open or closed to isolate the magneto’s ignition circuit?

why?

Answer 22

closed because the switch isolated the igintion circuit by connecting the primary circuit to ground