hey guys im taking some classes on engine performance and i kinda need some help on these questions so please help im desperate thanks


1. the relationship of the piston in the cylinder can be determined by the crankshaft position in degrees. How far from the top is a piston that is 67 degrees from To Dead Center and the throw of the crank is 1.1675 inches

2. Generally what is the maxium acceptable rang for mean piston speed in American Engines

3. How is volumetric efficiency effected by RPM and piston speed? Is this an inverse or proportional relationship

4. 1-2 inches of the stroke is usefull how does this relate to the stroke in high RPM Engines

 

1. you need the rod ratio as well.

2. depends on many things such as rpm and how well engine breathes. the piston speed engines lay over at is proportional to how big an intake port they have on a given bore for the most part.

3. VE has a swwet spot somewhere and then slowly (or quickly) falls off with increasing rpm. Your peak VE is nearly at peak TQ and then falls off.

4. can't understand what you mean by this statement?

 

Hey thanks ya i dont understand #4 either all well thank i guess your the only one here that is brave enough to try and help me thanks

 

1. Calculate the difference in the Y-direction between the crank at 67° versus 90°.

2. I believe the average maximum speed of the piston is 15 m/s halfway through the stroke.

3. An engine is most efficient around 3000 rpm at WOT. Lower than that and you don't get the inertial cylinder filling effect that higher RPM brings. Higher than that and you run into the mechanical limitations of the engine (ie. finite amount of time to fill the cylinder, open the valve, close the valve, etc.).

4. I could make an educated guess but I can't be sure of this one off the top of my head.

 

Regarding #1...

I wrote a short paper a while back to calculate piston position, velocity, acceleration...

this is the equation to calculate piston position x given: crank angle a, crank throw r, rod length l:

x = r.cos(a) + sqrt(l² - r².sin²(a))

where:
l = rod length (distance between piston pin and crank pin)
r = crank radius (distance between crank pin and crank center)
x = piston pin position (from crank center along cylinder bore centerline)
a = crank throw angle (from cylinder bore centerline at TDC)

This equation can be arrived at by drawing a triangle with corners at crank center, crank pin, piston pin and using the cosine triangle formula.

My .doc file is 112KB, and the upload limit is 100KB, what to do...?


Edit: So to x you have to add the height of the piston above the piston pin to get the position of the top of the piston.

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Here is what I wrote, cut down to fit...

Edit: To see the diagram and the math, open it using MS Word.