An idea for more high-RPM power

[VWRacer]

Great post, Jake! One thing though...

This explains the existence of pre chambers in diesels, and also of the significance of the pilot injection feature (which is what VW pioneered, with Bosch's help, for their TDI motors.)

I read somewhere (TDI Forum?) that the pilot injection's function is to raise the temperature and turbulence so as to achieve more complete fuel burning during the main injection phase, and hence raise their overall efficiency.

[fspGTD]

I don't know if that's accurate... it doesn't jibe with what I remember reading in the TDI SAE papers.  (I don't recall anything about pilot injection increasing efficiency, but it did cause a more gradual pressure rise during combustion.  By starting a "little fire" burning early in the combustion chamber before the main injection happens, the ignition delay time main fuel injection is reduced (it atomizes and begins burning quicker), and this reduces the otherwise sharp pressure rise and noise of the burning of the main injection, so pilot injection thereby "tames" the more efficient DI combustion process enough to make it suitable for use in passenger cars.)

I'll dig up that SAE paper (based on development of VW's first TDI engine...) and see what it says.

[VWRacer]

Jake, please do let us know what comes out of the SAE paper. As I said, I can't even recall where I read that, much less how accurate it might be...  :wink:

[fspGTD]

Just wanted to add to this topic that while I was browing the grant piston & rings web site, I stumbled across their "piston designs" page,
http://www.grantpistonrings.com/products/pistons/piston_styles.htm
which had this picture of various piston designs:


Notice at right, third up from the bottom is the piston that looks identical to the toyota patent, I'll bet it's from some toyota diesel engine but I'm curious to learn anything more about it.  Maybe someone up here who has a toyota diesel could look underneath their head sometime and see if this is the kind of piston it has.  (Feel free to take some detailed pictures and measurements. )  And IDI VW Diesel piston is pictured by the way at left in the bottom row.

[2446]

 Maybe someone up here who has a toyota diesel could look underneath their head sometime and see if this is the kind of piston it has.  (Feel free to take some detailed pictures and measurements. )  And IDI VW Diesel piston is pictured by the way at left in the bottom row.

I have a couple sets of 86-88 "2LT" (2.4L turbo IDI inline-4) pistons out, I will have a look at them and take some pictures if I have a chance.

[2446]

here's a picture with some rough measurments.
The piston top is just like described in the patent paper.



'85-90 2LT engine stock specs :
63kW / 86hp @ 4000rpm
139lbs.ft /188Nm @ 2400rpm
92mm bore x 92mm stroke
20:1 or 21:1 CR
8psi max. boost
4000rpm max. governed speed
OHC with rocker lifters

[malone]

Nice!! Thanks for your contribution, 2446

[fspGTD]

Wow - thanks for the info, 2446!  It's amazing the kinds of resources that can come out of the woodwork on this board.  

It seems like the 92mm toyota diesel bore is too big to consider swapping it into a VW Diesel block (considering VW Diesel pistons are usually under 80mm).  But it could be feasible to machine this pattern into a VW piston top.  Your measurments would prove very useful for anyone trying this.

[v8volvo]

FASCINATING thread! I'm starting to think I should drop out of college (engineering) and just spend all my time reading posts on this board--I swear I learn more per minute here than I ever could in any of my classes. Amazing how we go from some patent paper that Jake dug up describing a long-forgotten Toyota engineer's brainchild design, to a photo of an actual Toyota diesel piston that uses the very same principle!

Interesting that, despite the piston cut, the Toyota diesel is a pretty low-revver--it's capped at 4000 rpm. However, it is a substantially larger engine; maybe with the right mods, that method could be used to great advantage in a VW diesel. I have a nice 80,000-mile 1.6NA short block sitting on my bedroom floor at home waiting for me to do something with it--who wants to give it a try? (Although, without a turbo, it might prove pointless, as dropping compression down like that without filling it with extra boost won't help anything.)

Also interesting points about the TDI pilot injection. Are you sure they used that on the older rotary-pump TDIs, though? I know the injectors don't have any electronic controls on them, and the pump, outside of its electronic control and higher pressures, works basically the same as our old IDI pumps, as far as I am aware. I wonder how they would have accomplished the pilot injection at all, much less timed it precisely. I thought they didn't use pilot injection until the advent of PD and common rail. However, if they did, that does help explain why it is so difficult to make a mechanical TDI work well--I'm sure the people who do it do without the pilot injection, which, if VW does use it on the older motors, must be an important part of their functionality.

[2446]

Interesting that, despite the piston cut, the Toyota diesel is a pretty low-revver--it's capped at 4000 rpm. However, it is a substantially larger engine; maybe with the right mods, that method could be used to great advantage in a VW diesel.

Actually I'm convinced this engine as quite some revving potential. I pushed the accelerator linkage stop a good bit on my all stock NA 2.4, (VE style pump) and it pulls strong almost all the way to 4800 now. The smoke levels at WOT are consitently low all the way (fuel is adjusted at the max. "little grey smoke" level), so I'm assuming the combustion quality at higher revs. is fair.

[2446]

Nice!! Thanks for your contribution, 2446

Taking a photo and a couple measurements was the least I could do, given how much I've learnt reading this board so far  :wink:

denis

[VWRacer]

Let me add my thanks and welcome to the forum, Denis!

I assume that the numbers you added to the photo of the piston top represent the depth of the cut, right? Can you add the width and length, as well?

Thanks!  

[steve]

Interesting you mention the pilot injection.  A friend of mine works at www.sturmanindustries.com and they R&D injectors (and more) that are a competitor to the common rail and achieve multiple pilot injection events.  (I think the common rail does too).  Their injectors are installed on the new ford powerstroke (2004 and on, I think).

And oh yea, v8volvo, stay in school because to work at a place like Sturman you're gonna need it!!!!!!  If I knew about a place like that when I was in school I would have made it my goal to work there.  It's VERY cool.  Check out their web site which is just the tip of the iceberg.  I'm an aircraft engineer at Boeing, and Sturman is a million times more interesting and exciting than my job here.

My novice understanding of the benefits of the pilot injection is that it decreases noise and emissions.  Not sure about efficiency.  The Sturman web site might mention something.  I haven't read it recently...

I used to work about 2 miles from Sturman Industries up in the mountains in Woodland Park, CO.  Man I miss that...

[2446]

Can you add the width and length, as well?

The first cut starts at 16mm wide and finishes at 15mm, and is approx. 24mm long. The second cut starts goes from 14 to 13mm wide, is 21mm long.
The relative positions you can measure on the picture with the provided scale

The beginning part of the first cut curves somewhat roundly just like in fig. 6 in the patent document.

[16V-Sauger]

Can you add the width and length, as well?

The first cut starts at 16mm wide and finishes at 15mm, and is approx. 24mm long. The second cut starts goes from 14 to 13mm wide, is 21mm long.
The relative positions you can measure on the picture with the provided scale

The beginning part of the first cut curves somewhat roundly just like in fig. 6 in the patent document.

are these cuts like radiuses? i hope to get my 81mm pistons this week. because they are totally flat i have to mill these mickey mouse holes into the top and thats the time when i could do some aditional grinding