Why is excess air not entirely disadvantageous in combustion?

Excess air in combustion processes indeed plays a beneficial role when it comes to reducing toxic emissions. When combustion occurs with sufficient oxygen, it allows for a more complete and efficient burning of the fuel. This completeness of combustion leads to lower levels of harmful byproducts, such as carbon monoxide (CO) and unburned hydrocarbons, which would otherwise contribute to air pollution if the combustion is inefficient or occurring in an oxygen-starved environment.

By providing additional air, the combustion process promotes the conversion of carbon in the fuel to carbon dioxide (CO2) rather than carbon monoxide (CO). Thus, the presence of excess air is critical in decreasing the emission of toxic substances, contributing to a cleaner combustion process and environmental protection.

The other options do have their own merits, but they do not directly refer to the primary benefit of excess air in terms of emissions. Safety is typically associated with avoiding situations that lead to combustion hazards rather than just increasing air supply. Enhancing energy output can happen under certain conditions, but it is not a general advantage linked to excess air. Finally, while keeping the appliance cool might be a side effect in specific scenarios, it is not a primary advantage of excess air in combustion processes.