If your plane has a prop engine, you don't really have to do anything if the aircraft cfg file is set up right.

I'm hoping I'll be corrected if I've got this wrong.

The software reads the config file and sees that your plane has propellers and engines. From the config file it gets the locations of these engine in distances measured from the center of the aircraft. Then the software refers to an effects file in the effects folder, fx_engstrt.fx , which tells what effect to run, how long to run it and other little details. Some people have tweaked this file to get more smoke, smoke that is a different color, smoke that comes out longer, etc.

If you tweak the effects file, it'll change how every engine starts that refers to it, not just the aircraft you're working on.

You could make a custom effect file just for that airplane, put it in the effects folder and have it listed in your aircraft's cfg file under effects.

There is an effect that was included in FS2002 that was jet smoke at startup, not much, but it made it look good, there was also one that would provide VERY light smoke, you needed good eyes to even see it, when the plane was below 30000 feet, however, none of the default planes referred to those effects...thats MS for ya eh?