By creating a Material using one particle that's been rendered and linked to a multiple-image sprite sheet, we are able to take advantage of the Texture Sheet Animation module feature of Unity's Particle System.
The default Render Mode for particle systems is Billboard. This means that the image for each particle is always facing toward the camera. In this way, a 2D animation of a flame works very well since whatever direction the user is looking at the particle system from, they will always see the intended 2D flame animation, giving the visual effect of a 3D fire.
The particle system's Rendered component needs to be linked to the material for the sprite sheet, and the X- and Y-tile grid needs to match the number of columns (X) and rows (Y) in the sprite sheet file.
By having 0 for Start Speed and only one particle (Max Particles = 1), we ensure we have a single animated particle staying in one spot. The size of the particle may be limited...