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Thread: Mazda's new engine boosts fuel efficiency by 30%

  1. #16
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    With the temp here in Minnesota reaching -10*F last week, and normally is around 10-20*F in winter, I'm really curious to see how Mazda engineers overcome the cold start with HCCI.

  2. #17
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    This site indicates for every "1" compression increase, HP also increases 4%. So increasing to 18:1 means aprox a 30hp increase or 215HP.
    http://dsportmag.com/the-tech/boost-...ession-ratios/

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    Quote Originally Posted by CX-5um View Post
    This site indicates for every "1" compression increase, HP also increases 4%. So increasing to 18:1 means aprox a 30hp increase or 215HP.
    http://dsportmag.com/the-tech/boost-...ession-ratios/
    I think it's more complex than that, as you need to take valve overlap and cam timing and the like into account, too, but that does sound "about right" to me.

    I just wonder what kind of a beast of a starter that thing is going to require! Or if it will use an initial spark to kick it off or something.

  4. #19
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    Quote Originally Posted by Unobtanium View Post
    I think it's more complex than that, as you need to take valve overlap and cam timing and the like into account, too, but that does sound "about right" to me.

    I just wonder what kind of a beast of a starter that thing is going to require! Or if it will use an initial spark to kick it off or something.
    Yeah..maybe a combination of some alternately generated spark and the use of i-stop?

  5. #20
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    So if increasing compression makes for more power why did Mazda reduce the compression ratio for the diesel?

    Although they did increase the ratio for the petrol. Can someone explain.

  6. #21
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    Quote Originally Posted by xtrailman View Post
    So if increasing compression makes for more power why did Mazda reduce the compression ratio for the diesel?

    Although they did increase the ratio for the petrol. Can someone explain.
    I'll try.
    Lowering the compression ratio on the diesel allowed them to make the engine lighter, produce less NOX emissions (no urea after-treatment) and it allowed for a higher readline.

    It also allows for more fuel to burn closer to the top of the cylinder stroke, improving the amount of work done by the fuel.
    http://www.mazda.com/en/innovation/t...iv/skyactiv-d/

    The power improvement for compression increase also isn't nearly as much as CX-sum wrote.
    Going from 17:1 to 14:1 you'll only see a ~4% drop in power. Not hard to make up for that with more boost.

    You might see a 4% increase in power for 1 point compression increase when you step up from 7.0:1 to 8:1 in a turbo engine, but once you hit higher compression ratios the increase gets lower.

  7. #22
    Registered Member CX-5um's Avatar

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    Quote Originally Posted by xtrailman View Post
    So if increasing compression makes for more power why did Mazda reduce the compression ratio for the diesel?

    Although they did increase the ratio for the petrol. Can someone explain.
    Here's one reason for the reduced compression. "20 percent better fuel efficiency thanks to the low compression ratio of 14.0:1"

    http://www.mazda.com/en/innovation/t...iv/skyactiv-d/


    Plus there's this "Optimization of Combustion Timing by Lowering Compression Ratio
    When the compression ratio is lowered, compression temperature and pressure at TDC decrease. Consequently, ignition takes longer even when fuel is injected near TDC, enabling better mixture of air and fuel. This alleviates the formation of NOx and soot because the combustion becomes more uniform without localized high-temperature areas and oxygen insufficiencies. Furthermore, injection and combustion close to TDC result in a highly-efficient diesel engine, in which a larger amount of actual work (or, a higher expansion ratio) is obtained than in a high-compression-ratio diesel engine(Fig.2)."


    That said Mazda was probably okay with balancing out some HP for increased MPG and maybe better emissions as per above? I mean that engine already has ample TQ.
    Last edited by CX-5um; 01-11-2017 at 02:14 PM.

  8. #23
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    Quote Originally Posted by xtrailman View Post
    So if increasing compression makes for more power why did Mazda reduce the compression ratio for the diesel?

    Although they did increase the ratio for the petrol. Can someone explain.
    A big factor is the turbo on the diesel. When the piston is down it crams more air in raising the effective compression ratio. Example, in a 15 psi normal air pressure environment if the turbo is at 5 psi, you raised the effective compression ratio by 1/3, from say 15 to 20.

  9. #24
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    Quote Originally Posted by GAXIBM View Post
    A big factor is the turbo on the diesel. When the piston is down it crams more air in raising the effective compression ratio. Example, in a 15 psi normal air pressure environment if the turbo is at 5 psi, you raised the effective compression ratio by 1/3, from say 15 to 20.
    Yep. Static compression ratio is not the same as dynamic.

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