By on January 16, 2017

mazda skyactiv

While it wasn’t the only car company to make use of a rotary engine, it was certainly the only one to be competitive with them when pistons and pushrods would easily have sufficed. However, those days are gone. Mazda’s SkyActiv technology is well suited for squeezing out an engine’s true potential, but it doesn’t feel particularly quirky or unique.

That could change with the company’s second generation of SkyActiv engines. Mazda is one of only two automakers planning to introduce a motor with homogenous charge compression ignition (HCCI) sometime next year. If you’re unfamiliar, that’s a direct-injection gasoline-powered motor that uses compression, not spark, to ignite fuel — something typically reserved for diesel powerplants.

Mazda expects the HCCI engine to yield a 30 percent improvement in fuel economy over a similarly-sized conventional internal combustion unit. The new engine should debut in the Mazda 3 as part of its mid-cycle refresh in 2018, and then expand into other models.

According to the Nikkei Asian Review, the second generation SkyActiv engines should give the Mazda3 fuel economy “approaching 30 km per liter.” While only a rough estimate, that equates to over 70 miles to the gallon — enough to put hyper-mile hybrids to shame and meet stringent CAFE standards.

Of course, Mazda also plans to mass produce an electric vehicle by 2019 while it procrastinates on a plug-in hybrid until 2021. The company also remains committed to bringing its extremely emission-friendly Skyactiv diesel to the North American market.

[Image: Mazda]

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65 Comments on “Spark-free SkyActiv: Mazda Seems Well Prepared for the Future, Without Electricity’s Help...”

  • avatar

    Why is this engine so much more efficient?? Is it the compression ratio? Or does this technology allow using less fuel for propagating the flame front? Does the loss of the spark plug allow a redesign of the combustion chamber? Can it use different octanes, or even diesel in a pinch?

    • 0 avatar

      No pumping losses by virtue of eliminating the throttle plate.

      • 0 avatar

        There are plenty of throttle plate-less engines already (BMW Valvetronic, Fiat Multair, Nissan VVEL).

        HCCI basically runs like a diesel, but uses gasoline. They are ditching or at least not constantly using spark plugs. It runs super lean, which enables less fuel to make the same power.

        Big problem is the explosions are more violent… it’s basically controlled knock. Once that nut is cracked though, which I think is feasible with the current state of design and materials, it’s off to the races. I do feel like we might see a return to iron blocks though.

        • 0 avatar

          Throttling by limiting valve lift instead of using a throttle plate (as those engines do) still creates pumping losses.

        • 0 avatar

          It’s “controlled” knock, but depending on the injection sequence per cycle, it’s not really “knocking” all that much, for example if they are using a pre TDC pilot injection fuel that starts the flame front and then a TDC or slightly post TDC main injection for the stroke, the knock will be largely insignificant. As long as they have overlapping powerstrokes, i.e. inline 6 or v6 or greater, you’d never notice. Might be a little rough in a 4 cylinder though.

        • 0 avatar

          Except that with modern direct injection the amount of fuel burning can be controlled during the power cycle to give the desired cylinder pressure profile in real time.

    • 0 avatar

      The Wikipedia entry for HCCI engines is probably a good place to start for answering these questions.

    • 0 avatar

      Different thermodynamic cycle for compression ignition, “diesel cycle” vs otto cycle, look at the PV graphs for each cycle, the diesel cycle can extract more energy for pushing against the piston rather than just as waste heat.

    • 0 avatar

      gasser – – –

      Some reasons for the greatly increased “efficiency” of the HCCI approach are:
      1) With DI and multiple charge delivery, MUCH higher compression ratios are possible: think 16:1 as opposed to 10:1;
      2) Multiple charge delivery means a lean-run, transient explosion environment, which reduces the excessively rich, low-RPM fuel waste and less pollution;
      3) The “controlled knock” method is no longer a pure low-temp burn, but a high-temperature explosion, which generates MUCH higher pressures in cylinders AND much higher temperatures.

      1) Explosions in transient multi-charge applications are harder to control than real “burns”;
      2) Strength of engine materials must be much higher, even MORE so than in current diesel engines;
      3) Enormous temperatures will require ceramic materials in piston walls, rings (like MACOR) and cylinders;
      4) Expense of and maintenance on these ultra-efficient engines will much higher;
      5) Don’t plan on getting 200,000 miles out of these designs: longevity will be shortened.

      Will be interesting to see how Mazda tries to pull this off. I would think a variable displacement engine would be a more feasible approach than essentially putting little “bombs” inside you car.


      • 0 avatar

        “5) Don’t plan on getting 200,000 miles out of these designs: longevity will be shortened.”

        The US Government spec for endurance of General Purpose Utility vehicles (later called “Jeeps”) in 1940 was the ability to run its engine AT RED LINE for at least 1 hour. Barney Roos’s L-134, 4-cylinder L-head side-valve ran for over 100 hours at red line, before simply being shut down. Nobody else could even come close to that. My car contacts (various mfgrs) tell me that their modern engines could now only tolerate between 1 and 10 minutes at redline before “blewy”.

        How long at high RPM’s can we expect this HCCI “bomb” engine to run?


        • 0 avatar

          I’m not buying that. My engine passes a standard engine design test of 300 straight hours at full throttle cycling between the 4500 rpm torque peak and the 6500 rpm power peak – also the start of redline – and yet it could only run for 1 to 10 minutes at 6500 rpm, or even the 7100 rev limiter?

          I’d put good money on my next rental car lasting far longer than that driving at the rev limiter. Pretty much any length of time you’d be willing to sit in the passenger seat!

          Regardless, I would wait a few years for this technology to prove itself before I’d buy one.

      • 0 avatar
        Big Al from Oz

        There is one significant issue. Emissions with the HCCI engine.

        HCCI engines will produce increased quantities of NOx and a sh!tload more particulates.

        Mazda claimed the curtent Skyactive diesel would not require AdBlue to meet US standards. I would assume it will need a particulate filter (GPF).

        The cost of meeting emissions will jack up the price more than a comparable gas engine equivalent.

        • 0 avatar

          Mazda is using urea injection (Adblue) for the diesel in the the 2018 CX-5. It wouldn’t be surprising to see urea injection being used with HCCI engines. there has already been some talk of using urea injection on normal gas engines to meet future emissions targets.

        • 0 avatar
          Big Al From 'Murica

          On the plus side, if we start seeing these emissions controls proliferate to gas motors we should see them get better as more manufacturers get into the game of making them. We are rapidly approaching the stage however where automakers needn’t install a good since you won’t be able to do anything under it anyway though.

          • 0 avatar

            “We are rapidly approaching the stage however where automakers needn’t install a good since you won’t be able to do anything under it anyway though.” Same ninny hand wringing we heard when electronics and fuel injection were implemented.

        • 0 avatar

          That’s the opposite of what most of the stuff I’m reading this morning says – gasoline HCCI produces low NOx (“nearly no NOx emissions” according to Nissan) and PM, at the expense of increased CO and hydrocarbons.

          • 0 avatar
            heavy handle

            HCCI should produce lower level of NOx because it produces fewer hot spots in the combustion chamber. That remains to be seen in production motors.

            CO and HC should definitely be lower, that’s the whole point. A more efficient combustion produces lower unburnt hydrocarbons. CO hasn’t been an issue since the advent of catalytic converters.

    • 0 avatar

      Engineering Explained has a neat little video on HCCI engines that does a pretty good job of well err explaining it.

      Go… go… gadget Goggle!!!!


      • 0 avatar

        That gives a good explanation as to how it all works, thanks! Seems like I’ve heard about HCCI for a while now, it’s exciting that Mazda might finally have it figured out for production.

    • 0 avatar

      It’s not that much more efficient. The Japanese mileage testing cycle gives some very inflated numbers. Remember when the 3rd-gen Prius was about to come out and there were rumors of it getting 86 or 90mpg? Those were real numbers, but using the Japanese test.

  • avatar

    So would it act like a diesel and inject the fuel near TDC or inject in on the intake stroke and it would self-detonate on it’s own? Seem’s like if it’s the latter you would need something like Nissan’s variable compression engine to make it work with different gases. Since I don’t imagine the 93 octane at every gas station is exactly 93 octane.

    Also I’d assume these would be very susceptible to carbon buildup since cylinder compression would have to be so precise.

  • avatar
    Dave W

    I realize I’m math challenged but if a 30% reduction in fuel use results in 70MPG what engine are they currently getting ~54mpg out of?

  • avatar

    For all the love SkyActiv gets among the enthusiast press, doesn’t do much better than comparable powertrains when installed in comparable platforms, especially in tests that more closely approximate the real-world.

    Also, doesn’t HCCI share some of the same emissions concerns as diesel?

  • avatar

    The HCCI/DI setup will produce high levels of NOx on gasoline and will most likely require DEF additions just like a diesel engine. Higher compression = more NOx, less CO2.

    • 0 avatar

      Even though HCCI uses a lean mixture and high compression, this type of ignition supposedly has low peak cylinder temperatures, resulting in lower NOx production.

  • avatar

    30% better in ideal circumstances, sure, but 30km/l is a stretch for actual driving, 30 km per litre is 3.3l/100km in regulation speak.

    As a comparable car, the Golf TDI is rated at 5.2l/100 on the highway (Canada). The only car that is actually rated at 3.3l/100kn is the SmartForTwo.

    If we assume that HCCI approaches but does not exceed the efficiency of diesel, then the claim 30% improvement claim doesn’t pass muster unless they are using a very loose definition of “similar conventional engine.”

  • avatar

    Pretty amazing, if they can pull it off, for a use case as power requirement and driving environment variable, and intolerant of eccentric behavior, as a mass market passenger car. It honestly seems too good to be true, to put it that way.

  • avatar

    I believe in the Skyactiv diesel when they are for sale in the United States.

    It will be interesting to see where Mazda continues to go with engine technology to meet increasing standards.

  • avatar

    Companies could have been doing this for years. I suppose it’s making the engine meet emissions and superior fuel economy which really matters.

    There is a prototype Ford 302 (5.0) from the early 80s sitting in the “Museum of American Speed”, which is an HCCI gasoline engine, witnessed it with my own eyes.

  • avatar

    Just wanna say that this is some game-changer stuff here.

    I’m not deluded into thinking this will beat hybrids or plug-ins or other advanced tech on MPG.

    But for a gas-only engine, something still installed on what percent of every car sold today (98% 99%?) this has the potential to make a HUGE difference in fuel use if it spreads across the industry.

    I’d also like to know the dollars and sense of this vs adding say a hybrid drivetrain to a traditional gas engine. Is there also a big cost savings?

    Of course I’ll withhold final judgement until driven and its proven reliable. Wonder if it will be very diesel-like in the way it drives. Cool tech but might not be ideal for a Miata.

    • 0 avatar

      Maybe Mazda can license it to a company that sells cars.

      • 0 avatar

        Funny, OM, that made me snicker! But every other word I read about the Mazda brand other than “noise” and “rust” is flamboyantly positive. It’s a real driver’s car, they all proclaim. Tell me, how old will I have to get before that becomes a negative?

        I just had a 7mm stone forceably removed today, right down the ‘ol downspout. How’s that for playing the Geezer Card. But I still likes me some “Zoom-zoom.”

  • avatar

    THis would be really nice on a 3.5 ltr V 6. If you figure that they make it from scratch themselves it would end up with about 35mpg on the hwy.

  • avatar

    >>it was certainly the only one to be competitive with them when pistons and pushrods would easily have sufficed.<<

    Not really. Seems Mazda was the last automaker to know that Wankels weren't competitive.

  • avatar
    Sgt Beavis

    WoW and Good on Mazda. So many companies had been working on this yet Mazda is cracking the nut first.

    • 0 avatar

      As someone who has drunk the Mazda koolaid, I think they’ve done pretty incredible bits of engineering since Ford sold their shares. They’re a tiny company working with pretty limited resources coming up with advances in the ICE on par or better than much larger companies. Even if you don’t like their cars, there’s still a lot to admire about them as a company.

  • avatar

    Will by outlawed by the Trump administration a few days after he is inaugurated.

  • avatar

    Turbo, DPF, Adblue, all the baggage of a diesel on an unproven engine design. I think I’ll wait for a while.

    • 0 avatar

      I agree! As someone who maintains his own cars and keeps them long-term, something like this would be off of the table until proven. I have never heard of an HCCI so thanks to Matt P – I just came off of a 2 hour HCCI reading binge. Fascinating stuff!

    • 0 avatar
      Big Al From 'Murica

      I think we can scratch turbos off the “unproven” list…they have been around for a minute. As for the rest, yeah I’d wait for the “gen II” model assuming Mazda has the resources to make it happen.

  • avatar

    It’s going to be really interesting to see if they can pull this off. From what I’ve read, HCCI engines really like to run at a constant speed, making them ideal for a series-parallel hybrid or for use with a CVT.

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