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

Everyone has been working on a diesel-cycle gas engine. Emissions won't be a problem. When Mazda presented the SkyActive system and current patents to the USPTO last year they talked about this.

The engine would be the best of both worlds. Diesel efficiency without the diesel emissions problems. Diesel fuel's makeup is a huge problem with diesel emissions. Since they have a working, testing prototype for a few years now, they now know how to do the same thing with gasoline.

I remember GM announcing work on this back in the early 2000's at Vandy and said that they were going to dictate the time table. Someone asked "you are going to schedule innovation?" They responded yes. GM stock dropped a half a point the following day. It was funny, even if it was a coincidence.

We're already seeing direct injected vehicles have increased NOx and particulate emissions due to the high compression ratios and combustion temps. It shouldn't be surprising that an engine that operates like a diesel should struggle with similar emissions issues as diesels do. The fuel type helps lessen it to a degree, but emissions are still higher than previous gasoline engines. It wouldn't surprise me to see some sort of diesel-like emissions control devices in place on an engine like this.

If they really want it to avoid the Nox issues, they should make it capable of running on e85 instead of common gasoline. Of course that has it's own issues with availability, decreased fuel economy, burning a food source, etc.

HappyAndy wrote: In reply to alfadriver: But wouldn't you say that HCCI is a further development of GDI, and doesn't GDI borrow heavily from diesel engeering? Precisely metered and timed fuel is being introduced at very high pressure directly into the combustion chamber, combustion pressures are steadily climbing due to both increases in static compression and forced induction, that sounds pretty diesely to a somewhat knowledgeable non-engineer. Now the static compression is solidly in diesel territory, and the spark plug is gone. Will these engines have the same emissions issues (NOX) as true diesels, or does gasoline avoid that problem? Or is that not known yet?

No, I don't see them being as close as you do. Port injectors are as precisely metered and have the capability of being timed- it's just not as sensitive. And pressure is relative- right now, GDI engines run far closer to pfi pressures (max 2000 vs. 65 psi) compared to diesel (20,000 psi).

More importantly, the goal of combustion- SI engines require some kind of homogeneous overall air-fuel mixture, and then something to set it off, and all GDI engines run with injection timings 99% of the time very early timed into the intake stroke. CI engines just need high pressure and temp so that when they start injecting, it starts burning.

High compression isn't really a measure of style of combustion- although you see diesels at much higher (so they can generate the high pressures/temps). It's a more showing the ability of knock resistance.

Actual combustion pressures are not going up for GDI engines. Or at least not up a whole lot.

HCCI is very different than DI engines. Those are CI engines.

In reply to Flight Service:

Diesel's emissions problems have little to do with the fuel. It has everything to do with post combustion clean up and the make up of the post combustion chemistry.

I've posted this before- from an engine out standpoint- diesel engines are far cleaner than gas engines- lower NOx and FAR lower HC. The problem with diesels is that it's REALLY hard to reduce that to a level that is still safe to breathe. The excess O2 in the exhaust is entirely to blame on that at the moment.

In reply to STM317:

I'm not sure where you are seeing the higher NOx in DI engines- I don't. Some are higher than PFI, some are lower- I'd can't put a generalization on the difference that easily. Yes, PM is higher- as PFI pretty much does not make PM at all.

But it's the cycle that makes all the difference. Since SI engines run near stoich already- keeping them targeting there +- 3% or so, you can manipulate the chemistry in the exhaust so that catalysts can complete the combustion to well past 99% nominally.

THIS HCCI engine, from an emissions standpoint- it's going to be closer to diesel in the exhaust chemistry. So all the work I've done in the last 17 years does not apply... It will be interesting to see it work. The one thing going for it vs. diesel- given that it's very able to run stoic (which diesels are not), you can play with the exhaust chemistry to make ammonia, which can be used in an SCR. That's what I would speculate they are doing without knowing. It's pretty easy to do.

BTW, one other note- HCCI engines still have spark plugs- as they don't run HCCI all the time. So they can run like a gas engine sometimes and like a diesel engine other times.

Getting out to the over 25:1 a/f is where you can really use that combination economically.

In reply to alfadriver:

I have no hands on experience with modern DI gasoline engines. I was basing my claim off of articles I'd read, and the assumption that DI allowed for leaner air/fuel mix, which of course results in higher temps and more NOx. If you're seeing differently, then I concede to your experience and knowledge.

Can I ask why you say a diesel wouldn't be able to run stoich? I know the ratio is different than it would be for gasoline, but what is keeping a diesel from running at 14.5:1?

In reply to STM317:

At the moment, nobody is running lean burn DI. Can't get lean enough to make it worth it. That's where HCCI makes it worth it. Also, going leaner than about 15:1- the NOx starts to go down. So at 25:1, it's low enough that the exhaust technology is cheap enough to work it. It's not good enough to not be reduced, but it can be worked with.

Stoich on a diesel is wide open throttle. So when you want to get there for short periods every once in a while to mess with the chemistry, well- it's not feasible (imagine doing 25mph in your neighborhood when the diesel has to go WOT for a short time to generate ammonia....). For nominal use, WOT isn't really part of the process... Reference my words more toward nominal use and not outside of the boundary.

In other words, I worded my statement wrong. Diesels can do WOT. It's just not common, and not something you would be near to on a normal day for most drivers. And can't be used for emission control.

In reply to alfadriver:

Gotcha! That makes more sense. Diesels avoid that problem by running DEF I guess. I'm curious to see if Mazda will need a particulate filter for this HCCI engine. IF they have to use one, it will likely require regeneration, which will burn more fuel, hampering their fuel economy to a degree. They must believe that they can spend enough time in lean burn to more than offset the fuel economy losses of a regen.

In reply to STM317:

If it were me managing the project, I would make sure it would not need a GPF. Low PM/PN is possible with DI, it's just a matter of design. I hate having to remind people that all the time.

alfadriver wrote: Also, going leaner than about 15:1- the NOx starts to go down

Interesting... Is this valid pretty much across the board, or mostly for DI or HCCI?

In reply to rslifkin:

across the board. Peak combustion temps are at about 15:1, so that's peak NOx too. Lean of that, and everything goes down.

We were playing with lean burn 15 years ago, and running 18:1 regularly. DI can move that up some, but the carrot is leaner than that, which is what HCCI is able to do. It's where the cost-benefit ratio gets to be more appealing.

alfadriver wrote: In reply to rslifkin: across the board. Peak combustion temps are at about 15:1, so that's peak NOx too. Lean of that, and everything goes down. We were playing with lean burn 15 years ago, and running 18:1 regularly. DI can move that up some, but the carrot is leaner than that, which is what HCCI is able to do. It's where the cost-benefit ratio gets to be more appealing.

Interesting. If the emissions side of lean burn can be figured out, there's a big gain to be had in the MPG department, especially for the big N/A V8s and such in the world where pumping losses are a huge issue at cruise.

Even in my old tech port injected V8, there's a noticeable (easily 5% or more) improvement in fuel burn during steady cruise from running in closed loop around 15.7:1 instead of 14.7:1 and with a bit of extra timing for the slower burn.

rslifkin wrote:

alfadriver wrote: In reply to rslifkin: across the board. Peak combustion temps are at about 15:1, so that's peak NOx too. Lean of that, and everything goes down. We were playing with lean burn 15 years ago, and running 18:1 regularly. DI can move that up some, but the carrot is leaner than that, which is what HCCI is able to do. It's where the cost-benefit ratio gets to be more appealing.

Interesting. If the emissions side of lean burn can be figured out, there's a big gain to be had in the MPG department, especially for the big N/A V8s and such in the world where pumping losses are a huge issue at cruise. Even in my old tech port injected V8, there's a noticeable (easily 5% or more) improvement in fuel burn during steady cruise from running in closed loop around 15.7:1 instead of 14.7:1 and with a bit of extra timing for the slower burn.

Very true. They have partially been solved, but the cost is too high to make it worth it.

So the ideal future ICE will be OPOC port/direct fuel injected camless sparkplug free

1.0L 4 cly making.... 350hp? no idea just guessing here...

It will make exactly the power it needs to drive itself, and nothing more ;)

Paul_VR6 wrote: It will make exactly the power it needs to sell ;)

Fixed it.

STM317 wrote: We're already seeing direct injected vehicles have increased NOx and particulate emissions due to the high compression ratios and combustion temps. It shouldn't be surprising that an engine that operates like a diesel should struggle with similar emissions issues as diesels do. The fuel type helps lessen it to a degree, but emissions are still higher than previous gasoline engines.

Exactly... it's not the fuel type that leads to the emissions, it's the engine characteristics that are required for that fuel type. Diesels by definition run lean and extremely hot, they rely on high chamber temps to even run!