432 Q5 Class/Performance

Which of the following gives the 2-stroke opposed-piston engine advantages over conventional 4-stroke engines?

A) No need for timing belt, camshafts, or valves

B) No cylinder head that needs to be cooled, so a bigger fraction of combustion heat can be used to generate power

C) Cycle completes in 2 strokes only, so more power is produced, compared to 4-stroke cycle

• All of them
• A & B only
• B & C only
• A & C only

Scavenging (عملية الكسح) means

• the piston scavenges the exhaust out.
• the exhaust valve scavenges the exhaust out.
• the fresh charge scavenges the exhaust out.
• oil scavenges the exhaust out.

Scavenging (عملية الكسح) in the 2-stroke cycle is the equivalent process of exhaust+intake processes in the 4-stroke cycle.

• True.
• False.

In 2-stroke engines, which ports open first?

• The exhaust ports
• The intake ports
• Both exhaust and intake ports open at the same time
• It varies based on engine operation

Which of the following can be considered disadvantages of 2-stroke engines?

A) The fresh charge can never scavenge the exhaust fully effectively (i.e., some exhaust is left behind in the cylinder).

B) The fresh charge is partially mixed with some exhaust during scavenging, which impacts the combustion process.

C) A small portion of the fresh charge might be lost with the exhaust during scavenging.

• All of them
• A & B only
• B & C only
• A & C only

The 2-stroke cycle is called 2-stroke because the engine does not perform the intake and exhaust processes.

• True.
• False.

Which of the following statements are true for the top and bottom dead centers (TDC & BDC)?

(A) They are the end positions of piston stroke.

(B) They describe the minimum and maximum cylinder volumes.

(C) They are the positions where instantaneous piston speed = zero.

(D) They change depending on how fast the crankshaft rotates.

• All of them.
• A, B, C only
• A & B only
• A only

Compression ratio (r) =

• maximum volume / minimum volume
• maximum pressure / minimum pressure
• stroke volume / clearance volume
• TDC volume / BDC volume

The efficiency of an ICE is strongly dependent on its

• compression ratio
• peak cylinder pressure
• peak cylinder temperature
• stroke volume

Which engine has a knock limit on its compression ratio?

• SIEs only
• CIEs only
• both SIEs and CIEs
• neither type of engine