Most older heavy equipment, with large diesel engines, I have seen, had that "hr meter", that counted one hour for running 1 hour at, lets say 1800 rpm's. If engine run's for 1 hour at 900 rpms (1/2), it would only count 0.5 hr on the counter. So when the counter showed 1 000 hrs, the engine had turned
EDITED to be: 1 000 by 1800 by 60= 108000 000 revolutions. This is a way to count the lifetime useage of diesel engines, drive lines, pumps etc on this piece of equipment.
I think the point with this way of measuring hrs, is to keep track of wear and when to schedule maintenance. This system also tells me that you can't expect more than a certain amount of revolutions out of a engine crankshaft.
Even if you optimize maintenance, operation conditions, and run engine at optimized RPM and torque output (Power) I would say "RPL"="Revolutions Per Lifetime", is limited as the life expectancy of an engine.
Running at a fixed, optimized (a little above max torque output), rpm will benefit lower fuel consumption (CO2 footprint and $$) and also give more life out of the engine. Also if engine bogs down a little from load, torque will increase. But be careful, running an engine at the same fixed rpm for many 1000's of hours, can get expensive if you one day want to raise rpm to "the double".
However, diesel engines are so different in charcteristics, they do not bog down for load the same way as gas engines, due to a sophisticated fuel and rpm governor system.
I think, with small gas engines, like Honda and Briggs, used on logsplitters, it would benefit total economy better, if engine idles when no power is needed (CV in neutral), and then have a auto throttle system, that raise the rpm to a fixed setting (just above max torque mark) when the CV is moved a little, and pump starts creating pressure.
Most engines with NO aircharge (turbo etc), have max torque at about 60-70% of max rpm (and max power at 90-95% of max rpm).
This is the philosophy I have teached over the years....
opcorn:
Here is a good article about car engine, torque and power