Reciprocating Engine Theory and Operation Flashcards
7 cards from real AME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Reciprocating Engine Theory and Operation flashcards as text
What is the purpose of valve overlap in a 4-stroke reciprocating engine?
Answer: To improve scavenging of exhaust gases and increase volumetric efficiency
Valve overlap — both intake and exhaust valves briefly open simultaneously near TDC — allows outgoing exhaust gases to help draw in fresh charge, improving cylinder filling.
What does BMEP (Brake Mean Effective Pressure) represent in engine performance analysis?
Answer: An average effective pressure that would produce the measured brake torque throughout the full stroke
BMEP is a calculated mean pressure that, if acting constantly throughout the entire power stroke, would produce the same torque measured at the crankshaft, enabling comparison across engines of different displacements.
How is compression ratio defined for a reciprocating engine cylinder?
Answer: The ratio of total cylinder volume at BDC to clearance volume at TDC
Compression ratio equals the total cylinder volume when the piston is at BDC (swept volume plus clearance volume) divided by the remaining clearance volume at TDC.
What does a low manifold absolute pressure (MAP) reading at full throttle indicate on a normally aspirated reciprocating engine?
Answer: A possible induction system air leak or restriction
On a normally aspirated engine at full throttle, MAP should approach ambient pressure; a significantly lower reading indicates an induction system leak or obstruction preventing full atmospheric pressure from reaching the intake.
How does preignition differ from detonation in a reciprocating engine?
Answer: Preignition is ignition before the spark plug fires; detonation is explosive auto-ignition of the end charge after normal ignition
Preignition is caused by hot carbon deposits or incandescent spots igniting the mixture before the spark plug fires, while detonation is the explosive auto-ignition of the unburned end charge after normal spark ignition has occurred.
What is the primary purpose of cylinder cooling fins and baffles on an air-cooled reciprocating engine?
Answer: To direct airflow over cylinder surfaces and maximize heat dissipation to the passing air
Baffles channel ram air tightly around the cylinders while fins dramatically increase the heat-transfer surface area, together maximizing the rate at which combustion heat is removed.
What does a sudden, significant drop in oil pressure during flight most likely indicate?
Answer: A serious oil system malfunction such as a major leak or bearing failure requiring immediate action
A sudden oil pressure drop can indicate catastrophic oil loss, pump failure, or bearing failure — any of which can cause rapid engine destruction and require immediate emergency action.