I am told that FO can be used in diesel engines with proper filteration

What is FO?

FO is furnace oil and I do not think that it can be use in Diesel engines.Because sulphur is the main problem.

It greatly depends on where you are located. In my area of the US furnace oil is just red dyed #2 low sulfur diesel fuel blended with kerosene. You would need to ask the fuel distributor what the exact composition of their furnace oil is. It may be suitable and it may not. If your not sure then don't use it. If it does not meet diesel fuel standards it could end up causing more damage and repairs then you would in fuel cost savings.

The short answer is yes and no!

Furnace oil is basically the same as diesel. But, for furnace use, the cetane rating and the wax content is not an issue. It is for your diesel. On a slow running diesel, where the FO is at room temperature, It will run fine. Not in a high performance road diesel. If you are looking to reduce your cost, use coloured diesel (detaxed for off road use - see your local regulations).

Sulfur is a lubricant. Not a problem for the engine, screws up the environment... ;(
(acid rain).