engine efficiency related

[johnab]

As the pistion accelerates downward and air will drawn to cylinder will cause a presseure depression behind the valve.The pressure depression travels away from the valve at the speed of sound and reflected at the open end with 180 degree phase difference. Pressure pulse will arrive back around Intake valve closting time & helps to boost more air.

(1)Now, my question is to optimize volumetric efficiency, why its required to adjust only clean side of duct rather than dirty side of duct?

(2) 180 phase difference can only occur when the pressure wave comes to contact with atmospher & that is only possible at dirty side of duct. (opening to atmosphere)
so is it OK if we adjust length of any component between valve and dirty side of duct to optimize volumetric efficiency?

 

[GregLocock]

(1) the filter box decouples the dirty side from the valve

(2) doesn't make sense to me

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[johnab]

Regarding 2nd question from above post

The question was raised because - to increase the volumetric efficiency, we need to boost more air at the valve closing time that requires keeping specific length of intake (considering sound speed 1343 fps).

Assume it takes 0.015 seconds between when the valve closes and when it opens again. At 1,300 fps x 0.015 sec = 20 feet wave will travel. But the wave need to come back so it should travel around 10 feet and due to packaging issues we keep it around 1/4 th or 1/3 of 10 feet = 2.5 feet length of duct.

(1) So can you explain me what makes wave to travel back?

(2) Or can you direct me the specific location where the wave is hitting & travels back towards valve?

 

[SomptingGuy]

(2) You'll get a reflection at any area change. The entrance to the filter box has normally quite a big area change. Likewise the entrance from the runners into the manifold.