Lecture 7: Valve Timing and Diagram

These flashcards cover critical concepts about valve timing, including the differences between ideal and actual valve timing diagrams, the functions of valves in four-stroke and two-cycle engines, and diesel fuel injection timing.

What is the purpose of valve timing in an engine?

To coordinate intake and exhaust valves with piston strokes, ensuring proper air-fuel mixture intake and exhaust expulsion.

What occurs when the camshaft lobes push against the valve train components?

The valves are forced open at the correct crank angle.

What is the ideal valve timing diagram used to display?

Valve timing in relation to crankshaft angle, ensuring maximum volumetric efficiency.

When does the intake valve open and close in a four-stroke engine?

Opens at top dead center (TDC) and closes at bottom dead center (BDC).

What happens during the actual valve timing in a four-stroke engine?

The intake valve opens before TDC and closes well after BDC, with both valves overlapping near TDC.

Why is the intake valve kept open past 180° in engine timing?

To take advantage of air-fuel inertia, improving volumetric efficiency at high engine speeds.

What does the exhaust valve being open after TDC assist with?

It assists in the scavenging of burnt gases and prevents backflow into the cylinder.

What characterizes the timing system of a two-cycle engine?

It has no specific valve train; piston movement controls the opening and closing of intake and exhaust ports.

How is the timing of the two-cycle diesel engine valve events structured?

The exhaust valve opens at 97.5° before BDC and closes at 63° after BDC, with intake occurring before the exhaust valve closes.

When does fuel injection start and end in a diesel engine?

Injection starts ~23.5° before TDC and ends ~6° before TDC at full load.