Sadly, this article does not really say anything about the technology other than using lean burn and a supercharger. I have not read the SAE Paper, I have to admit. They also speak about increasing compression ratio to 18:1 in an older article at GCC. Both increasing CR and using excess air (via supercharging) is beneficial for efficiency. This we also know from diesel engines, i.e. nothing fundamentally new when it comes to thermodynamics. The interesting part is how they control combustion and in particular, knocking and flame speed. This is the Achilles’ heel for gasoline engines but pose no problem for diesels. The main disadvantage of lean burn is the difficulty to control NOx via exhaust aftertreatment. This we also know from experience on diesel engines and, in fact, also on gasoline engines. It was a significant problem on early GDI engines that all operated under lean-burn conditions. Mercedes are one of the few manufacturers who still pursue lean burn on some of their gasoline engines, albeit to my knowledge not on all markets. In summary, this article raises more questions than it answers. If anybody has well-founded technical insights into Mazda’s technology, I am all ears.

@Peter_XX

By having (assuming) homogeneous (very) lean air-fuel mixture, you reduce a lot, in theory, the combustion temperature and therefore you keep the production of NOx at a minimum. Assuming that is HCCI or PCCI, flame speed is not an issue.
Lean burn GDI engines are not lean enough to have so low NOx emissions, at least with the current and future emission legislations.

“Sustainable Zoom-Zoom” - who named that ?
It is not a toy car.

@DJ_D
Sorry to say, it is not that easy.

Flame speed is definitely an issue with HCCE and PCCI. It is almost like a detonation. It is much, much worse than diesel if you look at pressure rate for cylinder pressure. You would hear this car blocks away. Thus, something must be done to abate combustion noise.

You can have low NOx if air excess is high. Yes! HCCI/PCCI can run much leaner than GDI. However, this is not the full story. You have to reduce excess air at full torque (and close to full torque) and then NOx will rise sky-high (any joke about that is on me…). Try to imagine running excess air at 2:1 ratio at full load with high compression ratio and fast combustion. No engine structure in the world could handle such cylinder pressure. It would be much, much higher than for diesel. If you limit cylinder pressure to reasonable levels, power and torque would be a joke and you would have to do a lot of “anti-downsizing” This would ruin fuel economy. Recall research carried out by Huyndai/Delphi. They certainly had to deal with high cylinder pressure and you can find comments from me on that as well in the past on this forum. Furthermore, if you are just marginally on the lean side, TWC will not work. So, in essence, you would have sky-high NOx at high load but conventional aftertreatment would not work. Even if this problem would not be too bad in a conventional test cycle, RDE would kill such an engine. You could imagine replacing excess air with EGR, perhaps gradually, but this is not easy to control. Toyota tried this many years ago with homogenous lean-burn (long before GDI) but the result was not very good. I have tested such cars myself in the laboratory. Needless to say, NOx was much higher than from TWC cars. You could adopt similar aftertreatment as for diesel (NOx-trap + SCR) but it comes at a cost and you would still struggle in off-cycle conditions.

In summary, there are a lot of issues to explain. Perhaps Mazda has cracked a couple of the nuts but we have no idea about how they did it.

Toyota, with current best efficiency ICEs, will probably benefit with their recent limited FV with Mazda?