Article on their remaining Carrier.
https://nationalinterest.org/blog/buzz/admiral-kuznetsov-russias-only-aircraft-carrier-totally-beyond-fixing-210793
....snip...."Design flaws
"Unlike Western warships which are normally powered by nuclear power or gas turbines, Kuznetsov is conventionally powered by a unique fuel source- mazut. This thick and tarry substance allows enemy ships to detect the aircraft carrier from miles away due to the fumes of black smoke that persistently engulf the ship.
In the past, Russian naval officials have noted that the failure to preheat the fuel source prior to entering the combustion chamber may play a part in the heavy smoke trail associated with the cruiser." ...snip.
"Smoke pot" in the mast stack: unintentional smoke beacon and location aid for Russian pilots (and everyone else) in daylight launch and recovery ops. :)
Mazut (Russian: Мазут, romanized: Mazut) is a low-quality heavy fuel oil, used in power plants and similar applications in Iran and some countries of the former Soviet Union. In the West, through fluid catalytic cracking, mazut is distilled into diesel and other light distillates.[2][3] Mazut may be used for heating houses in some parts of the former USSR and in countries of the Far East[clarification needed] that do not have the facilities to blend or break it down into more conventional petro-chemicals.