Uber Crazy IDI to DI conversion idea.

[Greasemonkey]

If one was to run an IDI 1.6 engine without the pre-combustion chambers, would that bring it very close to being a DI? Fuel would be aimed more or less at the middle of the main combustion chamber, removing the insert would drop the compression, hopefully to not less than 18:1 and the glow plug would still be there for cold starting.

From what I understand, the reason the first diesels were IDI not DI was noise. If one could live with the noise (perhaps using 1.9L two stage nozzles would help with the noise), would this work and offer enough advantage, to the best of anyone's knowledge?

Any thoughts?

[BlackTieTD]

you're on the right track...yes that was one of the main reasons they went with pre-chambers... if not the #1 reason.

i'm no expert... but the pre chambers help mix the fuel/air and by the time you go through the trouble... why not buy a TDI engine if thats the route you want to go?

i'm not sure there will be huge gains from this, but i'd love if you'd prove me wrong.  

[janb]

well...
don't think there will be adequate 'mixing' to get an ignition flame front (inherent 'mechanical' timing of IDI compression cycle)  But it might be worth an 'experiment' if you have a scrap head.  I will guess it will not start at starter speed, and will not idle.  But if you tow it to start, and run it fast (never slow down :shock: ) it might run

You will notice the heads(DI injector location) and pistons(dished) are considerably different in the TDI, and the inj pump too,

so...  since buying that stuff is $$$
probably best to save yourself lots of time and grief, and buy a wrecked TDI (~$3000) and you should have all the stuff you need to be successful

janb

[AntonUK]

DI have swirl chamber in the piston were the fuel gets mixed and it is also injected at higher pressure and the pump timing is slightly different. I doubt you will gain any considerable (if any) results considering how much work will go into it.  :?

[Greasemonkey]

I wasn't thinking of doing an actual idi-di conversion, just maybe experimenting with it out of curiosity. If it turns out to work, it may be worth it. All you'd have to do is knock out the inserts, get a new head gasket and headbolts and away you go, fairly cheap experiment (if you have a spare head which wouldn't be that hard to get).

[Dr. Diesel]

The compression would be extremely low. The difference between head gasket thicknesses is roughly .006" (going from say a 2 notch to a 3 notch) which roughly equates to half a compression point. A big gaping hole in the head would drop it off the scale. I had an engine driving with 16.5:1 and it was terribly sluggish. Even 17.5:1 sucked. I don't think  18:1 is quite the magic number that it's reported to be.
IDI's are good engines. What the lack in efficiency compared to the DI engines can certainly be ignored in their revving potential. Even that sluggard abovementioned engine revved willingly off the deep end of the tach.

[Greasemonkey]

true, I read that thread but didn't you run yours in IDI mode, with the combustion chamber inserts in? you realise I'm suggesting removing them altogether, right?

[QuickTD]

From what I understand, the reason the first diesels were IDI not DI was noise. If one could live with the noise (perhaps using 1.9L two stage nozzles would help with the noise), would this work and offer enough advantage, to the best of anyone's knowledge?

Not exactly. The main reason for the use of prechambers was to provide the turbulence necessary to mix and burn the fuel at a rate comparable with a gasoline engine. With the fuel injection and combustion chamber technology of the time it was not possible to build a direct injection engine that would rev high enough to perform acceptably in an automotive application. Without the prechamber an IDI engine would run very poorly, if at all. Pulling the prechamber will simply give you a prechamber engine without the advantages of a prechamber, not a DI engine.