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Mazda is already discussing Skyactiv 3 as well

Mazda only recently started introducing its Skyactiv engines to its different vehicle models, but the automaker is already talking about the upcoming Skyactiv 2 -- and even Skyactiv 3 -- engines for the next decade and beyond. 
According to a new report from Automotive News, Mazda plans to gain 30 percent better fuel economy with its Skyactiv 2 engines, which are expected to have a 2020 release date. A 30 percent improvement in fuel economy would make the already impressive Mazda3 rise from 29/41 mpg (city/highway) in its more efficient trim to 38/53 on regular unleased gasoline.

2014 Mazda3

Mazda plans to achieve this 30 percent increase in fuel economy by improving the internal combustion of the Skyactiv 2 engines. More specifically, the Skyactiv 2 engine's compression ratio would be bumped up to 18:1 from a current level of 14:1. 
This higher compression is able to reach the same combustion temperature as the current engines, but with a leaner mix of fuel -- meaning improved fuel economy. 
The Skyactiv 2 engines will utilize homogeneous charge compression ignition (HCCI), which compresses the fuel-air mixture to a high enough pressure and temperature that it ignites by itself without needing a spark. This allows for more complete fuel combustion and lower nitrogen oxide emissions.
However, the Automotive News report indicates that HCCI won't come easy. Engineers must first expand the range of engine speeds for HCCI specifically, because the engine revving too quickly can result in a misfire due to the high number of revolutions, and if revved too slowly, it can misfire due to low temperatures.

2.0-liter Skyactiv four-cylinder engine
Aside from that, engine cooling and the engine's tendency to behave differently based on the use of different fuels need to be figured out.
The main goal with Skyactiv 2 is to meet European carbon dioxide emissions standards of 95 grams per kilometer in 2020, but Mazda is looking even further ahead at meeting Europe's standards of 65 grams per kilometer in 2025 with Skyactiv 3. 
Mazda didn't go into great detail about Skyactiv 3, but the automaker plans to make more energy available for powering the wheels by limiting the fluctuation of heat in the combustion chamber and reduce losses from exhaust and cooling. Mazda hopes to reach well-to-wheel carbon dioxide emissions with Skyactiv 3 that rival electric vehicles.
Mazda first introduced Skyactiv engines to the U.S. market in 2011, starting with the Mazda3 sedan. Since then, they've been added to the Mazda6 sedan and CX-5 crossover.
Mazda has been trying to bring the Skyactiv-D diesel engine to the U.S. via the Mazda6, and was supposed to have achieved this by the second half of 2013. However, in September of last year, it was announced that delays in emissions testing has pushed that timetable to late spring of 2014.

Source: Automotive News

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RE: Hmmm
By TheEquatorialSky on 1/6/2014 2:21:33 PM , Rating: 3
Efficiency only grows logarithmically with CR. Without doing the math, I'd say going from 13:1 to 14:1 is only a 1-2% boost in efficiency.

The Skyactiv engines don't really operate at 13-14:1 CR anyways, they only do so at part throttle. The engines use specially shaped pistons and a tuned exhaust to increase cylinder scavenging, reducing intake charge temperature. If they ran at 14:1 at max BMEP, the engine would detonate (even with GDI). They use a variable intake valve to limit high CR to part throttle operation only.

RE: Hmmm
By Spuke on 1/6/2014 7:09:45 PM , Rating: 2
I was wondering how they were able to get away with that high CR (even with DI). Thanks for that info.

RE: Hmmm
By Samus on 1/7/2014 1:50:21 AM , Rating: 2
You don't have to do the math. Thousands of others all over the world have already done it for you. A quick Google search shows many people in Great Britain, Australia and Japan average around 35mpg mixed driving in the 2013 CX-5 2.0 where our 2013 CX-5 2.0 averages 28. The 2.5 is said to reduce the economy only 1 mpg. Once I've owned mine long enough and it isn't -15f I will know my real-world fuel economy. But the point it, American versions of international vehicles with identical engines always get lower economy.

I had an SVT Focus, known as the ST170 in Europe, and imported an ECU, reflashed my PATS theft module, and tuned it with a builder in St. Albans, UK. I regularly achieved 35mpg mixed driving on 93 octane fuel. No other SVT in the United States could get over 32 HIGHWAY without hypermiling, even with economy tunes.

International Skyactive's run 14:1, ours run 13:1. Is there more to it? Of course. Emissions regulations (in which Japan is the world-leader, so this is irrelevant) and fuel quality play a roll. Any petrol engine ideally burns at "stoic" but running leaner and using technology to monitor the consequences will improve fuel economy. The compression ratio can be increased in a variety of ways to improve fuel efficiency; special intake and head cooling techniques, piston design, tuned headers, valve/cam timing, etc. This improves overall efficiency, but the industry PR simply calls it compression ratio, which is all I was referring too.

What you need to keep in mind, like you mention, is the purpose of direct injection is to keep peak compression ratio across the power band, which obviously isn't going to always be 13:1+ but even if you can get away burning above stoic at idle, you are going to save fuel.

RE: Hmmm
By TheEquatorialSky on 1/7/2014 12:07:53 PM , Rating: 2
The math is simple: thermal efficiency=(1-(1/CR^(specific heat-1)). I just did it and the improvement from 13:1 to 14:1 is 1.6%.

Unless you have scientific sources for those MPG numbers, the differences you cite are just anecdotal and thus suspect. I'm not saying you are wrong, but I can't assume you are right. According to the manufacturer's website, the CX-5 (2.0 manual) is rated at ~39mpg(US) combined on the British cycle and 29mpg(US) combined on the American cycle. Certainly a huge difference, but so are the drive cycles...

Mazda refers to the peak of their "dynamic" CR as though it were the static CR, as stated by nearly every car manufacturer since cars were invented. Late intake valve closure (LIVC), as pioneered by Ralph Miller with his work on industrial diesel engines, has muddied the water. As with any internal combustion engine, the value that really matters is the pressure ratio, as the CR refers to a geometric quantity.

The purpose of GDI is to increase volumetric efficiency, intake charge cooling and fuel metering. Nearly every engine in America is designed to run at stoichiometry (14.7:1) unless peak power is required (e.g. acceleration). Running lean results in high NOx and is almost always avoided. Notable exceptions include Honda hybrid vehicles, which use a NOx adsorption catalyst that it periodically flushes by running rich.

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