Mazda announces SKYACTIV-X: gasoline Spark Controlled Compression Ignition
08 August 2017
Mazda Motor Corporation announced “Sustainable Zoom-Zoom 2030,” a new long-term vision for technology development that looks ahead to the year 2030. As part of the new technology to achieve this vision, the company disclosed plans to introduce a next-generation gasoline engine called SKYACTIV-X in 2019.
SKYACTIV-X—which Mazda believes will be the first commercial gasoline engine to use compression ignition—uses a proprietary combustion method called Spark Controlled Compression Ignition (SPCCI). Mazda says that SCCI overcomes two issues that has impeded commercialization of compression ignition gasoline engines: maximizing the zone in which compression ignition is possible and achieving a seamless transition between compression ignition and spark ignition.
This new proprietary combustion engine combines the advantages of gasoline and diesel engines to optimize environmental performance, power and acceleration performance.
Compression ignition combined with a supercharger will improve fuel economy while delivering tremendous engine response and increased torque of 10–30% over the current SKYACTIV-G gasoline engine. (Earlier post.)
Compression ignition makes possible a super lean burn that improves engine efficiency up to 20–30% over the current SKYACTIV-G, and from 35–45% over Mazda’s 2008 gasoline engine of the same displacement. SKYACTIV-X even equals or exceeds the latest SKYACTIV-D diesel engine in fuel efficiency.
With high efficiency across a wide range of rpms and engine loads, the engine allows much more latitude in the selection of gear ratios, providing both superior fuel economy and driving performance.
In 2014, Mazda said that it was planning a second generation of SkyActiv gasoline engines around 2020 that would achieve approximately 30% better fuel economy than production SKYACTIV engines using a form of homogenous charge compression ignition (HCCI) (see Yamasaki et al., 2015). (Earlier post.)
Under the original “Sustainable Zoom-Zoom” vision announced in 2007, Mazda has endeavored to offer both driving pleasure and environmental and safety performance. In light of the rapid changes taking place in the automotive industry, the new vision takes a longer-term perspective and sets out how Mazda will use driving pleasure—the fundamental appeal of the automobile—to help solve issues facing people, the earth and society.Under Sustainable Zoom-Zoom 2030, Mazda aims to reduce corporate average well-to-wheel carbon dioxide emissions to 50% of 2010 levels by 2030, and achieve a 90% reduction by 2050. It intends to achieve this with a policy prioritizing efficiency improvements and measures for cleaner emissions that apply in the real world.
In line with this policy, Mazda will continue efforts to perfect the internal combustion engine, which will help power the majority of cars worldwide for many years to come and can therefore make the greatest contribution to reducing carbon dioxide emissions. Mazda will combined these optimized engines with effective electrification technologies.
From 2019, Mazda will begin introducing electric vehicles and other electric drive technologies in regions that use a high ratio of clean energy for power generation or restrict certain vehicles to reduce air pollution.
Mazda will also begin testing of autonomous driving technologies currently being developed in line with Mazda’s human-centered Mazda Co-Pilot Concept in 2020, aiming to make the system standard on all models by 2025.
Yamasaki, Y., Umahashi, S., Uesugi, Y., Ma, Q. et al. (2015) “Development of Dynamic Models for an HCCI Engine with Exhaust Gas Rebreathing System,” SAE Technical Paper 2015-01-1803 doi: 10.4271/2015-01-1803.
Sadly, this article does not really say anything about the technology other than using lean burn and a supercharger. I have not read the SAE Paper, I have to admit. They also speak about increasing compression ratio to 18:1 in an older article at GCC. Both increasing CR and using excess air (via supercharging) is beneficial for efficiency. This we also know from diesel engines, i.e. nothing fundamentally new when it comes to thermodynamics. The interesting part is how they control combustion and in particular, knocking and flame speed. This is the Achilles’ heel for gasoline engines but pose no problem for diesels. The main disadvantage of lean burn is the difficulty to control NOx via exhaust aftertreatment. This we also know from experience on diesel engines and, in fact, also on gasoline engines. It was a significant problem on early GDI engines that all operated under lean-burn conditions. Mercedes are one of the few manufacturers who still pursue lean burn on some of their gasoline engines, albeit to my knowledge not on all markets. In summary, this article raises more questions than it answers. If anybody has well-founded technical insights into Mazda’s technology, I am all ears.
Posted by: Peter_XX | 08 August 2017 at 03:43 AM
That's a good news. Im interrested that someone else buy as i already have a newer car.
Posted by: gorr | 08 August 2017 at 06:12 AM
By having (assuming) homogeneous (very) lean air-fuel mixture, you reduce a lot, in theory, the combustion temperature and therefore you keep the production of NOx at a minimum. Assuming that is HCCI or PCCI, flame speed is not an issue.
Lean burn GDI engines are not lean enough to have so low NOx emissions, at least with the current and future emission legislations.
Posted by: DJ_D | 08 August 2017 at 06:26 AM
I thought lean burn engines actually produced hotter temperatures and I also thought hcci was recently revealed to produce excessive PM 2.5 and NOx. Am I wrong?
Posted by: The Lurking Jerk | 08 August 2017 at 09:18 AM
“Sustainable Zoom-Zoom” - who named that ?
It is not a toy car.
Posted by: mahonj | 08 August 2017 at 12:04 PM
Don't get me wrong, I am all for this, especially if it can be done cheaply, and better still if it could be used in PHEVs.
(But maybe that is for another day.)
Posted by: mahonj | 08 August 2017 at 01:20 PM
Sorry to say, it is not that easy.
Flame speed is definitely an issue with HCCE and PCCI. It is almost like a detonation. It is much, much worse than diesel if you look at pressure rate for cylinder pressure. You would hear this car blocks away. Thus, something must be done to abate combustion noise.
You can have low NOx if air excess is high. Yes! HCCI/PCCI can run much leaner than GDI. However, this is not the full story. You have to reduce excess air at full torque (and close to full torque) and then NOx will rise sky-high (any joke about that is on me…). Try to imagine running excess air at 2:1 ratio at full load with high compression ratio and fast combustion. No engine structure in the world could handle such cylinder pressure. It would be much, much higher than for diesel. If you limit cylinder pressure to reasonable levels, power and torque would be a joke and you would have to do a lot of “anti-downsizing” This would ruin fuel economy. Recall research carried out by Huyndai/Delphi. They certainly had to deal with high cylinder pressure and you can find comments from me on that as well in the past on this forum. Furthermore, if you are just marginally on the lean side, TWC will not work. So, in essence, you would have sky-high NOx at high load but conventional aftertreatment would not work. Even if this problem would not be too bad in a conventional test cycle, RDE would kill such an engine. You could imagine replacing excess air with EGR, perhaps gradually, but this is not easy to control. Toyota tried this many years ago with homogenous lean-burn (long before GDI) but the result was not very good. I have tested such cars myself in the laboratory. Needless to say, NOx was much higher than from TWC cars. You could adopt similar aftertreatment as for diesel (NOx-trap + SCR) but it comes at a cost and you would still struggle in off-cycle conditions.
In summary, there are a lot of issues to explain. Perhaps Mazda has cracked a couple of the nuts but we have no idea about how they did it.
Posted by: Peter_XX | 09 August 2017 at 05:23 AM
Mazda says that full load, high speed etc, it will work like regular SI. They are using mode switching.
Pressure rise rates can be better controlled if you do PCCI, better than HCCI, but probably worse than regular diesel/gasoline. That's why i believe it will be closer to SA-PCCI rather than SA-HCCI. NOx emissions, maybe SCR or LNT i suppose, unless they are so much lower although Mazda says that they are using EGR as well. Still they have 1,5 year before releasing it if they go according to plan.
Huyndai/Delphi say, they can do RON91 calibration and keep NOx below limits without aftertreatment but i don't know how true that is, or within which load range.
Posted by: DJ_D | 09 August 2017 at 10:08 AM
Toyota, with current best efficiency ICEs, will probably benefit with their recent limited FV with Mazda?
Posted by: HarveyD | 10 August 2017 at 08:38 AM