TOPIC 02.2 - RECIPROCATING ENGINES OPERATING PRINCIPLES

Question 1

This is the distance that the piston moves in the cylinder when the crankshaft rotates between the TDC and BDC.

Answer 1

Stroke

Question 2

This is the distance between the centerline of the crankshaft journal to the centerline of the crank pins.

Answer 2

Crank throw

Question 3

1 stroke is equal to how many crank throws?

Answer 3

2

Question 4

This is defined as the internal diameter of the cylinder.

Answer 4

Bore

Question 5

This is defined as the minimal piston movement around the TDC and BDC.

Answer 5

Ineffective crank angle

Question 6

This is defined as the weight of the fuel burnt (lb) for the power produced (BHP) in unit time (hours).

Answer 6

Specific fuel consumption (SFC)

Question 7

This is defined as the volume that remains above the position when the crankshaft is at BDC.

Answer 7

Total volume

Question 8

Formula of total volume:

Answer 8

TV = SV + CV

Question 9

This is defined as the volume displaced by the piston in a single stroke.

Answer 9

Swept volume

Question 10

Formula of swept volume:

Answer 10

SV = AxL + CV

Question 11

This is defined as the volume that remains above the piston when the crankshaft is at TDC.

Answer 11

Clearance volume

Question 12

Formula of clearance volume:

Answer 12

CV = TV - SV

Question 13

This is the ratio of the volume in the cylinder with the piston at the bottom of its stroke, to the volume remaining with the piston at the top of its stroke.

Answer 13

Compression ratio

Question 14

Formula of compression stroke:

Answer 14

CR = TV / CV

Question 15

This represents the volume of air-fuel mixture that the piston moves through each stroke directly influencing the engine’s power.

Answer 15

Piston displacement

Question 16

This is equal to the displacement, or volume of once cylinder multiplied by the total number of cylinders.

Answer 16

Total piston displacement

Question 17

Formula of total piston displacement:

Answer 17

TSV = SV x N

Question 18

Formula of indicated engine horsepower:

Answer 18

IHP = PLANK / 33,000 for ft.lb/m
IHP = PLANK / 550 for ft.lb/s

Question 19

Define PLANK.

Answer 19

P - indicated mean effective pressure
L - length of stroke
A - area of cylinder
N - number of cylinders
K - effective working stroke

Question 20

Formula of bhp:

Answer 20

bhp = 2 x pi x N x T

where:
N = engine rpm
T = torque reading

Question 21

Formula of torque:

Answer 21

T = F x d

where:
F = force reading
d = distance lever arm

Question 22

Formula of brake horsepower:

Answer 22

BHP = IHP - FHP

Question 23

What is mechanical efficiency?

Answer 23

Usually 80% to 85%

Question 24

Formula of mechanical efficiency:

Answer 24

Me = (bhp / ihp) x 100%

Question 25

This is the ratio of work done by the engine to the mechanical equivalent of the heat supplied in the fuel.

Answer 25

Thermal efficiency

Question 26

What is the usual thermal efficiency?

Answer 26

25% to 28%

Question 27

Formula of thermal efficiency:

Answer 27

Te = (Heat converted into work / Heat energy available in the fuel) x 100% Te = BHP / Ti

Question 28

Formula of thermal input:

Answer 28

Ti = fc x hv where: fc = fuel consumption hv = heating value

Question 29

This is the ratio of the weight of air and fuel induced into the cylinder on the induction stroke to the weight of air and fuel which would fill the cylinder at standard temperatures and pressures, expressed as a percentage.

Answer 29

Volumetric efficiency

Question 30

What is the usual volumetric efficiency for normally aspirated engines?

Answer 30

80%

Question 31

Formula of volumetric efficiency:

Answer 31

Ve = (Weight of mixture actually induced / Weight of mixture which would fill cylinder at standard temperatures and pressure) x 100%