WMO is a moving target. It's made up of all kinds of oils, additives, solvents and even anti-freeze.
The varying concentrations of these components means that every user will have a different base fuel to compare to others.
What works for one person may fail miserably for another even though the engines are prepared identically. Why, because the fuels are almost guaranteed to be different (even though they are both WMO).
If your oil is free from other contaminants and is non-synthetic, you may have good luck using it as a fuel if you clean it adequately.
Some people add 10% gasoline to reduce the viscosity.
Just for contrast, here are nominal flash points for various fuels and oils..

Flash Point Under Compression Ignition:
===============================
Diesel #1 ---100f
Diesel #2 ---125f
Kerosene ---150f
Biodiesel ---260f
Motor oil --- 450 f
Petroleum synthetics--- 485f
PAO Synthetics ---525f
Olafin Ester Synthetics ---725f

As you can see, the high end synthetics have a strong resistance to auto-ignition. (Diesel=100f vs. Olafin Synthetics=725f)
That's why synthetic oil works well in severe heat applications.
One can clearly see the massive difference in "burnability" (if that's a word ?) and how varying concentrations of these oils could drastically effect the combustion process.

I have some WVO stored in a tote for 4 years now.
I does not smell bad or "painty".
It's de-watered and filtered before being stored.
Stored outdoors in the shade and it freezes every winter.
But I fear that this stuff must have a shelf life? 

What's your experience with the life of WVO ?

I use an oil reservoir used on hydraulic systems. Available in many sizes.
They are available in many shops and have the fill/drain ports already in place.

>> click picture to enlarge <<

Would it make sense to use use variable resistors (dial pots)  for the upper/lower band setting?
That would allow the user to tune the system to the Array and Heating element.

So these engine are only running only 12 to 14 degrees advance according to that manual.
I would have thought they would run 18 to 20 like most diesels I am familiar with.
I suppose the short stroke has something to do with it.
It doesn't explain why they knock an hammer so much.

Glort, from your experience, where is a good zone to target in order to quiet them down?
Something like 9 to 11 degrees?

Hi Glort
How do you determine the best wattage rating for the heating element? Or does it not matter with your system?

Interesting experiment.
My understanding of what you are doing is limited.
Does your assembly do a better job of using power when the panels are not in the sweet spot?

Wondering ... could these be used as a PM generator ?
With the appropriate rectification of course.