Why do exhaust valves 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.
When and why does the exhaust valve open?
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.
Does the exhaust valve opens before BDC?
Exhaust valves open 40°-60°before BDC to lower the pressure inside the cylinder, before the beginning of the exhaust stroke, but avoiding, on the other hand, a heavy reduction of the expansion work.
What happens if exhaust valve stays open?
An exhaust or intake valve that is stuck open or partially open will cause a noticeable drop in cylinder compression. A zero reading in a cylinder points to a valve stuck in a wide-open position.
What happens if the valve overlap is very high or very low?
At high rpm, overlap takes advantage of the Scavenging Effect. However, at idle and low rpm, overlap will produce low Engine Vacuum and a rough idle.
What keeps the engine running faster under a load?
More air and fuel causes more energy to be released, and thus the engine provides more power to the vehicle, so if the engine has to overcome a similar amount of torque to operate, most of the increased power will go toward speeding up the egine.
When does the exhaust valve open and close?
The exhaust valve has closed just after the piston started down and the intake valve is opening very quickly. This is called the intake stroke (figure 3), where the engine “breathes” and fills itself with another charge of fresh air/fuel mixture.
How do you open the exhaust valve on a car?
Lift up the exhaust valve with the engine room crane ( which makes the valve open). Connect compressed air to the Nonreturn valve on the air cylinder. The valve should now close. By disconnecting the compressed air supply and by venting the air cylinder, the exhaust valve should open.
When does the exhaust valve open on a cam?
Since the camshaft turns at half of the speed of the crank, the power stroke only sees one fourth of a turn of the cam, or 90 camshaft degrees. As we move closer to the bottom of the cylinder, a little before the piston reaches the bottom, the exhaust valve begins to open.
Can a reconditioned exhaust valve extend the life of the engine?
These occasionally get trapped under the valve seat and cause pitting. The life of an exhaust valve between reconditioning can be extended if the thermal loads to which it is subjected can be evenly distributed around the valve. This is accomplished by the rotating the valves slowly as the engine is working.