What must the air-to-gas ratio be within for fuels with a high surface-to-mass ratio to sustain combustion?

For fuels that possess a high surface-to-mass ratio, sustaining combustion requires that the air-to-gas ratio be maintained within defined levels of the Lower Explosive Limit (LEL) and the Upper Explosive Limit (UEL). This range is crucial because it allows for the right balance of flammable gases and oxygen, essential for combustion to occur effectively and safely.

When the air-to-gas mixture is below the LEL, there is not enough fuel to support ignition and combustion cannot happen. Conversely, when the mixture is above the UEL, there is an excess of fuel, which can lead to incomplete combustion and the production of harmful byproducts without sustaining the fire.

Thus, maintaining the air-to-gas ratio within the limits of the LEL and UEL ensures that there is sufficient fuel present for combustion, while allowing for the necessary oxygen to sustain the fire; this is particularly important for high surface-to-mass ratio fuels which can ignite more easily and burn more readily than denser materials.