In terms of the equivalence ratio, what does a value greater than 1 denote?

A value of the equivalence ratio greater than 1 indicates a rich mixture, meaning that there is more fuel present in the fuel-air mixture than what is needed for complete combustion. In combustion processes, the equivalence ratio is defined as the actual fuel-to-air ratio divided by the stoichiometric fuel-to-air ratio. When this ratio exceeds 1, it signifies that the mixture has an excess of fuel relative to air, leading to conditions where not all of the fuel can be completely burned. This is significant in various applications because a rich mixture can produce higher emissions and can be less efficient compared to a lean mixture, where the opposite holds true.

In contrast, a lean mixture, which has an equivalence ratio less than 1, signifies an abundance of air compared to the fuel, while a balanced mixture corresponds to an equivalence ratio precisely equal to 1, indicating a perfect balance between fuel and air for complete combustion. Excess air typically refers to the operational conditions of a combustion system being adjusted to have a slight surplus of air to ensure complete combustion but would typically indicate an equivalence ratio less than 1. Understanding these concepts is crucial for optimizing combustion efficiency and managing emissions effectively in various power generation and industrial applications.