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

[Perry Harrington]

> 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.

The other way is to do direct injection like diesels.

> 
> Note that the Georgia overdrive approach makes the throttling losses disappear.

That approach is more gas hungry.  If you treat the motor as entirely binary
with respect to throttle/running (which I interpret your description to mean),
you incurr a hit at the beginning of each acceleration.  You could get around
this by stopping the engine at BDC on the intake stroke (valve closed) and
resume on that charge (assuming it is enough to avoid enrichment).

A more prudent design would be to add a compression release so that you can use
the vehicle inertia to start and stop the engine without any initial enrichment.

This is where a heavy flywheel would be nice.

What you want is an engine configuration that requires no enrichment (use EGR
for enrichment) and has a flat torque curve.  You can cam the little motor to
peak torque really early, but a fully variable cam timing would be the best.

They replaced the head of the engine, so in theory they could convert it
into a valved 2-stroke and make up some of the difference.  That would reduce
pumping losses and inertial losses.

In all, there are a zillion different ideas that could be tried, but in the end
it's limited by time, budget, and expertise.

--Perry

-- 
Perry Harrington			Data Acquisition & Instrumentation, Inc	
perry at dainst dot com					 http://www.dainst.com/

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin

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