Mazda Skyactive X

Well, maybe Mazda is going to skip the Skyactive D in the US and go straight to the X. Sounds complicated.
http://jalopnik.com/mazdas-upcoming-skyactive-x-compression-ignition-engine-1797643172
https://www.autoblog.com/2017/08/08...iv-x-compression-ignition-engine-smart-hedge/

Interesting. Based on the roll out of the skyactiv d, I'd say they should be on the roads here around 2050.

How much more will it cost over the present sky active and what sort of emission controls will be required? Will CARB allow this?

gulfcoastguy said:

How much more will it cost over the present sky active and what sort of emission controls will be required? Will CARB allow this?

Click to expand...

Meet and beat the emission targets and the California Air Resources Board will be happy to approve. For close to 50 years Detroit auto makers have been telling California they (detroit auto makers) can not meet California emissions targets. Small Japanese automakers have done it (Honda with it's CVCC engine) in the 1970's lead the way.

If this system works the way I think it does, they should have few hurdles. The hardware is little different from a normal spark-ignition engine with variable valve timing and direct injection (think: existing Skyactiv-G). The difference is in the controls to manage the combustion system, and some cam timing trickery, and evidently a supercharger.

Will they suffer from high NOx emissions like a diesel?

My understanding is that more NOx is produced by Diesel engines because they can run a lean mixture with high compression, leading to high combustion chamber temperatures that form NOx. Similar to an HCCI engine?

Exhaust gas re-circulation has been used for decades to reduce peak combustion temperatures and NOX formation.

And, if I recall correctly, Mazda used to offer a supercharged Miller cycle engine about 15 years ago.

Part of the deal is "low temperature combustion" - dilute with high EGR. NOx doesn't form. The fuel is premixed, which means soot doesn't form. Air/fuel can be lean but dilute, or it can be stoichiometric but dilute with EGR, and in that case, a normal 3-way catalyst will work. Dunno about Mazda but the one Hyundai was working on used a plain ordinary 3-way catalyst.

There was also mention of simultaneous combustion when the piston reached TDC, eliminating the flame wavefront, which is where a lot of NOx is generated (if I'm reading correctly. Hope this comes to fruition.

I wonder if HCCI technology could be applied to a diesel-air mixture?

Would it be an improvement over HCCI with gasoline, or current direct-injection diesel?

At a research level, the HCCI concept has been applied using gasoline, diesel fuel, and custom / specialty / dedicated fuels.

The trouble with using diesel fuel is that it's harder to achieve the "H" (homogeneous) part of HCCI, because the fuel is not volatile enough. Gasoline is capable of evaporating almost completely in the available time and at the available temperature.

Using gasoline also enables using a spark to fire the mixture under "off design" conditions when compression-ignition is unreliable or is not going to happen. I am gathering that Mazda will be firing the spark plug no matter what. If it feels like compression-igniting before the spark plug fires (because conditions are favorable for HCCI operation), so be it. If it is far enough off the HCCI envelope to require spark ignition, so be it. If it is right on the threshold of a compression-ignition misfire, it won't take much ignition energy to fire it, the spark will tip the balance towards igniting it as opposed to having a misfire.