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

Bernd Felsche bernie at innovative.iinet.net.au
Mon Dec 16 15:57:43 GMT 2002


On Mon, Dec 16, 2002 at 04:36:24PM +0100, Alexei Pavlov wrote:
> bernie at innovative.iinet.net.au wrote:
> > On Mon, Dec 16, 2002 at 03:59:04PM +0100, Alexei Pavlov wrote:
> > > > Or gear it so that it is close to maximum torque load at the
> > > > design cruise speed, and then modulate power with the EGR
> > > > instead of a throttle.

> > > That seems to be a good idea. Did someone try to do that at least
> > > for a cruise control ?
> > 
> > Volkswagen and Audi use it under part-load conditions (where
> > lean-burn is possible) - the throttle is fully open and EGR,
> > along with stratified charge is used to determine engine output.

> I presume they use exhaust gazes instead of fresh air to lower 
> the NOx exhaust rate.

That's a side-effect of replacing some of the charge air with inert
exhaust gas... it lowers the combustion temperature because free
oxygen molecules are "harder to find" in the air-fuel mix - also
slowing combustion and hence also reducing tendency to knock; and
because the larger volume of gas absorbs more heat from the
combustion and compression without contributing to the total energy
inside the cylinder. 

In all three aspects; it acts as a "damper".

> And has that been used on indirect injection engines ?

Could be used in port-injection, but is of more use in DI; where
stratified charge is easier to control.

-- 
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