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Old 09-25-2007, 12:55 AM   #1
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Default Engine related fluid dynamics question

So I have this question for fluids. In each problem set our teacher makes up a problem without much thought and very little supplied information.

Here is this weeks:

Quote:
In an internal combustion engine (letí* say a Ford Taurus that always uses SAE 10-30W oil for
this example), what are the types of forces acting on the piston during the power stroke (the
volume in the cylinder is expanding and combustion has occured) when the piston has moved
half its total travel away from top dead center position? At this location, give a quantitative
estimate of the force due to viscosity between the piston and the cylinder. What percentage
of the total force acting on the piston is this? What is your impression of the size of this
number? What would the effect of using a different motor oil be?
I figured I would toss it out here for people to discuss/ponder/ignore
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Old 09-25-2007, 08:25 AM   #2
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I'm going to ponder.

Only the oil is a consideration right?
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Old 09-25-2007, 03:39 PM   #3
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Quote:
what are the types of forces acting on the piston during the power stroke (the
volume in the cylinder is expanding and combustion has occured) when the piston has moved
half its total travel away from top dead center position?
When the piston is halfway down, the rod is at it'* most extreme angle in relation to the bore. At this point during the power stroke, the rings are taking the most stress. I'm not too sure how you would get the force though..
A small portion of the force will be the piston moving through the oily crank case air. The crank case is slightly pressurized too due to blow-by. Although alot of the pressure is bled off through PCV..
Thats all I have for now.
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Old 09-25-2007, 03:57 PM   #4
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If the RPM is staying constant, you know the piston is at a point of 0 acceleration. So the force of combustion equals the reaction forces of the piston rod, cylinder wall, and oil/ring interaction. What percent of the reaction forces is what? I don't know. I never had to get into viscous fluid films quantitative effect on friction.

Quick diagram to consider:

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