VALVE OVERLAPPING

Valve overlapping

(Four Stroke Engines)

   Valve overlap is the period during engine operation when both intake and exhaust valves are open at the same time.

  

  It is defined as the number of degrees between when the inlet valve starts to open before TDC and when the exhaust valve closes after TDC.

     

                                                    

   Valve overlap in an IC engine is used to improve the  performance of the engine.

    

     Valve overlap is very important for SCAVENGING purpose.

    

    At high speed, overlap takes advantage of the Scavenging effect.

   However, at idle and low speed, overlap will produce low  vacuum and a rough idle.

   

    The further away from TDC that valve overlap is present, the  more effect the piston motion will have on the airflow.    

  

    Early overlap may result in exhaust gasses being expelled into  the intake manifold and late overlap may result in exhaust  gasses being drawn back into the cylinder.

Refer the following links:

https://www.youtube.com/watch?v=bUqc6OuUjG0&t=38s

 Composed By:                                                            E-Mail:

R.Satheesh, M.E., Asso Prof.,            rsatheeshemail@gmail.com.