Wear Mechanisms In a 4 Stroke Combustion Engine
Discussion
Hey guys and girls,
I was told a while ago that an engine at very low RPM's with a high load (i.e a lot of throttle... like having an engine at 20mph in fifth and with the right foot mashed into the carpet) will have significatinly more wear than an engine at high RPM with a high load. I'm trying to understand (in terms of physics) if this is correct and why this is.
My hyposthesis is this, and I would be greatful if anyone could guide me as to whether I am on the correct lines.
At higher RPM's with nice hot oil, the forces on the pistons will be high but because of the speed of the crankshaft, a film of oil sits between the bearing and the crankshaft (hydrodynamic effect), absorbing the mechanical work and coverting it to waste heat. Figure 1 below illustrates this:
Figure 1: Illustrating hydrodynamics between the shell bearing and crankshaft.
However, when an engine is at low RPM and under high load, there is less hydrodymanic effect between the crankshaft and bearing and thus the crankshaft is able to come into contact with the bearing due to the higher forces acting downwards on the piston, causing greater wear (esp with colder oil)
Can anyone advise me if I am thinking along the right lines? I'm just very interested to know!
Many thanks,
Matt
I was told a while ago that an engine at very low RPM's with a high load (i.e a lot of throttle... like having an engine at 20mph in fifth and with the right foot mashed into the carpet) will have significatinly more wear than an engine at high RPM with a high load. I'm trying to understand (in terms of physics) if this is correct and why this is.
My hyposthesis is this, and I would be greatful if anyone could guide me as to whether I am on the correct lines.
At higher RPM's with nice hot oil, the forces on the pistons will be high but because of the speed of the crankshaft, a film of oil sits between the bearing and the crankshaft (hydrodynamic effect), absorbing the mechanical work and coverting it to waste heat. Figure 1 below illustrates this:
Figure 1: Illustrating hydrodynamics between the shell bearing and crankshaft.
However, when an engine is at low RPM and under high load, there is less hydrodymanic effect between the crankshaft and bearing and thus the crankshaft is able to come into contact with the bearing due to the higher forces acting downwards on the piston, causing greater wear (esp with colder oil)
Can anyone advise me if I am thinking along the right lines? I'm just very interested to know!
Many thanks,
Matt
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