Date: Mon, 13 May 2002 07:52:13 +0100
From: "Andrew Hookins" <andrew.hookinsnopsamamnopsamodata.co.uk>
Subject: Re: My dealer hasn't got a clue, can you help? ('97 9000 Aero, Manual)


Dave, I think the short answer is that water injection is more fuel effecient using this scheme, but that conventional ignition mapping methods actually reduce fuel efficiency when water injection is used. I don't know how far SAAB have taken this scheme in T5 or new T7 ECUs. My interpretation of this paper is that water injection increases inlet manifold pressure and that a conventional MAP sensor based ignition advance/retard scheme would retard slightly to compensate for a perceived increase in engine load. This action actually reduces engine torque further because the humid air burns/ignites later than a dry air/fuel mixture. However, using this scheme to sense when peak cylinder pressure is achieved and using this to advance the ignition timing to compensate for the slower ignition/burn characteristic of the humidified air/fuel mixture actually increased engine torque by a couple of percent. Perhaps re-posting this under a different heading would give rise to an interesting thread, but for now I'm just happy that this is my first posting that someone has found interesting and that hasn't killed the thread stone dead :-) AndyH <davehinznopsamcop.net> wrote in message news:abdshj$hg4gs$3nopsam34476.news.dfncis.de... > Someone who looks an awful lot like Andrew Hookins <andrew.hookinsnopsamamnopsamodata.co.uk> wrote: > > Lee Marshalls, > > > My finger in the air guess is a pressure leak causing the ECU > > to either get an incorrect manifold pressure indication, or > > something preventing the wastegate working properly. > > One would hope they've checked for leaks in the components and ducts, but > yes, false air would cause all sorts of odd problems. Given all > they've changed, though, well I'd hope that's unlikely this far > in to the exercise. > > > Dave Hinz, > > > Have a look here to see how the DI cartridge / spark plugs are > > used sense what is going on in the combustion chamber: > > > http://www.vehicular.isy.liu.se/~larer/Projects/main.html > > Cool, thanks. It's even in English, which makes it a bit easier > to read. > > > Interestingly this control scheme can actually actually adapt to > > changes in air humidity because it can 'measure' when peak > > pressure occurs. > > I've just done a very cursory read, but am printing it out for > study. A question - is this how it's done in, say, the T7 ECU? > My initial thought is that I wonder if this means water injection > would be more, or less, effective using this sort of an engine > management system. > > Thanks for the link, Andy. > > Dave Hinz >

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