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Air flow in inlet manifold affecting engine performance

  1. Dec 21, 2011 #1
    i want to model air flow in the inlet manifold using CFD ,how do i predict
    how flow variations and other parameters affect engine performance ?
    i know how it affects but how do i show it virtually
  2. jcsd
  3. Dec 22, 2011 #2
    There are several important things to consider in modelling the intake manifold:

    a) Inlet vacuum that depends on the flow rate and throttle body size.
    b) Wave pulse dynamics that depend mostly on runner length. In a very simplified sense, you can see this behavior in the Hemholtz resonator model.
    c) manifold runner diameter and length which affects flow restriction and pressure drop.
    d) Engine rpm which affects all of the above.

    As you can see, this the problem is very dynamic. You could start with a fixed engine speed, and try to set up the model.
  4. Dec 22, 2011 #3
    After I set up the model how do I represent air flow in manifold affecting engine performance..changes in air flow affects a/f ratio and combustion ..but will I be able
    to represent that as a graph?
  5. Dec 23, 2011 #4
    You are basically asking how do I do CFD, and how can I get results.
    Which can't realistically be answered in a forum post.

    It's sort of like asking how do I write a best selling novel in French. When you can't speak French nor have any experience writing novels.

    Lets start from the beginning, what are you actually trying to achieve, that prompeted you need to use CFD to model an inlet manifold?
  6. Dec 23, 2011 #5
    I want to study the flow characteristics of air when it enters the inlet manifold and reaches the combustion chamber, considering a four cylinder naturally aspirated diesel engine.
    I have the required parameters such as temperature ,mass flow rate etc for the inlet air...i want to use ansys-cfx to model the component and solve it.I have a fair idea about defining domains ,boundary conditions etc.
  7. Dec 23, 2011 #6
    What do you mean by 'study the flow characteristics of the air'? What aspect specifically are you studying? What programmes do you have access to?

    When I say specific, I mean very very specific.

    Without comparing the changes to a running engine with known geometry, you simply can't tell what sort of changes air flow will make. How do you plan to verify and validate the model?

    It's still far too broad a remit to give a sensible answer. eg. You could be looking at inlet conditions past the valve, which is a whole different problem to looking at what happens to the air within the combustion chamber, which is again a whole different problem to modelling say, density distribution within a plenum.
  8. Dec 23, 2011 #7
    I want to study velocity,temperature and pressure variations from the time air
    enters (from plenum to runner)to the time before inlet valve opens.As you said
    I am also bothered about density distribution in plenum.I also want to vary the type of manifold being used helical ,spherical and observe the changes
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