I’ve had great success in using the smoke simulator to make a great looking gasoline explosion (the big hollywood-style fireball explosion).
…and as promised, the almighty .blend file is attached. You will need the build that allows for initial velocity of smoke based on particle velocity. Specifically, I used this build: http://blenderartists.org/forum/showpost.php?p=1526025&postcount=670
What I’ve done is run the smoke sim (with high res), but in addition to the smoke texture, I’ve added two cloud textures to affect the density and emission even further and their offsets are based on the positions of two empties. This just adds a bit more finer detail to the explosion to make it look less fluid-like and more fire-like. It makes it look like an explosion on a larger scale rather than say… a lighter being flicked on in slow motion.
ExplosionTest2.blend (163 KB)