Timeline of a Particle
A simple explosion produces a ball of flame that expands outward rapidly in all directions. The initial burst has a lot of energy and is therefore very hot (ie, bright) and moves very fast. This energy quickly dissipates which results in the expansion of flame slowing down and also cooling down (ie, getting less bright). Finally, as all the fuel is burned up, the flames will die away and soon disappear completely.
An explosion particle will typically have a short lifetime and you can vary several different properties over that lifetime to simulate the effect. The particle will start off moving very fast but then its speed should reduce greatly as it moves away from the centre of the explosion. Also, the color should start off bright but then darken and eventually fade to transparency. Finally, reducing the particle’s size over its lifetime will give the effect of the flames dispersing as the fuel is used up.