The term combustion includes a list of phenomena that have a fundamental common characteristic: it is a chemical reaction between a fuel and an oxidant. Speaking of burning gases, characteristics of physical and chemical phenomena are strongly affected by how fuel (gas) and oxidant (air) are mixed. Fixed Flames are usually divided into three classes depending on how the fuel and oxidant are combined: non-aerated, partially aerated, and fully aerated. In a diffusion flame or non-aerated, the diffusion combustion is performed by injecting into the combustion chamber unburned fuel. Alternatively, the flow of unburned fuel can be supplied with air (known as primary air), before combustion occurs. If all the air required for complete combustion is supplied as primary air, then the flame is said to be fully aired or fully premixed. If only a part of the total air required is provided in the primary air, then the flame is said to be partially aerated and the remaining air (known as secondary air) diffuses into the hot combustion gases downstream of the front flame. Moreover, in this paper we will refer to the premixed and diffused flames. These flames will be reviewed taking into account only the laminar regime, where the speed is ideally parallel to the axis of the wall with a parabolic distribution, as a function of the distance from the wall, while the pressure is a function of distance in downstream direction.
