Stratified Charge DI with EGR

[Bernd Felsche]

Mike writes:
>At 11:59 PM 11/3/2000 +0800, Bernd Felsche <bernie at perth.dialix.com.au> wrote:
>>Nor do you have stratified charge, or direct petrol injection one
>>would assume.

>mmm Are you implying this flybywire system is only direct injection, I

Only in terms of running at WOT for low loads.

>seem to recall volvo did something in that area early 80s but with
>port injection - though they did claim high NOx reductions but I also
>seem to recall they had a RF type ignition system duration which lasted
>throughout the whole downstroke and part of upstroke...

Probably extreme lean-burn with limited stratified charge.

>>>In the event the engine is undersized/powered in comparison with an AFM
>>>or MAP only setup then I suppose there is value - but are you saying with
>>>this fly by wire that gradual pedal pressing under load by human can result
>>>in wide open throttle plate by fly-by-wire.

>>Up to a certain load, the engine operates in stratified-charge, lean
>>burn, with the throttle wide open. Yes; a slight depression - i.e.
>>low torque demand - results in WOT and a lean-burn cycle. 

>During this time whats the estimated EGR rate - approximate ?

I would *guess* well in excess of 10% to achieve the desired NOx
reductions.

>>Note that the semantics of the pedal have changed; the driver
>>determines the torque output, not the throttle opening. So if you
>>keep pressing further, the engine will switch to homogenous
>>operation and start throttling airflow - though you'd probably be
>>hard-pressed to pick the transition.

>mmm Understood.

>>There are a few recent SAE papers; I don't have the funds to
>>undertake all the research in that direction. Interesting though it
>>may be. The first car to employ Bosch MED7 is the VW Lupo FSI.

>do you know when this came out ? Isn't it Bosch that also did some

1999. In production this year.

>work in early 80's on injection cycling with italian taxi cabs ?

I don't know.

>ie. Defer one injection from time to time but keep valve ops the same
>on a 4stroke - the compressed air and heat from previous cycles was
>enough on certain load ranges so the effect was not noticeable, saved
>10-15% depending on the driver - narrow range of operation, no cat IIRC.

Research into cylinder un-loading has been done for a long time.
The need to keep the cylinders at operating temperature is of
concern. There are mentions of the technology in the Bosch
instruction books on Motronic (I think), etc, as well as other Bosch
literature.

>>Very much leaner than stoich - Bosch describes mixtures as lean as
>>2.5; any leaner than 1.5 and stratified charge operation leads to
>>soot formation; any leaner than 1.3 in homogenous mixture formation
>>and ignition can fail, leading to a prohibited band of AFR which the
>>engine management system must skip on the load transitions.

>Sorry not with you on the numbers/terminology, in respect of AFR of 14.7
>to 1 stoich whats the 2.5, 1.5, 1.3 refer to in relation to AFR ?

Those are lambda values where 1 == 14.7:1 AFR

>>[In fact, the nature of the NOx storage cat (which stores the NOx as
>>nitrates) requires that the engine periodically switch from
>>lean-burn (LB) to homogenous so that sufficient CO is generated to
>>allow the reduction to N2 and CO2 to take place. This switching is
>>transparent to the driver as the ECU knows how to switch from LB and
>>back without any change in engine torque.]

>Did they use a deeply porous cat with rather more Pd or back to the
>Rhodium/Platinum mix ?

Don't know (yet) except that there's a separate NOx storage cat
which stores the NOx emissions as "nitrates" on the surface until CO
becomes available to allow the reduction. It appears that the ECU
monitors the NOx levels downstream of the storage cat and switches
out of LB when a threshold is reached. I don't know of further
details of the chemistry.

There's a tech-brief online and paper (1999-01-1284) available
either for download or in a compendium "Gas Direct Injection
Aftertreatment and Exhaust Aftertreatment Modeling" (SP-1455) on the
SAE web site - search for MED7.

-- 
Real Name: Bernd Felsche
    Email: nospam.bernie at perth.DIALix.com.au
     http://www.perth.dialix.com.au/~bernie - Private HP
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