Diesel engine

I need to know why a diesel engine expels a lot of white smoke and has no power

Most likely, the water is being passed to the combustion camera. bone inside the cylinders. Most likely, the packaging which is damaged and you have to change it.
In most of the case, it shows in the engine oil or in the refrigerant liquid (radiadior water), check the oil and water you want this one of the 2 ...

Bye lucky I hope it serves you ..

It is clearly a water filtration to some cylinder.
As Luchito2010 says it may be the cylinder head packing.
Check the water status, check the level and if it bubbles or blows. You will have a more occasional diagnosis.
Luck.