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Thread: PatEF; the "Ef" for efficiency

  1. #106
    apriliaforum Member
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    Hello all.

    Thanks for your “strictly technical”, well supported and polite posts, especially those signed with poster’s real names.


    Back to Strictly Technical:

    At Mazda’s SkyActive-X (an almost HCCI system) presentation the focus was on the way they activate the combustion:
    an expanding “fire-ball air-piston” (with center at the spark plug electrodes, containing burnt rich air-fuel mixture (which means stratified charge and secondary extreme pressure fuel injection towards the spark plug)) compresses the rest lean air-fuel mixture in the cylinder, causing its auto-ignition and rapid combustion.

    In order to support their SkyActi-X system (they plan to put in production in 2019, they have prototypes on the roads for test) they present the weaknesses of their previous SkyActiv-G.

    Among them, the slow / progressive combustion dominates:





    To put it simply:

    The expansion ratio of a fuel quantity burnt at 33 degrees after the TDC is 1:5.5 (for an 11:1 compression ratio engine and 2:1 con-rod to stroke ratio).

    The expansion ratio of a fuel quantity burnt 66 degrees after the TDC is 1:2.5.

    Such small expansion ratios “kill” the Brake Thermal Efficiency”.

    The combustion is far from being a “constant volume combustion”.

    A true constant volume combustion at the TDC is the ideal for top BTE.



    Quote from http://www.mazda.com/en/csr/special/2017_01/

    Pursuit of the ultimate engine

    Eiji Nakai (General Manager, Powertrain Development Division, Mazda):

    With compression ignition, gasoline burns vigorously only when the right temperature and pressure conditions are met. It's especially hard to combust when the air-fuel ratio is high. We had to create conditions for the combustion of a predetermined amount of fuel as planned in every combustion cycle and in various driving scenarios and operating conditions.

    End of Quote

    Quote from https://blog.caranddriver.com/mazdas...ine-explained/

    Controlling homogeneous combustion events—which amount to otherwise potentially damaging pre-ignition—is difficult without timed spark or injection events, requiring tight control over the amounts of air and fuel in the cylinder, as well as pressures and temperatures. As such, HCCI is intolerant of higher engine speeds and extremely sensitive to variances in atmospheric pressure that come with elevation changes or weather swings.

    End of Quote



    The PatBam HCCI,

    either as a 2-stroke Opposed Piston:



    or as a two-stroke single piston:



    or as a four stroke:



    does exactly what is considered difficult in the second quote above: “without timed spark or injection events (a spark plug is optional, not a requirement in the PatBam; and if desired the PatBam can operate with a carburetor for the preparation of the homogeneous lean mixture) it manages to burn (by the high compression in the auxiliary chamber) a small quantity of the charge and, just before the TDC, it burst the burnt gas from the auxiliary chamber into the main chamber (as a mechanical “fire-ball air-piston”) causing its auto-ignition / rapid combustion at almost constant volume.


    According Mazda’s Technical director (first quote above): “We had to create conditions for the combustion of a predetermined amount of fuel”

    The PatBam geometry does create these conditions for the combustion of a predetermined amount of fuel.

    And because the overall compression ratio needs not to be extreme, any longer, the peak pressure in the combustion chamber is not catastrophically high.

    Thanks
    Manolis Pattakos

  2. #107
    apriliaforum Junkie Satanic's Avatar
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    Hello all.

    Photosensitive epilepsy status: triggered

    Thanks
    Bruce Willis


  3. #108
    apriliaforum Member
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    Hello all.


    Here is a "more conventional" HCCI PatBam 2-stroke:





    wherein the piston-ring of the auxiliary piston slides permanently onto the cylinder liner of the auxiliary chamber.

    The same design fits with 4-strokes, too.


    Thanks
    Manolis Pattakos

  4. #109
    apriliaforum Member
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    Hello all.


    The following animation has been added at the bottom of the http://www.pattakon.com/pattakonPatBam.htm web page.





    It is a four-stroke PatBam HCCI control.


    Exhaust valve: red.
    Intake valve: blue.
    Auxiliary chamber "anvil": black.


    Thanks
    Manolis Pattakos

  5. #110
    apriliaforum Member
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    Hello all.


    Here is a youtube video - animation of the PatBam HCCI in a 4-stroke engine:





    Thanks
    Manolis Pattakos

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