Alternative to O2 injection, EGR? (Re: DIY_EFI Digest V5 #34)

Charles A. Fair chuck at
Sun Jan 30 17:25:44 GMT 2000

Hunt David wrote:

> Since the spend gas is added after the throttle plate the total gas in the
> combustion chamber is increased as compared to no recirculation. Thus the
> "dynamic" pressure (effective compression ratio) is increased.  At part
> throttle the chamber certainly doesn't fill due to the restriction of the
> throttle and the dynamic compression ratio is quite small, so even a small
> amount of recirculated gas increases the dynamic compression ratio.  It also
> increases the preignition temperature (promoting better vaporization
> (mixing)), and provides a (relatively) cooling effect for pockets of
> "leanness" reducing the possiblity of detonation.  REDUCING.
> That "leanness" might be caused by fuel dropout which means that the oxygen
> rich, low fuel (lean) areas will also have a lot of recirculation gasses.
> Win - Win - Win - Win situation, quite ingenous actually.

My question is, can EGR be used as a substitute to O2 injection for knock
suppression?  My mechanic friend warned me about O2 injection, that it will tend
to remove the oil from the cylinder walls and on the valve stems.  Supposedly it
will cause rapid engine wear, i.e. cylinder taper and stem wear.

My application for the use of EGR for knock suppression is with my turbo
engine.  The 4G63 turbo can put out over 450 hp without opening up the engine,
only bolt on parts.  3200lb cars have gone 11.4 sec 1/4th mile runs with 40,000
miles on them and over 400 1/4th mile passes, without ever having had the head
removed.  This is attainable in a STREETABLE car, capable of 28 mpg on the
highway.  Oh, you'll break stuff, like driveline parts, other than the engine
when dragging:)

The engine is a 2 liter 4 cylinder dohc 4 valve per cylinder utilizing
additional oil jets under the pistons in turbo form.  In stock form they put out
97.6 hp per liter or 1.63 hp per cubic inch.  In modified form that's 225 hp per
liter or 3.78 hp per from my earlier example...  If built up, one on a
chassie dyno put out 600 hp, 300 / liter, 5 per cu. in.

The reason I have illustrated this is in an engine with high volumetric
efficiency and working on the fringe of performance, I believe might benefit
from using EGR when under boost or/detonation might allow higher boost pressures
to be obtained without race gas.  For instance the limit with a stock turbo is
18 on a 1st gen. DSM with an upgraded fuel pump running 93 octane pump gas.
Yes, I am aware boost pressure does not equal lb. per hour of air flow, but in
my example it generally works out that way, over 18 psi = melt piston/valve.

I want a Win - Win situation with detonation suppression.  Water injection does
cause suppression, but kills hp.

Can EGR help under high boost conditions to prevent detonation, and not cause a
loss of HP, or would it just cause higher EGT, reducing thermal efficiency, in
the process killing HP.  The proverbial throwing the baby out with the bath

Chuck Fair.

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