[Diy_efi] Evaporative fuel injection (evolution of the evap carby)

[Bernd Felsche]

On Thursday 23 November 2006 23:38, Mike wrote:

> Suffice it say, it achieved great emissions with no cat and the same
> or slightly better performance with substantial economy gains claimed
> of from 20 to 40% but never went further, does that sound familiar ?

Low HC is easy to achieve with lean burn (20:1). The problem that
the lean burn creates his high NOx because of the inherent high
temperature. There's also an increased propensity to knock because
of the very same high temperature.

NOx and the increased propensity to knock can be reduced by (esp.
cooled) EGR, but reducing the fresh air volume also means that the
HC will increase as it finds less O2 with which to react.

The reason why 3-way catalytic convertors came to the fore is
because they make building the engine a lot easier (and thus
cheaper), compared to lean-burn in combination with the plumbing for
cooled EGR.

The same problems are now having to be tackled with DI,
stratified-charge gasoline engines because (3-way) catalytic
convertors have very narrow conversion windows and certainly don't
like being exposed to very hot exhaust, rich in NOx exhaust gases.
They become ineffective at reducing anything.

A common approach is to introduce a NOx storage "catalyst" that's
monitored for when it's full (using a special NOx sendor) and then
purged by making the DI engine run rich with homogeneous charge for
short intervals. That inherently requires a drive-by-wire throttle
so that the driver doesn't experience unintended acceleration during
a NOx purge cycle.

There is no "magic". It's all been done before.

-- 
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