MDE 3 Q4

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Meaning and Purpose of Valve Overlap

Question: What does the term "valve overlap" refer to, and what is its purpose in an engine?

A) Valve overlap refers to the period when both the intake and exhaust valves are closed to maximize compression. Its purpose is to prevent exhaust gases from entering the intake manifold.

C) Valve overlap refers to the period when the intake valve opens before the exhaust valve closes. Its purpose is to reduce engine noise and vibration.

B) Valve overlap refers to the period when both the intake and exhaust valves are open simultaneously. Its purpose is to enhance the engine’s performance by improving the scavenging of exhaust gases and increasing the intake of fresh air.

D) Valve overlap refers to the time when only the exhaust valve is open. Its purpose is to decrease the engine's fuel consumption.

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1. Valve Operation during the Intake Stroke

Question: In a four-stroke engine timing diagram, what happens to the intake valve during the intake stroke?

D) The intake valve is closed, and the fuel valve is open

B) The intake valve is open to allow air-fuel mixture into the cylinder

A) The intake valve is closed, and the exhaust valve is open

C) The intake valve is partially open while the exhaust valve is closed

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4. Valve Operation during the Exhaust Stroke

Question: What is the position of the valves during the exhaust stroke in a four-stroke engine timing diagram?

B) The intake valve remains closed, and the exhaust valve opens

C) Both the intake and exhaust valves are open

D) Both the intake and exhaust valves are closed

A) The intake valve opens, and the exhaust valve closes

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3. Valve Operation during the Power Stroke

Question: In a four-stroke engine timing diagram, what occurs with the valves during the power stroke?

C) The intake valve remains closed, and the exhaust valve remains closed

B) Both the intake and exhaust valves are open

D) The intake valve is closed, and the exhaust valve opens

A) The intake valve opens, and the exhaust valve remains closed

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Four-Stroke Timing Diagram

Question: What does a four-stroke timing diagram illustrate?

C) The fuel consumption rate at different engine speeds

A) The sequence of fuel injection and ignition events

D) The temperature variations of the engine during operation

B) The synchronization of valve openings and closings with the piston positions during the four-stroke cycle

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6. Timing of Valve Openings and Closings

Question: How is the timing of the valve openings and closings shown in a four-stroke timing diagram?

B) As overlapping lines representing the duration each valve is open or closed relative to the piston position

D) As a sequence of numbers representing engine RPM

A) As a series of graphs showing fuel consumption rates

C) As numerical values indicating the temperature of the exhaust gases

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5. Timing of Fuel Injection

Question: In a four-stroke timing diagram, when does the fuel valve typically operate?

A) Just before the intake valve closes and the compression stroke begins

D) Just after the exhaust valve opens and before the intake valve opens

B) During the power stroke

C) During the exhaust stroke

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2. Valve Operation during the Compression Stroke

Question: What is the position of the valves during the compression stroke in a four-stroke engine timing diagram?

C) The intake valve is open, and the exhaust valve is closed

D) The intake valve is closed, and the exhaust valve is open

A) Both the intake and exhaust valves are open

B) The intake valve is closed, and the exhaust valve is closed

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