Question

According to the valve adjustment diagram in gasoline engines, explain the following by stating on the figure. Intake valve opening, before 15o (top dead spot), Intake valve closing after 47o (bottom death spot), Exhaust valve opening before 41o (bottom death spot), Exhaust valve closing after 10o (top dead spot), Ignition advance before 15o (top dead spot)

Answer 1

Hey see the figure for reference below. The valve timing diagram, as shown we see that the inlet valve opens before the piston reaches
TDC or in other words, while the piston is still moving up before the beginning of the suction
stroke. Now the piston reaches the TDC and the suction stroke starts. The piston reaches the
BDC and then starts moving up. The inlet valve closes, when the crank has moved a little
beyond the BDC This is done as the incoming charge continues to flow into the cylinder
although the piston is moving upwards from BDC Now the charge is compressed (with both
valves closed) and then and temperature) push the piston downwards with full force and the
expansion or working stroke takes place. Now the exhaust valve opens before the piston again
reaches BDC and the burnt gases start leaving the engine cylinder. Now the piston reaches
BDC and then starts moving up, thus performing the exhaust stroke. The inlet valve opens
before the piston reaches TDC to start suction stroke. This is done as the fresh incoming charge
helps in pushing out the burnt gases. Now the piston again reaches TDC, and the suction stroke
starts. The exit valve closes after the crank has moved a little beyond the TDC. This is done as
the burnt gases continue to leave the engine cylinder although the piston is moving downwards.
It may be noted that for a small fraction of a crank revolution, both the inlet and outlet valves
are open. This is known as valve overlap.

This is the complete explanation why and which valve will open early or closes late. The values of time i.e angles is depends on various parameters and actually varies from engine to engine.

I hope this helps you alot to understand better.