Engine Technology Thread; starting with dimpled pistons

[The Dark Side of Will]

https://www.motortrend.com/news/golf-ba ... echnology/

Of course it's tied in to CA emissions BS, but the dimpled idea is interesting. A clean engine is making the most of its fuel and running efficiently and economically.

Some people have talked about dimpling intake ports improving the performance of some engine combos, but it's far from universal. My personal take on intake ports is that since dimpling works to thicken the boundary layer, the combos in which dimpling works probably had intake ports that were too big in some spots to begin with. Dimpling moved them toward a more optimal size/shape in the non-optimal locations without compromising the locations that were already pretty good... That's different than saying dimples are a good thing in their own right.

[ericjon262]

I haven't read the article yet, later tonight I'll give it a read.

me and a buddy used to talk about port dimpling alot, IMO it's not something easily done in a repeatable manner (port to port) without CNC tech. A while back I saw a youtube video on the subject, an engine builder took a head, and used several different dimpling schemes on the ports, doing the entire port, just the roof, just the floor, the walls, ect. and then flowed each port to show that the placement of the dimples can make a massive difference in flow, and that dimpling the entire port, in his application actually hurt flow. if I remember right, optimum dimpling in his application came from dimpling the floor ahead of the short turn, and the roof in the long turn, everything else was either not beneficial, or a detriment. if I can find the video, I'll link it.

[Shaun41178(2)]

Eric weingartner on YouTube did the dimple test on an LS head.

Without a flowbench you have no idea if it helps.

[ericjon262]

dimpled chambers, and piston crowns definitely seems like an interesting idea, if the company's claims are true, those aren't insignificant gains in performance and emissions, I just wonder if the pistons had any other improvements that could have altered the results? better rings, or ring grooves, skirt or crown coatings, ect. shit like this makes me wish I had an engine dyno, and time to test things, I'd be perfectly ok with getting a stock engine, doing a bunch of pulls, dimpling the pistons and slamming it back together and seeing if there was any significant change.

[pmbrunelle]

15% increase in hp/torque sounds like a lot...

Except at WOT, almost all fuel is burned nowadays in an engine... so that 15% gain cannot come from burning the near-zero amount of fuel that is normally unburned.

Maybe somehow the dimples increase the flame speed? If that's the case, then maybe the injection timing needs to be retuned to take advantage of this mod?

Dimples would be nearly free to add to a piston if they could be built into the casting mold, and not machined afterwards.

[Series8217]

This doesn't mention dimples specifically, but the level of modeling used for modern combustion is astounding.

https://podcasts.google.com/feed/aHR0cH ... ExOQ?ep=14

There's probably still some witchcraft left to figure out, but modern combustion chamber / DI timing / ignition time work is pretty amazingly optimized.

[SappySE107]

.

[Shaun41178(2)]

Without a (dyno) you have no idea if it helps.

Fixed that for ya.

Having both would be better

[zok15]

Maybe somehow the dimples increase the flame speed? If that's the case, then maybe the injection timing needs to be retuned to take advantage of this mod?

This theory makes the most sense IMO. Not sure how legit it was but there was a whole thing years ago about making little V grooves radially from the spark plug in the head to help increase flame speed. Makes me wonder if dimpling the combustion chamber would accomplish similar results to dimpling the piston.

[ericjon262]

15% increase in hp/torque sounds like a lot...

Except at WOT, almost all fuel is burned nowadays in an engine... so that 15% gain cannot come from burning the near-zero amount of fuel that is normally unburned.

Maybe somehow the dimples increase the flame speed? If that's the case, then maybe the injection timing needs to be retuned to take advantage of this mod?

Dimples would be nearly free to add to a piston if they could be built into the casting mold, and not machined afterwards.

I'm really wondering, the podcast Steven linked to included some discussion on the affect of boundary layers, but that particular discussion was questioning their effect on thermal transients, not flame speed. I would imagine an effective boundary layer could contribute to "smoothing" the shape of the combustion chamber, and having an effect on flame speed, and shape of the flame front, but that's all a bit above my experience and knowledge level. I really wish I could pick up two or three engines and try some of these ideas on an engine dyno and really see how they change the power curve, if at all, with no other change outside dimpling the pistons and/or chambers, and the associated compression/weight changes that go along with those changes. I would be extremely interested to see how the tune changes, does the engine want more or less timing now? if it makes more or the same power, with less overall timing, that would lead me to agree with your flame speed theory.

This doesn't mention dimples specifically, but the level of modeling used for modern combustion is astounding.

https://podcasts.google.com/feed/aHR0cH ... ExOQ?ep=14

There's probably still some witchcraft left to figure out, but modern combustion chamber / DI timing / ignition time work is pretty amazingly optimized.

500 hours full load alternating between peak hp and peak torque... damn! that was an interesting podcast, it left me questioning the things I "know" do you subscribe to HP academy? I've heard mixed opinions, but an interview with someone on that level rarely doesn't include useful information.

Without a (dyno) you have no idea if it helps.

Fixed that for ya.

Having both would be better

yeah, both are ideal, the flowbench gives an idea of what the expected change in dyno performance should be, but doesn't necessarily always correlate. it sucks that all of us live all over the country, if we live close enough we could pool resources and have all sorts of development tools at our disposal.

[ericjon262]

This doesn't mention dimples specifically, but the level of modeling used for modern combustion is astounding.

https://podcasts.google.com/feed/aHR0cH ... ExOQ?ep=14

There's probably still some witchcraft left to figure out, but modern combustion chamber / DI timing / ignition time work is pretty amazingly optimized.

so, FWIW, since Dewaye invited people to reach out to him via Linkdin in the podcast, I did. if he responds, I'll ask if he has any thoughts he would like to add to our discussion here. if he responds, are there any specific questions you guys want me to ask?

[ericjon262]

Dewayne responded to my message on Linkdin, here were some of his thoughts:

On a spark ignited engine I'd be worried fuel would puddle in the dimples with diesel there is no fuel to worry about until it ignites
Also, the air, at least in a good spark ignited engine, will be tumbling not swirling like a diesel. You do see some shaping going on in GDI engines now, they take some inspiration from modern diesels, but you can't use the full bowl effect

I guess tumble is preferred to swirl for better charge mixing? something that a diesel doesn't need because it doesn't have fuel in the mix?

In diesels you want the fuel to spread as quickly as possible, the centripetal acceleration from swirl helps that.
In a spark engine the centripetal acceleration from swirl will separate the fuel and air cause they have vastly different densities
Tumble helps keep them mixed

Rounding out our short discussion, Dewayne also said that if I prove him wrong, he'll rethink his position... lol! while I'd love to try, I'm not sure I have the resources to try ATM, although I would be very interested in trying.

My takeaway, the idea could provide improvement to a port injected engine, but the idea seems more far more suited to a directed injected engine based on the above discussion. my other takeaway, is that more than likely Patrick was on the right path with burn rate being the source of the improvements.

if anyone has any questions they would like me to bounce off of him, let me know and I'll see what I can do.

[The Dark Side of Will]

Just ran across this on the Book of Face

https://www.roadandtrack.com/new-cars/c ... -ignition/

[ericjon262]

I've been giving the dimpled pistons some thought, and I kinda want to try it. not the entire crown, but just the very outside perimeter, and maybe the same portions of the cylinder head. Dewayne said he would worry about fuel puddling, and I'm not sure that would be as big of a concern on the deck of the head compared to the crown of the piston. thoughts?

The RCCI engine is an interesting idea, I wouldn't have expected those kind of results, but I bet it's a nightmare from a control/tuning aspect, not that I expect something like this to be on the average tuners radar though. I wonder if GDI would be used too? it starts to sound like a crowded combustion chamber if it is. it would be interesting to see if the engine could run on either individual fuel as well.

before we get to far here, are we wanting this thread to center around combustion/combustion control, or are we wanting this thread to be all encompassing of engine related tech from the furthest tip of the air intake, to the last little bit of the exhaust?

[The Dark Side of Will]

I know I've followed up with about diddly on the dimpled pistons item...

But here's a post on oil I found a few years back, forgot about, then stumbled on again purely by accident over the weekend:

https://www.speed-talk.com/forum/viewto ... 53#p423853