[Diy_efi] Intro, and q's about fuel economy

[Bernd Felsche]

On Mon, Dec 16, 2002 at 10:49:27AM +0100, Alexei Pavlov wrote:
> pedward at apsoft.com wrote:

> > > What the EGR really does is reduce the pumping losses at
> > > cruise due to throttling.

> > It's simpler than that.  The exhaust gases already have fuel in
> > them to some degree.  You recycle that in place of actual fuel.
> > The only way to eliminate throttle losses is to have no throttle
> > at all.  You then do the throttling via modulation of the valve
> > timing.

> Could you explain why there are no pumping losses with variable valve
> timing or clearance ?
> I see variable valves exactly like throttles, the piston still has to
> pump the vacuum to reach the BDC. The energy loss is still here.

Using the valves to throttle the flow has different effects on the
flow. It's still throttling; i.e. restricting.

The main difference is that with variable lift, that the gas flow
speeds through the valves is higher and this results in greater
swirl and filling of the chamber.

Further; the flow upstream of the valve is unthrottled, so it's at
atmospheric pressure or greater, even when not supercharged. In
essence, the vacuum the piston has to draw is out of a smaller
volume; the cylinder itself instead of the whole inlet tract.
(A bit of a simplification, but it helps to draw the mental
picture.)

The main benefit is response to changes in "throttle".

-- 
/"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
\ /  ASCII ribbon campaign | I'm a .signature virus!
 X   against HTML mail     | Copy me into your ~/.signature
/ \  and postings          | to help me spread!

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi