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Old 08-24-2011, 08:51 AM   #1 (permalink)
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Mazda's Skyactiv-D (diesel) technology

Some interesting tidbits about Mazda's new Skyactiv-D technology. They're planning on replacing the current 2.2L with this new 2.2L which sports a 20% increase in fuel economy (they say it'll give 43 mpg on the hwy, no mention of what vehicle thats in). It has 14:1 compression ratio, the lowest of any passenger car diesel engine. It says that the lower compression ratio allows for better air/fuel mixing and optimized combustion timing. The article also explains how a higher compression ratio is needed for cold starts, but Mazda got around it by using variable lift on the exhaust valves. It keeps them open during cold starting to increase cylinder temps and thus the cold start ability. The lower compression ratio also lead to lighter weight components taking 6.6 lbs off the internal's weight. It also has an aluminum block which saves another 50 lbs over the previous engine.


Mazda ‘Reinvents’ Diesel With New Skyactiv-D

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Old 08-24-2011, 01:34 PM   #2 (permalink)
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This reads like the best part :

"Because combustion is more uniform with a lower ratio, nitrous oxide and soot emissions are minimized, negating the need for an expensive aftertreatment system."

That could save a lot of costs and hassle.
I wonder wether it can run on 100% biodiesel - as the current generation of hi-tech diesels can't.

Last edited by euromodder; 08-24-2011 at 01:47 PM..
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Old 08-24-2011, 02:04 PM   #3 (permalink)
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...elimination of "add-in" urea is definitely a BONUS!

...addition of VVT to diesel is new.
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Old 11-26-2012, 07:21 PM   #4 (permalink)
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What surprises me the most is the incredibly low compression ratio. I'd worry only about the cold-starting.
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Old 11-26-2012, 09:10 PM   #5 (permalink)
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Its about time someone comes out with a modern diesel (in the USA) that can compete against VW after all these years lol.
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Old 11-26-2012, 09:58 PM   #6 (permalink)
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Quote:
Originally Posted by Daox View Post
It has 14:1 compression ratio, the lowest of any passenger car diesel engine. It says that the lower compression ratio allows for better air/fuel mixing and optimized combustion timing.
I don't think whoever wrote this article knows what they're talking about.

For one thing, they actually report the compression ratio as "14:1.1". Aside from being a completely unorthodox way of defining compression ratio, that equates to only 12.7:1.

Secondly, I've tested various compression ratios in detail for years (with engines on a dyno) and have never seen a scenario where lowering the compression ratio increased the efficiency. Efficiency of the diesel cycle is fundamentally tied to the compression ratio, and is probably the biggest reason why diesels typically have higher efficiencies than gassers. See here:
The Diesel Engine

The drawback of higher compression ratios are that the max power output drops becuase the cylinder pressures go up and, therefore, components sometimes need to get heavier and more expensive. It's also not uncommon for smoke to increase some.
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Old 11-27-2012, 01:46 AM   #7 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
...addition of VVT to diesel is new.
Caterpillar ACERT 13L & 15L HD engines use variable intake timing.

Under high load intake valve closing is delayed to lower dynamic compression. Higher than typical boost levels (cooled to lower than normal temperatures) maintain the same effective compression allowing for cooler combustion and lowered NOx levels.
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Old 11-27-2012, 08:16 AM   #8 (permalink)
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Sounds to me like they are building a diesel with an engine they already produce but can't handle high compression. Sounds like a cheap shortcut.
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Old 11-27-2012, 09:42 AM   #9 (permalink)
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I think there is some serious technology going on with Mazda and their new engine line.

Green Car Congress: Mazda introducing 1.3L direct injection gasoline engine as first SKYACTIV-G unit

This is almost 2 years old. I know the Diesel seems to have low compression, but there are other things that must be considered like two stage supercharging, Direct sequential injection, and independent control of the exhaust camshaft, which allow the lower compression and avoids the issues with emissions aftertreatment.

Green Car Congress: Mazda introducing 1.3L direct injection gasoline engine as first SKYACTIV-G unit

I don't think this engine is cheap if they are using it in a racing version. I think Mazda saw the separation with Ford coming and knew they needed something truly trnasformational in order to survive in the World market.

I read that the gasoline version uses 5 injection sequences for every combustion stroke, so it's 14 to 1 compression ration is incapable of preignition as it is simply not possible with only a small precentage of the fuel injected intitially, and the peak pressure point is delayed and prolonged which improves efficiency.

Not sure how it will all work out but it is certainly interesting to watch. I was a fan of the rotaries until the fuel consumpltion issues became insurmountable, but at least Mazda is willing to take the risks involved with advancing combustion technology.

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Old 11-27-2012, 08:37 PM   #10 (permalink)
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I've already seen some carburettor-fed dedicated-ethanol spark-ignited engines with 14:1 compression.


Quote:
Originally Posted by Old Mechanic View Post
I was a fan of the rotaries until the fuel consumpltion issues became insurmountable, but at least Mazda is willing to take the risks involved with advancing combustion technology.
I was never a fan of the rotaries, but I didn't celebrate when they were phased out. Mazda had been done a great job developing it and overcoming reliability issues.

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