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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: Sounds much like a diesel here.
By Argon18 on 1/6/2014 3:14:03 PM , Rating: 3
"The Otto cycle is actually more efficient than the diesel cycle. If you look at diesel engine technology, you'll see a trend of them "walking in gasoline territory.""

You could not be more wrong. If you look at nearly every major engine development over the past few decades, it has become available first on diesel engines, and then years later, it trickled down to gasoline engines.

1. Direct Injection. Diesels have been doing this since the early 1990's. Gasoline engines are only now getting this, and it's limited to high-end cars mostly. The mass market gasoline engines still don't have it.

2. Variable geometry turbochargers. Diesels have been doing this since the mid 1990's. The only gasoline car I know of that's using this is the Porsche 911 turbo. I'm sure there are a few others, but certainly it isn't common.

3. High pressure injection. The newest diesels inject fuel at over 30,000 psi. Amazingly high pressures that produce superior fuel atomization. A gasoline fuel injector looks like it's taking a piss by comparison.

4. High compression ratios. Diesels are all in the 20:1 range for turbocharged engines. Gasoline is between 8:1 and 13:1. Higher compression extracts more power, and hence greater efficiency.

All this leads to diesels being technologically superior to gasoline engines, and this has been the case for years now. Diesels are more durable, more reliable, and consequently command a much higher re-sale price on the used market.

The HCCI engine has been under development for decades. The two primary advantages are high CR and removing the throttle plate (lower pumping losses).

Funny, diesels have had very high CR, (way higher than any gasoline engine), and no throttle plate required, for many decades now. These features "under development" for gasoline engines only further prove the point that gasoline engines are playing "catch up" trying to assimilate the innovations that came from diesel.

"The sticking point is reliably lighting off a charge with a such a wide AFR over all operating conditions."

Yep, and therein lies one of the fundamental flaws of a gasoline engine. Gasoline engines only work well in a narrow AFR range. Diesel engines already work very well in anything between 8:1 and 80:1 air:fuel ratio. Funny, gasoline engines playing catch-up again, trying to emulate the performance and efficiency of diesels.

By TheEquatorialSky on 1/6/2014 3:41:06 PM , Rating: 2
The point is that the diesel thermodynamic cycle has less peak efficiency than the Otto cycle. It's physics... hence diesel engines are being designed to operate closer to the Otto cycle (constant volume).

1. Gasoline direct injection (GDI) has been around for decades. The DB605 of the Bf109 fighter used GDI. Its true that diesel has used (in)direct injection earlier, but only because it *had* to.

2. Gasoline engines have a flatter torque curve, thus a turbo isn't as important as it is for a diesel. The trend towards decreasing displacement and improved bearing technology have removed the luster of VGT turbos anyways.

3. High pressure injection is required because charge mixing/combustion occur simultaneously in diesels. This is bad... high pressure injection is a band-aid... and it decreases reliability.

4. Efficiency only increases with CR logarithmically. High CR requires a heavier engine and generates more NOx. Both are reasons Mazda's new Skyactive diesel is designed around a 16:1 CR. Diesels going down in CR? Whaaat?

5. Diesels aren't inherently more durable than gasoline engines. That feature is a byproduct of designing around detonation, which is now being done largely through injector technology. Durable = heavy = inefficient. New alloy TDI diesels are *less* reliable than their iron block, mechanically injected, particulate-spewing predecessors.

By Monkey's Uncle on 1/7/2014 11:50:30 AM , Rating: 2
1. Direct Injection. Diesels have been doing this since the early 1990's. Gasoline engines are only now getting this, and it's limited to high-end cars mostly. The mass market gasoline engines still don't have it.

Beg to differ here.

My ford focus has gas direct injection (GDI) and a 12:1 compression ratio. The hyundai Veloster turbo and sonata 2.0 turbo both have GDI engines. And more are coming online over the next couple years.

None of these are what I would call high-end cars.

"If you look at the last five years, if you look at what major innovations have occurred in computing technology, every single one of them came from AMD. Not a single innovation came from Intel." -- AMD CEO Hector Ruiz in 2007

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