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  #1  
Old 03-14-2013, 02:46 PM
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Mazda Skyactiv-Diesel has 14:1 compression

Pretty cool article on the low compression diesel engine.

How Mazda Reinvented the Diesel Engine | Popular Science

Mazda must be the BMW of Japan when it comes to innovation. I think it is amazing that the air will get red hot at a low 14:1 compression ratio.

I guess I will believe it when I see it (and hear it).
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Old 03-14-2013, 05:06 PM
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it must be having some pretty cool stuff to get a 14:1 diesel to start.
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Old 03-14-2013, 06:17 PM
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Many newer OTR truck engines are in that range or a little higher. What the article doesn't say is that the engine still needs the DPF and oxidation catalyst.
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Old 03-14-2013, 06:20 PM
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The exhaust valve opens partially during the intake stroke when starting. This draws warm air in from the exhaust. I think this recaptures some glow heat. The choked expansion of air via a shock wave also heats it.

So uncombusted air could be heated by choked expansion and blown into the exhaust manifold, and then pulled back into the piston for a second compression, which will heat it to autoignition temp. This would be accomplished with special lift & timing of the exhaust valve for starting.

I thought they did this so they wouldnt need the DPF or urea device.
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Old 03-14-2013, 06:25 PM
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Is that the car that the gasoline and diesel versions share half of the engine?
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Old 03-14-2013, 06:25 PM
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Quote:
Diesel engines ignite fuel by combining it with air and compressing it to extremely high pressure.
Isn't this backward, shouldn't it read "Diesel engines ignite by compressing air to extremely high pressure then injecting fuel."
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Old 03-14-2013, 08:02 PM
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Quote:
Originally Posted by Zulfiqar View Post
it must be having some pretty cool stuff to get a 14:1 diesel to start.
they have improved so much the injection over the past years, now we can get so much more power and so much less smoke

I want to say the skyactiv does all this without the urea injection or lean-NOx trap, which is particularly interesting.

It seems the sweet spot for compression is somewhere around 13 - 15, as it gets more, the heat is too much and it gets lost into the cooling water...
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Old 03-15-2013, 09:34 AM
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it says the starting price is $20k. I wonder if they are referring to the gasoline version.

$20k is not bad. I think the TDI VW Passat is quite a bit more.
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Old 03-15-2013, 10:01 AM
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That's an insanely low compression ratio. I've heard of hot gas cars running 12:1

I like to surprise people who talk about CR with the 617's stock 22.5:1
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Old 03-15-2013, 11:53 AM
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A low compression ratio for a diesel isn't that unheard of

Compression ratio - Wikipedia, the free encyclopedia

I think they must have done lots of tricks to get it to be so economical and green though.

I wonder what it will be like in service - imagine a bad turbo on one of those => there goes a large chunk of your compression ratio...

...perhaps people will be fitting spark plugs to keep it going!
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Old 03-15-2013, 12:29 PM
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Originally Posted by Stretch View Post
A low compression ratio for a diesel isn't that unheard of

Compression ratio - Wikipedia, the free encyclopedia

I think they must have done lots of tricks to get it to be so economical and green though.

I wonder what it will be like in service - imagine a bad turbo on one of those => there goes a large chunk of your compression ratio...

...perhaps people will be fitting spark plugs to keep it going!
I'd drive a 14:1 gas car and spray water to keep the knocking down
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Old 03-15-2013, 02:58 PM
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Old 03-15-2013, 03:02 PM
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Sounds like it's based on the same underlying engine design. Both the highest compression gas engine and lowest compression diesel engine! lol
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Old 03-15-2013, 06:08 PM
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I saw a video once of a SAAB variable compression engine, it was being translated to me by a Swedish guy, in between the video they spoke of using this technology to lower diesel compression ratio.

What they meant was that the engine would do to a high ratio 22:1 to start and would change to about 16:1 to run.

It had a connecting rod type setup to tilt the block away from the cylinders.

I think that Mazda must have been using their history books for this - their miller cycle engine was also a strange design that played around with compression (not static)
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Old 03-15-2013, 06:41 PM
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Uberwgn,

We are talking about the Skyactive-D engine. There is a gas and Diesel version.


I showed the new Mazda 6 to my girlfriend and now she wants one. Can't afford it but still wants one.

I wonder how the engine holds up over time. A lightened aluminum block and heads plus Diesel sounds iffy to me but then again they are using very low compression. It is a thoughtful design but I'll venture a guess that it won't have the reliability of a 617. Top that off with the added difficulty of working on it.
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