ID-DI crosbreed engine thoughts

[greg123]

Hi guys,

Been having some wild thoughts again on other forums and thought I would run it by you.  I was thinking if it was possible to make a half way house between an IDI engine and a DI engine, particularly with alt fuel in mind.

IDI motors and the Elsbett specifically designed vegoil motor (a DI motor, but with an almost IDI like sphere in the piston rather than just a recess) like a sphere for fuel to be injected in, say it's good for mixing too.  They also say for vegoil in particular, a good 'lip' eg a hole in the top of a sphere, as opossed to a can with no end, stops partially burnt fuel heading right for the cylinder walls and improves efficiency and combustion as keeps combustion in the centre of the sphere more.

So....

I know we can't make an IDI a DI without a different head, but how about taking the philosophy that it doesn't matter if the combustion chamber is in the head or the piston, if we use DI style injectors with atomisation a lot better and open up the pre-comp chamber to give a 17:1 or so compression and open up the tiny IDI intake port to make a good sized opening but still retaining a lip (the opening being maybe half the width of the sphere) then pumping losses would be down to more or less DI levels and friction too.

We wouldn't need to open it as wide as they did, but here is a pic of the chamber in the Elsbett piston - imagine that in our head instead:



As it's in the head it would be a bit more gentle than a DI and retain some of the ID drivability and higher rpm, and also the suitability thanks to the 'lip' and sphere construction to be used with oil/biofuel.

I have NO idea what injector nozzles could be used, I have been unable to find a good website with lots of spray patterns.  Opening up the pre-comp chamber and porting a larger intake/exit (still pointing toward the middle of the piston some, as the chamber is ofsett unlike in the piston where it's in the middle) wouldn't be impossible to do.

Ceramic coating could help with reducing heat loss to the head/piston and hopefully a better atomising di style injector at higher pressure would allow it to run okay, just like a di does under similar conditions.  We may actually have a bit more swirl going on than a DI does (and they manage fine) but obviously not as much as in the current, albeit restrictive, setup.  So without better injection it might not like running as well, Di's didn't really come on till injection pressures and atomisation from the nozzle went up - don't have to churn up the mixture so much then.

Throw in some 2 stage injectors to allow the pilot injection to get things cooking and the temp up before the main charge hits and I think we'd have a smooth engine with DI efficiency, but more suitable to higher rpm, more boost and alternative fuels.

Just a thought....  Now hypothetically attack my idea...  

Greg.
PS if anyone has links to injector spray patters and nozzle types, I'd love a link.

[saurkraut]

As a quick test, take out the swirl chamber covers, bolt 'er up and see if it runs.

Let us know what happens.

[greg123]

The thought had crossed my mind, but it also crossed my mind that the change is MASSIVE, about halves the C/R and may not run....  I'd try it for a laugh though.  

Anyone else actually done this, just to see if it would run?  I have no doubt if it did it wouldn't run well...   :shock:

As a quick test, take out the swirl chamber covers, bolt 'er up and see if it runs.

Let us know what happens.

[jtanguay]

i think the DI lower revs are related to high injection pressures.  i wonder if adding a counterweight flywheel on the injection pump sprocket would help smooth out the higher rpm's like on 5 cyl TDI pumps.

[burnt_servo]

funny i was thinking something similar  this morning .......

what not take a tdi bottom end , add a  1.6 idi head and  pump and turbo ?

might have to add a grid type heater ( ie cummins )  to help the glow plugs out due to the lower compresion .

might have to deck the head and block to raise the compresion a bit ( the gains would be small , but might make a difference ) .

but retain the older style  1.6 injectors , this way the burning / unburnt fuel won't go straight to the cylinder wall , but rather into the piston chamber first , then get deflected upwards creating more turbulance , and creating a more complete burn .

[jimfoo]

That would reduce the CR by more than half. You can't deck the block as the pistons would then hit the head. Decking the head with no chambers might gain a little CR, but then the valves would have to be countersunk or risk hitting the pistons. Doing it with the chambers in would gain about nothing. With two chambers you will also be losing a ton of heat, so there goes your efficiency.

[greg123]

Pass on that!  Even with stock di pressures it's fine to 5k anyhow, this doesn't have to be a mega rpm motor.

i think the DI lower revs are related to high injection pressures.  i wonder if adding a counterweight flywheel on the injection pump sprocket would help smooth out the higher rpm's like on 5 cyl TDI pumps.

[greg123]

Interesting idea, but as Jimfoo says the CR would be WAY down, also you have the issue that due to the piston bowl and lack of time not much air would get up the restrictive port into the pre-comp.  You would likely not get enough heat in there to get an ignition.

I have heard of a sort of similar thing though, where passages and grooves were machined to guide the flow from the pre-comp across and out over the piston - more radical than the usual slightly indentations.

My idea here would have no greater surface area than a di, hopefully not much more friction thanks to much larger entry port but a more IDI-like combustion with a bit better mixing thanks to the sphere and lip.  Of course all that's a theory and relies I guess on better injection atomisation to get it cooking, no idea if something suitable would do that job.

Greg

funny i was thinking something similar  this morning .......

what not take a tdi bottom end , add a  1.6 idi head and  pump and turbo ?

might have to add a grid type heater ( ie cummins )  to help the glow plugs out due to the lower compresion .

might have to deck the head and block to raise the compresion a bit ( the gains would be small , but might make a difference ) .

but retain the older style  1.6 injectors , this way the burning / unburnt fuel won't go straight to the cylinder wall , but rather into the piston chamber first , then get deflected upwards creating more turbulance , and creating a more complete burn .

[burnt_servo]

lets see....... ways to increase the compression ......  

decking the head ... worth a bit but not nearly enough alone .....

decking the block , thus raising the pistons above the deck , then having to toss the pistons into a lath to cut the tops down a bit to maintain clearance between the head and valves .....

offset grinding the crank journels , take a standard bearing sized crank , and grind it to the smallest bearing size available , BUT only a couple thou is taken off one side , and everything else is taken off the other , thus increasing the stroke , and pushing the pistons higher above the deck line , resulting in having to take more off of the tops of the pistons for clearances , but making the bowl in the pistons smaller .

longer rods ... expensive , and still have the piston clearance issues ....

custom pistons .....  expensive , but possibly the easiest .
are there different sizes of bowls for different years of tdi engines ?

what about cutting  shallow bowls into  stock idi pistons ? possibly the easiest and cheapest route .

messing with the precombustion chambers , maybe reducing their  volume .

larger valves .... will take up more area in the combustion chamber if not sunk into the head .

need at least 15 to one to get it to light ( it's possible with less, but would be too much of a pain in the ass )  , but that would also include glow plugs and a modified cummins grid heater ... AND a huge battery .

the easiest way to figure out if it might work is to mock a engine up and measure the cranking presure .

[greg123]

Yeah, I have a idi motor + a couple of spare engines, one bigger cc, so stuff to mess with.  Maybe if I use the steel gasket and keep it all clean I can re-use the gasket, at least to do running tests - also need some head studs as this motor (not vw) is stretch bolts.  And time.  And some money.....

Annoys me that I can do all sorts with the computer and the internet but bits of info like a database of bore centres, pictures of nozzle spray patterns, manifold bolt patterns etc... all hard to come by. As is a simple working model of an engine that we can 'mock' and 'alter' on the computer...

Greg.

the easiest way to figure out if it might work is to mock a engine up and measure the cranking presure .

[burnt_servo]

funny thing is , most of the guys i know who have that kind of info , are not overly computer savvy , or don't have to the time to post info / greate websites and programs ...  ect.....


i'm really starting to think using a 1.9 idi psitons with a shallow  bowl cut into it might be worth exploring ....

just need a piston to see how much might be removed to create a bowl .

[jimfoo]

The total thickness of the piston top is 1.75mm, though I don't know how much has to be there for strength.

[burnt_servo]

The total thickness of the piston top is 1.75mm, though I don't know how much has to be there for strength.

your kidding ..... that is it

i've seen motorcycle and  many gas engine pistons much thicker than that .

[greg123]

Oops that's not good.... no machining there then :-o

The total thickness of the piston top is 1.75mm, though I don't know how much has to be there for strength.

[jimfoo]

I meant cm, not mm :oops: