[Diy_efi] Re: Diy_efi Digest, Vol 31, Issue 29

ian spyro
Mon Oct 1 09:42:12 UTC 2007

On Mon, 2007-10-01 at 17:34 +1000, Bill Washington wrote:
> Buck,
>     Good on you, a little contentment with what we have achieved can 
> often save a lot of pain ....... and expense! Happy motoring!


> Back to diesels.....
>     The latest generation of diesels gain their economy and the 
> potential to produce a lot more power because of the ultra high 
> (dangerous) pressure common rail/ electronic injection. This produces 
> much finer atomisation, and thus much more complete burning - ie burning 
> much more of the fuel and spitting less of it out the exhaust.

I *somewhat* would dispute that. My little diesel is indirect, and
manages better economy than many of the production common rails that are
20 years its junior.

The key is that whilst the new diesels get similar or slightly worse MPG
figures, they are a HELL of a lot more powerful.

>     Ian, did you say you were wanting to incorporate this into your 
> 'new' engine intended to get the 'works'?

I'd love to but...

>  - that would be an extremely 
> interesting project - I would love to add common rail injection to my 
> old 2.3l and 2.5l Peugeot diesels - unfortunately they are indirect 
> injection engines - ie there is a spherical combustion chamber set into 
> the head, and this contains the glowplug and injection point.

And that is the problem - I've spoken to some experts on this and the
biggest problems are:

1) There isnt a (modern) common rail injector on gods green earth thats
even remotely similar in size/shape to the old types

2) Common rail injectors have a very wide (almost 180 degree) spray
pattern, more a fan than a cone. Im informed that putting this into a
combustion chamber would very quickly erode away the combustion chamber
insert walls, then followed by the head.

And then...

>  The piston 
> at TDC comes within a gnat's whisker of the head - the only thing that 
> stops them hitting is the head gasket - the piston (flat top) protrudes 
> above the top of the block at TDC and the head is dead flat

Yes, same on mine - pistons rise above the deck. the tolerance is

I suppose thats the one thing thats easily fixed, you could install
shorter rods, or pistons with higher wrists or something.

I suppose technically, one could do that and machine up 'fake'
combustion chamber inserts (or fill the holes with weld) so that a DI
injector would go through and poke out into the combustion chamber...

Actually, that sounds like a scarily simple way to do it. You bastard, I
though I had this project all worked out ;-)

I'll have to do some thinking on this now :)

That said, Im still gonna be stuck with a non-crossflow SOHC head and it
kinda detracts from the 'charm' of the engine...

>  ..... valve 
> timing, therefore, is also critical to avoid piston and valves meeting, 
> and making expensive noises! .... but still it would be nice to add 
> common rail.... if only I could afford it and source the parts, 
> including the computer to drive it! ... I'll dream on!

I wouldnt have thought the computer would be hard to build - after all,
it would probably run with a single pulse at TDC, although granted that
wouldnt be optimal... you could just trigger it with a hall effect
sensor and a A/B/G timing type setup...

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