pressure wave in intake system?

[par1]

The Volumetric efficiency can be maximized by increasing pressure in the intake port at around Intake valve closes?

(page 102 from Vehicle Refinement Controlling Noise & Vibration in Road vehicles by Matthew Harrison)

By choosing the a suitable primary length one can phase the pressure peak to arrive back at the valva around Intake valve closes (page 103 of same book , 2nd paragraph)

But, what I read from different website is "If the intake runner is just the right length, that pressure wave will arrive back at the intake valve just as it opens for the next cycle. This extra pressure helps cram more air-fuel mix into the cylinder -- effectively like a turbocharger."

Can anyone explain me how does the theory related to noise attenuation, duct length & volumetric efficiency is related?

Thnks

 

[GregLocock]

For a quiet intake you want cancellation at the end of the intake tube, where it meets the atmosphere.

For a high VE you want positive reinforcement of the pressure wave when the valve is open.

Your job is to develop a system that fulfils both of these - simplified because the plenum somewhat isolates the manifold from the intake tube and vice versa.

In practice this is far too big a subject to be covered in a dscussion forum, you need to buy books, read papers, and start calculating and measuring.


Cheers

Greg Locock

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

 

[par1]

I definitely understand this topic require lot of other material & currently working on it but,
getting confused with two contradict statment that maximize volumetric efficiency by increasing pressure at the intake valve closing & other is need postive(high) rainforcement of pressure when intake valve open as need to boost more air.

(1) So what is the correct statment?

(2) or does it mean to have more preesure is necessary when intake valve closes (Ram effect) to get more pressure when intake valve open?

Thank you for time,

 

[SomptingGuy]

A good primer is this book if you have money to spend is:

Theory of Engine Manifold Design: Wave Action Methods for IC Engines
D.E. Winterbone, Richard Pearson

ISBN: 1860582095


(note that I am not in any way affiliated with the authors)

 

[Rob45]

For maximum power output, you want the refelected pressure pulse to arrive at the intake just as it is opening: this coincides with the brief overlap period when both intake ans exhaust valves are open, and provides improved scavenging, or removal of the exhaust gas, as well as getting the intake charge moving into the cylinder.

A great deal of work on this topic, though focused more on two-stroke engines, was done some years ago at Queens University, Belfast, by Gordon Blair.

 

[facty]

Greg is right - there is a lot of reading to do to fully understand this topic. Rob45 is also correct and Blair's book on the "Design and Simulation of 4-Stroke engines is very good reading.

Just a short point on the contradictions posed by the instigator of this post: In some high performance engines you will find that, just before intake valve closes, some fresh charge is expelled back into the intake port due to the cylinder pressure rise. Ideally a plugging pulse will arrive in the intake port and push this fresh charge back into the cylinder as the valve closes!