Reciprocating Engines

Question 1

What is a constant-volume cycle?

Answer 1

In a reciprocating engine heat energy is added to the air

Question 2

What is a four-stroke also refereed to?

Answer 2

Otto-cycle

Question 3

How many cycles are in a four stroke?

Answer 3

Five-event cycle

Question 4

What are the five cycles of a stroke?

Answer 4

Intake, compression, ignition, power, and exhaust

Question 5

What is a stroke?

Answer 5

The distance the piston moves inside the cylinder

Question 6

How is the duration of a stroke measured?

Answer 6

In degrees of crankshaft rotation

Question 7

How many degrees is each stroke?

Answer 7

180°

Question 8

Why are more cylinders better?

Answer 8

More cylinders the more power and the smoother the operation

The firing impulses are closer together

Question 8

What is the bore of a cylinder?

Answer 8

The inside diameter of a cylinder

Question 9

Explain the five event cycles

Answer 9

-Intake-draws the fuel-air mixture into the cylinder
-Compression-compresses the mixture
-Ignition-ignites the mixture
-Power-the mechanical energy is produced
-Exhaust-spent gases are forced out of the cylinder

Question 10

When does ignition occur?

Answer 10

Before the piston reaches TDC

Question 11

What happens during the power stroke?

Answer 11

Both valves are closed. The piston is forced down by the pressure. The only time useful work is done

Question 12

What happens if the ignition timing is correct?

Answer 12

The fuel-air mixture will completely burn shortly after the piston passes TDC on the power stroke

Question 13

What is valve overlap and why is it important?

Answer 13

-The portion of the operating cycle of a four-stroke reciprocating engine during which both the intake and exhaust valves are open at the same time
-Its important for volumetric efficiency and proper cooling

Question 14

When does the intake valve open?

Answer 14

During the exhaust stroke just before the piston reaches TDC

Question 15

When does the exhaust valve closes?

Answer 15

During the intake stroke just after the piston passes TDC

Question 16

When does the intake valve close?

Answer 16

During the compression stroke just after the piston passes BDC

Question 17

When does ignition occur?

Answer 17

During the compression stroke just before the piston reaches TDC

Question 18

When does the exhaust valve open?

Answer 18

During the power stroke just before the piston reaches BDC

Question 19

1hp equals?

Answer 19

550ft-lbs per second

Question 20

What are the three types of horsepower involved in recip engines?

Answer 20

Indicated horsepower
Friction horsepower
Brake horsepower

Question 21

What is brake horsepower?

Answer 21

The actual horsepower delivered to the propeller shaft

Question 22

What is torque?

Answer 22

The force that produces a twisting or rotational motion of the crankshaft

Question 23

What are the three major efficiency groups in a recip engine?

Answer 23

Thermal efficiency
Mechanical efficiency
Volumetric efficiency

Question 24

What is brake thermal efficiency?

Answer 24

The ratio of useful work done by an engine to the heat of the fuel it uses

Question 25

What is volumetric efficiency?

Answer 25

It's the ratio of the volume of fuel-air charge inside the cylinder to the single cylinder displacement

Question 26

What factors affect engine power?

Answer 26

Piston displacement Compression ratio Valve timing Ignition timing Air density

Question 27

What is compression ratio?

Answer 27

The ratio of the volume of the cylinder with the piston at the BDC to the volume of the cylinder with the piston at TDC

Question 28

What is detonation?

Answer 28

An uncontrolled explosion inside the cylinder caused by fuel exceeding it's critical temperature and pressure

Question 29

What is pre-ignition?

Answer 29

Ignition of the fuel-air mixture inside the cylinder before the normal spark occurs

Question 30

What major parts make up the top end of an engine?

Answer 30

Cylinders Valve assemblies Pistons

Question 31

What is choke-ground cylinder?

Answer 31

The barrels are ground so its diameter at the top is slightly smaller than diameter at the bottom -The top of the barrel expands more than the rest

Question 32

What is cylinder honing?

Answer 32

-The barrel is honed with a 45° cris-cross finish -holds oil for lubrication

Question 33

What are the two ways cylinder walls are hardened?

Answer 33

Chrome plating-orange Nitriding-blue

Question 33

What is an interference fit?

Answer 33

The barrel is chilled and the head is heated and then screwed together

Question 34

How can you tell the difference between the exhaust and intake side of a cylinder head

Answer 34

The exhaust side has more fins

Question 35

Why does the exhaust valve hollow in the middle?

Answer 35

Its filled with metallic sodium that aids in cooling the valve

Question 36

To what degree are intake valves ground?

Answer 36

30° to provide for better airflow into the cylinder

Question 37

To what degree are exhaust valves ground?

Answer 37

45° to make sure of proper seating

Question 38

What is interference angle?

Answer 38

The difference between the angles of the valve seat and the valve face

Question 39

How are valves open and closed?

Answer 39

Opened by pressure from the camshaft and closed by the force of two or more coil springs

Question 40

Why are two springs used for valves?

Answer 40

So if a spring has a resonant frequency it will lose spring pressure

Question 41

What are cam-ground pistons?

Answer 41

The boss area absorbs more heat because of extra metal and expands more

Question 42

What are the function of piston rings?

Answer 42

-Sealing action to prevent gas leakage -transfer heat from the piston to the cylinder wall -oil control on the cylinder wall preventing oil entering the combustion chamber

Question 43

Why should you use a different material on piston rings from the piston

Answer 43

They will not wear out the rings initially to provide a good seal

Question 44

What are the three critical measurements for piston rings?

Answer 44

Eng-gap clearance Tension Side clearance

Question 45

Why should compression rings be staggered?

Answer 45

To minimize leakage