2007 Skoda Superb smoke

i have a 2007 superb 20lt tdi pd the problem is smoke fills the engine compartment there is no set time or reason for this to happen , no lights come on, on the dash board . It has happened 4 times in a week . We have checked for plastic bags, done engine flush and oil change , changed oil feed pipe to turbo, you can also get a sooty carbon taste when in the car. Smoke stays untill engine is switched ,the amount of smoke is you cannot see around the engine. Hope you can help