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SKYACTIV-X: first commercial gasoline engine to use compression ignition

www2.mazda.com

31–40 of 241 posts

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#31
post #2

Mazda is one of those companies just don't stop revolutionizing. First they got rotary to be actually usable. Now this.

Did they get the rotary to be usable? I thought even at its best, it was finicky and temperamental. I have never owned or driven one, just doing some idle reading online, so asking this as a serious question.

Owned one. Enjoyed the heck out of it.

Lots of torque, lots of pep, though from what I heard, the US version (mine) had substantial increases in pollution controls which hobbled the car. Always first off the line when I wanted to be.

Yes, it burned oil by design. I'd add a half-quart of non synthetic 5W-20 maybe every 1000 miles. The rear bumper required additional car washes, as it'd get a black film, no doubt from cold starts. That wasn't much of a problem.

The big issue it had was flooding the engine. To trigger the condition, turn on engine, let it run for less than 1 minute, and turn it off (like pulling it in or out of a garage). Unless you floored it in neutral before shutting it off, the car would end up near-bricked.

The fix was to have it towed to the dealer where they'd clean out the engine for a few hundred dollars. Later I learned you could tow-start it if you could get it up past 20mph. It'd put all kinds of foul smoke out the back when you did that but in terms of hassle, it was much better.

The car had a POS OEM fuel pump under the rear seat. On hot days you'd get a vapor lock. Not the rotary's fault. Took years to find that problem, and didn't get very long with the fixed version before the stork came and the rotary had to leave.

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#32
post #13

Gah, terribly confusing terminology. This is a Diesel engine. "Compression ignition" is what the Diesel cycle is all about. It's just carefully tuned such that it can run on gasoline instead of kerosene (i.e. "diesel fuel "). And mostly I don't get it. This is just a convenience factor. If you want a high-efficiency diesel right now you can buy one already. Low-volatility fuels are already more energy-dense (i.e. few…

It's not exactly the same as a diesel engine. Diesels use a stratified charge (SCCI), meaning fuel is injected at the end of the compression stroke and burns immediately, without having a chance to mix thoroughly with the air. This engine uses a homogeneous charge (HCCI), meaning fuel is injected at the beginning of the intake stroke but does not ignite until the end of the compression stroke, therefore having time to mix with the air. This subtle difference makes the engine much harder to control, but should yield lower NOx and particulate emissions as well as higher power output.

Also, the engine is capable of running in HCCI mode under light-ish load. It still has spark plugs, and can run as a normal gasoline engine (HCSI) when high power is demanded.

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#33

A reuters story on how it works: https://www.reuters.com/article/us-mazda-strategy-idUSKBN1AO... So this is 'gasoline' diesel. Or diesel without the NOx. Which, in theory, would give better fuel economy and possibly better torque. And it will ship in cars in the 2019 model year (so possibly as early as late next year). To me, it sounds like a "Don't pass"[1] bet on electric cars. Which they also are working with Toyo…

Or a bet on hybrids. Hybrids enable new types of engines that for instance operate at constant rate or that are under-powered for acceleration from a stop or going uphill.

I don't think hybrids have any future except in the heaviest of vehicles, where batteries won't make sense for another few decades.

We're already seeing companies being interested in making battery-only buses, tractors, semis, and even airplanes. Not all models of those types of vehicles may work with batteries, but it's a sign of what the future could bring.

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#34
post #27

Earlier quoted context omitted.

Heh. I mean an engine rebuild at 80k seems kind of crazy. I am both continually amazed at the ICE and at the same time can't wait for it to die out. It's such an archaic technology. Hell, a turbine engine would be so much more fun to have in a car!

... as long as it isn't directly connected to the wheels? The rotational inertia would make for a very uncomfortable drive.

Chrysler made several generations of turbine cars in the '60s.

http://www.allpar.com/mopar/turbine.html

It was not, in the end, a production car, but there was a lot of data gathered as to performance and reliability in real-world settings.

Not too long ago, Jaguar had a concept CX-75, which was a hybrid mid-engined supercar where the piston engine was replaced with two Bladon Jets micro gas turbines. After 2008, they didn't want to commit to an expensive limited production vehicle, too bad.

https://www.theengineer.co.uk/issues/18-october-2010/jet-pow...

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#35

A reuters story on how it works: https://www.reuters.com/article/us-mazda-strategy-idUSKBN1AO... So this is 'gasoline' diesel. Or diesel without the NOx. Which, in theory, would give better fuel economy and possibly better torque. And it will ship in cars in the 2019 model year (so possibly as early as late next year). To me, it sounds like a "Don't pass"[1] bet on electric cars. Which they also are working with Toyo…

Gasoline engines aren't going away for a while; even when every self-driving car is electric, there will be a market for people who want gasoline engines. If it gives a bump in fuel economy to the next (last?) generation of gasoline and hybrid vehicles, great!

I also wonder if the maintainability of these engines will be the same as with diesel. That would be another big benefit.

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#36
post #3

>Compression ignition and a supercharger fitted to improve fuel economy together deliver unprecedented engine response and increase torque 10-30 percent over the current SKYACTIV-G gasoline engine.*3 Wow. I already have a 2016 Mazda 3 that gets around 40MPG (even though it's not a hybrid) and it's already pretty peppy. Probably the best car I've owned, and I've owned several nice sports sedans. Getting 40MPG is too c…

That is horrible mileage. I remember averaging that on a 1997 Opel Astra.

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#37
post #13

Gah, terribly confusing terminology. This is a Diesel engine. "Compression ignition" is what the Diesel cycle is all about. It's just carefully tuned such that it can run on gasoline instead of kerosene (i.e. "diesel fuel "). And mostly I don't get it. This is just a convenience factor. If you want a high-efficiency diesel right now you can buy one already. Low-volatility fuels are already more energy-dense (i.e. few…

Yes, however common diesel fuels tend to be higher in NOx and particulates. My understanding is that because gasoline is refined to a higher degree it burns a fair bit cleaner in similar environments(and also makes it a PITA to store for more than a few months). [edit] We've got a pair of tractors around the house here, '81 diesel(pre-emissions), and '47 gasser. I can tell you which one I prefer to run from an exhaus…

NOx emissions from a diesel engine are from atmospheric nitrogen and oxygen, not from the fuel. I welcome further clarifications, but my understanding is that this engine will not produce NOx like a standard diesel because the fuel/air mix will be tightly controlled like in a gasoline engine, and temperature and pressure will be significantly less than a standard diesel. Additionally, it seems the timing of the fuel injection will be much earlier than a diesel, resulting in more complete air/fuel mixture; this is possible because gasoline has a higher ignition temperature, so fuel can be injected early and ignition won't happen until the compression stroke; diesel fuel would ignite during injection regardless of where in the cycle.

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#38

A reuters story on how it works: https://www.reuters.com/article/us-mazda-strategy-idUSKBN1AO... So this is 'gasoline' diesel. Or diesel without the NOx. Which, in theory, would give better fuel economy and possibly better torque. And it will ship in cars in the 2019 model year (so possibly as early as late next year). To me, it sounds like a "Don't pass"[1] bet on electric cars. Which they also are working with Toyo…

Gasoline engines aren't going away for a while; even when every self-driving car is electric, there will be a market for people who want gasoline engines. If it gives a bump in fuel economy to the next (last?) generation of gasoline and hybrid vehicles, great! I also wonder if the maintainability of these engines will be the same as with diesel. That would be another big benefit.

> I also wonder if the maintainability of these engines will be the same as with diesel

They also include traditional spark plugs and the engine automatically switches between modes. So, I fear that maintenance wise, it may be the worst of both worlds -- but with less wear and tear on the spark side, perhaps it will be better.

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#39

Earlier quoted context omitted.

Did they get the rotary to be usable? I thought even at its best, it was finicky and temperamental. I have never owned or driven one, just doing some idle reading online, so asking this as a serious question.

Owned one. Enjoyed the heck out of it. Lots of torque, lots of pep, though from what I heard, the US version (mine) had substantial increases in pollution controls which hobbled the car. Always first off the line when I wanted to be. Yes, it burned oil by design. I'd add a half-quart of non synthetic 5W-20 maybe every 1000 miles. The rear bumper required additional car washes, as it'd get a black film, no doubt from…

> before the stork came and the rotary had to leave

One of my friends had an rx-8, the backseats were useless for adults, but glorious for car seats.

Re: SKYACTIV-X: first commercial gasoline engine to use compression ignition

#40
post #2

Mazda is one of those companies just don't stop revolutionizing. First they got rotary to be actually usable. Now this.

The rotaries leaked oil and got terrible mileage, and good luck finding someone to work on them. Other than that, they were zippy. "Usable" they might have been if you keep a low bar, but "practical" they were not.

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