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996 Ducati - Performance simulation

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  • 13-12-2005 1:06am
    #1
    TE0N
    Closed Accounts Posts: 42 ✭


    Hi,
    I am a second year Mechanical Eng student, and we (group of 10) have been given the task of drawing a P-V and P-Crank. Ang. diagrams for a 996 Ducati 4-stroke engine.

    We solved the valve lift w/crank angle table, valve timing, and the vol. change with crank angle. Now, we have started the intake process, (assuming air only, for simplicity). The initial temp is 320K (47C),
    There is a vacuum of 3000Pa in the manifold, and I assume (correct me if im wrong) that there is atmospheric pressure (101325Pa) in the cylinder - this gives a difference of 98325Pa
    Now, the problem arises when we calculate the change in mass with crank angle. I have derived a formula this using mass flow, here

    Change in Mass = (density)(A)( V)(change in time over 1 degree crank angle)
    A=(PI)(Lv)(Dv)(Cd)
    V=SQRT((2)(change in pressure)/(density) is the change in Pa 98325 or 3000?
    Also, the Prof. said that assume a sonic vel of 400m/s.
    Change in time=(1/9000rpm)(1/360)

    Now I am starting my calcs at -360 CA (start of intake stroke), and have calculated the lift at this angle (2.7mm)

    This formula seems right, but when I plug in the Professor's values from his example (Excel macros - visual basic), I don’t get his value for a change in mass at -360 degree CA. We have been scratching our heads on this for 2 days, any help will be appreciated.

    PS: I know I haven’t given even a 1/3 of the starting values or the calculated values but the problem seems to be with the formula.

    Thanks.


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    #2
    TE0N
    Closed Accounts Posts: 42 ✭TE0N


    I think Ill put a close to this, we finished it yesterday. Yes that was the correct formula for mass change/degree but the pressure difference across the valve was just atm minus manifold vac minus pressure at -359 degree.

    The change in temp was got with a bit of fiddling with the first law for an open system. (intake and exhaust processes)

    The closed system and performance calculations were relatively easy. (Lots of info on these).

    Getting this to work in Excel took a good 2 1/2 days, but our P-V diagram looked ok.

    If there is any questions on the ideal or actual 4 stroke cycle dont hesitate to ask.


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