The simplest way is to create a textured, transparent, billboarded plane that displays the explosion. If something explodes, make it invisible and show this explosion object instead for a few seconds.
Object3D plane=Primitives.getPlane(1, 20);
plane.setBillboarding(true);
plane.setTexture("yourExplosionTexture");
plane.setTransparency(20);
plane.build();
It won't be animated of course. If that's needed, change the texture over time (Object3D.setTexture("..."));