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

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

#21

Post by philipkglass »

IgorPartola wrote: post #12

So how exactly does this work? And why is it more effective and how does it allow you to run super lean while producing the same amount of power? Also, presumably running lean would mean lower emissions, but is that really true?

Running lean, highly compressed, and highly efficient reduces expected production of carbon monoxide and residual hydrocarbons. But it significantly increases nitrogen oxide formation, as in diesel engines. So I wonder how the emissions control system deals with the extra NOx -- that has (see Dieselgate and continuing related fallout) proven quite a sticky problem for high efficiency diesel engines in passenger vehicles. The cheap "solutions" were mostly cheats and the actual solutions cost more.

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

#22

Post by vvanders »

ajross wrote: 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 exhaust perspective, the diesel may have torque and is a dead-simple engine but you don't want to be downwind of it when cutting heavy brush.

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

#23

Post by ddeck »

IgorPartola wrote: post #10
Danihan wrote: 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…

I think you are misreading that. The increase of 10-30 percent is in torque, not MPG.

This is correct, but they're are also predicting an equivalent improvement in fuel consumption:

"Compared to the current lineup of SkyActiv-G engines, the SkyActiv-X line should use between 20 and 30 percent less fuel."

http://newatlas.com/mazda-skyactiv-x-compression-ignition/50...

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

#24

Post by pedrocr »

ajross wrote: 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…

This is much more interesting than that. It's a gasoline engine (fuel injected at intake and spark to ignite) that can operate in compression ignition in some of its range and thus get better mileage[1]. It should get efficiencies much similar to diesel but me much cleaner (less NOx).

[1] https://en.wikipedia.org/wiki/Homogeneous_charge_compression...

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

#25

Post by ynniv »

quake wrote: post #16
IgorPartola wrote: post #5

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.

More or less usable. They did have a tendency to blow apex seals after 80k miles, which was could end up as a full rebuild of the engine. As far as how finicky a rotary can be, the biggest thing to do is let them warm up before driving, and let them cool right down after you're done. They were never an engine to replace the standard fourbanger, but they weren't any more finicky than say a BMW or Audi at the time of t…

weren't any more finicky than say a BMW or Audi at the time of the RX-8

YMMV, but my E46 BMW has been very reliable compared to an RX-8 bought at the same time. Audi was still in the process of applying the lessons of the RS4 to their everyday cars, but I still wouldn't call the RX-8 reliable compared to its peers. As you hinted, there are a couple of problems that lead to full rebuilds before 150k miles.

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

#26

Post by silassales »

ajross wrote: 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…

Taken from the article linked above: https://www.reuters.com/article/us-mazda-strategy-idUSKBN1AO...

> Its fuel economy potentially matches that of a diesel engine without high emissions of nitrogen oxides or sooty particulates.

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

#27

Post by ynniv »

IgorPartola wrote: post #17
quake wrote: post #16

Earlier quoted context omitted.

More or less usable. They did have a tendency to blow apex seals after 80k miles, which was could end up as a full rebuild of the engine. As far as how finicky a rotary can be, the biggest thing to do is let them warm up before driving, and let them cool right down after you're done. They were never an engine to replace the standard fourbanger, but they weren't any more finicky than say a BMW or Audi at the time of t…

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.

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

#28

Post by bigtech »

borski wrote: post #7
Danihan wrote: 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…

OK, so honest question: I have a 2012 Mazda 3 which, presumably, gets 40mpg. But I can't realistically get anything above 29mpg on average. Am I just an aggressive driver? :) [edit] I agree, by the way, that the cars are incredibly fun to drive, for being "fuel efficient."

Have you tried 'hypermiling'? https://en.wikipedia.org/wiki/Energy-efficient_driving

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

#29

Post by greggyb »

borski wrote: post #14
greggyb wrote: post #9

Earlier quoted context omitted.

2012 had half Skyactiv and half .. non-Skyactiv. The expected MPG on the non is around 30. You'd have a badge on the rear of the car (if sold in US, at least) that would indicate Skyactiv.

I have the badge.

I had the 2012 for a few years. When I was driving 80%+ highway, I would struggle to get below 35MPG or above 42MPG.

On a 50%-50% split, I would be in the mid 30s, usually 36MPG or 37MPG.

When I was 80% city, I would be around 32MPG on average.

That car does not have much low-end torque, so if you accelerate aggressively from stops you can definitely tank the MPG. I didn't see much impact from aggressive acceleration at highway speeds (e.g. going from 30MPH to 70MPH on an on-ramp, or pulling around a slow group of cars going from 45MPH-70+MPH). I did see a lot of impact from flooring it 0-30.

Hope this context is helpful.

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

#30

Post by bsdetector »

ChuckMcM wrote: post #18

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.
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