Compression ignition engines - Mazda Skyactive X engine

WildScotsRacingCampbellCougarSeed said:

And the theoretical downsides?

A bit of added complexity (aka cost) and some NVH to keep under wraps are about the only two I've seen noted... Assuming they can get the transition between SPCCI and conventional SI driving modes fully seamless rather than 'just' the mostly seamless indicated in prototype test drive reviews. Of course, as with anything new, even when using purely existing conventional technologies, there is also the question if long term reliability and durability.

alfadriver said:

Yes, it's all about cost.  It will be also be interesting to see a detailed cost break down analysis, especially considering how limited the HCCI can be used. 

And exactly how limited  can the HCCI be used?  These are excerpt from first-hand journalist test drives of a Skyactiv-X equipped prototype:

And lest you think Mazda pulled this off by just running the engine in spark ignition mode the whole time, take a look at that column on the right side of the two graphics above: over 90 percent of my driving was done in SPCCI mode.

Really hammer on it at full load and it'll switch to spark ignition, seamlessly. It's only a tablet running on the dashboard that gives away which combustion type is happening, and in normal driving it's almost always in SPCCI mode. 

In reply to Driven5 :

We will see.  Forgive me for not actually taking the reporters data without a huge grain of salt.  I'll wait until we've tested it, and we see when it's doing what it's doing.

BTW, there's running compression ignition and then there's running hyper lean compression ignition.  Personally, I don't see a huge benefit of compression vs. spark when burning a stoich mixture of fuel.  For those conditions, it's a normal OTTO cycle, anyway. 

Again, we will see.

BUT- my honest opinion is that it will not rock the industry as the Toyota engine has.

Driven5 said:

I believe conventional wisdom states that CO2 emissions should go down and NOX emissions should go up with engines like this.  Since this engine is part of Mazda's effort to cut CO2 emissions this makes sense.  But apparently Mazda further claims that NOX emissions during SPCCI operation to also be low enough to not require a lean-NOX catalyst to meet emissions requirements.  I do realize that you probably know infinitely more than me on the subject.  But since they're the only ones actually developing such an engine, I'll also still tend to give their direct experience with it the benefit of the doubt...At least until proven otherwise.

Leaner a/f typically means increased NOx production, but apparently beyond a certain point, NOx production actually decreases.

Mazda claims their SPCCI engine operates in the 1.5 lambda range, and if the following chart is correct then they might not need additional exhaust components.

Mazda claims a compression ratio of "between 15:1 and 16:1" for the SkyActive X, which seems like a good region to target on the following chart if max fuel efficiency is a prioroity.

I don't have the depth of knowledge on the subject required to confirm or deny Mazda's claims. It is a really fascinating claim to make though.

The tables came from this long, but interesting research study from 2014

STM317 said:

Mazda claims their SPCCI engine operates in the 1.5 lambda range,

I've seen multiple references from Mazda claiming they are actually running it in the 2.0-2.5 lambda range.

One thing I'm unclear on, is how Mazda claims their engine has low NOx production at 1.5Lambda, but also runs a/f between 15:1 and 16:1, which is just a bit over 1Lambda. It can't be both of those at the same time right? Is it possible that the 1.06 is like static Lambda while 1.5Lambda occurs when the supercharger induces extra air as needed?

In reply to STM317 :

That's the compression ratio.

In reply to STM317 :

Re- the physics that NOx goes down the leaner and leaner you go- that is accurate.

MY issue is that it does not go to near zero- which is pretty much what is needed to run without a lean operating catalyst.  And Lambda of 1.5 isn't going to lower the NOx enough.

(one also note- diesels run leaner than lambda a 2)

Can't wait to see real data on it.

alfadriver said:

Can't wait to see real data on it.

Something we most certainly agree on.

Driven5 said:

alfadriver said:

Can't wait to see real data on it.

Something we can agree on.

Sadly, I won't be able to share the data that I will get on it.... 

alfadriver said:

Driven5 said:

alfadriver said:

Can't wait to see real data on it.

Something we can agree on.

Sadly, I won't be able to share the data that I will get on it.... 

That's ok. I probably wouldn't understand most of that particular data anyway...Nor do I realistically need to.

Driven5 said:

In reply to STM317 :

That's the compression ratio.

You're right. I was looking at the second chart I posted, that seems to indicate that peak fuel efficiency occurs with an a/f of 15.4:1 @ Lambda 1.06 and just assumed they'd want to be operating in that range. The chart doesn't show any data for leaner conditions, so I suppose it could be about anything out there in lean burn land, but the trend certainly seems to indicate increased fuel consumption and decreased power, which is obviously not ideal.

Guess I need to do more reading.

Driven5 said: conventional wisdom states that CO2 emissions should go down and NOX emissions should go up with engines like this.  Since this engine is part of Mazda's effort to cut CO2 emissions this makes sense.  But apparently Mazda further claims that NOX emissions during SPCCI operation to also be low enough to not require a lean-NOX catalyst to meet emissions requirements.  

Reading between the lines, the lean combustion happens SO lean of stoich that the burn is too cool for NOx production, and the spark plug is sort of there only to facilitate the process if it hang-fires.  Maybe. 

So, I went to look at the Toyota 2.5. As far as I can tell, it's basically clever port design and a wider valve angle married with a long stroke. Nothing revolutionary, just tweaks to a conventional engine that eke out a little more efficiency. Do I have that right? I like what's presented in the video.

It won't be getting as much press as the Skyactive-X because it's evolution instead of a new concept and Mazda is better at branding their technology than Toyota is Everybody is.

https://newsroom.toyota.co.jp/en/powertrain/engine/

In reply to Keith Tanner :

Exactly correct.  And it's not a little efficiency, especially when put in the context of actual usage.  It's turned into a very big deal.

It's also (like Skyactive) more about system than the engine- so you find all of that benefit, and can actually use it.

For sure, not press sexy.  Boardroom HOT CAKES, though.  

Sometimes, we need some basic evolution.  The problem is that it takes a lot of boring hard work.  Very non-sexy hard work.  Nobody is getting a patent bonus hard work.

Evolution only takes you so far, sometimes you need that step change or the meteor will kill all. Then you evolve that for a while. They're both valid.

People always have trouble distinguishing between a rough new concept and a well-honed established one, you can't directly compare them immediately. Sometimes you have to look down the road to whence the new concept is polished up to see where it's going to have troubles. The inherent complexity of the Skyactive-X, for example, isn't going to go away no matter how much further development as long as it requires that supercharger. But can you apply Toyota's "Dynamic Force" thinking to it and improve it further?

You probably can't say - but couldn't you just bolt a Dynamic Force design head to any long stroke engine and duplicate the results? What part is the big step, the port design with that little kicker in it, or the laser clad seat? Can the laser clad seat be serviced, or will it simply never need it?

The more time I spend working on the ND Miata, the more I realize that thinking of an engine as a thing that lives in a car is wrong. Cars are platforms.

In reply to Keith Tanner :

Now you are getting the idea.  

The real key to evolution is to realize that the "optimum" version of an ICE still has not been found.  As modeling and computers get better, the better chance we can find that optimum.

Which then feeds into every single other additive technology (which most try to be).

As for the ripples of the engine- yes, you can roughly bolt one on.  But it's not just the head.  BTW, in theory, you can 3D print a head, too.

Again, the most important thing is that there is no big step.  There is no new technology.  There's no single key.  It's just effort.  Effort that takes away from someone else's sexy additive tech.

And that's the real thing.

One thing I noticed about both the Mazda design and the Toyota is that neither one uses cam timing to achieve "in cylinder" EGR. Is that more a function of higher compression ratios, or does using the cams for EGR activities have a negative effect on efficiency?

In reply to STM317 :

I think that the industry is finding that making the EGR cooler than just post combustion is better than doing it internally.  And it does not mean a cam timing compromise on top of that.  

Right, so we agree that no matter what is being done it will have to undergo lots of careful close optimization and there will always be smaller and smaller gains available for a given amount of effort.

But I don't think that new technology should be ignored. Is this X engine (I forget all the acronyms so I'm using the shortest option) really all that different than the jump to a turbocharged DI engine in terms of change and complexity?

In reply to Keith Tanner :

Of course technology stuff should not be ignored.  The corollary is the part I fear is getting ignored.  Or know it has been.

As for difference, given when I know about the HCCI tech, yes, it's different than a basic turbo DI engine.  But I don't know that much, so can't be that specific.  If it were :"free" everyone would be working a lot harder to make it work.. 

And I have some real questions how clean it is, and how it gets there.