The below photo will show you what I'm trying to achieve. (I can find plenty of smoke images on the web so creating the smoke is not an issue. It's the blending that I'm having issues with).
So far I can add the smoke on as a layer above the car layer. Then adjust the opacity. I then set the blend mode to 'Exclusion'. But keep in mind that both the smoke and car image have black backgrounds so it 'works' better. (Actually that's not true as the black background is a separate layer as well. The car being cutout in its own layer). However where the smoke is blended over the car, blue areas, the smoke tends to get very 'dirty' and begins to change colour if I increase the opacity too much. Over 50% and it actually becomes orange/brown in places! Ideally I want to delete the background colour on the smoke but because it is so transparent that's all but impossible to do.