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Old 11-09-2017, 04:07 PM   #31 (permalink)
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Originally Posted by serialk11r View Post
The toughest standard is something like 0.02g/mile NOx (need to check on that again), which works out to something in the tens of ppm depending on how much fuel you burn in a mile.

I think if you drop the combustion temperature by a little bit it is easy to go below 100ppm (which should be able to squeak by the minimum standards on a smaller engine car). HCCI supposedly should be able to control the burn speed so that maximum temperature is lower.

I am not sure exactly how this works, but my hunch is that they use a lot of hot EGR to control the charge temperature (to induce autoignition) and reduce the burn temperature, and somehow avoid knock.
Cooled EGR, plus intercooled supercharging. Gives you a nice, dense, temperature controlled mix in the cylinder that's primed to go off when the small ball of "rich" air-fuel mixture around the plug ignites.

I bet they're using supercharging so they can keep using the long-tube scavenging header of the naturally aspirated SkyActiv G. But I haven't seen the engine fully dressed yet, so I could be wrong.

SkyActiv X is going to be wild. And it won't be using unobtanium engine internals, stratospheric injection pressures or ridiculously fast and expensive knock detectors.

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