Hello
The heavy black fuel is a paste at room temperature and indeed it must be overheated and injected in a particular way
there is another category of black fuel called "light" which is mainly used in collective and agricultural heating which has the same characteristics as the HV in diesel combustion.
I ran a heavy fuel oil boiler room for seven years and I can tell you that it is really shit in terms of pollution and maintenance.
there are three categories of heavy fuel oil n ° 1, n ° 2 and n ° 3.
number 3 is the worst it is crude. Running a boiler with this fuel oil is a real hassle it has a lot of mud, water and even stones it must be preheated to 170 degrees and start with light.It pollutes serious but it is the cheapest, that is why a stupid shopping had provided us with this shit that is actually bitumen all just good for the roads.
N ° 2 c is the same without mud and without pebbles it can run on very large diesel but hello the hassle (several hours of maintenance per day, especially the filters)
for N ° 3 preheating to 140 degrees it goes pretty well but it's still a lot of maintenance (weekly shutdown for complete cleaning) and it pollutes.
I have never heard of light black fuel oil!