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

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?

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.

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

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.

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.

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.

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.

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.

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.

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.

What do you mean by "primed"?

It likely stops the engine at or near the start of the compression stroke with just enough fuel to charge that volume under no compression. Quick hit of the starter to make sure the engine rotates the right direction, fire the spark plug, instant power stroke, suddenly doing 600rpm.

iStop? I don't know why iMac annoyed me so much, but I can't believe 2 decades later and marketing still thinks preceeding things with a lowercase "i" makes the name cool. I'm already embarrassed at having to explain this nonsense to my future children.

Anyhow, I have a 2017 Mazda CX5 on order. I'm guessing it won't have any of this cool stuff mentioned here. I know very little about the vehicle since it is company provided.

The one issue is that you require a deep cycle battery, which costs... well... not an arm and a leg, but a few fingers and toes, at least.

Friend uses a regular battery in his car.

He simply wedges the iStop button down with a piece of folded paper. No iStop, no need for deep cycle. :D

Why is a deep cycle battery needed?

Because of the start stop function you require an AGM battery. This allows multiple starts and rapid charging in between, something a normal car battery doesn't need to do.

IIRC Mazda was featuring its newer vehicles with capacitors, which are basically maintenance-free, in order to handle the start-stop without any harm to the regular battery. Anyway, those deep-cycle batteries are still quite expensive, but seem to worth it even in a more conventional application.

The caps are there, but you still need the special battery for the odd charging-discharging cycles.

Especially when running cabin ventilation, lights and entertainment while the engine is stopped.

Indeed. But what would be that so-called "special" battery? Something similar to those Optima batteries that have been around for a while?


Indeed.

Pretty much. Japanese units use Panasonic batteries that cost around the same as an Optima. Our units use locally produced batteries that are slightly cheaper... but only because they're not shipped from overseas.

EPA 5-cycle testing goes all the way up to 85 mph (US06 cycle). The 5-cycle test is used for the window sticker. The 2-cycle test (FTP75+HwFET) is used for GHG and CAFE compliance and the highest speed on the HwFET is 65 mph as stated. 5-cycle test results are much closer to real-world averages. Also, iStop would get GHG credit from EPA through their off-cycle credit program - so if the Mazda chooses iStop in the U.S., they can put it on the vehicle and take the credit towards their GHG compliance. If it isn't offered, it may be for consumer acceptance reasons or it could be that they just don't need it to meet the current standards.

Any of the vehicles switching over to 48V electrical systems between 2018 and 2022 will be doing so in part to better enable idle-stop systems. This is showing up in expensive vehicles first (Mercedes), but once economies of scale kick in with additional offerings among EU market vehicles, we should start to see more 48V systems on vehicles in the U.S. It's a no-brainer for luxury cars - their 12V electrical systems are already overtaxed with the content that is going into higher end vehicles these days.

It actually is exactly lean burn. The only reason they are doing a spark-assisted variant of HCCI is to allow leaner operation. It will be interesting to see what they have to do for NOx emissions control to meet the Tier 3 emissions standards in the U.S. - that is a real challenge for any lean strategy, whether it is some sort of gasoline HCCI concept or diesel.

I've got to do an infographic on that system soon. It's uttelry fantastic.

The way some of these cars drain their batteries when parked is unacceptable. That change can't come soon enough.

All that "content" leaves me cold. Not impressed.

Make mine a modern Model T with about that level of amenities.

Guess I'll have to make my own.

I drove a Russkie truck that might suit you. The UAZ Hunter (military Jeep)

Sliding windows. Good old dip switches for the fuel tank switchover, headlamps and running lights. No radio. Simple AC system. Only electronics are the engine management systems.

Built to go way, way off-road. Dual live axles, near-vertical approach angle. Cloth roof. Diesel economy. As a bonus, rides a bit better on road than a Wrangler, to boot.

How lean, exactly, I wonder? Honda's lean burn motors run well at 22.5-24.0:1.

Are they going to need exotic emission controls?

Yep, the "first" *S* in the K.I.S.S. principle, "simple."

My gutted '60 Kombi is darn close, but a bit large for a DD.

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.

Guys the numbers are conflicting here but look promising. Skyactiv X is targeting "27% better thermal efficiency"... Don't quote me on this but isn't their current engine around 36.5% thermal efficient. Thats a boost to 46.4% thermal efficiency which agrees with whats currently possible with ICE on the cheapest energy currently available to run a car aka 87 octane.
Imagine a 2016 Mazda 3 gets 33 mpg combined that could result in 42 mpg combined and 51 highway. I'd also assumme if they're going to these lengths to bust EV and Hybrid balls they will probably drop the cd down to at least 0.23. Seems neat in 2800 pound car.
(https://pdfs.semanticscholar.org/226...3adda2e15f.pdf)
(Mazda Skyactiv-3 Engine to achieve 56% thermal efficiency)
Think of the hypermiling for the love of god. lol

The only question is when will they put HCCI in the Mx5/ Miata.

As long as they run port injection as well (only way I've seen to keep the intake valves clean).

My understanding is that there is a small in cylinder injector for providing a richer mixture in vicinity of spark plug and a port injector for fuel to rest of cylinder. i.e stratified combustion

Having re-read Mazda's literature, it would appear that there is 1 direct high pressure injector per cylinder.

https://insidemazda.mazdausa.com/pre...s-information/

Adding back to the list it looks like Mazda isn't just targeting peak thermal efficiency by using compression ignition and lean burn, they are also using it to increase thermal efficiency to a much greater amount under higher loads where a Prius would say be less efficient than a Bmw m3 (see top gear test) unless its in its peak small operation window. So it sounds like it should hit the Miata.

https://www.forbes.com/sites/peterly.../#4872e924d7ff

The count down is getting close. I'm loving what I hear so far. We are either good guessers or they browse this forum. ;)
"The SkyActiv-X is a 2.0-liter gasoline engine employs a common rail-style system from a diesel engine, a supercharger and a mild hybrid system (24V System) to create an engine that produces 178hp, generates beefy bottom-end torque, like a diesel, but spins freely to 6500 revs, like a gasoline engine."

Also from a separate article: "Toyota has used a Subaru boxer engine in its GT86 coupe, and more recently, employed a BMW 6-cylinder powerplant for its reborn Supra sports car, the same engine fitted to the new Z4. And in return, Toyota has allowed its THS II hybrid system to be incorporated into models including the Mazda3 hybrid."

So it looks like Toyota has really taken over when it comes to hybrid transaxles. Good to hear... At least there will be reliability.