Mazda Sky Active X! (HCCI gas engine: compression & spark ignition)

[hayden55]

Anybody else excited to see the new Mazda sky active x implementation? Mazda predicts a 30%+ fuel economy gain over current sky active G engines and it makes more horsepower similar to a 2.5 vs a 2.0. What is really curious is that under light load condition it runs on lean compression ignition, but under high load it swaps to spark ignition. I hear similarities to a new and improved vtec-e. Thoughts?

[oldtamiyaphile]

Always beware of the term 'up to'.

It's a 30% gain only in the narrow band that HCCI will operate in. So owners won't be seeing 30% reductions at the pump. It's a bit like lean burn or cylinder deactivation.

[cRiPpLe_rOoStEr]

I thought it would resort to spark ignition only to keep it smooth while idling or at an extremely low RPM.

[Hersbird]

But if the 30% is specific to say 65mph that's perfect for highway cruising. The EPA test cycle doesn't pick up these kind of things which means manufacturers are discouraged from trying things that may actually be really effective in the real world. I have no idea if this is the case with this car but I always like to dig into the EPA raw data and look at the old standard highway cycle results. That number better shows what is possible to get if you try.

[niky]

This was the same problem with Mazda's iStop. The EPA city cycle doesn't show its effects, even though real world testing has shown a 0.5 to 1 km/l difference in 8 km/l traffic.

We have to wait to see what Mazda does. I am assuming that it uses HCCI over a wider cycle than GM's older system precisely because it uses spark-controlled compression ignition.

[Daschicken]

Originally Posted by hayden55

Anybody else excited to see the new Mazda sky active x implementation? Mazda predicts a 30%+ fuel economy gain over current sky active G engines and it makes more horsepower similar to a 2.5 vs a 2.0. What is really curious is that under light load condition it runs on lean compression ignition, but under high load it swaps to spark ignition. I hear similarities to a new and improved vtec-e. Thoughts?

I'm still excited about the i-stop. Restarting the engine WITH the engine is just too cool! I hope they pair it up in the mazda 3 with a manual! The new Mazda 3 is my go-to brand new car choice right now.

[JockoT]

Just read up on the i-Stop and it sounds amazing. How they get it to do what it does, reliably and without stressing the engine, is a feat of engineering.

[oldtamiyaphile]

Idle stop is pretty much ubiquitous nowadays. Renault's is said to be good for 400,000 cycles. That's once a mile for... well you know.

Mazda's is the best system, but in practice, I've tried to beat Renault's system and can't. My Fiat's is much more of a 'first gen' system, no where near as polished, but gets the job done usually.

[cRiPpLe_rOoStEr]

Nowadays with idle-stop, regen braking and some mild degrees of electric power assist are becoming more widespread, it would not suprise me to see starter motors becoming more overbuilt to stand those operating conditions, eventually integrated with the alternator/stator/whatever type of generator for a more compact packaging.

[niky]

Originally Posted by JockoT

Just read up on the i-Stop and it sounds amazing. How they get it to do what it does, reliably and without stressing the engine, is a feat of engineering.

To be fair, you still use a starter motor, but having the engine "parked" with one cylinder primed to fire lessens the strain on the starter and minimizes the amount of juice needed.

And, as oldtamiyaphile says: It's the best system. Much smoother than the auto-stop systems the Germans use.

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Similar in concept to SkyActiv X. Integrating separately clever but (relatively) simple solutions into a system that is greater than the sum of its parts.