Why does the exhaust valve open before BDC?

Why does the exhaust valve open before BDC?

The gases inside the cylinder posses a higher pressure even after the expansion stroke. Thus the exhaust valve is made to open before the piston reaches the BDC thus enabling the gases to escape outside on its own and the remaining gases are pushed out by the upward motion of the piston.

Why does the exhaust valve open early?

It is confirmed that opening the exhaust valve earlier increases the exhaust gas temperature, and hence lower EGR flow rates are needed to improve combustion efficiency. Performance of the DOC was drastically improved and higher amounts of unburnt hydrocarbons were oxidized by increasing the exhaust gas temperature.

Why is the exhaust valve opened before the power stroke is completed on a 4 stroke cycle engine?

On the power stroke, the combustion pushes the piston down in the cylinder. During this stroke, it is necessary to open the exhaust valve before the piston gets to the bottom of the cylinder. This will allow the excess pressure in the cylinder to “vent out” just before the piston reaches the bottom of the stroke.

Why do exhaust valves close after BDC?

The exhaust valve closes after TDC so that some exhaust gas will also be sucked back into cylinder. In this work, the intake and exhaust valve lifts were reduced to 3 mm to avoid the contact of the piston and valves at TDC during gas exchange.

How do intake and exhaust valves open and close?

As the pushrod rises on the cam it pivots the rocker arm, which pushes the valve down (open) against the pressure of its spring. As the cam lobe rotates further, the valve spring acts to close the valve. If the gap is too large, the valves open late and close early, reducing power and increasing engine noise.

Why does the intake valve open before TDC?

The inlet valve usually opens few degrees before the piston reaches TDC in its exhaust stroke. This is because the downward movement of the piston creates the vacuum (or negative pressure) in the cylinder and the air-fuel mixture gets filled in the empty space.

What happens when the exhaust valve opens before BDC?

In the exhaust stroke, the piston again moves upwards; pushing the exhaust gas out through the open exhaust valve. The exhaust valve opens before the piston reaches BDC in its power stroke. As the exhaust valve opens just before BDC, it causes some of the pressurized exhaust gases to escape even before the piston starts it’s upwards stroke.

How does the piston move up from BDC to TDC?

Piston moves up from BDC to TDC. Exhaust gases are pushed out of the cylinder. To know the details about the four strokes of the IC engine click here. The Actual Valve Timing Diagram has slight variations with respect to the Theoretical Valve Timing Diagram. The variations are made in order to maximize the engine performance.

When does the exhaust valve of a diesel engine open?

So the valve opens after BDC of power stroke when piston starts pushing the spent charge out and remains open till TDC of suction stroke. In some high speed engines, the valve timing for exhaust valve is advanced to allow to overcome spent charge inertia.

When does the inlet valve open and close in an engine?

The inlet valve usually opens few degrees before the piston reaches TDC in its exhaust stroke. It closes after quite a few degrees of piston reaching the BDC, i.e. when the piston starts to move up the cylinder in the compression stroke.