AME Reciprocating Engine Theory and Operation 2

Question 1

What is the purpose of valve overlap in a 4-stroke reciprocating engine?

Accepted Answer

To improve scavenging of exhaust gases and increase volumetric efficiency

Answer

To allow intake and exhaust valves to cool between opening events

Answer

To prevent valve float at high RPM power settings

Answer

To synchronize ignition timing precisely with valve events

Question 2

What does BMEP (Brake Mean Effective Pressure) represent in engine performance analysis?

Accepted Answer

An average effective pressure that would produce the measured brake torque throughout the full stroke

Answer

The peak cylinder pressure measured during the power stroke

Answer

The pressure differential between intake manifold and exhaust back-pressure

Answer

The minimum oil pressure required at maximum rated power output

Question 3

How is compression ratio defined for a reciprocating engine cylinder?

Accepted Answer

The ratio of total cylinder volume at BDC to clearance volume at TDC

Answer

The ratio of cylinder bore diameter to piston stroke length

Answer

The ratio of intake manifold pressure to exhaust back-pressure

Answer

The ratio of fuel injection pressure to induction air pressure

Question 4

What does a low manifold absolute pressure (MAP) reading at full throttle indicate on a normally aspirated reciprocating engine?

Accepted Answer

A possible induction system air leak or restriction

Answer

Normal operation at cruise altitude

Answer

Excessive fuel enrichment causing back-pressure

Answer

High outside air temperature reducing induction air density

Question 5

How does preignition differ from detonation in a reciprocating engine?

Accepted Answer

Preignition is ignition before the spark plug fires; detonation is explosive auto-ignition of the end charge after normal ignition

Answer

Preignition occurs after TDC while detonation always occurs before TDC

Answer

Preignition is harmless at normal power while detonation causes immediate structural damage

Answer

Preignition and detonation are interchangeable terms for the same abnormal combustion event

Question 6

What is the primary purpose of cylinder cooling fins and baffles on an air-cooled reciprocating engine?

Accepted Answer

To direct airflow over cylinder surfaces and maximize heat dissipation to the passing air

Answer

To reduce the overall installed weight of the engine

Answer

To reduce intake air turbulence for more uniform combustion

Answer

To dampen mechanical vibration during high-power operation

Question 7

What does a sudden, significant drop in oil pressure during flight most likely indicate?

Accepted Answer

A serious oil system malfunction such as a major leak or bearing failure requiring immediate action

Answer

The engine has reached its normal operating temperature

Answer

Normal pressure variation during a power reduction

Answer

The need to add oil at the next scheduled maintenance stop