In reply to WonkoTheSane:
That's a really neat article! I think we've seen Diesel and Gas tech moving closer toward a common ground for several years. Diesel compression ratios hahve been decreasing (to reduce NOx emissions), and gasoline compression ratios have been increasing (to gain fuel economy). Seems like HCCI is more or less that common ground.
WonkoTheSane wrote:Knurled wrote: In reply to alfadriver: That's something I hadn't even considered. My mind was focused on combustion hot enough that it starts at autoignition. Such a weird place Mazda is in. They're working on 14:1+ gasoline engines that can drivably run without spark, and they're working on 14:1 Diesel engines that can build enough compression heat to run at all...I just stumbled across this MotoIQ article that puts a lot of these thoughts together. Their hypothesis (and note a LOT of this article is "it would makes sense if...") is that they're able to do it it BECAUSE of their development of the 14.x:1 gas & multi-injection-per-cycle diesels. Made a lot of sense to me, and it shows that the past two "skyactive" engine platforms were really research steps to the HCCI goal.
One thing I will want to point out in that article- the problem with running lean isn't the excess N2, it's the unused O2.
That O2 in the exhaust messes up some core physics in converting any NOx to something else. So unless the HCCI motor is putting out less than 20ppm NOx, it's not going to be clean enough for 2020. And I don't see that happening.
That's the reason diesel is so hard to clean up, even though the engine is cleaner than a gas engine on an engine out standpoint.
Sure, the HCCI motor can run with urea injection. But then you have the combination of a gas AND a diesel aftertreatment system. I can't picture that as being cheap.
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