Materials and Mechanical Engineering Project
Piston Construction and High Performance Engines
Introduction
This project is concerned with the possible materials used for the pistons in a high
performance internal combustion engine. We will look at the forces exerted and what
different materials off what advantages to such an application.
Background Needed
Physics I, Calculus I.
Part One Internal Combustion Basics
An internal combustion engine of the 4-stroke type, whether your lawn mower, SUV, or a
Formula One race car always has the same basic components:
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crankshaft
connecting rod
piston
intake valve(s)
exhaust valve(s)
One complete cycle of it consists of a total of 4 movements up and down. If you are not
familiar with how a 4 stroke works, please review the material at the following web site:
http://homepage.mac.com/dgiessel/engine/basics.html
How many revolutions per minute the engine makes is abbreviated to its RPM. Values
exceeding 10,000 RPM are not uncommon, especially for high performance motorcycle
engines.
Any engine has a “red line”. This is an RPM limit. Above such an RPM, the parts of the
engine may no longer be able to withstand the stress. Some cars have automatic cut-offs
at the red line.
Part Two The difficult life of a piston.
The top of the piston becomes the bottom of the combustion chamber when firing occurs.
So it sees enormous amounts of heat as well as heat change. When the pressure builds up
in the combustion chamber it has considerable force placed on it since the pressure may
be 10 times as great as prior to ignition (this in reference to whatever the compression
ratio of the design is).
There are tremendous forces placed on the piston due to the rapid changes in velocity as a
result of the up and down motion. Recall Newton’s Second Law: the force on an object
is the product of its mass and its acceleration – F = ma. Acceleration is the derivative of
velocity. In other words changes in velocity are equivalent to acceleration. F = m dv/dt.
Velocity is a vector quantity. Changes in direction matter as much as changes in
magnitude.
Problem #1 At what point in the motion is the acceleration greater? top or middle?
Why? your answer should be explained in terms of basic physics and calculus.
Good…you have a start in understanding the motion of the piston. Now go and do some
carefully reading and experimentation at the following web site
http://www.wfu.edu/~rollins/piston/animation/interactive_2/
Problem 2 When you are done, write a summary of what you found .
Problem 3 We need something specific to focus on. Suppose our crankshaft and
connecting rod have the following parameters:
crank pin offset: 1.5"
connecting rod length: 4.5"
and that our piston is for a bore of 62 mm. Also assume that one style of piston has a
weight of 163 grams (the sand cast version). For an RPM of 9500, calculate the
maximum force that the piston is subjected to. Show all calculations and assumptions
which were used by you in your work; your answer should be completely explained and
defendable.
Now at this point, the Materials people are asking themselves: what does this have to do
with my area? First of all the sample piston was a "sand cast" piston. That is certainly
not the only choice of material or method.
Problem 4
a) What materials can pistons be made of? (try to find at least 2 more in addition to sand
cast).
b) What are the pros and cons of all types listed? (include sand cast) (a table would be a
good presentation vehicle).
Problem 5 Pick a type of material that is lighter. Make an estimate of how much lighter
it should be than the sand cast piston originally cited. Recalculate the maximum force on
the piston.
Problem 6 For your hypothetical piston from Problem 5, compute how much higher the
Red Line can be due to the lower force on it.
Finally, please write a Conclusion summarizing what you have accomplished in your
project. Also include a Reference section listing all sources used by you.