Stratified Charge DI with EGR

[Mike (Perth, Western Australia)]

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
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...

>>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 ?

>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.

>>70% EGR does sound awfully high though, any observations that this is
>>used on turbo engines. And on the n/a ones is there much attention to
>>EGR cooling ?
>
>Sorry, I mis-read the section (it's quite a lot crammed into a few
>pages) - it's a 70% reduction in NOx via EGR - No actual rate of EGR
>is given other than being high.
>
>>By the way whats does conventional "WOT" stand for ?
>
>Wide-Open-Throttle; implying maximum torque demand.
>
>>The stability and PID equations must be interesting ;-)
>
>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
work in early 80's on injection cycling with italian taxi cabs ?
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.

>>This sounds bizarre, especially as I would have expected AFR to be kept
>>as close to stoich (or slightly) lean unless its a diesel...
>
>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 ?

>[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 ?

>Direct injection allows injecting the fuel immediately before the
>spark (during compression) so that an ignitable mixture surrounds
>the plug. The lower the load, the less the fuel injected, always
>finishing just before the spark - I guess to ensure a dense mixture
>cloud to light.

I see, use the cloud around the plug burn to compress/charge the lean
air reducing HC's etc...

>>Can you please clarify particularly this last paragraph of yours ?
>
>Hmmm. I'd like to order a few of the tomes of SAE papers on DI and
>EGR over the past few years first. Unfortunately, it adds up to many
>hundreds of US dollars, which is probably better invested in me
>exploding microcontroller chips as a hobby.

mmm me too :)


Rgds


Mike Massen

Ancient Sufi saying:
        "Should your God save you from adversity, choose another God"

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