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post #1 of 77 (permalink) Old 01-16-2017, 03:16 PM Thread Starter
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New Skyactive Engine???

Here's a link to the article...


Mazda's next-gen SkyActiv engines will drop spark plugs in favor of high compression - Autoblog


Does anyone know much about this technology? What are the chances of this happening?
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post #2 of 77 (permalink) Old 01-16-2017, 03:38 PM
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That's a unicorn that everyone has chased to 20+ years. The military had an engine that could run on gas (but was actually a diesel) a LONG time ago (1960s, I think) but it ran like crap on gasoline -- although it WOULD run. It was more of a "if you have nothing else available..." sort of option.

If Mazda has actually solved it, and it appears they're confident they have, then they've truly come up with something special. I have a couple of ideas that might be involved in how they've done it -- we'll see if I'm right or not when it hits the streets. My guess is that their answer involves using variable compression along with very careful combustion-chamber design and flow dynamic modeling of the incoming charge as the entire trick to making HCCI work is having temperatures high enough in the ENTIRE air charge so when injection occurs ignition is even and immediate. It also likely involves a means of sensing the ignition event so as to be able to vary both injection timing and compression ratio to adjust for fuel variation (e.g. octane differences.) This means that at lower RPM and load the compression ratio is materially higher so as to drive way up the charge temperature under those conditions, while at higher load and output it can be lower and still work. Variable-intake timing can (potentially) accomplish that. If you can sense actual ignition delay then you can also time the injection event to account for variations caused by fuel octane (and OAT) differences.

The greatest improvement in efficiency is due to greater volumetric expansion, which extracts more of the heat of combustion. There is likely also a higher combustion temperature component since detonation is not a consideration and thus you do not need to intentionally reduce combustion temperatures to combat it (however, NOx emissions are still at issue, and higher combustion temps produce more NOx....)
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post #3 of 77 (permalink) Old 01-16-2017, 09:26 PM
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BTW if they really have made this work and it shows up there suddenly is an avenue for modding that hasn't existed (really) on the current Skyactiv platform.

See, Skyactiv has a high compression ratio, which is how they get their efficiency. But this means they have to be very "active" in management to avoid detonation, including VVT, ignition timing and similar. That in turn means adding a scroll to get more power is problematic as you quickly run into the limits of pump fuel.

CI engines have no such limit because detonation is not a consideration. As such as long as you can deliver the fuel you can shove more air in there and the penalty for coming up short on the fuel is that you don't make more power -- CI engines by definition run lean all the time except at full output, and that's perfectly ok!

The limit on being able to add more boost and fuel is strength and heat-dissipation related; if you go too far you lift the head (the pressure exceeds what the head gasket and/or bolts can hold), you melt something or something in the driveline (usually the bottom end) fails mechanically and catastrophically. That's wildly different than the world you live under the rules of in the SI world where you are forced into higher and higher octane fuel in order to prevent detonation, and ultimately the area under the curve that results in safe combustion makes further boost ill-advised (unless you want to run straight methanol for fuel or some silliness like that!)

It is entirely possible to get 50% output increases out of most CI engines from "factory" configurations while running straight-up and CHEAP pump fuel with "reasonable" safety, and with some strengthening (e.g. girdles on the bottom end, high-strength studs for the head, etc) a fair number of people have gone quite a bit further without winding up with internal engine parts on the outside of the block. I know a couple of people who have doubled the output of the ALH TDI engines (bigger turbo, crazy-increased flow injectors, higher-range MAP sensor plus the tune to use all that) but you wind up changing a LOT of other parts in the driveline (final drive, clutch, etc) because utterly nothing was originally designed for that and some (the clutch, specifically) will be destroyed immediately if you don't.

This could quite-easily be in our future if those crazy Japanese Mazda dudes have actually made HCCI work.
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post #4 of 77 (permalink) Old 01-17-2017, 11:10 AM Thread Starter
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It definitely sounds like if the Mazda engineers were able to achieve this technology, they will be ahead of the curve on pretty much all car manufactures. You definitely know your stuff about engines and how HCCI functions.


I know there are other threads about possible changes to the 2018 Mazda 6 (possibly using turbocharging), but I wonder if Mazda has cracked the barrier on this technology if this would be the direction they go?
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post #5 of 77 (permalink) Old 01-17-2017, 11:45 AM
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HCCI sounds promising, but managing the high compression has been the challenge. I think Mazda will be cautious about HCCI until they have some long term real world data. Remember, Mazda was one of the leaders in Wankel rotary engine technology, but outside of the RX7/RX8 it didn't get any traction.
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post #6 of 77 (permalink) Old 01-17-2017, 11:55 AM Thread Starter
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Quote:
Originally Posted by michael95350 View Post
HCCI sounds promising, but managing the high compression has been the challenge. I think Mazda will be cautious about HCCI until they have some long term real world data. Remember, Mazda was one of the leaders in Wankel rotary engine technology, but outside of the RX7/RX8 it didn't get any traction.


Well, if I'm to believe that article....and autoblog is typically a good website for car info, Mazda is past the testing stage and could be ready to use the HCCI engine in the 2018 Mazda 3.


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post #7 of 77 (permalink) Old 01-17-2017, 01:26 PM
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I only mean that they will offer it in the Mazda 3 in limited numbers until they can get that long term data. I don't see them going gung-ho and offering it across the entire line-up.
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post #8 of 77 (permalink) Old 01-18-2017, 09:53 AM Thread Starter
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Quote:
Originally Posted by michael95350 View Post
I only mean that they will offer it in the Mazda 3 in limited numbers until they can get that long term data. I don't see them going gung-ho and offering it across the entire line-up.


Gotcha, and I agree.


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post #9 of 77 (permalink) Old 01-18-2017, 10:09 AM
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Wankel engine has never panned out for Mazda, I'd be shocked to see them try an unknown technology in the North American market. Car makers used to use the public to test experimental stuff in the 70's and 80's, but they have all but stopped doing that as warranty costs or potential liability when it goes horribly wrong will stop them from anything like that.

It makes a good news soundbite, but the reality is that if they do not have a fully functioning product to show the world in physical driving form then there is little chance we'll see this tech this decade.

I also struggle mightily to believe that this technology would be able to handle extreme temperature changes like we have in Canada and the rust belt in the US. What are they going to use to help a cold engine start? I don't see warmed up gasoline or glow plugs doing the trick.

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post #10 of 77 (permalink) Old 01-22-2017, 07:49 AM
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I just hope it does not sound like a diesel.
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